DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

Twelve catalyst test runs were made; ten of these runs used catalysts that contained cobalt as the metal component, while the remaining two runs used catalysts that contained iron as the metal component. Five of the ten cobalt catalyst test runs were made with the catalysts containing one of two different shape selective components (UCC-101 and UCC-108) at two different metal component: shape selective component ratios (1:1 and 3:14). The remaining five cobalt catalyst test runs were made with the catalysts containing different additives incorporated into the cobalt. The five cobalt catalyst test runs using catalysts with different additives showedmore » that these additives had pronounced effects on the catalysts' activity, selectivity, and stability. The most outstanding effect was realized with the additive used in the Run 9 catalyst. This additive greatly improved the stability of the catalyst. While having the same initial activity of an additive-free catalyst, its deactivation rate was only one fourth of that of the additive-free catalyst. Futhermore, this additive improved the quality of the hydrocarbon product, which had a high, stable yield of olefins, and, unlike the product of any other cobalt/UCC-101 catalyst, was free of suspended wax. This lack of suspended wax resulted in jet fuel and diesel oil fractions that had substantially lower pour points than did the fractions produced from an additive-free catalyst.« less

Catalytic ozonation of p-chlorobenzoic acid by activated carbon and nickel supported activated carbon prepared from petroleum coke.

PubMed

Li, Xukai; Zhang, Qiuyun; Tang, Lili; Lu, Ping; Sun, Fengqiang; Li, Laisheng

2009-04-15

The aim of this research was to investigate catalytic activity of petroleum coke, activated carbon (AC) prepared from this material, Ni supported catalyst on activated carbon (Ni/AC) in the ozonation of aqueous phase p-chlorobenzoic acid (p-CBA). Activated carbon and Ni/AC catalyst were characterized by XRD and SEM. The presence of petroleum coke did not improve the degradation of p-CBA compared to ozonation alone, but it was advantageous for p-CBA mineralization (total organic carbon, TOC, reduction), indicating the generation of highly oxidant species (*OH) in the medium. The presence of either activated carbon or Ni/AC considerably improves TOC removal during p-CBA ozonation. Ni/AC catalyst shows the better catalytic activity and stability based on five repeated tests during p-CBA ozonation. During the ozonation (50 mg/h ozone flow rate) of a 10 mg/L p-CBA (pH 4.31), it can be more mineralized in the presence of Ni/AC catalyst (5.0 g/L), TOC removal rate is over 60% in 60 min, 43% using activated carbon as catalyst, only 30% with ozonation alone.

Computationally Probing the Performance of Hybrid, Heterogeneous, and Homogeneous Iridium-Based Catalysts for Water Oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

García-Melchor, Max; Vilella, Laia; López, Núria

2016-04-29

An attractive strategy to improve the performance of water oxidation catalysts would be to anchor a homogeneous molecular catalyst on a heterogeneous solid surface to create a hybrid catalyst. The idea of this combined system is to take advantage of the individual properties of each of the two catalyst components. We use Density Functional Theory to determine the stability and activity of a model hybrid water oxidation catalyst consisting of a dimeric Ir complex attached on the IrO 2(110) surface through two oxygen atoms. We find that homogeneous catalysts can be bound to its matrix oxide without losing significant activity.more » Hence, designing hybrid systems that benefit from both the high tunability of activity of homogeneous catalysts and the stability of heterogeneous systems seems feasible.« less

An Efficient and Reusable Embedded Ru Catalyst for the Hydrogenolysis of Levulinic Acid to γ-Valerolactone.

PubMed

Wei, Zuojun; Lou, Jiongtao; Su, Chuanmin; Guo, Dechao; Liu, Yingxin; Deng, Shuguang

2017-04-22

To achieve a higher activity and reusability of a Ru-based catalyst, Ru nanoparticles were embedded in N-doped mesoporous carbon through a hard-template method. The catalyst showed excellent catalytic performance (314 h -1 turnover frequency) and recyclability (reusable five times with 3 % activity loss) for the hydrogenolysis of levulinic acid to γ-valerolactone. Compared with the mesoporous carbon without N-doping and conventional activated carbon, the introduction of N-dopant effectively improved the dispersion of Ru nanoparticles, decreased the average size of Ru nanoparticles to as small as 1.32 nm, and improved the adsorption of levulinic acid, which contributed to the increase in the activity of the catalyst. Additionally, the embedding method increased the interaction between Ru nanoparticles and carbon support in contrast with the conventional impregnation method, thus preventing the Ru nanoparticles from migration, aggregation, and leaching from the carbon surface and therefore increasing the reusability of the catalyst. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nano-Structured Bio-Inorganic Hybrid Material for High Performing Oxygen Reduction Catalyst.

PubMed

Jiang, Rongzhong; Tran, Dat T; McClure, Joshua P; Chu, Deryn

2015-08-26

In this study, we demonstrate a non-Pt nanostructured bioinorganic hybrid (BIH) catalyst for catalytic oxygen reduction in alkaline media. This catalyst was synthesized through biomaterial hemin, nanostructured Ag-Co alloy, and graphene nano platelets (GNP) by heat-treatment and ultrasonically processing. This hybrid catalyst has the advantages of the combined features of these bio and inorganic materials. A 10-fold improvement in catalytic activity (at 0.8 V vs RHE) is achieved in comparison of pure Ag nanoparticles (20-40 nm). The hybrid catalyst reaches 80% activity (at 0.8 V vs RHE) of the state-of-the-art catalyst (containing 40% Pt and 60% active carbon). Comparable catalytic stability for the hybrid catalyst with the Pt catalyst is observed by chronoamperometric experiment. The hybrid catalyst catalyzes 4-electron oxygen reduction to produce water with fast kinetic rate. The rate constant obtained from the hybrid catalyst (at 0.6 V vs RHE) is 4 times higher than that of pure Ag/GNP catalyst. A catalytic model is proposed to explain the oxygen reduction reaction at the BIH catalyst.

Effect of plasma-induced surface charging on catalytic processes: application to CO2 activation

NASA Astrophysics Data System (ADS)

Bal, Kristof M.; Huygh, Stijn; Bogaerts, Annemie; Neyts, Erik C.

2018-02-01

Understanding the nature and effect of the multitude of plasma-surface interactions in plasma catalysis is a crucial requirement for further process development and improvement. A particularly intriguing and rather unique property of a plasma-catalytic setup is the ability of the plasma to modify the electronic structure, and hence chemical properties, of the catalyst through charging, i.e. the absorption of excess electrons. In this work, we develop a quantum chemical model based on density functional theory to study excess negative surface charges in a heterogeneous catalyst exposed to a plasma. This method is specifically applied to investigate plasma-catalytic CO2 activation on supported M/Al2O3 (M = Ti, Ni, Cu) single atom catalysts. We find that (1) the presence of a negative surface charge dramatically improves the reductive power of the catalyst, strongly promoting the splitting of CO2 to CO and oxygen, and (2) the relative activity of the investigated transition metals is also changed upon charging, suggesting that controlled surface charging is a powerful additional parameter to tune catalyst activity and selectivity. These results strongly point to plasma-induced surface charging of the catalyst as an important factor contributing to the plasma-catalyst synergistic effects frequently reported for plasma catalysis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winter, Lea R.; Gomez, Elaine; Yan, Binhang

CO 2 hydrogenation over Fe-modified Ni/CeO 2 catalysts was investigated in a batch reactor using time-resolved in situ FTIR spectroscopy. Low loading of Ni/CeO 2 was associated with high selectivity to CO over CH 4, while higher Ni loading improved CO 2 hydrogenation activity with a reduced CO selectivity. X-ray absorption near-edge structure (XANES) analysis revealed Ni to be metallic for all catalysts including the CO-selective low loading 0.5% Ni catalyst, suggesting that the selectivity trend is due to structural rather than oxidation state effects. The loading amount of 1.5% Ni was selected for co-impregnation with Fe, based on themore » significant shift in product selectivity towards CH 4 for that loading amount, in order to shift the selectivity towards CO while maintaining high activity. Temperature programmed reduction (TPR) results indicated bimetallic interactions between Ni and Fe, and XANES analysis showed that about 70% of Fe in the bimetallic catalysts was oxidized. The Ni-Fe catalysts demonstrated improved selectivity towards CO without significantly compromising activity, coupling the high activity of Ni catalysts and the high CO selectivity of Fe. The general trends in Ni loading and bimetallic modification should guide efforts to develop non-precious metal catalysts for the selective production of CO by CO 2 hydrogenation.« less

Direct liquid-feed fuel cell with membrane electrolyte and manufacturing thereof

NASA Technical Reports Server (NTRS)

Narayanan, Sekharipuram (Inventor); Surampudi, Subbarao (Inventor); Halpert, Gerald (Inventor)

1999-01-01

An improved direct liquid-feed fuel cell having a solid membrane electrolyte for electrochemical reactions of an organic fuel. Improvements in interfacing of the catalyst layer and the membrane and activating catalyst materials are disclosed.

Activity and Stability of Dispersed Multi Metallic Pt-based Catalysts for CO Tolerance in Proton Exchange Membrane Fuel Cell Anodes.

PubMed

Hassan, Ayaz; Ticianelli, Edson A

2018-01-01

Studies aiming at improving the activity and stability of dispersed W and Mo containing Pt catalysts for the CO tolerance in proton exchange membrane fuel cell (PEMFC) anodes are revised for the following catalyst systems: (1) a carbon supported PtMo electrocatalyst submitted to heat treatments; (2) Pt and PtMo nanoparticles deposited on carbon-supported molybdenum carbides (Mo2C/C); (3) ternary and quaternary materials formed by PtMoFe/C, PtMoRu/C and PtMoRuFe/C and; (4) Pt nanoparticles supported on tungsten carbide/carbon catalysts and its parallel evaluation with carbon supported PtW catalyst. The heat-treated (600 oC) Pt-Mo/C catalyst showed higher hydrogen oxidation activity in the absence and in the presence of CO and better stability, compared to all other Mo-containing catalysts. PtMoRuFe, PtMoFe, PtMoRu supported on carbon and Pt supported on Mo2C/C exhibited similar CO tolerances but better stability, as compared to as-prepared PtMo supported on carbon. Among the tungsten-based catalysts, tungsten carbide supported Pt catalyst showed reasonable performance and reliable stability in comparison to simple carbon supported PtW catalyst, though an uneven level of catalytic activity towards H2 oxidation in presence of CO is observed for the former as compared to Mo containing catalyst. However, a small dissolution of Mo, Ru, Fe and W from the anodes and their migration toward cathodes during the cell operation is observed. These results indicate that the fuel cell performance and stability has been improved but not yet totally resolved.

Technology development for cobalt F-T catalysts. Quarterly technical progress report number 10, January 1--March 31, 1995

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singleton, A.H.

1995-06-28

The goal of this project is the development of a commercially-viable, cobalt-based Fischer-Tropsch (F-T) catalyst for use in a slurry bubble column reactor. The major objectives of this work are (1) to develop a cobalt-based F-T catalyst with low (< 5%) methane selectivity, (2) to develop a cobalt-based F-T catalyst with water-gas shift activity, and (3) to combine both these improvements into one catalyst. The project consists of five major tasks: catalyst development; catalyst testing; catalyst reproducibility tests; catalyst aging tests; and preliminary design and cost estimate for a demonstrate scale catalyst production facility. Technical accomplishments during this reporting periodmore » include the following. It appears that the higher activity obtained for the catalysts prepared using an organic solution and reduced directly without prior calcination was the result of higher dispersions obtained under such pretreatment. A Ru-promoted Co catalyst on alumina with 30% Co loading exhibited a 4-fold increase in dispersion and a 2-fold increase in activity in the fixed-bed reactor from that obtained with the non-promoted catalyst. Several reactor runs have again focused on pushing conversion to higher levels. The maximum conversion obtained has been 49.7% with 26g catalyst. Further investigations of the effect of reaction temperature on the performance of Co catalysts during F-T synthesis were started using a low activity catalyst and one of the most active catalysts. The three 1 kg catalyst batches prepared by Calsicat for the reproducibility and aging studies were tested in both the fixed-bed and slurry bubble column reactors under the standard reaction conditions. The effects of adding various promoters to some cobalt catalysts have also been addressed. Results are presented and discussed.« less

Constrained Geometry Organotitanium Catalysts Supported on Nanosized Silica for Ethylene (co)Polymerization.

PubMed

Li, Kuo-Tseng; Wu, Ling-Huey

2017-05-05

Supported olefin polymerization catalysts can prevent reactor-fouling problems and produce uniform polymer particles. Constrained geometry complexes (CGCs) have less sterically hindered active sites than bis-cyclopentadienyl metallocene catalysts. In the literature, micrometer-sized silica particles were used for supporting CGC catalysts, which might have strong mass transfer limitations. This study aims to improve the activity of supported CGC catalysts by using nanometer-sized silica. Ti[(C₅Me₄)SiMe₂(N t Bu)]Cl₂, a "constrained-geometry" titanium catalyst, was supported on MAO-treated silicas (nano-sized and micro-sized) by an impregnation method. Ethylene homo-polymerization and co-polymerization with 1-octene were carried out in a temperature range of 80-120 °C using toluene as the solvent. Catalysts prepared and polymers produced were characterized. For both catalysts and for both reactions, the maximum activities occurred at 100 °C, which is significantly higher than that (60 °C) reported before for supported bis-cyclopentadienyl metallocene catalysts containing zirconium, and is lower than that (≥140 °C) used for unsupported Ti[(C₅Me₄)SiMe₂(N t Bu)]Me₂ catalyst. Activities of nano-sized catalyst were 2.6 and 1.6 times those of micro-sized catalyst for homopolymerization and copolymerization, respectively. The former produced polymers with higher crystallinity and melting point than the latter. In addition, copolymer produced with nanosized catalyst contained more 1-octene than that produced with microsized catalyst.

Investigating the effects of alkali metal Na addition on catalytic activity of HZSM-5 for methyl mercaptan elimination

NASA Astrophysics Data System (ADS)

Yu, Jie; He, Dedong; Chen, Dingkai; Liu, Jiangping; Lu, Jichang; Liu, Feng; Liu, Pan; Zhao, Yutong; Xu, Zhizhi; Luo, Yongming

2017-10-01

Na-modified HZSM-5 catalysts with different Na loading amounts were prepared by incipient-wetness impregnation method and their catalytic activities for methyl mercaptan catalytic elimination were analyzed. XRD, N2 adsorption-desorption, NH3-TPD, CO2-TPD and FT-IR measurements were carried out to investigate the effects of modification of alkali metal Na on the physicochemical properties of the HZSM-5 zeolite catalyst. Research results illustrated that the introduction of alkali metal Na can improve catalytic activity for CH3SH catalytic elimination. CH3SH can be almost completely converted over 3%-Na/HZSM-5 at 450 °C compared to pure HZSM-5 at 600 °C based on our experimental results and the results from previous research. The improved catalytic activity could be attributed to the regulated acid-base properties of the HZSM-5 catalysts by doping with alkali metal Na. High alkali concentration treatment, however, may destroy the framework structure of the catalyst sample, thus causing the poor stability performance of the obtained catalyst.

Supported transition metal catalysts for para- to ortho-hydrogen conversion

NASA Technical Reports Server (NTRS)

Brooks, Christopher J.; Wang, Wei; Eyman, Darrell P.

1994-01-01

The main goal of this study was to develop and improve on existing catalysts for the conversion of ortho- to para-hydrogen. Starting with a commercially available Air Products nickel silicate, which had a beta value of 20, we were trying to synthesize catalysts that would be an improvement to AP. This was accomplished by preparing silicates with various metals as well as different preparation methods. We also prepared supported ruthenium catalysts by various techniques using several metal precursors to improve present technology. What was also found was that the activation conditions prior to catalytic testing was highly important for both the silicates and the supported ruthenium catalysts. While not the initial focus of the research, we made some interesting observations into the adsorption of H2 on ruthenium. This helped us to get a better understanding of how ortho- to para-H2 conversion takes place, and what features in a catalyst are important to optimize activity. Reactor design was the final area in which some interesting conclusions were drawn. As discussed earlier, the reactor catalyst bed must be constructed using straight 1/8 feet OD stainless steel tubing. It was determined that the use of 1/4 feet OD tubing caused two problems. First, the radius from the center of the bed to the wall was too great for thermal equilibrium. Since the reaction of ortho- to para-H2 is exothermic, the catalyst bed center was warmer than the edges. Second, the catalyst bed was too shallow using a 1/4 feet tube. This caused reactant blow-by which was thought to decrease the measured activity when the flow rate was increased. The 1/8 feet tube corrected both of these concerns.

Activation of surface lattice oxygen in single-atom Pt/CeO 2 for low-temperature CO oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nie, Lei; Mei, Donghai; Xiong, Haifeng

While single-atom catalysts can provide high catalytic activity and selectivity, application in industrial catalysts demands long term performance and the ability to regenerate the catalysts. We have investigated the factors that lead to improved catalytic activity of a Pt/CeO2 catalyst for low temperature CO oxidation. Single-atom Pt/CeO2 becomes active for CO oxidation under lean condition only at elevated temperatures, because CO is strongly bound to ionic Pt sites. Reducing the catalyst, even under mild conditions, leads to onset of CO oxidation activity even at room temperature. This high activity state involves the transformation of mononuclear Pt species to sub-nanometer sizedmore » Pt particles. Under oxidizing conditions, the Pt can be restored to its stable, single-atom state. The key to facile regeneration is the ability to create mobile Pt species and suitable trapping sites on the support, making this a prototypical catalyst system for industrial application of single-atom catalysis.« less

Catalysis using hydrous metal oxide ion exchanges

DOEpatents

Dosch, Robert G.; Stephens, Howard P.; Stohl, Frances V.

1985-01-01

In a process which is catalyzed by a catalyst comprising an active metal on a carrier, said metal being active as a catalyst for the process, an improvement is provided wherein the catalyst is a hydrous, alkali metal or alkaline earth metal titanate, zirconate, niobate or tantalate wherein alkali or alkaline earth metal cations have been exchanged with a catalytically effective amount of cations of said metal.

Catalysis using hydrous metal oxide ion exchangers

DOEpatents

Dosch, R.G.; Stephens, H.P.; Stohl, F.V.

1983-07-21

In a process which is catalyzed by a catalyst comprising an active metal on a carrier, said metal being active as a catalyst for the process, an improvement is provided wherein the catalyst is a hydrous, alkali metal or alkaline earth metal titanate, zirconate, niobate or tantalate wherein alkali or alkaline earth metal cations have been exchanged with a catalytically effective amount of cations of said metal.

Thermocatalytic process for CO.sub.2-free production of hydrogen and carbon from hydrocarbons

DOEpatents

Muradov, Nazim Z [Melbourne, FL

2011-08-23

A novel process and apparatus are disclosed for sustainable CO.sub.2-free production of hydrogen and carbon by thermocatalytic decomposition (dissociation, pyrolysis, cracking) of hydrocarbon fuels over carbon-based catalysts in the absence of air and/or water. The apparatus and thermocatalytic process improve the activity and stability of carbon catalysts during the thermocatalytic process and produce both high purity hydrogen (at least, 99.0 volume %) and carbon, from any hydrocarbon fuel, including sulfurous fuels. In a preferred embodiment, production of hydrogen and carbon is achieved by both internal and external activation of carbon catalysts. Internal activation of carbon catalyst is accomplished by recycling of hydrogen-depleted gas containing unsaturated and aromatic hydrocarbons back to the reactor. External activation of the catalyst can be achieved via surface gasification with hot combustion gases during catalyst heating. The process and apparatus can be conveniently integrated with any type of fuel cell to generate electricity.

Stereoselectivity of supported alkene metathesis catalysts: a goal and a tool to characterize active sites.

PubMed

Copéret, Christophe

2011-01-05

Stereoselectivity in alkene metathesis is a challenge and can be used as a tool to study active sites under working conditions. This review describes the stereochemical relevance and problems in alkene metathesis (kinetic vs. thermodynamic issues), the use of (E/Z) ratio at low conversions as a tool to characterize active sites of heterogeneous catalysts and finally to propose strategies to improve catalysts based on the current state of the art.

Identifying the role of N-heteroatom location in the activity of metal catalysts for alcohol oxidation

DOE PAGES

Chan-Thaw, Carine E.; Veith, Gabriel M.; Villa, Alberto; ...

2015-04-02

Here, this work focuses on understanding how the bonding of nitrogen heteroatoms contained on/in a activated carbon support influence the stability and reactivity of a supported Pd catalyst for the oxidation of alcohols in solution. The results show that simply adding N groups via solution chemistry is insufficient to improve catalytic properties. Instead a strongly bound N moiety is required to activate the catalyst and stabilize the metal particles.

Enhancing H2 evolution performance of an immobilised cobalt catalyst by rational ligand design† †Electronic supplementary information (ESI) available: Additional figures and tables, synthetic procedures, experimental details for NMR and UV-vis spectroscopy, electrochemistry and photocatalytic experiments. See DOI: 10.1039/c4sc03946g

PubMed Central

Willkomm, Janina; Muresan, Nicoleta M.

2015-01-01

The catalyst [CoIIIBr((DO)(DOH)(4-BnPO3H2)(2-CH2py)pn)]Br, CoP3, has been synthesised to improve the stability and activity of cobalt catalysts immobilised on metal oxide surfaces. The CoP3 catalyst contains an equatorial diimine–dioxime ligand, (DOH)2pn = N2,N2′-propanediyl-bis(2,3-butanedione-2-imine-3-oxime), with a benzylphosphonic acid (4-BnPO3H2) group and a methylpyridine (2-CH2py) ligand covalently linked to the bridgehead of the pseudo-macrocyclic diimine–dioxime ligand. The phosphonic acid functionality provides a robust anchoring group for immobilisation on metal oxides, whereas the pyridine is coordinated to the Co ion to enhance the catalytic activity of the catalyst. Electrochemical investigations in solution confirm that CoP3 shows electrocatalytic activity for the reduction of aqueous protons between pH 3 and 7. The metal oxide anchor provides the catalyst with a high affinity for mesostructured Sn-doped In2O3 electrodes (mesoITO; loading of approximately 22 nmol cm–2) and the electrostability of the attached CoP3 was confirmed by cyclic voltammetry. Finally, immobilisation of the catalyst on ruthenium-dye sensitised TiO2 nanoparticles in aqueous solutions in the presence of a hole scavenger establishes the activity of the catalyst in this photocatalytic scheme. The advantages of the elaborate catalyst design in CoP3 in terms of stability and catalytic activity are shown by direct comparison with previously reported phosphonated Co catalysts. We therefore demonstrate that rational ligand design is a viable route for improving the performance of immobilised molecular catalysts. PMID:29142677

Simple-Cubic Carbon Frameworks with Atomically Dispersed Iron Dopants toward High-Efficiency Oxygen Reduction.

PubMed

Wang, Biwei; Wang, Xinxia; Zou, Jinxiang; Yan, Yancui; Xie, Songhai; Hu, Guangzhi; Li, Yanguang; Dong, Angang

2017-03-08

Iron and nitrogen codoped carbons (Fe-N-C) have attracted increasingly greater attention as electrocatalysts for oxygen reduction reaction (ORR). Although challenging, the synthesis of Fe-N-C catalysts with highly dispersed and fully exposed active sites is of critical importance for improving the ORR activity. Here, we report a new type of graphitic Fe-N-C catalysts featuring numerous Fe single atoms anchored on a three-dimensional simple-cubic carbon framework. The Fe-N-C catalyst, derived from self-assembled Fe 3 O 4 nanocube superlattices, was prepared by in situ ligand carbonization followed by acid etching and ammonia activation. Benefiting from its homogeneously dispersed and fully accessible active sites, highly graphitic nature, and enhanced mass transport, our Fe-N-C catalyst outperformed Pt/C and many previously reported Fe-N-C catalysts for ORR. Furthermore, when used for constructing the cathode for zinc-air batteries, our Fe-N-C catalyst exhibited current and power densities comparable to those of the state-of-the-art Pt/C catalyst.

Attrition Resistant Fischer-Tropsch Catalysts Based on FCC Supports

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adeyiga, Adeyinka

2010-02-05

Commercial spent fluid catalytic cracking (FCC) catalysts provided by Engelhard and Albemarle were used as supports for Fe-based catalysts with the goal of improving the attrition resistance of typical F-T catalysts. Catalysts with the Ruhrchemie composition (100 Fe/5 Cu/4.2 K/25 spent FCC on mass basis) were prepared by wet impregnation. XRD and XANES analysis showed the presence of Fe{sub 2}O{sub 3} in calcined catalysts. FeC{sub x} and Fe{sub 3}O{sub 4} were present in the activated catalysts. The metal composition of the catalysts was analyzed by ICP-MS. F-T activity of the catalysts activated in situ in CO at the same conditionsmore » as used prior to the attrition tests was measured using a fixed bed reactor at T = 573 K, P = 1.38 MPa and H{sub 2}:CO ratio of 0.67. Cu and K promoted Fe supported over Engelhard provided spent FCC catalyst shows relatively good attrition resistance (8.2 wt% fines lost), high CO conversion (81%) and C{sub 5}+ hydrocarbons selectivity (18.3%).« less

Progress in the Development of Oxygen Reduction Reaction Catalysts for Low-Temperature Fuel Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Dongguo; Lv, Haifeng; Kang, Yijin

2016-04-06

In this paper, we present a brief summary on the most recent progress in the design of catalysts for electrochemical reduction of oxygen. The main challenge in the wide spread of fuel cell technology is to lower the content of, or even eliminate, Pt and other precious metals in catalysts without sacrificing their performance. Pt-based nanosized catalysts with novel and refined architectures continue to dominate in catalytic performance, and formation of Pt-skin-like surfaces is key to achieving the highest values in activity. Moreover, durability has also been improved in Pt-based systems with addition of Au, which plays an important rolemore » in stabilizing the Pt topmost layers against dissolution. However, various carbon-based materials without precious metal have shown improvement in activity and durability and have been explored to serve as catalyst supports. Finally, understanding how the doped elements interact with each other and/or carbon is challenging and necessary in the design of robust fuel cell catalysts.« less

Tuning Ni-catalyzed CO 2 hydrogenation selectivity via Ni-ceria support interactions and Ni-Fe bimetallic formation

DOE PAGES

Winter, Lea R.; Gomez, Elaine; Yan, Binhang; ...

2017-10-16

CO 2 hydrogenation over Fe-modified Ni/CeO 2 catalysts was investigated in a batch reactor using time-resolved in situ FTIR spectroscopy. Low loading of Ni/CeO 2 was associated with high selectivity to CO over CH 4, while higher Ni loading improved CO 2 hydrogenation activity with a reduced CO selectivity. X-ray absorption near-edge structure (XANES) analysis revealed Ni to be metallic for all catalysts including the CO-selective low loading 0.5% Ni catalyst, suggesting that the selectivity trend is due to structural rather than oxidation state effects. The loading amount of 1.5% Ni was selected for co-impregnation with Fe, based on themore » significant shift in product selectivity towards CH 4 for that loading amount, in order to shift the selectivity towards CO while maintaining high activity. Temperature programmed reduction (TPR) results indicated bimetallic interactions between Ni and Fe, and XANES analysis showed that about 70% of Fe in the bimetallic catalysts was oxidized. The Ni-Fe catalysts demonstrated improved selectivity towards CO without significantly compromising activity, coupling the high activity of Ni catalysts and the high CO selectivity of Fe. The general trends in Ni loading and bimetallic modification should guide efforts to develop non-precious metal catalysts for the selective production of CO by CO 2 hydrogenation.« less

Acid treatment and formation of MnWO4 belts for NH3-SCR performance of MnWOx/TiO2 catalysts

NASA Astrophysics Data System (ADS)

Zhang, Zekai; Lu, Weizhe; Zhang, Xinying; Liu, Huayan; Lu, Hanfeng

2018-06-01

NH3-SCR is an important technology to remove NOx, and non-V based catalysts development is still a hot topic in the field. To improve N2 selectivity, acid treatment was carried out to modify the properties of a MnWOx/TiO2 catalyst. Influences of acid concentration, time and temperature on the catalyst were investigated. The TEM results showed that the acid treatment removed more MnO2 species than Mn2O3 and MnWO4 and disclosed more crystal faces of the active species. The active species even formed hollow structures by Ostwald ripening mechanism, which was then corroded by acid to form the nanobelts on the surface. The working temperature window of the MnWOx/TiO2 catalyst was thereby moved to the high temperature attitude and the N2 selectivity is clearly improved.

Catalysts for the selective oxidation of hydrogen sulfide to sulfur

DOEpatents

Srinivas, Girish; Bai, Chuansheng

2000-08-08

This invention provides catalysts for the oxidation of hydrogen sulfide. In particular, the invention provides catalysts for the partial oxidation of hydrogen sulfide to elemental sulfur and water. The catalytically active component of the catalyst comprises a mixture of metal oxides containing titanium oxide and one or more metal oxides which can be selected from the group of metal oxides or mixtures of metal oxides of transition metals or lanthanide metals. Preferred metal oxides for combination with TiO.sub.2 in the catalysts of this invention include oxides of V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Tc, Ru, Rh, Hf, Ta, W, Au, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Catalysts which comprise a homogeneous mixture of titanium oxide and niobium (Nb) oxide are also provided. A preferred method for preparing the precursor homogenous mixture of metal hydroxides is by coprecipitation of titanium hydroxide with one or more other selected metal hydroxides. Catalysts of this invention have improved activity and/or selectivity for elemental sulfur production. Further improvements of activity and/or selectivity can be obtained by introducing relatively low amounts (up to about 5 mol %)of a promoter metal oxide (preferably of metals other than titanium and that of the selected second metal oxide) into the homogeneous metal/titanium oxide catalysts of this invention.

Catalyst and method for production of methylamines

DOEpatents

Klier, Kamil; Herman, Richard G.; Vedage, Gamini A.

1987-01-01

This invention relates to an improved catalyst and method for the selective production of methylamines. More particularly, it is concerned with the preparation of stable highly active catalysts for producing methylamines by a catalytic reaction of ammonia or substituted amines and binary synthesis gas (CO+H.sub.2).

Fischer-Tropsch Cobalt Catalyst Activation and Handling Through Wax Enclosure Methods

NASA Technical Reports Server (NTRS)

Klettlinger, Jennifer L. S.; Yen, Chia H.; Nakley, Leah M.; Surgenor, Angela D.

2016-01-01

Fischer-Tropsch (F-T) synthesis is considered a gas to liquid process which converts syn-gas, a gaseous mixture of hydrogen and carbon monoxide, into liquids of various hydrocarbon chain length and product distributions. Cobalt based catalysts are used in F-T synthesis and are the focus of this paper. One key concern with handling cobalt based catalysts is that the active form of catalyst is in a reduced state, metallic cobalt, which oxidizes readily in air. In laboratory experiments, the precursor cobalt oxide catalyst is activated in a fixed bed at 350 ?C then transferred into a continuous stirred tank reactor (CSTR) with inert gas. NASA has developed a process which involves the enclosure of active cobalt catalyst in a wax mold to prevent oxidation during storage and handling. This improved method allows for precise catalyst loading and delivery into a CSTR. Preliminary results indicate similar activity levels in the F-T reaction in comparison to the direct injection method. The work in this paper was supported by the NASA Fundamental Aeronautics Subsonics Fixed Wing Project.

Turning Biodiesel Waste Glycerol into 1,3-Propanediol: Catalytic Performance of Sulphuric acid-Activated Montmorillonite Supported Platinum Catalysts in Glycerol Hydrogenolysis.

PubMed

Samudrala, Shanthi Priya; Kandasamy, Shalini; Bhattacharya, Sankar

2018-05-10

Direct C-O hydrogenolysis of bioglycerine to produce 1,3-propanediol selectively is a vital technology that can expand the scope of biodiesel industry and green chemical production from biomass. Herein we report sulphuric acid-activated montmorillonite clay supported platinum nanoparticles as highly effective solid acid catalysts for the selective production of 1,3-propanediol from glycerol. The catalytic performances of the catalysts were investigated in the hydrogenolysis of glycerol with a fixed bed reactor under ambient pressure. The results were found promising and showed that the activation of montmorillonite by sulphuric acid incorporated Brønsted acidity in the catalyst and significantly improved the selectivity to 1,3-propanediol. The catalytic performance of different platinum loaded catalysts was examined and 2 wt% Pt/S-MMT catalyst presented superior activity among others validating 62% 1,3-propanediol selectivity at 94% glycerol conversion. The catalytic activity of 2Pt/S-MMT was systematically investigated under varying reaction parameters including reaction temperature, hydrogen flow rate, glycerol concentration, weight hourly space velocity, and contact time to derive the optimum conditions for the reaction. The catalyst stability, reusability and structure-activity correlation were also elucidated. The high performance of the catalyst could be ascribed to well disperse Pt nanoparticles immobilized on acid-activated montmorillonite, wider pore-structure and appropriate acid sites of the catalyst.

Highly efficient nonprecious metal catalyst prepared with metal–organic framework in a continuous carbon nanofibrous network

PubMed Central

Shui, Jianglan; Chen, Chen; Grabstanowicz, Lauren; Zhao, Dan; Liu, Di-Jia

2015-01-01

Fuel cell vehicles, the only all-electric technology with a demonstrated >300 miles per fill travel range, use Pt as the electrode catalyst. The high price of Pt creates a major cost barrier for large-scale implementation of polymer electrolyte membrane fuel cells. Nonprecious metal catalysts (NPMCs) represent attractive low-cost alternatives. However, a significantly lower turnover frequency at the individual catalytic site renders the traditional carbon-supported NPMCs inadequate in reaching the desired performance afforded by Pt. Unconventional catalyst design aiming at maximizing the active site density at much improved mass and charge transports is essential for the next-generation NPMC. We report here a method of preparing highly efficient, nanofibrous NPMC for cathodic oxygen reduction reaction by electrospinning a polymer solution containing ferrous organometallics and zeolitic imidazolate framework followed by thermal activation. The catalyst offers a carbon nanonetwork architecture made of microporous nanofibers decorated by uniformly distributed high-density active sites. In a single-cell test, the membrane electrode containing such a catalyst delivered unprecedented volumetric activities of 3.3 A⋅cm−3 at 0.9 V or 450 A⋅cm−3 extrapolated at 0.8 V, representing the highest reported value in the literature. Improved fuel cell durability was also observed. PMID:26261338

Highly efficient nonprecious metal catalyst prepared with metal–organic framework in a continuous carbon nanofibrous network

DOE PAGES

Shui, Jianglan; Chen, Chen; Grabstanowicz, Lauren; ...

2015-08-25

Fuel cell vehicles, the only all-electric technology with a demonstrated >300 miles per fill travel range, use Pt as the electrode catalyst. The high price of Pt creates a major cost barrier for large-scale implementation of polymer electrolyte membrane fuel cells. Nonprecious metal catalysts (NPMCs) represent attractive low-cost alternatives. However, a significantly lower turnover frequency at the individual catalytic site renders the traditional carbon-supported NPMCs inadequate in reaching the desired performance afforded by Pt. Unconventional catalyst design aiming at maximizing the active site density at much improved mass and charge transports is essential for the next-generation NPMC. We report heremore » a method of preparing highly efficient, nanofibrous NPMC for cathodic oxygen reduction reaction by electrospinning a polymer solution containing ferrous organometallics and zeolitic imidazolate framework followed by thermal activation. The catalyst offers a carbon nanonetwork architecture made of microporous nanofibers decorated by uniformly distributed high-density active sites. In a single-cell test, the membrane electrode containing such a catalyst delivered unprecedented volumetric activities of 3.3 A∙cm -3 at 0.9 V or 450 A∙cm -3 extrapolated at 0.8 V, representing the highest reported value in the literature. Improved fuel cell durability was also observed.« less

Highly efficient nonprecious metal catalyst prepared with metal-organic framework in a continuous carbon nanofibrous network.

PubMed

Shui, Jianglan; Chen, Chen; Grabstanowicz, Lauren; Zhao, Dan; Liu, Di-Jia

2015-08-25

Fuel cell vehicles, the only all-electric technology with a demonstrated >300 miles per fill travel range, use Pt as the electrode catalyst. The high price of Pt creates a major cost barrier for large-scale implementation of polymer electrolyte membrane fuel cells. Nonprecious metal catalysts (NPMCs) represent attractive low-cost alternatives. However, a significantly lower turnover frequency at the individual catalytic site renders the traditional carbon-supported NPMCs inadequate in reaching the desired performance afforded by Pt. Unconventional catalyst design aiming at maximizing the active site density at much improved mass and charge transports is essential for the next-generation NPMC. We report here a method of preparing highly efficient, nanofibrous NPMC for cathodic oxygen reduction reaction by electrospinning a polymer solution containing ferrous organometallics and zeolitic imidazolate framework followed by thermal activation. The catalyst offers a carbon nanonetwork architecture made of microporous nanofibers decorated by uniformly distributed high-density active sites. In a single-cell test, the membrane electrode containing such a catalyst delivered unprecedented volumetric activities of 3.3 A ⋅ cm(-3) at 0.9 V or 450 A ⋅ cm(-3) extrapolated at 0.8 V, representing the highest reported value in the literature. Improved fuel cell durability was also observed.

The synergistic effect in the Fe-Co bimetallic catalyst system for the growth of carbon nanotube forests

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hardeman, D.; Esconjauregui, S., E-mail: cse28@cam.ac.uk; Cartwright, R.

2015-01-28

We report the growth of multi-walled carbon nanotube forests employing an active-active bimetallic Fe-Co catalyst. Using this catalyst system, we observe a synergistic effect by which—in comparison to pure Fe or Co—the height of the forests increases significantly. The homogeneity in the as-grown nanotubes is also improved. By both energy dispersive spectroscopy and in-situ x-ray photoelectron spectroscopy, we show that the catalyst particles consist of Fe and Co, and this dramatically increases the growth rate of the tubes. Bimetallic catalysts are thus potentially useful for synthesising nanotube forests more efficiently.

Non-noble electrocatalysts for alkaline fuel cells

NASA Technical Reports Server (NTRS)

Sarangapani, S.; Lessner, P.; Manoukian, M.; Giner, J.

1989-01-01

The doping of solid phase precursors followed by pyrolysis or the copyrolysis of gas phase precursors has allowed us to produce catalysts with good activity toward oxygen reduction. Efforts are currently underway to better understand the reasons for the catalytic activity of the bulk doped catalysts with a view toward further improving their activity.

Relevance of the Interaction between the M-Phthalocyanines and Carbon Nanotubes in the Electroactivity toward ORR.

PubMed

González-Gaitán, Carolina; Ruiz-Rosas, Ramiro; Morallón, Emilia; Cazorla-Amorós, Diego

2017-10-31

In this work, the influence of the interaction between the iron and cobalt-phthalocyanines (FePc and CoPc) and carbon nanotubes (CNTs) used as support in the electroactivity toward oxygen reduction reaction (ORR) in alkaline media has been investigated. A series of thermal treatments were performed on these materials in order to modify the interaction between the CNTs and the phthalocyanines. The FePc-based catalysts showed the highest activity, with comparable performance to the state-of-the-art Pt-Vulcan catalyst. A heat treatment at 400 °C improved the activity of FePc-based catalysts, while the use of higher temperatures or oxidative atmosphere rendered the decomposition of the macrocyclic compound and consequently the loss of the electrochemical activity of the complex. CoPc-based catalysts performance was negatively affected for all of the tested treatments. Thermogravimetric analyses demonstrated that the FePc was stabilized when loaded onto CNTs, while CoPc did not show such a feature, pointing to a better interaction of the FePc instead of the CoPc. Interestingly, electrochemical measurements demonstrated an improvement of the electron transfer rate in thermally treated FePc-based catalysts. They also allowed us to assess that only 15% of the iron in the catalyst was available for direct electron transfer. This is the same iron amount that remains on the catalyst after a strong acid washing with concentrated HCl (ca. 0.3 wt %), which is enough to deliver a comparable ORR activity. Durability tests confirmed that the catalysts deactivation occurs at a slower rate in those catalysts where FePc is strongly attached to the CNT surface. Thus, the highest ORR activity seems to be provided by those FePc molecules that are strongly attached to the CNT surface, pointing out the relevance of the interaction between the support and the FePc in these catalysts.

Novel anode catalyst for direct methanol fuel cells.

PubMed

Basri, S; Kamarudin, S K; Daud, W R W; Yaakob, Z; Kadhum, A A H

2014-01-01

PtRu catalyst is a promising anodic catalyst for direct methanol fuel cells (DMFCs) but the slow reaction kinetics reduce the performance of DMFCs. Therefore, this study attempts to improve the performance of PtRu catalysts by adding nickel (Ni) and iron (Fe). Multiwalled carbon nanotubes (MWCNTs) are used to increase the active area of the catalyst and to improve the catalyst performance. Electrochemical analysis techniques, such as energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS), are used to characterize the kinetic parameters of the hybrid catalyst. Cyclic voltammetry (CV) is used to investigate the effects of adding Fe and Ni to the catalyst on the reaction kinetics. Additionally, chronoamperometry (CA) tests were conducted to study the long-term performance of the catalyst for catalyzing the methanol oxidation reaction (MOR). The binding energies of the reactants and products are compared to determine the kinetics and potential surface energy for methanol oxidation. The FESEM analysis results indicate that well-dispersed nanoscale (2-5 nm) PtRu particles are formed on the MWCNTs. Finally, PtRuFeNi/MWCNT improves the reaction kinetics of anode catalysts for DMFCs and obtains a mass current of 31 A g(-1) catalyst.

Novel Anode Catalyst for Direct Methanol Fuel Cells

PubMed Central

Basri, S.; Kamarudin, S. K.; Daud, W. R. W.; Yaakob, Z.; Kadhum, A. A. H.

2014-01-01

PtRu catalyst is a promising anodic catalyst for direct methanol fuel cells (DMFCs) but the slow reaction kinetics reduce the performance of DMFCs. Therefore, this study attempts to improve the performance of PtRu catalysts by adding nickel (Ni) and iron (Fe). Multiwalled carbon nanotubes (MWCNTs) are used to increase the active area of the catalyst and to improve the catalyst performance. Electrochemical analysis techniques, such as energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS), are used to characterize the kinetic parameters of the hybrid catalyst. Cyclic voltammetry (CV) is used to investigate the effects of adding Fe and Ni to the catalyst on the reaction kinetics. Additionally, chronoamperometry (CA) tests were conducted to study the long-term performance of the catalyst for catalyzing the methanol oxidation reaction (MOR). The binding energies of the reactants and products are compared to determine the kinetics and potential surface energy for methanol oxidation. The FESEM analysis results indicate that well-dispersed nanoscale (2–5 nm) PtRu particles are formed on the MWCNTs. Finally, PtRuFeNi/MWCNT improves the reaction kinetics of anode catalysts for DMFCs and obtains a mass current of 31 A g−1 catalyst. PMID:24883406

Synthesis of CaO-CeO2 catalysts by soft template method for biodiesel production

NASA Astrophysics Data System (ADS)

Zheng, Y. C.; Yu, X. H.; Yang, J.

2017-06-01

Biodiesel has recently gained extensive attention. Catalysts play an important role in producing biodiesel by transesterification reaction. In this study, CaO-CeO2 catalysts are developed as the solid base catalyst. Using PDMS-PEO as a structure-directing agent, the prepared CaO-CeO2 catalysts have a three-dimensional interconnected porous structure, which benefits the transesterification reaction. While the added Ce slightly decreases the catalytic activity, the stability of the catalyst shows remarkable improvement. Considering the catalytic activity and stability, the best catalyst is determined to be catalyst 0.15-1073 (Ce/Ca molar ratio of 0.15 and calcination temperature of 1073 K). Under optimum reaction conditions, the biodiesel yield reaches to 97.5% and metal leaching is 117.7 ppm. For catalyst 0.15-1073 regenerated after four reaction cycles, the biodiesel yield is 94.1%. The results reveal that the CaO-CeO2 catalyst has good potential for application in large-scale biodiesel production in the future.

An optimization study of PtSn/C catalysts applied to direct ethanol fuel cell: Effect of the preparation method on the electrocatalytic activity of the catalysts

NASA Astrophysics Data System (ADS)

Almeida, T. S.; Palma, L. M.; Leonello, P. H.; Morais, C.; Kokoh, K. B.; De Andrade, A. R.

2012-10-01

The aim of this work was to perform a systematic study of the parameters that can influence the composition, morphology, and catalytic activity of PtSn/C nanoparticles and compare two different methods of nanocatalyst preparation, namely microwave-assisted heating (MW) and thermal decomposition of polymeric precursors (DPP). An investigation of the effects of the reducing and stabilizing agents on the catalytic activity and morphology of Pt75Sn25/C catalysts prepared by microwave-assisted heating was undertaken for optimization purposes. The effect of short-chain alcohols such as ethanol, ethylene glycol, and propylene glycol as reducing agents was evaluated, and the use of sodium acetate and citric acid as stabilizing agents for the MW procedure was examined. Catalysts obtained from propylene glycol displayed higher catalytic activity compared with catalysts prepared in ethylene glycol. Introduction of sodium acetate enhanced the catalytic activity, but this beneficial effect was observed until a critical acetate concentration was reached. Optimization of the MW synthesis allowed for the preparation of highly dispersed catalysts with average sizes lying between 2.0 and 5.0 nm. Comparison of the best catalyst prepared by MW with a catalyst of similar composition prepared by the polymeric precursors method showed that the catalytic activity of the material can be improved when a proper condition for catalyst preparation is achieved.

Networks of connected Pt nanoparticles supported on carbon nanotubes as superior catalysts for methanol electrooxidation

NASA Astrophysics Data System (ADS)

Huang, Meihua; Zhang, Jianshuo; Wu, Chuxin; Guan, Lunhui

2017-02-01

The high cost and short lifetime of the Pt-based anode catalyst for methanol oxidation reaction (MOR) hamper the widespread commercialization of direct methanol fuel cell (DMFC). Therefore, improving the activity of Pt-based catalysts is necessary for their practical application. For the first time, we prepared networks of connected Pt nanoparticles supported on multi-walled carbon nanotubes with loading ratio as high as 91 wt% (Pt/MWCNTs). Thanks for the unique connected structure, the Pt mass activity of Pt/MWCNTs for methanol oxidation reaction is 4.4 times as active as that of the commercial Pt/C (20 wt%). When carbon support is considered, the total mass activity of Pt/MWCNTs is 20 times as active as that of the commercial Pt/C. The durability and anti-poisoning ability are also improved greatly.

Simple preparation of Fenton catalyst@bacterial cellulose for waste water treatment

NASA Astrophysics Data System (ADS)

Wibowo, Arie; Febi Indrawan, Radian; Triadhi, Untung; Hasdi Aimon, Akfiny; Iskandar, Ferry; Ardy, Husaini

2018-02-01

Heterogeneous fenton catalyst is one of the attractive technologies for destruction of persistent and non-biodegradable pollutant in wastewater, because it can be used in wide range of pH and recyclable. Herein, commercial bacterial celluloses (BCs) were used as an alternative support of fenton catalyst to improve their catalytic activity. Scanning Electron Microscope (SEM) observations indicated that the presence of BCs and decreasing precursor concentration might promote formation of smaller particle sizes of catalyst from 3.5 μm of bare catalyst to 0.7 μm of catalyst@BC. UV-vis measurement showed that fast degradation of dyes with half-time degradation at around 25 min was observed in sample using catalyst@BCs with precursor concentration of 0.01 M. Successful preparation of heterogeneous fenton catalyst with smaller particle size and better catalytic activity is important for their application in wastewater treatment.

A palladium-doped ceria@carbon core-sheath nanowire network: a promising catalyst support for alcohol electrooxidation reactions

NASA Astrophysics Data System (ADS)

Tan, Qiang; Du, Chunyu; Sun, Yongrong; Du, Lei; Yin, Geping; Gao, Yunzhi

2015-08-01

A novel palladium-doped ceria and carbon core-sheath nanowire network (Pd-CeO2@C CSNWN) is synthesized by a template-free and surfactant-free solvothermal process, followed by high temperature carbonization. This hierarchical network serves as a new class of catalyst support to enhance the activity and durability of noble metal catalysts for alcohol oxidation reactions. Its supported Pd nanoparticles, Pd/(Pd-CeO2@C CSNWN), exhibit >9 fold increase in activity toward the ethanol oxidation over the state-of-the-art Pd/C catalyst, which is the highest among the reported Pd systems. Moreover, stability tests show a virtually unchanged activity after 1000 cycles. The high activity is mainly attributed to the superior oxygen-species releasing capability of Pd-doped CeO2 nanowires by accelerating the removal of the poisoning intermediate. The unique interconnected one-dimensional core-sheath structure is revealed to facilitate immobilization of the metal catalysts, leading to the improved durability. This core-sheath nanowire network opens up a new strategy for catalyst performance optimization for next-generation fuel cells.A novel palladium-doped ceria and carbon core-sheath nanowire network (Pd-CeO2@C CSNWN) is synthesized by a template-free and surfactant-free solvothermal process, followed by high temperature carbonization. This hierarchical network serves as a new class of catalyst support to enhance the activity and durability of noble metal catalysts for alcohol oxidation reactions. Its supported Pd nanoparticles, Pd/(Pd-CeO2@C CSNWN), exhibit >9 fold increase in activity toward the ethanol oxidation over the state-of-the-art Pd/C catalyst, which is the highest among the reported Pd systems. Moreover, stability tests show a virtually unchanged activity after 1000 cycles. The high activity is mainly attributed to the superior oxygen-species releasing capability of Pd-doped CeO2 nanowires by accelerating the removal of the poisoning intermediate. The unique interconnected one-dimensional core-sheath structure is revealed to facilitate immobilization of the metal catalysts, leading to the improved durability. This core-sheath nanowire network opens up a new strategy for catalyst performance optimization for next-generation fuel cells. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03023d

Development of attrition resistant iron-based Fischer-Tropsch catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

2000-09-20

The Fischer-Tropsch (F-T) reaction provides a way of converting coal-derived synthesis gas (CO+H{sub 2}) to liquid fuels. Since the reaction is highly exothermic, one of the major problems in control of the reaction is heat removal. Recent work has shown that the use of slurry bubble column reactors (SBCRs) can largely solve this problem. The use of iron-based catalysts is attractive not only due to their low cost and ready availability, but also due to their high water-gas shift activity which makes it possible to use these catalysts with low H{sub 2}/CO ratios. However, a serious problem with use ofmore » Fe catalysts in a SBCR is their tendency to undergo attrition. This can cause fouling/plugging of downstream filters and equipment, makes the separation of catalyst from the oil/wax product very difficult if not impossible, and results a steady loss of catalyst from the reactor. The objective of this research is to develop robust iron-based Fischer-Tropsch catalysts that have suitable activity, selectivity and stability to be used in the slurry bubble column reactor. Specifically we aim to develop to: (1) improve the performance and preparation procedure of the high activity, high attrition resistant, high alpha iron-based catalysts synthesized at Hampton University (2) seek improvements in the catalyst performance through variations in process conditions, pretreatment procedures and/or modifications in catalyst preparation steps and (3) investigate the performance in a slurry reactor. The effort during the reporting period has been devoted to effects of pretreating procedures, using H{sub 2}, CO and syngas (H{sub 2}/CO = 0.67) as reductants, on the performance (activity, selectivity and stability with time) of a precipitated iron catalyst (100Fe/5Cu/4.2K/10SiO{sub 2} on a mass basis ) during F-T synthesis were studied in a fixed-bed reactor.« less

Non-carbon titanium cobalt nitride nanotubes supported platinum catalyst with high activity and durability for methanol oxidation reaction

NASA Astrophysics Data System (ADS)

Chen, Xiaoxiang; Li, Wuyi; Pan, Zhanchang; Xu, Yanbin; Liu, Gen; Hu, Guanghui; Wu, Shoukun; Li, Jinghong; Chen, Chun; Lin, Yingsheng

2018-05-01

Titanium cobalt nitride nanotubes (Ti0.95Co0.05N NTs) hybrid support, a novel robust non-carbon support material prepared by solvothermal and post-nitriding processes, is further decorated with Pt nanoparticles for the electrooxidation of methanol. The catalyst is characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and electrochemical measurements. The morphology, structure and composition of the synthesized Ti0.95Co0.05N NTs suggest that the nanotube wall is porous and consists of homogeneous cohesively attached nitrides nanocube particles. Notable, Ti0.95Co0.05N NTs supported Pt catalyst exhibits significantly improved catalytic activity and durability for methanol electrooxidation compared with the conventional JM Pt/C catalyst. The experimental data indicate that enhanced catalytic activity and stability of Pt/Ti0.95Co0.05N NTs towards methanol electrooxidation might be mainly attributed to the tubular nanostructures and synergistic effect introduced by the Co doping. Both of them are playing an important role in improving the activity and durability of the Ti0.95Co0.05N NTs catalyst.

Promoting effect of alkaline earth metal doping on catalytic activity of HC and NOx conversion over Pd-only three-way catalyst.

PubMed

Yang, Linyan; Lin, Siyu; Yang, Xue; Fang, Weimin; Zhou, Renxian

2014-08-30

The influence of alkaline earth metal (M=Mg, Ca, Sr and Ba) promoter on the structural/textural properties of Ce0.67Zr0.33O2 (designated as CZ) and the catalytic behavior of its supported Pd-only three-way catalyst (Pd/CZM) have been investigated. The results show that the modification with alkaline earth metal obviously improves the catalytic activity for hydrocarbon (HC) and nitrogen oxides (NOx) conversion, especially the introduction of Ba. Furthermore, the operation window of the promoted catalysts has also been widened. The doping of alkaline earth metal leads to the formation of more homogeneous Ce-Zr-M ternary solid solution with higher surface area and smaller crystallite size, and the corresponding Pd/CZM catalysts present improved reducibility of PdO species. The modification with Ca, Sr and Ba improves the thermal aging resistance, especially Ba. DRIFTS results reveal that the doping of alkaline earth metal enhances the oxygen and electron transfer ability and favors the dissociation of NO, which promotes the activation and storage capacity of the acidic atoms like NOx, and leads to enhanced catalytic activity performance. Copyright © 2014 Elsevier B.V. All rights reserved.

Visible light-induced degradation of acetone over SO42-/MoOx/MgF2 catalysts.

PubMed

He, Yiming; Sheng, Tianlu; Wu, Ying; Chen, Jianshan; Fu, Ruibiao; Hu, Shengming; Wu, Xintao

2009-08-30

A visible light active photodegration catalyst was prepared by doping MoO(3) into MgF(2) matrix. The addition of SO(4)(2-) into MoO(x)/MgF(2) could improve the catalytic activity greatly and an acetone conversion of 96.1% under visible light was obtained on the SO(4)(2-)/5%MoO(x)/MgF(2) (SMM) catalyst. By BET, XRD, Raman, FT-IR, XPS, UV-vis technology the specific area, structure and photoadsorption ability of the catalysts were characterized. The high photocatlaytic activity of the SMM catalyst is attributed to its large specific area, the high dispersal of MoO(3) domains in MgF(2) and the inhibiting effect of MgF(2) matrix on the electron-hole pair recombination.

Method for regeneration and activity improvement of syngas conversion catalyst

DOEpatents

Lucki, Stanley J.; Brennan, James A.

1980-01-01

A method is disclosed for the treatment of single particle iron-containing syngas (synthes.s gas) conversion catalysts comprising iron, a crystalline acidic aluminosilicate zeolite having a silica to alumina ratio of at least 12, a pore size greater than about 5 Angstrom units and a constraint index of about 1-12 and a matrix. The catalyst does not contain promoters and the treatment is applicable to either the regeneration of said spent single particle iron-containing catalyst or for the initial activation of fresh catalyst. The treatment involves air oxidation, hydrogen reduction, followed by a second air oxidation and contact of the iron-containing single particle catalyst with syngas prior to its use for the catalytic conversion of said syngas. The single particle iron-containing catalysts are prepared from a water insoluble organic iron compound.

Catalytic dehydrogenation of isobutane in the presence of hydrogen over Cs-modified Ni2P supported on active carbon

NASA Astrophysics Data System (ADS)

Xu, Yanli; Sang, Huanxin; Wang, Kang; Wang, Xitao

2014-10-01

In this article, an environmentally friendly non-noble-metal class of Cs-Ni2P/active carbon (AC) catalyst was prepared and demonstrated to exhibit enhanced catalytic performance in isobutane dehydrogenation. The results of activity tests reveal that Ni/AC catalyst was highly active for isobutane cracking, which led to the formation of abundant methane and coke. After the introduction of phosphorus through impregnation with ammonium di-hydrogen phosphate and H2-temperature programmed reduction, undesired cracking reactions were effectively inhibited, and the selectivity to isobutene and stability of catalyst increased remarkably. The characterization results indicate that, after the addition of phosphorous, the improvement of dehydrogenation selectivity is ascribed to the partial positive charges carried on Ni surface in Ni2P particles, which decreases the strength of Nisbnd C bond between Ni and carbonium-ion intermediates and the possibility of excessive dehydrogenation. In addition, Cs-modified Ni2P/AC catalysts display much higher catalytic performance as compared to Ni2P/AC catalyst. Cs-Ni2P-6.5 catalyst has the highest catalytic performance, and the selectivity to isobutene higher than 93% can be obtained even after 4 h reaction. The enhancement in catalytic performance of the Cs-modified catalysts is mainly attributed to the function of Cs to improve the dispersion of Ni2P particles, transfer electron from Cs to Ni, and decrease acid site number and strength.

Application of sodium carbonate prevents sulphur poisoning of catalysts in automated total mercury analysis

NASA Astrophysics Data System (ADS)

McLagan, David S.; Huang, Haiyong; Lei, Ying D.; Wania, Frank; Mitchell, Carl P. J.

2017-07-01

Analysis of high sulphur-containing samples for total mercury content using automated thermal decomposition, amalgamation, and atomic absorption spectroscopy instruments (USEPA Method 7473) leads to rapid and costly SO2 poisoning of catalysts. In an effort to overcome this issue, we tested whether the addition of powdered sodium carbonate (Na2CO3) to the catalyst and/or directly on top of sample material increases throughput of sulphur-impregnated (8-15 wt%) activated carbon samples per catalyst tube. Adding 5 g of Na2CO3 to the catalyst alone only marginally increases the functional lifetime of the catalyst (31 ± 4 g of activated carbon analyzed per catalyst tube) in relation to unaltered catalyst of the AMA254 total mercury analyzer (17 ± 4 g of activated carbon). Adding ≈ 0.2 g of Na2CO3 to samples substantially increases (81 ± 17 g of activated carbon) catalyst life over the unaltered catalyst. The greatest improvement is achieved by adding Na2CO3 to both catalyst and samples (200 ± 70 g of activated carbon), which significantly increases catalyst performance over all other treatments and enables an order of magnitude greater sample throughput than the unaltered samples and catalyst. It is likely that Na2CO3 efficiently sequesters SO2, even at high furnace temperatures to produce Na2SO4 and CO2, largely negating the poisonous impact of SO2 on the catalyst material. Increased corrosion of nickel sampling boats resulting from this methodological variation is easily resolved by substituting quartz boats. Overall, this variation enables an efficient and significantly more affordable means of employing automated atomic absorption spectrometry instruments for total mercury analysis of high-sulphur matrices.

Catalyst evaluation for oxygen reduction reaction in concentrated phosphoric acid at elevated temperatures

NASA Astrophysics Data System (ADS)

Hu, Yang; Jiang, Yiliang; Jensen, Jens Oluf; Cleemann, Lars N.; Li, Qingfeng

2018-01-01

Phosphoric acid is the common electrolyte for high-temperature polymer electrolyte fuel cells (HT-PEMFCs) that have advantages such as enhanced CO tolerance and simplified heat and water management. The currently used rotating disk electrode technique is limited to tests in dilute solutions at low temperatures and hence is not suitable for catalyst evaluation for HT-PEMFCs. In this study, we have designed and constructed a half-cell setup to measure the intrinsic activities of catalysts towards the oxygen reduction reaction (ORR) in conditions close to HT-PEMFC cathodes. By optimization of the hydrophobic characteristics of electrodes and the catalyst layer thickness, ORR activities of typical Pt/C catalysts are successfully measured in concentrated phosphoric acid at temperatures above 100 °C. In terms of mass-specific activities, the catalyst exhibits about two times higher activity in the half-cell electrode than that observed in fuel cells, indicating the feasibility of the technique as well as the potential for further improvement of fuel cell electrode performance.

Non-noble catalysts and catalyst supports for phosphoric acid fuel cells

NASA Technical Reports Server (NTRS)

Mcalister, A. J.

1981-01-01

Four different samples of the cubic alloys W sub x-1 Ti sub x C sub 1-y were prepared and found to be active and CO tolerant. When the activities of these cubic alloys were weighted by the reciprocal of the square of the W exchange, they displayed magnitudes and dependence on bulk C deficiency comparable to those of highly active forms of WC. It is concluded that they may offer important insight into the nature of the active sites on, and means for improving the performance of, W-C anode catalysts for use in phosphoric acid fuel cells.

Characterization of Deactivated Bio-oil Hydrotreating Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Huamin; Wang, Yong

Deactivation of bio-oil hydrotreating catalysts remains a significant challenge because of the poor quality of pyrolysis bio-oil input for hydrotreating and understanding their deactivation mode is critical to developing improved catalysts and processes. In this research, we developed an understanding of the deactivation of two-step bio-oil hydrotreating catalysts (sulfided Ru/C and sulfided CoMo/C) through detailed characterization of the catalysts using various complimentary analytical techniques. Severe fouling of both catalysts by carbonaceous species was the major form of deactivation, which is consistent with the significant loss of surface area and pore volume of both deactivated catalysts and the significant increase ofmore » the bulk density. Further analysis of the carbonaceous species by thermogravimetric analysis and x-ray photoelectron spectroscopy indicated that the carbonaceous species was formed by condensation reaction of active species such as sugars and sugar derivatives (aldehydes and ketones) in bio-oil feedstock during bio-oil hydrotreating under the conditions and catalysts used. Microscopy results did not show metal sintering of the Ru/C catalyst. However, X-ray diffraction indicated a probable transformation of the highly-active CoMoS phase in the sulfided CoMo/C catalyst to Co8S9 and MoS2 phase with low activity. Loss of the active site by transport of inorganic elements from the bio-oil and the reactor construction material onto the catalyst surface also might be a cause of deactivation as indicated by elemental analysis of spent catalysts.« less

Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides

DOE PAGES

Sulmonetti, Taylor P.; Pang, Simon H.; Claure, Micaela Taborga; ...

2016-03-09

The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the othermore » catalysts, with promising activity compared to related catalysts in the literature. In conclusion, the use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions.« less

Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sulmonetti, Taylor P.; Pang, Simon H.; Claure, Micaela Taborga

2016-05-01

The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the othermore » catalysts, with promising activity compared to related catalysts in the literature. The use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions.« less

One-pot solvothermal synthesis of ordered intermetallic Pt{sub 2}In{sub 3} as stable and efficient electrocatalyst towards direct alcohol fuel cell application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jana, Rajkumar; Peter, Sebastian C., E-mail: sebastiancp@jncasr.ac.in

Ordered intermetallic Pt{sub 2}In{sub 3} nanoparticles have been synthesized by superhydride reduction of K{sub 2}PtCl{sub 4} and InCl{sub 3}.xH{sub 2}O precursors using facile, one-pot solvothermal method. We report surfactant free solvothermal synthesis of a novel ordered Pt{sub 2}In{sub 3} intermetallic nanoparticles for the first time. The structure and morphology of the catalyst has been confirmed by powder X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive spectrometry and X-ray photoelectron spectroscopy. The electrocatalytic properties of the catalysts have been investigated by cyclic voltammetry and chronoamperometry. The as prepared Pt{sub 2}In{sub 3} catalyst exhibit far superior electrocatalytic activity andmore » stability towards alcohol oxidation over commercial Pt/C. The specific activity of as synthesized catalyst was found to be ~3.2 and ~2.3 times higher than commercial Pt/C for methanol and ethanol oxidation, respectively. This improved activity and durability of the Pt{sub 2}In{sub 3} nanoparticles can make the catalyst an ideal catalyst candidate for direct alcohol fuel cell. - Graphical abstract: The ordered structure of Pt{sub 2}In{sub 3} nanoparticles synthesized by solvothermal method has confirmed through XRD and TEM. Cyclic voltametry and chronoamperometry showed improved catalytic activity and stability compared to commercial Pt/C. - Highlights: • Ordered Pt{sub 2}In{sub 3} nanoparticles were synthesized by solvothermal method. • Electrooxidation of alcohols on Pt{sub 2}In{sub 3} catalyst was investigated in acidic medium. • Pt{sub 2}In{sub 3} catalyst has superior catalytic activity compared to commercial Pt/C. • Pt{sub 2}In{sub 3} catalyst exhibited much higher stability than commercial Pt/C.« less

Steam reforming of n-hexane on pellet and monolithic catalyst beds. A comparative study on improvements due to heat transfer

NASA Technical Reports Server (NTRS)

1981-01-01

Monolithic catalysts with higher available active surface areas and better thermal conductivity than conventional pellets beds, making possible the steam reforming of fuels heavier than naphtha, were examined. Performance comparisons were made between conventional pellet beds and honeycomb monolith catalysts using n-hexane as the fuel. Metal-supported monoliths were examined. These offer higher structural stability and higher thermal conductivity than ceramic supports. Data from two metal monoliths of different nickel catalyst loadings were compared to pellets under the same operating conditions. Improved heat transfer and better conversion efficiencies were obtained with the monolith having higher catalyst loading. Surface-gas interaction was observed throughout the length of the monoliths.

Electrochemical characterization of nano-sized Pd-based catalysts as cathode materials in direct methanol fuel cells.

PubMed

Choi, M; Han, C; Kim, I T; An, J C; Lee, J J; Lee, H K; Shim, J

2011-01-01

To improve the catalytic activity of palladium (Pd) as a cathode catalyst in direct methanol fuel cells (DMFCs), we prepared palladium-titanium oxide (Pd-TiO2) catalysts which the Pd and TiO2 nanoparticles were simultaneously impregnated on carbon. We selected Pd and TiO2 as catalytic materials because of their electrochemical stability in acid solution. The crystal structure and the loading amount of Pd and TiO2 on carbon were characterized by X-ray diffraction (XRD) and energy dispersive X-ray microanalysis (EDX). The electrochemical characterization of Pd-TiO2/C catalysts for the oxygen reduction reaction was carried out in half and single cell systems. The catalytic activities of the Pd-TiO2 catalysts were strongly influenced by the TiO2 content. In the single cell test, the Pd-TiO2 catalysts showed very comparable performance to the Pt catalyst.

Heterogenised Molecular Catalysts for the Reduction of CO₂ to Fuels.

PubMed

Windle, Christopher D; Reisner, Erwin

2015-08-19

CO2 conversion provides a possible solution to curtail the growing CO2 levels in our atmosphere and reduce dependence on fossil fuels. To this end, it is essential to develop efficient catalysts for the reduction of CO2. The structure and activity of molecular CO2 reduction catalysts can be tuned and they offer good selectivity with reasonable stability. Heterogenisation of these molecules reduces solvent restrictions, facilitates recyclability and can dramatically improve activity by preventing catalyst inactivation and perturbing the kinetics of intermediates. The nature and morphology of the solid-state material upon which the catalyst is immobilised can significantly influence the activity of the hybrid assembly. Although work in this area began forty years ago, it has only drawn substantial attention in recent years. This review article gives an overview of the historical development of the field.

Heterogenised Molecular Catalysts for the Reduction of CO2 to Fuels.

PubMed

Windle, Christopher D; Reisner, Erwin

2015-01-01

CO(2) conversion provides a possible solution to curtail the growing CO(2) levels in our atmosphere and reduce dependence on fossil fuels. To this end, it is essential to develop efficient catalysts for the reduction of CO(2). The structure and activity of molecular CO(2) reduction catalysts can be tuned and they offer good selectivity with reasonable stability. Heterogenisation of these molecules reduces solvent restrictions, facilitates recyclability and can dramatically improve activity by preventing catalyst inactivation and perturbing the kinetics of intermediates. The nature and morphology of the solid-state material upon which the catalyst is immobilised can significantly influence the activity of the hybrid assembly. Although work in this area began forty years ago, it has only drawn substantial attention in recent years. This review article gives an overview of the historical development of the field.

New porous titanium–niobium oxide for photocatalytic degradation of bromocresol green dye in aqueous solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chaleshtori, Maryam Zarei, E-mail: mzarei@utep.edu; Hosseini, Mahsa; Edalatpour, Roya

2013-10-15

Graphical abstract: The photocatalytic activity of different porous titanium–niobium oxides was evaluated toward degradation of bromocresol green (BG) under UV light. A better catalytic activity was observed for all samples at lower pH. Catalysts have a stronger ability for degradation of BG in acid media than in alkaline media. - Highlights: • Different highly structured titanium–niobium oxides have been prepared using improved methods of synthesis. • Photo-degradation of bromocresol green dye (BG) with nanostructure titanium–niobium oxide catalysts was carried out under UV light. • The photo-catalytic activity of all catalysts was higher in lower pH. • Titanium–niobium oxide catalysts aremore » considerably stable and reusable. - Abstract: In this study, high surface area semiconductors, non porous and porous titanium–niobium oxides derived from KTiNbO{sub 5} were synthesized, characterized and developed for their utility as photocatalysts for decontamination with sunlight. These materials were then used in the photocatalytic degradation of bromocresol green dye (BG) in aqueous solution using UV light and their catalytic activities were evaluated at various pHs. For all catalysts, the photocatalytic degradation of BG was most efficient in acidic solutions. Results show that the new porous oxides have large porous and high surface areas and high catalytic activity. A topotactic dehydration treatment greatly improves catalyst performance at various pHs. Stability and long term activity of porous materials (topo and non-topo) in photocatalysis reactions was also tested. These results suggest that the new materials can be used to efficiently purify contaminated water.« less

Approaches to efficient molecular catalyst systems for photochemical H2 production using [FeFe]-hydrogenase active site mimics.

PubMed

Wang, Mei; Chen, Lin; Li, Xueqiang; Sun, Licheng

2011-12-28

The research on structural and functional biomimics of the active site of [FeFe]-hydrogenases is in an attempt to elucidate the mechanisms of H(2)-evolution and uptake at the [FeFe]-hydrogenase active site, and to learn from Nature how to create highly efficient H(2)-production catalyst systems. Undoubtedly, it is a challenging, arduous, and long-term work. In this perspective, the progresses in approaches to photochemical H(2) production using mimics of the [FeFe]-hydrogenase active site as catalysts in the last three years are reviewed, with emphasis on adjustment of the redox potentials and hydrophilicity of the [FeFe]-hydrogenase active site mimics to make them efficient catalysts for H(2) production. With gradually increasing understanding of the chemistry of the [FeFe]-hydrogenases and their mimics, more bio-inspired proton reduction catalysts with significantly improved efficiency of H(2) production will be realized in the future. This journal is © The Royal Society of Chemistry 2011

Facile solid-state synthesis of highly dispersed Cu nanospheres anchored on coal-based activated carbons as an efficient heterogeneous catalyst for the reduction of 4-nitrophenol

NASA Astrophysics Data System (ADS)

Wang, Shan; Gao, Shasha; Tang, Yakun; Wang, Lei; Jia, Dianzeng; Liu, Lang

2018-04-01

Coal-based activated carbons (AC) were acted as the support, Cu/AC catalysts were synthesized by a facile solid-state reaction combined with subsequent heat treatment. In Cu/AC composites, highly dispersed Cu nanospheres were anchored on AC. The catalytic activity for 4-nitrophenol (4-NP) was investigated, the effects of activation temperature and copper loading on the catalytic performance were studied. The catalysts exhibited very high catalytic activity and moderate chemical stability due to the unique characteristics of the particle-assembled nanostructures, the high surface area and the porous structure of coal-based AC and the good dispersion of metal particles. Design and preparation of non-noble metal composite catalysts provide a new direction for improving the added value of coal.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yung, Matthew M.; Starace, Anne K.; Mukarakate, Calvin

Here in this work, Ni/ZSM-5 catalysts with varied nickel loadings were evaluated for their ability to produce aromatic hydrocarbons by upgrading of pine pyrolysis vapors. The effect of catalyst pretreatment by hydrogen reduction was also investigated. Results indicate that the addition of nickel increases the yield of aromatic hydrocarbons while simultaneously increasing the conversion of oxygenates, relative to ZSM-5, and these effects are more pronounced with increasing nickel loading. Additionally, while initial activity differences were observed between the oxidized and reduced forms of nickel on ZSM-5 (i.e., NiO/ZSM-5 versus Ni/ZSM-5), the activity of both catalysts converges with increasing time onmore » stream. These reaction results coupled with characterization of pristine and spent catalysts suggest that the catalysts reach similar active states during catalytic pyrolysis, regardless of pretreatment, as NiO undergoes in situ reduction to Ni by biomass pyrolysis vapors. This reduction of NiO to Ni was confirmed by reaction results and characterization by NH 3 temperature-programmed desorption, temperature-programmed reduction, and X-ray diffraction. This finding is significant in that the ability to reduce or eliminate the need for a pre-reaction H 2 reduction of Ni-modified zeolite catalysts could reduce process complexity and operating costs in a biorefinery-based vapor-phase upgrading process to produce biomass-derived fuels and chemicals. The ability to monitor catalyst activity in real time with a molecular beam mass spectrometer used to measure uncondensed, hot pyrolysis vapors allows for an improved understanding of the mechanism for improved activity with Ni addition to ZSM-5, which is attributed to the ability to prevent deactivation by deposition of coke and capping of zeolite micropores.« less

Biomass Catalytic Pyrolysis on Ni/ZSM-5: Effects of Nickel Pretreatment and Loading

DOE PAGES

Yung, Matthew M.; Starace, Anne K.; Mukarakate, Calvin; ...

2016-04-25

Here in this work, Ni/ZSM-5 catalysts with varied nickel loadings were evaluated for their ability to produce aromatic hydrocarbons by upgrading of pine pyrolysis vapors. The effect of catalyst pretreatment by hydrogen reduction was also investigated. Results indicate that the addition of nickel increases the yield of aromatic hydrocarbons while simultaneously increasing the conversion of oxygenates, relative to ZSM-5, and these effects are more pronounced with increasing nickel loading. Additionally, while initial activity differences were observed between the oxidized and reduced forms of nickel on ZSM-5 (i.e., NiO/ZSM-5 versus Ni/ZSM-5), the activity of both catalysts converges with increasing time onmore » stream. These reaction results coupled with characterization of pristine and spent catalysts suggest that the catalysts reach similar active states during catalytic pyrolysis, regardless of pretreatment, as NiO undergoes in situ reduction to Ni by biomass pyrolysis vapors. This reduction of NiO to Ni was confirmed by reaction results and characterization by NH 3 temperature-programmed desorption, temperature-programmed reduction, and X-ray diffraction. This finding is significant in that the ability to reduce or eliminate the need for a pre-reaction H 2 reduction of Ni-modified zeolite catalysts could reduce process complexity and operating costs in a biorefinery-based vapor-phase upgrading process to produce biomass-derived fuels and chemicals. The ability to monitor catalyst activity in real time with a molecular beam mass spectrometer used to measure uncondensed, hot pyrolysis vapors allows for an improved understanding of the mechanism for improved activity with Ni addition to ZSM-5, which is attributed to the ability to prevent deactivation by deposition of coke and capping of zeolite micropores.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barroo, Cedric; Janvelyan, Nare; Zugic, Branko

To improve the understanding of catalytic processes, the surface structure and composition of the active materials need to be determined before and after reaction. Morphological changes may occur under reaction conditions and can dramatically influence the reactivity and/or selectivity of a catalyst. Goldbased catalysts with different architectures are currently being developed for selective oxidation reactions at low temperatures. Specifically, nanoporous Au (npAu) with a composition of Au 97-Ag 3 is obtained by dealloying a Ag 70-Au 30 bulk alloy. Recent studies highlight the efficiency of npAu catalysts for methanol oxidation using ozone to activate the catalysts before methanol oxidation. Inmore » this paper, we studied the morphological and compositional changes occurring at the surface of Au-based catalysts in certain conditions.« less

Ce-Sn binary oxide catalyst for the selective catalytic reduction of NOx by NH3

NASA Astrophysics Data System (ADS)

Liu, Zhiming; Feng, Xu; Zhou, Zizheng; Feng, Yongjun; Li, Junhua

2018-01-01

Ce-Sn binary oxide catalysts prepared by the hydrothermal method have been investigated for the selective catalytic reduction (SCR) of NOx with NH3. Compared with pure CeO2 and SnO2, Ce-Sn binary oxide catalyst showed significantly higher NH3-SCR activity. Moreover, Ce-Sn catalyst showed high resistance against H2O and SO2. The high catalytic performance of Ce-Sn binary oxide is attributed to the synergetic effect between Ce and Sn species, which not only enhances the redox property of the catalyst but also increases the Lewis acidity, thus promoting the adsorption and activation of NH3 species, which contributes to improving the NH3-SCR performance.

Development of HAN-based Liquid Propellant Thruster

NASA Astrophysics Data System (ADS)

Hisatsune, K.; Izumi, J.; Tsutaya, H.; Furukawa, K.

2004-10-01

Many of propellants that are applied to the conventional spacecraft propulsion system are toxic propellants. Because of its toxicity, considering the environmental pollution or safety on handling, it will be necessary to apply the "green" propellant to the spacecraft propulsion system. The purpose of this study is to apply HAN based liquid propellant (LP1846) to mono propellant thruster. Compared to the hydrazine that is used in conventional mono propellant thruster, HAN based propellant is not only lower toxic but also can obtain higher specific impulse. Moreover, HAN based propellant can be decomposed by the catalyst. It means there are the possibility of applying to the mono propellant thruster that can leads to the high reliability of the propulsion system.[1],[2] However, there are two technical subjects, to apply HAN based propellant to the mono propellant thruster. One is the high combustion temperature. The catalyst will be damaged under high temperature condition. The other is the low catalytic activity. It is the serious problem on application of HAN based propellant to the mono propellant thruster that is used for attitude control of spacecraft. To improve the catalytic activity of HAN based propellant, it is necessary to screen the best catalyst for HAN based propellant. The adsorption analysis is conducted by Monte Carlo Simulation to screen the catalyst metal for HAN and TEAN. The result of analysis shows the Iridium is the best catalyst metal for HAN and TEAN. Iridium is the catalyst metal that is used at conventional mono propellant thruster catalyst Shell405. Then, to confirm the result of analysis, the reaction test about catalyst is conducted. The result of this test is the same as the result of adsorption analysis. That means the adsorption analysis is effective in screening the catalyst metal. At the evaluating test, the various types of carrier of catalyst are also compared to Shell 405 to improve catalytic activity. The test result shows the inorganic porous media is superior to Shell405 in catalytic activity. Next, the catalyst life with HAN based propellant (LP1846) is evaluated. The Shell405 and inorganic porous media catalyst are compared at the life test. The test result shows the inorganic porous media catalyst is superior to Shell405 in catalyst life. In this paper, the detail of the result of adsorption analysis and evaluating test are reported.

Enhanced Oxidation Catalysts for Water Reclamation

NASA Technical Reports Server (NTRS)

Jolly, Clifford D.

1999-01-01

This effort seeks to develop and test high-performance, long operating life, physically stable catalysts for use in spacecraft water reclamation systems. The primary goals are to a) reduce the quantity of expendable water filters used to purify water aboard spacecraft, b) to extend the life of the oxidation catalysts used for eliminating organic contaminants in the water reclamation systems, and c) reduce the weight/volume of the catalytic oxidation systems (e.g. VRA) used. This effort is targeted toward later space station utilization and will consist of developing flight-qualifiable catalysts and long-term ground tests of the catalyst prior to their utilization in flight. Fixed -bed catalytic reactors containing 5% platinum on granular activated carbon have been subjected to long-term dynamic column tests to measure catalyst stability vs throughput. The data generated so far indicate that an order of magnitude improvement can be obtained with the treated catalysts vs the control catalyst, at only a minor loss (approx 10%) in the initial catalytic activity.

Catalytic wet peroxide oxidation of benzoic acid over Fe/AC catalysts: Effect of nitrogen and sulfur co-doped activated carbon.

PubMed

Qin, Hangdao; Xiao, Rong; Chen, Jing

2018-06-01

The parent activated carbon (ACP) was modified with urea and thiourea to obtain N-doped activated carbon (ACN) and N, S co-doped activated carbon (ACNS), respectively. Iron supported on activated carbon (Fe/ACP, Fe/ACN and Fe/ACNS) were prepared and worked as catalyst for catalytic wet peroxide oxidation of benzoic acid (BA). The catalysts were characterized by N 2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM), and their performance was evaluated in terms of benzoic acid and TOC removal. The results indicated the doped N and S improved the adsorption capacity as well as catalytic activity of activated carbon. Besides, the catalytic activity toward benzoic acid degradation was found to be enhanced by Fe/ACNS compared to that of Fe/ACP and Fe/ACN. The enhanced catalytic performance was attributed to the presence of the nitrogen and sulfur atoms may serve to improve the relative amount of Fe 2+ on iron oxide surface and also help prevent leaching of Fe. It was also observed that the stability or reutilization of Fe/ACNS catalyst was fairly good. Copyright © 2018 Elsevier B.V. All rights reserved.

Facile Fabrication of Platinum-Cobalt Alloy Nanoparticles with Enhanced Electrocatalytic Activity for a Methanol Oxidation Reaction

NASA Astrophysics Data System (ADS)

Huang, Huihong; Hu, Xiulan; Zhang, Jianbo; Su, Nan; Cheng, Jiexu

2017-03-01

Decreasing the cost associated with platinum-based catalysts along with improving their catalytic properties is a major challenge for commercial direct methanol fuel cells. In this work, a simple and facile strategy was developed for the more efficient preparation of multi-walled carbon nanotube (MWCNT) -supported Pt/CoPt composite nanoparticles (NPs) via solution plasma sputtering with subsequent thermal annealing. Quite different from general wet synthesis methods, Pt/CoPt composite NPs were directly derived from metal wire electrodes without any additions. The obtained Pt/CoPt/MWCNTs composite catalysts exhibited tremendous improvement in the electro-oxidation of methanol in acidic media with mass activities of 1719 mA mg-1Pt. This value is much higher than that of previous reports of Pt-Co alloy and commercial Pt/C (3.16 times) because of the many active sites and clean surface of the catalysts. The catalysts showed good stability due to the special synergistic effects of the CoPt alloy. Pt/CoPt/MWCNTs can be used as a promising catalyst for direct methanol fuel cells. In addition, this solution plasma sputtering-assisted synthesis method introduces a general and feasible route for the synthesis of binary alloys.

Facile Fabrication of Platinum-Cobalt Alloy Nanoparticles with Enhanced Electrocatalytic Activity for a Methanol Oxidation Reaction.

PubMed

Huang, Huihong; Hu, Xiulan; Zhang, Jianbo; Su, Nan; Cheng, JieXu

2017-03-30

Decreasing the cost associated with platinum-based catalysts along with improving their catalytic properties is a major challenge for commercial direct methanol fuel cells. In this work, a simple and facile strategy was developed for the more efficient preparation of multi-walled carbon nanotube (MWCNT) -supported Pt/CoPt composite nanoparticles (NPs) via solution plasma sputtering with subsequent thermal annealing. Quite different from general wet synthesis methods, Pt/CoPt composite NPs were directly derived from metal wire electrodes without any additions. The obtained Pt/CoPt/MWCNTs composite catalysts exhibited tremendous improvement in the electro-oxidation of methanol in acidic media with mass activities of 1719 mA mg -1 Pt . This value is much higher than that of previous reports of Pt-Co alloy and commercial Pt/C (3.16 times) because of the many active sites and clean surface of the catalysts. The catalysts showed good stability due to the special synergistic effects of the CoPt alloy. Pt/CoPt/MWCNTs can be used as a promising catalyst for direct methanol fuel cells. In addition, this solution plasma sputtering-assisted synthesis method introduces a general and feasible route for the synthesis of binary alloys.

Improved hydrous oxide ion-exchange compound catalysts

DOEpatents

Dosch, R.G.; Stephens, H.P.

1986-04-09

Disclosed is a catalytic material of improved activity which comprises a hydrous, alkali metal or alkaline earth metal or quaternary ammonium titanate, zirconate, niobate, or tantalate, in which the metal or ammonium cations have been exchanged with a catalytically effective quantity of a catalyst metal, and which has been subsequently treated with a solution of a Bronsted acid.

UV Light-Assisted Synthesis of Highly Efficient Pd-Based Catalyst over NiO for Hydrogenation of o-Chloronitrobenzene

PubMed Central

Jiang, Weidong; Xu, Bin; Fan, Guangyin; Zhang, Kaiming; Xiang, Zhen; Liu, Xiaoqiang

2018-01-01

Supported Pd-based catalyst over active nickel oxide (NiO) was repared using the impregnation method companying with UV-light irradiation. Moreover, the catalytic performance of the obtained Pd-based catalysts was evaluated towards the hydrogenation of o-chloronitrobenzene (o-CNB). Observations indicate that the as-prepared UV-irradiated Pd/NiO catalyst with a mole fraction 0.2% (0.2%Pd/NiO) has higher activity and selectivity in the o-CNB hydrogenation. Especially, UV-light irradiation played a positive role in the improvement of catalytic activity of 0.2%Pd/NiO catalyst, exhibiting an excess 11-fold activity superiority in contrast with non-UV-irradiated 0.2%Pd/NiO catalyst. In addition, it was investigated that effects of varied factors (i.e., reaction time, temperature, o-CNB/Pd ratio, Pd loading, hydrogen pressure) on the selective hydrogenation of ο-CNB catalyzed by UV-irradiated 0.2%Pd/NiO catalyst. Under the reaction conditions of 60 °C, 0.5 h, 1 MPa H2 pressure, 100% conversion of o-CNB, and 81.1% o-CAN selectivity were obtained, even at high molar ratio (8000:1) of o-CNB to Pd. PMID:29662004

UV Light-Assisted Synthesis of Highly Efficient Pd-Based Catalyst over NiO for Hydrogenation of o-Chloronitrobenzene.

PubMed

Jiang, Weidong; Xu, Bin; Fan, Guangyin; Zhang, Kaiming; Xiang, Zhen; Liu, Xiaoqiang

2018-04-14

Supported Pd-based catalyst over active nickel oxide (NiO) was repared using the impregnation method companying with UV-light irradiation. Moreover, the catalytic performance of the obtained Pd-based catalysts was evaluated towards the hydrogenation of o -chloronitrobenzene ( o -CNB). Observations indicate that the as-prepared UV-irradiated Pd/NiO catalyst with a mole fraction 0.2% (0.2%Pd/NiO) has higher activity and selectivity in the o -CNB hydrogenation. Especially, UV-light irradiation played a positive role in the improvement of catalytic activity of 0.2%Pd/NiO catalyst, exhibiting an excess 11-fold activity superiority in contrast with non-UV-irradiated 0.2%Pd/NiO catalyst. In addition, it was investigated that effects of varied factors (i.e., reaction time, temperature, o -CNB/Pd ratio, Pd loading, hydrogen pressure) on the selective hydrogenation of ο -CNB catalyzed by UV-irradiated 0.2%Pd/NiO catalyst. Under the reaction conditions of 60 °C, 0.5 h, 1 MPa H₂ pressure, 100% conversion of o -CNB, and 81.1% o -CAN selectivity were obtained, even at high molar ratio (8000:1) of o -CNB to Pd.

New insight into the promoting role of process on the CeO₂-WO₃/TiO₂ catalyst for NO reduction with NH₃ at low-temperature.

PubMed

Zhang, Shule; Zhong, Qin; Shen, Yuge; Zhu, Li; Ding, Jie

2015-06-15

This study aimed at investigating the reason of high catalytic activity for CeO2-WO3/TiO2 catalyst from the aspects of WO3 interaction with other species and the NO oxidation process. Analysis by X-ray diffractometry, photoluminescence spectra, diffuse reflectance UV-visible, X-ray photoelectron spectroscopy, density functional theory calculations, electron paramagnetic resonance spectroscopy, temperature-programmed-desorption of NO and in situ diffuse reflectance infrared transform spectroscopy showed that WO3 could interact with CeO2 to improve the electron gaining capability of CeO2 species. In addition, WO3 species acted as electron donating groups to transfer the electrons to CeO2 species. The two aspects enhanced the formation of reduced CeO2 species to improve the formation of superoxide ions. Furthermore, the Ce species were the active sites for the NO adsorption and the superoxide ions over the catalyst needed oxidizing the adsorbed NO to improve the NO oxidation. This process was responsible for the high catalytic activity of CeO2-WO3/TiO2 catalyst. Copyright © 2015 Elsevier Inc. All rights reserved.

Gallium-rich Pd-Ga phases as supported liquid metal catalysts

NASA Astrophysics Data System (ADS)

Taccardi, N.; Grabau, M.; Debuschewitz, J.; Distaso, M.; Brandl, M.; Hock, R.; Maier, F.; Papp, C.; Erhard, J.; Neiss, C.; Peukert, W.; Görling, A.; Steinrück, H.-P.; Wasserscheid, P.

2017-09-01

A strategy to develop improved catalysts is to create systems that merge the advantages of heterogeneous and molecular catalysis. One such system involves supported liquid-phase catalysts, which feature a molecularly defined, catalytically active liquid film/droplet layer adsorbed on a porous solid support. In the past decade, this concept has also been extended to supported ionic liquid-phase catalysts. Here we develop this idea further and describe supported catalytically active liquid metal solutions (SCALMS). We report a liquid mixture of gallium and palladium deposited on porous glass that forms an active catalyst for alkane dehydrogenation that is resistant to coke formation and is thus highly stable. X-ray diffraction and X-ray photoelectron spectroscopy, supported by theoretical calculations, confirm the liquid state of the catalytic phase under the reaction conditions. Unlike traditional heterogeneous catalysts, the supported liquid metal reported here is highly dynamic and catalysis does not proceed at the surface of the metal nanoparticles, but presumably at homogeneously distributed metal atoms at the surface of a liquid metallic phase.

A palladium-doped ceria@carbon core-sheath nanowire network: a promising catalyst support for alcohol electrooxidation reactions.

PubMed

Tan, Qiang; Du, Chunyu; Sun, Yongrong; Du, Lei; Yin, Geping; Gao, Yunzhi

2015-08-28

A novel palladium-doped ceria and carbon core-sheath nanowire network (Pd-CeO2@C CSNWN) is synthesized by a template-free and surfactant-free solvothermal process, followed by high temperature carbonization. This hierarchical network serves as a new class of catalyst support to enhance the activity and durability of noble metal catalysts for alcohol oxidation reactions. Its supported Pd nanoparticles, Pd/(Pd-CeO2@C CSNWN), exhibit >9 fold increase in activity toward the ethanol oxidation over the state-of-the-art Pd/C catalyst, which is the highest among the reported Pd systems. Moreover, stability tests show a virtually unchanged activity after 1000 cycles. The high activity is mainly attributed to the superior oxygen-species releasing capability of Pd-doped CeO2 nanowires by accelerating the removal of the poisoning intermediate. The unique interconnected one-dimensional core-sheath structure is revealed to facilitate immobilization of the metal catalysts, leading to the improved durability. This core-sheath nanowire network opens up a new strategy for catalyst performance optimization for next-generation fuel cells.

Steam Reforming of Acetic Acid over Co-Supported Catalysts: Coupling Ketonization for Greater Stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davidson, Stephen D.; Spies, Kurt A.; Mei, Donghai

We report on the markedly improved stability of a novel 2-bed catalytic system, as compared to a conventional 1-bed steam reforming catalyst, for the production of H2 from acetic acid. The 2-bed catalytic system comprises of i) a basic oxide ketonization catalyst for the conversion of acetic acid to acetone, and a ii) Co-based steam reforming catalyst, both catalytic beds placed in sequence within the same unit operation. Steam reforming catalysts are particularly prone to catalytic deactivation when steam reforming acetic acid, used here as a model compound for the aqueous fraction of bio-oil. Catalysts comprising MgAl2O4, ZnO, CeO2, andmore » activated carbon (AC) both with and without Co-addition were evaluated for conversion of acetic acid and acetone, its ketonization product, in the presence of steam. It was found that over the bare oxide support only ketonization activity was observed and coke deposition was minimal. With addition of Co to the oxide support steam reforming activity was facilitated and coke deposition was significantly increased. Acetone steam reforming over the same Co-supported catalysts demonstrated more stable performance and with less coke deposition than with acetic acid feedstock. DFT analysis suggests that over Co surface CHxCOO species are more favorably formed from acetic acid versus acetone. These CHxCOO species are strongly bound to the Co catalyst surface and could explain the higher propensity for coke formation from acetic acid. Based on these findings, in order to enhance stability of the steam reforming catalyst a dual-bed (2-bed) catalyst system was implemented. Comparing the 2-bed and 1-bed (Co-supported catalyst only) systems under otherwise identical reaction conditions the 2-bed demonstrated significantly improved stability and coke deposition was decreased by a factor of 4.« less

CeO2 nanocubes-graphene oxide as durable and highly active catalyst support for proton exchange membrane fuel cell

PubMed Central

Lei, M.; Wang, Z. B.; Li, J. S.; Tang, H. L.; Liu, W. J.; Wang, Y. G.

2014-01-01

Rapid degradation of cell performance still remains a significant challenge for proton exchange membrane fuel cell (PEMFC). In this work, we develop novel CeO2 nanocubes-graphene oxide nanocomposites as durable and highly active catalyst support for proton exchange membrane fuel cell. We show that the use of CeO2 as the radical scavenger in the catalysts remarkably improves the durability of the catalyst. The catalytic activity retention of Pt-graphene oxide-8 wt.% CeO2 nanocomposites reaches as high as 69% after 5000 CV-cycles at a high voltage range of 0.8–1.23 V, in contrast to 19% for that of the Pt-graphene oxide composites. The excellent durability of the Pt-CeO2 nanocubes-graphene oxide catalyst is attributed to the free radical scavenging activity of CeO2, which significantly slows down the chemical degradation of Nafion binder in catalytic layers, and then alleviates the decay of Pt catalysts, resulting in the excellent cycle life of Pt-CeO2-graphene oxide nanocomposite catalysts. Additionally, the performance of single cell assembled with Nafion 211 membrane and Pt-CeO2-graphene oxide catalysts with different CeO2 contents in the cathode as well as the Pt-C catalysts in the anode are also recorded and discussed in this study. PMID:25491655

CeO2 nanocubes-graphene oxide as durable and highly active catalyst support for proton exchange membrane fuel cell.

PubMed

Lei, M; Wang, Z B; Li, J S; Tang, H L; Liu, W J; Wang, Y G

2014-12-10

Rapid degradation of cell performance still remains a significant challenge for proton exchange membrane fuel cell (PEMFC). In this work, we develop novel CeO2 nanocubes-graphene oxide nanocomposites as durable and highly active catalyst support for proton exchange membrane fuel cell. We show that the use of CeO2 as the radical scavenger in the catalysts remarkably improves the durability of the catalyst. The catalytic activity retention of Pt-graphene oxide-8 wt.% CeO2 nanocomposites reaches as high as 69% after 5000 CV-cycles at a high voltage range of 0.8-1.23 V, in contrast to 19% for that of the Pt-graphene oxide composites. The excellent durability of the Pt-CeO2 nanocubes-graphene oxide catalyst is attributed to the free radical scavenging activity of CeO2, which significantly slows down the chemical degradation of Nafion binder in catalytic layers, and then alleviates the decay of Pt catalysts, resulting in the excellent cycle life of Pt-CeO2-graphene oxide nanocomposite catalysts. Additionally, the performance of single cell assembled with Nafion 211 membrane and Pt-CeO2-graphene oxide catalysts with different CeO2 contents in the cathode as well as the Pt-C catalysts in the anode are also recorded and discussed in this study.

CeO2 nanocubes-graphene oxide as durable and highly active catalyst support for proton exchange membrane fuel cell

NASA Astrophysics Data System (ADS)

Lei, M.; Wang, Z. B.; Li, J. S.; Tang, H. L.; Liu, W. J.; Wang, Y. G.

2014-12-01

Rapid degradation of cell performance still remains a significant challenge for proton exchange membrane fuel cell (PEMFC). In this work, we develop novel CeO2 nanocubes-graphene oxide nanocomposites as durable and highly active catalyst support for proton exchange membrane fuel cell. We show that the use of CeO2 as the radical scavenger in the catalysts remarkably improves the durability of the catalyst. The catalytic activity retention of Pt-graphene oxide-8 wt.% CeO2 nanocomposites reaches as high as 69% after 5000 CV-cycles at a high voltage range of 0.8-1.23 V, in contrast to 19% for that of the Pt-graphene oxide composites. The excellent durability of the Pt-CeO2 nanocubes-graphene oxide catalyst is attributed to the free radical scavenging activity of CeO2, which significantly slows down the chemical degradation of Nafion binder in catalytic layers, and then alleviates the decay of Pt catalysts, resulting in the excellent cycle life of Pt-CeO2-graphene oxide nanocomposite catalysts. Additionally, the performance of single cell assembled with Nafion 211 membrane and Pt-CeO2-graphene oxide catalysts with different CeO2 contents in the cathode as well as the Pt-C catalysts in the anode are also recorded and discussed in this study.

Nanostructured Perovskite LaCo1-xMnxO3 as Bifunctional Catalysts for Rechargeable Metal-Air Batteries

NASA Astrophysics Data System (ADS)

Ge, Xiaoming; Li, Bing; Wuu, Delvin; Sumboja, Afriyanti; An, Tao; Hor, T. S. Andy; Zong, Yun; Liu, Zhaolin

2015-09-01

Bifunctional catalyst that is active for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the most important components of rechargeable metal-air batteries. Nanostructured perovskite bifunctional catalysts comprising La, Co and Mn(LaCo1-xMnxO3, LCMO) are synthesized by hydrothermal methods. The morphology, structure and electrochemical activity of the perovskite bifunctional catalysts are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and rotating disk electrode (RDE) techniques. Nanorod, nanodisc and nanoparticle are typical morphologies of LCMO. The electrocatalytic activity of LCMO is significantly improved by the addition of conductive materials such as carbon nanotube. To demonstrate the practical utilization, LCMO in the composition of LaCo0.8Mn0.2O3(LCMO82) is used as air cathode catalysts for rechargeable zinc-air batteries. The battery prototype can sustain 470 h or 40 discharge-charge cycles equivalent.

A Non-sulfided flower-like Ni-PTA Catalyst that Enhances the Hydrotreatment Efficiency of Plant Oil to Produce Green Diesel

PubMed Central

Liu, Jing; Chen, Pan; Deng, Lihong; He, Jing; Wang, Luying; Rong, Long; Lei, Jiandu

2015-01-01

The development of a novel non-sulfided catalyst with high activity for the hydrotreatment processing of plant oils, is of high interest as a way to improve the efficient production of renewable diesel. To attempt to develop such a catalyst, we first synthesized a high activity flower-like Ni-PTA catalyst used in the hydrotreatment processes of plant oils. The obtained catalyst was characterized with SEM, EDX, HRTEM, BET, XRD, H2-TPR, XPS and TGA. A probable formation mechanism of flower-like Ni(OH)2 is proposed on the basis of a range of contrasting experiments. The results of GC showed that the conversion yield of Jatropha oil was 98.95%, and the selectivity of C11-C18 alkanes was 70.93% at 360 °C, 3 MPa, and 15 h−1. The activity of this flower-like Ni-PTA catalyst was more than 15 times higher than those of the conventional Ni-PTA/Al2O3 catalysts. Additionally, the flower-like Ni-PTA catalyst exhibited good stability during the process of plant oil hydrotreatment. PMID:26503896

Hybrid NiCoOx adjacent to Pd nanoparticles as a synergistic electrocatalyst for ethanol oxidation

NASA Astrophysics Data System (ADS)

Wang, Wei; Yang, Yan; Liu, Yanqin; Zhang, Zhe; Dong, Wenkui; Lei, Ziqiang

2015-01-01

To improve the electrocatalytic activity of Pd for ethanol oxidation, hybrid NiCoOx adjacent to Pd catalyst (Pd-NiCoOx/C) is successfully synthesized. Physical characterization shows NiCoOx is closely adjacent to Pd nanoparticles in Pd-NiCoOx/C catalyst, which leads to Strong Metal-Support Interactions (SMSI) between the NiCoOx and Pd nanoparticles, in favor of the electrocatalytic properties. The Pd-NiCoOx/C catalyst is estimated to own larger electrochemically active surface area than Pd/C and Pd-NiO/C catalysts. Moreover, compared to Pd/C catalyst, the onset potential of Pd-NiCoOx/C catalyst is negative 40 mV for ethanol oxidation. Noticeably, the current density of Pd-NiCoOx/C catalyst is 2.05 and 1.43 times higher contrasted to Pd/C and Pd-NiO/C catalysts accordingly. Importantly, the Pd-NiCoOx/C catalyst exhibits better stability during ethanol oxidation, which is a promising electrocatalyst for application in direct alkaline alcohol fuel cells.

Cobalt doped CuMnOx catalysts for the preferential oxidation of carbon monoxide

NASA Astrophysics Data System (ADS)

Dey, Subhashish; Dhal, Ganesh Chandra; Mohan, Devendra; Prasad, Ram; Gupta, Rajeev Nayan

2018-05-01

Carbon monoxide (CO) is a poisonous gas, recognized as a silent killer for the 21st century. It is produced from the partial oxidation of carbon containing compounds. The catalytic oxidation of CO receives a huge attention due to its applications in different fields. In the present work, hopcalite (CuMnOx) catalysts were synthesized using a co-precipitation method for CO oxidation purposes. Also, it was doped with the cobalt by varying concentration from 1 to 5wt%. It was observed that the addition of cobalt into the CuMnOx catalyst (by the deposition-precipitation method) improved the catalytic performance for the low-temperature CO oxidation. CuMnOx catalyst doped with 3wt% of cobalt exhibited most active performance and showed the highest activity than other cobalt concentrations. Different analytical tools (i.e. XRD, FTIR, BET, XPS and SEM-EDX) were used to characterize the as-synthesized catalysts. It was expected that the introduction of cobalt will introduce new active sites into the CuMnOx catalyst that are associated with the cobalt nano-particles. The order of calcination strategies based on the activity for cobalt doped CuMnOx catalysts was observed as: Reactive calcinations (RC) > flowing air > stagnant air. Therefore, RC (4.5% CO in air) route can be recommended for the synthesis of highly active catalysts. The catalytic activity of doped CuMnOx catalysts toward CO oxidation shows a correlation among average oxidation number of Mn and the position and the nature of the doped cobalt cation.

Catalyst characterization in the presence of solvent: development of liquid phase structure–activity relationships

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gould, Nicholas S.; Xu, Bingjun

Due to the low volatility and highly oxygenated nature of biomass derived feedstocks, biomass upgrade reactions are frequently conducted in the presence of solvent to improve substrate mass transfer to the catalyst surface.

Catalyst characterization in the presence of solvent: development of liquid phase structure–activity relationships

DOE PAGES

Gould, Nicholas S.; Xu, Bingjun

2018-01-01

Due to the low volatility and highly oxygenated nature of biomass derived feedstocks, biomass upgrade reactions are frequently conducted in the presence of solvent to improve substrate mass transfer to the catalyst surface.

Novel synthesis of highly durable and active Pt catalyst encapsulated in nitrogen containing carbon for polymer electrolyte membrane fuel cell

NASA Astrophysics Data System (ADS)

Lee, Hyunjoon; Sung, Yung-Eun; Choi, Insoo; Lim, Taeho; Kwon, Oh Joong

2017-09-01

Novel synthesis of a Pt catalyst encapsulated in a N-containing carbon layer for use in a polymer electrolyte membrane fuel cell is described in this study. A Pt-aniline complex, formed by mixing Pt precursor and aniline monomer, was used as the source of Pt, C, and N. Heat treatment of the Pt-aniline complex with carbon black yielded 5 nm Pt nanoparticles encapsulated by a N-containing carbon layer originating from aniline carbonization. The synthesized Pt catalyst exhibited higher mass specific activity to oxygen reduction reaction than that shown by conventional Pt/C catalyst because pyridinic N with graphitic carbon in the carbon layer provided active sites for oxygen reduction reaction in addition to those provided by Pt. In single cell testing, initial performance of the synthesized catalyst was limited because the thick catalyst layer increased resistance related to mass transfer. However, it was observed that the carbon layer successfully prevented Pt nanoparticles from growing via agglomeration and Ostwald ripening under fuel cell operation, thereby improving durability. Furthermore, a mass specific performance of the synthesized catalyst higher than that of a conventional Pt/C catalyst was achieved by modifying the synthesized catalyst's layer thickness.

Iron catalyzed coal liquefaction process

DOEpatents

Garg, Diwakar; Givens, Edwin N.

1983-01-01

A process is described for the solvent refining of coal into a gas product, a liquid product and a normally solid dissolved product. Particulate coal and a unique co-catalyst system are suspended in a coal solvent and processed in a coal liquefaction reactor, preferably an ebullated bed reactor. The co-catalyst system comprises a combination of a stoichiometric excess of iron oxide and pyrite which reduce predominantly to active iron sulfide catalysts in the reaction zone. This catalyst system results in increased catalytic activity with attendant improved coal conversion and enhanced oil product distribution as well as reduced sulfide effluent. Iron oxide is used in a stoichiometric excess of that required to react with sulfur indigenous to the feed coal and that produced during reduction of the pyrite catalyst to iron sulfide.

n-hydrocarbons conversions over metal-modified solid acid catalysts

NASA Astrophysics Data System (ADS)

Zarubica, A.; Ranđelović, M.; Momčilović, M.; Radulović, N.; Putanov, P.

2013-12-01

The quality of a straight-run fuel oil can be improved if saturated n-hydrocarbons of low octane number are converted to their branched counterparts. Poor reactivity of traditional catalysts in isomerization reactions imposed the need for the development of new catalysts among which noble metal promoted acid catalysts, liquid and/or solid acid catalysts take a prominent place. Sulfated zirconia and metal promoted sulfated zirconia exhibit high activity for the isomerization of light alkanes at low temperatures. The present paper highlights the original results which indicate that the modification of sulfated zirconia by incorporation of metals (platinum and rhenium) significantly affects catalytic performances in n-hydrocarbon conversion reactions. Favourable activity/selectivity of the promoted sulfated zirconia depends on the crystal phase composition, critical crystallites sizes, platinum dispersion, total acidity and type of acidity. Attention is also paid to the recently developed solid acid catalysts used in other conversion reactions of hydrocarbons.

Cu3(BTC)2: CO oxidation over MOF based catalysts.

PubMed

Ye, Jing-yun; Liu, Chang-jun

2011-02-21

Crystalline and amorphized MOFs (Cu(3)(BTC)(2)) have been demonstrated to be excellent catalysts for CO oxidation. The catalytic activity can be further improved by loading PdO(2) nanoparticles onto the amorphized Cu(3)(BTC)(2).

Understanding low temperature oxidation activity of nanoarray-based monolithic catalysts: from performance observation to structural and chemical insights

DOE PAGES

Du, Shoucheng; Tang, Wenxiang; Guo, Yanbing; ...

2016-12-30

Monolithic catalysts have been widely used in automotive, chemical, and energy relevant industries. Nano-array based monolithic catalysts have been developed, demonstrating high catalyst utilization efficiency and good thermal/mechanical robustness. Compared with the conventional wash-coat based monolithic catalysts, they have shown advances in precise and optimum microstructure control and feasibility in correlating materials structure with properties. Recently, the nano-array based monolithic catalysts have been studied for low temperature oxidation of automotive engine exhaust and exhibited interesting and promising catalytic activities. Here, this review focuses on discussing the key catalyst structural parameters that affect the catalytic performance from the following aspects, (1)more » geometric shape and crystal planes, (2) guest atom doping and defects, (3) array size and size-assisted active species loading, and (4) the synergy effect of metal oxide in composite nano-arrays. Prior to the discussion, an overview of the current status of synthesis and development of the nano-array based monolithic catalysts is introduced. The performance of these materials in low temperature simulated engine exhaust oxidation is also demonstrated. Finally, we hope this review will elucidate the science and chemistry behind the good oxidation performance of the nanoarray- based monolithic catalysts, and serve as a timely and useful research guide for rational design and further improvement of the nano-array based monolithic catalysts for automobile emission control.« less

Understanding low temperature oxidation activity of nanoarray-based monolithic catalysts: from performance observation to structural and chemical insights

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Shoucheng; Tang, Wenxiang; Guo, Yanbing

Monolithic catalysts have been widely used in automotive, chemical, and energy relevant industries. Nano-array based monolithic catalysts have been developed, demonstrating high catalyst utilization efficiency and good thermal/mechanical robustness. Compared with the conventional wash-coat based monolithic catalysts, they have shown advances in precise and optimum microstructure control and feasibility in correlating materials structure with properties. Recently, the nano-array based monolithic catalysts have been studied for low temperature oxidation of automotive engine exhaust and exhibited interesting and promising catalytic activities. Here, this review focuses on discussing the key catalyst structural parameters that affect the catalytic performance from the following aspects, (1)more » geometric shape and crystal planes, (2) guest atom doping and defects, (3) array size and size-assisted active species loading, and (4) the synergy effect of metal oxide in composite nano-arrays. Prior to the discussion, an overview of the current status of synthesis and development of the nano-array based monolithic catalysts is introduced. The performance of these materials in low temperature simulated engine exhaust oxidation is also demonstrated. Finally, we hope this review will elucidate the science and chemistry behind the good oxidation performance of the nanoarray- based monolithic catalysts, and serve as a timely and useful research guide for rational design and further improvement of the nano-array based monolithic catalysts for automobile emission control.« less

New Horizons in C-F Activation by Main Group Electrophiles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ozerov, Oleg V.

2016-02-13

This technical report describes progress on the DOE sponsored project "New Horizons in C-F Activation by Main Group Electrophiles" during the period of 09/15/2010 – 08/31/2015. The main goal of this project was to develop improved catalysts for conversion of carbon-fluorine bonds in potentially harmful compounds. The approach involved combining of a highly reactive positively charged main-group compound with a highly unreactive negatively charged species (anions) as a way to access potent catalysts for carbon-fluorine bond activation. This report details progress made in improving synthetic pathways to a variety of new anions with improved properties and analysis of their potentialmore » in catalysis.« less

Efficiency of bimetallic PtPd on polydopamine modified on various carbon supports for alcohol oxidations

NASA Astrophysics Data System (ADS)

Pinithchaisakula, A.; Ounnunkad, K.; Themsirimongkon, S.; Promsawan, N.; Waenkaew, P.; Saipanya, S.

2017-02-01

In this work, the preparation, characterization, and electrocatalytic analysis of the catalysts on various carbon substrates for direct alcohol fuel cells were studied. Selected carbons were modified with/without polydopamine (labelled as PDA-C and C) and further metal electrodeposited incorporated onto the glassy carbon (labelled as 5Pt1Pd/PDA-C and 5Pt1Pd/C). Four various carbon materials were used e.g. graphite (G), carbon nanotube (CNT), graphene (GP) and graphene oxide (GO) and the carbons were modified with PDA denoted as PDA-G, PDA-CNT, PDA-GP and PDA-GO, respectively. The transmission electron microscopy (TEM) and scanning electron microscopy (SEM) experimental observation showed narrow size distribution of metal anchored on the PDA-C and C materials. Chemical compositions and oxidation states of the catalysts were determined by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX). The catalytic performances for small organic electro-oxidation (e.g. methanol and ethanol) were measured by cyclic voltammetry (CV). Among different PDA-C and C catalysts, monometallic Pt showed less activity than the bimetallic catalysts. Among catalysts with PDA, the 5Pt1Pd/PDA-GO catalyst facilitated methanol and ethanol oxidations with high oxidation currents and If/Ib value and stability with low potentials while among catalysts without PDA, the 5Pt1Pd/CNT provides highest activity and stability. It was found that the catalysts with PDA provided high activity and stability than the catalysts without PDA. The improved catalytic performance of the prepared catalysts could be related to the higher active surface area from polymer modification and bimetallic catalyst system in the catalyst composites.

Effect of plasma treatments to graphite nanofibers supports on electrochemical behaviors of metal catalyst electrodes.

PubMed

Lee, Hochun; Jung, Yongju; Kim, Seok

2012-02-01

In the present work, we had studied the graphite nanofibers as catalyst supports after a plasma treatment for studying the effect of surface modification. By controlling the plasma intensity, a surface functional group concentration was changed. The nanoparticle size, loading efficiency, and catalytic activity were studied, after Pt-Ru deposition by a chemical reduction. Pt-Ru catalysts deposited on the plasma-treated GNFs showed the smaller size, 3.58 nm than the pristine GNFs. The catalyst loading contents were enhanced with plasma power and duration time increase, meaning an enhanced catalyst deposition efficiency. Accordingly, cyclic voltammetry result showed that the specific current density was increased proportionally till 200 W and then the value was decreased. Enhanced activity of 40 (mA mg(-1)-catalyst) was accomplished at 200 W and 180 sec duration time. Consequently, it was found that the improved electroactivity was originated from the change of size or morphology of catalysts by controlling the plasma intensity.

An extraordinarily stable catalyst: Pt NPs supported on two-dimensional Ti3C2X2 (X = OH, F) nanosheets for oxygen reduction reaction.

PubMed

Xie, Xiaohong; Chen, Siguo; Ding, Wei; Nie, Yao; Wei, Zidong

2013-10-03

High dispersion Pt nanoparticles supported on 2D Ti3C2X2 (X = OH, F) nanosheets are presented and electro-chemical measurements confirm that the Pt/Ti3C2X2 catalyst shows enhanced durability and improved ORR activity compared with the commercial Pt/C catalyst.

Nickel-silicide colloid prepared under mild conditions as a versatile Ni precursor for more efficient CO2 reforming of CH4 catalysts.

PubMed

Baudouin, David; Szeto, Kaï Chung; Laurent, Pierre; De Mallmann, Aimery; Fenet, Bernard; Veyre, Laurent; Rodemerck, Uwe; Copéret, Christophe; Thieuleux, Chloé

2012-12-26

Preparing highly active and stable non-noble-metal-based dry reforming catalysts remains a challenge today. In this context, supported nickel nanoparticles with sizes of 1.3 ± 0.2 and 2.1 ± 0.2 nm were synthesized on silica and ceria, respectively, via a two-step colloidal approach. First, 2-nm nickel-silicide colloids were synthesized from Ni(COD)(2) and octylsilane at low temperature; they were subsequently dispersed onto supports prior to reduction under H(2). The resulting catalysts display high activity in dry reforming compared to their analogues prepared using conventional approaches, ceria providing greatly improved catalyst stability.

Synthesis of Pt/rGO catalysts with two different reducing agents and their methanol electrooxidation activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vu, Thu Ha Thi, E-mail: ptntd2004@yahoo.fr; Tran, Thanh Thuy Thi, E-mail: tranthithanhthuygl@gmail.com; Le, Hong Ngan Thi

2016-01-15

Highlights: • Pt/rGO catalysts were successfully synthesized using either NaBH{sub 4} or ethylene glycol. • Synthesis using NaBH{sub 4} could improve electrocatalytic towards methanol oxidation of Pt/rGO catalyst. • 40%Pt/rGO synthesized using NaBH{sub 4} showed the best electrocatalytic performance. - Abstract: The synthesis processes of Platinum (Pt) on reduced graphene oxide (rGO) catalysts from graphene oxide (GO) using two reducing agents including sodium borohydride and ethylene glycol is reported. Structure and morphology of Pt/rGO catalysts are characterized by X-ray powder diffraction, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Electrocatalytic methanol oxidation properties of these catalysts are evaluated bymore » cyclic voltammetry and chronoamperometry. The results show that catalyst synthesized using sodium borohydride has a higher metallic Pt content and an improved catalytic performance in comparison to catalyst synthesized using ethylene glycol. Moreover, effect of Pt loading amount on electrocatalytic methanol oxidation performance of catalysts synthesized using sodium borohydride is systematically investigated. The optimal Pt loading amount on graphene is determined to be 40%.« less

Current advances in precious metal core-shell catalyst design.

PubMed

Wang, Xiaohong; He, Beibei; Hu, Zhiyu; Zeng, Zhigang; Han, Sheng

2014-08-01

Precious metal nanoparticles are commonly used as the main active components of various catalysts. Given their high cost, limited quantity, and easy loss of catalytic activity under severe conditions, precious metals should be used in catalysts at low volumes and be protected from damaging environments. Accordingly, reducing the amount of precious metals without compromising their catalytic performance is difficult, particularly under challenging conditions. As multifunctional materials, core-shell nanoparticles are highly important owing to their wide range of applications in chemistry, physics, biology, and environmental areas. Compared with their single-component counterparts and other composites, core-shell nanoparticles offer a new active interface and a potential synergistic effect between the core and shell, making these materials highly attractive in catalytic application. On one hand, when a precious metal is used as the shell material, the catalytic activity can be greatly improved because of the increased surface area and the closed interfacial interaction between the core and the shell. On the other hand, when a precious metal is applied as the core material, the catalytic stability can be remarkably improved because of the protection conferred by the shell material. Therefore, a reasonable design of the core-shell catalyst for target applications must be developed. We summarize the latest advances in the fabrications, properties, and applications of core-shell nanoparticles in this paper. The current research trends of these core-shell catalysts are also highlighted.

Development of highly active and stable hybrid cathode catalyst for PEMFCs

NASA Astrophysics Data System (ADS)

Jung, Won Suk

Polymer electrolyte membrane fuel cells (PEMFCs) are attractive power sources of the future for a variety of applications including portable electronics, stationary power, and automobile application. However, sluggish cathode kinetics, high Pt cost, and durability issues inhibit the commercialization of PEMFCs. To overcome these drawbacks, research has been focused on alloying Pt with transition metals since alloy catalysts show significantly improved catalytic properties like high activity, selectivity, and durability. However, Pt-alloy catalysts synthesized using the conventional impregnation method exhibit uneven particle size and poor particle distribution resulting in poor performance and/or durability in PEMFCs. In this dissertation, a novel catalyst synthesis methodology is developed and compared with catalysts prepared using impregnation method and commercial catalysts. Two approaches are investigated for the catalyst development. The catalyst durability was studied under U. S. DRIVE Fuel Cell Tech Team suggested protocols. In the first approach, the carbon composite catalyst (CCC) having active sites for oxygen reduction reaction (ORR) is employed as a support for the synthesis of Pt/CCC catalyst. The structural and electrochemical properties of Pt/CCC catalyst are investigated using high-resolution transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, while RDE and fuel cell testing are carried out to study the electrochemical properties. The synergistic effect of CCC and Pt is confirmed by the observed high activity towards ORR for the Pt/CCC catalyst. The second approach is the synthesis of Co-doped hybrid cathode catalysts (Co-doped Pt/CCC) by diffusing the Co metal present within the CCC support into the Pt nanoparticles during heat-treatment. The optimized Co-doped Pt/CCC catalyst performed better than the commercial catalysts and the catalyst prepared using the impregnation method in PEMFCs and showed high stability under 30,000 potential cycles between 0.6 and 1.0 V. To further increase the stability of the catalyst at high potential cycles (1.0-1.5 V), high temperature treatment is used to obtain graphitized carbon having optimum BET surface area. The novel catalyst synthesis procedure developed in this study was successfully applied for the synthesis of Co-doped Pt catalysts supported on the graphitized carbon which showed high activity and enhanced stability at high potentials.

Improved Oxygen Reduction Activity and Durability of Dealloyed PtCo x Catalysts for Proton Exchange Membrane Fuel Cells: Strain, Ligand, and Particle Size Effects.

PubMed

Jia, Qingying; Caldwell, Keegan; Strickland, Kara; Ziegelbauer, Joseph M; Liu, Zhongyi; Yu, Zhiqiang; Ramaker, David E; Mukerjee, Sanjeev

2015-01-02

The development of active and durable catalysts with reduced platinum content is essential for fuel cell commercialization. Herein we report that the dealloyed PtCo/HSC and PtCo 3 /HSC nanoparticle (NP) catalysts exhibit the same levels of enhancement in oxygen reduction activity (~4-fold) and durability over pure Pt/C NPs. Surprisingly, ex situ high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) shows that the bulk morphologies of the two catalysts are distinctly different: D-PtCo/HSC catalyst is dominated by NPs with solid Pt shells surrounding a single ordered PtCo core; however, the D-PtCo 3 /HSC catalyst is dominated by NPs with porous Pt shells surrounding multiple disordered PtCo cores with local concentration of Co. In situ X-ray absorption spectroscopy (XAS) reveals that these two catalysts possess similar Pt-Pt and Pt-Co bond distances and Pt coordination numbers (CNs), despite their dissimilar morphologies. The similar activity of the two catalysts is thus ascribed to their comparable strain, ligand, and particle size effects. Ex situ XAS performed on D-PtCo 3 /HSC under different voltage cycling stage shows that the continuous dissolution of Co leaves behind the NPs with a Pt-like structure after 30k cycles. The attenuated strain and/or ligand effects caused by Co dissolution are presumably counterbalanced by the particle size effects with particle growth, which likely accounts for the constant specific activity of the catalysts along with voltage cycling.

Improved Oxygen Reduction Activity and Durability of Dealloyed PtCo x Catalysts for Proton Exchange Membrane Fuel Cells: Strain, Ligand, and Particle Size Effects

DOE PAGES

Jia, Qingying; Caldwell, Keegan; Strickland, Kara; ...

2014-11-19

The development of active and durable catalysts with reduced platinum content is essential for fuel cell commercialization. Here in this paper, we report that the dealloyed PtCo/HSC and PtCo 3/HSC nanoparticle (NP) catalysts exhibit the same levels of enhancement in oxygen reduction activity (~4-fold) and durability over pure Pt/C NPs. Surprisingly, ex situ high-angle annular dark field scanning transmission electron microscopy (HAADF STEM) shows that the bulk morphologies of the two catalysts are distinctly different: D-PtCo/HSC catalyst is dominated by NPs with solid Pt shells surrounding a single ordered PtCo core; however, the D-PtCo 3/HSC catalyst is dominated by NPsmore » with porous Pt shells surrounding multiple disordered PtCo cores with local concentration of Co. In situ X-ray absorption spectroscopy (XAS) reveals that these two catalysts possess similar Pt–Pt and Pt–Co bond distances and Pt coordination numbers (CNs), despite their dissimilar morphologies. The similar activity of the two catalysts is thus ascribed to their comparable strain, ligand, and particle size effects. Ex situ XAS performed on D-PtCo 3/HSC under different voltage cycling stage shows that the continuous dissolution of Co leaves behind the NPs with a Pt-like structure after 30k cycles. The attenuated strain and/or ligand effects caused by Co dissolution are presumably counterbalanced by the particle size effects with particle growth, which likely accounts for the constant specific activity of the catalysts along with voltage cycling.« less

N, P-codoped Mesoporous Carbon Supported PtCox Nanoparticles and Their Superior Electrochemical toward Methanol Oxidation

NASA Astrophysics Data System (ADS)

Cui, Hangjun; Li, Yueming; Liu, Shimin

2018-03-01

In this report, a novel strategy by using the N, P co-doped mesoporous carbon structure as catalyst support to enhance the electrochemical catalytic activity of Pt-based catalysts is proposed. The as-synthesized PtCox@N, P-doped mesoporous carbon nanocomposties have been studied as an anode catalyst toward methanol oxidation, exhibiting greatly improved electrochemical activity and stability compared with Pt@mesoporous carbon. The synergistic effects of N, P dual-doping and porous carbon structure help to achieve better electron transport at the electrode surface, which eventually leads to greatly enhanced catalytic activity compared to the pristine Pt/mesoporous carbon.…

Heterogeneous catalytic ozonation of dibutyl phthalate in aqueous solution in the presence of iron-loaded activated carbon.

PubMed

Huang, Yuanxing; Cui, Chenchen; Zhang, Daofang; Li, Liang; Pan, Ding

2015-01-01

Iron-loaded activated carbon was prepared and used as catalyst in heterogeneous catalytic ozonation of dibutyl phthalate (DBP). The catalytic activity of iron-loaded activated carbon was investigated under various conditions and the mechanisms of DBP removal were deduced. Characterization of catalyst indicated that the iron loaded on activated carbon was mainly in the form of goethite, which reduced its surface area, pore volume and pore diameter. The presence of metals on activated carbon positively contributed to its catalytic activity in ozonation of DBP. Iron loading content of 15% and initial water pH of 8 achieved highest DBP removal among all the tried conditions. Catalyst dosage of 10 mg L(-1) led to approximately 25% of increase in DBP (initial concentration 2 mg L(-1)) removal in 60 min as compared with ozone alone, and when catalyst dosage increased to 100 mg L(-1), the DBP removal was further improved by 46%. Based on a comparison of reaction rates for direct and indirect transformation of DBP, the increased removal of DBP in this study likely occurred via transformation of ozone into hydroxyl radicals on the catalyst surface. Copyright © 2014 Elsevier Ltd. All rights reserved.

High-Performance Core–Shell Catalyst with Nitride Nanoparticles as a Core: Well-Defined Titanium Copper Nitride Coated with an Atomic Pt Layer for the Oxygen Reduction Reaction

DOE PAGES

Tian, Xinlong; Tang, Haibo; Luo, Junming; ...

2017-04-25

A class of core–shell structured low-platinum catalysts with well-dispersed inexpensive titanium copper nitride nanoparticles as cores and atomic platinum layers as shells exhibiting high activity and stability for the oxygen reduction reaction is successfully developed. In using nitrided carbon nanotubes (NCNTs) as the support greatly improved the morphology and dispersion of the nitride nanoparticles, resulting in significant enhancement of the performance of the catalyst. The optimized catalyst, Ti 0.9Cu 0.1N@Pt/NCNTs, has a Pt mass activity 5 times higher than that of commercial Pt/C, comparable to that of core–shell catalysts with precious metal nanoparticles as the core, and much higher thanmore » that the latter if we take into account the mass activity of all platinum group metals. Furthermore, only a minimal loss of activity can be observed after 10000 potential cycles, demonstrating the catalyst’s high stability. After durability testing, atomic-scale elemental mapping confirmed that the core–shell structure of the catalyst remained intact. This approach may open a pathway for the design and preparation of high-performance inexpensive core–shell catalysts for a wide range of applications in energy conversion processes.« less

High-Performance Core–Shell Catalyst with Nitride Nanoparticles as a Core: Well-Defined Titanium Copper Nitride Coated with an Atomic Pt Layer for the Oxygen Reduction Reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Xinlong; Tang, Haibo; Luo, Junming

A class of core–shell structured low-platinum catalysts with well-dispersed inexpensive titanium copper nitride nanoparticles as cores and atomic platinum layers as shells exhibiting high activity and stability for the oxygen reduction reaction is successfully developed. In using nitrided carbon nanotubes (NCNTs) as the support greatly improved the morphology and dispersion of the nitride nanoparticles, resulting in significant enhancement of the performance of the catalyst. The optimized catalyst, Ti 0.9Cu 0.1N@Pt/NCNTs, has a Pt mass activity 5 times higher than that of commercial Pt/C, comparable to that of core–shell catalysts with precious metal nanoparticles as the core, and much higher thanmore » that the latter if we take into account the mass activity of all platinum group metals. Furthermore, only a minimal loss of activity can be observed after 10000 potential cycles, demonstrating the catalyst’s high stability. After durability testing, atomic-scale elemental mapping confirmed that the core–shell structure of the catalyst remained intact. This approach may open a pathway for the design and preparation of high-performance inexpensive core–shell catalysts for a wide range of applications in energy conversion processes.« less

Facile Fabrication of Platinum-Cobalt Alloy Nanoparticles with Enhanced Electrocatalytic Activity for a Methanol Oxidation Reaction

PubMed Central

Huang, Huihong; Hu, Xiulan; Zhang, Jianbo; Su, Nan; Cheng, JieXu

2017-01-01

Decreasing the cost associated with platinum-based catalysts along with improving their catalytic properties is a major challenge for commercial direct methanol fuel cells. In this work, a simple and facile strategy was developed for the more efficient preparation of multi-walled carbon nanotube (MWCNT) -supported Pt/CoPt composite nanoparticles (NPs) via solution plasma sputtering with subsequent thermal annealing. Quite different from general wet synthesis methods, Pt/CoPt composite NPs were directly derived from metal wire electrodes without any additions. The obtained Pt/CoPt/MWCNTs composite catalysts exhibited tremendous improvement in the electro-oxidation of methanol in acidic media with mass activities of 1719 mA mg−1Pt. This value is much higher than that of previous reports of Pt-Co alloy and commercial Pt/C (3.16 times) because of the many active sites and clean surface of the catalysts. The catalysts showed good stability due to the special synergistic effects of the CoPt alloy. Pt/CoPt/MWCNTs can be used as a promising catalyst for direct methanol fuel cells. In addition, this solution plasma sputtering-assisted synthesis method introduces a general and feasible route for the synthesis of binary alloys. PMID:28358143

Peptide-templated noble metal catalysts: syntheses and applications

PubMed Central

Wang, Wei; Anderson, Caleb F.; Wang, Zongyuan; Wu, Wei

2017-01-01

Noble metal catalysts have been widely used in many applications because of their high activity and selectivity. However, a controllable preparation of noble metal catalysts still remains as a significant challenge. To overcome this challenge, peptide templates can play a critical role in the controllable syntheses of catalysts owing to their flexible binding with specific metallic surfaces and self-assembly characteristics. By employing peptide templates, the size, shape, facet, structure, and composition of obtained catalysts can all be specifically controlled under the mild synthesis conditions. In addition, catalysts with spherical, nanofiber, and nanofilm structures can all be produced by associating with the self-assembly characteristics of peptide templates. Furthermore, the peptide-templated noble metal catalysts also reveal significantly enhanced catalytic behaviours compared with conventional catalysts because the electron conductivity, metal dispersion, and reactive site exposure can all be improved. In this review, we summarize the research progresses in the syntheses of peptide-templated noble metal catalysts. The applications of the peptide-templated catalysts in organic reactions, photocatalysis, and electrocatalysis are discussed, and the relationship between structure and activity of these catalysts are addressed. Future opportunities, including new catalytic materials designed by using biological principles, are indicated to achieve selective, eco-friendly, and energy neutral synthesis approaches. PMID:28507701

[Synergetic effects of silicon carbide and molecular sieve loaded catalyst on microwave assisted catalytic oxidation of toluene].

PubMed

Wang, Xiao-Hui; Bo, Long-Li; Liu, Hai-Nan; Zhang, Hao; Sun, Jian-Yu; Yang, Li; Cai, Li-Dong

2013-06-01

Molecular sieve loaded catalyst was prepared by impregnation method, microwave-absorbing material silicon carbide and the catalyst were investigated for catalytic oxidation of toluene by microwave irradiation. Research work examined effects of silicon carbide and molecular sieve loading Cu-V catalyst's mixture ratio as well as mixed approach changes on degradation of toluene, and characteristics of catalyst were measured through scanning electron microscope, specific surface area test and X-ray diffraction analysis. The result showed that the fixed bed reactor had advantages of both thermal storage property and low-temperature catalytic oxidation when 20% silicon carbide was filled at the bottom of the reactor, and this could effectively improve the utilization of microwave energy as well as catalytic oxidation efficiency of toluene. Under microwave power of 75 W and 47 W, complete-combustion temperatures of molecular sieve loaded Cu-V catalyst and Cu-V-Ce catalyst to toluene were 325 degrees C and 160 degrees C, respectively. Characteristics of the catalysts showed that mixture of rare-earth element Ce increased the dispersion of active components in the surface of catalyst, micropore structure of catalyst effectively guaranteed high adsorption capacity for toluene, while amorphous phase of Cu and V oxides increased the activity of catalyst greatly.

Exceptional oxygen reduction reaction activity and durability of platinum–nickel nanowires through synthesis and post-treatment optimization

DOE PAGES

Alia, Shaun M.; Ngo, Chilan; Shulda, Sarah; ...

2017-04-11

For the first time, extended nanostructured catalysts are demonstrated with both high specific activity (>6000 μA cm Pt –2 at 0.9 V) and high surface areas (>90 m 2 g Pt –1). Platinum–nickel (Pt—Ni) nanowires, synthesized by galvanic displacement, have previously produced surface areas in excess of 90 m 2 g Pt –1, a significant breakthrough in and of itself for extended surface catalysts. Unfortunately, these materials were limited in terms of their specific activity and durability upon exposure to relevant electrochemical test conditions. Through a series of optimized postsynthesis steps, significant improvements were made to the activity (3-fold increasemore » in specific activity), durability (21% mass activity loss reduced to 3%), and Ni leaching (reduced from 7 to 0.3%) of the Pt—Ni nanowires. Finally, these materials show more than a 10-fold improvement in mass activity compared to that of traditional carbon-supported Pt nanoparticle catalysts and offer significant promise as a new class of electrocatalysts in fuel cell applications.« less

Exceptional oxygen reduction reaction activity and durability of platinum–nickel nanowires through synthesis and post-treatment optimization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alia, Shaun M.; Ngo, Chilan; Shulda, Sarah

For the first time, extended nanostructured catalysts are demonstrated with both high specific activity (>6000 μA cm Pt –2 at 0.9 V) and high surface areas (>90 m 2 g Pt –1). Platinum–nickel (Pt—Ni) nanowires, synthesized by galvanic displacement, have previously produced surface areas in excess of 90 m 2 g Pt –1, a significant breakthrough in and of itself for extended surface catalysts. Unfortunately, these materials were limited in terms of their specific activity and durability upon exposure to relevant electrochemical test conditions. Through a series of optimized postsynthesis steps, significant improvements were made to the activity (3-fold increasemore » in specific activity), durability (21% mass activity loss reduced to 3%), and Ni leaching (reduced from 7 to 0.3%) of the Pt—Ni nanowires. Finally, these materials show more than a 10-fold improvement in mass activity compared to that of traditional carbon-supported Pt nanoparticle catalysts and offer significant promise as a new class of electrocatalysts in fuel cell applications.« less

Oxyhydrochlorination catalyst

DOEpatents

Taylor, Charles E.; Noceti, Richard P.

1992-01-01

An improved catalyst and method for the oxyhydrochlorination of methane is disclosed. The catalyst includes a pyrogenic porous support on which is layered as active material, cobalt chloride in major proportion, and minor proportions of an alkali metal chloride and of a rare earth chloride. On contact of the catalyst with a gas flow of methane, HCl and oxygen, more than 60% of the methane is converted and of that converted more than 40% occurs as monochloromethane. Advantageously, the monochloromethane can be used to produce gasoline boiling range hydrocarbons with the recycle of HCl for further reaction. This catalyst is also of value for the production of formic acid as are analogous catalysts with lead, silver or nickel chlorides substituted for the cobalt chloride.

Enhancing low-temperature activity and durability of Pd-based diesel oxidation catalysts using ZrO 2 supports

DOE PAGES

Kim, Mi -Young; Kyriakidou, Eleni A.; Choi, Jae -Soon; ...

2016-01-18

In this study, we investigated the impact of ZrO 2 on the performance of palladium-based oxidation catalysts with respect to low-temperature activity, hydrothermal stability, and sulfur tolerance. Pd supported on ZrO 2 and SiO 2 were synthesized for a comparative study. Additionally, in an attempt to maximize the ZrO 2 surface area and improve sulfur tolerance, a Pd support with ZrO 2-dispersed onto SiO 2 was studied. The physicochemical properties of the catalysts were examined using ICP, N 2 sorption, XRD, SEM, TEM, and NH 3-, CO 2-, and NO x-TPD. The activity of the Pd catalysts were measured frommore » 60 to 600 °C in a flow of 4000 ppm CO, 500 ppm NO, 1000 ppm C 3H 6, 4% O 2, 5% H 2O, and Ar balance. The Pd catalysts were evaluated in fresh, sulfated, and hydrothermally aged states. Overall, the ZrO 2-containing catalysts showed considerably higher CO and C 3H 6 oxidation activity than Pd/SiO 2 under the reaction conditions studied.« less

The Effect of Copper Addition on the Activity and Stability of Iron-Based CO₂ Hydrogenation Catalysts.

PubMed

Bradley, Matthew J; Ananth, Ramagopal; Willauer, Heather D; Baldwin, Jeffrey W; Hardy, Dennis R; Williams, Frederick W

2017-09-20

Iron-based CO₂ catalysts have shown promise as a viable route to the production of olefins from CO₂ and H₂ gas. However, these catalysts can suffer from low conversion and high methane selectivity, as well as being particularly vulnerable to water produced during the reaction. In an effort to improve both the activity and durability of iron-based catalysts on an alumina support, copper (10-30%) has been added to the catalyst matrix. In this paper, the effects of copper addition on the catalyst activity and morphology are examined. The addition of 10% copper significantly increases the CO₂ conversion, and decreases methane and carbon monoxide selectivity, without significantly altering the crystallinity and structure of the catalyst itself. The FeCu/K catalysts form an inverse spinel crystal phase that is independent of copper content and a metallic phase that increases in abundance with copper loading (>10% Cu). At higher loadings, copper separates from the iron oxide phase and produces metallic copper as shown by SEM-EDS. An addition of copper appears to increase the rate of the Fischer-Tropsch reaction step, as shown by modeling of the chemical kinetics and the inter- and intra-particle transport of mass and energy.

One-pot solvothermal synthesis of ordered intermetallic Pt2In3 as stable and efficient electrocatalyst towards direct alcohol fuel cell application

NASA Astrophysics Data System (ADS)

Jana, Rajkumar; Peter, Sebastian C.

2016-10-01

Ordered intermetallic Pt2In3 nanoparticles have been synthesized by superhydride reduction of K2PtCl4 and InCl3.xH2O precursors using facile, one-pot solvothermal method. We report surfactant free solvothermal synthesis of a novel ordered Pt2In3 intermetallic nanoparticles for the first time. The structure and morphology of the catalyst has been confirmed by powder X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive spectrometry and X-ray photoelectron spectroscopy. The electrocatalytic properties of the catalysts have been investigated by cyclic voltammetry and chronoamperometry. The as prepared Pt2In3 catalyst exhibit far superior electrocatalytic activity and stability towards alcohol oxidation over commercial Pt/C. The specific activity of as synthesized catalyst was found to be 3.2 and 2.3 times higher than commercial Pt/C for methanol and ethanol oxidation, respectively. This improved activity and durability of the Pt2In3 nanoparticles can make the catalyst an ideal catalyst candidate for direct alcohol fuel cell.

High efficient preparation of carbon nanotube-grafted carbon fibers with the improved tensile strength

NASA Astrophysics Data System (ADS)

Fan, Wenxin; Wang, Yanxiang; Wang, Chengguo; Chen, Jiqiang; Wang, Qifen; Yuan, Yan; Niu, Fangxu

2016-02-01

An innovative technique has been developed to obtain the uniform catalyst coating on continuously moving carbon fibers. Carbon nanotube (CNT)-grafted carbon fibers with significantly improved tensile strength have been succeeded to produce by using chemical vapor deposition (CVD) when compared to the tensile strength of untreated carbon fibers. The critical requirements for preparation of CNT-grafted carbon fibers with high tensile strength have been found, mainly including (i) the obtainment of uniform coating of catalyst particles with small particle size, (ii) the low catalyst-induced and mechano-chemical degradation of carbon fibers, and (iii) the high catalyst activity which could facilitate the healing and strengthening of carbon fibers during the growth of CNTs. The optimum growth temperature was found to be about 500 °C, and the optimum catalyst is Ni due to its highest activity, there is a pronounced increase of 10% in tensile strength of carbon fibers after CNT growth at 500 °C by using Ni catalyst. Based on the observation from HRTEM images, a healing and crosslink model of neighboring carbon crystals by CNTs has been formulated to reveal the main reason that causes an increase in tensile strength of carbon fibers after the growth of CNTs. Such results have provided the theoretical and experimental foundation for the large-scale preparation of CNT-grafted carbon fibers with the improved tensile strength, significantly promoting the development of CNT-grafted carbon fiber reinforced polymer composites.

Surface Modifications during a Catalytic Reaction: A Combined APT and FIB/SEM Analysis of Surface Segregation

DOE PAGES

Barroo, Cedric; Janvelyan, Nare; Zugic, Branko; ...

2016-07-25

To improve the understanding of catalytic processes, the surface structure and composition of the active materials need to be determined before and after reaction. Morphological changes may occur under reaction conditions and can dramatically influence the reactivity and/or selectivity of a catalyst. Goldbased catalysts with different architectures are currently being developed for selective oxidation reactions at low temperatures. Specifically, nanoporous Au (npAu) with a composition of Au 97-Ag 3 is obtained by dealloying a Ag 70-Au 30 bulk alloy. Recent studies highlight the efficiency of npAu catalysts for methanol oxidation using ozone to activate the catalysts before methanol oxidation. Inmore » this paper, we studied the morphological and compositional changes occurring at the surface of Au-based catalysts in certain conditions.« less

Pt monolayer shell on nitrided alloy core — A path to highly stable oxygen reduction catalyst

DOE PAGES

Hu, Jue; Kuttiyiel, Kurian A.; Sasaki, Kotaro; ...

2015-07-22

The inadequate activity and stability of Pt as a cathode catalyst under the severe operation conditions are the critical problems facing the application of the proton exchange membrane fuel cell (PEMFC). Here we report on a novel route to synthesize highly active and stable oxygen reduction catalysts by depositing Pt monolayer on a nitrided alloy core. The prepared Pt MLPdNiN/C catalyst retains 89% of the initial electrochemical surface area after 50,000 cycles between potentials 0.6 and 1.0 V. By correlating electron energy-loss spectroscopy and X-ray absorption spectroscopy analyses with electrochemical measurements, we found that the significant improvement of stability ofmore » the Pt MLPdNiN/C catalyst is caused by nitrogen doping while reducing the total precious metal loading.« less

Directed surfaces structures and interfaces for enhanced electrocatalyst activity, selectivity, and stability for energy conversion reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaramillo, Thomas F.

In this project, we have employed a systematic approach to develop active, selective, and stable catalyst materials for important electrochemical reactions involving energy conversion. In particular, we have focused our attention on developing active catalyst materials for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). HER: We have synthesized and investigated several highly active and acid stable non-precious metal HER catalysts, including: [Mo 3S 13] 2- nanoclusters (Nature Chemistry, 2014) and molybdenum phosphosulfide (MoP|S) (Angewandte Chemie, 2014). We have also aimed to engineer these catalyst formulations in a membrane electrode assembly (MEA) for fundamentalmore » studies of water electrolysis at high current densities, approximately 1 A/cm 2 (ChemSusChem, 2015). We furthermore investigated transition metal phosphide (TMP) catalysts for HER by a combined experimental–theoretical approach (Energy & Environmental Science, 2015). By synthesizing different TMPs and comparing experimentally determined HER activities with the hydrogen adsorption free energies, ΔG H, calculated by density functional theory, we showed that the TMPs follow a volcano relationship for the HER. Using our combined experimental–theoretical model, we predicted that the mixed metal TMP, Fe 0.5Co 0.5P, should have a near-optimal ΔG H. We synthesized several mixtures of Co and Fe phosphides alloys and confirmed that Fe 0.5Co 0.5P exhibits the highest HER activity of the investigated TMPs (Energy & Environmental Science, 2015). The understanding gained as to how to improve catalytic activity for the HER, particularly for non-precious metal materials, is important to DOE targets for sustainable H 2 production. OER: We have developed a SrIrO 3/IrO x catalyst for acidic conditions (submitted, 2016). The SrIrO 3/IrO x catalyst significantly outperforms rutile IrO 2 and RuO 2, the only other OER catalysts to have reasonable stability and activity in acidic electrolyte, and in fact demonstrates the best activity for any known OER catalyst measured in either acidic or in alkaline electrolyte. For alkaline conditions we have demonstrated that the combined effect of cerium as a dopant and gold as a metal support, significantly enhances the OER activity of electrodeposited NiO x films. This NiCeO x-Au catalyst delivers high OER activity in alkaline media, and is among the most active OER electrocatalysts reported to date (Nature Energy, accepted 2016). These studies of new catalysts for the OER, both in acid and in base, are fundamental to enabling new technologies of interest for the DOE, including the production of sustainable fuels and chemicals. ORR: One method to significantly reduce the Pt loading in fuel cell devices is to increase the ORR activity of Pt based systems. To this end we have synthesized a high surface area supported meso-structured Pt xNi alloy thin film with a double gyroid morphology that both exhibits high activity and stability for the ORR (submitted, 2016). We have furthermore developed a Ru-core, Pt-shell system that improves the per Pt site activity by more than a factor of 2 (ChemElectroChem, 2014). Further refinement, optimizing Pt-shell thickness and reducing particle sintering during processing, enabled us to obtain a mass activity that is 2 times higher than commercial Pt/C from TKK. These are important contributions to the DOE goal of reducing Pt loading since an improved understanding of how to increase mass activity and stability helps enable low Pt content fuel cells.« less

Understanding Interactions between Manganese Oxide and Gold That Lead to Enhanced Activity for Electrocatalytic Water Oxidation

PubMed Central

2015-01-01

To develop active nonprecious metal-based electrocatalysts for the oxygen evolution reaction (OER), a limiting reaction in several emerging renewable energy technologies, a deeper understanding of the activity of the first row transition metal oxides is needed. Previous studies of these catalysts have reported conflicting results on the influence of noble metal supports on the OER activity of the transition metal oxides. Our study aims to clarify the interactions between a transition metal oxide catalyst and its metal support in turning over this reaction. To achieve this goal, we examine a catalytic system comprising nanoparticulate Au, a common electrocatalytic support, and nanoparticulate MnOx, a promising OER catalyst. We conclusively demonstrate that adding Au to MnOx significantly enhances OER activity relative to MnOx in the absence of Au, producing an order of magnitude higher turnover frequency (TOF) than the TOF of the best pure MnOx catalysts reported to date. We also provide evidence that it is a local rather than bulk interaction between Au and MnOx that leads to the observed enhancement in the OER activity. Engineering improvements in nonprecious metal-based catalysts by the addition of Au or other noble metals could still represent a scalable catalyst as even trace amounts of Au are shown to lead a significant enhancement in the OER activity of MnOx. PMID:24661269

Understanding interactions between manganese oxide and gold that lead to enhanced activity for electrocatalytic water oxidation.

PubMed

Gorlin, Yelena; Chung, Chia-Jung; Benck, Jesse D; Nordlund, Dennis; Seitz, Linsey; Weng, Tsu-Chien; Sokaras, Dimosthenis; Clemens, Bruce M; Jaramillo, Thomas F

2014-04-02

To develop active nonprecious metal-based electrocatalysts for the oxygen evolution reaction (OER), a limiting reaction in several emerging renewable energy technologies, a deeper understanding of the activity of the first row transition metal oxides is needed. Previous studies of these catalysts have reported conflicting results on the influence of noble metal supports on the OER activity of the transition metal oxides. Our study aims to clarify the interactions between a transition metal oxide catalyst and its metal support in turning over this reaction. To achieve this goal, we examine a catalytic system comprising nanoparticulate Au, a common electrocatalytic support, and nanoparticulate MnO(x), a promising OER catalyst. We conclusively demonstrate that adding Au to MnO(x) significantly enhances OER activity relative to MnO(x) in the absence of Au, producing an order of magnitude higher turnover frequency (TOF) than the TOF of the best pure MnO(x) catalysts reported to date. We also provide evidence that it is a local rather than bulk interaction between Au and MnO(x) that leads to the observed enhancement in the OER activity. Engineering improvements in nonprecious metal-based catalysts by the addition of Au or other noble metals could still represent a scalable catalyst as even trace amounts of Au are shown to lead a significant enhancement in the OER activity of MnO(x).

DEVELOPMENT OF ATTRITION RESISTANT IRON-BASED FISCHER-TROPSCH CATALYSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adeyinka A. Adeyiga

2001-09-01

The Fischer-Tropsch (F-T) reaction provides a way of converting coal-derived synthesis gas (CO+H{sub 2}) to liquid fuels. Since the reaction is highly exothermic, one of the major problems in control of the reaction is heat removal. Recent work has shown that the use of slurry bubble column reactors (SBCRs) can largely solve this problem. The use of iron-based catalysts is attractive not only due to their low cost and ready availability, but also due to their high water-gas shift activity which makes it possible to use these catalysts with low H{sub 2}/CO ratios. However, a serious problem with use ofmore » Fe catalysts in a SBCR is their tendency to undergo attrition. This can cause fouling/plugging of downstream filters and equipment, makes the separation of catalyst from the oil/wax product very difficult if not impossible, and results in a steady loss of catalyst from the reactor. Recently, fundamental understanding of physical attrition is being addressed by incorporating suitable binders into the catalyst recipe. This has resulted in the preparation of a spray dried Fe-based catalyst having aps of 70 mm with high attrition resistance. This Fe-based attrition resistant, active and selective catalyst gave 95% CO conversion through 125 hours of testing in a fixed-bed at 270 C, 1.48 MPa, H{sub 2}/CO=0.67 and 2.0 NL/g-cat/h with C{sub 5}{sup +} selectivity of >78% and methane selectivity of <5%. However, further development of the catalyst is needed to address the chemical attrition due to phase changes that any Fe-catalyst goes through potentially causing internal stresses within the particle and resulting in weakening, spalling or cracking. The objective of this research is to develop robust iron-based Fischer-Tropsch catalysts that have suitable activity, selectivity and stability to be used in the slurry bubble column reactor. Specifically we aim to develop to: (i) improve the performance and preparation procedure of the high activity, high attrition resistant, high alpha iron-based catalysts synthesized at Hampton University, (ii) seek improvements in the catalyst performance through variations in process conditions, pretreatment procedures and/or modifications in catalyst preparation steps and (iii) investigate the performance in a slurry reactor. The effort during the reporting period has been devoted to attrition study of the iron-based catalysts. Precipitated silica appeared to decrease attrition resistance of spray-dried iron FT catalysts. It was found that the catalyst with precipitated silica content at around 12wt% showed the lowest attrition resistance. The results of net change in volume moment and catalyst morphology showed supporting evidences to the attrition results. Catalysts with low attrition resistance generated more fines loss, had higher net change in volume moment and showed more breakage of particles. BET surface area and pore volume of this catalyst series fluctuated; therefore no conclusion can be drawn from the data obtained. However, catalyst with no precipitated silica showed the lowest in BET surface area and pore volume, as expected. Addition of precipitated silica to the catalysts had no effect to the phase changes of iron that could have significant influence to catalyst attrition. The presence of precipitated silica is needed for enhancing catalyst surface area; however, the amount of silica added should be compromising with attrition resistance of catalysts.« less

Catalytic ozonation of dimethyl phthalate over cerium supported on activated carbon.

PubMed

Li, Laisheng; Ye, Weiying; Zhang, Qiuyun; Sun, Fengqiang; Lu, Ping; Li, Xukai

2009-10-15

Cerium supported on activated carbon (Ce/AC), which was prepared by dipping method, was employed to degrade dimethyl phthalate (DMP) in water. The mineral matter present in the activated carbon positively contributes to its activity to enhance DMP ozonation process. A higher dipping Ce(NO(3))(3) concentration and calcination process increase its microporous volume and surface area, and decreases its exterior surface area. The catalytic activity reaches optimal when 0.2% (w/w) cerium is deposited on activated carbon. Ce/AC catalyst was characterized by XRD, SEM and BET. The presence of either activated carbon or Ce/AC catalyst considerably improves their degradation and mineralization in the ozonation of DMP. During the ozonation (50mg/h ozone flow rate) of a 30 mg/L DMP (initial pH 5.0) with the presence of Ce/AC catalyst, TOC removal rate reaches 68% at 60 min oxidation time, 48% using activated carbon as catalyst, only 22% with ozonation alone. The presence of tert-butanol (a well known OH radical scavenger) strongly inhibits DMP degradation by activated carbon or Ce/AC catalytic ozonation. TOC removal rate follows the second-order kinetics model well. In the ozonation of DMP with 50mg/h ozone flow rate, its mineralization rate constant with the presence of Ce/AC catalyst is 2.5 times higher than that of activated carbon, 7.5 times higher than that of O(3) alone. Ce/AC catalyst shows the better catalytic activity and stability based on 780 min sequential reaction in the ozonation of DMP. Ce/AC was a promising catalyst for ozonizing organic pollutants in the aqueous solution.

Comparative Study of the ORR Activity and Stability of Pt and PtM (M = Ni, Co, Cr, Pd) Supported on Polyaniline/Carbon Nanotubes in a PEM Fuel Cell.

PubMed

Kaewsai, Duanghathai; Hunsom, Mali

2018-05-04

The oxygen reduction reaction (ORR) activity and stability of platinum (Pt) and PtM (M = Ni, Co, Cr, Pd) supported on polyaniline/carbon nanotube (PtM/PANI-CNT) were explored and compared with the commercial Pt/C catalyst (ETEK). The Pt/PANI-CNT catalyst exhibited higher ORR activity and stability than the commercial Pt/C catalyst even though it had larger crystallite/particle sizes, lower catalyst dispersion and lower electrochemical surface area (ESA), probably because of its high electrical conductivity. The addition of second metal (M) enhanced the ORR activity and stability of the Pt/PANI-CNT catalyst, because the added M induced the formation of a PtM alloy and shifted the d -band center to downfield, leading to a weak chemical interaction between oxygenated species and the catalyst surface and, therefore, affected positively the catalytic activity. Among all the tested M, the addition of Cr was optimal. Although it improved the ORR activity of the Pt/PANI-CNT catalyst slightly less than that of Pd (around 4.98%) in low temperature (60 °C)/pressure (1 atm abs), it reduced the ESA loss by around 14.8% after 1000 cycles of repetitive cyclic voltammetry (CV). In addition, it is cheaper than Pd metal. Thus, Cr was recommended as the second metal to alloy with Pt on the PANI-CNT support.

Comparative Study of the ORR Activity and Stability of Pt and PtM (M = Ni, Co, Cr, Pd) Supported on Polyaniline/Carbon Nanotubes in a PEM Fuel Cell

PubMed Central

Kaewsai, Duanghathai; Hunsom, Mali

2018-01-01

The oxygen reduction reaction (ORR) activity and stability of platinum (Pt) and PtM (M = Ni, Co, Cr, Pd) supported on polyaniline/carbon nanotube (PtM/PANI-CNT) were explored and compared with the commercial Pt/C catalyst (ETEK). The Pt/PANI-CNT catalyst exhibited higher ORR activity and stability than the commercial Pt/C catalyst even though it had larger crystallite/particle sizes, lower catalyst dispersion and lower electrochemical surface area (ESA), probably because of its high electrical conductivity. The addition of second metal (M) enhanced the ORR activity and stability of the Pt/PANI-CNT catalyst, because the added M induced the formation of a PtM alloy and shifted the d-band center to downfield, leading to a weak chemical interaction between oxygenated species and the catalyst surface and, therefore, affected positively the catalytic activity. Among all the tested M, the addition of Cr was optimal. Although it improved the ORR activity of the Pt/PANI-CNT catalyst slightly less than that of Pd (around 4.98%) in low temperature (60 °C)/pressure (1 atm abs), it reduced the ESA loss by around 14.8% after 1000 cycles of repetitive cyclic voltammetry (CV). In addition, it is cheaper than Pd metal. Thus, Cr was recommended as the second metal to alloy with Pt on the PANI-CNT support. PMID:29734719

Electrocatalysis of carbon black- or poly(diallyldimethylammonium chloride)-functionalized activated carbon nanotubes-supported Pd-Tb towards methanol oxidation in alkaline media

NASA Astrophysics Data System (ADS)

Wang, Li; Wang, Yi; Li, An; Yang, Yunshang; Tang, Qinghu; Cao, Hongbin; Qi, Tao; Li, Changming

2014-07-01

The Pd-Tb/C catalysts with different Pd/Tb ratios were synthesized by a simple simultaneous reduction reaction with sodium borohydride in aqueous solution. The structure and morphology of those catalysts had been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrocatalytic performance of those catalysts for methanol oxidation in alkaline media was investigated using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and CO stripping experiments. It is found that the 20%Pd-1%Tb/C catalyst has a higher catalytic activity than the 20%Pd/C catalyst, but the effect of Tb cannot be explained by a bi-functional mechanism. According to the X-Ray photoelectron spectroscopy (XPS) analyses, it is suggested that the higher content of metallic Pd caused by the addition of Tb contributes to the better catalytic activity of 20%Pd-1%Tb/C. Based on the good electrocatalytic performance of 20%Pd-1%Tb/C, the 20%Pd-1%Tb catalyst supported on poly(diallyldimethylammonium chloride) (PDDA)-functionalized activated carbon nanotubes was prepared, and it exhibits a better catalytic activity. The improvement mainly results from the further increase of metallic Pd due to the presence of PDDA.

Electrochemical dopamine sensor based on P-doped graphene: Highly active metal-free catalyst and metal catalyst support.

PubMed

Chu, Ke; Wang, Fan; Zhao, Xiao-Lin; Wang, Xin-Wei; Tian, Ye

2017-12-01

Heteroatom doping is an effective strategy to enhance the catalytic activity of graphene and its hybrid materials. Despite a growing interest of P-doped graphene (P-G) in energy storage/generation applications, P-G has rarely been investigated for electrochemical sensing. Herein, we reported the employment of P-G as both metal-free catalyst and metal catalyst support for electrochemical detection of dopamine (DA). As a metal-free catalyst, P-G exhibited prominent DA sensing performances due to the important role of P doping in improving the electrocatalytic activity of graphene toward DA oxidation. Furthermore, P-G could be an efficient supporting material for loading Au nanoparticles, and resulting Au/P-G hybrid showed a dramatically enhanced electrocatalytic activity and extraordinary sensing performances with a wide linear range of 0.1-180μM and a low detection limit of 0.002μM. All these results demonstrated that P-G might be a very promising electrode material for electrochemical sensor applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Counting Active Sites on Titanium Oxide-Silica Catalysts for Hydrogen Peroxide Activation through In Situ Poisoning with Phenylphosphonic Acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eaton, Todd R.; Boston, Andrew M.; Thompson, Anthony B.

2015-06-04

Quantifying specific active sites in supported catalysts improves our understanding and assists in rational design. Supported oxides can undergo significant structural changes as surface densities increase from site-isolated cations to monolayers and crystallites, which changes the number of kinetically relevant sites. Herein, TiO x domains are titrated on TiO x–SiO 2 selectively with phenylphosphonic acid (PPA). An ex situ method quantifies all fluid-accessible TiO x, whereas an in situ titration during cis-cyclooctene epoxidation provides previously unavailable values for the number of tetrahedral Ti sites on which H 2O 2 activation occurs. We use this method to determine the active sitemore » densities of 22 different catalysts with different synthesis methods, loadings, and characteristic spectra and find a single intrinsic turnover frequency for cis-cyclooctene epoxidation of (40±7) h -1. This simple method gives molecular-level insight into catalyst structure that is otherwise hidden when bulk techniques are used.« less

Intermetallic nickel silicide nanocatalyst—A non-noble metal–based general hydrogenation catalyst

PubMed Central

Pohl, Marga-Martina; Agapova, Anastasiya

2018-01-01

Hydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds including fine chemicals, agrochemicals, and pharmachemicals. On an industrial scale, hydrogenations are typically performed with precious metal catalysts or with base metal catalysts, such as Raney nickel, which requires special handling due to its pyrophoric nature. We report a stable and highly active intermetallic nickel silicide catalyst that can be used for hydrogenations of a wide range of unsaturated compounds. The catalyst is prepared via a straightforward procedure using SiO2 as the silicon atom source. The process involves thermal reduction of Si–O bonds in the presence of Ni nanoparticles at temperatures below 1000°C. The presence of silicon as a secondary component in the nickel metal lattice plays the key role in its properties and is of crucial importance for improved catalytic activity. This novel catalyst allows for efficient reduction of nitroarenes, carbonyls, nitriles, N-containing heterocycles, and unsaturated carbon–carbon bonds. Moreover, the reported catalyst can be used for oxidation reactions in the presence of molecular oxygen and is capable of promoting acceptorless dehydrogenation of unsaturated N-containing heterocycles, opening avenues for H2 storage in organic compounds. The generality of the nickel silicide catalyst is demonstrated in the hydrogenation of over a hundred of structurally diverse unsaturated compounds. The wide application scope and high catalytic activity of this novel catalyst make it a nice alternative to known general hydrogenation catalysts, such as Raney nickel and noble metal–based catalysts. PMID:29888329

Ozone assisted oxidation of gaseous PCDD/Fs over CNTs-containing composite catalysts at low temperature.

PubMed

Wang, Qiulin; Tang, Minghui; Peng, Yaqi; Du, Cuicui; Lu, Shengyong

2018-05-01

Ozone assisted carbon nanotubes (CNTs) supported vanadium oxide/titanium dioxide (V/Ti-CNTs) or vanadium oxide-manganese oxide/titanium dioxide (V-Mn/Ti-CNTs) catalysts towards gaseous PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) catalytic oxidations at low temperature (150 °C) were investigated. The removal efficiency (RE) and decomposition efficiency (DE) of PCDD/Fs achieved with V-Mn/Ti-CNTs alone were 95% and 45% at 150 °C under a space velocity (SV) of 14000 h -1 ; yet, these values reached 99% and 91% when catalyst and low concentration (50 ppm) ozone were used in combined. The ozone promotion effect on catalytic activity was further enhanced with the addition of manganese oxide (MnO x ) and CNTs. Adding MnO x and CNTs in V/Ti catalysts facilitated the ozone decomposition (creating more active species on catalyst surface), thus, improved ozone utilization (demanding relatively lower ozone addition concentration). On the other hand, this study threw light upon ozone promotion mechanism based on the comparison of catalyst properties (i.e. components, surface area, surface acidity, redox ability and oxidation state) before and after ozone treatment. The experimental results indicate that a synergistic effect exists between catalyst and ozone: ozone is captured and decomposed on catalyst surface; meanwhile, the catalyst properties are changed by ozone in return. Reactive oxygen species from ozone decomposition and the accompanied catalyst properties optimization are crucial reasons for catalyst activation at low temperature. Copyright © 2018 Elsevier Ltd. All rights reserved.

Intermetallic nickel silicide nanocatalyst-A non-noble metal-based general hydrogenation catalyst.

PubMed

Ryabchuk, Pavel; Agostini, Giovanni; Pohl, Marga-Martina; Lund, Henrik; Agapova, Anastasiya; Junge, Henrik; Junge, Kathrin; Beller, Matthias

2018-06-01

Hydrogenation reactions are essential processes in the chemical industry, giving access to a variety of valuable compounds including fine chemicals, agrochemicals, and pharmachemicals. On an industrial scale, hydrogenations are typically performed with precious metal catalysts or with base metal catalysts, such as Raney nickel, which requires special handling due to its pyrophoric nature. We report a stable and highly active intermetallic nickel silicide catalyst that can be used for hydrogenations of a wide range of unsaturated compounds. The catalyst is prepared via a straightforward procedure using SiO 2 as the silicon atom source. The process involves thermal reduction of Si-O bonds in the presence of Ni nanoparticles at temperatures below 1000°C. The presence of silicon as a secondary component in the nickel metal lattice plays the key role in its properties and is of crucial importance for improved catalytic activity. This novel catalyst allows for efficient reduction of nitroarenes, carbonyls, nitriles, N-containing heterocycles, and unsaturated carbon-carbon bonds. Moreover, the reported catalyst can be used for oxidation reactions in the presence of molecular oxygen and is capable of promoting acceptorless dehydrogenation of unsaturated N-containing heterocycles, opening avenues for H 2 storage in organic compounds. The generality of the nickel silicide catalyst is demonstrated in the hydrogenation of over a hundred of structurally diverse unsaturated compounds. The wide application scope and high catalytic activity of this novel catalyst make it a nice alternative to known general hydrogenation catalysts, such as Raney nickel and noble metal-based catalysts.

Stable carbonous catalyst particles and method for making and utilizing same

DOEpatents

Ganguli, Partha S.; Comolli, Alfred G.

2005-06-14

Stable carbonous catalyst particles composed of an inorganic catalytic metal/metal oxide powder and a carbonaceous binder material are formed having a basic inner substantially uniform-porous carbon coating of the catalytic powder, and may include an outer porous carbon coating layer. Suitable inorganic catalytic powders include zinc-chromite (ZnO/Cr.sub.2 03) and suitable carbonaceous liquid binders having molecular weight of 200-700 include partially polymerized furfuryl alcohol, which are mixed together, shaped and carbonized and partially oxidized at elevated temperature. Such stable carbonous catalyst particles such as 0.020-0.100 inch (0.51-2.54 mm) diameter extrudates, have total carbon content of 2-25 wt. % and improved crush strength of 1.0-5 1b/mn, 50-300 m.sup.2 /g surface area, and can be advantageously utilized in fixed bed or ebullated/fluidized bed reactor operations. This invention also includes method steps for making the stable carbonous catalyst particles having improved particle strength and catalytic activity, and processes for utilizing the active stable carbonous carbon-coated catalysts such as for syn-gas reactions in ebullated/fluidized bed reactors for producing alcohol products and Fischer-Tropsch synthesis liquid products.

Highly porous non-precious bimetallic electrocatalysts for efficient hydrogen evolution

DOE PAGES

Lu, Qi; Hutchings, Gregory S.; Yu, Weiting; ...

2015-03-16

One of the key components of carbon dioxide-free hydrogen production is a robust and efficient non-precious metal catalyst for the hydrogen evolution reaction. We report that a hierarchical nanoporous copper-titanium bimetallic electrocatalyst is able to produce hydrogen from water under a mild overpotential at more than twice the rate of state-of-the- art carbon-supported platinum catalyst. Although both copper and titanium are known to be poor hydrogen evolution catalysts, the combination of these two elements creates unique copper-copper-titanium hollow sites, which have a hydrogen-binding energy very similar to that of platinum, resulting in an exceptional hydrogen evolution activity. Moreover, the hierarchicalmore » porosity of the nanoporous-copper titanium catalyst also contributes to its high hydrogen evolution activity, because it provides a large-surface area for electrocatalytic hydrogen evolution, and improves the mass transport properties. Moreover, the catalyst is self-supported, eliminating the overpotential associated with the catalyst/support interface.« less

Ordered micro/macro porous K-OMS-2/SiO2 nanocatalysts: Facile synthesis, low cost and high catalytic activity for diesel soot combustion

PubMed Central

Yu, Xuehua; Zhao, Zhen; Wei, Yuechang; Liu, Jian

2017-01-01

A series of novel oxide catalysts, which contain three-dimensionally ordered macroporous (3DOM) and microporous structure, were firstly designed and successfully synthesized by simple method. In the as-prepared catalysts, 3DOM SiO2 is used as support and microporous K-OMS-2 oxide nanoparticles are supported on the wall of SiO2. 3DOM K-OMS-2/SiO2 oxide catalysts were firstly used in soot particle oxidation reaction and they show very high catalytic activities. The high activities of K-OMS-2/SiO2 oxide catalysts can be assigned to three possible reasons: macroporous effect of 3DOM structure for improving contact between soot and catalyst, microporous effect of K-OMS-2 for adsorption of small gas molecules and interaction of K and Mn for activation of gas molecules. The catalytic activities of catalysts are comparable to or even higher than noble metal catalyst in the medium and high temperature range. For example, the T50 of K-OMS-2/SiO2-50, 328 °C, is much lower than those of Pt/Al2O3 and 3DOM Au/LaFeO3, 464 and 356 °C,respectively. Moreover, catalysts exhibited high catalytic stability. It is attributed to that the K+ ions are introduced into the microporous structure of OMS-2 and stabilized in the catalytic reaction. Meanwhile, the K+ ions play an important role in templating and stabilizing the tunneled framework of OMS-2. PMID:28443610

Single-layer transition metal sulfide catalysts

DOEpatents

Thoma, Steven G [Albuquerque, NM

2011-05-31

Transition Metal Sulfides (TMS), such as molybdenum disulfide (MoS.sub.2), are the petroleum industry's "workhorse" catalysts for upgrading heavy petroleum feedstocks and removing sulfur, nitrogen and other pollutants from fuels. We have developed an improved synthesis technique to produce SLTMS catalysts, such as molybdenum disulfide, with potentially greater activity and specificity than those currently available. Applications for this technology include heavy feed upgrading, in-situ catalysis, bio-fuel conversion and coal liquefaction.

Engineering Ru@Pt Core-Shell Catalysts for Enhanced Electrochemical Oxygen Reduction Mass Activity and Stability.

PubMed

Jackson, Ariel; Strickler, Alaina; Higgins, Drew; Jaramillo, Thomas Francisco

2018-01-12

Improving the performance of oxygen reduction reaction (ORR) electrocatalysts is essential for the commercial efficacy of many renewable energy technologies, including low temperature polymer electrolyte fuel cells (PEFCs). Herein, we report highly active and stable carbon-supported Ru@Pt core-shell nanoparticles (Ru@Pt/C) prepared by a wet chemical synthesis technique. Through rotating disc electrode testing, the Ru@Pt/C achieves an ORR Pt mass-based activity of 0.50 A mg Pt -1 at 0.9 V versus the reversible hydrogen electrode (RHE), which exceeds the activity of the state-of-the-art commercial Pt/C catalyst as well as the Department of Energy 2020 PEFC electrocatalyst activity targets for transportation applications. The impact of various synthetic parameters, including Pt to Ru ratios and catalyst pretreatments (i.e., annealing) are thoroughly explored. Pt-based mass activity of all prepared Ru@Pt/C catalysts was found to exceed 0.4 mg Pt -1 across the range of compositions investigated, with the maximum activity catalyst having a Ru:Pt ratio of 1:1. This optimized composition of Ru@Pt/C catalyst demonstrated remarkable stability after 30,000 accelerated durability cycles (0.6 to 1.0 V vs. RHE at 125 mV s -1 ), maintaining 85% of its initial mass activity. Scanning transmission electron microscopy energy dispersive spectroscopy (STEM-EDS) analysis at various stages of electrochemical testing demonstrated that the Pt shell can provide sufficient protection against the dissolution of the otherwise unstable Ru core.

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance.

PubMed

Alia, Shaun M; Pivovar, Bryan S

2018-04-27

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing to 250 °C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 °C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. These techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.

Studies on photocatalytic activity of the synthesised TiO2 and Ag/TiO2 photocatalysts under UV and sunlight irradiations.

PubMed

Vaithiyanathan, R; Sivakumar, T

2011-01-01

Photocatalytic decolorisation and degradation of Reactive Red 120 (RR 120) has been investigated under UV (365 nm) and solar light as radiation sources using synthesised nano titania catalyst prepared via sol-gel method. The study encompassed calcination of synthesised titania catalyst at a range of temperature up to 1,000°C. The effects of calcination temperature on titania catalyst have been evaluated on the decolorisation of RR 120. The analysis revealed complete decolorisation of dye solution in 100 min under UV light with the TiO2 catalyst calcined at 200°C. Only a maximum of 47% dye decolorisation was achieved under sunlight in 4 h with no improvement even after prolonged irradiation. In an endeavour to improve the catalytic activity, bare titania was modified with silver metal and a comprehensive study on the characteristics of silver modified catalyst was made. The result was an enhancement of the rate of decolorisation of dye under both UV and solar light sources. All the catalysts were characterised by XRD and BET analyses. Optimisation of the degradation of RR 120 has been carried out using the unmodified catalyst by varying the amount of catalyst, substrate concentration, pH of dye solution. Effects of addition of small amounts of various oxidants such as H2O2, KBrO3 and (NH4)2S2O8 have also been studied. Pseudo first order kinetics was observed in the photocatalytic decolorisation of dye. The mineralisation of RR 120 was monitored by TOC analysis.

Uniform Pt/Pd Bimetallic Nanocrystals Demonstrate Platinum Effect on Palladium Methane Combustion Activity and Stability

DOE PAGES

Goodman, Emmett D.; Dai, Sheng; Yang, An-Chih; ...

2017-05-18

Bimetallic catalytic materials are in widespread use for numerous reactions, as the properties of a monometallic catalyst are often improved upon addition of a second metal. In studies with bimetallic catalysts, it remains challenging to establish clear structure–property relationships using traditional impregnation techniques, due to the presence of multiple coexisting active phases of different sizes, shapes, and compositions. Here, a convenient approach to prepare small and uniform Pt/Pd bimetallic nanocrystals with tailorable composition is demonstrated, despite the metals being immiscible in the bulk. By depositing this set of controlled nanocrystals onto a high-surface-area alumina support, we systematically investigate the effectmore » of adding platinum to palladium catalysts for methane combustion. At low temperatures and in the absence of steam, all bimetallic catalysts show activity nearly identical with that of Pt/Al 2O 3, with much lower rates in comparison to that of the Pd/Al 2O 3 sample. BUt, unlike Pd/Al 2O 3, which experiences severe low-temperature steam poisoning, all Pt/Pd bimetallic catalysts maintain combustion activity on exposure to excess steam. These features are due to the influence of Pt on the Pd oxidation state, which prevents the formation of a bulk-type PdO phase. Despite lower initial combustion rates, hydrothermal aging of the Pd-rich bimetallic catalyst induces segregation of a PdO phase in close contact to a Pd/Pt alloy phase, forming more active and highly stable sites for methane combustion. Altogether, this work unambiguously clarifies the activity and stability attributes of Pt/Pd phases which often coexist in traditionally synthesized bimetallic catalysts and demonstrates how well-controlled bimetallic catalysts elucidate structure–property relationships.« less

Uniform Pt/Pd Bimetallic Nanocrystals Demonstrate Platinum Effect on Palladium Methane Combustion Activity and Stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goodman, Emmett D.; Dai, Sheng; Yang, An-Chih

Bimetallic catalytic materials are in widespread use for numerous reactions, as the properties of a monometallic catalyst are often improved upon addition of a second metal. In studies with bimetallic catalysts, it remains challenging to establish clear structure–property relationships using traditional impregnation techniques, due to the presence of multiple coexisting active phases of different sizes, shapes, and compositions. Here, a convenient approach to prepare small and uniform Pt/Pd bimetallic nanocrystals with tailorable composition is demonstrated, despite the metals being immiscible in the bulk. By depositing this set of controlled nanocrystals onto a high-surface-area alumina support, we systematically investigate the effectmore » of adding platinum to palladium catalysts for methane combustion. At low temperatures and in the absence of steam, all bimetallic catalysts show activity nearly identical with that of Pt/Al 2O 3, with much lower rates in comparison to that of the Pd/Al 2O 3 sample. BUt, unlike Pd/Al 2O 3, which experiences severe low-temperature steam poisoning, all Pt/Pd bimetallic catalysts maintain combustion activity on exposure to excess steam. These features are due to the influence of Pt on the Pd oxidation state, which prevents the formation of a bulk-type PdO phase. Despite lower initial combustion rates, hydrothermal aging of the Pd-rich bimetallic catalyst induces segregation of a PdO phase in close contact to a Pd/Pt alloy phase, forming more active and highly stable sites for methane combustion. Altogether, this work unambiguously clarifies the activity and stability attributes of Pt/Pd phases which often coexist in traditionally synthesized bimetallic catalysts and demonstrates how well-controlled bimetallic catalysts elucidate structure–property relationships.« less

Activity of platinum/carbon and palladium/carbon catalysts promoted by Ni2 P in direct ethanol fuel cells.

PubMed

Li, Guoqiang; Feng, Ligang; Chang, Jinfa; Wickman, Björn; Grönbeck, Henrik; Liu, Changpeng; Xing, Wei

2014-12-01

Ethanol is an alternative fuel for direct alcohol fuel cells, in which the electrode materials are commonly based on Pt or Pd. Owing to the excellent promotion effect of Ni2 P that was found in methanol oxidation, we extended the catalyst system of Pt or Pd modified by Ni2 P in direct ethanol fuel cells. The Ni2 P-promoted catalysts were compared to commercial catalysts as well as to reference catalysts promoted with only Ni or only P. Among the studied catalysts, Pt/C and Pd/C modified by Ni2 P (30 wt %) showed both the highest activity and stability. Upon integration into the anode of a homemade direct ethanol fuel cell, the Pt-Ni2 P/C-30 % catalyst showed a maximum power density of 21 mW cm(-2) , which is approximately two times higher than that of a commercial Pt/C catalyst. The Pd-Ni2 P/C-30 % catalyst exhibited a maximum power density of 90 mW cm(-2) . This is approximately 1.5 times higher than that of a commercial Pd/C catalyst. The discharge stability on both two catalysts was also greatly improved over a 12 h discharge operation. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Improving the electrocatalytic performance of carbon nanotubes for VO2+/VO2+ redox reaction by KOH activation

NASA Astrophysics Data System (ADS)

Dai, Lei; Jiang, Yingqiao; Meng, Wei; Zhou, Huizhu; Wang, Ling; He, Zhangxing

2017-04-01

In this paper, carbon nanotubes (CNTs) was activated by KOH treatment at high temperature and investigated as catalyst for VO2+/VO2+ redox reaction for vanadium redox flow battery (VRFB). X-ray photoelectron spectroscopy results suggest that the oxygen-containing groups can be introduced on CNTs by KOH activation. The mass transfer of vanadium ions can be accelerated by chemical etching by KOH activation and improved wettability due to the introduction of hydrophilic groups. The electrochemical properties of VO2+/VO2+ redox reaction can be enhanced by introduced oxygen-containing groups as active sites. The sample treated at 900 °C with KOH/CNTs mass ratio of 3:1 (CNTs-3) exhibits the highest electrocatalytic activity for VO2+/VO2+ redox reaction. The cell using CNTs-3 as positive catalyst demonstrates the smallest electrochemical polarization, the highest capacity and efficiency among the samples. Using KOH-activated CNTs-3 can increase the average energy efficiency of the cell by 4.4%. This work suggests that KOH-activated CNTs is a low-cost, efficient and promising catalyst for VO2+/VO2+ redox reaction for VRFB system.

Understanding the performance and mechanism of Mg-containing oxides as support catalysts in the thermal dry reforming of methane.

PubMed

Khairudin, Nor Fazila; Sukri, Mohd Farid Fahmi; Khavarian, Mehrnoush; Mohamed, Abdul Rahman

2018-01-01

Dry reforming of methane (DRM) is one of the more promising methods for syngas (synthetic gas) production and co-utilization of methane and carbon dioxide, which are the main greenhouse gases. Magnesium is commonly applied in a Ni-based catalyst in DRM to improve catalyst performance and inhibit carbon deposition. The aim of this review is to gain better insight into recent developments on the use of Mg as a support or promoter for DRM catalysts. Its high basicity and high thermal stability make Mg suitable for introduction into the highly endothermic reaction of DRM. The introduction of Mg as a support or promoter for Ni-based catalysts allows for good metal dispersion on the catalyst surface, which consequently facilitates high catalytic activity and low catalyst deactivation. The mechanism of DRM and carbon formation and reduction are reviewed. This work further explores how different constraints, such as the synthesis method, metal loading, pretreatment, and operating conditions, influence the dry reforming reactions and product yields. In this review, different strategies for enhancing catalytic activity and the effect of metal dispersion on Mg-containing oxide catalysts are highlighted.

Poisoning of a Silica-Supported Cobalt Catalyst due to Presence of Sulfur Impurities in Syngas during Fischer–Tropsch Synthesis: Effects of Chelating Agent

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bambal, Ashish S.; Guggilla, Vidya S.; Kugler, Edwin L.

2014-04-09

The effects of sulfur impurities on the performance of cobalt-based Fischer–Tropsch catalysts are evaluated under industrially relevant operating conditions of temperature, pressure, and impurity levels. Chelating agents (CAs) were used to modify the SiO 2 support, and the performances of the CA-modified catalysts are compared with conventional Co/SiO 2 catalysts. For both the Co/SiO 2 and CA-modified catalysts, the presence of sulfur in the inlet syngas results in a notable drop in the CO conversion, an undesired shift in the hydrocarbon selectivity toward short-chain hydrocarbons, more olefins in the products, and lower product yields. In the post-poisoning stage, i.e., aftermore » termination of sulfur introduction in the inlet syngas, the CA-modified catalysts recover activity and selectivity (to some extent at least), whereas such trends are not observed for the base-case, i.e., unmodified Co/SiO 2 catalyst. Finally, the improved performance of the CA-modified catalysts in the presence of sulfur is attributed to higher densities of active sites.« less

Understanding the performance and mechanism of Mg-containing oxides as support catalysts in the thermal dry reforming of methane

PubMed Central

Khairudin, Nor Fazila; Sukri, Mohd Farid Fahmi; Khavarian, Mehrnoush

2018-01-01

Dry reforming of methane (DRM) is one of the more promising methods for syngas (synthetic gas) production and co-utilization of methane and carbon dioxide, which are the main greenhouse gases. Magnesium is commonly applied in a Ni-based catalyst in DRM to improve catalyst performance and inhibit carbon deposition. The aim of this review is to gain better insight into recent developments on the use of Mg as a support or promoter for DRM catalysts. Its high basicity and high thermal stability make Mg suitable for introduction into the highly endothermic reaction of DRM. The introduction of Mg as a support or promoter for Ni-based catalysts allows for good metal dispersion on the catalyst surface, which consequently facilitates high catalytic activity and low catalyst deactivation. The mechanism of DRM and carbon formation and reduction are reviewed. This work further explores how different constraints, such as the synthesis method, metal loading, pretreatment, and operating conditions, influence the dry reforming reactions and product yields. In this review, different strategies for enhancing catalytic activity and the effect of metal dispersion on Mg-containing oxide catalysts are highlighted. PMID:29719767

Nitrogen-Doped Carbon Nanotube-Supported Pd Catalyst for Improved Electrocatalytic Performance toward Ethanol Electrooxidation

NASA Astrophysics Data System (ADS)

Wei, Ying; Zhang, Xinyuan; Luo, Zhiyong; Tang, Dian; Chen, Changxin; Zhang, Teng; Xie, Zailai

2017-07-01

In this study, hydrothermal carbonization (HTC) was applied for surface functionalization of carbon nanotubes (CNTs) in the presence of glucose and urea. The HTC process allowed the deposition of thin nitrogen-doped carbon layers on the surface of the CNTs. By controlling the ratio of glucose to urea, nitrogen contents of up to 1.7 wt% were achieved. The nitrogen-doped carbon nanotube-supported Pd catalysts exhibited superior electrochemical activity for ethanol oxidation relative to the pristine CNTs. Importantly, a 1.5-fold increase in the specific activity was observed for the Pd/HTC-N1.67%CNTs relative to the catalyst without nitrogen doping (Pd/HTC-CNTs). Further experiments indicated that the introduction of nitrogen species on the surface of the CNTs improved the Pd(0) loading and increased the binding energy.

Enhancing Cooperativity in Bifunctional Acid–Pd Catalysts with Carboxylic Acid-Functionalized Organic Monolayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coan, Patrick D.; Ellis, Lucas D.; Griffin, Michael B.

Here, cooperative catalysts containing a combination of noble metal hydrogenation sites and Bronsted acid sites are critical for many reactions, including the deoxygenation (DO) of biomass-derived oxygenates in the upgrading of pyrolysis oil. One route toward the design of cooperative catalysts is to tether two different catalytically active functions so that they are in close proximity while avoiding undesirable interactions that can block active sites. Here, we deposited carboxylic acid (CA)-functionalized organophosphonate monolayers onto Al 2O 3-supported Pd nanoparticle catalysts to prepare bifunctional catalysts containing both Bronsted acid and metal sites. Modification with phosphonic acids (PAs) improved activity and selectivitymore » for gas-phase DO reactions, but the degree of improvement was highly sensitive to both the presence and positioning of the CA group, suggesting a significant contribution from both the PA and CA sites. Short spacer lengths of 1-2 methylene groups between the phosphonate head and CA tail were found to yield the best DO rates and selectivities, whereas longer chains performed similarly to self-assembled monolayers having alkyl tails. Results from a combination of density functional theory and Fourier transform infrared spectroscopy suggested that the enhanced catalyst performance on the optimally positioned CAs was due to the generation of strong acid sites on the Al 2O 3 support adjacent to the metal. Furthermore, the high activity of these sites was found to result from a hydrogen-bonded cyclic structure involving cooperativity between the phosphonate head group and CA tail function. More broadly, these results indicate that functional groups tethered to supports via organic ligands can influence catalytic chemistry on metal nanoparticles.« less

Enhancing Cooperativity in Bifunctional Acid–Pd Catalysts with Carboxylic Acid-Functionalized Organic Monolayers

DOE PAGES

Coan, Patrick D.; Ellis, Lucas D.; Griffin, Michael B.; ...

2018-03-05

Here, cooperative catalysts containing a combination of noble metal hydrogenation sites and Bronsted acid sites are critical for many reactions, including the deoxygenation (DO) of biomass-derived oxygenates in the upgrading of pyrolysis oil. One route toward the design of cooperative catalysts is to tether two different catalytically active functions so that they are in close proximity while avoiding undesirable interactions that can block active sites. Here, we deposited carboxylic acid (CA)-functionalized organophosphonate monolayers onto Al 2O 3-supported Pd nanoparticle catalysts to prepare bifunctional catalysts containing both Bronsted acid and metal sites. Modification with phosphonic acids (PAs) improved activity and selectivitymore » for gas-phase DO reactions, but the degree of improvement was highly sensitive to both the presence and positioning of the CA group, suggesting a significant contribution from both the PA and CA sites. Short spacer lengths of 1-2 methylene groups between the phosphonate head and CA tail were found to yield the best DO rates and selectivities, whereas longer chains performed similarly to self-assembled monolayers having alkyl tails. Results from a combination of density functional theory and Fourier transform infrared spectroscopy suggested that the enhanced catalyst performance on the optimally positioned CAs was due to the generation of strong acid sites on the Al 2O 3 support adjacent to the metal. Furthermore, the high activity of these sites was found to result from a hydrogen-bonded cyclic structure involving cooperativity between the phosphonate head group and CA tail function. More broadly, these results indicate that functional groups tethered to supports via organic ligands can influence catalytic chemistry on metal nanoparticles.« less

La-doped Al2O3 supported Au nanoparticles: highly active and selective catalysts for PROX under PEMFC operation conditions.

PubMed

Lin, Qingquan; Qiao, Botao; Huang, Yanqiang; Li, Lin; Lin, Jian; Liu, Xiao Yan; Wang, Aiqin; Li, Wen-Cui; Zhang, Tao

2014-03-14

La-doped γ-Al2O3 supported Au catalysts show high activity and selectivity for the PROX reaction under PEMFC operation conditions. The superior performance is attributed to the formation of LaAlO3, which suppresses H2 oxidation and strengthens CO adsorption on Au sites, thereby improving competitive oxidation of CO at elevated temperature.

Fe2P as a novel efficient catalyst promoter in Pd/C system for formic acid electro-oxidation in fuel cells reaction

NASA Astrophysics Data System (ADS)

Wang, Fulong; Xue, Huaiguo; Tian, Zhiqun; Xing, Wei; Feng, Ligang

2018-01-01

Developing catalyst promoter for Pd/C catalyst is significant for the catalytic ability improvement in energy transfer related electrochemical reactions. Herein, we demonstrate Fe2P as an efficient catalyst promoter in Pd/C catalyst system for formic acid electro-oxidation in fuel cells reactions. Adding Fe2P in the Pd/C catalyst system greatly increases the performances for formic acid oxidation by 3-4 times; the CO stripping technique displays two kinds of active sites formation in the Pd-Fe2P/C catalyst system coming from the interaction of Pd, Fe2P and Pd oxide species and both are more efficient for formic acid and CO-species electrooxidation. The smaller charge transfer resistance and Tafel slope for formic acid oxidation indicate the improvements in kinetics by Fe2P in the Pd-Fe2P/C system. The nanostructured hybrid units of Pd, Fe2P and carbon are evidently visible in the high resolution microscopy images and XPS technique confirmes the electronic effect in the catalyst system. The promotion effect of Fe2P in the catalyst system arising from the structure, composition and electronic effect changes is discussed with the help from multiple physical and electrochemical techniques. It is concluded that Fe2P as a significant catalyst promoter will have potential application in energy transfer related electrochemical reactions.

Highly Selective TiN-Supported Highly Dispersed Pt Catalyst: Ultra Active toward Hydrogen Oxidation and Inactive toward Oxygen Reduction.

PubMed

Luo, Junming; Tang, Haibo; Tian, Xinlong; Hou, Sanying; Li, Xiuhua; Du, Li; Liao, Shijun

2018-01-31

The severe dissolution of the cathode catalyst, caused by an undesired oxygen reduction reaction at the anode during startup and shutdown, is a fatal challenge to practical applications of polymer electrolyte membrane fuel cells. To address this important issue, according to the distinct structure-sensitivity between the σ-type bond in H 2 and the π-type bond in O 2 , we design a HD-Pt/TiN material by highly dispersing Pt on the TiN surface to inhibit the unwanted oxygen reduction reaction. The highly dispersed Pt/TiN catalyst exhibits excellent selectivity toward hydrogen oxidation and oxygen reduction reactions. With a Pt loading of 0.88 wt %, our catalyst shows excellent hydrogen oxidation reaction activity, close to that of commercial 20 wt % Pt/C catalyst, and much lower oxygen reduction reaction activity than the commercial 20 wt % Pt/C catalyst. The lack of well-ordered Pt facets is responsible for the excellent selectivity of the HD-Pt/TiN materials toward hydrogen oxidation and oxygen reduction reactions. Our work provides a new and cost-effective solution to design selective catalysts toward hydrogen oxidation and oxygen reduction reactions, making the strategy of using oxygen-tolerant anode catalyst to improve the stability of polymer electrolyte membrane fuel cells during startup and shutdown more affordable and practical.

Application, Deactivation, and Regeneration of Heterogeneous Catalysts in Bio-Oil Upgrading

DOE PAGES

Cheng, Shouyun; Wei, Lin; Zhao, Xianhui; ...

2016-12-07

The massive consumption of fossil fuels and associated environmental issues are leading to an increased interest in alternative resources such as biofuels. The renewable biofuels can be upgraded from bio-oils that are derived from biomass pyrolysis. Catalytic cracking and hydrodeoxygenation (HDO) are two of the most promising bio-oil upgrading processes for biofuel production. Heterogeneous catalysts are essential for upgrading bio-oil into hydrocarbon biofuel. Although advances have been achieved, the deactivation and regeneration of catalysts still remains a challenge. This review focuses on the current progress and challenges of heterogeneous catalyst application, deactivation, and regeneration. The technologies of catalysts deactivation, reduction,more » and regeneration for improving catalyst activity and stability are discussed. Some suggestions for future research including catalyst mechanism, catalyst development, process integration, and biomass modification for the production of hydrocarbon biofuels are provided.« less

Application, Deactivation, and Regeneration of Heterogeneous Catalysts in Bio-Oil Upgrading

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Shouyun; Wei, Lin; Zhao, Xianhui

The massive consumption of fossil fuels and associated environmental issues are leading to an increased interest in alternative resources such as biofuels. The renewable biofuels can be upgraded from bio-oils that are derived from biomass pyrolysis. Catalytic cracking and hydrodeoxygenation (HDO) are two of the most promising bio-oil upgrading processes for biofuel production. Heterogeneous catalysts are essential for upgrading bio-oil into hydrocarbon biofuel. Although advances have been achieved, the deactivation and regeneration of catalysts still remains a challenge. This review focuses on the current progress and challenges of heterogeneous catalyst application, deactivation, and regeneration. The technologies of catalysts deactivation, reduction,more » and regeneration for improving catalyst activity and stability are discussed. Some suggestions for future research including catalyst mechanism, catalyst development, process integration, and biomass modification for the production of hydrocarbon biofuels are provided.« less

Synthesis of nanoporous CuO/TiO2/Pd-NiO composite catalysts by chemical dealloying and their performance for methanol and ethanol electro-oxidation

NASA Astrophysics Data System (ADS)

Niu, Mengying; Xu, Wence; Zhu, Shengli; Liang, Yanqin; Cui, Zhenduo; Yang, Xianjin; Inoue, Akihisa

2017-09-01

Nanoporous CuO/TiO2/Pd-NiO-x (x = 0, 1, 3, 5, 7 at%) catalysts have been synthesized by dealloying Cu-Ti-Pd-Ni alloy ribbons in acid solution. The nanoporous structure and chemical composition of the catalysts distribute uniformly. Based on the electrochemical active area (EASA), electrocatalytic activity and stability, the np-CuO/TiO2/Pd-NiO-3 catalyst possesses the best performance for methanol and ethanol electro-oxidation. For methanol and ethanol electro-oxidation, the anodic current densities in forward scan of the np-CuO/TiO2/Pd-NiO-3 catalyst are about 5.6 times and 2.1 times larger than that of the np-CuO/TiO2/Pd catalyst, respectively. The introduction of NiO provides more electrochemical active sites due to the improved geometrical and bifunctional mechanism. NiO promotes the adsorption of oxygen-containing species (OHads) on the catalyst surface, and electron effect between Pd and Ni is favorable for charge transfer. This accelerates the removal of intermediate products during the oxidation process. The electrocatalytic processes of methanol and ethanol oxidation in alkaline solution are controlled by both charge transfer and diffusion.

Influence of physicochemical treatments on iron-based spent catalyst for catalytic oxidation of toluene.

PubMed

Kim, Sang Chai; Shim, Wang Geun

2008-06-15

The catalytic oxidation of toluene was studied over an iron-based spent and regenerated catalysts. Air, hydrogen, or four different acid solutions (oxalic acid (C2H2O4), citric acid (C6H8O7), acetic acid (CH3COOH), and nitric acid (HNO3)) were employed to regenerate the spent catalyst. The properties of pretreated spent catalyst were characterized by the Brunauer Emmett Teller (BET), inductively coupled plasma (ICP), temperature programmed reduction (TPR), and X-ray diffraction (XRD) analyses. The air pretreatment significantly enhanced the catalytic activity of the spent catalyst in the pretreatment temperature range of 200-400 degrees C, but its catalytic activity diminished at the pretreatment temperature of 600 degrees C. The catalytic activity sequence with respect to the air pretreatment temperatures was 400 degrees C>200 degrees C>parent>600 degrees C. The TPR results indicated that the catalytic activity was correlated with both the oxygen mobility and the amount of available oxygen on the catalyst. In contrast, the hydrogen pretreatment had a negative effect on the catalytic activity, and toluene conversion decreased with increasing pretreatment temperatures (200-600 degrees C). The XRD and TPR results confirmed the formation of metallic iron which had a negative effect on the catalytic activity with increasing pretreatment temperature. The acid pretreatment improved the catalytic activity of the spent catalyst. The catalytic activity sequence with respect to different acids pretreatment was found to be oxalic acid>citric acid>acetic acid>or=nitric acid>parent. The TPR results of acid pretreated samples showed an increased amount of available oxygen which gave a positive effect on the catalytic activity. Accordingly, air or acid pretreatments were more promising methods of regenerating the iron-based spent catalyst. In particular, the oxalic acid pretreatment was found to be most effective in the formation of FeC2O4 species which contributed highly to the catalytic combustion of toluene.

Effect of nanostructured carbon support on copper electrocatalytic activity toward CO 2 electroreduction to hydrocarbon fuels

DOE PAGES

Baturina, Olga; Lu, Qin; Xu, Feng; ...

2016-11-10

The effect of support on electrocatalytic activity of Cu nanoparticles (NPs) towards CO 2 electroreduction to hydrocarbon fuels (CH 4 and C 2H 4) is investigated for three types of nanostructured carbons: single wall carbon nanotubes (SWNT), graphene (GP) and onion-like carbon (OLC). Cu/SWNT, Cu/GP and Cu/OLC composite catalysts are synthesized and characterized by X-Ray diffraction analysis, transmission electron microscopy and electrochemical surface area measurements. Electrocatalytic activities of the synthesized materials, as measured in an electrochemical cell connected to a gas chromatograph, are compared to that of Cu NPs supported on Vulcan carbon. All four catalysts demonstrate higher activity towardsmore » C 2H 4 generation vs CH 4, with production of the latter mostly suppressed on Cu NPs supported on nanostructured substrates. Onset potentials for C 2H 4 vs CH 4 generation are shifted positively by 200 mV for Cu/SWNT, Cu/GP, and Cu/OLC catalysts. The Cu/OLC catalyst is found to be superior to the other two nanostructured catalysts in terms of stability, activity and selectivity towards C 2H 4 generation. Its faradaic efficiency reached 60% at -1.8 V vs Ag/AgCl. The enhanced activity and stability of Cu/OLC catalyst can be attributed to the unique catalyst design, wherein a shell of OLC surrounds the Cu NPs such that the outer layer acts as a filter that protects the Cu surface from adsorption of undesirable species, enhances its electrocatalytic performance, and improves its viability in CO 2 electroreduction reaction.« less

Effect of nanostructured carbon support on copper electrocatalytic activity toward CO 2 electroreduction to hydrocarbon fuels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baturina, Olga; Lu, Qin; Xu, Feng

The effect of support on electrocatalytic activity of Cu nanoparticles (NPs) towards CO 2 electroreduction to hydrocarbon fuels (CH 4 and C 2H 4) is investigated for three types of nanostructured carbons: single wall carbon nanotubes (SWNT), graphene (GP) and onion-like carbon (OLC). Cu/SWNT, Cu/GP and Cu/OLC composite catalysts are synthesized and characterized by X-Ray diffraction analysis, transmission electron microscopy and electrochemical surface area measurements. Electrocatalytic activities of the synthesized materials, as measured in an electrochemical cell connected to a gas chromatograph, are compared to that of Cu NPs supported on Vulcan carbon. All four catalysts demonstrate higher activity towardsmore » C 2H 4 generation vs CH 4, with production of the latter mostly suppressed on Cu NPs supported on nanostructured substrates. Onset potentials for C 2H 4 vs CH 4 generation are shifted positively by 200 mV for Cu/SWNT, Cu/GP, and Cu/OLC catalysts. The Cu/OLC catalyst is found to be superior to the other two nanostructured catalysts in terms of stability, activity and selectivity towards C 2H 4 generation. Its faradaic efficiency reached 60% at -1.8 V vs Ag/AgCl. The enhanced activity and stability of Cu/OLC catalyst can be attributed to the unique catalyst design, wherein a shell of OLC surrounds the Cu NPs such that the outer layer acts as a filter that protects the Cu surface from adsorption of undesirable species, enhances its electrocatalytic performance, and improves its viability in CO 2 electroreduction reaction.« less

Heterolytic Activation of Hydrogen Promoted by Ruthenium Nanoparticles immobilized on Basic Supports and Hydrogenation of Aromatic Compounds

NASA Astrophysics Data System (ADS)

Fang, Minfeng

Despite the aggressive development and deployment of new renewable and nuclear technologies, petroleum-derived transportation fuels---gasoline, diesel and jet fuels---will continue to dominate the markets for decades. Environmental legislation imposes severe limits on the tolerable proportion of aromatics, sulfur and nitrogen contents in transportation fuels, which is difficult to achieve with current refining technologies. Catalytic hydrogenation plays an important role in the production of cleaner fuels, both as a direct means to reduce the aromatics and as a key step in the hydrodenitrogenation (HDN) and hydrodesulfurization (HDS) processes. However, conventional catalysts require drastic conditions and/or are easily poisoned by S or N aromatics. Therefore, there is still a need for new efficient catalysts for hydrogenation reactions relevant to the production of cleaner fossil fuels. Our catalyst design involves metallic nanoparticles intimately associated with a basic support, with the aim of creating a nanostructure capable of promoting the heterolytic activation of hydrogen and ionic hydrogenation mechanisms, as a strategy to avoid catalyst poisoning and enhance catalytic activity. We have designed and prepared a new nanostructured catalytic material composed of RuNPs immobilized on the basic polymer P4VPy. We have demonstrated that the Ru/P4VPy catalyst can promote heterolytic hydrogen activation and a unique surface ionic hydrogenation mechanism for the efficient hydrogenation of N-aromatics. This is the first time these ionic hydrogenation pathways have been demonstrated on solid surfaces. For the RuNPs surfaces without basic sites in close proximity, the conventional homolytic H2 splitting is otherwise involved. Using the mechanistic concepts from Ru/P4VPy, we have designed and prepared the Ru/MgO catalyst, with the aim to improve the catalytic efficiency for the hydrogenation of heteroatom aromatics operating by the ionic hydrogenation mechanism. The Ru/MgO catalyst significantly improves the catalytic efficiency for hydrogenation of a variety of N-/S-heteroaromatics and mono-/polycyclic aromatic hydrocarbons representative of components of petroleum-derived fuels. The catalyst is superior to the few other known supported noble metal catalysts for these reactions. Mechanistic studies also point to the ionic hydrogenation mechanism on the Ru/MgO surfaces. In addition, the Ru/MgO catalyst is highly recyclable and long-lived.

Energy curable compositions having improved cure speeds

DOEpatents

Halm, L.W.

1993-05-18

The composition and method provide improved physical properties and cure speed of polyurethane precursors, with or without free radical polymerizable monomers or oligomers present, by use of a two component catalyst system. The resin blend can be activated with a latent organometallic catalyst combined with an organic peroxide which can be a hydroperoxide or an acyl peroxide to decrease the cure time while increasing the break energy and tangent modulus of the system.

Energy curable compositions having improved cure speeds

DOEpatents

Halm, Leo W.

1993-01-01

A composition and method provide improved physical properties and cure speed of polyurethane precursors, with or without free radical polymerizable monomers or oligomers present, by use of a two component catalyst system. The resin blend can be activated with a latent organometallic catalyst combined with an organic peroxide which can be a hydroperoxide or an acyl peroxide to decrease the cure time while increasing the break energy and tangent modulus of the system.

Sintering-resistant Single-Site Nickel Catalyst Supported by Metal-Organic Framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhanyong; Schweitzer, Neil; League, Aaron

2016-02-17

Developing supported single-site catalysts is an important goal in heterogeneous catalysis, since the well-defined active sites afford opportunities for detailed mechanistic studies, thereby facilitating the design of improved catalysts. We present herein a method for installing Ni ions uniformly and precisely on the node of a Zr-based MOF, NU-1000, in high density and large quantity (denoted as Ni-AIM) using atomic layer deposition (ALD) in a metal–organic framework (MOF) (AIM). Ni-AIM is demonstrated to be an efficient gas-phase hydrogenation catalyst upon activation. The structure of the active sites in Ni-AIM is proposed, revealing its single-site nature. More importantly, due to themore » organic linker used to construct the MOF support, the Ni ions stay isolated throughout the hydrogenation catalysis, in accord with its long-term stability. A quantum chemical characterization of the catalyst and the catalytic process complements the experimental results. With validation of computational modeling protocols, we further targeted ethylene oligomerization catalysis by Ni-AIM guided by theoretical prediction. Given the generality of the AIM methodology, this emerging class of materials should prove ripe for the discovery of new catalysts for the transformation of volatile substrates.« less

Longitudinal Hierarchy Co3O4 Mesocrystals with High-dense Exposure Facets and Anisotropic Interfaces for Direct-Ethanol Fuel Cells.

PubMed

Hassen, Diab; El-Safty, Sherif A; Tsuchiya, Koichi; Chatterjee, Abhijit; Elmarakbi, Ahmed; Shenashen, Mohamed A; Sakai, Masaru

2016-04-14

Novel electrodes are needed for direct ethanol fuel cells with improved quality. Hierarchical engineering can produce catalysts composed of mesocrystals with many exposed active planes and multi-diffused voids. Here we report a simple, one-pot, hydrothermal method for fabricating Co3O4/carbon/substrate electrodes that provides control over the catalyst mesocrystal morphology (i.e., corn tubercle pellets or banana clusters oriented along nanotube domains, or layered lamina or multiple cantilevered sheets). These morphologies afforded catalysts with a high density of exposed active facets, a diverse range of mesopores in the cage interior, a window architecture, and vertical alignment to the substrate, which improved efficiency in an ethanol electrooxidation reaction compared with a conventional platinum/carbon electrode. On the atomic scale, the longitudinally aligned architecture of the Co3O4 mesocrystals resulted in exposed low- and high-index single and interface surfaces that had improved electron transport and diffusion compared with currently used electrodes.

Longitudinal Hierarchy Co3O4 Mesocrystals with High-dense Exposure Facets and Anisotropic Interfaces for Direct-Ethanol Fuel Cells

NASA Astrophysics Data System (ADS)

Hassen, Diab; El-Safty, Sherif A.; Tsuchiya, Koichi; Chatterjee, Abhijit; Elmarakbi, Ahmed; Shenashen, Mohamed. A.; Sakai, Masaru

2016-04-01

Novel electrodes are needed for direct ethanol fuel cells with improved quality. Hierarchical engineering can produce catalysts composed of mesocrystals with many exposed active planes and multi-diffused voids. Here we report a simple, one-pot, hydrothermal method for fabricating Co3O4/carbon/substrate electrodes that provides control over the catalyst mesocrystal morphology (i.e., corn tubercle pellets or banana clusters oriented along nanotube domains, or layered lamina or multiple cantilevered sheets). These morphologies afforded catalysts with a high density of exposed active facets, a diverse range of mesopores in the cage interior, a window architecture, and vertical alignment to the substrate, which improved efficiency in an ethanol electrooxidation reaction compared with a conventional platinum/carbon electrode. On the atomic scale, the longitudinally aligned architecture of the Co3O4 mesocrystals resulted in exposed low- and high-index single and interface surfaces that had improved electron transport and diffusion compared with currently used electrodes.

Longitudinal Hierarchy Co3O4 Mesocrystals with High-dense Exposure Facets and Anisotropic Interfaces for Direct-Ethanol Fuel Cells

PubMed Central

Hassen, Diab; El-Safty, Sherif A.; Tsuchiya, Koichi; Chatterjee, Abhijit; Elmarakbi, Ahmed; Shenashen, Mohamed. A.; Sakai, Masaru

2016-01-01

Novel electrodes are needed for direct ethanol fuel cells with improved quality. Hierarchical engineering can produce catalysts composed of mesocrystals with many exposed active planes and multi-diffused voids. Here we report a simple, one-pot, hydrothermal method for fabricating Co3O4/carbon/substrate electrodes that provides control over the catalyst mesocrystal morphology (i.e., corn tubercle pellets or banana clusters oriented along nanotube domains, or layered lamina or multiple cantilevered sheets). These morphologies afforded catalysts with a high density of exposed active facets, a diverse range of mesopores in the cage interior, a window architecture, and vertical alignment to the substrate, which improved efficiency in an ethanol electrooxidation reaction compared with a conventional platinum/carbon electrode. On the atomic scale, the longitudinally aligned architecture of the Co3O4 mesocrystals resulted in exposed low- and high-index single and interface surfaces that had improved electron transport and diffusion compared with currently used electrodes. PMID:27075551

Catalysts synthesized by selective deposition of Fe onto Pt for the water-gas shift reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aragao, Isaias Barbosa; Ro, Insoo; Liu, Yifei

FePt bimetallic catalysts with intimate contact between the two metals were synthesized by controlled surface reactions (CSR) of (cyclohexadiene)iron tricarbonyl with hydrogen-treated supported Pt nanoparticles. Adsorption of the iron precursor on a Pt/SiO2 catalyst was studied, showing that the Fe loading could be increased by performing multiple CSR cycles, and the efficiency of this process was linked to the renewal of adsorption sites by a reducing pretreatment. The catalytic activity of these bimetallic catalysts for the water gas shift reaction was improved due to promotion by iron, likely linked to H2O activation on FeOx species at or near the Ptmore » surface, mostly in the (II) oxidation state.« less

Catalysts synthesized by selective deposition of Fe onto Pt for the water-gas shift reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aragao, Isaias Barbosa; Ro, Insoo; Liu, Yifei

FePt bimetallic catalysts with intimate contact between the two metals were synthesized by controlled surface reactions (CSR) of (cyclohexadiene)iron tricarbonyl with hydrogen-treated supported Pt nanoparticles. Adsorption of the iron precursor on a Pt/SiO 2 catalyst was studied, showing that the Fe loading could be increased by performing multiple CSR cycles, and the efficiency of this process was linked to the renewal of adsorption sites by a reducing pretreatment. Here, the catalytic activity of these bimetallic catalysts for the water gas shift reaction was improved due to promotion by iron, likely linked to H 2O activation on FeO x species atmore » or near the Pt surface, mostly in the (II) oxidation state.« less

Catalysts synthesized by selective deposition of Fe onto Pt for the water-gas shift reaction

DOE PAGES

Aragao, Isaias Barbosa; Ro, Insoo; Liu, Yifei; ...

2017-10-04

FePt bimetallic catalysts with intimate contact between the two metals were synthesized by controlled surface reactions (CSR) of (cyclohexadiene)iron tricarbonyl with hydrogen-treated supported Pt nanoparticles. Adsorption of the iron precursor on a Pt/SiO 2 catalyst was studied, showing that the Fe loading could be increased by performing multiple CSR cycles, and the efficiency of this process was linked to the renewal of adsorption sites by a reducing pretreatment. Here, the catalytic activity of these bimetallic catalysts for the water gas shift reaction was improved due to promotion by iron, likely linked to H 2O activation on FeO x species atmore » or near the Pt surface, mostly in the (II) oxidation state.« less

Ternary Pt9RhFex Nanoscale Alloys as Highly Efficient Catalysts with Enhanced Activity and Excellent CO-Poisoning Tolerance for Ethanol Oxidation.

PubMed

Wang, Peng; Yin, Shibin; Wen, Ying; Tian, Zhiqun; Wang, Ningzhang; Key, Julian; Wang, Shuangbao; Shen, Pei Kang

2017-03-22

To address the problems of high cost and poor stability of anode catalysts in direct ethanol fuel cells (DEFCs), ternary nanoparticles Pt 9 RhFe x (x = 1, 3, 5, 7, and 9) supported on carbon powders (XC-72R) have been synthesized via a facile method involving reduction by sodium borohydride followed by thermal annealing in N 2 at ambient pressure. The catalysts are physically characterized by X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy, and their catalytic performance for the ethanol oxidation reaction (EOR) is evaluated by cyclic and linear scan voltammetry, CO-stripping voltammograms, and chronopotentiometry. All the Pt 9 RhFe x /C catalysts of different atomic ratios produce high EOR catalytic activity. The catalyst of atomic ratio composition 9:1:3 (Pt/Rh/Fe) has the highest activity and excellent CO-poisoning tolerance. Moreover, the enhanced EOR catalytic activity on Pt 9 RhFe 3 /C when compared to Pt 9 Rh/C, Pt 3 Fe/C, and Pt/C clearly demonstrates the presence of Fe improves catalytic performance. Notably, the onset potential for CO oxidation on Pt 9 RhFe 3 /C (0.271 V) is ∼55, 75, and 191 mV more negative than on Pt 9 Rh/C (0.326 V), Pt 3 Fe/C (0.346 V), and Pt/C (0.462 V), respectively, which implies the presence of Fe atoms dramatically improves CO-poisoning tolerance. Meanwhile, compared to the commercial PtRu/C catalyst, the peak potential on Pt 9 RhFe 3 /C for CO oxidation was just slightly changed after several thousand cycles, which shows high stability against the potential cycling. The possible mechanism by which Fe and Rh atoms facilitate the observed enhanced performance is also considered herein, and we conclude Pt 9 RhFe 3 /C offers a promising anode catalyst for direct ethanol fuel cells.

Dynamic restructuring drives catalytic activity on nanoporous gold–silver alloy catalysts

DOE PAGES

Zugic, Branko; Wang, Lucun; Heine, Christian; ...

2016-12-19

Bimetallic, nanostructured materials hold promise for improving catalyst activity and selectivity, yet little is known about the dynamic compositional and structural changes that these systems undergo during pretreatment that leads to efficient catalyst function. Here we use ozone-activated silver–gold alloys in the form of nanoporous gold as a case study to demonstrate the dynamic behaviour of bimetallic systems during activation to produce a functioning catalyst. We show that it is these dynamic changes that give rise to the observed catalytic activity. Advanced in situ electron microscopy and X-ray photoelectron spectroscopy are used to demonstrate that major restructuring and compositional changesmore » occur along the path to catalytic function for selective alcohol oxidation. Transient kinetic measurements correlate the restructuring to three types of oxygen on the surface. The direct influence of changes in surface silver concentration and restructuring at the nanoscale on oxidation activity is demonstrated. Finally, our results demonstrate that characterization of these dynamic changes is necessary to unlock the full potential of bimetallic catalytic materials.« less

Dynamic restructuring drives catalytic activity on nanoporous gold–silver alloy catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zugic, Branko; Wang, Lucun; Heine, Christian

Bimetallic, nanostructured materials hold promise for improving catalyst activity and selectivity, yet little is known about the dynamic compositional and structural changes that these systems undergo during pretreatment that leads to efficient catalyst function. Here we use ozone-activated silver–gold alloys in the form of nanoporous gold as a case study to demonstrate the dynamic behaviour of bimetallic systems during activation to produce a functioning catalyst. We show that it is these dynamic changes that give rise to the observed catalytic activity. Advanced in situ electron microscopy and X-ray photoelectron spectroscopy are used to demonstrate that major restructuring and compositional changesmore » occur along the path to catalytic function for selective alcohol oxidation. Transient kinetic measurements correlate the restructuring to three types of oxygen on the surface. The direct influence of changes in surface silver concentration and restructuring at the nanoscale on oxidation activity is demonstrated. Finally, our results demonstrate that characterization of these dynamic changes is necessary to unlock the full potential of bimetallic catalytic materials.« less

Self-Supported Mesostructured Pt-Based Bimetallic Nanospheres Containing an Intermetallic Phase as Ultrastable Oxygen Reduction Electrocatalysts.

PubMed

Kim, Ho Young; Cho, Seonghun; Sa, Young Jin; Hwang, Sun-Mi; Park, Gu-Gon; Shin, Tae Joo; Jeong, Hu Young; Yim, Sung-Dae; Joo, Sang Hoon

2016-10-01

Developing highly active and stable cathode catalysts is of pivotal importance for proton exchange membrane fuel cells (PEMFCs). While carbon-supported nanostructured Pt-based catalysts have so far been the most active cathode catalysts, their durability and single-cell performance are yet to be improved. Herein, self-supported mesostructured Pt-based bimetallic (Meso-PtM; M = Ni, Fe, Co, Cu) nanospheres containing an intermetallic phase are reported, which can combine the beneficial effects of transition metals (M), an intermetallic phase, a 3D interconnected framework, and a mesoporous structure. Meso-PtM nanospheres show enhanced oxygen reduction reaction (ORR) activity, compared to Pt black and Pt/C catalysts. Notably, Meso-PtNi containing an intermetallic phase exhibits ultrahigh stability, showing enhanced ORR activity even after 50 000 potential cycles, whereas Pt black and Pt/C undergo dramatic degradation. Importantly, Meso-PtNi with an intermetallic phase also demonstrated superior activity and durability when used in a PEMFC single-cell, with record-high initial mass and specific activities. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly active non-PGM catalysts prepared from metal organic frameworks

DOE PAGES

Barkholtz, Heather M.; Chong, Lina; Kaiser, Zachary B.; ...

2015-06-11

Finding inexpensive alternatives to platinum group metals (PGMs) is essential for reducing the cost of proton exchange membrane fuel cells (PEMFCs). Numerous materials have been investigated as potential replacements of Pt, of which the transition metal and nitrogen-doped carbon composites (TM/N x/C) prepared from iron doped zeolitic imidazolate frameworks (ZIFs) are among the most active ones in catalyzing the oxygen reduction reaction based on recent studies. In this report, we demonstrate that the catalytic activity of ZIF-based TM/N x/C composites can be substantially improved through optimization of synthesis and post-treatment processing conditions. Ultimately, oxygen reduction reaction (ORR) electrocatalytic activity mustmore » be demonstrated in membrane-electrode assemblies (MEAs) of fuel cells. The process of preparing MEAs using ZIF-based non-PGM electrocatalysts involves many additional factors which may influence the overall catalytic activity at the fuel cell level. Evaluation of parameters such as catalyst loading and perfluorosulfonic acid ionomer to catalyst ratio were optimized. Our overall efforts to optimize both the catalyst and MEA construction process have yielded impressive ORR activity when tested in a fuel cell system.« less

Investigation of process variables and intensification effects of ultrasound applied in oxidative desulfurization of model diesel over MoO3/Al2O3 catalyst.

PubMed

Akbari, Azam; Omidkhah, Mohammadreza; Darian, Jafar Towfighi

2014-03-01

A new heterogeneous sonocatalytic system consisting of a MoO3/Al2O3 catalyst and H2O2 combined with ultrasonication was studied to improve and accelerate the oxidation of model sulfur compounds of diesel, resulting in a significant enhancement in the process efficiency. The influence of ultrasound on properties, activity and stability of the catalyst was studied in detail by means of GC-FID, PSD, SEM and BET techniques. Above 98% conversion of DBT in model diesel containing 1000 μg/g sulfur was obtained by new ultrasound-assisted desulfurization at H2O2/sulfur molar ratio of 3, temperature of 318 K and catalyst dosage of 30 g/L after 30 min reaction, contrary to the 55% conversion obtained during the silent process. This improvement was considerably affected by operation parameters and catalyst properties. The effects of main process variables were investigated using response surface methodology in silent process compared to ultrasonication. Ultrasound provided a good dispersion of catalyst and oxidant by breakage of hydrogen bonding and deagglomeration of them in the oil phase. Deposition of impurities on the catalyst surface caused a quick deactivation in silent experiments resulting only 5% of DBT oxidation after 6 cycles of silent reaction by recycled catalyst. Above 95% of DBT was oxidized after 6 ultrasound-assisted cycles showing a great improvement in stability by cleaning the surface during ultrasonication. A considerable particle size reduction was also observed after 3 h sonication that could provide more dispersion of catalyst in model fuel.

Palladium-catalyzed Reppe carbonylation.

PubMed

Kiss, G

2001-11-01

PdX2L2/L/HA (A = weakly coordinating anion, L = phosphine) complexes are active catalysts in the hydroesterification of alkenes, alkynes, and conjugated dienes. Shell, the only major corporate player in the field, recently developed two very active catalyst systems tailored to the hydroesterification of either alkenes or alkynes. The hydroesterification of propyne with their Pd(OAc)2/PN/HA (PN = (2-pyridyl)diphenylphosphine, HA = strong acid with weakly coordinating anion, like methanesulfonic acid) catalyst has been declared commercially ready. However, despite the significant progress in the activity of Pd-hydroesterification catalysts, further improvements are warranted. Thus, for example, activity maintenance still seems to be an issue. Homogeneous Pd catalysts are prone to a number of deactivation reactions. Activity and stability promoters are often corrosive and add to the complexity of the system, making it less attractive. Nonetheless, the versatility of the process and its tolerance toward the functional groups of substrates should appeal especially to the makers of specialty products. Although hydroesterification yields esters from alkenes, alkynes, and dienes in fewer steps than hydroformylation does, the latter has some advantages at the current state of the art. (1) Hydroformylation catalysts, particularly some recently published phosphine-modified Rh systems, can achieve very high regioselectivity for the linear product that hydroesterification catalysts cannot match yet. By analogy with hydroformylation, bulkier ligands ought to be tested in hydroesterification to increase normal-ester selectivity. (2) Hydroformylation is proven, commercial. Hydroesterification can only replace it if it can provide significant economic incentives. Similar or just marginally better performance could not justify the cost of development of a new technology. (3) Hydroesterification requires pure CO while hydroformylation uses syngas, a mixture of CO and H2. The latter is typically more available and less expensive (for industrial applications CO is most often separated from syngas). (4) The acid component of the hydroesterification catalyst makes the process corrosive. It would be desirable to develop new hydroesterification catalysts that do not require acid stabilizer/activity booster. Clearly, any new hydroesterification technology will directly compete with the hydroformylation route. This is especially true for olefin feeds, since both processes add one CO to the olefin, yielding oxygenates that can be converted into identical products. For some niche applications, like the production of MMA from propyne, hydroesterification seems to have an advantage as compared to hydroformylation due to the high activity and selectivity of the Pd(OAc)2/(2-pyridyl)diphenylphosphine catalyst. Since hydroesterification is an emerging technology, it is reasonable to assume that the potential for improvement is greater than in the mature hydroformylation. It is therefore possible that hydroesterification will become competitive in the future; thus, continued effort in the field is warranted.

Effects of H sub 2 S addition on the performance of fresh vs. used CoMo catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rankel, L.A.

1991-01-01

When a Co/Mo catalyst is used for processing vanadium-containing heavy oils, vanadium deposits on the catalyst. As the amount of vanadium on the CoMo catalyst increases, the catalytic effects of CoMo decline and the presence of vanadium starts to influence the hydroprocessing products. Model feeds have been used to explore the changes in the catalytic activity of CoMo, aged CoMo, and VS{sub x} on alumina. Desulfurization, denitrogenation, deoxygenation, aromatics hydrogenation, and metals removal were monitored. This paper reports that, upon the addition of hydrogen sulfide to hydrogen, improvements in the catalysts for aromatics hydrogenation, denitrogenation and metals removal were observed.

A facile preparation of TiO2/ACF with Csbnd Ti bond and abundant hydroxyls and its enhanced photocatalytic activity for formaldehyde removal

NASA Astrophysics Data System (ADS)

Liu, R. F.; Li, W. B.; Peng, A. Y.

2018-01-01

The quantum yields and efficiency(ACF) was prepared via a modified deposition-precipitation method to facilitate its photon absorption and of photogenerated charge carriers have been the major issues for photocatalysis on titania catalyst. The TiO2/ACF catalyst with anatase TiO2 uniformly dispersed on activated carbon fibers electron transfer, thus improve the quantum yields and efficiency of the photogenerated electrons and holes. XPS analysis on the catalyst demonstrates the existence of Ti3+ and Ti2+ species, Csbnd Ti bond and abundant hydroxyls, which are also proved by UV-vis DRS and TG-DSC analysis. It is believed that the acid environment in preparation plays an essential role in the formation of Csbnd Ti bond and surface hydroxyls, which can be tuned by changing hydrothermal synthesis time. The Csbnd Ti bond can improve the electron transfer in the catalyst and the substantial surface hydroxyls lead to high absorption for UV lines and enhanced adsorption of water and formaldehyde, resulting in more active OH free radicals and the outstanding photocatalytic activity of TiO2/ACF, which is much higher than the titania powder for photocatalytic removal of low concentration formaldehyde. The essential role of surface hydroxyls for photocatalytic activity was confirmed surpassing that of chemical bond between carbon and titanium in TiO2-carbon composite for the first time.

Redox-Active Nitroxide Radical Polymers: From Green Catalysts to Energy Storage Devices

NASA Astrophysics Data System (ADS)

Waskitoaji, Wihatmoko; Suga, Takeo; Nishide, Hiroyuki

2009-09-01

Robust but redox-active radical polymers bearing 2, 2, 6, 6-tetramethylpiperidin-N-oxy (TEMPO) were investigated as a metal-free, green mediator/catalyst for the oxidation of alcohol derivatives, and as a new electrode-active and charge-storage material. The TEMPO-mediated oxidation of the primary alcohol group of the natural cellulose improved the water-dispersivity of cellulose, and the polymer-supported catalysts or redox resins allow facile removal of catalysts from products by simple filtration. Other radical molecule (e.g. galvinoxyl) was also used as a mediator, which is coupled with the molecular oxygen. A reversible one-electron redox reaction of TEMPO allowed its application as an electrode-active material featuring high cyclability (>500 cycles), relatively high battery electrode capacity (100-135 mAh/g), and fast electrode kinetics, leading to the high power rate capability of the battery. The radical polymer-based electrodes also provided good processability and shape flexibility, which promised the paper-like and wearable energy-storage devices.

Heterogeneous catalytic ozonation of biologically pretreated Lurgi coal gasification wastewater using sewage sludge based activated carbon supported manganese and ferric oxides as catalysts.

PubMed

Zhuang, Haifeng; Han, Hongjun; Hou, Baolin; Jia, Shengyong; Zhao, Qian

2014-08-01

Sewage sludge of biological wastewater treatment plant was converted into sewage sludge based activated carbon (SBAC) with ZnCl₂ as activation agent, which supported manganese and ferric oxides as catalysts (including SBAC) to improve the performance of ozonation of real biologically pretreated Lurgi coal gasification wastewater. The results indicated catalytic ozonation with the prepared catalysts significantly enhanced performance of pollutants removal and the treated wastewater was more biodegradable and less toxic than that in ozonation alone. On the basis of positive effect of higher pH and significant inhibition of radical scavengers in catalytic ozonation, it was deduced that the enhancement of catalytic activity was responsible for generating hydroxyl radicals and the possible reaction pathway was proposed. Moreover, the prepared catalysts showed superior stability and most of toxic and refractory compounds were eliminated at successive catalytic ozonation runs. Thus, the process with economical, efficient and sustainable advantages was beneficial to engineering application. Copyright © 2014 Elsevier Ltd. All rights reserved.

Nitrogen-doped graphene anchored with mixed growth patterns of CuPt alloy nanoparticles as a highly efficient and durable electrocatalyst for the oxygen reduction reaction in an alkaline medium.

PubMed

Illathvalappil, Rajith; Dhavale, Vishal M; Bhange, Siddheshwar N; Kurungot, Sreekumar

2017-07-06

A highly active and durable CuPt alloy catalyst with trigonal bipyramidal and truncated cube-type mixed morphologies, anchored on the nitrogen-doped graphene (NGr) surface (CuPt-TBTC/NGr), was prepared by a simple and fast method. The obtained CuPt alloy showed improved oxygen reduction reaction (ORR) activity, with a 30 mV positive shift in the half-wave potential value, as compared to the state-of-the-art Pt/C catalyst in a 0.1 M KOH solution. The CuPt alloy with the trigonal bipyramidal morphology possesses porous type inter-connected sides, which help to achieve improved mass transport of oxygen during the ORR. The exposure of the (111) plane of the CuPt alloy further improved the catalytic activity towards the dioxygen reduction in alkaline media. The ORR activity of the NGr-supported CuPt alloy was found to be dependent on the reaction time, and improved activity was obtained on the material derived at a reaction time of 90 min (CuPt-TBTC/NGr-90). The material synthesized at a lower or higher reaction time than 90 min resulted in a partially formed trigonal bipyramidal morphology with more truncated cubes or agglomerated trigonal bipyramidal and truncated cubes with closed type structures, respectively. Along with the high intrinsic ORR activity, CuPt-TBTC/NGr-90 displayed excellent electrochemical stability. Even after repeated 1000 potential cycling in a window ranging from 0.10 to 1.0 V (vs. RHE), the system clearly outperformed the state-of-the-art Pt/C catalyst with 15 and 60 mV positive shifts in the onset and half-wave potentials, respectively. CuPt-TBTC/NGr-90 also exhibited 2.1 times higher mass activity and 2.2 times higher specific activity, compared to Pt/C at 0.90 V (vs. RHE). Finally, a zinc-air battery fabricated with the alloy catalyst as the air electrode displayed a peak power density of 300 mW cm -2 , which is much higher than the peak power density of 253 mW cm -2 obtained for the state-of-the-art Pt/C catalyst as the air electrode.

Characterization of three-way automotive catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kenik, E.A.; More, K.L.; LaBarge, W.

1997-04-01

The CRADA between Delphi Automotive Systems (Delphi; formerly General Motors - AC Delco, Systems) and Lockheed Martin Energy Research (LMER) on automotive catalysts was completed at the end of FY96, after a ten month, no-cost extension. The CRADA was aimed at improved performance and lifetime of noble metal based three-way-catalysts (TWC), which are the primary catalytic system for automotive emission control systems. While these TWC can meet the currently required emission standards, higher than optimum noble metal loadings are often required to meet lifetime requirements. In addition, more stringent emission standards will be imposed in the near future, demanding improvedmore » performance and service life from these catalysts. Understanding the changes of TWC conversion efficiency with ageing is a critical need in improving these catalysts. Initially in a fresh catalyst, the active material is often distributed on a very fine scale, approaching single atoms or small atomic clusters. As such, a wide range of analytical techniques have been employed to provide high spatial resolution characterization of the evolving state of the catalytic material.« less

Catalyst and process development for synthesis gas conversion to isobutylene. Final report, September 1, 1990--January 31, 1994

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anthony, R.G.; Akgerman, A.

1994-05-06

Previous work on isosynthesis (conversion of synthesis gas to isobutane and isobutylene) was performed at very low conversions or extreme process conditions. The objectives of this research were (1) determine the optimum process conditions for isosynthesis; (2) determine the optimum catalyst preparation method and catalyst composition/properties for isosynthesis; (3) determine the kinetics for the best catalyst; (4) develop reactor models for trickle bed, slurry, and fixed bed reactors; and (5) simulate the performance of fixed bed trickle flow reactors, slurry flow reactors, and fixed bed gas phase reactors for isosynthesis. More improvement in catalyst activity and selectivity is needed beforemore » isosynthesis can become a commercially feasible (stand-alone) process. Catalysts prepared by the precipitation method show the most promise for future development as compared with those prepared hydrothermally, by calcining zirconyl nitrate, or by a modified sol-gel method. For current catalysts the high temperatures (>673 K) required for activity also cause the production of methane (because of thermodynamics). A catalyst with higher activity at lower temperatures would magnify the unique selectivity of zirconia for isobutylene. Perhaps with a more active catalyst and acidification, oxygenate production could be limited at lower temperatures. Pressures above 50 atm cause an undesirable shift in product distribution toward heavier hydrocarbons. A model was developed that can predict carbon monoxide conversion an product distribution. The rate equation for carbon monoxide conversion contains only a rate constant and an adsorption equilibrium constant. The product distribution was predicted using a simple ratio of the rate of CO conversion. This report is divided into Introduction, Experimental, and Results and Discussion sections.« less

Effect of Ni Core Structure on the Electrocatalytic Activity of Pt-Ni/C in Methanol Oxidation

PubMed Central

Kang, Jian; Wang, Rongfang; Wang, Hui; Liao, Shijun; Key, Julian; Linkov, Vladimir; Ji, Shan

2013-01-01

Methanol oxidation catalysts comprising an outer Pt-shell with an inner Ni-core supported on carbon, (Pt-Ni/C), were prepared with either crystalline or amorphous Ni core structures. Structural comparisons of the two forms of catalyst were made using transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), and methanol oxidation activity compared using CV and chronoamperometry (CA). While both the amorphous Ni core and crystalline Ni core structures were covered by similar Pt shell thickness and structure, the Pt-Ni(amorphous)/C catalyst had higher methanol oxidation activity. The amorphous Ni core thus offers improved Pt usage efficiency in direct methanol fuel cells. PMID:28811402

Hydrous oxide ion-exchange compound catalysts

DOEpatents

Dosch, Robert G.; Stephens, Howard P.

1990-01-01

A catalytic material of improved activity which comprises a hydrous, alkali metal or alkaline earth metal or quaternary ammonium titanate, zirconate, niobate, or tantalate, in which the metal or ammonium cations have been exchange with a catalytically effective quantity of a catalyst metal, and which has been subsequently treated with a solution of a Bronsted acid.

The stability of the active medium of RF-exited CO2 lasers with gold as catalyst

NASA Astrophysics Data System (ADS)

Cherezov, V. M.; Novgorodov, M. Z.; Ochkin, V. N.; Samorodov, V. G.; Shishkanov, E. F.; Stepanov, V. A.; Witteman, W. J.

Using mass-spectrometric investigations the gas composition of the active medium of sealed-off cw RF-excited CO2 waveguide lasers have been studied. It has been found that a low degree of CO2 dissociation and a laser power improvement can be achieved by means of a gold catalyst in the laser discharge volume. The conditions for long operational lifetimes of these lasers are described.

A novel metal organic framework-derived carbon-based catalyst for oxygen reduction reaction in a microbial fuel cell

NASA Astrophysics Data System (ADS)

Zhang, Lihua; Hu, Yongyou; Chen, Junfeng; Huang, Wantang; Cheng, Jianhua; Chen, Yuancai

2018-04-01

To improve the power generation of microbial fuel cell (MFC), the cathode is modified to increase its oxygen reduction reaction (ORR) activity by using a Cu, N-incorporated carbon-based material as catalyst, which obtained from pyrolyzing ORR active Cu (II)-based metal organic framework (MOF; Cu-bipy-BTC, bipy = 2,2‧-bipyridine, BTC = 1,3,5-tricarboxylate). MOF-800 (the product of pyrolyzing Cu-bipy-BTC at 800 °C) shows porous structure with micropores ranging from 0.5 to 1.3 nm and mesopores ranging from 27 to 46 nm. It also exhibits improved ORR electrocatalytic activity with a higher current density of -3.06 mA cm-2 compared to Cu-bipy-BTC. Moreover, the charge transfer resistance of MOF-800 cathode (1.38 Ω) is much smaller than that of Cu-bipy-BTC cathode (176.8 Ω). A maximum power density of 326 ± 11 mW m-2 is achieved by MOF-800-MFC, which is 2.6 times of that of Cu-bipy-BTC-MFC and comparable with Pt/C-MFC (402 ± 17 mW m-2). The results imply the enhancements of ORR catalytic activity and electrical conductivity of MOF-800 are due to the enhanced porous structure and abundant active sites (C-N, Cu-Nχ), which result in the improved power generation of MFC. This study provides technical and theoretical validation for the MFC performance improvement by ORR active MOF-derived catalysts modified cathodes.

CaO Nanocatalyst for Transesterification Reaction of Palm Oil to Biodiesel: Effect of Precursor’s Concentration on the Catalyst Behavior

NASA Astrophysics Data System (ADS)

Hassan, N.; Ismail, K. N.; Hamid, K. H. Ku; Hadi, Abdul

2018-05-01

Depletion of fossil fuel sources in a few decades due to industrialization and motorization has led to a keen interest in the production of alternative fuels like biodiesel. Research on the development and improvement of more efficient transesterification process for biodiesel production has attain great attention in the last decade. The using of low cost catalyst is one of the main focuses on the biodiesel production. As a basic heterogeneous catalyst, CaO has been examined in the transesterification of vegetable oils for biodiesel production. In this research, calcium oxide (CaO-X) catalysts were prepared by sol-gel method at different Ca2+ precursor concentration (X = 1.0, 1.5, 2.0 M). The crystalline structure and morphology of the synthesized catalysts were characterized by means of x-ray diffraction (XRD) and N2 adsorption-desorption analysis. All the synthesized catalysts were then applied to transesterification reaction of palm oil to produce biodiesel. The characterization by x-ray diffraction demonstrate CaO-1.0 was partially hydrated due to the incomplete reaction during synthesis. As a matter of fact, formation of H2O on the surface of CaO causes lower basic strength of the catalysts, thus responsible in lowering the catalytic activity. It is demonstrated that CaO-2.0 exhibits mesoporous structure with least chemisorb amount of H2O on the catalysts surface has a very active catalytic activity. It was found that 2.0M of calcium precursor has high catalytic activity and 81% FAME yield was obtained within 3h reaction.

Facile synthesis of a platinum-lead oxide nanocomposite catalyst with high activity and durability for ethanol electrooxidation.

PubMed

Yang, Wei-Hua; Wang, Hong-Hui; Chen, De-Hao; Zhou, Zhi-You; Sun, Shi-Gang

2012-12-21

Aimed at searching for highly active and stable nano-scale Pt-based catalysts that can improve significantly the energy conversion efficiency of direct ethanol fuel cells (DEFCs), a novel Pt-PbO(x) nanocomposite (Pt-PbO(x) NC) catalyst with a mean size of 3.23 nm was synthesized through a simple wet chemistry method without using a surfactant, organometallic precursors and high temperature. Electrocatalytic tests demonstrated that the as-prepared Pt-PbO(x) NC catalyst possesses a much higher catalytic activity and a longer durability than Pt nanoparticles (nm-Pt) and commercial Pt black catalysts for ethanol electrooxidation. For instance, Pt-PbO(x) NC showed an onset potential that was 30 mV and 44 mV less positive, together with a peak current density 1.7 and 2.6 times higher than those observed for nm-Pt and Pt black catalysts in the cyclic voltammogram tests. The ratio of current densities per unit Pt mass on Pt-PbO(x) NC, nm-Pt and Pt black catalysts is 27.3 : 3.4 : 1 for the long-term (2 hours) chronoamperometric experiments measured at -0.4 V (vs. SCE). In situ FTIR spectroscopic studies revealed that the activity of breaking C-C bonds of ethanol of the Pt-PbO(x) NC is as high as 5.17 times that of the nm-Pt, which illustrates a high efficiency of ethanol oxidation to CO(2) on the as-prepared Pt-PbO(x) NC catalyst.

Methane Conversion to Ethylene and Aromatics on PtSn Catalysts

DOE PAGES

Gerceker, Duygu; Motagamwala, Ali Hussain; Rivera-Dones, Keishla R.; ...

2017-02-03

Pt and PtSn catalysts supported on SiO 2 and H-ZSM-5 were studied for methane conversion under nonoxidative conditions. Addition of Sn to Pt/SiO 2 increased the turnover frequency for production of ethylene by a factor of 3, and pretreatment of the catalyst at 1123 K reduced the extent of coke formation. Pt and PtSn catalysts supported on H-ZSM-5 zeolite were prepared to improve the activity and selectivity to non-coke products. Ethylene formation rates were 20 times faster over a PtSn(1:3)/H-ZSM-5 catalyst with SiO 2:Al 2O 3 = 280 in comparison to those over PtSn(3:1)/SiO 2. H-ZSM-5-supported catalysts were also activemore » for the formation of aromatics, and the rates of benzene and naphthalene formation were increased by using more acidic H-ZSM-5 supports. These catalysts operate through a bifunctional mechanism, in which ethylene is first produced on highly dispersed PtSn nanoparticles and then is subsequently converted to benzene and naphthalene on Brønsted acid sites within the zeolite support. The most active and stable PtSn catalyst forms carbon products at a rate, 2.5 mmol of C/((mol of Pt) s), which is comparable to that of state-of-the-art Mo/H-ZSM-5 catalysts with same metal loading operated under similar conditions (1.8 mmol of C/((mol of Mo) s)). Scanning transmission electron microscopy measurements suggest the presence of smaller Pt nanoparticles on H-ZSM-5-supported catalysts, in comparison to SiO 2-supported catalysts, as a possible source of their high activity. As a result, a microkinetic model of methane conversion on Pt and PtSn surfaces, built using results from density functional theory calculations, predicts higher coupling rates on bimetallic and stepped surfaces, supporting the experimental observations that relate the high catalytic activity to small PtSn particles.« less

Green diesel production via catalytic hydrogenation/decarboxylation of triglycerides and fatty acids of vegetable oil and brown grease

NASA Astrophysics Data System (ADS)

Sari, Elvan

Increase in the petroleum prices, projected increases in the world's energy demand and environmental awareness have shifted the research interest to the alternative fuel technologies. In particular, green diesel, vegetable oil/animal fat/waste oil and grease derived hydrocarbons in diesel boiling range, has become an attractive alternative to biodiesel---a mixture of fatty acid methyl esters, particularly due to its superior fuel properties that are similar to petroleum diesel. Hence, green diesel can be used as a drop-in fuel in the current diesel engines. The current technology for production of green diesel-hydrodeoxygenation of triglycerides and fatty acids over conventional hydrotreating catalysts suffers from fast catalyst deactivation in the absence of hydrogen combined with high temperatures and high fatty acid content in the feedstock. Additionally, excess hydrogen requirement for hydrodeoxygenation technique leads to high production costs. This thesis proposes a new technology-selective decarboxylation of brown grease, which is a mixture of fats and oils collected from waste water trap and rich in fatty acids, over a supported noble metal catalyst that overcomes the green diesel production challenges. In contrast to other feedstocks used for liquid biofuel production, brown grease is inexpensive and non-food competing feedstock, therefore the process finds solution to waste management issues, reduces the renewable fuel production cost and does not add to the global food shortage problems. Special catalyst formulations were developed to have a high activity and stability in the absence of hydrogen in the fatty acid decarboxylation process. The study shows how catalyst innovations can lead to a new technology that overcomes the process challenges. First, the effect of reaction parameters on the activity and the selectivity of brown grease decarboxylation with minimum hydrogen consumption over an activated carbon supported palladium catalyst were investigated. A 90% conversion of brown grease in a semi-batch mode was obtained in 7 hours. In contrast, in a batch reaction the conversion was roughly 40% in the same reaction time. However, by pre-treating the "as received" brown grease with H 2, the conversion in a batch reactor was increased 1.4--fold; and when the H2 to BG ratio was increased to 3/1 (mol/mol), the conversion was further improved. Therefore, such a two-step processing with selective hydrogenation prior to the decarboxylation of BG improves the product selectivity. The commercial 5% Pd/C catalyst was highly active for the decarboxylation of brown grease to green diesel at 300 °C and 1.5 MPa. Second, a class of Pd catalyst supported on a silica-activated carbon nanocomposite for free fatty acid decarboxylation was developed, and displayed excellent activity and operation stability selectively for the green diesel hydrocarbons formation in the absence of hydrogen under mild reaction conditions. The decarboxylation activities of different amount of silica containing catalysts were investigated in a batch reactor under inert gas. Among them, the formulation with the fewer oxygen surface groups (Pd/Si--C--4) was the most active catalyst for the decarboxylation of an unsaturated fatty acid. The high activity of the Pd/Si--C--4 catalyst is attributed to its accessible and well-distributed metallic Pd nanoparticles inside hybrid mesopores as well as to its low acidity, weak surface interactions and inertness. Thus, Pd supported on carbon modified with silica may be regarded as a prospective decarboxylation catalyst for the removal of oxygen from vegetable oil/animal fat without the need of additional hydrogen. Third, in order to design a suitable catalyst for conversion of brown grease to green diesel, a systematic study of the model compounds--oleic acid was conducted on various catalysts in super-critical water to understand the reaction pathways in the absence of hydrogen. A Si--C support was more effective than activated carbon itself for both decarboxylation of oleic acid and hydrogenation of alkenes. In an additional effort to reduce Pd amount in the catalyst, Pd2Co/C catalysts with various Pd content were prepared and the catalytic activity study showed that 0.5 wt% Pd2Co/C catalyst performs even better than a 5 wt% Pd/C catalyst. Pd and Co alloys were very well dispersed and formed fine clusters, which led to a higher active metal surface area and hence favored the decarboxylation of oleic acid. This study showed that an alloy of Pd on carbon with a significantly low Pd content is much more active and selective to diesel hydrocarbons production from an unsaturated fatty acid in super-critical water and may be regarded as a prospective feasible decarboxylation catalyst for the removal of oxygen from vegetable oil/animal fat without the need of additional hydrogen.

Attrition of precipitated iron Fischer-Tropsch catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Datye, A.K.; Reardon, J.; Hanprasopwattana, A.

1996-12-31

Precipitated Iron catalysts used in slurry phase bubble column reactors are known to undergo attrition during use. The attrition reduces the lifetime of the catalyst as well as causing problems in separating the product liquids from the catalyst. In this study, the authors have investigated the underlying mechanisms that lead to attrition in precipitated iron catalysts. They have discovered that attrition takes place on two length scales. On the macro scale, attrition is caused by the break-up of the weak agglomerates that constitute this catalyst into individual crystallites. Addition of binders such as kaolin does not help significantly in strengtheningmore » the catalyst particles. In addition, there is a second process leading to nanoscale attrition that is caused by the break-up of individual iron oxide crystallites into nano particles of iron carbide as the catalyst is activated for reaction. Design of attrition resistant F-T catalysts must consider these two modes of catalyst attrition. Preliminary work in the laboratory directed at improving the attrition resistance of precipitated iron catalysts will also be described in this paper.« less

Engineering Ru@Pt Core-Shell Catalysts for Enhanced Electrochemical Oxygen Reduction Mass Activity and Stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, Ariel; Strickler, Alaina; Higgins, Drew

Improving the performance of oxygen reduction reaction (ORR) electrocatalysts is essential for the commercial efficacy of many renewable energy technologies, including low temperature polymer electrolyte fuel cells (PEFCs). Herein, we report highly active and stable carbon-supported Ru@Pt core-shell nanoparticles (Ru@Pt/C) prepared by a wet chemical synthesis technique. Through rotating disc electrode testing, the Ru@Pt/C achieves an ORR Pt mass-based activity of 0.50 A mg Pt -1 at 0.9 V versus the reversible hydrogen electrode (RHE), which exceeds the activity of the state-of-the-art commercial Pt/C catalyst as well as the Department of Energy 2020 PEFC electrocatalyst activity targets for transportation applications.more » The impact of various synthetic parameters, including Pt to Ru ratios and catalyst pretreatments (i.e., annealing) are thoroughly explored. Pt-based mass activity of all prepared Ru@Pt/C catalysts was found to exceed 0.4 mg Pt -1 across the range of compositions investigated, with the maximum activity catalyst having a Ru:Pt ratio of 1:1. This optimized composition of Ru@Pt/C catalyst demonstrated remarkable stability after 30,000 accelerated durability cycles (0.6 to 1.0 V vs. RHE at 125 mV s -1), maintaining 85% of its initial mass activity. Scanning transmission electron microscopy energy dispersive spectroscopy (STEM-EDS) analysis at various stages of electrochemical testing demonstrated that the Pt shell can provide sufficient protection against the dissolution of the otherwise unstable Ru core.« less

Engineering Ru@Pt Core-Shell Catalysts for Enhanced Electrochemical Oxygen Reduction Mass Activity and Stability

DOE PAGES

Jackson, Ariel; Strickler, Alaina; Higgins, Drew; ...

2018-01-12

Improving the performance of oxygen reduction reaction (ORR) electrocatalysts is essential for the commercial efficacy of many renewable energy technologies, including low temperature polymer electrolyte fuel cells (PEFCs). Herein, we report highly active and stable carbon-supported Ru@Pt core-shell nanoparticles (Ru@Pt/C) prepared by a wet chemical synthesis technique. Through rotating disc electrode testing, the Ru@Pt/C achieves an ORR Pt mass-based activity of 0.50 A mg Pt -1 at 0.9 V versus the reversible hydrogen electrode (RHE), which exceeds the activity of the state-of-the-art commercial Pt/C catalyst as well as the Department of Energy 2020 PEFC electrocatalyst activity targets for transportation applications.more » The impact of various synthetic parameters, including Pt to Ru ratios and catalyst pretreatments (i.e., annealing) are thoroughly explored. Pt-based mass activity of all prepared Ru@Pt/C catalysts was found to exceed 0.4 mg Pt -1 across the range of compositions investigated, with the maximum activity catalyst having a Ru:Pt ratio of 1:1. This optimized composition of Ru@Pt/C catalyst demonstrated remarkable stability after 30,000 accelerated durability cycles (0.6 to 1.0 V vs. RHE at 125 mV s -1), maintaining 85% of its initial mass activity. Scanning transmission electron microscopy energy dispersive spectroscopy (STEM-EDS) analysis at various stages of electrochemical testing demonstrated that the Pt shell can provide sufficient protection against the dissolution of the otherwise unstable Ru core.« less

Metal-organic frameworks derived platinum-cobalt bimetallic nanoparticles in nitrogen-doped hollow porous carbon capsules as a highly active and durable catalyst for oxygen reduction reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ying, Jie; Li, Jing; Jiang, Gaopeng

Pt-based nanomaterials are regarded as the most efficient electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, widespread adoption of PEMFCs requires solutions to major challenges encountered with ORR catalysts, namely high cost, sluggish kinetics, and low durability. In this paper, a new efficient method utilizing Co-based metal-organic frameworks is developed to produce PtCo bimetallic nanoparticles embedded in unique nitrogen-doped hollow porous carbon capsules. The obtained catalyst demonstrates an outstanding ORR performance, with a mass activity that is 5.5 and 13.5 times greater than that of commercial Pt/C and Pt black, respectively. Most importantly,more » the product exhibits dramatically improved durability in terms of both electrochemically active surface area (ECAS) and mass activity compared to commercial Pt/C and Pt black catalysts. Finally, the remarkable ORR performance demonstrated here can be attributed to the structural features of the catalyst (its alloy structure, high dispersion and fine particle size) and the carbon support (its nitrogen dopant, large surface area and hollow porous structure).« less

Metal-organic frameworks derived platinum-cobalt bimetallic nanoparticles in nitrogen-doped hollow porous carbon capsules as a highly active and durable catalyst for oxygen reduction reaction

DOE PAGES

Ying, Jie; Li, Jing; Jiang, Gaopeng; ...

2017-11-29

Pt-based nanomaterials are regarded as the most efficient electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, widespread adoption of PEMFCs requires solutions to major challenges encountered with ORR catalysts, namely high cost, sluggish kinetics, and low durability. In this paper, a new efficient method utilizing Co-based metal-organic frameworks is developed to produce PtCo bimetallic nanoparticles embedded in unique nitrogen-doped hollow porous carbon capsules. The obtained catalyst demonstrates an outstanding ORR performance, with a mass activity that is 5.5 and 13.5 times greater than that of commercial Pt/C and Pt black, respectively. Most importantly,more » the product exhibits dramatically improved durability in terms of both electrochemically active surface area (ECAS) and mass activity compared to commercial Pt/C and Pt black catalysts. Finally, the remarkable ORR performance demonstrated here can be attributed to the structural features of the catalyst (its alloy structure, high dispersion and fine particle size) and the carbon support (its nitrogen dopant, large surface area and hollow porous structure).« less

Design of Pd/PANI/Pd sandwich-structured nanotube array catalysts with special shape effects and synergistic effects for ethanol electrooxidation.

PubMed

Wang, An-Liang; Xu, Han; Feng, Jin-Xian; Ding, Liang-Xin; Tong, Ye-Xiang; Li, Gao-Ren

2013-07-24

Low cost, high activity, and long-term durability are the main requirements for commercializing fuel cell electrocatalysts. Despite tremendous efforts, developing non-Pt anode electrocatalysts with high activity and long-term durability at low cost remains a significant technical challenge. Here we report a new type of hybrid Pd/PANI/Pd sandwich-structured nanotube array (SNTA) to exploit shape effects and synergistic effects of Pd-PANI composites for the oxidation of small organic molecules for direct alcohol fuel cells. These synthesized Pd/PANI/Pd SNTAs exhibit significantly improved electrocatalytic activity and durability compared with Pd NTAs and commercial Pd/C catalysts. The unique SNTAs provide fast transport and short diffusion paths for electroactive species and high utilization rate of catalysts. Besides the merits of nanotube arrays, the improved electrocatalytic activity and durability are especially attributed to the special Pd/PANI/Pd sandwich-like nanostructures, which results in electron delocalization between Pd d orbitals and PANI π-conjugated ligands and in electron transfer from Pd to PANI.

Metal-Ion Distribution and Oxygen Vacancies That Determine the Activity of Magnetically Recoverable Catalysts in Methanol Synthesis.

PubMed

Oracko, Troy; Jaquish, Rigel; Losovyj, Yaroslav B; Morgan, David Gene; Pink, Maren; Stein, Barry D; Doluda, Valentin Yu; Tkachenko, Olga P; Shifrina, Zinaida B; Grigoriev, Maxim E; Sidorov, Alexander I; Sulman, Esther M; Bronstein, Lyudmila M

2017-10-04

Here, we report on the development of novel Zn-, Zn-Cr-, and Zn-Cu-containing catalysts using magnetic silica (Fe 3 O 4 -SiO 2 ) as the support. Transmission electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) showed that the iron oxide nanoparticles are located in mesoporous silica pores and the magnetite (spinel) structure remains virtually unchanged despite the incorporation of Zn and Cr. According to XPS data, the Zn and Cr species are intermixed within the magnetite structure. In the case of the Zn-Cu-containing catalysts, a separate Cu 2 O phase was also observed along with the spinel structure. The catalytic activity of these catalysts was tested in methanol synthesis from syngas (CO + H 2 ). The catalytic experiments showed an improved catalytic performance of Zn- and Zn-Cr-containing magnetic silicas compared to that of the ZnO-SiO 2 catalyst. The best catalytic activity was obtained for the Zn-Cr-containing magnetic catalyst prepared with 1 wt % Zn and Cr each. X-ray absorption spectroscopy demonstrated the presence of oxygen vacancies near Fe and Zn in Zn-containing, and even more in Zn-Cr-containing, magnetic silica (including oxygen vacancies near Cr ions), revealing a correlation between the catalytic properties and oxygen vacancies. The easy magnetic recovery, robust synthetic procedure, and high catalytic activity make these catalysts promising for practical applications.

Well-defined iron catalyst for improved hydrogenation of carbon dioxide and bicarbonate.

PubMed

Ziebart, Carolin; Federsel, Christopher; Anbarasan, Pazhamalai; Jackstell, Ralf; Baumann, Wolfgang; Spannenberg, Anke; Beller, Matthias

2012-12-26

The most efficient, stable, and easy-to-synthesize non-noble metal catalyst system for the reduction of CO(2) and bicarbonates is presented. In the presence of the iron(II)-fluoro-tris(2-(diphenylphosphino)phenyl)phosphino]tetrafluoroborate complex 3, the hydrogenation of bicarbonates proceeds in good yields with high catalyst productivity and activity (TON > 7500, TOF > 750). High-pressure NMR studies of the hydrogenation of carbon dioxide demonstrate that the corresponding iron-hydridodihydrogen complex 4 is crucial in the catalytic cycle.

Esther Wilcox | NREL

Science.gov Websites

Research Associate, University of Colorado, 2004-2007 Patents "Methods for improving syngas-to-alcohol catalyst activity and selectivity," U.S. Patent No. 8,318,986 (2012) "Methods for improving

The effect of titanium nickel nitride decorated carbon nanotubes-reduced graphene oxide hybrid support for methanol oxidation

NASA Astrophysics Data System (ADS)

Liu, Gen; Pan, Zhanchang; Li, Wuyi; Yu, Ke; Xia, Guowei; Zhao, Qixiang; Shi, Shikun; Hu, Guanghui; Xiao, Chumin; Wei, Zhigang

2017-07-01

Titanium nickel nitride (TiNiN) decorated three-dimensional (3D) carbon nanotubes-reduced graphene oxide (CNT-rGO), a fancy 3D platinum (Pt)-based catalyst hybrid support, is prepared by a solvothermal process followed by a nitriding process, which is tested as anodic catalyst support for the methanol oxidation reaction (MOR). The structure, morphology and composition of the synthesized TiNiN/CNT-rGO exhibits a uniform particle dispersion with high purity and interpenetrating 3D network structure. Notably, Pt/TiNiN/CNT-rGO catalyst exhibits significantly improved catalytic activity and durability for methanol oxidation in comparison with Pt/CNT-rGO and conventional Pt/C (JM). The outstanding electrochemical performance was attributed to structure and properties. That is, the 3D CNT-rGO provided a fast transport network for charge-transfer and mass-transfer as well as TiNiN NPs with good synergistic effect and the strong electronic coupling between different domains in TiNiN/CNT-rGO, thus the catalytic activity of the novel catalyst is greatly improved. These results evidences 3D TiNiN/CNT-rGO as a promising catalyst support for a wide range of applications in fuel cells.

Engineering Single-Atom Cobalt Catalysts toward Improved Electrocatalysis.

PubMed

Wan, Gang; Yu, Pengfei; Chen, Hangrong; Wen, Jianguo; Sun, Cheng-Jun; Zhou, Hua; Zhang, Nian; Li, Qianru; Zhao, Wanpeng; Xie, Bing; Li, Tao; Shi, Jianlin

2018-04-01

The development of cost-effective catalysts to replace noble metal is attracting increasing interests in many fields of catalysis and energy, and intensive efforts are focused on the integration of transition-metal sites in carbon as noble-metal-free candidates. Recently, the discovery of single-atom dispersed catalyst (SAC) provides a new frontier in heterogeneous catalysis. However, the electrocatalytic application of SAC is still subject to several theoretical and experimental limitations. Further advances depend on a better design of SAC through optimizing its interaction with adsorbates during catalysis. Here, distinctive from previous studies, favorable 3d electronic occupation and enhanced metal-adsorbates interactions in single-atom centers via the construction of nonplanar coordination is achieved, which is confirmed by advanced X-ray spectroscopic and electrochemical studies. The as-designed atomically dispersed cobalt sites within nonplanar coordination show significantly improved catalytic activity and selectivity toward the oxygen reduction reaction, approaching the benchmark Pt-based catalysts. More importantly, the illustration of the active sites in SAC indicates metal-natured catalytic sites and a media-dependent catalytic pathway. Achieving structural and electronic engineering on SAC that promotes its catalytic performances provides a paradigm to bridge the gap between single-atom catalysts design and electrocatalytic applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A durable PtRu/C catalyst with a thin protective layer for direct methanol fuel cells.

PubMed

Shimazaki, Yuzuru; Hayasaka, Sho; Koyama, Tsubasa; Nagao, Daisuke; Kobayashi, Yoshio; Konno, Mikio

2010-11-15

A methanol oxidation catalyst with improved durability in acidic environments is reported. The catalyst consists of PtRu alloy nanoparticles on a carbon support that were stabilized with a silane-coupling agent. The catalyst was prepared by reducing ions of Pt and Ru in the presence of a carbon support and the silane-coupling agent. The careful choice of preparatory conditions such as the concentration of the silane-coupling agent and solution pH resulted in the preparation of catalyst in which the PtRu nanoparticles were dispersively adsorbed onto the carbon support. The catalytic activity was similar to that of a commercial catalyst and was unchanged after immersion in sulfuric acid solution for 1000 h, suggesting the high durability of the PtRu catalyst for the anode of direct methanol fuel cells. Copyright © 2010 Elsevier Inc. All rights reserved.

ECUT: Energy Conversion and Utilization Technologies program. Heterogeneous catalysis modeling program concept

NASA Technical Reports Server (NTRS)

Voecks, G. E.

1983-01-01

Insufficient theoretical definition of heterogeneous catalysts is the major difficulty confronting industrial suppliers who seek catalyst systems which are more active, selective, and stable than those currently available. In contrast, progress was made in tailoring homogeneous catalysts to specific reactions because more is known about the reaction intermediates promoted and/or stabilized by these catalysts during the course of reaction. However, modeling heterogeneous catalysts on a microscopic scale requires compiling and verifying complex information on reaction intermediates and pathways. This can be achieved by adapting homogeneous catalyzed reaction intermediate species, applying theoretical quantum chemistry and computer technology, and developing a better understanding of heterogeneous catalyst system environments. Research in microscopic reaction modeling is now at a stage where computer modeling, supported by physical experimental verification, could provide information about the dynamics of the reactions that will lead to designing supported catalysts with improved selectivity and stability.

Role of CeO2 promoter in NiO/α-Al2O3 catalyst for dry reforming of methane

NASA Astrophysics Data System (ADS)

Loc, Luu Cam; Phuong, Phan Hong; Tri, Nguyen

2017-09-01

A series of Ni/α-Al2O3 (NiAl) catalysts promoted by CeO2 was prepared by co-impregnation methods with content of (NiO+CeO2) being in the range of 10-30 wt%. The NiO:CeO2 weight ratio was fluctuated at 1:1, 1:2 and 1:3. Several techniques, including X-ray powder diffraction (XRD), Hydrogen temperature-programmed reduction (H2-TPR), and transmission electron microscopy (TEM) were used to investigate catalysts' physico-chemical properties. The activity of these catalysts in dry reforming of CH4 was investigated at temperature range of 550-800 °C. The results revealed that the most suitable CeO2 promoted Ni catalyst contained 20 wt% of (NiO+CeO2) and NiO:CeO2 weight ratio of 1:2. The best catalytic performance of catalyst [20(1Ni2Ce)Al] due to a better reducibility resulted in a higher amount of free small particle NiO. At 700 °C and CH4:CO2 molar ratio of 1:1, the conversion of CH4 and CO2 on the most suitable CeO2 promoted Ni catalyst reached 86% and 67%, respectively; H2 and CO selectivity of 90% and H2:CO molar ratio of 1.15 were obtained. Being similar to MgO [1], promoter CeO2 could improve catalytic activity of Ni/α-Al2O3 catalyst at a lower range of temperature. Besides, both MgO and CeO2 had a great impact on improving coke resistance of Ni catalysts. At higher temperature, the role of CeO2 as well as MgO in preventing coke formation on catalyst was clarified by temperature-programmed oxidation (TPO) technique. Coke amount formed after 30-h TOS on 20(1Ni2Ce) catalyst was found to be 22.18 mgC/gcat, being less than on non-promoted catalyst (36.75 mgC/gcat), but more than on 20(1Ni2Mg)Al one (5.25 mgC/gcat).

Development of Advanced ISS-WPA Catalysts for Organic Oxidation at Reduced Pressure/Temperature

NASA Technical Reports Server (NTRS)

Yu, Ping; Nalette, Tim; Kayatin, Matthew

2016-01-01

The Water Processor Assembly (WPA) at International Space Station (ISS) processes a waste stream via multi-filtration beds, where inorganic and non-volatile organic contaminants are removed, and a catalytic reactor, where low molecular weight organics not removed by the adsorption process are oxidized at elevated pressure in the presence of oxygen and elevated temperature above the normal water boiling point. Operation at an elevated pressure requires a more complex system design compared to a reactor that could operate at ambient pressure. However, catalysts currently available have insufficient activity to achieve complete oxidation of the organic load at a temperature less than the water boiling point and ambient pressure. Therefore, it is highly desirable to develop a more active and efficient catalyst at ambient pressure and a moderate temperature that is less than water boiling temperature. This paper describes our efforts in developing high efficiency water processing catalysts. Different catalyst support structures and coating metals were investigated in subscale reactors and results were compared against the flight WPA catalyst. Detailed improvements achieved on alternate metal catalysts at ambient pressure and 200 F will also be presented in the paper.

Synthesis, characterization and catalytic activity of nanosized Ni complexed aminoclay

NASA Astrophysics Data System (ADS)

Ranchani, A. Amala Jeya; Parthasarathy, V.; Devi, A. Anitha; Meenarathi, B.; Anbarasan, R.

2017-11-01

A novel Ni complexed aminoclay (AC) catalyst was prepared by complexation method followed by reduction reaction. Various analytical techniques such as FTIR spectroscopy, UV-visible spectroscopy, DSC, TGA, SEM, HRTEM, EDX, XPS and WCA measurement are used to characterize the synthesized material. The AC-Ni catalyst system exhibited improved thermal stability and fiber-like morphology. The XPS results declared the formation of Ni nanoparticles. Thus, synthesized catalyst was tested towards the Schiff base formation reaction between various bio-medical polymers and aniline under air atmosphere at 85 °C for 24 h. The catalytic activity of the catalyst was studied by varying the % weight loading of the AC-Ni system towards the Schiff base formation. The Schiff base formation was quantitatively calculated by the 1H-NMR spectroscopy. While increasing the % weight loading of the AC-Ni catalyst, the % yield of Schiff base was also increased. The k app and Ti values were determined for the reduction of indole and α-terpineol in the presence of AC-Ni catalyst system. The experimental results were compared with the literature report.

hcp-Co nanowires grown on metallic foams as catalysts for the Fischer-Tropsch synthesis.

PubMed

Soulantica, Katerina; Harmel, Justine; Peres, Laurent; Estrader, Marta; Berliet, Adrien; Maury, Sylvie; Fécant, Antoine; Chaudret, Bruno; Serp, Philippe

2018-06-12

The possibility to control the structural characteristics of the active phase of supported catalysts offers the opportunity to improve catalyst performance, especially in structure sensitive catalytic reactions. In parallel, heat management is of critical importance for the catalytic performance in highly endo- or exothermic reactions. The Fisher-Tropsch synthesis (FTS) is a structure sensitive exothermic reaction, which enables catalytic transformation of syngas to high quality liquid fuels. We have elaborated monolithic cobalt based heterogeneous catalysts through a wet chemistry approach that allows control over nanocrystal shape and crystallographic phase, while at the same time enables heat management. Copper and nickel foams have been employed as supports for the epitaxial growth of hcp-Co nanowires, directly from a solution containing a coordination compound of cobalt and stabilizing ligands. The Co/Cufoam catalyst has been tested for the Fischer-Tropsch synthesis in fixed bed reactor, showing stability, and significantly superior activity and selectivity towards C5+ compared to a Co/SiO2-Al2O3 reference catalyst under the same conditions. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Catalytic evaluation on liquid phase oxidation of vanillyl alcohol using air and H2O2 over mesoporous Cu-Ti composite oxide

NASA Astrophysics Data System (ADS)

Saha, Subrata; Hamid, Sharifah Bee Abd; Ali, Tammar Hussein

2017-02-01

A mesoporous, highly crystalline Cu-Ti composite oxide catalyst was prepared via facile, simple and modified solution method varying Cu and Ti ratio for selective liquid phase oxidation of vanillyl alcohol. Various spectroscopic procedures were employed to systematically characterize the catalyst structural and physicochemical properties. The defect chemistry of the catalyst was confirmed from the presence of surface defects revealed through HRTEM imagery between the TiO2 (101) and Cu3TiO4 (012) planes, complemented by the XRD profiling. Further, presence of oxygen vacancy evidenced by O 1s XPS spectra were observed on the catalyst surface. Moreover, the stoichiometry of Cu and Ti in the catalyst synthesis protocol was notably found to be the vital determinant to alter the redox properties of Cu-Ti composite oxide catalyst supported by H2-TPR. O2-TPD analysis. Moreover, a rational investigation was done using different oxidants such as air and H2O2 with variables reaction conditions. The catalyst was active for liquid phase oxidation of vanillyl alcohol to vanillin with performance of 66% conversion and 71% selectivity using H2O2 in base free condition. And also, catalytic activity was significantly improved by 94% conversion with 86% selectivity to vanillin in liquid phase aerobic oxidation at the optimum reaction conditions. To expand the superiority of the catalyst, three times reusability study was also examined with appreciable catalytic activity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rabo, J.A.

Eight catalysts were tested from November, 1983 through January, 1984. One catalyst had only water gas shift activity. The other seven catalysts had Fischer-Tropsch synthesis activity from cobalt/thorium intimately mixed with either UCC-101 or UCC-103. This intimate mixture, either alone or promoted with X/sub 4/ or X/sub 6/, was then used by itself or used with other physically added shape selective and water gas shift components. The over-riding feature of these catalysts was the high degree of stability achieved from the intimate mixing of the metal component with UCC-103. The intimate mixing of the Co/Th with the UCC-101 or UCC-103more » gave other characteristics to these catalysts that were not seen in their physically mixed versions. On the positive side, these intimately mixed catalysts produced liquid hydrocarbons that contained less suspended wax and had a lower olefin content. On the negative side, these intimately mixed catalysts had significantly lower water gas shift activities. The incorporation of a second shape selective component or of other ingredients to the intimately mixed Co/Th+UCC-103 constituent was even less satisfactory. It should be understood that these initial drawbacks for the intimately mixed catalysts are far less important than their achievement of obtaining good stability. Such stability was one of the major goals of this contract. Such stability was one of the major goals of this contract. Its accomplishment is a major milestone towards the development of an improved Fischer-Tropsch catalyst. Appendix B has been entered individually into EDB and ERA.« less

Low-temperature abatement of toluene over Mn-Ce oxides catalysts synthesized by a modified hydrothermal approach

NASA Astrophysics Data System (ADS)

Du, Jinpeng; Qu, Zhenping; Dong, Cui; Song, Lixin; Qin, Yuan; Huang, Na

2018-03-01

Mn-Ce oxides catalysts were synthesized by a novel method combining redox-precipitation and hydrothermal approach. The results indicate that the ratio between manganese and cerium plays a crucial role in the formation of catalysts, and the textual properties as well as catalytic activity are remarked affected. Mn0.6Ce0.4O2 possesses a predominant catalytic activity in the oxidation of toluene, over 70% of toluene is converted at 200 °C, and the complete conversion temperature is 210 °C. The formation of Mn-Ce solid solution markedly improves the surface area as well as pore volume of Mn-Ce oxide catalyst, and Mn0.6Ce0.4O2 possesses the largest surface area of 298.5 m2/g. The abundant Ce3+ and Mn3+ on Mn0.6Ce0.4O2 catalyst facilitate the formation of oxygen vacancies, and improve the transfer of oxygen in the catalysts. Meanwhile, it is found that cerium in Mn-Ce oxide plays a key role in the adsorption of toluene, while manganese is proved to be crucial in the oxidation of toluene, the cooperation between manganese and cerium improves the catalytic reaction process. In addition, the reaction process is investigated by in situ DRIFT measurement, and it is found that the adsorbed toluene could be oxidized to benzyl alcohol as temperature rises around 80-120 °C that can be further be oxidized to benzoic acid. Then benzoic acid could be decomposed to formate and/or carbonate species as temperature rises to form CO2 and H2O. In addition, the formed by-product phenol could be further oxidized into CO2 and H2O when the temperature is high enough.

Catalysts and method

DOEpatents

Taylor, Charles E.; Noceti, Richard P.

1991-01-01

An improved catlayst and method for the oxyhydrochlorination of methane is disclosed. The catalyst includes a pyrogenic porous support on which is layered as active material, cobalt chloride in major proportion, and minor proportions of an alkali metal chloride and of a rare earth chloride. On contact of the catalyst with a gas flow of methane, HC1 and oxygen, more than 60% of the methane is converted and of that converted more than 40% occurs as monochloromethane. Advantageously, the monochloromethane can be used to produce gasoline boiling range hydrocarbons with the recycle of HCl for further reaction. This catalyst is also of value for the production of formic acid as are analogous catalysts with lead, silver or nickel chlorides substituted for the cobalt chloride.

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

DOE PAGES

Alia, Shaun M.; Pivovar, Bryan S.

2018-01-01

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing tomore » 250 degrees C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 degrees C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. Furthermore, these techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.« less

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alia, Shaun M.; Pivovar, Bryan S.

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing tomore » 250 degrees C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 degrees C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. Furthermore, these techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.« less

Plasma and catalyst for the oxidation of NOx

NASA Astrophysics Data System (ADS)

Jõgi, Indrek; Erme, Kalev; Levoll, Erik; Raud, Jüri; Stamate, Eugen

2018-03-01

Efficient exhaust gas cleaning from NO x (NO and NO2) by absorption and adsorption based methods requires the oxidation of NO. The application of non-thermal plasma is considered as a promising oxidation method but the oxidation of NO by direct plasma remains limited due to the back-reaction of NO2 to NO mediated by O radicals in plasma. Indirect NO oxidation by plasma produced ozone allows to circumvent the back-reaction and further oxidize NO2 to N2O5 but the slow reaction rate for the latter process limits the efficiency of this process. Present paper gives an overview of the role of metal-oxide catalysts in the improvement of oxidation efficiency for both direct and indirect plasma oxidation of NO x . The plasma produced active oxygen species (O, O3) were shown to play an important role in the reactions taking place on the catalyst surfaces while the exact mechanism and extent of the effect were different for direct and indirect oxidation. In the case of direct plasma oxidation, both short and long lifetime oxygen species could reach the catalyst and participate in the oxidation of NO to NO2. The back-reaction in the plasma phase remained still important factor and limited the effect of catalyst. In the case of indirect oxidation, only ozone could reach the catalyst surface and improve the oxidation of NO2 to N2O5. The effect of catalyst at different experimental conditions was quantitatively described with the aid of simple global chemical kinetic models derived for the NO x oxidation either by plasma or ozone. The models allowed to compare the effect of different catalysts and to analyze the limitations for the efficiency improvement by catalyst.

Reverse Micelle Synthesis and Characterization of Supported Pt/Ni Bimetallic Catalysts on gamma-Al2O3

DOE Office of Scientific and Technical Information (OSTI.GOV)

B Cheney; J Lauterbach; J Chen

2011-12-31

Reverse micelle synthesis was used to improve the nanoparticle size uniformity of bimetallic Pt/Ni nanoparticles supported on {gamma}-Al{sub 2}O{sub 3}. Two impregnation methods were investigated to optimize the use of the micelle method: (1) step-impregnation, where Ni nanoparticles were chemically reduced in microemulsion and then supported, followed by Pt deposition using incipient wetness impregnation, and (2) co-impregnation, where Ni and Pt were chemically reduced simultaneously in microemulsion and then supported. Transmission electron microscopy (TEM) was used to characterize the particle size distribution. Atomic absorption spectroscopy (AAS) was used to perform elemental analysis of bimetallic catalysts. Extended X-ray absorption fine structuremore » (EXAFS) measurements were utilized to confirm the formation of the Pt-Ni bimetallic bond in the step-impregnated catalyst. CO pulse chemisorption and Fourier transform infrared spectroscopy (FTIR) studies of 1,3-butadiene hydrogenation in a batch reactor were performed to determine the catalytic activity. Step-impregnated Pt/Ni catalyst demonstrated enhanced hydrogenation activity over the parent monometallic Pt and Ni catalysts due to bimetallic bond formation. The catalyst synthesized using co-impregnation showed no enhanced activity, behaving similarly to monometallic Ni. Overall, our results indicate that reverse micelle synthesis combined with incipient wetness impregnation produced small, uniform nanoparticles with bimetallic bonds that enhanced hydrogenation activity.« less

Comparative study of different carbon-supported Fe2O3-Pt catalysts for oxygen reduction reaction.

PubMed

Tellez-Cruz, M M; Padilla-Islas, M A; Pérez-González, M; Solorza-Feria, O

2017-11-01

One of the challenges in electrocatalysis is the adequate dispersion of the catalyst on an appropriate porous support matrix, being up to now the most commonly used the carbon-based supports. To overcome this challenge, carbon supports must first be functionalized to guide the catalyst's nucleation, thereby, improving the dispersion and allowing the use of smaller amount of the catalyst material to achieve a higher electrochemically active surface area. This study present the effect of functionalized Vulcan carbon XC72 (FVC) and functionalized Black Pearl carbon (FBPC) as supports on the catalytic activity of decorated Fe 2 O 3 with Pt. Both carbons were functionalized with HNO 3 and subsequently treated with ethanolamine. Fe 2 O 3 nanoparticles were synthesized by chemical reduction and decorated with platinum by epitaxial growth. Pt and Fe 2 O 3 structural phases were identified by XRD and XPS; the Pt content was measured by XPS, and results showed to a high Pt content in Fe 2 O 3 -Pt/FBPC. TEM micrographs reveal nanoparticles with an average size of 2 nm in both supported catalysts. The Fe 2 O 3 -Pt/FVC catalyst presents the highest specific activity and mass activity, 0.21 mA cm -2 Pt and 140 mA mg Pt -1 , respectively, associated to the appropriate distribution of platinum on the Fe 2 O 3 nanoparticles.

Improved reaction kinetics and selectivity by the TiO2-embedded carbon nanofiber support for electro-oxidation of ethanol on PtRu nanoparticles

NASA Astrophysics Data System (ADS)

Nakagawa, Nobuyoshi; Ito, Yudai; Tsujiguchi, Takuya; Ishitobi, Hirokazu

2014-02-01

The electro-oxidation of ethanol by the catalyst of PtRu nanoparticles supported on a TiO2-embedded carbon nanofiber (PtRu/TECNF), which has recently been proposed by the authors as a highly active catalyst for methanol oxidation, is investigated by cyclic voltammetry using a glassy carbon electrode and by operating a direct ethanol fuel cell (DEFC) with the catalyst. The mass activity obtained from the cyclic voltammogram for the ethanol oxidation is compared to that for the methanol oxidation reported in our recent paper. The mass activity for the ethanol oxidation is comparable or slightly higher than that for the methanol oxidation, and the relationship between the TECNF composition, i.e., the Ti/C mass ratio, and the activity are also similar to that for the methanol oxidation. A DEFC fabricated with the PtRu/TECNF shows a higher power output compared to that with the commercial PtRu/C catalyst. An analysis of the reaction products by a simple two-step reaction model reveals that the PtRu/TECNF increases the rate constant for the reaction steps from ethanol to acetaldehyde and subsequently to CO2, but decreases that from acetaldehyde to acetic acid. This means that the PtRu/TECNF improves not only the kinetics, but also the selectivity to acetaldehyde.

Synthesis of biodiesel from a model waste oil feedstock using a carbon-based solid acid catalyst: reaction and separation.

PubMed

Shu, Qing; Nawaz, Zeeshan; Gao, Jixian; Liao, Yuhui; Zhang, Qiang; Wang, Dezheng; Wang, Jinfu

2010-07-01

A solid acid catalyst that can keep high activity and stability is necessary when low cost feedstocks are utilized for biodiesel synthesis because the reaction medium contains a large amount of water. Three solid acid catalysts were prepared by the sulfonation of carbonized vegetable oil asphalt and petroleum asphalt. The structure of these catalysts was characterized by a variety of techniques. A new process that used the coupling of the reaction and separation was employed, which greatly improved the conversion of cottonseed oil (triglyceride) and free fatty acids (FFA) when a model waste oil feedstock was used. The vegetable oil asphalt-based catalyst showed the highest catalytic activity. This was due to the high density and stability of its acid sites, its loose irregular network, its hydrophobicity that prevented the hydration of -OH species, and large pores that provided more acid sites for the reactants. Copyright (c) 2010 Elsevier Ltd. All rights reserved.

Study to improve the quality of a Mexican straight run gasoil over NiMo/γ-Al 2O 3 catalysts

NASA Astrophysics Data System (ADS)

Domínguez-Crespo, M. A.; Díaz-García, L.; Arce-Estrada, E. M.; Torres-Huerta, A. M.; Cortéz-De la Paz, M. T.

2006-11-01

Four NiMo catalyst supported on Al 2O 3 with different textural properties have been studied in the hydrodesulfurization (HDS), hydrodenitrogenation (HDN) and hydrodearomatization (HDA) of a Mexican straight run gasoil (SRGO). All reactions were carried out at three different temperatures 613, 633, and 653 K. Alumina supports were analysed by pyridine FTIR-TPD and nitrogen physisorption in order to determine their surface acidity and textural properties, respectively. TPR studies of the NiMo catalysts were analysed to correlate their hydrogenating properties. Metallic particles were characterized (after sulfidation) using transmission electron microscopy (TEM). Catalytic activities are discussed in relation to the physicochemical properties of NiMo catalysts. The importance of textural properties on coke deposition has been emphasized. The results of catalytic activity of these materials varied depending on dispersed MoS particles and pore distribution in final catalysts. The optimum pore diameter was found around 80 Å for HDS and HDN.

CATALYTIC OXIDATION OF DIMETHYL SULFIDE WITH OZONE: EFFECT OF PROMOTER AND PHYSICO-CHEMICAL PROPERTIES OF METAL OXIDE CATALYSTS

EPA Science Inventory

This study reports improved catalytic activities and stabilities for the oxidation of dimethyl sulfide (DMS), a major pollutant of pulp and paper mills. Ozone was used as an oxidant and Cu, Mo, V, Cr and Mn metal oxides, and mixed metal oxides support on y-alumina as catalysts ov...

Reactivation of a Tin-Oxide-Containing Catalyst

NASA Technical Reports Server (NTRS)

Hess, Robert; Sidney, Barry; Schryer, David; Miller, Irvin; Miller, George; Upchurch, Bill; Davis, Patricia; Brown, Kenneth

2010-01-01

The electrons in electric-discharge CO2 lasers cause dissociation of some CO2 into O2 and CO, and attach themselves to electronegative molecules such as O2, forming negative O2 ions, as well as larger negative ion clusters by collisions with CO or other molecules. The decrease in CO2 concentration due to dissociation into CO and O2 will reduce the average repetitively pulsed or continuous wave laser power, even if no disruptive negative ion instabilities occur. Accordingly, it is the primary object of this invention to extend the lifetime of a catalyst used to combine the CO and O2 products formed in a laser discharge. A promising low-temperature catalyst for combining CO and O2 is platinum on tin oxide (Pt/SnO2). First, the catalyst is pretreated by a standard procedure. The pretreatment is considered complete when no measurable quantity of CO2 is given off by the catalyst. After this standard pretreatment, the catalyst is ready for its low-temperature use in the sealed, high-energy, pulsed CO2 laser. However, after about 3,000 minutes of operation, the activity of the catalyst begins to slowly diminish. When the catalyst experiences diminished activity during exposure to the circulating gas stream inside or external to the laser, the heated zone surrounding the catalyst is raised to a temperature between 100 and 400 C. A temperature of 225 C was experimentally found to provide an adequate temperature for reactivation. During this period, the catalyst is still exposed to the circulating gas inside or external to the laser. This constant heating and exposing the catalyst to the laser gas mixture is maintained for an hour. After heating and exposing for an appropriate amount of time, the heated zone around the catalyst is allowed to return to the nominal operating temperature of the CO2 laser. This temperature normally resides in the range of 23 to 100 C. Catalyst activity can be measured as the percentage conversion of CO to CO2. In the specific embodiment described above, the initial steady-state conversion percentage was 70 percent. After four days, this conversion percentage decreased to 67 percent. No decrease in activity is acceptable because the catalyst must maintain its activity for long periods of time. After being subjected to the reactivation process of the present invention, the conversion percentage rose to 77 percent. Such a reactivation not only returned the catalyst to its initial steady state but resulted in a 10-percent improvement over the initial steady state value.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerceker, Duygu; Motagamwala, Ali Hussain; Rivera-Dones, Keishla R.

Pt and PtSn catalysts supported on SiO 2 and H-ZSM-5 were studied for methane conversion under nonoxidative conditions. Addition of Sn to Pt/SiO 2 increased the turnover frequency for production of ethylene by a factor of 3, and pretreatment of the catalyst at 1123 K reduced the extent of coke formation. Pt and PtSn catalysts supported on H-ZSM-5 zeolite were prepared to improve the activity and selectivity to non-coke products. Ethylene formation rates were 20 times faster over a PtSn(1:3)/H-ZSM-5 catalyst with SiO 2:Al 2O 3 = 280 in comparison to those over PtSn(3:1)/SiO 2. H-ZSM-5-supported catalysts were also activemore » for the formation of aromatics, and the rates of benzene and naphthalene formation were increased by using more acidic H-ZSM-5 supports. These catalysts operate through a bifunctional mechanism, in which ethylene is first produced on highly dispersed PtSn nanoparticles and then is subsequently converted to benzene and naphthalene on Brønsted acid sites within the zeolite support. The most active and stable PtSn catalyst forms carbon products at a rate, 2.5 mmol of C/((mol of Pt) s), which is comparable to that of state-of-the-art Mo/H-ZSM-5 catalysts with same metal loading operated under similar conditions (1.8 mmol of C/((mol of Mo) s)). Scanning transmission electron microscopy measurements suggest the presence of smaller Pt nanoparticles on H-ZSM-5-supported catalysts, in comparison to SiO 2-supported catalysts, as a possible source of their high activity. As a result, a microkinetic model of methane conversion on Pt and PtSn surfaces, built using results from density functional theory calculations, predicts higher coupling rates on bimetallic and stepped surfaces, supporting the experimental observations that relate the high catalytic activity to small PtSn particles.« less

Engineering the internal surfaces of three-dimensional nanoporous catalysts by surfactant-modified dealloying.

PubMed

Wang, Zhili; Liu, Pan; Han, Jiuhui; Cheng, Chun; Ning, Shoucong; Hirata, Akihiko; Fujita, Takeshi; Chen, Mingwei

2017-10-20

Tuning surface structures by bottom-up synthesis has been demonstrated as an effective strategy to improve the catalytic performances of nanoparticle catalysts. Nevertheless, the surface modification of three-dimensional nanoporous metals, fabricated by a top-down dealloying approach, has not been achieved despite great efforts devoted to improving the catalytic performance of three-dimensional nanoporous catalysts. Here we report a surfactant-modified dealloying method to tailor the surface structure of nanoporous gold for amplified electrocatalysis toward methanol oxidation and oxygen reduction reactions. With the assistance of surfactants, {111} or {100} faceted internal surfaces of nanoporous gold can be realized in a controllable manner by optimizing dealloying conditions. The surface modified nanoporous gold exhibits significantly enhanced electrocatalytic activities in comparison with conventional nanoporous gold. This study paves the way to develop high-performance three-dimensional nanoporous catalysts with a tunable surface structure by top-down dealloying for efficient chemical and electrochemical reactions.

Water Oxidation Mechanisms of Metal Oxide Catalysts by Vibrational Spectroscopy of Transient Intermediates.

PubMed

Zhang, Miao; Frei, Heinz

2017-05-05

Water oxidation is an essential reaction of an artificial photosystem for solar fuel generation because it provides electrons needed to reduce carbon dioxide or protons to a fuel. Earth-abundant metal oxides are among the most attractive catalytic materials for this reaction because of their robustness and scalability, but their efficiency poses a challenge. Knowledge of catalytic surface intermediates gained by vibrational spectroscopy under reaction conditions plays a key role in uncovering kinetic bottlenecks and provides a basis for catalyst design improvements. Recent dynamic infrared and Raman studies reveal the molecular identity of transient surface intermediates of water oxidation on metal oxides. Combined with ultrafast infrared observations of how charges are delivered to active sites of the metal oxide catalyst and drive the multielectron reaction, spectroscopic advances are poised to play a key role in accelerating progress toward improved catalysts for artificial photosynthesis.

Improved capacitance characteristics of electrospun ACFs by pore size control and vanadium catalyst.

PubMed

Im, Ji Sun; Woo, Sang-Wook; Jung, Min-Jung; Lee, Young-Seak

2008-11-01

Nano-sized carbon fibers were prepared by using electrospinning, and their electrochemical properties were investigated as a possible electrode material for use as an electric double-layer capacitor (EDLC). To improve the electrode capacitance of EDLC, we implemented a three-step optimization. First, metal catalyst was introduced into the carbon fibers due to the excellent conductivity of metal. Vanadium pentoxide was used because it could be converted to vanadium for improved conductivity as the pore structure develops during the carbonization step. Vanadium catalyst was well dispersed in the carbon fibers, improving the capacitance of the electrode. Second, pore-size development was manipulated to obtain small mesopore sizes ranging from 2 to 5 nm. Through chemical activation, carbon fibers with controlled pore sizes were prepared with a high specific surface and pore volume, and their pore structure was investigated by using a BET apparatus. Finally, polyacrylonitrile was used as a carbon precursor to enrich for nitrogen content in the final product because nitrogen is known to improve electrode capacitance. Ultimately, the electrospun activated carbon fibers containing vanadium show improved functionality in charge/discharge, cyclic voltammetry, and specific capacitance compared with other samples because of an optimal combination of vanadium, nitrogen, and fixed pore structures.

Chromium-doped Raney nickel catalyst for hydrogen electrodes in alkaline fuel cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kenjo, T.

Raney nickel is a relatively inexpensive and highly active nonnoble metal catalyst for hydrogen electrodes in alkaline fuel cells. Mund et al. (1977) have found that its catalytic activity is increased by doping involving transition metals, such a titanum, iron, and molybdenum. The present investigation is concerned with the preparation of hydrogen electrodes catalyzed with chromium-doped Raney nickel and the measurement of their polarization characteristics. On the basis of the obtained results, it is concluded that chromium is a good dopant for Raney nickel which is employed for hydrogen electrodes. Chromium improves and stabilizes the polarization characteristics of Raney nickelmore » electrodes. It is found that chromium-doped Raney nickel is more active than the titanium-doped catalyst. 6 references.« less

A new V-doped Bi2(O,S)3 oxysulfide catalyst for highly efficient catalytic reduction of 2-nitroaniline and organic dyes.

PubMed

Abay, Angaw Kelemework; Kuo, Dong-Hau; Chen, Xiaoyun; Saragih, Albert Daniel

2017-12-01

A new type of convenient, and environmentally friendly, Vanadium (V)-doped Bi 2 (O,S) 3 oxysulfide catalyst with different V contents was successfully synthesized via a simple and facile method. The obtained V-doped Bi 2 (O,S) 3 solid solution catalysts were fully characterized by conventional methods. The catalytic performance of the samples was tested by using the reduction of 2-nitroaniline (2-NA) in aqueous solution. The reduction/decolorization of methylene blue (MB) and rhodamine B (RhB) was also chosen to evaluate the universality of catalysts. It was observed that the introduction of V can improve the catalytic performance, and 20%V-Bi 2 (O,S) 3 was found to be the optimal V doping concentration for the reduction of 2-NA, MB, and RhB dyes. For comparative purposes, a related V-free Bi 2 (O, S) 3 oxysulfide material was synthesized and tested as the catalyst. The superior activity of V-doped Bi 2 (O,S) 3 over pure Bi 2 (O,S) 3 was ascribed mainly to an increase in active sites of the material and also due to the presence of synergistic effects. The presence of V 5+ as found from XPS analysis may interact with Bi atoms and enhancing the catalytic activity of the sample. In the catalytic reduction of 2-NA, MB and RhB, the obtained V-doped Bi 2 (O,S) 3 oxysulfide catalyst exhibited excellent catalytic activity as compared with other reported catalysts. Furthermore this highly efficient, low-cost and easily reusable V-doped Bi 2 (O,S) 3 catalyst is anticipated to be of great potential in catalysis in the future. Copyright © 2017 Elsevier Ltd. All rights reserved.

Design of Heterogeneous Hoveyda-Grubbs Second-Generation Catalyst-Lipase Conjugates.

PubMed

Neville, Anthony; Iniesta, Javier; Palomo, Jose M

2016-12-06

Heterogeneous catalysts have been synthesi zed by the conjugation of Hoveyda-Grubbs second-generation catalyst with a lipase. The catalytic properties of the organometallic compound in solution were firstly optimized, evaluating the activity of Ru in the ring-closing metathesis of diethyldiallymalonate at 25 °C at different solvents and in the presence of different additives. The best result was found using tetrahydrofuran as a solvent. Some additives such as phenylboronic acid or polyetheneglycol slightly improved the activity of the Ru catalyst whereas others, such as pyridine or dipeptides affected it negatively. The organometallic compound immobilized on functionalized-surface materials activated with boronic acid or epoxy groups (around 50-60 µg per mg support) and showed 50% conversion at 24 h in the ring-closing metathesis. Cross-linked enzyme aggregates (CLEA's) of the Hoveyda-Grubbs second-generation catalyst with Candida antarctica lipase (CAL-B) were prepared, although low Ru catalyst was found to be translated in low conversion. Therefore, a sol-gel preparation of the Hoveyda-Grubbs second-generation and CAL-B was performed. This catalyst exhibited good activity in the metathesis of diethyldiallymalonate in toluene and in aqueous media. Finally, a new sustainable approach was used by the conjugation lipase-Grubbs in solid phase in aqueous media. Two strategies were used: one using lipase previously covalently immobilized on an epoxy-Sepharose support (hydrophilic matrix) and then conjugated with grubbs; and in the second, the free lipase was incubated with organometallic in aqueous solution and then immobilized on epoxy-Sepharose. The different catalysts showed excellent conversion values in the ring-closing metathesis of diethyldiallymalonate in aqueous media at 25 °C.

Enhancement of the catalytic activity of Pt nanoparticles toward methanol electro-oxidation using doped-SnO2 supporting materials

NASA Astrophysics Data System (ADS)

Merati, Zohreh; Basiri Parsa, Jalal

2018-03-01

Catalyst supports play important role in governing overall catalyst activity and durability. In this study metal oxides (SnO2, Sb and Nb doped SnO2) were electrochemically deposited on titanium substrate (Ti) as a new support material for Pt catalyst in order to electro-oxidation of methanol. Afterward platinum nanoparticles were deposited on metal oxide film via electro reduction of platinum salt in an acidic solution. The surface morphology of modified electrodes were evaluated by field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDX) techniques. The electro-catalytic activities of prepared electrodes for methanol oxidation reaction (MOR) and oxidation of carbon monoxide (CO) absorbed on Pt was considered with cyclic voltammetry. The results showed high catalytic activity for Pt/Nb-SnO2/Ti electrode. The electrochemical surface area (ECSA) of a platinum electro-catalyst was determined by hydrogen adsorption. Pt/Nb-SnO2/Ti electrode has highest ECSA compared to other electrode resulting in high activity toward methanol electro-oxidation and CO stripping experiments. The doping of SnO2 with Sb and Nb improved ECSA and MOR activity, which act as electronic donors to increase electronic conductivity.

Fabrication of three-dimensional buckypaper catalyst layer with Pt nanoparticles supported on polyelectrolyte functionalized carbon nanotubes for proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Zhu, Shiyao; Zheng, Junsheng; Huang, Jun; Dai, Ningning; Li, Ping; Zheng, Jim P.

2018-07-01

Polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) functionalized carbon nanotubes (CNTs) supported Pt electrocatalyst was synthesized as a substitute for commonly used Pt/C and Pt/CNTs (modified by harsh acid-oxidation treatment) catalysts. In addition, this catalyst was fabricated as the cathode catalyst layer (CL) with a unique double-layered structure for proton exchange membrane fuel cells (PEMFCs). Thermogravimetric analysis shows an enhanced thermal stability of Pt/PDDA-CNTs. The Pt/PDDA-CNTs catalyst with an average Pt particle size of ∼3.1 nm exhibits the best electrocatalytic activity and a significantly enhanced electrochemical stability. Scanning electron microscope, energy dispersive spectrometer and mercury intrusion porosimetry results demonstrate the gradient distribution of Pt content and pore size along the thickness of buckypaper catalyst layer (BPCL). The accelerated degradation test results of BPCLs indicate that this gradient structure can ensure a high Pt utilization in the BPCLs (up to 90%) and further improve the catalyst durability. In addition, the membrane electrode assembly (MEA) fabricated with cathode BPCL-PDDA shows the best single cell performance and long-term stability, and a reduction of Pt loading can be achieved. The feasibility of BPCL for improving the Pt utilization is also demonstrated by the cathode cyclic voltammetry in MEA.

NH 3-SCR on Cu, Fe and Cu + Fe exchanged beta and SSZ-13 catalysts: Hydrothermal aging and propylene poisoning effects

DOE PAGES

Wang, Aiyong; Wang, Yilin; Walter, Eric D.; ...

2017-10-07

Cu, Fe and Cu + Fe ion exchanged Beta and SSZ-13 catalysts were prepared by solution ion exchange using commercial NH 4/Beta, and NH 4/SSZ-13 that was prepared in-house. To study hydrothermal aging effects, Beta supported catalysts were aged hydrothermally at 700 °C and SSZ-13 supported catalysts were aged at 750 °C. In order to reveal the effects of Fe addition in the co-exchanged catalysts, these catalysts were characterized by means of powder X-ray diffraction (XRD), N 2 adsorption-desorption, electron paramagnetic resonance (EPR), 27Al-nuclear magnetic resonance ( 27Al-NMR) and propylene coking followed with temperature programmed reaction (TPR), and further testedmore » with standard NH 3-SCR with and without the presence of propylene. Collectively, the catalyst characterizations and reaction testing indicated minor beneficial effects of Fe addition in Cu,Fe/Beta, where NH 3-SCR activity, N 2 selectivity and hydrothermal stability were all slightly improved. In contrast, Fe addition did not show apparent beneficial effects in low-temperature SCR for the Cu,Fe/SSZ-13 case. In conclusion, at elevated reaction temperatures, however, the presence of Fe indeed considerably improved NO conversion and N 2 selectivity for the hydrothermally aged Cu,Fe/SSZ-13 catalyst in the presence of propylene.« less

NH 3-SCR on Cu, Fe and Cu + Fe exchanged beta and SSZ-13 catalysts: Hydrothermal aging and propylene poisoning effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Aiyong; Wang, Yilin; Walter, Eric D.

Cu, Fe and Cu + Fe ion exchanged Beta and SSZ-13 catalysts were prepared by solution ion exchange using commercial NH 4/Beta, and NH 4/SSZ-13 that was prepared in-house. To study hydrothermal aging effects, Beta supported catalysts were aged hydrothermally at 700 °C and SSZ-13 supported catalysts were aged at 750 °C. In order to reveal the effects of Fe addition in the co-exchanged catalysts, these catalysts were characterized by means of powder X-ray diffraction (XRD), N 2 adsorption-desorption, electron paramagnetic resonance (EPR), 27Al-nuclear magnetic resonance ( 27Al-NMR) and propylene coking followed with temperature programmed reaction (TPR), and further testedmore » with standard NH 3-SCR with and without the presence of propylene. Collectively, the catalyst characterizations and reaction testing indicated minor beneficial effects of Fe addition in Cu,Fe/Beta, where NH 3-SCR activity, N 2 selectivity and hydrothermal stability were all slightly improved. In contrast, Fe addition did not show apparent beneficial effects in low-temperature SCR for the Cu,Fe/SSZ-13 case. In conclusion, at elevated reaction temperatures, however, the presence of Fe indeed considerably improved NO conversion and N 2 selectivity for the hydrothermally aged Cu,Fe/SSZ-13 catalyst in the presence of propylene.« less

Fuel Cell Measurements with Cathode Catalysts of Sputtered Pt3 Y Thin Films.

PubMed

Lindahl, Niklas; Eriksson, Björn; Grönbeck, Henrik; Lindström, Rakel Wreland; Lindbergh, Göran; Lagergren, Carina; Wickman, Björn

2018-05-09

Fuel cells are foreseen to have an important role in sustainable energy systems, provided that catalysts with higher activity and stability are developed. In this study, highly active sputtered thin films of platinum alloyed with yttrium (Pt 3 Y) are deposited on commercial gas diffusion layers and their performance in a proton exchange membrane fuel cell is measured. After acid pretreatment, the alloy is found to have up to 2.5 times higher specific activity than pure platinum. The performance of Pt 3 Y is much higher than that of pure Pt, even if all of the alloying element was leached out from parts of the thin metal film on the porous support. This indicates that an even higher performance is expected if the structure of the Pt 3 Y catalyst or the support could be further improved. The results show that platinum alloyed with rare earth metals can be used as highly active cathode catalyst materials, and significantly reduce the amount of platinum needed, in real fuel cells. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Engineering New Catalysts for In-Process Elimination of Tars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Felix, Larry G.

2012-09-30

The key objective of this project was to develop a new and more efficient methodology for engineering and economically producing optimized robust catalysts for the reduction or elimination of tars in biomass gasification. Whereas current catalyst technology typically disposes thin layers of catalytically-active material onto rigid supports via wet chemistry-based methods, this project investigated novel thermal methods for directly incorporating catalytically active materials onto robust supports as well as novel approaches for incorporating catalytically active materials on and/or within an otherwise inert refractory support material which is then subsequently formed and processed to create a catalytically-active material on all exposedmore » surfaces. Specifically, the focus of this engineered catalyst development was on materials which were derived from, or otherwise related to, olivine-like minerals, due to the inherent attrition resistance and moderate catalytic properties exhibited by natural olivine when used in a fluidized bed biomass gasifier. Task 1 of this project successfully demonstrated the direct thermal impregnation of catalytically-active materials onto an olivine substrate, with the production of a Ni-olivine catalyst. Nickel and nickel oxide were thermally impregnated onto an olivine substrate and when reduced were shown to demonstrate improved catalytic activity over the baseline olivine material and equal the tar-decomposing performance of Ni-olivine catalysts prepared by conventional wet impregnation. Task 2 involved coordination with our subcontracted project partners to further develop and characterize catalyst formulations and to optimize activity and production methods. Within this task, several significant new materials were developed. NexTech Materials developed a sintered ceramic nickel-magnesium-silicate catalyst that demonstrated superb catalytic activity and high resistance to deactivation by H2S. Alfred University developed both supported and integrated (bulk) catalysts via a glass-ceramic processing route which were shown to exhibit excellent catalytic activity and superior resistance to attrition deactivation. With the discovery of these active, robust, glass-based catalysts, and with the permission of the project officer, the investigation of waste-based materials as originally proposed for Task 3 and pilot-scale testing proposed in Task 5 were deferred indefinitely in favor of further investigation of the glass-ceramic based catalyst materials. This choice was justified in part because during FY 2006 and through FY 2007, funding restrictions imposed by congressional budget choices significantly reduced funding for DOE biomass-related projects. Funding for this project was limited to what had been authorized which slowed the pace of project work at GTI so that our project partners could continue in their work. Thereafter, project work was allowed to resume and with restored funding, the project continued and concentrated on the development and testing of glass-ceramic catalysts in bulk or supported formats. Work concluded with a final development devoted to increasing the surface area of glass-ceramic catalysts in the form of microspheres. Following that development, project reporting was completed and the project was concluded.« less

Bimetallic platinum group metal-free catalysts for high power generating microbial fuel cells

NASA Astrophysics Data System (ADS)

Kodali, Mounika; Santoro, Carlo; Herrera, Sergio; Serov, Alexey; Atanassov, Plamen

2017-10-01

M1-M2-N-C bimetallic catalysts with M1 as Fe and Co and M2 as Fe, Co, Ni and Mn were synthesized and investigated as cathode catalysts for oxygen reduction reaction (ORR). The catalysts were prepared by Sacrificial Support Method in which silica was the template and aminoantipyrine (AAPyr) was the organic precursor. The electro-catalytic properties of these catalysts were investigated by using rotating ring disk (RRDE) electrode setup in neutral electrolyte. Fe-Mn-AAPyr outperformed Fe-AAPyr that showed higher performances compared to Fe-Co-AAPyr and Fe-Ni-AAPyr in terms of half-wave potential. In parallel, Fe-Co-AAPyr, Co-Mn-AAPyr and Co-Ni-AAPyr outperformed Co-AAPyr. The presence of Co within the catalyst contributed to high peroxide production not desired for efficient ORR. The catalytic capability of the catalysts integrated in air-breathing cathode was also verified. It was found that Co-based catalysts showed an improvement in performance by the addition of second metal compared to simple Co- AAPyr. Fe-based bimetallic materials didn't show improvement compared to Fe-AAPyr with the exception of Fe-Mn-AAPyr catalyst that had the highest performance recorded in this study with maximum power density of 221.8 ± 6.6 μWcm-2. Activated carbon (AC) was used as control and had the lowest performances in RRDE and achieved only 95.6 ± 5.8 μWcm-2 when tested in MFC.

Cooperative dual catalysis: application to the highly enantioselective conjugate cyanation of unsaturated imides.

PubMed

Sammis, Glenn M; Danjo, Hiroshi; Jacobsen, Eric N

2004-08-18

Cooperative heterobimetallic catalysis was used as a design principle to achieve a highly reactive system for the enantioselective conjugate addition of cyanide to alpha,beta-unsaturated imides. A dual-catalyst pathway involving chiral (salen)Al complex 1b and chiral (pybox)Er complex 4b provides measurable improvements in rates and enantioselectivities relative to single-catalyst systems. Mechanistic studies point to a cooperative bimetallic mechanism involving activation of the imide by the Al complex and activation of cyanide by the Er complex.

Highly dispersed Pt-Ni nanoparticles on nitrogen-doped carbon nanotubes for application in direct methanol fuel cells.

PubMed

Jiang, Shujuan; Ma, Yanwen; Tao, Haisheng; Jian, Guoqiang; Wang, Xizhang; Fan, Yining; Zhu, Jianmin; Hu, Zheng

2010-06-01

Binary Pt-Ni alloyed nanoparticles supported on nitrogen-doped carbon nanotubes (NCNTs) have been facilely constructed without pre-modification by making use of the active sites in NCNTs due to the N-participation. So-obtained binary Pt-Ni alloyed nanoparticles have been highly dispersed on the outer surface of the support with the size of about 3-4 nm. The electrochemical properties of the catalysts for methanol oxidation have been systematically evaluated. Binary Pt-Ni alloyed composites with molar ratio (Pt:Ni) of 3:2 and 3:1 present enhanced electrocatalytic activities and improved tolerance to CO poisoning as well as the similar stability, in comparison with the commercial Pt/C catalyst and the monometallic Pt/NCNTs catalysts. These results imply that so-constructed nanocomposite catalysts have the potential for applications in direct methanol fuel cells.

Directing reaction pathways by catalyst active-site selection using self-assembled monolayers.

PubMed

Pang, Simon H; Schoenbaum, Carolyn A; Schwartz, Daniel K; Medlin, J Will

2013-01-01

One key route for controlling reaction selectivity in heterogeneous catalysis is to prepare catalysts that exhibit only specific types of sites required for desired product formation. Here we show that alkanethiolate self-assembled monolayers with varying surface densities can be used to tune selectivity to desired hydrogenation and hydrodeoxygenation products during the reaction of furfural on supported palladium catalysts. Vibrational spectroscopic studies demonstrate that the selectivity improvement is achieved by controlling the availability of specific sites for the hydrogenation of furfural on supported palladium catalysts through the selection of an appropriate alkanethiolate. Increasing self-assembled monolayer density by controlling the steric bulk of the organic tail ligand restricts adsorption on terrace sites and dramatically increases selectivity to desired products furfuryl alcohol and methylfuran. This technique of active-site selection simultaneously serves both to enhance selectivity and provide insight into the reaction mechanism.

Dry Reforming of Ethane and Butane with CO 2 over PtNi/CeO 2 Bimetallic Catalysts

DOE PAGES

Yan, Binhang; Yang, Xiaofang; Yao, Siyu; ...

2016-09-21

Dry reforming is a potential process to convert CO 2 and light alkanes into syngas (H 2 and CO), which can be subsequently transformed to chemicals and fuels. Here in this work, PtNi bimetallic catalysts have been investigated for dry reforming of ethane and butane using both model surfaces and supported powder catalysts. The PtNi bimetallic catalyst shows an improvement in both activity and stability as compared to the corresponding monometallic catalysts. The formation of PtNi alloy and the partial reduction of Ce 4+ to Ce 3+ under reaction conditions are demonstrated by in-situ Ambient Pressure X-ray Photoemission Spectroscopy (AP-XPS),more » X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements. A Pt-rich bimetallic surface is revealed by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) following CO adsorption. Combined in-situ experimental results and Density Functional Theory (DFT) calculations suggest that the Pt-rich PtNi bimetallic surface structure would weaken the binding of surface oxygenates/carbon species and reduce the activation energy for C-C bond scission, leading to an enhanced dry reforming activity.« less

Dry Reforming of Ethane and Butane with CO 2 over PtNi/CeO 2 Bimetallic Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Binhang; Yang, Xiaofang; Yao, Siyu

Dry reforming is a potential process to convert CO 2 and light alkanes into syngas (H 2 and CO), which can be subsequently transformed to chemicals and fuels. Here in this work, PtNi bimetallic catalysts have been investigated for dry reforming of ethane and butane using both model surfaces and supported powder catalysts. The PtNi bimetallic catalyst shows an improvement in both activity and stability as compared to the corresponding monometallic catalysts. The formation of PtNi alloy and the partial reduction of Ce 4+ to Ce 3+ under reaction conditions are demonstrated by in-situ Ambient Pressure X-ray Photoemission Spectroscopy (AP-XPS),more » X-ray Diffraction (XRD) and X-ray Absorption Fine Structure (XAFS) measurements. A Pt-rich bimetallic surface is revealed by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) following CO adsorption. Combined in-situ experimental results and Density Functional Theory (DFT) calculations suggest that the Pt-rich PtNi bimetallic surface structure would weaken the binding of surface oxygenates/carbon species and reduce the activation energy for C-C bond scission, leading to an enhanced dry reforming activity.« less

A comparative study of CeO2-Al2O3 support prepared with different methods and its application on MoO3/CeO2-Al2O3 catalyst for sulfur-resistant methanation

NASA Astrophysics Data System (ADS)

Jiang, Minhong; Wang, Baowei; Yao, Yuqin; Li, Zhenhua; Ma, Xinbin; Qin, Shaodong; Sun, Qi

2013-11-01

The CeO2-Al2O3 supports prepared with impregnation (IM), deposition precipitation (DP), and solution combustion (SC) methods for MoO3/CeO2-Al2O3 catalyst were investigated in the sulfur-resistant methanation. The supports and catalysts were characterized by N2-physisorption, transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy (RS), and temperature-programmed reduction (TPR). The N2-physisorption results indicated that the DP method was favorable for obtaining better textural properties. The TEM and RS results suggested that there is a CeO2 layer on the surface of the support prepared with DP method. This CeO2 layer not only prevented the interaction between MoO3 and γ-Al2O3 to form Al2(MoO4)3 species, but also improved the dispersion of MoO3 in the catalyst. Accordingly, the catalysts whose supports were prepared with DP method exhibited the best catalytic activity. The catalysts whose supports were prepared with SC method had the worst catalytic activity. This was caused by the formation of Al2(MoO4)3 and crystalline MoO3. Additionally, the CeO2 layer resulted in the instability of catalysts in reaction process. The increasing of calcination temperature of supports reduced the catalytic activity of all catalysts. The decrease extent of the catalysts whose supports were prepared with DP method was the lowest as the CeO2 layer prevented the interaction between MoO3 and γ-Al2O3.

Nitrogen-based catalysts for the electrochemical reduction of CO2 to CO.

PubMed

Tornow, Claire E; Thorson, Michael R; Ma, Sichao; Gewirth, Andrew A; Kenis, Paul J A

2012-12-05

The synthesis and application of carbon-supported, nitrogen-based organometallic silver catalysts for the reduction of CO(2) is studied using an electrochemical flow reactor. Their performance toward the selective formation of CO is similar to the performance achieved when using Ag as the catalyst, but comparatively at much lower silver loading. Faradaic efficiencies of the organometallic catalyst are higher than 90%, which are comparable to those of Ag. Furthermore, with the addition of an amine ligand to Ag/C, the partial current density for CO increases significantly, suggesting a possible co-catalyst mechanism. Additional improvements in activity and selectivity may be achieved as greater insight is obtained on the mechanism of CO(2) reduction and on how these complexes assemble on the carbon support.

Catalytic oxidation of soot on mesoporous ceria-based mixed oxides with cetyltrimethyl ammonium bromide (CTAB)-assisted synthesis.

PubMed

Zhu, Hongjian; Xu, Jing; Yichuan, Yuge; Wang, Zhongpeng; Gao, Yibo; Liu, Wei; Yin, Henan

2017-12-15

Mesoporous ceria and transition metal-doped ceria (M 0.1 Ce 0.9 O 2 (M=Mn, Fe, Co, Cu)) catalysts were synthesized via CTAB-assisted method. The physicochemical properties of the prepared catalysts were characterized by XRD, DLS analysis, SEM, BET, Raman, H 2 -TPR and in situ DRIFT techniques. The catalytic activity tests for soot oxidation were performed under tight contact of soot/catalyst mixtures in the presence of O 2 and NO+O 2 , respectively. The obtained results show that mesoporous ceria-based solid solutions can be formed with large surface areas and small crystallite size. Transition metals doping enhances the oxygen vacancies and improves redox properties of the solids, resulting in the increased NO oxidation capacity and NO x adsorption capacity. The soot oxidation activity in the presence of O 2 is enhanced by doping transition metal, which may be related to their high surface area, increased oxygen vacancies and improved redox properties. The soot combustion is accelerated by the NO 2 -assisted mechanism under NO+O 2 atmosphere, facilitating an intimate contact between the soot and the catalyst. Copyright © 2017 Elsevier Inc. All rights reserved.

Synthesis and Characterization of Cluster-Derived Supported Bimetallic Catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Richard D; Amiridis, Michael D

2008-10-10

New procedures have been developed for synthesizing di- and tri-metallic cluster complexes. The chemical properties of the new complexes have been investigated, particularly toward the activation of molecular hydrogen. These complexes were then converted into bi- and tri-metallic nanoparticles on silica and alumina supports. These nanoparticles were characterized by electron microscopy and were then tested for their ability to produce catalytic hydrogenation of unsaturated hydrocarbons and for the preferential oxidation of CO in the presence of hydrogen. The bi- and tri-metallic nanoparticles exhibited far superior activity and selectivity as hydrogenation catalysts when compared to the individual metallic components. It wasmore » found that the addition of tin greatly improved the selectivity of the catalysts for the hydrogenation of polyolefins. The addition of iron improves the catalysts for the selective oxidation of CO by platinum in the presence of hydrogen. The observations should lead to the development of lower cost routes to molecules that can be used to produce polymers and plastics for use by the general public and for procedures to purify hydrogen for use as an alternative energy in the hydrogen economy of the future.« less

A two step method to synthesize palladium-copper nanoparticles on reduced graphene oxide and their extremely high electrocatalytic activity for the electrooxidation of methanol and ethanol

NASA Astrophysics Data System (ADS)

Na, HeYa; Zhang, Lei; Qiu, HaiXia; Wu, Tao; Chen, MingXi; Yang, Nian; Li, LingZhi; Xing, FuBao; Gao, JianPing

2015-08-01

Palladium-copper nanoparticles (Pd-Cu NPs) supported on reduced graphene oxide (RGO) with different Pd/Cu ratios (Pd-Cu/RGO) were prepared by a two step method. The Pd-Cu/RGO hybrids were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction and thermogravimetric analyses. Cyclic voltammetry and chronoamperometry were used to investigate the electrochemical activities and stabilities of the Pd-Cu/RGO catalysts for the electro-oxidation of methanol and ethanol in alkaline media. The Pd-Cu/RGO catalysts exhibited high catalytic activities and good stabilities. This is because the catalysts have a bimetallic structure consisting of a small Pd-Cu core surrounded by a thin Pd-rich shell which improves the catalytic activities of the Pd-Cu/RGO hybrids. Thus they should be useful in direct methanol and ethanol fuel cells.

Toward highly efficient electrocatalyst for Li–O 2 batteries using biphasic N-doping cobalt@graphene multiple-capsule heterostructures

DOE PAGES

Tan, Guoqiang; Chong, Lina; Amine, Rachid; ...

2017-04-12

To promote lithium-oxygen batteries available for practical applications, the development of advanced cathode catalysts with low-cost, high activity and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport, and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@graphene multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium-oxygen cells. The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electro-active zones possible; furthermore, the colander-like porous electrode facilitates themore » oxygen diffusion, catalytic reaction, and stable deposition of discharge products. Finally, the electrode exhibits much improved electrocatalytic properties associated with unique morphologies of electrochemically grown lithium peroxides.« less

Toward highly efficient electrocatalyst for Li–O 2 batteries using biphasic N-doping cobalt@graphene multiple-capsule heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, Guoqiang; Chong, Lina; Amine, Rachid

To promote lithium-oxygen batteries available for practical applications, the development of advanced cathode catalysts with low-cost, high activity and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport, and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@graphene multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium-oxygen cells. The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electro-active zones possible; furthermore, the colander-like porous electrode facilitates themore » oxygen diffusion, catalytic reaction, and stable deposition of discharge products. Finally, the electrode exhibits much improved electrocatalytic properties associated with unique morphologies of electrochemically grown lithium peroxides.« less

Metal catalysts for steam reforming of tar derived from the gasification of lignocellulosic biomass.

PubMed

Li, Dalin; Tamura, Masazumi; Nakagawa, Yoshinao; Tomishige, Keiichi

2015-02-01

Biomass gasification is one of the most important technologies for the conversion of biomass to electricity, fuels, and chemicals. The main obstacle preventing the commercial application of this technology is the presence of tar in the product gas. Catalytic reforming of tar appears a promising approach to remove tar and supported metal catalysts are among the most effective catalysts. Nevertheless, improvement of catalytic performances including activity, stability, resistance to coke deposition and aggregation of metal particles, as well as catalyst regenerability is greatly needed. This review focuses on the design and catalysis of supported metal catalysts for the removal of tar in the gasification of biomass. The recent development of metal catalysts including Rh, Ni, Co, and their alloys for steam reforming of biomass tar and tar model compounds is introduced. The role of metal species, support materials, promoters, and their interfaces is described. Copyright © 2014 Elsevier Ltd. All rights reserved.

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

NASA Astrophysics Data System (ADS)

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-05-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

One-dimensional manganese-cobalt oxide nanofibres as bi-functional cathode catalysts for rechargeable metal-air batteries

PubMed Central

Jung, Kyu-Nam; Hwang, Soo Min; Park, Min-Sik; Kim, Ki Jae; Kim, Jae-Geun; Dou, Shi Xue; Kim, Jung Ho; Lee, Jong-Won

2015-01-01

Rechargeable metal-air batteries are considered a promising energy storage solution owing to their high theoretical energy density. The major obstacles to realising this technology include the slow kinetics of oxygen reduction and evolution on the cathode (air electrode) upon battery discharging and charging, respectively. Here, we report non-precious metal oxide catalysts based on spinel-type manganese-cobalt oxide nanofibres fabricated by an electrospinning technique. The spinel oxide nanofibres exhibit high catalytic activity towards both oxygen reduction and evolution in an alkaline electrolyte. When incorporated as cathode catalysts in Zn-air batteries, the fibrous spinel oxides considerably reduce the discharge-charge voltage gaps (improve the round-trip efficiency) in comparison to the catalyst-free cathode. Moreover, the nanofibre catalysts remain stable over the course of repeated discharge-charge cycling; however, carbon corrosion in the catalyst/carbon composite cathode degrades the cycling performance of the batteries. PMID:25563733

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

PubMed Central

Sun, Shuhui; Zhang, Gaixia; Gauquelin, Nicolas; Chen, Ning; Zhou, Jigang; Yang, Songlan; Chen, Weifeng; Meng, Xiangbo; Geng, Dongsheng; Banis, Mohammad N.; Li, Ruying; Ye, Siyu; Knights, Shanna; Botton, Gianluigi A.; Sham, Tsun-Kong; Sun, Xueliang

2013-01-01

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

Performance of Ni/dolomite pellet catalyst on gas distribution from cassava rhizome gasification with a modular fixed-bed gasifier.

PubMed

Sricharoenchaikul, V; Atong, D; Sornkade, P; Nisamaneenate, J

2017-05-01

Thermal conversion of cassava rhizome was performed using a modular downdraft gasifier with the addition of Ni-based catalysts as promising tar eliminating and produced gas upgrading techniques. The activities of a synthesized 5% Ni/dolomite pellet catalyst prepared by impregnation method were investigated in a secondary reactor downstream of the gasifier. High reforming activity of the Ni/dolomite pellet catalyst on tar reduction was achieved. The conversion to H 2 and CO was improved via steam reforming of methane and char reaction with CO 2 . Moreover, the formation of CH 4 and C x H y was diminished through the tar or condensable hydrocarbon reformed on the catalyst surface. The carbon and hydrogen conversions of cassava rhizome with prepared catalyst were 83.79% and 61.78%, respectively, at an air flow rate of 1.98 m 3 /hr. At this condition, tar formation was low, while the lower heating value was 4.39 MJ/m 3 and H 2 to CO molar ratio was 1.22. Generally, the addition of a catalyst not only enhanced gas production, but also reduced tar and particulate matter generation; thus, its implementation should help lessen the pollution control requirement and cost of operation, while allowing higher quality fuel gas production.

New insights into non-precious metal catalyst layer designs for proton exchange membrane fuel cells: Improving performance and stability

NASA Astrophysics Data System (ADS)

Banham, Dustin; Kishimoto, Takeaki; Sato, Tetsutaro; Kobayashi, Yoshikazu; Narizuka, Kumi; Ozaki, Jun-ichi; Zhou, Yingjie; Marquez, Emil; Bai, Kyoung; Ye, Siyu

2017-03-01

The activity of non-precious metal catalysts (NPMCs) has now reached a stage at which they can be considered as possible alternatives to Pt for some proton exchange membrane fuel cell (PEMFC) applications. However, despite significant efforts over the past 50 years on catalyst development, only limited studies have been performed on NPMC-based cathode catalyst layer (CCL) designs. In this work, an extensive ionomer study is performed to investigate the impact of ionomer equivalent weight on performance, which has uncovered two crucial findings. Firstly, it is demonstrated that beyond a critical CCL conductance, no further improvement in performance is observed. The procedure used to determine this critical conductance can be used by other researchers in this field to aid in their design of high performing NPMC-based CCLs. Secondly, it is shown that the stability of NPMC-based CCLs can be improved through the use of low equivalent weight ionomers. This represents a completely unexplored pathway for further stability improvements, and also provides new insights into the possible degradation mechanisms occurring in NPMC-based CCLs. These findings have broad implications on all future NPMC-based CCL designs.

Late-Transition-Metal-Modified β-Mo 2C Catalysts for Enhanced Hydrogenation during Guaiacol Deoxygenation

DOE PAGES

Baddour, Frederick G.; Witte, Vanessa A.; Nash, Connor P.; ...

2017-10-26

Molybdenum carbide has been identified as a promising bifunctional catalyst in the deoxygenation of a variety of pyrolysis vapor model compounds. Although high deoxygenation activity has been demonstrated, complementary hydrogenation activity has been limited, especially for lignin-derived, aromatic model compounds. The ability to control the relative site densities of acidic and hydrogenation functionalities represents a catalyst design challenge for these materials with the goal to improve hydrogenation activity under ex situ catalytic fast pyrolysis (CFP) conditions. Here in this paper, we demonstrate that the addition of Pt and Ni to Mo 2C resulted in an increase in the H*-site densitymore » with only a minor decrease in the acid-site density. In contrast, the addition of Pd did not significantly alter the H* or acid site densities. High conversions (>94%) and high selectivities to 0-oxygen products (>80%) were observed in guaiacol deoxygenation under ex situ CFP conditions (350 °C and 0.44 MPa H 2) for all catalysts. Pt addition resulted in the greatest deoxygenation, and site-time yields to hydrogenated products over the Pt/Mo 2C catalyst were increased to 0.048 s -1 compared to 0.015-0.019 s -1 for all other catalysts. The Pt/Mo 2C catalyst demonstrated the highest hydrogenation performance, but modification with Ni also significantly enhanced hydrogenation performance, representing a promising lower-cost alternative.« less

Late-Transition-Metal-Modified β-Mo 2C Catalysts for Enhanced Hydrogenation during Guaiacol Deoxygenation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baddour, Frederick G.; Witte, Vanessa A.; Nash, Connor P.

Molybdenum carbide has been identified as a promising bifunctional catalyst in the deoxygenation of a variety of pyrolysis vapor model compounds. Although high deoxygenation activity has been demonstrated, complementary hydrogenation activity has been limited, especially for lignin-derived, aromatic model compounds. The ability to control the relative site densities of acidic and hydrogenation functionalities represents a catalyst design challenge for these materials with the goal to improve hydrogenation activity under ex situ catalytic fast pyrolysis (CFP) conditions. Here in this paper, we demonstrate that the addition of Pt and Ni to Mo 2C resulted in an increase in the H*-site densitymore » with only a minor decrease in the acid-site density. In contrast, the addition of Pd did not significantly alter the H* or acid site densities. High conversions (>94%) and high selectivities to 0-oxygen products (>80%) were observed in guaiacol deoxygenation under ex situ CFP conditions (350 °C and 0.44 MPa H 2) for all catalysts. Pt addition resulted in the greatest deoxygenation, and site-time yields to hydrogenated products over the Pt/Mo 2C catalyst were increased to 0.048 s -1 compared to 0.015-0.019 s -1 for all other catalysts. The Pt/Mo 2C catalyst demonstrated the highest hydrogenation performance, but modification with Ni also significantly enhanced hydrogenation performance, representing a promising lower-cost alternative.« less

Lattice Matched Carbide–Phosphide Composites with Superior Electrocatalytic Activity and Stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Regmi, Yagya N.; Roy, Asa; King, Laurie A.

Composites of electrocatalytically active transition-metal compounds present an intriguing opportunity toward enhanced activity and stability. Here, to identify potentially scalable pairs of a catalytically active family of compounds, we demonstrate that phosphides of iron, nickel, and cobalt can be deposited on molybdenum carbide to generate nanocrystalline heterostructures. Composites synthesized via solvothermal decomposition of metal acetylacetonate salts in the presence of highly dispersed carbide nanoparticles show hydrogen evolution activities comparable to those of state-of-the-art non-noble metal catalysts. Investigation of the spent catalyst using high resolution microscopy and elemental analysis reveals that formation of carbide–phosphide composite prevents catalyst dissolution in acid electrolyte.more » Lattice mismatch between the two constituent electrocatalysts can be used to rationally improve electrochemical stability. Among the composites of iron, nickel, and cobalt phosphide, iron phosphide displays the lowest degree of lattice mismatch with molybdenum carbide and shows optimal electrochemical stability. Turnover rates of the composites are higher than that of the carbide substrate and compare favorably to other electrocatalysts based on earth-abundant elements. Lastly, our findings will inspire further investigation into composite nanocrystalline electrocatalysts that use molybdenum carbide as a stable catalyst support.« less

Lattice Matched Carbide–Phosphide Composites with Superior Electrocatalytic Activity and Stability

DOE PAGES

Regmi, Yagya N.; Roy, Asa; King, Laurie A.; ...

2017-10-19

Composites of electrocatalytically active transition-metal compounds present an intriguing opportunity toward enhanced activity and stability. Here, to identify potentially scalable pairs of a catalytically active family of compounds, we demonstrate that phosphides of iron, nickel, and cobalt can be deposited on molybdenum carbide to generate nanocrystalline heterostructures. Composites synthesized via solvothermal decomposition of metal acetylacetonate salts in the presence of highly dispersed carbide nanoparticles show hydrogen evolution activities comparable to those of state-of-the-art non-noble metal catalysts. Investigation of the spent catalyst using high resolution microscopy and elemental analysis reveals that formation of carbide–phosphide composite prevents catalyst dissolution in acid electrolyte.more » Lattice mismatch between the two constituent electrocatalysts can be used to rationally improve electrochemical stability. Among the composites of iron, nickel, and cobalt phosphide, iron phosphide displays the lowest degree of lattice mismatch with molybdenum carbide and shows optimal electrochemical stability. Turnover rates of the composites are higher than that of the carbide substrate and compare favorably to other electrocatalysts based on earth-abundant elements. Lastly, our findings will inspire further investigation into composite nanocrystalline electrocatalysts that use molybdenum carbide as a stable catalyst support.« less

The application of aberration-corrected electron microscopy to the characterization of gold-based catalysts

NASA Astrophysics Data System (ADS)

Herzing, Andrew A.

Electron microscopy has long been used to study the morphology of heterogeneous catalysts. Recent advances in electron optics now allow for the correction of the inherent spherical aberration (Cs) produced by the objective lens in the scanning transmission electron microscope (STEM, resulting in a significantly improved spatial resolution as well as the ability to use a much larger probe-current than was previously possible. In this thesis, the combination of high-angle annular dark-field (HAADF) imaging and microanalysis by x-ray energy dispersive spectroscopy (XEDS) in an aberration-corrected STEM has been applied for the first time to the characterization of gold-based heterogeneous catalysts. Multi-variate statistical analysis (MSA) has been employed in order to further improve the STEM-XEDS spectrum image data acquired with this technique. In addition, supplemental analysis using electron-energy loss spectroscopy (EELS) and energy-filtered transmission electron microscopy (EFTEM) in an aberration-corrected instrument has also been attempted. These techniques have proven extremely valuable in providing complimentary information to more traditional catalyst characterization techniques such as x-ray photoelectron spectroscopy and x-ray diffraction in four specific problems relating to catalysis. Firstly, the atomic-scale resolution of Cs-corrected HAADF imaging has been utilized to study Au/FeOx catalysts in order to determine the size and structure of the Au clusters present on the support surface. It was discovered that, while both inactive and active catalysts for low-temperature CO oxidation contained large Au particles (> 5 nm) and individual Au atoms, the active catalyst also contained sub-nm clusters comprised of only a few Au atoms. Secondly, novel CeO2 support materials for Au and Au-Pd catalysts were synthesized by precipitation with supercritical CO2. These supports were found to produce significantly more active catalysts than those based on CeO2 prepared using more traditional methods. The combination of STEM-HAADF imaging and XEDS mapping has been used to characterize these catalysts and a strong correlation between the catalytic activity and the enhanced degree of metal dispersion over the support is demonstrated. Thirdly, a systematic series of Au-Pd/Al2O3 catalysts has been studied in order to characterize the effects of various heat treatments on the development of core-shell morphologies within the bi-metallic particles and its subsequent effect on their catalytic performance for H2O 2 synthesis. STEM-XEDS spectrum imaging was employed in order to determine the degree of alloying and segregation behavior within the individual Au-Pd particles as a function of calcination/reduction temperature. It was found that the as prepared catalyst contained homogeneous Au-Pd alloy particles and that a Pd-rich shell/Au-rich core morphology gradually developed upon calcination. Subsequent reduction of the catalyst caused a large fraction of the particles to invert and form Pd-rich core/Au-rich shell structures. These changes are related to both the activity and stability of the catalyst. Finally, the washing of activated carbon support materials in acid was found to be extremely beneficial for producing Au-Pd catalysts for the direct synthesis of H2O2. STEM-HAADF imaging revealed that the acid-washing treatment increased the dispersion of the metal on the carbon supports. Aberration-corrected STEM-XEDS spectrum imaging demonstrated a strong size dependence of the Au-Pd particle composition. Crucially, the acid-washing pre-treatment enhanced the alloying of Au and Pd by suppressing the formation of large (> 25 nm) Au-rich particles. In summary, the application of aberration-corrected HAADF imaging and STEM-XEDS spectrum imaging to the characterization of Au-based catalysts has enhanced the understanding of the structural and chemical features that determine their catalytic behavior. Specifically, they have allowed us to achieve the following: (a) image individual metal atoms and clusters of just a few atoms dispersed in a real, high surface area catalyst, (b) detect and follow the development of core-shell structures in Au-Pd bi-metallic catalysts, (c) determine composition/size correlations in Au-Pd catalysts, (d) detect minor alloying elements in bi-metallic catalysts, (e) and chemically map atomic or near atomic dispersions of metals on oxide supports.

Highly Dispersed and Active ReOx on Alumina-Modified SBA-15 Silica for 2-Butanol Dehydration

DOE Office of Scientific and Technical Information (OSTI.GOV)

She, Xiaoyan; Kwak, Ja Hun; Sun, Junming

2012-05-23

SBA-15 silica supported rhenium catalysts were synthesized using solution-based atomic layer deposition method, and their activity and stability were studied in the acid-catalyzed 2-butanol dehydration. We find that ReOx/SBA-15 exhibited an extremely high initial activity but a fast deactivation for 2-butanol dehydration at 90-105 C. Fast deactivation was likely due to the sintering, sublimation, and reduction of rhenia as confirmed by TEM, elemental analysis, and in situ UV vis (DRS) measurements. To overcome these issues, ReOx/AlOx/SBA-15 catalysts with significantly improved stability were prepared by first modifying the surface identity of SBA-15 with alumina followed by dispersion of rhenia using atomicmore » layer deposition. The AlOx phase stabilizes the dispersion of small and uniform rhenia clusters (<2 nm) as as confirmed by TEM, STEM and UV-vis (DRS) characterizations. Additional 27Al MAS NMR characterization revealed that modification of the SBA-15 surface with alumina introduces a strong interaction between rhenia and alumina, which consequently improves the stability of supported rhenia catalysts by suppressing the sintering, sublimation, and reduction of rhenia albeit at a moderately reduced initial catalytic dehydration activity« less

Development of Molecular Catalysts to Bridge the Gap between Heterogeneous and Homogeneous Catalysts

NASA Astrophysics Data System (ADS)

Ye, Rong

Catalysts, heterogeneous, homogeneous, and enzymatic, are comprised of nanometer-sized inorganic and/or organic components. They share molecular factors including charge, coordination, interatomic distance, bonding, and orientation of catalytically active atoms. By controlling the governing catalytic components and molecular factors, catalytic processes of a multichannel and multiproduct nature could be run in all three catalytic platforms to create unique end-products. Unifying the fields of catalysis is the key to achieving the goal of 100% selectivity in catalysis. Recyclable catalysts, especially those that display selective reactivity, are vital for the development of sustainable chemical processes. Among available catalyst platforms, heterogeneous catalysts are particularly well-disposed toward separation from the reaction mixture via filtration methods, which renders them readily recyclable. Furthermore, heterogeneous catalysts offer numerous handles - some without homogeneous analogues - for performance and selectivity optimization. These handles include nanoparticle size, pore profile of porous supports, surface ligands and interface with oxide supports, and flow rate through a solid catalyst bed. Despite these available handles, however, conventional heterogeneous catalysts are themselves often structurally heterogeneous compared to homogeneous catalysts, which complicates efforts to optimize and expand the scope of their reactivity and selectivity. Ongoing efforts are aimed to address the above challenge by heterogenizing homogeneous catalysts, which can be defined as the modification of homogeneous catalysts to render them in a separable (solid) phase from the starting materials and products. Specifically, we grow the small nanoclusters in dendrimers, a class of uniform polymers with the connectivity of fractal trees and generally radial symmetry. Thanks to their dense multivalency, shape persistence and structural uniformity, dendrimers have proven to be versatile scaffolds for the synthesis and stabilization of small nanoclusters. Then these dendrimer-encapsulated metal clusters (DEMCs) are adsorbed onto mesoporous silica. Through this method, we have achieved selective transformations that had been challenging to accomplish in a heterogeneous setting, e.g. pi-bond activation and aldol reactions. Extensive investigation into the catalytic systems under reaction conditions allowed us to correlate the structural features (e.g. oxidation states) of the catalysts and their activity. Moreover, we have demonstrated that supported DEMCs are also excellent catalysts for typical heterogeneous reactions, including hydrogenation and alkane isomerization. Critically, these investigations also confirmed that the supported DEMCs are heterogeneous and stable against leaching. Catalysts optimization is achieved through the modulation of various parameters. The clusters are oxidized (e.g., with PhICl2) or reduced (e.g., with H2) in situ. Changing the dendrimer properties (e.g., generation, terminal functional groups) is analogous to ligand modification in homogeneous catalysts, which affect both catalytic activity and selectivity. Similarly, pore size of the support is another factor in determining product distribution. In a flow reactor, the flow rate is adjusted to control the residence time of the starting material and intermediates, and thus the final product selectivity. Our approach to heterogeneous catalysis affords various advantages: (1) the catalyst system can tap into the reactivity typical to homogeneous catalysts, which conventional heterogeneous catalysts could not achieve; (2) unlike most homogeneous catalysts with comparable performance, the heterogenized homogeneous catalysts can be recycled; (3) improved activity or selectivity compared to conventional homogeneous catalysts is possible because of uniquely heterogeneous parameters for optimization. While localized surface plasmon resonance (LSPR) provides a powerful platform for nanoparticle catalysis, our studies suggest that in some cases interband transitions should be considered as an alternative mechanism of light-driven nanoparticle catalysis. The benefits already demonstrated by plasmonic nanostructures as catalysts provided the impetus for examining complementary activation modes based on the metal nanoparticle itself. Leveraging these transitions has the potential to provide a means to highly active catalysis modes that would otherwise be challenging to access. For example, for the preparation of highly active metal catalysts on a subnanosized scale is challenging, thus limiting their exploitation and study in catalysis. Our work suggests a novel and facile strategy for the formation of highly active gold nanocluster catalysts by light illumination of the interband transitions in the presence of the appropriate substrate.

Production of Biodiesel by Esterification of Free Fatty Acid over Solid Catalyst from Biomass Waste

NASA Astrophysics Data System (ADS)

Mukti, N. I. F.; Sutrisno, B.; Hidayat, A.

2018-05-01

Recently, low cost feedstocks have been utilized to replace vegetable oils in order to improve the economic feasibility of biodiesel. The esterification of free fatty acid (FFA) on Palm Fatty Acid Distillate (PFAD) with methanol using solid catalyst generated from bagasse fly ash is a promising method to convert FFA into biodiesel. In this research, the esterification of FFA on PFAD using the sulfonated bagasse fly ash catalyst was studied. The performances of the catalysts were evaluated in terms of the reaction temperatures, the molar ratios of methanol to PFAD, and the catalyst loading. The effects of the mass ratio of catalyst to oil (1-10%), the molar ratio of methanol to oil (6:1-12:1), and the reaction temperature (40-60°C) were studied for the conversion of PFAD to optimize the reaction conditions. The results showed that the optimum conditions were methanol to PFAD molar ratio of 12:1, the amount of catalyst of 10%wt. of PFAD, and reaction temperature of 6°C. The reusability of the solid acid carbon catalysts was also studied in this work. The catalytic activity decreased up to 38% after third cycle. The significant decline in catalyst esterification activity was due to acid site leaching. The physico-characteristics and acid site densities were analyzed by Nitrogen gas adsorption, surface functional groups by Fourier transform infrared spectroscopy (FT-IR), elemental analysis using X-ray fluorescent (XRF), and acid-base back titration methods for determination of acid density.

Fuel cell performance of palladium-platinum core-shell electrocatalysts synthesized in gram-scale batches

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khateeb, Siddique; Su, Dong; Guerreo, Sandra

This article presents the performance of palladium-platinum core-shell catalysts (Pt/Pd/C) for oxygen reduction synthesized in gram-scale batches in both liquid cells and polymer-electrolyte membrane fuel cells. Core-shell catalyst synthesis and characterization, ink fabrication, and cell assembly details are discussed. The Pt mass activity of the Pt/Pd core-shell catalyst was 0.95 A mg –1 at 0.9 V measured in liquid cells (0.1 M HClO4), which was 4.8 times higher than a commercial Pt/C catalyst. The performances of Pt/Pd/C and Pt/C in large single cells (315 cm 2) were assessed under various operating conditions. The core-shell catalyst showed consistently higher performance thanmore » commercial Pt/C in fuel cell testing. A 20–60 mV improvement across the whole current density range was observed on air. Sensitivities to temperature, humidity, and gas composition were also investigated and the core-shell catalyst showed a consistent benefit over Pt under all conditions. However, the 4.8 times activity enhancement predicated by liquid cell measurements was not fully realized in fuel cells.« less

Alternative Fuel Research in Fischer-Tropsch Synthesis

NASA Technical Reports Server (NTRS)

Surgenor, Angela D.; Klettlinger, Jennifer L.; Yen, Chia H.; Nakley, Leah M.

2011-01-01

NASA Glenn Research Center has recently constructed an Alternative Fuels Laboratory which is solely being used to perform Fischer-Tropsch (F-T) reactor studies, novel catalyst development and thermal stability experiments. Facility systems have demonstrated reliability and consistency for continuous and safe operations in Fischer-Tropsch synthesis. The purpose of this test facility is to conduct bench scale Fischer-Tropsch (F-T) catalyst screening experiments while focusing on reducing energy inputs, reducing CO2 emissions and increasing product yields within the F-T process. Fischer-Tropsch synthesis is considered a gas to liquid process which reacts syn-gas (a gaseous mixture of hydrogen and carbon monoxide), over the surface of a catalyst material which is then converted into liquids of various hydrocarbon chain length and product distributions1. These hydrocarbons can then be further processed into higher quality liquid fuels such as gasoline and diesel. The experiments performed in this laboratory will enable the investigation of F-T reaction kinetics to focus on newly formulated catalysts, improved process conditions and enhanced catalyst activation methods. Currently the facility has the capability of performing three simultaneous reactor screening tests, along with a fourth fixed-bed reactor used solely for cobalt catalyst activation.

Fuel cell performance of palladium-platinum core-shell electrocatalysts synthesized in gram-scale batches

DOE PAGES

Khateeb, Siddique; Su, Dong; Guerreo, Sandra; ...

2016-05-03

This article presents the performance of palladium-platinum core-shell catalysts (Pt/Pd/C) for oxygen reduction synthesized in gram-scale batches in both liquid cells and polymer-electrolyte membrane fuel cells. Core-shell catalyst synthesis and characterization, ink fabrication, and cell assembly details are discussed. The Pt mass activity of the Pt/Pd core-shell catalyst was 0.95 A mg –1 at 0.9 V measured in liquid cells (0.1 M HClO4), which was 4.8 times higher than a commercial Pt/C catalyst. The performances of Pt/Pd/C and Pt/C in large single cells (315 cm 2) were assessed under various operating conditions. The core-shell catalyst showed consistently higher performance thanmore » commercial Pt/C in fuel cell testing. A 20–60 mV improvement across the whole current density range was observed on air. Sensitivities to temperature, humidity, and gas composition were also investigated and the core-shell catalyst showed a consistent benefit over Pt under all conditions. However, the 4.8 times activity enhancement predicated by liquid cell measurements was not fully realized in fuel cells.« less

Hierarchically porous Fe-N-C derived from covalent-organic materials as a highly efficient electrocatalyst for oxygen reduction

NASA Astrophysics Data System (ADS)

Zuo, Quan; Zhao, Pingping; Luo, Wei; Cheng, Gongzhen

2016-07-01

Developing high-performance non-precious catalysts to replace platinum as oxygen reduction reaction (ORR) catalysts is still a big scientific and technological challenge. Herein, we report a simple method for the synthesis of a FeNC catalyst with a 3D hierarchically micro/meso/macro porous network and high surface area through a simple carbonization method by taking the advantages of a high specific surface area and diverse pore dimensions in 3D porous covalent-organic material. The resulting FeNC-900 electrocatalyst with improved reactant/electrolyte transport and sufficient active site exposure, exhibits outstanding ORR activity with a half-wave potential of 0.878 V, ca. 40 mV more positive than Pt/C for ORR in alkaline solution, and a half-wave potential of 0.72 V, which is comparable to that of Pt/C in acidic solution. In particular, the resulting FeNC-900 exhibits a much higher stability and methanol tolerance than those of Pt/C, which makes it among the best non-precious catalysts ever reported for ORR.Developing high-performance non-precious catalysts to replace platinum as oxygen reduction reaction (ORR) catalysts is still a big scientific and technological challenge. Herein, we report a simple method for the synthesis of a FeNC catalyst with a 3D hierarchically micro/meso/macro porous network and high surface area through a simple carbonization method by taking the advantages of a high specific surface area and diverse pore dimensions in 3D porous covalent-organic material. The resulting FeNC-900 electrocatalyst with improved reactant/electrolyte transport and sufficient active site exposure, exhibits outstanding ORR activity with a half-wave potential of 0.878 V, ca. 40 mV more positive than Pt/C for ORR in alkaline solution, and a half-wave potential of 0.72 V, which is comparable to that of Pt/C in acidic solution. In particular, the resulting FeNC-900 exhibits a much higher stability and methanol tolerance than those of Pt/C, which makes it among the best non-precious catalysts ever reported for ORR. Electronic supplementary information (ESI) available: Fig. S1-S12 and Tables S1 and S2. See DOI: 10.1039/c6nr03273g

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yung, Matthew M.; Stanton, Alexander R.; Iisa, Kristiina

Metal-impregnated (Ni or Ga) ZSM-5 catalysts were studied for biomass pyrolysis vapor upgrading to produce hydrocarbons using three reactors constituting a 100 000x change in the amount of catalyst used in experiments. Catalysts were screened for pyrolysis vapor phase upgrading activity in two small-scale reactors: (i) a Pyroprobe with a 10 mg catalyst in a fixed bed and (ii) a fixed-bed reactor with 500 mg of catalyst. The best performing catalysts were then validated with a larger scale fluidized-bed reactor (using ~1 kg of catalyst) that produced measurable quantities of bio-oil for analysis and evaluation of mass balances. Despite somemore » inherent differences across the reactor systems (such as residence time, reactor type, analytical techniques, mode of catalyst and biomass feed) there was good agreement of reaction results for production of aromatic hydrocarbons, light gases, and coke deposition. Relative to ZSM-5, Ni or Ga addition to ZSM-5 increased production of fully deoxygenated aromatic hydrocarbons and light gases. In the fluidized bed reactor, Ga/ZSM-5 slightly enhanced carbon efficiency to condensed oil, which includes oxygenates in addition to aromatic hydrocarbons, and reduced oil oxygen content compared to ZSM-5. Ni/ZSM-5, while giving the highest yield of fully deoxygenated aromatic hydrocarbons, gave lower overall carbon efficiency to oil but with the lowest oxygen content. Reaction product analysis coupled with fresh and spent catalyst characterization indicated that the improved performance of Ni/ZSM-5 is related to decreasing deactivation by coking, which keeps the active acid sites accessible for the deoxygenation and aromatization reactions that produce fully deoxygenated aromatic hydrocarbons. The addition of Ga enhances the dehydrogenation activity of the catalyst, which leads to enhanced olefin formation and higher fully deoxygenated aromatic hydrocarbon yields compared to unmodified ZSM-5. Catalyst characterization by ammonia temperature programmed desorption, surface area measurements, and postreaction temperature-programmed oxidation (TPO) also showed that the metal-modified zeolites retained a greater percentage of their initial acidity and surface area, which was consistent between the reactor scales. These results demonstrate that the trends observed with smaller (milligram to gram) catalyst reactors are applicable to larger, more industrially relevant (kg) scales to help guide catalyst research toward application.« less

Photodecolorisation of melanoidins in vinasse with illuminated TiO2-ZnO/activated carbon composite.

PubMed

Otieno, Benton O; Apollo, Seth O; Naidoo, Bobby E; Ochieng, Aoyi

2017-06-07

A hybrid photo-catalyst, TiO 2 -ZnO, was synthesized by immobilizing ZnO on commercial TiO 2 (aeroxide P25). Activated carbon (AC) was subsequently used to support the hybrid, thus forming a TiO 2 -ZnO/AC composite catalyst. Fourier transform infrared (FTIR) analysis and scanning electron microscopy integrated with energy-dispersive X-ray spectroscopy (SEM-EDX) investigations revealed successful catalyst synthesis. Optical properties of the hybrid determined from photoluminescence (PL) and Ultraviolet-visible (UV-vis) spectroscopy confirmed a restrained recombination of electron-hole pairs and reduced energy band gap due to a successful heterojunction formation. The prepared catalysts were used to photodecolorise vinasse in a 12-W UVC batch photoreactor. TiO 2 -ZnO had improved photocatalytic activity compared with TiO 2 and ZnO separately. On supporting the hybrid onto AC, both adsorption and photocatalytic activities were further enhanced with improved overall color removal of 86% from 68%. Photodecolorisation followed the pseudo-first-order reaction model with the rate constant ([Formula: see text]) observed decreasing from 0.0701 to 0.0436 min -1 on increasing the initial concentration from 5,000 to 14,000 ppm. The UV process was found to be 33-fold less energy intensive for color reduction as compared to total organic carbon (TOC) reduction. Formation of nitrates during the photodecolorisation process was attributed to the mineralization of nitrogen heteroatoms in the color-causing melanoidin compounds.

Iridium-Based Nanowires as Highly Active, Oxygen Evolution Reaction Electrocatalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alia, Shaun M.; Shulda, Sarah; Ngo, Chilan

Iridium-nickel (Ir-Ni) and iridium-cobalt (Ir-Co) nanowires have been synthesized by galvanic displacement and studied for their potential to increase the performance and durability of electrolysis systems. Performances of Ir-Ni and Ir-Co nanowires for the oxygen evolution reaction (OER) have been measured in rotating disk electrode half-cells and single-cell electrolyzers and compared with commercial baselines and literature references. The nanowire catalysts showed improved mass activity, by more than an order of magnitude compared with commercial Ir nanoparticles in half-cell tests. The nanowire catalysts also showed greatly improved durability, when acid-leached to remove excess Ni and Co. Both Ni and Co templatesmore » were found to have similarly positive impacts, although specific differences between the two systems are revealed. In single-cell electrolysis testing, nanowires exceeded the performance of Ir nanoparticles by 4-5 times, suggesting that significant reductions in catalyst loading are possible without compromising performance.« less

Iridium-Based Nanowires as Highly Active, Oxygen Evolution Reaction Electrocatalysts

DOE PAGES

Alia, Shaun M.; Shulda, Sarah; Ngo, Chilan; ...

2018-01-22

Iridium-nickel (Ir-Ni) and iridium-cobalt (Ir-Co) nanowires have been synthesized by galvanic displacement and studied for their potential to increase the performance and durability of electrolysis systems. Performances of Ir-Ni and Ir-Co nanowires for the oxygen evolution reaction (OER) have been measured in rotating disk electrode half-cells and single-cell electrolyzers and compared with commercial baselines and literature references. The nanowire catalysts showed improved mass activity, by more than an order of magnitude compared with commercial Ir nanoparticles in half-cell tests. The nanowire catalysts also showed greatly improved durability, when acid-leached to remove excess Ni and Co. Both Ni and Co templatesmore » were found to have similarly positive impacts, although specific differences between the two systems are revealed. In single-cell electrolysis testing, nanowires exceeded the performance of Ir nanoparticles by 4-5 times, suggesting that significant reductions in catalyst loading are possible without compromising performance.« less

Fundamentals of Hydrocarbon Upgrading to Liquid Fuels and Commodity Chemicals over Catalytic Metallic Nanoparticles

NASA Astrophysics Data System (ADS)

Chen, Tao

Promising new technologies for biomass conversion into fuels and chemical feedstocks rely on the production of bio-oils, which need to be upgraded in order to remove oxygen-containing hydrocarbons and water. A high oxygen concentration makes bio-oils acidic and corrosive, unstable during storage, and less energetically valuable per unit weight than petroleum-derived hydrocarbons. Although there are efficient processes for the production of bio-oils, there are no efficient technologies for their upgrading. Current technologies utilize traditional petroleum refining catalysts, which are not optimized for biomass processing. New upgrading technologies are, therefore, urgently needed for development of sustainable energy resources. Development of such new technologies, however, is severely hindered by a lack of fundamental understanding of how oxygen and oxygen-containing hydrocarbons derived from biomass interact with promising noble-metal catalysts. In this study, kinetic reaction measurements, catalyst characterization and quantum chemical calculations using density functional theory were combined for determining adsorption modes and reaction mechanisms of hydrocarbons in the presence of oxygen on surfaces of catalytic noble-metal nanoparticles. The results were used for developing improved catalyst formulations and optimization of reaction conditions. The addition of molybdenum to platinum catalysts was shown to improve catalytic activity, stability, and selectivity in hydrodeoxygenation of acetic acid, which served as a model biomass compound. The fundamental results that describe interactions of oxygen and hydrocarbons with noble-metal catalysts were extended to other reactions and fields of study: evaluation of the reaction mechanism for hydrogen peroxide decomposition, development of improved hydrogenation catalysts and determination of adsorption modes of a spectroscopic probe molecule.

Silver Nanoparticles with Surface-Bonded Oxygen for Highly Selective CO 2 Reduction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Kun; Kharel, Priti; Peng, Yande

Here, the surface electronic structures of catalysts need to be carefully engineered in CO 2 reduction reaction (CO 2RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lows the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO 2RR reaction intermediates, which may significantly improve the catalyst activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO 2RR performances. A comparative investigation on air-annealedmore » Ag (Air-Ag) catalyst with or without the post-treatment of H 2 thermal annealing (H 2-Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O-Ag δ+) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rather than H 2 in CO 2RR electrolysis. As a result, while the maximal CO Faradaic efficiency of H 2-Ag is at ~ 30 %, the Air-Ag catalyst presented a high CO selectivity of more than 90 % under a current density of ~ 21 mA/cm 2.« less

Silver Nanoparticles with Surface-Bonded Oxygen for Highly Selective CO 2 Reduction

DOE PAGES

Jiang, Kun; Kharel, Priti; Peng, Yande; ...

2017-09-12

Here, the surface electronic structures of catalysts need to be carefully engineered in CO 2 reduction reaction (CO 2RR), where the hydrogen evolution side reaction usually takes over under a significant overpotential, and thus dramatically lows the reaction selectivity. Surface oxides can play a critical role in tuning the surface oxidation state of metal catalysts for a proper binding with CO 2RR reaction intermediates, which may significantly improve the catalyst activity and selectivity. Here, we demonstrate the importance of surface-bonded oxygen on silver nanoparticles in altering the reaction pathways and improving the CO 2RR performances. A comparative investigation on air-annealedmore » Ag (Air-Ag) catalyst with or without the post-treatment of H 2 thermal annealing (H 2-Ag) was performed. In Air-Ag, the subsurface chemically bonded O species (O-Ag δ+) was identified by angle resolved X-ray photoelectron spectroscopy and X-ray absorption spectroscopy techniques, and contributed to the improved CO selectivity rather than H 2 in CO 2RR electrolysis. As a result, while the maximal CO Faradaic efficiency of H 2-Ag is at ~ 30 %, the Air-Ag catalyst presented a high CO selectivity of more than 90 % under a current density of ~ 21 mA/cm 2.« less

Hydrodeoxygenation of prairie cordgrass bio-oil over Ni based activated carbon synergistic catalysts combined with different metals.

PubMed

Cheng, Shouyun; Wei, Lin; Zhao, Xianhui; Kadis, Ethan; Cao, Yuhe; Julson, James; Gu, Zhengrong

2016-06-25

Bio-oil can be upgraded through hydrodeoxygenation (HDO). Low-cost and effective catalysts are crucial for the HDO process. In this study, four inexpensive combinations of Ni based activated carbon synergistic catalysts including Ni/AC, Ni-Fe/AC, Ni-Mo/AC and Ni-Cu/AC were evaluated for HDO of prairie cordgrass (PCG) bio-oil. The tests were carried out in the autoclave under mild operating conditions with 500psig of H2 pressure and 350°C temperature. The catalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and transmission electron microscope (TEM). The results show that all synergistic catalysts had significant improvements on the physicochemical properties (water content, pH, oxygen content, higher heating value and chemical compositions) of the upgraded PCG bio-oil. The higher heating value of the upgraded bio-oil (ranging from 29.65MJ/kg to 31.61MJ/kg) improved significantly in comparison with the raw bio-oil (11.33MJ/kg), while the oxygen content reduced to only 21.70-25.88% from 68.81% of the raw bio-oil. Compared to raw bio-oil (8.78% hydrocarbons and no alkyl-phenols), the Ni/AC catalysts produced the highest content of gasoline range hydrocarbons (C6-C12) at 32.63% in the upgraded bio-oil, while Ni-Mo/AC generated the upgraded bio-oil with the highest content of gasoline blending alkyl-phenols at 38.41%. Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of nitrogen-containing impurities on the activity of perovskitic catalysts for the catalytic combustion of methane.

PubMed

Buchneva, Olga; Gallo, Alessandro; Rossetti, Ilenia

2012-11-05

LaMnO(3), either pure or doped with 10 mol % Sr, has been prepared by flame pyrolysis in nanostructured form. Such catalysts have been tested for the catalytic flameless combustion of methane, achieving very high catalytic activity. The resistance toward poisoning by some model N-containing impurities has been checked in order to assess the possibility of operating the flameless catalytic combustion with biogas, possibly contaminated by S- or N-based compounds. This would be a significant improvement from the environmental point of view because the application of catalytic combustion to gas turbines would couple improved energy conversion efficiency and negligible noxious emissions, while the use of biogas would open the way to energy production from a renewable source by means of very efficient technologies. A different behavior has been observed for the two catalysts; namely, the undoped sample was more or less heavily poisoned, whereas the Sr-doped sample showed slightly increasing activity upon dosage of N-containing compounds. A possible reaction mechanism has been suggested, based on the initial oxidation of the organic backbone, with the formation of NO. The latter may adsorb more or less strongly depending on the availability of surface oxygen vacancies (i.e., depending on doping). Decomposition of NO may leave additional activated oxygen species on the surface, available for low-temperature methane oxidation and so improving the catalytic performance.

Aqueous-Phase Hydrogenolysis of Glycerol over Re Promoted Ru Catalysts Encapuslated in Porous Silica Nanoparticles

PubMed Central

Li, Kuo-Tseng; Yen, Ruey-Hsiang

2018-01-01

Activity improvement of Ru-based catalysts is needed for efficient production of valuable chemicals from glycerol hydrogenolysis. In this work, a series of Re promoted Ru catalysts encapuslated in porous silica nanoparticles (denoted as Re-Ru@SiO2) were prepared by coating silica onto the surface of chemically reduced Ru-polyvinylpyrrolidone colloids, and were used to catalyze the conversion of glycerol to diols and alcohols in water. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR) were used to characterize these nanoparticles. Effects of Ru/Si atomic ratio, Re addition, glycerol and catalyst concentrations, reaction time, temperature, and hydrogen pressure were investigated. Re addition retarded the reduction of ruthenium oxide, but increased the catalyst reactivity for glycerol hydrogenolysis. Due to its greater Ru content, Re-Ru@ SiO2 showed much better activity (reacted at much lower temperature) and more yields of 1,2-propanediol and overall liquid-phase products than Re-Ru/SiO2 (prepared by conventional impregnation method) reported before. The rate of glycerol disappearance exhibited first-order dependence on glycerol concentration and hydrogen pressure, with an activation energy of 107.8 kJ/mol. The rate constant increased linearly with increasing Ru/Si atomic ratio and catalyst amount. The yield of overall liquid-phase products correlated well with glycerol conversion. PMID:29522432

Enhanced activity and stability of La-doped CeO2 monolithic catalysts for lean-oxygen methane combustion.

PubMed

Zhu, Wenjun; Jin, Jianhui; Chen, Xiao; Li, Chuang; Wang, Tonghua; Tsang, Chi-Wing; Liang, Changhai

2018-02-01

Effective utilization of coal bed methane is very significant for energy utilization and environment protection. Catalytic combustion of methane is a promising way to eliminate trace amounts of oxygen in the coal bed methane and the key to this technology is the development of high-efficiency catalysts. Herein, we report a series of Ce 1-x La x O 2-δ (x = 0-0.8) monolithic catalysts for the catalytic combustion of methane, which are prepared by citric acid method. The structural characterization shows that the substitution of La enhance the oxygen vacancy concentration and reducibility of the supports and promote the migration of the surface oxygen, as a result improve the catalytic activity of CeO 2 . M-Ce 0.8 La 0.2 O 2-δ (monolithic catalyst, Ce 0.8 La 0.2 O 2-δ coated on cordierite honeycomb) exhibits outstanding activity for methane combustion, and the temperature for 10 and 90% methane conversion are 495 and 580 °C, respectively. Additionally, Ce 0.8 La 0.2 O 2-δ monolithic catalyst presents excellent stability at high temperature. These Ce 1-x La x O 2-δ monolithic materials with a small amount of La incorporation therefore show promises as highly efficient solid solution catalysts for lean-oxygen methane combustion. Graphical abstract ᅟ.

In Situ Electrochemical Oxidation Tuning of Transition Metal Disulfides to Oxides for Enhanced Water Oxidation

DOE PAGES

Chen, Wei; Wang, Haotian; Li, Yuzhang; ...

2015-07-15

The development of catalysts with earth-abundant elements for efficient oxygen evolution reactions is of paramount significance for clean and sustainable energy storage and conversion devices. Our group demonstrated recently that the electrochemical tuning of catalysts via lithium insertion and extraction has emerged as a powerful approach to improve catalytic activity. Here we report a novel in situ electrochemical oxidation tuning approach to develop a series of binary, ternary, and quaternary transition metal (e.g., Co, Ni, Fe) oxides from their corresponding sulfides as highly active catalysts for much enhanced water oxidation. The electrochemically tuned cobalt–nickel–iron oxides grown directly on the three-dimensionalmore » carbon fiber electrodes exhibit a low overpotential of 232 mV at current density of 10 mA cm –2, small Tafel slope of 37.6 mV dec –1, and exceptional long-term stability of electrolysis for over 100 h in 1 M KOH alkaline medium, superior to most non-noble oxygen evolution catalysts reported so far. The materials evolution associated with the electrochemical oxidation tuning is systematically investigated by various characterizations, manifesting that the improved activities are attributed to the significant grain size reduction and increase of surface area and electroactive sites. This work provides a promising strategy to develop electrocatalysts for large-scale water-splitting systems and many other applications.« less

Toluene decomposition performance and NOx by-product formation during a DBD-catalyst process.

PubMed

Guo, Yufang; Liao, Xiaobin; Fu, Mingli; Huang, Haibao; Ye, Daiqi

2015-02-01

Characteristics of toluene decomposition and formation of nitrogen oxide (NOx) by-products were investigated in a dielectric barrier discharge (DBD) reactor with/without catalyst at room temperature and atmospheric pressure. Four kinds of metal oxides, i.e., manganese oxide (MnOx), iron oxide (FeOx), cobalt oxide (CoOx) and copper oxide (CuO), supported on Al2O3/nickel foam, were used as catalysts. It was found that introducing catalysts could improve toluene removal efficiency, promote decomposition of by-product ozone and enhance CO2 selectivity. In addition, NOx was suppressed with the decrease of specific energy density (SED) and the increase of humidity, gas flow rate and toluene concentration, or catalyst introduction. Among the four kinds of catalysts, the CuO catalyst showed the best performance in NOx suppression. The MnOx catalyst exhibited the lowest concentration of O3 and highest CO2 selectivity but the highest concentration of NOx. A possible pathway for NOx production in DBD was discussed. The contributions of oxygen active species and hydroxyl radicals are dominant in NOx suppression. Copyright © 2014. Published by Elsevier B.V.

Non-conventional Pt-Cu alloy/carbon paper electrochemical catalyst formed by electrodeposition using hydrogen bubble as template

NASA Astrophysics Data System (ADS)

Kim, Youngkwang; Lee, Hyunjoon; Lim, Taeho; Kim, Hyun-Jong; Kwon, Oh Joong

2017-10-01

With emerging stability issues in fuel cell technology, a non-conventional catalyst not supported on carbon materials has been highlighted because it can avoid negative influences of carbon support materials on the stability, such as carbon corrosion. The nanostructured thin film catalyst is representative of non-conventional catalysts, which shows improved stability, enhanced mass specific activity, and fast mass transfer at high current densities. However, the nanostructured thin film catalyst usually requires multi-step processes for fabrication, making its mass production complex and irreproducible. We introduce a Pt-Cu alloy nanostructured thin film catalyst, which can be simply prepared by electrodeposition. By using hydrogen bubbles as a template, a three-dimensional free-standing foam of Cu was electrodeposited directly on the micro-porous layer/carbon paper and it was then displaced with Pt by simple immersion. The structure characterization revealed that a porous thin Pt-Cu alloy catalyst layer was successfully formed on the micro-porous layer/carbon paper. The synthesized Pt-Cu alloy catalyst exhibited superior durability compared to a conventional Pt/C in single cell test.

Summary of engineering-scale experiments for the Solar Detoxification of Water project

NASA Astrophysics Data System (ADS)

Pacheco, J. E.; Yellowhorse, L.

1992-03-01

This report contains a summary of large-scale experiments conducted at Sandia National Laboratories under the Solar Detoxification of Water project. The objectives of the work performed were to determine the potential of using solar radiation to destroy organic contaminants in water by photocatalysis and to develop the process and improve its performance. For these experiments, we used parabolic troughs to focus sunlight onto glass pipes mounted at the trough's focus. Water spiked with a contaminant and containing suspended titanium dioxide catalyst was pumped through the illuminated glass pipe, activating the catalyst with the ultraviolet portion of the solar spectrum. The activated catalyst creates oxidizers that attack and destroy the organics. Included in this report are a summary and discussion of the implications of experiments conducted to determine: the effect of process kinetics on the destruction of chlorinated solvents (such as trichloroethylene, perchloroethylene, trichloroethane, methylene chloride, chloroform and carbon tetrachloride), the enhancement due to added hydrogen peroxide, the optimal catalyst loading, the effect of light intensity, the inhibition due to bicarbonates, and catalyst issues.

Metal Doping Effect of the M-Co2P/Nitrogen-Doped Carbon Nanotubes (M = Fe, Ni, Cu) Hydrogen Evolution Hybrid Catalysts.

PubMed

Pan, Yuan; Liu, Yunqi; Lin, Yan; Liu, Chenguang

2016-06-08

The enhancement of catalytic performance of cobalt phosphide-based catalysts for the hydrogen evolution reaction (HER) is still challenging. In this work, the doping effect of some transition metal (M = Fe, Ni, Cu) on the electrocatalytic performance of the M-Co2P/NCNTs (NCNTs, nitrogen-doped carbon nanotubes) hybrid catalysts for the HER was studied systematically. The M-Co2P/NCNTs hybrid catalysts were synthesized via a simple in situ thermal decomposition process. A series of techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma-optical emission spectrometry, transmission electron microscopy, and N2 sorption were used to characterize the as-synthesized M-Co2P/NCNTs hybrid catalysts. Electrochemical measurements showed the catalytic performance according to the following order of Fe-Co2P/NCNTs > Ni-Co2P/NCNTs > Cu-Co2P/NCNTs, which can be ascribed to the difference of structure, morphology, and electronic property after doping. The doping of Fe atoms promote the growth of the [111] crystal plane, resulting in a large specific area and exposing more catalytic active sites. Meanwhile, the Fe(δ+) has the highest positive charge among all the M-Co2P/NCNTs hybrid catalysts after doping. All these changes can be used to contribute the highest electrocatalytic activity of the Fe-Co2P/NCNTs hybrid catalyst for HER. Furthermore, an optimal HER electrocatalytic activity was obtained by adjusting the doping ratio of Fe atoms. Our current research indicates that the doping of metal is also an important strategy to improve the electrocatalytic activity for the HER.

In situ DRIFTS investigation of NH3-SCR reaction over CeO2/zirconium phosphate catalyst

NASA Astrophysics Data System (ADS)

Zhang, Qiulin; Fan, Jie; Ning, Ping; Song, Zhongxian; Liu, Xin; Wang, Lanying; Wang, Jing; Wang, Huimin; Long, Kaixian

2018-03-01

A series of ceria modified zirconium phosphate catalysts were synthesized for selective catalytic reduction of NO with ammonia (NH3-SCR). Over 98% NOx conversion and 98% N2 selectivity were obtained by the CeO2/ZrP catalyst with 20 wt.% CeO2 loading at 250-425 °C. The interaction between CeO2 and zirconium phosphate enhanced the redox abilities and surface acidities of the catalysts, resulting in the improvement of NH3-SCR activity. The in situ DRIFTS results indicated that the NH3-SCR reaction over the catalysts followed both Eley-Rideal and Langmuir-Hinshelwood mechanisms. The amide (sbnd NH2) groups and the NH4+ bonded to Brønsted acid sites were the important intermediates of Eley-Rideal mechanism.

Ozonation of return activated sludge for disintegration and solubilisation with synthesized titanium oxide as catalyst

NASA Astrophysics Data System (ADS)

Sarif, S. F. Z. Mohd; Alias, S. S.; Ridwan, F. Muhammad; Salim, K. S. Ku; Abidin, C. Z. A.; Ali, U. F. Md.

2018-03-01

Ozonation of activated sludge in the present of titanium dioxide (TiO2) as catalyst to enhance the production of hydroxyl radical was evaluated in comparison to the sole ozonation process. In this process, the catalytic ozontion showed improvement in increasing ozone consumption and improving activated sludge disintegration and solubilisation. The reduction of total suspended solid (TSS), volatile suspended solid (VSS) and soluble chemical oxygen demand (SCOD) solubilisation was better in the catalytic ozonation system. Initial pH 7 of activated sludge was found best to disintegrate and solubilise the sludge flocs. However upon additional of sodium hydroxide (NaOH) in pH adjustment enhanced the solubilisation of organic matter from the flocs and cells, making the initial pH 9 is the best condition for activated sludge solubilisation. Yet the initial pH 7 of activated sludge supernatant was the best condition to achieve SCOD solubilisation due to sludge floc disintegration, when it had stronger correlation between TSS reduction and SCOD solubilisation (R2=0.961). Lower amount of catalyst of 100 mgTiO2/gTSS was found to disintegrate and solubilise the activated sludge better with 30.4% TSS reduction and 25.2% SCOD solubilisation efficiency, compared to 200 mgTiO2/gTSS with 21.9% and 17.1% TSS reduction and SCOD solubilisation, respectively.

Synthesis of a molecularly defined single-active site heterogeneous catalyst for selective oxidation of N-heterocycles.

PubMed

Zhang, Yujing; Pang, Shaofeng; Wei, Zhihong; Jiao, Haijun; Dai, Xingchao; Wang, Hongli; Shi, Feng

2018-04-13

Generally, a homogeneous catalyst exhibits good activity and defined active sites but it is difficult to recycle. Meanwhile, a heterogeneous catalyst can easily be reused but its active site is difficult to reveal. It is interesting to bridge the gap between homogeneous and heterogeneous catalysis via controllable construction of a heterogeneous catalyst containing defined active sites. Here, we report that a molecularly defined, single-active site heterogeneous catalyst has been designed and prepared via the oxidative polymerization of maleimide derivatives. These polymaleimide derivatives can be active catalysts for the selective oxidation of heterocyclic compounds to quinoline and indole via the recycling of -C=O and -C-OH groups, which was confirmed by tracing the reaction with GC-MS using maleimide as the catalyst and by FT-IR analysis with polymaleimide as the catalyst. These results might promote the development of heterogeneous catalysts with molecularly defined single active sites exhibiting a comparable activity to homogeneous catalysts.

Catalytic decomposition of gaseous 1,2-dichlorobenzene over CuOx/TiO₂ and CuOx/TiO₂-CNTs catalysts: Mechanism and PCDD/Fs formation.

PubMed

Wang, Qiu-lin; Huang, Qun-xing; Wu, Hui-fan; Lu, Sheng-yong; Wu, Hai-long; Li, Xiao-dong; Yan, Jian-hua

2016-02-01

Gaseous 1,2-dichlorobenzene (1,2-DCBz) was catalytically decomposed in a fixed-bed catalytic reactor using composite copper-based titanium oxide (CuOx/TiO2) catalysts with different copper ratios. Carbon nanotubes (CNTs) were introduced to produce novel CuOx/TiO2-CNTs catalysts by the sol-gel method. The catalytic performances of CuOx/TiO2 and CuOx/TiO2-CNTs on 1,2-DCBz oxidative destruction under different temperatures (150-350 °C) were experimentally examined and the correlation between catalyst structure and catalytic activity was characterized and the role of oxygen in catalytic reaction was discussed. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) generation during 1,2-DCBz catalytic oxidation by CuOx/TiO2-CNTs composite catalyst was also examined. Results indicate that the 1,2-DCBz destruction/removal efficiencies of CuOx (4 wt%)/TiO2 catalyst at 150 °C and 350 °C with a GHSV of 3400 h(-1) are 59% and 94% respectively and low-temperature (150 °C) catalytic activity of CuOx/TiO2 on 1,2-DCBz oxidation can be improved from 59 to 77% when CNTs are introduced. Furthermore, oxygen either in catalyst or from reaction atmosphere is indispensible in reaction. The former is offered to activate and oxidize the 1,2-DCBz adsorbed on catalyst, thus can be generally consumed during reaction and the oxygen content in catalyst is observed lost from 39.9 to 35.0 wt% after reacting under inert atmosphere; the latter may replenish the vacancy in catalyst created by the consumed oxygen thus extends the catalyst life and raises the destruction/removal efficiency. The introduction of CNTs also increases the Cu(2+)/Cu(+) ratio, chemisorbed oxygen concentration and surface lattice oxygen binding energy which are closely related with catalytic activity. PCDD/Fs is confirmed to be formed when 1,2-DCBz catalytically oxidized by CuOx/TiO2-CNTs composite catalyst with sufficient oxygen (21%), proper temperature (350 °C) and high concentration of 1,2-DCBz feed (120 ppm). Copyright © 2015 Elsevier Ltd. All rights reserved.

MnO2/CNT supported Pt and PtRu nanocatalysts for direct methanol fuel cells.

PubMed

Zhou, Chunmei; Wang, Hongjuan; Peng, Feng; Liang, Jiahua; Yu, Hao; Yang, Jian

2009-07-07

Pt/MnO2/carbon nanotube (CNT) and PtRu/MnO2/CNT nanocomposites were synthesized by successively loading hydrous MnO2 and Pt (or PtRu alloy) nanoparticles on CNTs and were used as anodic catalysts for direct methanol fuel cells (DMFCs). The existence of MnO2 on the surface of CNTs effectively increases the proton conductivity of the catalyst, which then could remarkably improve the performance of the catalyst in methanol electro-oxidation. As a result, Pt/MnO2/CNTs show higher electrochemical active surface area and better methanol electro-oxidation activity, compared with Pt/CNTs. As PtRu alloy nanoparticles were deposited on the surface of MnO2/CNTs instead of Pt, the PtRu/MnO2/CNT catalyst shows not only excellent electro-oxidation activity to methanol with forward anodic peak current density of 901 A/gPt but also good CO oxidation ability with lower preadsorbed CO oxidation onset potential (0.33 V vs Ag/AgCl) and peak potential (0.49 V vs Ag/AgCl) at room temperature.

Enhanced Activity and Durability of Nanosized Pt-SnO2/IrO2/CNTs Catalyst for Methanol Electrooxidation.

PubMed

Wang, Hongjuan; Wang, Xiaohui; Zheng, Jiadao; Peng, Feng; Yu, Hao

2015-05-01

Pt-SnO2/IrO2/CNTs anode catalyst for direct methanol fuel cell was designed and prepared with IrO2/CNTs as support for the subsequent immobilization of Pt and SnO2 at the same time. The structure of the catalysts and their catalytic performance in methanol electrooxidation were investigated and the roles of IrO2 and SnO2 in methanol electrooxidation were discussed as well. Results show that Pt-SnO2/IrO2/CNTs catalyst exhibits the best activity and durability for methanol electrooxidation when compared with Pt/CNTs, Pt/IrO2/CNTs and Pt-SnO2/CNTs. According to the results of electrochemical tests and physicochemical characterizations, the enhancements of Pt-SnO2/IrO2/CNTs were attributed to the special properties of IrO2 and SnO2, in which IrO2 mainly increases the methanol oxidation activity and SnO2 mainly improves the CO oxidation ability and durability. Therefore, Pt-SnO2/IrO2/CNTs exhibits excellent performance for methanol oxidation with higher electrocatalytic activity (I(f) of 1054 A g(Pt(-1)) and powerful anti-poisoning ability (the onset potential for CO oxidation of 0.3 V) and outstanding durability (the sustained time t in CP of 617 s), revealing a suitable anode catalyst for DMFCs.

Conversion of biomass-derived sorbitol to glycols over carbon-materials supported Ru-based catalysts

PubMed Central

Guo, Xingcui; Guan, Jing; Li, Bin; Wang, Xicheng; Mu, Xindong; Liu, Huizhou

2015-01-01

Ruthenium (Ru) supported on activated carbon (AC) and carbon nanotubes (CNTs) was carried out in the hydrogenolysis of sorbitol to ethylene glycol (EG) and 1,2-propanediol (1,2-PD) under the promotion of tungsten (WOx) species and different bases. Their catalytic activities and glycols selectivities strongly depended on the support properties and location of Ru on CNTs, owning to the altered metal-support interactions and electronic state of ruthenium. Ru located outside of the tubes showed excellent catalytic performance than those encapsulated inside the nanotubes. Additionally, the introduction of WOx into Ru/CNTs significantly improved the hydrogenolysis activities, and a complete conversion of sorbitol with up to 60.2% 1,2-PD and EG yields was obtained on RuWOx/CNTs catalyst upon addition of Ca(OH)2. Stability study showed that this catalyst was highly stable against leaching and poisoning and could be recycled several times. PMID:26578426

Conversion of biomass-derived sorbitol to glycols over carbon-materials supported Ru-based catalysts

NASA Astrophysics Data System (ADS)

Guo, Xingcui; Guan, Jing; Li, Bin; Wang, Xicheng; Mu, Xindong; Liu, Huizhou

2015-11-01

Ruthenium (Ru) supported on activated carbon (AC) and carbon nanotubes (CNTs) was carried out in the hydrogenolysis of sorbitol to ethylene glycol (EG) and 1,2-propanediol (1,2-PD) under the promotion of tungsten (WOx) species and different bases. Their catalytic activities and glycols selectivities strongly depended on the support properties and location of Ru on CNTs, owning to the altered metal-support interactions and electronic state of ruthenium. Ru located outside of the tubes showed excellent catalytic performance than those encapsulated inside the nanotubes. Additionally, the introduction of WOx into Ru/CNTs significantly improved the hydrogenolysis activities, and a complete conversion of sorbitol with up to 60.2% 1,2-PD and EG yields was obtained on RuWOx/CNTs catalyst upon addition of Ca(OH)2. Stability study showed that this catalyst was highly stable against leaching and poisoning and could be recycled several times.

Boron-doped graphene as promising support for platinum catalyst with superior activity towards the methanol electrooxidation reaction

NASA Astrophysics Data System (ADS)

Sun, Yongrong; Du, Chunyu; An, Meichen; Du, Lei; Tan, Qiang; Liu, Chuntao; Gao, Yunzhi; Yin, Geping

2015-12-01

We report the synthesis of boron-doped graphene by thermally annealing the mixture of graphene oxide and boric acid, and its usage as the support of Pt catalyst towards the methanol oxidation reaction. The composition, structure and morphology of boron-doped graphene and its supported Pt nanoparticles (Pt/BG) are characterized by transmission electron microscopy, inductively coupled plasma mass spectrometry, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. It is revealed that boron atoms are doped into graphene network in the form of BC2O and BCO2 bonds, which lead to the increase in defect sites and facilitate the subsequent deposition of Pt nanoparticles. Therefore, the Pt/BG catalyst presents smaller particle size and narrower size distribution than the graphene supported Pt (Pt/G) catalyst. When evaluated as the electrocatalyst for the methanol oxidation reaction, the Pt/BG catalyst exhibits excellent electrochemical activity and stability demonstrated by cyclic voltammetry and chronoamperometry tests. The enhanced activity is mainly ascribed to the electronic interaction between boron-doped graphene and Pt nanoparticles, which lowers the d-band center of Pt and thus weakens the absorption of the poisoning intermediate CO. Our work provides an alternative approach of improving the reaction kinetics for the oxidation of small organic molecules.

The enhancement of CuO modified V2O5-WO3/TiO2 based SCR catalyst for Hg° oxidation in simulated flue gas

NASA Astrophysics Data System (ADS)

Chen, Chuanmin; Jia, Wenbo; Liu, Songtao; Cao, Yue

2018-04-01

CuO modified V2O5-WO3/TiO2 based SCR catalysts prepared by improved impregnation method were investigated to evaluate the catalytic activity for elemental mercury (Hg°) oxidation in simulated flue gas at 150-400 °C. Nitrogen adsorption, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the catalysts. It was found that V0.8WTi-Cu3 catalyst exhibited the superior Hg° oxidation activity and wide operating temperature window at the gas hourly space velocity (GHSV) of 3 × 105 h-1. The BET and XRD results showed that CuO was well loaded and highly dispersed on the catalysts surface. The XPS results suggested that the addition of CuO generated abundant chemisorbed oxygen, which was due to the synergistic effect between CuO and V2O5. The existence of the redox cycle of V4+ + Cu2+ ↔ V5+ + Cu+ in V0.8WTi-Cu3 catalyst enhanced Hg° oxidation activity. The effects of flue gas components (O2, NO, SO2 and H2O) on Hg° oxidation over V0.8WTi-Cu3 catalyst were also explored. Moreover, the co-presence of NO and NH3 remarkably inhibited Hg° oxidation, which was due to the competitive adsorption and reduction effect of NH3 at SCR condition. Fortunately, this inhibiting effect was gradually scavenged with the decrease of GHSV. The mechanism of Hg° oxidation was also investigated.

Molecular system identification for enzyme directed evolution and design

NASA Astrophysics Data System (ADS)

Guan, Xiangying; Chakrabarti, Raj

2017-09-01

The rational design of chemical catalysts requires methods for the measurement of free energy differences in the catalytic mechanism for any given catalyst Hamiltonian. The scope of experimental learning algorithms that can be applied to catalyst design would also be expanded by the availability of such methods. Methods for catalyst characterization typically either estimate apparent kinetic parameters that do not necessarily correspond to free energy differences in the catalytic mechanism or measure individual free energy differences that are not sufficient for establishing the relationship between the potential energy surface and catalytic activity. Moreover, in order to enhance the duty cycle of catalyst design, statistically efficient methods for the estimation of the complete set of free energy differences relevant to the catalytic activity based on high-throughput measurements are preferred. In this paper, we present a theoretical and algorithmic system identification framework for the optimal estimation of free energy differences in solution phase catalysts, with a focus on one- and two-substrate enzymes. This framework, which can be automated using programmable logic, prescribes a choice of feasible experimental measurements and manipulated input variables that identify the complete set of free energy differences relevant to the catalytic activity and minimize the uncertainty in these free energy estimates for each successive Hamiltonian design. The framework also employs decision-theoretic logic to determine when model reduction can be applied to improve the duty cycle of high-throughput catalyst design. Automation of the algorithm using fluidic control systems is proposed, and applications of the framework to the problem of enzyme design are discussed.

Degradation of atenolol via heterogeneous activation of persulfate by using BiOCl@Fe3O4 catalyst under simulated solar light irradiation.

PubMed

Shi, Yahong; Chen, Hongche; Wu, Yanlin; Dong, Wenbo

2018-01-01

Efficient oxidative degradation of pharmaceutical pollutants in aquatic environments is of great importance. This study used magnetic BiOCl@Fe 3 O 4 catalyst to activate persulfate (PS) under simulated solar light irradiation. This degradation system was evaluated using atenolol (ATL) as target pollutant. Four reactive species were identified in the sunlight/BiOCl@Fe 3 O 4 /PS system. The decreasing order of the contribution of each reactive species on ATL degradation was as follows: h +  ≈ HO ·  > O 2 ·-  > SO 4 ·- . pH significantly influenced ATL degradation, and an acidic condition favored the reaction. High degradation efficiencies were obtained at pH 2.3-5.5. ATL degradation rate increased with increased catalyst and PS contents. Moreover, ATL mineralization was higher in the sunlight/BiOCl@Fe 3 O 4 /PS system than in the sunlight/BiOCl@Fe 3 O 4 or sunlight/PS system. Nine possible intermediate products were identified through LC-MS analysis, and a degradation pathway for ATL was proposed. The BiOCl@Fe 3 O 4 nanomagnetic composite catalyst was synthesized in this work. This catalyst was easily separated and recovered from a treated solution by using a magnet, and it demonstrated a high catalytic activity. Increased amount of the BiOCl@Fe 3 O 4 catalyst obviously accelerated the efficiency of ATL degradation, and the reusability of the catalyst allowed the addition of a large dosage of BiOCl@Fe 3 O 4 to improve the degradation efficiency.

Heterogeneous Electrocatalyst of Palladium-Cobalt-Phosphorus on Carbon Support for Oxygen Reduction Reaction in High Temperature Proton Exchange Membrane Fuel Cells.

PubMed

You, Dae Jong; Pak, Chanho; Jin, Seon-Ah; Lee, Kang Hee; Kwon, Kyungjung; Choi, Kyoung Hwan; Heo, Pil Won; Jang, Hongchul; Kim, Jun Young; Kim, Ji Man

2016-05-01

Palladium-cobalt-phosphorus (PdCoP) catalysts supported on carbon (Ketjen Black) were investigated as a cathode catalyst for oxygen reduction reaction (ORR) in high temperature proton exchange membrane fuel cells (HT-PEMFCs). The PdCoP catalyst was synthesized via a modified polyol process in teflon-sealed reactor by microwave-heating. From X-ray diffraction and transmission electron microscopic analysis, the PdCoP catalyst exhibits a face-centered cubic structure, similar to palladium (Pd), which is attributed to form a good solid solution of Co atoms and P atoms in the Pd lattice. The PdCoP nanoparticles with average diameter of 2.3 nm were uniformly distributed on the carbon support. The electrochemical surface area (ECSA) and ORR activity of PdP, PdCo and PdCoP catalysts were measured using a rotating disk electrode technique with cyclic voltammetry and the linear sweep method. The PdCoP catalysts showed the highest performances for ECSA and ORR, which might be attributed both to formation of small nanoparticle by phosphorus atom and to change in lattice constant of Pd by cobalt atom. Furthermore, The HT-PEMFCs single cell performance employing PdCoP catalyst exhibited an enhanced cell performance compared to a single cell using the PdP and PdCo catalysts. This result indicates the importance of electric and geometric control of Pd alloy nanoparticles that can improve the catalytic activity. This synergistic combination of Co and P with Pd could provide the direction of development of non-Pt catalyst for fuel cell system.

Improved Anode for a Direct Methanol Fuel Cell

NASA Technical Reports Server (NTRS)

Valdez, Thomas; Narayanan, Sekharipuram

2005-01-01

A modified chemical composition has been devised to improve the performance of the anode of a direct methanol fuel cell. The main feature of the modified composition is the incorporation of hydrous ruthenium oxide into the anode structure. This modification can reduce the internal electrical resistance of the cell and increase the degree of utilization of the anode catalyst. As a result, a higher anode current density can be sustained with a smaller amount of anode catalyst. These improvements can translate into a smaller fuel-cell system and higher efficiency of conversion. Some background information is helpful for understanding the benefit afforded by the addition of hydrous ruthenium oxide. The anode of a direct methanol fuel cell sustains the electro-oxidation of methanol to carbon dioxide in the reaction CH3OH + H2O--->CO2 + 6H(+) + 6e(-). An electrocatalyst is needed to enable this reaction to occur. The catalyst that offers the highest activity is an alloy of approximately equal numbers of atoms of the noble metals platinum and ruthenium. The anode is made of a composite material that includes high-surface-area Pt/Ru alloy particles and a proton-conducting ionomeric material. This composite is usually deposited onto a polymer-electrolyte (proton-conducting) membrane and onto an anode gas-diffusion/current-collector sheet that is subsequently bonded to the proton-conducting membrane by hot pressing. Heretofore, the areal density of noble-metal catalyst typically needed for high performance has been about 8 mg/cm2. However, not all of the catalyst has been utilized in the catalyzed electro-oxidation reaction. Increasing the degree of utilization of the catalyst would make it possible to improve the performance of the cell for a given catalyst loading and/or reduce the catalyst loading (thereby reducing the cost of the cell). The use of carbon and possibly other electronic conductors in the catalyst layer has been proposed for increasing the utilization of the catalyst by increasing electrical connectivity between catalyst particles. However, the relatively low density of carbon results in thick catalyst layers that impede the mass transport of methanol to the catalytic sites. Also, the electrical conductivity of carbon is less than 1/300th of typical metals. Furthermore, the polymer-electrolyte membrane material is acidic and most metals are not chemically stable in contact with it. Finally, a material that conducts electrons (but not protons) does not contribute to the needed transport of protons produced in the electro-oxidation reaction.

Highly Stable and Active Catalyst for Sabatier Reactions

NASA Technical Reports Server (NTRS)

Hu, Jianli; Brooks, Kriston P.

2012-01-01

Highly active Ru/TiO2 catalysts for Sabatier reaction have been developed. The catalysts have shown to be stable under repeated shutting down/startup conditions. When the Ru/TiO2 catalyst is coated on the engineered substrate Fe-CrAlY felt, activity enhancement is more than doubled when compared with an identically prepared engineered catalyst made from commercial Degussa catalyst. Also, bimetallic Ru-Rh/TiO2 catalysts show high activity at high throughput.

Cobalt-Catalyzed C(sp(2))-H Borylation: Mechanistic Insights Inspire Catalyst Design.

PubMed

Obligacion, Jennifer V; Semproni, Scott P; Pappas, Iraklis; Chirik, Paul J

2016-08-24

A comprehensive study into the mechanism of bis(phosphino)pyridine (PNP) cobalt-catalyzed C-H borylation of 2,6-lutidine using B2Pin2 (Pin = pinacolate) has been conducted. The experimentally observed rate law, deuterium kinetic isotope effects, and identification of the catalyst resting state support turnover limiting C-H activation from a fully characterized cobalt(I) boryl intermediate. Monitoring the catalytic reaction as a function of time revealed that borylation of the 4-position of the pincer in the cobalt catalyst was faster than arene borylation. Cyclic voltammetry established the electron withdrawing influence of 4-BPin, which slows the rate of C-H oxidative addition and hence overall catalytic turnover. This mechanistic insight inspired the next generation of 4-substituted PNP cobalt catalysts with electron donating and sterically blocking methyl and pyrrolidinyl substituents that exhibited increased activity for the C-H borylation of unactivated arenes. The rationally designed catalysts promote effective turnover with stoichiometric quantities of arene substrate and B2Pin2. Kinetic studies on the improved catalyst, 4-(H)2BPin, established a change in turnover limiting step from C-H oxidative addition to C-B reductive elimination. The iridium congener of the optimized cobalt catalyst, 6-(H)2BPin, was prepared and crystallographically characterized and proved inactive for C-H borylation, a result of the high kinetic barrier for reductive elimination from octahedral Ir(III) complexes.

Free-standing ternary NiWP film for efficient water oxidation reaction

NASA Astrophysics Data System (ADS)

Yang, Yunpeng; Zhou, Kuo; Ma, Lili; Liang, Yanqin; Yang, Xianjin; Cui, Zhenduo; Zhu, Shengli; Li, Zhaoyang

2018-03-01

High-efficient catalysts for oxygen evolution reaction (OER) is of great concern in improving energy efficiency for water splitting. Here we report a high-performance OER electrocatalyst of nickel-tungsten-phosphorus (NiWP) film prepared by template method. This free-standing ternary electrocatalyst exhibits a remarkable electrocatalytic activity of OER in alkaline medium due to the synergetic effect among these elements and the good electrical conductivity. The reported NiWP composite catalyst has an overpotential of as low as 0.4 V (vs. RHE) at 30 mA cm-2, better than that of the commercial RuO2 catalyst. Moreover, a small charge transfer resistance of 4.06 Ω and a Tafel slope of 68 mV dec-1 demonstrate the outstanding catalytic activity.

Improving the durability of methanol oxidation reaction electro-catalysts through the modification of carbon architectures

NASA Astrophysics Data System (ADS)

Wood, Kevin N.

Carbon materials represent one of the largest areas of studied research today, having integrated applications stretching from energy production and storage to medical use and far beyond. One of these many intriguing applications is fuel cells, which offers the promise of clean electricity through a direct electrochemical energy conversion process. Unfortunately, at the present time the cost per watt-hour produced by fuel cells is more expensive than conventional methods of energy production/storage (i.e. combustion engines, batteries, etc.). Under the umbrella of fuel cell systems, methanol is a promising fuel source because of its high energy density and convenience of direct liquid fuel operation. In this field, recent advancements are bringing direct methanol fuel cells (DMFCs) closer to commercial viability. However, just as in other fuel cell systems, further improvements are greatly needed, particularly in the area of catalyst durability. This need for improved durability has led to increased research activity focused on improving catalyst stability and utilization. This thesis explores one of the most promising areas of enhancing catalyst-support interactions; namely, modification of carbon support architectures. Through the use of heteroatom modifiers, such as nitrogen, fuel cell support systems can be enhanced in such a way as to improve metal nucleation and growth, catalyst durability and catalytic activity. To this end, this thesis employs advanced characterization techniques to study the changes in catalyst particle morphology before and after nitrogen modification of the support structure. These results clearly show the beneficial effects of nitrogen moieties on carbon structures and help elucidate the effects of nitrogen on the stability of supported catalytic nanoparticles systems. Similarly, the novel concept of post-modifying commercially available supported catalysts with nitrogen ion implantation gives further insight into the behavior of modified support structures. This result shows a method by which current industry leading benchmarks can be improved, in some cases by up to 100%. This thesis also explores the intriguing prospect of heteroatom modification beyond the effects of just nitrogen. Specifically, the consequences of halide functionalization are explored and shown to significantly improve durability, even to a greater extent than nitrogen modification. In total these results give great promise for the future of fuel cell technology and the field of carbon modification in general. While the techniques and results presented in this thesis are employed to study durability in direct methanol fuel cells, the benefits of heteroatom modified carbon structures can be applied to other polymer electrolyte fuel cells and beyond. Many other devices and applications, including batteries, supercapacitors, hydrogen storage, and even biosensing and drug delivery can benefit from the work discussed within these pages.

Effect of preparation method and CuO promotion in the conversion of ethanol into 1,3-butadiene over SiO₂-MgO catalysts.

PubMed

Angelici, Carlo; Velthoen, Marjolein E Z; Weckhuysen, Bert M; Bruijnincx, Pieter C A

2014-09-01

Silica-magnesia (Si/Mg=1:1) catalysts were studied in the one-pot conversion of ethanol to butadiene. The catalyst synthesis method was found to greatly influence morphology and performance, with materials prepared through wet-kneading performing best both in terms of ethanol conversion and butadiene yield. Detailed characterization of the catalysts synthesized through co-precipitation or wet-kneading allowed correlation of activity and selectivity with morphology, textural properties, crystallinity, and acidity/basicity. The higher yields achieved with the wet-kneaded catalysts were attributed to a morphology consisting of SiO2 spheres embedded in a thin layer of MgO. The particle size of the SiO2 catalysts also influenced performance, with catalysts with smaller SiO2 spheres showing higher activity. Temperature-programmed desorption (TPD) measurements showed that best butadiene yields were obtained with SiO2-MgO catalysts characterized by an intermediate amount of acidic and basic sites. A Hammett indicator study showed the catalysts' pK(a) value to be inversely correlated with the amount of dehydration by-products formed. Butadiene yields could be further improved by the addition of 1 wt% of CuO as promoter to give butadiene yields and selectivities as high as 40% and 53%, respectively. The copper promoter boosts the production of the acetaldehyde intermediate changing the rate-determining step of the process. TEM-energy-dispersive X-ray (EDX) analyses showed CuO to be present on both the SiO2 and MgO components. UV/Vis spectra of promoted catalysts in turn pointed at the presence of cluster-like CuO species, which are proposed to be responsible for the increased butadiene production. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Characterization and Catalytic Upgrading of Aqueous Stream Carbon from Catalytic Fast Pyrolysis of Biomass

DOE PAGES

Starace, Anne K.; Black, Brenna A.; Lee, David D.; ...

2017-10-23

Catalytic fast pyrolysis (CFP) of biomass produces a liquid product consisting of organic and aqueous streams. The organic stream is typically slated for hydrotreating to produce hydrocarbon biofuels, while the aqueous stream is considered a waste stream, resulting in the loss of residual biogenic carbon. Here, we report the detailed characterization and catalytic conversion of a CFP wastewater stream with the ultimate aim to improve overall biomass utilization within a thermochemical biorefinery. An aqueous stream derived from CFP of beech wood was comprehensively characterized, quantifying 53 organic compounds to a total of 17% organics. The most abundant classes of compoundsmore » are acids, aldehydes, and alcohols. The most abundant components identified in the aqueous stream were C1-C2 organics, comprising 6.40% acetic acid, 2.16% methanol, and 1.84% formaldehyde on wet basis. The CFP aqueous stream was catalytically upgraded to olefins and aromatic hydrocarbons using a Ga/HZSM-5 catalyst at 500 degrees C. When the conversion yield of the upgraded products was measured with fresh, active catalyst, 33% of the carbon in the aqueous stream was recovered as aromatic hydrocarbons and 29% as olefins. The majority of the experiments were conducted using a molecular beam mass spectrometer and separate GC-MS/FID experiments were used to confirm the assignments and quantification of products with fresh excess catalyst. The recovered 62% carbon in the form of olefins and aromatics can be used to make coproducts and/or fuels potentially improving biorefinery economics and sustainability. Spent catalysts were collected after exposure to varying amounts of the feed, and were characterized using multipoint-Brunauer-Emmett-Teller (BET) adsorption, ammonia temperature programmed desorption (TPD), and thermogravimetric analysis (TGA) to monitor deactivation of Ga/HZSM-5. These characterization data revealed that deactivation was caused by coke deposits, which blocked access to active sites of the catalyst and spent catalysts regained total activity after regeneration.« less

Characterization and Catalytic Upgrading of Aqueous Stream Carbon from Catalytic Fast Pyrolysis of Biomass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Starace, Anne K.; Black, Brenna A.; Lee, David D.

Catalytic fast pyrolysis (CFP) of biomass produces a liquid product consisting of organic and aqueous streams. The organic stream is typically slated for hydrotreating to produce hydrocarbon biofuels, while the aqueous stream is considered a waste stream, resulting in the loss of residual biogenic carbon. Here, we report the detailed characterization and catalytic conversion of a CFP wastewater stream with the ultimate aim to improve overall biomass utilization within a thermochemical biorefinery. An aqueous stream derived from CFP of beech wood was comprehensively characterized, quantifying 53 organic compounds to a total of 17% organics. The most abundant classes of compoundsmore » are acids, aldehydes, and alcohols. The most abundant components identified in the aqueous stream were C1-C2 organics, comprising 6.40% acetic acid, 2.16% methanol, and 1.84% formaldehyde on wet basis. The CFP aqueous stream was catalytically upgraded to olefins and aromatic hydrocarbons using a Ga/HZSM-5 catalyst at 500 degrees C. When the conversion yield of the upgraded products was measured with fresh, active catalyst, 33% of the carbon in the aqueous stream was recovered as aromatic hydrocarbons and 29% as olefins. The majority of the experiments were conducted using a molecular beam mass spectrometer and separate GC-MS/FID experiments were used to confirm the assignments and quantification of products with fresh excess catalyst. The recovered 62% carbon in the form of olefins and aromatics can be used to make coproducts and/or fuels potentially improving biorefinery economics and sustainability. Spent catalysts were collected after exposure to varying amounts of the feed, and were characterized using multipoint-Brunauer-Emmett-Teller (BET) adsorption, ammonia temperature programmed desorption (TPD), and thermogravimetric analysis (TGA) to monitor deactivation of Ga/HZSM-5. These characterization data revealed that deactivation was caused by coke deposits, which blocked access to active sites of the catalyst and spent catalysts regained total activity after regeneration.« less

Systematic Structure–Property Relationship Studies in Palladium-Catalyzed Methane Complete Combustion

DOE PAGES

Willis, Joshua J.; Gallo, Alessandro; Sokaras, Dimosthenis; ...

2017-10-09

To limit further rising levels in methane emissions from stationary and mobile sources and to enable promising technologies based on methane, the development of efficient combustion catalysts that completely oxidize CH 4 to CO 2 and H 2O at low temperatures in the presence of high steam concentrations is required. Palladium is widely considered as one of the most promising materials for this reaction, and a better understanding of the factors affecting its activity and stability is crucial to design even more improved catalysts that efficiently utilize this precious metal. Here we report a study of the effect of threemore » important variables (particle size, support, and reaction conditions including water) on the activity of supported Pd catalysts. We use uniform palladium nanocrystals as catalyst precursors to prepare a library of well-defined catalysts to systematically describe structure–property relationships with help from theory and in situ X-ray absorption spectroscopy. With this approach, we confirm that PdO is the most active phase and that small differences in reaction rates as a function of size are likely due to variations in the surface crystal structure. We further demonstrate that the support exerts a limited influence on the PdO activity, with inert (SiO 2), acidic (Al 2O 3), and redox-active (Ce 0.8Zr 0.2O 2) supports providing similar rates, while basic (MgO) supports show remarkably lower activity. Finally, we show that the introduction of steam leads to a considerable decrease in rates that is due to coverage effects, rather than structural and/or phase changes. Altogether, the data suggest that to further increase the activity and stability of Pd-based catalysts for methane combustion, increasing the surface area of supported PdO phases while avoiding strong adsorption of water on the catalytic surfaces is required. Furthermore, this study clarifies contrasting reports in the literature about the active phase and stability of Pd-based materials for methane combustion.« less

Systematic Structure–Property Relationship Studies in Palladium-Catalyzed Methane Complete Combustion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Willis, Joshua J.; Gallo, Alessandro; Sokaras, Dimosthenis

To limit further rising levels in methane emissions from stationary and mobile sources and to enable promising technologies based on methane, the development of efficient combustion catalysts that completely oxidize CH 4 to CO 2 and H 2O at low temperatures in the presence of high steam concentrations is required. Palladium is widely considered as one of the most promising materials for this reaction, and a better understanding of the factors affecting its activity and stability is crucial to design even more improved catalysts that efficiently utilize this precious metal. Here we report a study of the effect of threemore » important variables (particle size, support, and reaction conditions including water) on the activity of supported Pd catalysts. We use uniform palladium nanocrystals as catalyst precursors to prepare a library of well-defined catalysts to systematically describe structure–property relationships with help from theory and in situ X-ray absorption spectroscopy. With this approach, we confirm that PdO is the most active phase and that small differences in reaction rates as a function of size are likely due to variations in the surface crystal structure. We further demonstrate that the support exerts a limited influence on the PdO activity, with inert (SiO 2), acidic (Al 2O 3), and redox-active (Ce 0.8Zr 0.2O 2) supports providing similar rates, while basic (MgO) supports show remarkably lower activity. Finally, we show that the introduction of steam leads to a considerable decrease in rates that is due to coverage effects, rather than structural and/or phase changes. Altogether, the data suggest that to further increase the activity and stability of Pd-based catalysts for methane combustion, increasing the surface area of supported PdO phases while avoiding strong adsorption of water on the catalytic surfaces is required. Furthermore, this study clarifies contrasting reports in the literature about the active phase and stability of Pd-based materials for methane combustion.« less

Combustion behaviors and kinetics of sewage sludge blended with pulverized coal: With and without catalysts.

PubMed

Wang, Zhiqiang; Hong, Chen; Xing, Yi; Li, Yifei; Feng, Lihui; Jia, Mengmeng

2018-04-01

The combustion behaviors of sewage sludge (SS), pulverized coal (PC), and their blends were studied using a thermogravimetric analyzer. The effect of the mass ratio of SS to PC on the co-combustion characteristics was analyzed. The experiments showed that the ignition performance of the blends improved significantly as the mass percentage of SS increased, but its combustion intensity decreased. The burnout temperature (T b ) and comprehensive combustibility index (S) of the blends were almost unchanged when the mass percentage of SS was less than 10%. However, a high mass percentage of SS (>10%) resulted in a great increase in T b and a notable decrease in S. Subsequently, the effects of different catalysts (CaO, CeO 2 , MnO 2 , and Fe 2 O 3 ) on the combustion characteristics and activation energy of the SS/PC blend were investigated. The four catalysts promoted the release and combustion of volatile matters in the blended fuels and shifted their combustion profiles to a low temperature. In addition, their peak separating tendencies were obvious at 350-550 C, resulting in high peak widths. All the catalysts improved combustion activity of the blended fuel and accelerated fixed carbon combustion, which decreased the ignition temperature and burnout temperature of the fuels. CeO 2 had the best catalytic effects in terms of the comprehensive combustion performance and activation energy, followed closely by Fe 2 O 3 . However, the rare-earth compounds are expensive to be applied in the catalytic combustion process of SS/PC blend at present. Based on both catalytic effects and economy, Fe 2 O 3 was potentially an optimal option for catalytic combustion among the tested catalysts. Copyright © 2018 Elsevier Ltd. All rights reserved.

Fischer-Tropsch Catalyst for Aviation Fuel Production

NASA Technical Reports Server (NTRS)

DeLaRee, Ana B.; Best, Lauren M.; Bradford, Robyn L.; Gonzalez-Arroyo, Richard; Hepp, Aloysius F.

2012-01-01

As the oil supply declines, there is a greater need for cleaner alternative fuels. There will undoubtedly be a shift from crude oil to nonpetroleum sources as a feedstock for aviation (and other transportation) fuels. The Fischer-Tropsch process uses a gas mixture of carbon monoxide and hydrogen which is converted into various liquid hydrocarbons; this versatile gas-to-liquid technology produces a complex product stream of paraffins, olefins, and oxygenated compounds such as alcohols and aldehydes. The Fischer-Tropsch process can produce a cleaner diesel oil fraction with a high cetane number (typically above 70) without any sulfur and aromatic compounds. It is most commonly catalyzed by cobalt supported on alumina, silica, or titania or unsupported alloyed iron powders. Cobalt is typically used more often than iron, in that cobalt is a longer-active catalyst, has lower water-gas shift activity, and lower yield of modified products. Promoters are valuable in improving Fischer-Tropsch catalyst as they can increase cobalt oxide dispersion, enhance the reduction of cobalt oxide to the active metal phase, stabilize a high metal surface area, and improve mechanical properties. Our goal is to build up the specificity of the Fischer-Tropsch catalyst while adding less-costly transition metals as promoters; the more common promoters used in Fischer-Tropsch synthesis are rhenium, platinum, and ruthenium. In this report we will describe our preliminary efforts to design and produce catalyst materials to achieve our goal of preferentially producing C8 to C18 paraffin compounds in the NASA Glenn Research Center Gas-To-Liquid processing plant. Efforts at NASA Glenn Research Center for producing green fuels using non-petroleum feedstocks support both the Sub-sonic Fixed Wing program of Fundamental Aeronautics and the In Situ Resource Utilization program of the Exploration Technology Development and Demonstration program.

Fischer-Tropsch Catalyst for Aviation Fuel Production

NASA Technical Reports Server (NTRS)

deLaRee, Ana B.; Best, Lauren M.; Hepp, Aloysius F.

2011-01-01

As the oil supply declines, there is a greater need for cleaner alternative fuels. There will undoubtedly be a shift from crude oil to non-petroleum sources as a feedstock for aviation (and other transportation) fuels. The Fischer-Tropsch process uses a gas mixture of carbon monoxide and hydrogen which is converted into various liquid hydrocarbons; this versatile gas-to-liquid technology produces a complex product stream of paraffins, olefins, and oxygenated compounds such as alcohols and aldehydes. The Fischer-Tropsch process can produce a cleaner diesel oil fraction with a high cetane number (typically above 70) without any sulfur and aromatic compounds. It is most commonly catalyzed by cobalt supported on alumina, silica, or titania or unsupported alloyed iron powders. Cobalt is typically used more often than iron, in that cobalt is a longer-active catalyst, has lower water-gas shift activity, and lower yield of modified products. Promoters are valuable in improving Fischer-Tropsch catalyst as they can increase cobalt oxide dispersion, enhance the reduction of cobalt oxide to the active metal phase, stabilize a high metal surface area, and improve mechanical properties. Our goal is to build up the specificity of the Fischer-Tropsch catalyst while adding less-costly transition metals as promoters; the more common promoters used in Fischer-Tropsch synthesis are rhenium, platinum, and ruthenium. In this report we will describe our preliminary efforts to design and produce catalyst materials to achieve our goal of preferentially producing C8 to C18 paraffin compounds in the NASA Glenn Research Center Gas-To-Liquid processing plant. Efforts at NASA Glenn Research Center for producing green fuels using non-petroleum feedstocks support both the Sub-sonic Fixed Wing program of Fundamental Aeronautics and the In Situ Resource Utilization program of the Exploration Technology Development and Demonstration program.

Hydrogen production and purification for fuel cell applications

NASA Astrophysics Data System (ADS)

Chin, Soo Yin

The increased utilization of proton-exchange membrane (PEM) fuel cells as an alternative to internal combustion engines is expected to increase the demand for hydrogen, which is used as the energy source in these systems. Currently, production of hydrogen for fuel cells is primarily achieved via steam reforming, partial oxidation or autothermal reforming of natural gas, or steam reforming of methanol. However, in all of these processes CO is a by-product that must be subsequently removed due to its adverse effects on the Pt-based electrocatalysts of the PEM fuel cell. Our efforts have focused on production of CO-free hydrogen via catalytic decomposition of hydrocarbons and purification of H2 via the preferential oxidation of CO. The catalytic decomposition of hydrocarbons is an attractive alternative for the production of H2. Previous studies utilizing methane have shown that this approach can indeed produce CO-free hydrogen, with filamentous carbon formed as the by-product and deposited on the catalyst. We have further extended this approach to the decomposition of ethane. In addition to hydrogen and filamentous carbon however, methane is also formed in this case as a by-product. Studies conducted at different temperatures and space velocities suggest that hydrogen is the primary product while methane is formed in a secondary step. Ni/SiO2 catalysts are active for ethane decomposition at temperatures above 500°C. Although the yield of hydrogen increases with temperature, the catalyst deactivation rate also accelerates at higher temperatures. The preferential oxidation of CO is currently used for the purification of CO-contaminated hydrogen streams due to its efficiency and simplicity. Conventional Pt catalysts used for this reaction have been shown to effectively remove CO, but have limited selectivity (i.e., substantial amounts of H 2 also react with O2). Our work focused on alternative catalytic materials, such as Ru and bimetallic Ru-based catalysts (Pt-Ru, Ru-Sn). We have investigated the effects of various synthetic parameters (namely, supports, pretreatment conditions and precursors) on the performance of supported Ru catalysts. Kinetic results indicate that use of a nitrate precursor, SiO 2 support and a direct H2 treatment results in a highly dispersed catalyst that is active and selective towards CO. The results of extensive characterization studies indicate that a combination of particle size and residual precursor anion poisoning effects are responsible for the observed performance differences. Bimetallic Ru-Sn catalysts were also examined. Fresh catalyst exhibit lower activity for the preferential oxidation of CO as compared to fresh monometallic Ru. However, the activity of these bimetallic catalysts can be improved significantly by aging under reaction conditions, eventually becoming higher than that of monometallic Ru. By conducting a series of kinetic measurements following treatments with different components of the reacting gas mixture, we were able to deconvolute the effect of the different components and demonstrate that the observed improvement in activity is caused by the interaction of CO and H2O with the catalyst.

Nano or micro? A mechanism on thermal decomposition of ammonium perchlorate catalyzed by cobalt oxalate.

PubMed

Zou, Min; Jiang, Xiaohong; Lu, Lude; Wang, Xin

2012-07-30

Micrometer-sized cobalt oxalates with different morphologies have been prepared in the presence of surfactants. The effect of catalysts morphology on the thermal decomposition of ammonium perchlorate (AP) was evaluated by differential thermal analysis (DSC). Remarkably, contrary to the well-accepted concepts, no direct relationship between the morphologies of catalysts and their activities has been observed. Based on the structural and morphological variation of the catalysts during the reaction, a catalytic mechanism on thermal decomposition of ammonium perchlorate catalyzed by cobalt oxalate is proposed. We believe that it is the "self-crushing and self-distributed" occurred within the reaction that really works for the improvement of the overall catalytic activities. In this process, both catalysts and reactants have been crashed and distributed uniformly in an automatic way. This work provides an in-depth insight into the thermal decomposition mechanism of AP as catalyzed by oxalates. Copyright © 2012 Elsevier B.V. All rights reserved.

Simple synthesized Pt/GNs/TiO2 with good mass activity and stability for methanol oxidation

NASA Astrophysics Data System (ADS)

Zhang, Jianbo; Hu, Xiulan; Zhu, Faquan; Su, Nan; Huang, Huihong; Cheng, Jiexu; Yang, Hui

2017-12-01

Pt/GNs/TiO2 (GNs, graphene nanosheets) catalyst was synthesized by a simple two-step method, including a rapid solution plasma technique to obtained Pt nanoparticles with a size of 2-5 nm and followed by an ultrasonic mixing of the Pt, GNs and TiO2 nanoparticles. After coupling with TiO2 nanoparticles, the Pt/GNs/TiO2 catalyst exhibited a promoting catalytic activity towards methanol oxidation, which was superior to the Pt/GNs catalyst. The mass activity of the Pt/GNs/TiO2 catalyst was 3464 mA mgPt -1, which was 3.5 and 3.4 times higher than those of the Pt/GNs and the commercial Pt/C, respectively. And the Pt/GNs/TiO2 showed a strongly negative shift onset potential of methanol oxidation. The results of long-term cyclic voltammetry and CO-stripping tests showed an improved CO tolerance of the Pt/GNs/TiO2. Moreover, the mass activity of the Pt/GNs/TiO2 was further enhanced under light irradiation, with the mass activity of 4715 mA mgPt -1, which was 1.4 times higher than that of in dark. This work provides new opportunities for exploiting efficient visible photo-assisted electro-catalytic methanol oxidation.

Slurry hydrocracking of Arab heavy vacuum resid with new bifunctional catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rankel, L.A.

1993-12-31

Co-processing coal with hydrogenated vacuum resids can solubilize coal and aid in metals removals from the hydrotreated resid. Several bifunctional NiW catalysts were evaluated for resid hydrocracking in a slurry reactor. Autoclave runs were made to determine whether a hydrogenative metal function (NiW) plus support with cracking activity might be an effective catalyst for high resid 1000F{degrees}{sup +} conversion, H-content enrichment, deS, and demetallation at low coke make. An Arab Heavy 895{degrees}F{sup +} vacuum resid (262 ppm Ni+V, 5.3% S and 24% CCR) was hydrocracked over sulfided and unsulfided NiW catalysts on alumina, silica-alumina, US-Y, etc. at 800{degrees}F and 2000more » psig hydrogen in a batch reactor and compared to oil soluble mixtures of Ni and W homogenous organometallics. Of the catalysts tested here, results indicate that addition of sulfided NiW/aluminum to slurry type processing might improve hydrogenation activity and produce more 1000{degrees}F{sup +} conversion at a particular severity while generating the low coke make necessary for a continuous process. Once the resid is hydrotreated, coal could be added to the NiW bifunctional catalyst/resid slurry for co-processing.« less

Enhancement of the electrooxidation of ethanol on Pt-Sn-P/C catalysts prepared by chemical deposition process

NASA Astrophysics Data System (ADS)

Xue, Xinzhong; Ge, Junjie; Tian, Tian; Liu, Changpeng; Xing, Wei; Lu, Tianhong

In this paper, five Pt 3Sn 1/C catalysts have been prepared using three different methods. It was found that phosphorus deposited on the surface of carbon with Pt and Sn when sodium hypophosphite was used as reducing agent by optimization of synthetic conditions such as pH in the synthetic solution and temperature. The deposition of phosphorus should be effective on the size reduction and markedly reduces PtSn nanoparticle size, and raise electrochemical active surface (EAS) area of catalyst and improve the catalytic performance. TEM images show PtSnP nanoparticles are highly dispersed on the carbon surface with average diameters of 2 nm. The optimum composition is Pt 3Sn 1P 2/C (note PtSn/C-3) catalyst in my work. With this composition, it shows very high activity for the electrooxidation of ethanol and exhibit enhanced performance compared with other two Pt 3Sn 1/C catalysts that prepared using ethylene glycol reduction method (note PtSn/C-EG) and borohydride reduction method (note PtSn/-B). The maximum power densities of direct ethanol fuel cell (DEFC) were 61 mW cm -2 that is 150 and 170% higher than that of the PtSn/C-EG and PtSn/C-B catalyst.

A Study of Iron-Nitrogen-Carbon Fuel Cell Catalysts: Chemistry - Nanostructure - Performance

NASA Astrophysics Data System (ADS)

Workman, Michael J., Jr.

Fuel cells have the potential to be a pollution-free, low-cost, and energy efficient alternative to the internal combustion engine for transportation and small-scale stationary power applications. The current state of fuel cell technology has already achieved two of these three lofty goals. The remaining barrier to wide-scale deployment is the high cost, which is primarily caused by dependence on large amounts of platinum to catalyze the energy conversion reactions. To overcome this barrier and facilitate the integration of fuel cells into mainstream applications, research into a new class of catalyst materials that do not require platinum is needed. There has been a significant amount of research effort directed toward the development of platinum-group metal free (PGM-free) catalysts, yet there is a lack of consensus on both the engineering parameters necessary to improve the technology and the fundamental science that would facilitate rational design. I have engaged in research on PGM-free catalysts based on inexpensive and abundant reagents, specifically: nicarbazin and iron. Catalysts made from these precursors have previously proven to be among the best PGM-free catalysts, but their continued advancement suffered from the same lack of understanding that besets all catalysts in this class. The work I have performed address both engineering concerns and fundamental underlying principles. I present results demonstrating correlations between physical structure, chemical speciation, and synthesis parameters, as well as addressing active site chemistry and likely locations. My research presented herein introduces new morphology analysis techniques and elucidates several key structure-to-property characteristics of catalysts derived from iron and nicarbazin. I discuss the development and application of a new length-scale specific surface analysis technique that allows for analysis of well-defined size ranges from a few nm to several microns. The existing technique of focused ion beam tomography is modified and optimized for platinum-group metal free catalyst layers, facilitating direct observation of catalyst integration into catalyst layers. I present evidence supporting the hypothesis that atomically dispersed iron coordinated with nitrogen are the dominant active sites in these catalysts. Further, that the concentration of surface oxides in the carbon structure, which can be directly influenced by synthesis parameters, correlates with both the concentration of active sites in the material and with fuel cell performance. Catalyst performance is hindered by the addition of carbon nanotubes and by the presence of metallic iron. Evidence consistent with the catalytic active sites residing in the graphitic plane is also presented.

Energy Level Engineering of MoS2 by Transition-Metal Doping for Accelerating Hydrogen Evolution Reaction.

PubMed

Shi, Yi; Zhou, Yue; Yang, Dong-Rui; Xu, Wei-Xuan; Wang, Chen; Wang, Feng-Bin; Xu, Jing-Juan; Xia, Xing-Hua; Chen, Hong-Yuan

2017-11-01

Water-splitting devices for hydrogen generation through electrolysis (hydrogen evolution reaction, HER) hold great promise for clean energy. However, their practical application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. We previously reported that HER can be largely enhanced through finely tuning the energy level of molybdenum sulfide (MoS 2 ) by hot electron injection from plasmonic gold nanoparticles. Under this inspiration, herein, we propose a strategy to improve the HER performance of MoS 2 by engineering its energy level via direct transition-metal doping. We find that zinc-doped MoS 2 (Zn-MoS 2 ) exhibits superior electrochemical activity toward HER as evidenced by the positively shifted onset potential to -0.13 V vs RHE. A turnover of 15.44 s -1 at 300 mV overpotential is achieved, which by far exceeds the activity of MoS 2 catalysts reported. The large enhancement can be attributed to the synergistic effect of electronic effect (energy level matching) and morphological effect (rich active sites) via thermodynamic and kinetic acceleration, respectively. This design opens up further opportunities for improving electrocatalysts by incorporating promoters, which broadens the understanding toward the optimization of electrocatalytic activity of these unique materials.

Designing supported palladium-on-gold bimetallic nano-catalysts for controlled hydrogenation of acetylene in large excess of ethylene

NASA Astrophysics Data System (ADS)

Malla, Pavani

Ethylene is used as a starting point for many chemical intermediates in the petrochemical industry. It is predominantly produced through steam cracking of higher hydrocarbons (ethane, propane, butane, naphtha, and gas oil). During the cracking process, a small amount of acetylene is produced as a side product. However, acetylene must be removed since it acts as a poison for ethylene polymerization catalysts at even ppm concentrations (>5 ppm). Thus, the selective hydrogenation of acetylene to ethylene is an important process for the purification of ethylene. Conventional, low weight loading Pd catalysts are used for this selective reaction in high concentration ethylene streams. Gold was initially considered to be catalytically inactive for a long time. This changed when gold was seen in the context of the nanometric scale, which has indeed shown it to have excellent catalytic activity as a homogeneous or a heterogeneous catalyst. Gold is proved to have high selectivity to ethylene but poor at conversion. Bimetallic Au and Pd catalysts have exhibited superior activity as compared to Pd particles in semi-hydrogenation. Hydrogenation of acetylene was tested using this bimetallic combination. The Pd-on-Au bimetallic catalyst structure provides a new synthesis approach in improving the catalytic properties of monometallic Pd materials. TiO 2 as a support material and 0.05%Pd loading on 1%Au on titania support and used different treatment methods like washing plasma and reduction between the two metal loadings and was observed under 2:1 ratio. In my study there were two set of catalysts which were prepared by a modified incipient wetness impregnation technique. Out of all the reaction condition the catalyst which was reduced after impregnating gold and then impregnating palladium which was further treated in non-thermal hydrogen plasma and then pretreated in hydrogen till 250°C for 1 hour produced the best activity of 76% yield at 225°C. Stability tests were conducted on the catalysts which were followed by TGA analysis to analyze the coke formation on the catalyst in a period of time at a particular temperature. The catalysts were characterized by the hydrogen chemisorption and atomic absorption spectroscopy.

3D Polymer Hydrogel for High-Performance Atomic Fe and Mn Catalysts for Oxygen Reduction in Challenging Acids

NASA Astrophysics Data System (ADS)

Qiao, Zhi

Current platinum group metal (PGM)-free carbon nanocomposite catalysts for the oxygen reduction reaction (ORR) in acidic electrolyte often suffer from rapid degradation associated with carbon corrosion due to the use of large amount of the amorphoous carbon black supports. Here, we developed a new concept of using freestanding 3D hydrogel to design support-free Fe-N-C catalysts. A 3D polyaniline (PANI)-based hydrogel approach was used for preparing a new type of single atomic iron site-rich catalyst, which has exhibited exceptionally enhanced activity and stability compared to conventional Fe-N-C catalysts supported on amorphous carbon blacks. The achieved performance metric on the hydrogel PANI-Fe catalysts is one of the best ever reported PGM-free catalysts, reaching a half-wave potential up to 0.83 V vs. RHE and only leaving 30 mV gap with Pt/C catalysts (60mugPt/cm 2) in challenging acidic media. Remarkable ORR stability was accomplished as well on the same catalyst evidenced by using harsh potential cycling tests. The well dispersion of atomic iron into partially graphitized carbon, featured with dominance of micropores and porous network structures, is capable of accommodating increased number of active sites, strengthening local bonding among iron, nitrogen and carbon, and facilitating mass transfer. On the other hand, in order to decrease the produced Fenton reagent, which will oxidize the proton exchange membrane and ionomer in membrane electrode assembly (MEA), we produce Mn-based catalysts by this novel hydrogel method. This is the first time that Mn-based catalysts can show such outstanding performance in acid media, whose half-wave potential is up to 0.80 V vs. RHE. The work related to the performance improvement is still in processing. We believe the 3D polymer hydrogel approach would be a new pathway to advance PGM-free catalysts.

A facile reflux procedure to increase active surface sites form highly active and durable supported palladium@platinum bimetallic nanodendrites

NASA Astrophysics Data System (ADS)

Wang, Qin; Li, Yingjun; Liu, Baocang; Xu, Guangran; Zhang, Geng; Zhao, Qi; Zhang, Jun

2015-11-01

A series of well-dispersed bimetallic Pd@Pt nanodendrites uniformly supported on XC-72 carbon black are fabricated by using different capping agents. These capping agents are essential for the branched morphology control. However, the surfactant adsorbed on the nanodendrites surface blocks the access of reactant molecules to the active surface sites, and the catalytic activities of these bimetallic nanodendrites are significantly restricted. Herein, a facile reflux procedure to effectively remove the capping agent molecules without significantly affecting their sizes is reported for activating supported nanocatalysts. More significantly, the structure and morphology of the nanodendrites can also be retained, enhancing the numbers of active surface sites, catalytic activity and stability toward methanol and ethanol electro-oxidation reactions. The as-obtained hot water reflux-treated Pd@Pt/C catalyst manifests superior catalytic activity and stability both in terms of surface and mass specific activities, as compared to the untreated catalysts and the commercial Pt/C and Pd/C catalysts. We anticipate that this effective and facile removal method has more general applicability to highly active nanocatalysts prepared with various surfactants, and should lead to improvements in environmental protection and energy production.

Supported Dendrimer-Encapsulated Metal Clusters: Toward Heterogenizing Homogeneous Catalysts

DOE PAGES

Ye, Rong; Zhukhovitskiy, Aleksandr V.; Deraedt, Christophe V.; ...

2017-07-13

Recyclable catalysts, especially those that display selective reactivity, are vital for the development of sustainable chemical processes. Among available catalyst platforms, heterogeneous catalysts are particularly well-disposed toward separation from the reaction mixture via filtration methods, which renders them readily recyclable. Furthermore, heterogeneous catalysts offer numerous handles—some without homogeneous analogues—for performance and selectivity optimization. These handles include nanoparticle size, pore profile of porous supports, surface ligands and interface with oxide supports, and flow rate through a solid catalyst bed. Despite these available handles, however, conventional heterogeneous catalysts are themselves often structurally heterogeneous compared to homogeneous catalysts, which complicates efforts to optimizemore » and expand the scope of their reactivity and selectivity. Ongoing efforts in our laboratories are aimed to address the above challenge by heterogenizing homogeneous catalysts, which can be defined as the modification of homogeneous catalysts to render them in a separable (solid) phase from the starting materials and products. Specifically, we grow the small nanoclusters in dendrimers, a class of uniform polymers with the connectivity of fractal trees and generally radial symmetry. Thanks to their dense multivalency, shape persistence, and structural uniformity, dendrimers have proven to be versatile scaffolds for the synthesis and stabilization of small nanoclusters. Then these dendrimer-encapsulated metal clusters (DEMCs) are adsorbed onto mesoporous silica. Through this method, we have achieved selective transformations that had been challenging to accomplish in a heterogeneous setting, e.g., π-bond activation and aldol reactions. Extensive investigation into the catalytic systems under reaction conditions allowed us to correlate the structural features (e.g., oxidation states) of the catalysts and their activity. Moreover, we have demonstrated that supported DEMCs are also excellent catalysts for typical heterogeneous reactions, including hydrogenation and alkane isomerization. Critically, these investigations also confirmed that the supported DEMCs are heterogeneous and stable against leaching. Catalysts optimization is achieved through the modulation of various parameters. The clusters are oxidized (e.g., with PhICl 2) or reduced (e.g., with H 2) in situ. Changing the dendrimer properties (e.g., generation, terminal functional groups) is analogous to ligand modification in homogeneous catalysts, which affect both catalytic activity and selectivity. Similarly, pore size of the support is another factor in determining product distribution. In a flow reactor, the flow rate is adjusted to control the residence time of the starting material and intermediates, and thus the final product selectivity. Our approach to heterogeneous catalysis affords various advantages: (1) the catalyst system can tap into the reactivity typical to homogeneous catalysts, which conventional heterogeneous catalysts could not achieve; (2) unlike most homogeneous catalysts with comparable performance, the heterogenized homogeneous catalysts can be recycled; (3) improved activity or selectivity compared to conventional homogeneous catalysts is possible because of uniquely heterogeneous parameters for optimization. Here in this Account, we will briefly introduce metal clusters and describe the synthesis and characterizations of supported DEMCs. We will present the catalysis studies of supported DEMCs in both the batch and flow modes. Lastly, we will summarize the current state of heterogenizing homogeneous catalysis and provide future directions for this area of research.« less

Nanostructured nonprecious metal catalysts for oxygen reduction reaction.

PubMed

Wu, Gang; Zelenay, Piotr

2013-08-20

Platinum-based catalysts represent a state of the art in the electrocatalysis of oxygen reduction reaction (ORR) from the point of view of their activity and durability in harnessing the chemical energy via direct electrochemical conversion. However, because platinum is both expensive and scarce, its widespread implementation in such clean energy applications is limited. Recent breakthroughs in the synthesis of high-performance nonprecious metal catalysts (NPMCs) make replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. In this Account, we discuss how we can obtain highly promising M-N-C (M: Fe and/or Co) catalysts by simultaneously heat-treating precursors of nitrogen, carbon, and transition metals at 800-1000 °C. The activity and durability of resulting catalysts depend greatly on the selection of precursors and synthesis chemistry. In addition, they correlate quite well with the catalyst nanostructure. While chemists have presented no conclusive description of the active catalytic site for this class of NPMCs, they have developed a designed approach to making active and durable materials, focusing on the catalyst nanostructure. The approach consists of nitrogen doping, in situ carbon graphitization, and the usage of graphitic structures (possibly graphene and graphene oxides) as carbon precursors. Various forms of nitrogen, particularly pyridinic and quaternary, can act as n-type carbon dopants in the M-N-C catalysts, assisting in the formation of disordered carbon nanostructures and donating electrons to the carbon. The CNx structures are likely a crucial part of the ORR active site(s). Noteworthy, the ORR activity is not necessarily governed by the amount of nitrogen, but by how the nitrogen is incorporated into the nanostructures. Apart from the possibility of a direct participation in the active site, the transition metal often plays an important role in the in situ formation of various carbon nanostructures by catalyzing the decomposition of the nitrogen/carbon precursor. We can control the formation of different nanostructures during the synthesis of M-N-C catalysts. For example, in situ formed nitrogen-doped graphene-sheets can only be derived from polyaniline (PANI), probably due to structural similarities between the aromatic structures of PANI and graphene. Highly-graphitized carbon nanostructures may serve as a matrix for the formation of ORR-active groups with improved catalytic activity and durability, containing nitrogen and most probably also metal atoms. In the future, we will likely focus NPMC synthesis approaches on precise control of interactions between precursors of the metal and carbon/nitrogen during the heat treatment. The main purposes will be to maximize the number of active sites, optimize nitrogen doping levels, and generate morphologies capable of hosting active and stable ORR sites.

Multiscale Evaluation of Catalytic Upgrading of Biomass Pyrolysis Vapors on Ni- and Ga-Modified ZSM-5

DOE PAGES

Yung, Matthew M.; Stanton, Alexander R.; Iisa, Kristiina; ...

2016-10-07

Metal-impregnated (Ni or Ga) ZSM-5 catalysts were studied for biomass pyrolysis vapor upgrading to produce hydrocarbons using three reactors constituting a 100 000x change in the amount of catalyst used in experiments. Catalysts were screened for pyrolysis vapor phase upgrading activity in two small-scale reactors: (i) a Pyroprobe with a 10 mg catalyst in a fixed bed and (ii) a fixed-bed reactor with 500 mg of catalyst. The best performing catalysts were then validated with a larger scale fluidized-bed reactor (using ~1 kg of catalyst) that produced measurable quantities of bio-oil for analysis and evaluation of mass balances. Despite somemore » inherent differences across the reactor systems (such as residence time, reactor type, analytical techniques, mode of catalyst and biomass feed) there was good agreement of reaction results for production of aromatic hydrocarbons, light gases, and coke deposition. Relative to ZSM-5, Ni or Ga addition to ZSM-5 increased production of fully deoxygenated aromatic hydrocarbons and light gases. In the fluidized bed reactor, Ga/ZSM-5 slightly enhanced carbon efficiency to condensed oil, which includes oxygenates in addition to aromatic hydrocarbons, and reduced oil oxygen content compared to ZSM-5. Ni/ZSM-5, while giving the highest yield of fully deoxygenated aromatic hydrocarbons, gave lower overall carbon efficiency to oil but with the lowest oxygen content. Reaction product analysis coupled with fresh and spent catalyst characterization indicated that the improved performance of Ni/ZSM-5 is related to decreasing deactivation by coking, which keeps the active acid sites accessible for the deoxygenation and aromatization reactions that produce fully deoxygenated aromatic hydrocarbons. The addition of Ga enhances the dehydrogenation activity of the catalyst, which leads to enhanced olefin formation and higher fully deoxygenated aromatic hydrocarbon yields compared to unmodified ZSM-5. Catalyst characterization by ammonia temperature programmed desorption, surface area measurements, and postreaction temperature-programmed oxidation (TPO) also showed that the metal-modified zeolites retained a greater percentage of their initial acidity and surface area, which was consistent between the reactor scales. These results demonstrate that the trends observed with smaller (milligram to gram) catalyst reactors are applicable to larger, more industrially relevant (kg) scales to help guide catalyst research toward application.« less

Eco-friendly films prepared from plantain flour/PCL blends under reactive extrusion conditions using zirconium octanoate as a catalyst.

PubMed

Gutiérrez, Tomy J; Alvarez, Vera A

2017-12-15

Plantain flour (Musa ssp., group AAB, sub-group clone Harton)/poly(ε-caprolactone) (PCL) blends, containing glycerol as a plasticizer, were prepared by reactive extrusion (REx) in a twin-screw extruder using zirconium octanoate (Zr(Oct) 4 ) as a catalyst, followed by thermo-compression molding for film development. The films were then characterized in terms of their: infrared (FTIR) spectra, water solubility, thermogravimetric (TGA) curves, differential scanning calorimetry (DSC) thermograms, and X-ray diffraction (XDR) diffractograms, as well as their microstructural, mechanical and antimicrobial properties in order to (1) compare the effects of PCLs with two different molecular weights (M w ) on the characteristics of the plantain flour/PCL blends, and (2) determine whether using Zr(Oct) 4 in the production of active composite polymer materials improves their properties. The plantain flour/PCL blends were all developed successfully. The higher M w PCL gave more hydrophobic and thermally stable films with improved mechanical properties. The addition of the Zr(Oct) 4 catalyst to the plantain flour/PCL blends also resulted in films with similar characteristics to those described above, due to the cross-linking of the polymers. In addition, the films containing the catalyst showed antimicrobial activity against Escherichia coli O157:H7 and Staphylococcus aureus indicating a dual effect of Zr(Oct) 4 , and making it an attractive alternative for the development of active films. Copyright © 2017 Elsevier Ltd. All rights reserved.

Cobalt Fischer-Tropsch catalysts having improved selectivity

DOEpatents

Miller, James G.; Rabo, Jule A.

1989-01-01

The promoter(s) Mn oxide or Mn oxide and Zr oxide are added to a cobalt Fischer-Tropsch catalyst combined with the molecular sieve TC-103 or TC-123 such that the resultant catalyst demonstrates improved product selectivity, stability and catalyst life. The improved selectivity is evidenced by lower methane production, higher C5+ yield and increased olefin production.

Performance and life cycle environmental benefits of recycling spent ion exchange brines by catalytic treatment of nitrate.

PubMed

Choe, Jong Kwon; Bergquist, Allison M; Jeong, Sangjo; Guest, Jeremy S; Werth, Charles J; Strathmann, Timothy J

2015-09-01

Salt used to make brines for regeneration of ion exchange (IX) resins is the dominant economic and environmental liability of IX treatment systems for nitrate-contaminated drinking water sources. To reduce salt usage, the applicability and environmental benefits of using a catalytic reduction technology to treat nitrate in spent IX brines and enable their reuse for IX resin regeneration were evaluated. Hybrid IX/catalyst systems were designed and life cycle assessment of process consumables are used to set performance targets for the catalyst reactor. Nitrate reduction was measured in a typical spent brine (i.e., 5000 mg/L NO3(-) and 70,000 mg/L NaCl) using bimetallic Pd-In hydrogenation catalysts with variable Pd (0.2-2.5 wt%) and In (0.0125-0.25 wt%) loadings on pelletized activated carbon support (Pd-In/C). The highest activity of 50 mgNO3(-)/(min - g(Pd)) was obtained with a 0.5 wt%Pd-0.1 wt%In/C catalyst. Catalyst longevity was demonstrated by observing no decrease in catalyst activity over more than 60 days in a packed-bed reactor. Based on catalyst activity measured in batch and packed-bed reactors, environmental impacts of hybrid IX/catalyst systems were evaluated for both sequencing-batch and continuous-flow packed-bed reactor designs and environmental impacts of the sequencing-batch hybrid system were found to be 38-81% of those of conventional IX. Major environmental impact contributors other than salt consumption include Pd metal, hydrogen (electron donor), and carbon dioxide (pH buffer). Sensitivity of environmental impacts of the sequencing-batch hybrid reactor system to sulfate and bicarbonate anions indicate the hybrid system is more sustainable than conventional IX when influent water contains <80 mg/L sulfate (at any bicarbonate level up to 100 mg/L) or <20 mg/L bicarbonate (at any sulfate level up to 100 mg/L) assuming 15 brine reuse cycles. The study showed that hybrid IX/catalyst reactor systems have potential to reduce resource consumption and improve environmental impacts associated with treating nitrate-contaminated water sources. Copyright © 2015 Elsevier Ltd. All rights reserved.

Design, Synthesis, and Mechanistic Evaluation of Iron-Based Catalysis for Synthesis Gas Conversion to Fuels and Chemicals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Enrique Iglesia; Akio Ishikawa; Manual Ojeda

2007-09-30

A detailed study of the catalyst composition, preparation and activation protocol of Fe-based catalysts for the Fischer-Tropsch Synthesis (FTS) have been carried out in this project. We have studied the effects of different promoters on the catalytic performance of Fe-based catalysts. Specifically, we have focused on how their sequence of addition dramatically influences the performance of these materials in the Fischer-Tropsch synthesis. The resulting procedures have been optimized to improve further upon the already unprecedented rates and C{sub 5+} selectivities of the Fe-based catalysts that we have developed as part of this project. Selectivity to C{sub 5+} hydrocarbon was closemore » to 90 % (CO{sub 2}-free basis) and CO conversion rate was about 6.7 mol h{sup -1} g-at Fe{sup -1} at 2.14 MPa, 508 K and with substoichiometric synthesis gas; these rates were larger than any reported previously for Fe-based FTS catalysts at these conditions. We also tested the stability of Fe-based catalysts during FTS reaction (10 days); as a result, the high hydrocarbon formation rates were maintained during 10 days, though the gradual deactivation was observed. Our investigation has also focused on the evaluation of Fe-based catalysts with hydrogen-poor synthesis gas streams (H{sub 2}/CO=1). We have observed that the Fe-based catalysts prepared in this project display also a high hydrocarbon synthesis rate with substoichiometric synthesis gas (H{sub 2}/CO=1) stream, which is a less desirable reactant mixture than stoichiometric synthesis gas (H{sub 2}/CO=2). We have improved the catalyst preparation protocols and achieved the highest FTS reaction rates and selectivities so far reported at the low temperatures required for selectivity and stability. Also, we have characterized the catalyst structural change and active phases formed, and their catalytic behavior during the activation process to evaluate their influences on FTS reaction. The efforts of this project led to (i) structural evolution of Fe-Zn oxide promoted with K and Cu, and (ii) evaluation of hydrocarbon and CH{sub 4} formation rates during activation procedures at various temperature and H{sub 2}/CO ratios. On the basis of the obtained results, we suggest that lower reactor temperature can be sufficient to activate catalysts and lead to the high FTS performance. In this project, we have also carried out a detailed kinetic and mechanistic study of the Fischer-Tropsch Synthesis with Fe-based catalysts. We have proposed a reaction mechanism with two CO activation pathways: unassisted and H-assisted. Both routes lead to the formation of the same surface monomers (CH{sub 2}). However, the oxygen removal mechanism is different. In the H-assisted route, oxygen is removed exclusively as water, while oxygen is rejected as carbon dioxide in the unassisted CO dissociation. The validity of the mechanism here proposed has been found to be in agreement with the experimental observation and with theoretical calculations over a Fe(110) surface. Also, we have studied the validity of the mechanism that we propose by analyzing the H{sub 2}/D{sub 2} kinetic isotope effect (r{sub H}/r{sub D}) over a conventional iron-based Fischer-Tropsch catalyst Fe-Zn-K-Cu. We have observed experimentally that the use of D{sub 2} instead of H{sub 2} leads to higher hydrocarbons formation rates (inverse kinetic isotopic effect). On the contrary, primary carbon dioxide formation is not influenced. These experimental observations can be explained by two CO activation pathways. We have also explored the catalytic performance of Co-based catalysts prepared by using inverse micelles techniques. We have studied several methods in order to terminate the silanol groups on SiO{sub 2} support including impregnation, urea homogeneous deposition-precipitation, or zirconium (IV) ethoxide titration. Although hydroxyl groups on the SiO{sub 2} surface are difficult to be stoichiometrically titrated by ZrO{sub 2}, a requirement to prevent the formation of strongly-interacting Co oxide species on SiO{sub 2}, modification of ZrO{sub 2} on SiO{sub 2} surface can improve the Co clusters dispersion leading to a marked increase in the number of accessible Co sites. Inverse micelle method allowed the synthesis of small Co clusters on SiO{sub 2}, but the required surfactant removal steps led to the re-oxidation of Co metal clusters and to the formation of difficult to reduce CoO{sub x} species.« less

Toward Highly Efficient Electrocatalyst for Li–O 2 Batteries Using Biphasic N-Doping Cobalt@Graphene Multiple-Capsule Heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, Guoqiang; Chong, Lina; Amine, Rachid

For the promotion of lithium oxygen batteries available for :practical applications, the development of advanced cathode catalysts with low-high activity, and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@grapbene Multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium oxygen cells. 'The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electroactive zones possible; furthermore the colander-like porousmore » electrode facilitates the oxygen diffusion, catalytic reaction,and stable deposition of discharge products. As a result, the electrode exhibits much improved electrocatalytic properties associated with unique morphologies of electrochemically grown lithium peroxides.« less

Toward Highly Efficient Electrocatalyst for Li-O2 Batteries Using Biphasic N-Doping Cobalt@Graphene Multiple-Capsule Heterostructures.

PubMed

Tan, Guoqiang; Chong, Lina; Amine, Rachid; Lu, Jun; Liu, Cong; Yuan, Yifei; Wen, Jianguo; He, Kun; Bi, Xuanxuan; Guo, Yuanyuan; Wang, Hsien-Hau; Shahbazian-Yassar, Reza; Al Hallaj, Said; Miller, Dean J; Liu, Dijia; Amine, Khalil

2017-05-10

For the promotion of lithium-oxygen batteries available for practical applications, the development of advanced cathode catalysts with low-cost, high activity, and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@graphene multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium-oxygen cells. The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electroactive zones possible; furthermore, the colander-like porous electrode facilitates the oxygen diffusion, catalytic reaction, and stable deposition of discharge products. As a result, the electrode exhibits much improved electrocatalytic properties associated with unique morphologies of electrochemically grown lithium peroxides.

Forecasting the zeolite-containing catalyst activity in catalytic cracking technology taking into account the feedstock composition

NASA Astrophysics Data System (ADS)

Ivashkina, Elena; Nazarova, Galina; Shafran, Tatyana; Stebeneva, Valeriya

2017-08-01

The effect of the feedstock composition and the process conditions on the current catalyst activity in catalytic cracking technology using a mathematical model is performed in this research. The mathematical model takes into account the catalyst deactivation by coke for primary and secondary cracking reactions. The investigation results have shown that the feedstock has significant effect on the yield and the content of coke on the catalyst. Thus, the relative catalyst activity is significantly reduced by 7.5-10.7 %. With increasing the catalytic cracking temperature due to the catalyst flow temperature rising, the coke content and the yield per feedstock increase and the catalyst activity decreases by 5.3-7.7%. Rising the process temperature together with the catalyst circulation ratio contributes to increase of the coke yield per feedstock in the catalytic cracking and decrease of the coke content on the catalyst. It is connected with the catalyst flow rising to the riser and the contact time decreasing in the reaction zone. Also, the catalyst activity decreases in the range of 3.8-5.5% relatively to the regenerated catalyst activity (83 %).

Combinatorial high-throughput optical screening of high performance Pd alloy cathode for hybrid Li-air battery.

PubMed

Jun, Young Jin; Park, Sung Hyeon; Woo, Seong Ihl

2014-12-08

Combinatorial high-throughput optical screening method was developed to find the optimum composition of highly active Pd-based catalysts at the cathode of the hybrid Li-air battery. Pd alone, which is one-third the cost of Pt, has difficulty in replacing Pt; therefore, the integration of other metals was investigated to improve its performance toward oxygen reduction reaction (ORR). Among the binary Pd-based catalysts, the composition of Pd-Ir derived catalysts had higher performance toward ORR compared to other Pd-based binary combinations. The composition at 88:12 at. % (Pd: Ir) showed the highest activity toward ORR at the cathode of the hybrid Li-air battery. The prepared Pd(88)Ir(12)/C catalyst showed a current density of -2.58 mA cm(-2) at 0.8 V (vs RHE), which was around 30% higher compared to that of Pd/C (-1.97 mA cm(-2)). When the prepared Pd(88)Ir(12)/C catalyst was applied to the hybrid Li-air battery, the polarization of the cell was reduced and the energy efficiency of the cell was about 30% higher than that of the cell with Pd/C.

Ultrathin layered double hydroxide nanosheets with Ni(III) active species obtained by exfoliation for highly efficient ethanol electrooxidation.

PubMed

Xu, Liang; Wang, Zhe; Chen, Xu; Qu, Zongkai; Li, Feng; Yang, Wensheng

2018-01-10

The development of non-precious metal electrocatalysts for renewable energy conversion and storage is compelling but greatly challenging due to low activity of the existing catalysts. Herein, the ultrathin NiAl-layered double hydroxide nanosheets (NiAl-LDH-NSs) are prepared by simple liquid-exfoliation of bulk NiAl-LDHs and first used as ethanol electrooxidation catalysts. The ultrathin two-dimensional (2D) structure ensures that the LDH nanosheets expose a greater number of active sites. More importantly, much Ni(III) active species (NiOOH) in the ultrathin nanosheets are formed by the exfoliation process, which play an authentic catalytic role in the ethanol oxidation reaction (EOR). The presence of NiOOH remarkably improves the reactivity and electrical conductivity of LDH nanosheets. These synergistic effects lead to strikingly more than 30 times enhanced EOR activity of NiAl-LDH-NSs compared to bulk NiAl-LDHs. The obtained electrocatalytic activity is also much better than those of most Ni- and LDH-based EOR catalysts reported to date. In addition, the ultrathin NiAl-LDH-NS electrocatalyst also exhibits good long-term stability (maintain 81.8% of the original value after 10000 s). This study not only provides a highly competitive EOR catalyst, but also opens new avenues toward the design of highly efficient electrode materials that have various potential applications in supercapacitor, Ni-MH battery and other electrocatalytic systems.

Flexibility Matters: Cooperative Active Sites in Covalent Organic Framework and Threaded Ionic Polymer.

PubMed

Sun, Qi; Aguila, Briana; Perman, Jason; Nguyen, Nicholas; Ma, Shengqian

2016-12-07

The combination of two or more reactive centers working in concert on a substrate to facilitate the reaction is now considered state of the art in catalysis, yet there still remains a tremendous challenge. Few heterogeneous systems of this sort have been exploited, as the active sites spatially separated within the rigid framework are usually difficult to cooperate. It is now shown that this roadblock can be surpassed. The underlying principle of the strategy presented here is the integration of catalytic components with excellent flexibility and porous heterogeneous catalysts, as demonstrated by the placement of linear ionic polymers in close proximity to surface Lewis acid active sites anchored on the walls of a covalent organic framework (COF). Using the cycloaddition of the epoxides and CO 2 as a model reaction, dramatic activity improvements have been achieved for the composite catalysts in relation to the individual catalytic component. Furthermore, they also clearly outperform the benchmark catalytic systems formed by the combination of the molecular organocatalysts and heterogeneous Lewis acid catalysts, while affording additional recyclability. The extraordinary flexibility and enriched concentration of the catalytically active moieties on linear polymers facilitate the concerted catalysis, thus leading to superior catalytic performance. This work therefore uncovers an entirely new strategy for designing bifunctional catalysts with double-activation behavior and opens a new avenue in the design of multicapable systems that mimic biocatalysis.

Attrition Resistant Iron-Based Catalysts For F-T SBCRs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adeyinka A. Adeyiga

2006-01-31

The Fischer-Tropsch (F-T) reaction provides a way of converting coal-derived synthesis gas (CO+ H{sub 2}) to liquid fuels. Since the reaction is highly exothermic, one of the major problems in control of the reaction is heat removal. Recent work has shown that the use of slurry bubble column reactors (SBCRs) can largely solve this problem. The use of iron-(FE) based catalysts is attractive not only due to their low cost and ready availability, but also due to their high water-gas shift activity which makes it possible to use these catalysts with low H{sub 2}/CO ratios. However, a serious problem withmore » the use of Fe catalysts in a SBCR is their tendency to undergo attrition. This can cause fouling/plugging of downstream filters and equipment; makes the separation of catalyst from the oil/wax product very difficult, if not impossible; and results in a steady loss of catalyst from the reactor. Under a previous Department of Energy (DOE)/University Research Grant (UCR) grant, Hampton University reported, for the first time, the development of demonstrably attrition-resistant Fe F-T synthesis catalysts having good activity, selectivity, and attrition resistance. These catalysts were prepared by spray drying Fe catalysts with potassium (K), copper (Cu), and silica (SiO{sub 2}) as promoters. SiO{sub 2} was also used as a binder for spray drying. These catalysts were tested for activity and selectivity in a laboratory-scale fixed-bed reactor. Fundamental understanding of attrition is being addressed by incorporating suitable binders into the catalyst recipe. This has resulted in the preparation of a spray dried HPR-43 catalyst having average particle size (aps) of 70 {micro}m with high attrition resistance. This HPR-43 attrition resistant, active and selective catalyst gave 95% CO conversion through 125 hours of testing in a fixed-bed at 270 C, 1.48 MPa, H{sub 2}/CO=0.67 and 2.0 NL/g-cat/h with C{sub 5+} selectivity of >78% and methane selectivity of less than 5% at an {alpha} of 0.9. Research is proposed to enable further development and optimization of these catalysts by (1) better understanding the role and interrelationship of various catalyst composition and preparation parameters on attrition resistance, activity, and selectivity of these catalysts, (2) the presence of sulfide ions on a precipitated iron catalyst, and (3) the effect of water on sulfided iron F-T catalysts for its activity, selectivity, and attrition. Catalyst preparations will be based on spray drying. The research employed, among other measurements, attrition testing and F-T synthesis at high pressure. Catalyst activity and selectivity is evaluated using a small fixed-bed reactor and a continuous stirred tank reactor (CSTR). The catalysts were prepared by co-precipitation, followed by binder addition and spray drying at 250 C in a 1-m-diameter, 2-m-tall spray dryer. The binder silica content was varied from 0 to 20 wt%. The results show that the use of small amounts of precipitated SiO{sub 2} alone in spray-dried Fe catalysts can result in good attrition resistance. All catalysts investigated with SiO2 wt% {le} 12 produced fines less than 10 wt% during the jet cup attrition test, making them suitable for long-term use in a slurry bubble column reactor. Thus, concentration rather than the type of SiO{sub 2} incorporated into catalyst has a more critical impact on catalyst attrition resistance of spray-dried Fe catalysts. Lower amounts of SiO{sub 2} added to a catalyst give higher particle densities and therefore higher attrition resistances. In order to produce a suitable SBCR catalyst, however, the amount of SiO{sub 2} added has to be optimized to provide adequate surface area, particle density, and attrition resistance. Two of the catalysts with precipitated and binder silica were tested in Texas A&M University's CSTR (Autoclave Engineers). The two catalysts were also tested at The Center for Applied Energy Research in Lexington, Kentucky of the University of Kentucky. Spray-dried catalysts with compositions 100 Fe/5 Cu/4.2 K/11 (P) SiO{sub 2} and 100 Fe/5 Cu/4.2 K/1.1 (B) SiO{sub 2} have excellent selectivity characteristics (low methane and high C{sub 5+} yields), but their productivity and stability (deactivation rate) need to be improved. Mechanical integrity (attrition strength) of these two catalysts was markedly dependent upon their morphological features. The attrition strength of the catalyst made out of largely spherical particles (1.1 (B) SiO{sub 2}) was considerably higher than that of the catalyst consisting of irregularly shaped particles (11 (P) SiO{sub 2}).« less

Visible light driven mineralization of spiramycin over photostructured N-doped TiO2 on up conversion phosphors.

PubMed

Sacco, Olga; Vaiano, Vincenzo; Sannino, Diana; Ciambelli, Paolo

2017-04-01

A novel visible light-active photocatalyst formulation (NdT/OP) was obtained by supporting N-doped TiO 2 (NdT) particles on up-conversion luminescent organic phosphors (OP). The photocatalytic activity of such catalysts was evaluated for the mineralization process of spiramycin in aqueous solution. The effect of NdT loading in the range 15-60wt.% on bulk and surface characteristics of NdT/OP catalysts was investigated by several chemico-physical characterization techniques. The photocatalytic performance of NdT/OP catalysts in the removal of spyramicin from aqueous solution was assessed through photocatalytic tests under visible light irradiation. Total organic carbon (TOC) of aqueous solution, and CO and CO 2 gas concentrations evolved during the photodegradation were analyzed. A dramatic enhancement of photocatalytic activity of the photostructured visible active NdT/OP catalysts, compared to NdT catalyst, was observed. Only CO 2 was detected in gas-phase during visible light irradiation, proving that the photocatalytic process is effective in the mineralization of spiramycin, reaching very high values of TOC removal. The photocatalyst NdT/OP at 30wt.% of NdT loading showed the highest photocatalytic activity (58% of TOC removed after 180min irradiation against only 31% removal after 300min of irradiation of NdT). We attribute this enhanced activity to the high effectiveness in the utilization of visible light through improved light harvesting and exploiting. OP particles act as "photoactive support", able to be excited by the external visible light irradiation, and reissue luminescence of wavelength suitable to promote NdT photomineralization activity. Copyright © 2016. Published by Elsevier B.V.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ye, Rong; Zhukhovitskiy, Aleksandr V.; Deraedt, Christophe V.

Recyclable catalysts, especially those that display selective reactivity, are vital for the development of sustainable chemical processes. Among available catalyst platforms, heterogeneous catalysts are particularly well-disposed toward separation from the reaction mixture via filtration methods, which renders them readily recyclable. Furthermore, heterogeneous catalysts offer numerous handles—some without homogeneous analogues—for performance and selectivity optimization. These handles include nanoparticle size, pore profile of porous supports, surface ligands and interface with oxide supports, and flow rate through a solid catalyst bed. Despite these available handles, however, conventional heterogeneous catalysts are themselves often structurally heterogeneous compared to homogeneous catalysts, which complicates efforts to optimizemore » and expand the scope of their reactivity and selectivity. Ongoing efforts in our laboratories are aimed to address the above challenge by heterogenizing homogeneous catalysts, which can be defined as the modification of homogeneous catalysts to render them in a separable (solid) phase from the starting materials and products. Specifically, we grow the small nanoclusters in dendrimers, a class of uniform polymers with the connectivity of fractal trees and generally radial symmetry. Thanks to their dense multivalency, shape persistence, and structural uniformity, dendrimers have proven to be versatile scaffolds for the synthesis and stabilization of small nanoclusters. Then these dendrimer-encapsulated metal clusters (DEMCs) are adsorbed onto mesoporous silica. Through this method, we have achieved selective transformations that had been challenging to accomplish in a heterogeneous setting, e.g., π-bond activation and aldol reactions. Extensive investigation into the catalytic systems under reaction conditions allowed us to correlate the structural features (e.g., oxidation states) of the catalysts and their activity. Moreover, we have demonstrated that supported DEMCs are also excellent catalysts for typical heterogeneous reactions, including hydrogenation and alkane isomerization. Critically, these investigations also confirmed that the supported DEMCs are heterogeneous and stable against leaching. Catalysts optimization is achieved through the modulation of various parameters. The clusters are oxidized (e.g., with PhICl 2) or reduced (e.g., with H 2) in situ. Changing the dendrimer properties (e.g., generation, terminal functional groups) is analogous to ligand modification in homogeneous catalysts, which affect both catalytic activity and selectivity. Similarly, pore size of the support is another factor in determining product distribution. In a flow reactor, the flow rate is adjusted to control the residence time of the starting material and intermediates, and thus the final product selectivity. Our approach to heterogeneous catalysis affords various advantages: (1) the catalyst system can tap into the reactivity typical to homogeneous catalysts, which conventional heterogeneous catalysts could not achieve; (2) unlike most homogeneous catalysts with comparable performance, the heterogenized homogeneous catalysts can be recycled; (3) improved activity or selectivity compared to conventional homogeneous catalysts is possible because of uniquely heterogeneous parameters for optimization. Here in this Account, we will briefly introduce metal clusters and describe the synthesis and characterizations of supported DEMCs. We will present the catalysis studies of supported DEMCs in both the batch and flow modes. Lastly, we will summarize the current state of heterogenizing homogeneous catalysis and provide future directions for this area of research.« less

Cresol Izomerization in the Presence of Acid Catalysts

NASA Astrophysics Data System (ADS)

Tarasov, A. L.; Dunaev, S. F.; Kustov, L. M.

2018-02-01

It is shown for toluene oxidation with nitrous oxide that modifying HZSM-5 zeolite with zinc oxide nanoparticles considerably improves the selectivity and yield of cresols. It is found that a 2% ZnO/HZSM-5 composite catalyst also exhibits enhanced and stable activity at high temperatures. For the o-cresol isomerization reaction, this modification of HZSM-5 zeolite greatly reduces the contribution from disproportionation and cracking reactions proceeding with formation of phenol, C6-C9 aromatic hydrocarbons, and xylenols. The regularities of their formation in the presence of the studied catalysts are determined using the results from thermodynamic calculations for the equilibrium concentrations of cresol isomers.

Catalytic wet air oxidation of coke-plant wastewater on ruthenium-based eggshell catalysts in a bubbling bed reactor.

PubMed

Yang, M; Sun, Y; Xu, A H; Lu, X Y; Du, H Z; Sun, C L; Li, C

2007-07-01

Catalytic wet air of coke-plant wastewater was studied in a bubbling bed reactor. Two types of supported Ru-based catalysts, eggshell and uniform catalysts, were employed. Compared with the results in the wet air oxidation of coke-plant wastewater, supported Ru uniform catalysts showed high activity for chemical oxygen demand (COD) and ammonia/ammonium compounds (NH3-N) removal at temperature of 250 degrees C and pressure of 4.8 MPa, and it has been demonstrated that the catalytic activity of uniform catalyst depended strongly on the distribution of active sites of Ru on catalyst. Compared to the corresponding uniform catalysts with the same Ru loading (0.25 wt.% and 0.1 wt.%, respectively), the eggshell catalysts showed higher activities for CODcr removal and much higher activities for NH3-N degradation. The high activity of eggshell catalyst for treatment of coke-plant wastewater can be attributed to the higher density of active Ru sites in the shell layer than that of the corresponding uniform catalyst with the same Ru loading. It has been also evidenced that the active Ru sites in the internal core of uniform catalyst have very little or no contribution to CODcr and NH3-N removal in the total oxidation of coke-plant wastewater.

Towards Highly Performing and Stable PtNi Catalysts in Polymer Electrolyte Fuel Cells for Automotive Application

PubMed Central

Zignani, Sabrina C.; Baglio, Vincenzo; Sebastián, David; Saccà, Ada; Gatto, Irene; Aricò, Antonino S.

2017-01-01

In order to help the introduction on the automotive market of polymer electrolyte fuel cells (PEFCs), it is mandatory to develop highly performing and stable catalysts. The main objective of this work is to investigate PtNi/C catalysts in a PEFC under low relative humidity and pressure conditions, more representative of automotive applications. Carbon supported PtNi nanoparticles were prepared by reduction of metal precursors with formic acid and successive thermal and leaching treatments. The effect of the chemical composition, structure and surface characteristics of the synthesized samples on their electrochemical behavior was investigated. The catalyst characterized by a larger Pt content (Pt3Ni2/C) presented the highest catalytic activity (lower potential losses in the activation region) among the synthesized bimetallic PtNi catalysts and the commercial Pt/C, used as the reference material, after testing at high temperature (95 °C) and low humidification (50%) conditions for automotive applications, showing a cell potential (ohmic drop-free) of 0.82 V at 500 mA·cm−2. In order to assess the electro-catalysts stability, accelerated degradation tests were carried out by cycling the cell potential between 0.6 V and 1.2 V. By comparing the electrochemical and physico-chemical parameters at the beginning of life (BoL) and end of life (EoL), it was demonstrated that the Pt1Ni1/C catalyst was the most stable among the catalyst series, with only a 2% loss of voltage at 200 mA·cm−2 and 12.5% at 950 mA·cm−2. However, further improvements are needed to produce durable catalysts. PMID:28772677

Direct deposit of catalyst on the membrane of direct feed fuel cells

NASA Technical Reports Server (NTRS)

Chun, William (Inventor); Narayanan, Sekharipuram R. (Inventor); Jeffries-Nakamura, Barbara (Inventor); Valdez, Thomas I. (Inventor); Linke, Juergen (Inventor)

2001-01-01

An improved direct liquid-feed fuel cell having a solid membrane electrolyte for electrochemical reactions of an organic fuel. Catalyst utilization and catalyst/membrane interface improvements are disclosed. Specifically, the catalyst layer is applied directly onto the membrane electrolyte.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Junming; Baylon, Rebecca A.; Liu, Changjun

The effects of surface acidity on the cascade ethanol-to-isobutene conversion were studied using ZnxZryOz catalysts. The ethanol-to-isobutene reaction was found to be limited by the secondary reaction of the key intermediate, acetone, namely the acetone-to-isobutene reaction. Although the catalysts with coexisting Brønsted acidity could catalyze the rate-limiting acetone-to-isobutene reaction, the presence of Brønsted acidity is also detrimental. First, secondary isobutene isomerization is favored, producing a mixture of butene isomers. Second, undesired polymerization and coke formation prevail, leading to rapid catalyst deactivation. Most importantly, both steady-state and kinetic reaction studies as well as FTIR analysis of adsorbed acetone-d6 and D2O unambiguouslymore » showed that a highly active and selective nature of balanced Lewis acid-base pairs was masked by the coexisting Brønsted acidity in the aldolization and self-deoxygenation of acetone to isobutene. As a result, ZnxZryOz catalysts with only Lewis acid-base pairs were discovered, on which nearly a theoretical selectivity to isobutene (~88.9%) was successfully achieved, which has never been reported before. Moreover, the absence of Brønsted acidity in such ZnxZryOz catalysts also eliminates the side isobutene isomerization and undesired polymerization/coke reactions, resulting in the production of high purity isobutene with significantly improved catalyst stability (< 2% activity loss after 200 h time-on-stream). This work not only demonstrates a balanced Lewis acid-base pair for the highly active and selective cascade ethanol-to-isobutene reaction, but also sheds light on the rational design of selective and robust acid-base catalyst for C-C coupling via aldolization reaction.« less

Nickel(0) nanoparticles supported on bare or coated cobalt ferrite as highly active, magnetically isolable and reusable catalyst for hydrolytic dehydrogenation of ammonia borane.

PubMed

Manna, Joydev; Akbayrak, Serdar; Özkar, Saim

2017-12-15

Nickel(0) nanoparticles supported on cobalt ferrite (Ni 0 /CoFe 2 O 4 ), polydopamine coated cobalt ferrite (Ni 0 /PDA-CoFe 2 O 4 ) or silica coated cobalt ferrite (Ni 0 /SiO 2 -CoFe 2 O 4 ) are prepared and used as catalysts in hydrogen generation from the hydrolysis of ammonia borane at room temperature. Ni 0 /CoFe 2 O 4 (4.0% wt. Ni) shows the highest catalytic activity with a TOF value of 38.3min -1 in hydrogen generation from the hydrolysis of ammonia borane at 25.0±0.1°C. However, the initial catalytic activity of Ni 0 /CoFe 2 O 4 catalyst is not preserved in subsequent runs of hydrolysis. Coating the surface of cobalt ferrite support with polydopamine or silica leads to a significant improvement in the stability of catalysts. The TOF values of Ni 0 /PDA-CoFe 2 O 4 and Ni 0 /SiO 2 -CoFe 2 O 4 are found to be 7.6 and 5.3min -1 , respectively, at 25.0±0.1°C. Ni 0 /PDA-CoFe 2 O 4 catalyst shows high reusability as compared to the Ni 0 /CoFe 2 O 4 and Ni 0 /SiO 2 -CoFe 2 O 4 catalysts in hydrolytic dehydrogenation of ammonia borane at room temperature. All the catalysts are characterized by using a combination of various advanced analytical techniques. The results reveal that nickel nanoparticles with an average size of 12.3±0.7nm are well dispersed on the surface of PDA-CoFe 2 O 4 . . Copyright © 2017 Elsevier Inc. All rights reserved.

Surface hydrophobicity and acidity effect on alumina catalyst in catalytic methanol dehydration reaction

PubMed Central

Osman, Ahmed I; Thompson, Jillian; Halawy, Samih A; Mohamed, Mohamed A

2017-01-01

Abstract BACKGROUND Methanol to dimethyl ether (MTD) is considered one of the main routes for the production of clean bio‐fuel. The effect of copper loading on the catalytic performance of different phases of alumina that formed by calcination at two different temperatures was examined for the dehydration of methanol to dimethyl ether (DME). RESULTS A range of Cu loadings of (1, 2, 4, 6, 10 and 15% Cu wt/wt) on Al2O3 calcined at 350 and 550 °C were prepared and characterized by TGA, XRD, BET, NH3‐TPD, TEM, H2‐TPR, SEM, EDX, XPS and DRIFT‐Pyridine techniques. The prepared catalysts were used in a fixed bed reactor under reaction conditions in which the temperature ranged from 180–300 °C with weight hourly space velocity (WHSV) = 12.1 h‐1. It was observed that all catalysts calcined at 550 °C (γ‐Al2O3 support phase) exhibited higher activity than those calcined at 350 °C (γ‐AlOOH), and this is due to the phase support change. Furthermore, the optimum Cu loading was found to be 6% Cu/γ‐Al2O3 with this catalyst also showing a high degree of stability under steady state conditions and this is attributed to the enhancement in surface acidity and hydrophobicity. CONCLUSION The addition of copper to the support improved the catalyst properties and activity. For all the copper modified catalysts, the optimum catalyst with high degree of activity and stability was 6% copper loaded on gamma alumina. © 2017 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. PMID:29200585

Spongy Raney nickel hydrogen electrodes for alkaline fuel cells

NASA Astrophysics Data System (ADS)

Tomida, Tahei; Nakabayashi, Ichiro

1989-11-01

Spongy Raney nickel catalysts for use as hydrogen electrodes of fuel cells were prepared by a new method. In this method molten aluminum was sprayed on both sides of a spongy plate of nickel as substrate with an acetylene-oxygen flame gun. Then, the spongy nickel electrodes were activated by alloying at a given temperature of from 550 to 750 C, and leaching the aluminum from the alloy in alkaline solution. This type of catalyst showed good thermal and electrical conductivity and also mechanical strength by itself. Its polarization resistance was very low, and the characteristics of the electrodes improved with increase in the temperature of heat-treatment for alloying. The finding that activity depended on the alloying temperature was consistent with observations by scanning electron microscope on the surface textures of catalysts alloyed at different temperatures.

Mechanistic Studies at the Interface Between Organometallic Chemistry and Homogeneous Catalysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Casey, Charles P

Mechanistic Studies at the Interface Between Organometallic Chemistry and Homogeneous Catalysis Charles P. Casey, Principal Investigator Department of Chemistry, University of Wisconsin - Madison, Madison, Wisconsin 53706 Phone 608-262-0584 FAX: 608-262-7144 Email: casey@chem.wisc.edu http://www.chem.wisc.edu/main/people/faculty/casey.html Executive Summary. Our goal was to learn the intimate mechanistic details of reactions involved in homogeneous catalysis and to use the insight we gain to develop new and improved catalysts. Our work centered on the hydrogenation of polar functional groups such as aldehydes and ketones and on hydroformylation. Specifically, we concentrated on catalysts capable of simultaneously transferring hydride from a metal center and a proton frommore » an acidic oxygen or nitrogen center to an aldehyde or ketone. An economical iron based catalyst was developed and patented. Better understanding of fundamental organometallic reactions and catalytic processes enabled design of energy and material efficient chemical processes. Our work contributed to the development of catalysts for the selective and mild hydrogenation of ketones and aldehydes; this will provide a modern green alternative to reductions by LiAlH4 and NaBH4, which require extensive work-up procedures and produce waste streams. (C5R4OH)Ru(CO)2H Hydrogenation Catalysts. Youval Shvo described a remarkable catalytic system in which the key intermediate (C5R4OH)Ru(CO)2H (1) has an electronically coupled acidic OH unit and a hydridic RuH unit. Our efforts centered on understanding and improving upon this important catalyst for reduction of aldehydes and ketones. Our mechanistic studies established that the reduction of aldehydes by 1 to produce alcohols and a diruthenium bridging hydride species occurs much more rapidly than regeneration of the ruthenium hydride from the diruthenium bridging hydride species. Our mechanistic studies require simultaneous transfer of hydride from ruthenium to the aldehyde carbon and of a proton from the CpOH unit to the aldehyde oxygen and support reduction of the aldehyde without its prior coordination to ruthenium. Another important step in the catalysis is the regeneration of 1 from reaction of H2 with the stable diruthenium bridging hydride complex 2. Studies of the microscopic reverse of this process (hydrogen evolution from 1 which occurs at 80°C) in the presence of alcohol (the product of aldehyde hydrogenation) have shown that a dihydrogen complex is formed reversibly at a rate much faster than hydrogen evolution. Kinetic and theoretical studies in collaboration with Professor Qiang Cui of Wisconsin indicated an important role for alcohol in mediating transfer of hydrogen to ruthenium. One key to developing more active catalysts was to destabilize the bridging hydride intermediate 2 to prevent its formation or to speed its conversion to a reactive monohydride 1 by reaction with H2. We found several successful ways to destabilize the bridging hydride and to obtain more active catalysts. Most recently, we discovered related iron catalysts for hydrogenation that do not form dimers; the cost advantage of iron catalysts is spectacular. Iron Catalysts. In an exciting development, we found that a related iron complex is also a very active ketone hydrogenation catalyst. This hydrogenation catalyst shows high chemoselectivity for aldehydes, ketones, and imines and isolated C=C, CºC, C-X, -NO2, epoxides, and ester functions are unaffected by the hydrogenation conditions. Mechanistic studies have established a reversible hydrogen transfer step followed by rapid dihydrogen activation. The same iron complex also catalyzes transfer hydrogenation of ketones.« less

Study of catalysis for solid oxide fuel cells and direct methanol fuel cells

NASA Astrophysics Data System (ADS)

Jiang, Xirong

Fuel cells offer the enticing promise of cleaner electricity with lower environmental impact than traditional energy conversion technologies. Driven by the interest in power sources for portable electronics, and distributed generation and automotive propulsion markets, active development efforts in the technologies of both solid oxide fuel cell (SOFC) and direct methanol fuel cell (DMFC) devices have achieved significant progress. However, current catalysts for fuel cells are either of low catalytic activity or extremely expensive, presenting a key barrier toward the widespread commercialization of fuel cell devices. In this thesis work, atomic layer deposition (ALD), a novel thin film deposition technique, was employed to apply catalytic Pt to SOFC, and investigate both Pt skin catalysts and Pt-Ru catalysts for methanol oxidation, a very important reaction for DMFC, to increase the activity and utilization levels of the catalysts while simultaneously reducing the catalyst loading. For SOFCs, we explored the use of ALD for the fabrication of electrode components, including an ultra-thin Pt film for use as the electrocatalyst, and a Pt mesh structure for a current collector for SOFCs, aiming for precise control over the catalyst loading and catalyst geometry, and enhancement in the current collect efficiency. We choose Pt since it has high chemical stability and excellent catalytic activity for the O2 reduction reaction and the H2 oxidation reaction even at low operating temperatures. Working SOFC fuel cells were fabricated with ALD-deposited Pt thin films as an electrode/catalyst layer. The measured fuel cell performance reveals that comparable peak power densities were achieved for ALD-deposited Pt anodes with only one-fifth of the Pt loading relative to a DC-sputtered counterpart. In addition to the continuous electrocatalyst layer, a micro-patterned Pt structure was developed via the technique of area selective ALD. By coating yttria-stabilized zirconia, a typical solid oxide electrolyte, with patterned (octadecyltrichlorosilane) ODTS self-assembled monolayers (SAMs), Pt thin films were grown selectively on the SAM-free surface regions. Features with sizes as small as 2 mum were deposited by this combined ALD-muCP method. The micro-patterned Pt structure deposited by area selective ALD was applied to SOFCs as a current collector grid/patterned catalyst. An improvement in the fuel cell performance by a factor of 10 was observed using the Pt current collector grids/patterned catalyst integrated onto cathodic La0.6Sr 0.4Co0.2Fe0.8O3-delta. For possible catalytic anodes in DMFCs employing a 1:1 stoichiometric methanol-water reforming mixture, two strategies were employed in this thesis. One approach is to fabricate skin catalysts, where ALD Pt films of various thicknesses were used to coat sputtered Ru films forming Pt skin catalysts for study of methanol oxidation. Another strategy is to replace or alloy Pt with Ru; for this effort, both dc-sputtering and atomic layer deposition were employed to fabricate Pt-Ru catalysts of various Ru contents. The electrochemical behavior of all of the Pt skin catalysts, the DC co-sputtered Pt-Ru catalysts and the ALD co-deposited Pt-Ru catalysts were evaluated at room temperature for methanol oxidation using cyclic voltammetry and chronoamperometry in highly concentrated 16.6 M MeOH, which corresponds to the stoichiometric fuel that will be employed in next generation DMFCs that are designed to minimize or eliminate methanol crossover. The catalytic activity of sputtered Ru catalysts toward methanol oxidation is strongly enhanced by the ALD Pt overlayer, with such skin layer catalysts displaying superior catalytic activity over pure Pt. For both the DC co-sputtered catalysts and ALD co-deposited catalysts, the electrochemical studies illustrate that the optimal stoichiometry ratio for Pt to Ru is approximately 1:1, which is in good agreement with most literature.

Nanoporous gold as an active low temperature catalyst toward CO oxidation in hydrogen-rich stream

PubMed Central

Li, Dongwei; Zhu, Ye; Wang, Hui; Ding, Yi

2013-01-01

Preferential CO oxidation (PROX) was investigated by using dealloyed nanoporous gold (NPG) catalyst under ambient conditions. Systematic investigations were carried out to characterize its catalytic performance by varying reaction parameters such as temperature and co-existence of CO2 and H2O, which revealed that NPG was a highly active and selective catalyst for PROX, especially at low temperature. At 20°C, the exit CO concentration could be reduced to less than 2 ppm with a turnover frequency of 4.1 × 10−2 s−1 at a space velocity of 120,000 mL h−1 g−1cat. and its high activity could retain for more than 24 hours. The presence of residual Ag species in the structure did not seem to improve the intrinsic activity of NPG for PROX; however, they contributed to the stabilization of the NPG structure and apparent catalytic activity. These results indicated that NPG might be readily applicable for hydrogen purification in fuel cell applications. PMID:24145317

Process for the synthesis of aliphatic alcohol-containing mixtures

DOEpatents

Greene, Marvin I.; Gelbein, Abraham P.

1984-01-01

A process for the synthesis of mixtures which include saturated aliphatic alcohols is disclosed. In the first step of the process, the first catalyst activation stage, a catalyst, which comprises the oxides of copper, zinc, aluminum, potassium and one or two additional metals selected from the group consisting of chromium, magnesium, cerium, cobalt, thorium and lanthanum, is partially activated. In this step, a reducing gas stream, which includes hydrogen and at least one inert gas, flows past the catalyst at a space velocity of up to 5,000 liters (STP) per hour, per kilogram of catalyst. The partially activated catalyst is then subjected to the second step of the process, second-stage catalyst activation. In this step, the catalyst is contacted by an activation gas stream comprising hydrogen and carbon monoxide present in a volume ratio of 0.5:1 and 4:1, respectively, at a temperature of 200.degree. to 450.degree. C. and a pressure of between 35 and 200 atmospheres. The activation gas flows at a space velocity of from 1,000 to 20,000 liters (STP) per hour, per kilogram of catalyst. Second-stage activation continues until the catalyst is contacted with at least 500,000 liters (STP) of activation gas per kilogram of catalyst. The fully activated catalyst, in the third step of the process, contacts a synthesis gas stream comprising hydrogen and carbon monoxide.

Process for the synthesis of aliphatic alcohol-containing mixtures

DOEpatents

Greene, M.I.; Gelbein, A.P.

1984-10-16

A process for the synthesis of mixtures which include saturated aliphatic alcohols is disclosed. In the first step of the process, the first catalyst activation stage, a catalyst, which comprises the oxides of copper, zinc, aluminum, potassium and one or two additional metals selected from the group consisting of chromium, magnesium, cerium, cobalt, thorium and lanthanum, is partially activated. In this step, a reducing gas stream, which includes hydrogen and at least one inert gas, flows past the catalyst at a space velocity of up to 5,000 liters (STP) per hour, per kilogram of catalyst. The partially activated catalyst is then subjected to the second step of the process, second-stage catalyst activation. In this step, the catalyst is contacted by an activation gas stream comprising hydrogen and carbon monoxide present in a volume ratio of 0.5:1 and 4:1, respectively, at a temperature of 200 to 450 C and a pressure of between 35 and 200 atmospheres. The activation gas flows at a space velocity of from 1,000 to 20,000 liters (STP) per hour, per kilogram of catalyst. Second-stage activation continues until the catalyst is contacted with at least 500,000 liters (STP) of activation gas per kilogram of catalyst. The fully activated catalyst, in the third step of the process, contacts a synthesis gas stream comprising hydrogen and carbon monoxide.

A ship-in-a-bottle strategy to synthesize encapsulated intermetallic nanoparticle catalysts: Exemplified for furfural hydrogenation

DOE PAGES

Maligal-Ganesh, Raghu V.; Xiao, Chaoxian; Goh, Tian Wei; ...

2016-01-28

In this paper, intermetallic compounds are garnering increasing attention as efficient catalysts for improved selectivity in chemical processes. Here, using a ship-in-a-bottle strategy, we synthesize single-phase platinum-based intermetallic nanoparticles (NPs) protected by a mesoporous silica (mSiO 2) shell by heterogeneous reduction and nucleation of Sn, Pb, or Zn in mSiO 2-encapsulated Pt NPs. For selective hydrogenation of furfural to furfuryl alcohol, a dramatic increase in activity and selectivity is observed when intermetallic NPs catalysts are used in comparison to Pt@mSiO 2. Among the intermetallic NPs, PtSn@mSiO 2 exhibits the best performance, requiring only one-tenth of the quantity of Pt usedmore » in Pt@mSiO 2 for similar activity and near 100% selectivity to furfuryl alcohol. A high-temperature oxidation–reduction treatment easily reverses any carbon deposition-induced catalyst deactivation. X-ray photoelectron spectroscopy shows the importance of surface composition to the activity, whereas density functional theory calculations reveal that the enhanced selectivity on PtSn compared to Pt is due to the different furfural adsorption configurations on the two surfaces.« less

Interfaces in Heterogeneous Catalysts: Advancing Mechanistic Understanding through Atomic-Scale Measurements.

PubMed

Gao, Wenpei; Hood, Zachary D; Chi, Miaofang

2017-04-18

Developing novel catalysts with high efficiency and selectivity is critical for enabling future clean energy conversion technologies. Interfaces in catalyst systems have long been considered the most critical factor in controlling catalytic reaction mechanisms. Interfaces include not only the catalyst surface but also interfaces within catalyst particles and those formed by constructing heterogeneous catalysts. The atomic and electronic structures of catalytic surfaces govern the kinetics of binding and release of reactant molecules from surface atoms. Interfaces within catalysts are introduced to enhance the intrinsic activity and stability of the catalyst by tuning the surface atomic and chemical structures. Examples include interfaces between the core and shell, twin or domain boundaries, or phase boundaries within single catalyst particles. In supported catalyst nanoparticles (NPs), the interface between the metallic NP and support serves as a critical tuning factor for enhancing catalytic activity. Surface electronic structure can be indirectly tuned and catalytically active sites can be increased through the use of supporting oxides. Tuning interfaces in catalyst systems has been identified as an important strategy in the design of novel catalysts. However, the governing principle of how interfaces contribute to catalyst behavior, especially in terms of interactions with intermediates and their stability during electrochemical operation, are largely unknown. This is mainly due to the evolving nature of such interfaces. Small changes in the structural and chemical configuration of these interfaces may result in altering the catalytic performance. These interfacial arrangements evolve continuously during synthesis, processing, use, and even static operation. A technique that can probe the local atomic and electronic interfacial structures with high precision while monitoring the dynamic interfacial behavior in situ is essential for elucidating the role of interfaces and providing deeper insight for fine-tuning and optimizing catalyst properties. Scanning transmission electron microscopy (STEM) has long been a primary characterization technique used for studying nanomaterials because of its exceptional imaging resolution and simultaneous chemical analysis. Over the past decade, advances in STEM, that is, the commercialization of both aberration correctors and monochromators, have significantly improved the spatial and energy resolution. Imaging atomic structures with subangstrom resolution and identifying chemical species with single-atom sensitivity are now routine for STEM. These advancements have greatly benefitted catalytic research. For example, the roles of lattice strain and surface elemental distribution and their effect on catalytic stability and reactivity have been well documented in bimetallic catalysts. In addition, three-dimensional atomic structures revealed by STEM tomography have been integrated in theoretical modeling for predictive catalyst NP design. Recent developments in stable electronic and mechanical devices have opened opportunities to monitor the evolution of catalysts in operando under synthesis and reaction conditions; high-speed direct electron detectors have achieved sub-millisecond time resolutions and allow for rapid structural and chemical changes to be captured. Investigations of catalysts using these latest microscopy techniques have provided new insights into atomic-level catalytic mechanisms. Further integration of new microscopy methods is expected to provide multidimensional descriptions of interfaces under relevant synthesis and reaction conditions. In this Account, we discuss recent insights on understanding catalyst activity, selectivity, and stability using advanced STEM techniques, with an emphasis on how critical interfaces dictate the performance of precious metal-based heterogeneous catalysts. The role of extended interfacial structures, including those between core and shell, between separate phases and twinned grains, between the catalyst surface and gas, and between metal and support are discussed. We also provide an outlook on how emerging electron microscopy techniques, such as vibrational spectroscopy and electron ptychography, will impact future catalysis research.

ZIF-67-derived hollow nanocages with layered double oxides shell as high-Efficiency catalysts for CO oxidation

NASA Astrophysics Data System (ADS)

Kong, Wenpeng; Li, Jing; Chen, Yao; Ren, Yuqing; Guo, Yonghua; Niu, Shengli; Yang, Yanzhao

2018-04-01

Constructing non-precious hybrid metal oxides with specific morphology as cost-effective and highly efficient catalysts is a promising way for the automotive exhaust purification. In this work, we report a facile strategy for the fabrication of a unique hollow Co-Ni layered double oxides (HLDO) nanocages by using zeolitic imidazole frameworks (ZIFs) as template. The synthesis of intermediate core-shell and hollow Co-Ni layered double hydroxides (HLDH) nanoflakes as well as the corresponding Co-Ni oxides products were successfully controlled, and the formation process was also explained. Among ZIF-67-derived oxides, HLDO exhibits excellent catalytic activities (complete conversion of CO into CO2 at 118 °C) and long-term stability for CO oxidation. The remarkable catalytic activities of HLDO can be attributed to high surface area (258 m2 g-1) inherited from the HLDH, which could provide more active sites for CO oxidation. In addition, active oxygen species indicated by the O 1 s XPS spectrum and improved synergistic effect between NiO and Co3O4 reflected by H2-TPR, further explain the enhanced performance of the HLDO catalysts. The presented strategy for controlled design and synthesis of hollow multicomponent metal oxides will provide prospects in developing highly effective catalysts.

Preparation and Characterization of TiO2-Based Photocatalysts by Chemical Vapour Deposition

NASA Astrophysics Data System (ADS)

Nacevski, Goran; Marinkovski, Mirko; Tomovska, Radmila; Fajgar, Radek

In the present work, a novel technique for the preparation of TiO2-based photocatalysts modified with SiO2 is presented, using a pulsed ArF laser to induce a chemical vapor deposition process. The irradiated gas mixture was composed of TiCl4/SiCl4 precursors in excess of oxygen. Laser irradiation at 193 nm with a repetition frequency of 10 Hz induced the deposition of thin nano-sized mixed oxide films. In order to improve the photocatalytic activity of the catalysts and to expand the activity from the UV to the visible part of the spectrum, doping of the catalysts with chromium oxides was performed. For that aim, the same technique of catalyst preparation was used, irradiating the same gas mixture with the addition of chromyl chloride as Cr precursor. The thin films prepared were annealed up to 500°C in order to remove crystal defects, which could be responsible for poor photocatalytic activity. The dependence of structure and properties on reaction process and irradiation conditions (laser energy and fluence, precursors pressure) were examined. The main aim was to find the best conditions for the production of highly photoactive catalysts and to decrease deactivation processes during the photo-oxidation. The composition, structure and morphology of the oxide catalysts prepared were studied by various spectroscopies, electron microscopy and diffraction techniques.

Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts

PubMed Central

Varnell, Jason A.; Tse, Edmund C. M.; Schulz, Charles E.; Fister, Tim T.; Haasch, Richard T.; Timoshenko, Janis; Frenkel, Anatoly I.; Gewirth, Andrew A.

2016-01-01

The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites. PMID:27538720

Dealloyed Pt3Co nanoparticles with higher geometric strain for superior hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Saquib, Mohammad; Halder, Aditi

2018-06-01

In the present work, the effect of surface strain in the carbon supported Pt3Co dealloy catalyst towards hydrogen evolution reaction (HER) has been reported. Dealloying process is adopted to generate the geometric strain in Pt3Co/C alloy by preferential dissolution of non-noble metal (Co) from the alloy. The developed geometric strain has been estimated by different microstructural characterization techniques. Electrochemical studies showed that the highest current density for HER was obtained for Pt3Co/C dealloy catalyst and it was nearly 2 and 5 times higher than Pt3Co/C alloy and Pt/C respectively. Tafel slope for HER was improved from 49 (Pt/C) to 34 mV dec-1 (Pt3Co/C dealloy), indicating that the surface strain plays important role in the improvement of the catalytic activity of Pt3Co catalyst. The chronoamperometry data, LSV curves and ECSA values before and after chronoamperometry confirmed that Pt3Co/C dealloy catalyst was a stable as well as a durable electrocatalyst for HER.

[Biosynthesis of indigo and indirubin by whole-cell catalyst designed by combination of protein engineering and metabolic engineering].

PubMed

Li, Yang; Zhu, Junge; Wang, Jianjun; Xia, Huanzhang; Wu, Sheng

2016-01-01

The phenylacetone monooxygenase, isolated from Thermobifida fusca, mainly catalyzes Baeyer-Villiger oxidation reaction towards aromatic compounds. Met446 plays a vital role in catalytic promiscuity, based on the structure and function of phenylacetone monooxygenase. Mutation in Met446 locus can offer enzyme new catalytic feature to activate C-H bond, oxidizing indole to finally generate indigo and indirubin, but the yield was only 1.89 mg/L. In order to further improve the biosynthesis efficiency of the whole-cell catalyst, metabolic engineering was applied to change glucose metabolism pathway of Escherichia coli. Blocking glucose isomerase gene pgi led to pentose phosphate pathway instead of the glycolytic pathway to become the major metabolic pathways of glucose, which provided more cofactor NADPH needed in enzymatic oxidation of indole. Engineering the host E. coli led to synthesis of indigo and indirubin efficiency further increased to 25 mg/L. Combination of protein and metabolic engineering to design efficient whole-cell catalysts not only improves the synthesis of indigo and indirubin, but also provides a novel strategy for whole-cell catalyst development.

The Effect of K and Acidity of NiW-Loaded HY Zeolite Catalyst for Selective Ring Opening of 1-Methylnaphthalene.

PubMed

Lee, You-Jin; Kim, Eun-Sang; Kim, Jeong-Rang; Kim, Joo-Wan; Kim, Tae-Wan; Chae, Ho-Jeong; Kim, Chul-Ung; Lee, Chang-Ha; Jeong, Soon-Yong

2016-05-01

Bi-functional catalysts were prepared using HY zeolites with various SiO2/Al2O3 ratios for acidic function, NiW for metallic function, and K for acidity control. 1-Methylnaphthalene was selected as a model compound for multi-ring aromatics in heavy oil, and its selective ring opening reaction was investigated using the prepared bi-functional catalysts with different levels of acidity in a fixed bed reactor system. In NiW/HY catalysts without K addition, the acidity decreased with the SiO2/Al2O3 mole ratio of the HY zeolite. Ni1.1W1.1/HY(12) catalyst showed the highest acidity but slightly lower yields for the selective ring opening than Ni1.1W1.1/HY(30) catalyst. The acidity of the catalyst seemed to play an important role as the active site for the selective ring opening of 1-methylnaphthalene but there should be some optimum catalyst acidity for the reaction. Catalyst acidity could be controlled between Ni1.1W1.1/HY(12) and Ni1.1W1.1/HY(30) by adding a moderate amount of K to Ni1.1W1.1/HY(12) catalyst. K0.3Ni1.1W1.1/HY(12) catalyst should have the optimum acidity for the selective ring opening. The addition of a moderate amount of K to the NiW/HY catalyst must improve the catalytic performance due to the optimization of catalyst acidity.

CO2 methanation on the catalyst of Ni/MCM-41 promoted with CeO2.

PubMed

Wang, Xiaoliu; Zhu, Lingjun; Liu, Yincong; Wang, Shurong

2018-06-01

CO 2 as a raw feed combined with renewable hydrogen for the production of useful chemicals and alternative energy products is one of the solutions to environmental and energy problems. In this study, a series of Ni-xCeO 2 /MCM-41 catalysts with a nickel content of 20wt% were prepared through deposition precipitation method for CO 2 methanation. Different characterization methods, including BET, XRD, TEM, SEM, H 2 -TPR and H 2 -TPD were applied to help explore the influence mechanism of CeO 2 on Ni/MCM-41 in CO 2 methanation. It was found that all CeO 2 -promoted catalysts exhibited enhanced catalytic activity when compared to Ni/MCM-41. The catalyst modified with 20wt% CeO 2 showed the best catalytic performance, with CO 2 conversion and CH 4 selectivity of 85.6% and 99.8%, respectively, at the temperature of 380°C under atmospheric pressure. The synergetic effects among Ni 0 active sites, the promoter and the support, including nickel dispersion improvement and increased CO 2 adsorption sites due to the addition of CeO 2 , were considered as important factors for high reactivity of the promoted catalysts. The stability test showed that the promoted catalyst maintained its high reactivity after 30h. Copyright © 2017 Elsevier B.V. All rights reserved.

Enhanced selective photocatalytic reduction of CO2 to CH4 over plasmonic Au modified g-C3N4 photocatalyst under UV-vis light irradiation

NASA Astrophysics Data System (ADS)

Li, Hailong; Gao, Yan; Xiong, Zhuo; Liao, Chen; Shih, Kaimin

2018-05-01

A series of Au-g-C3N4 (Au-CN) catalysts were prepared through a NaBH4-reduction method using g-C3N4 (CN) from pyrolysis of urea as precursor. The catalysts' surface area, crystal structure, surface morphology, chemical state, functional group composition and optical properties were characterized by X-ray diffraction, transmission electron microscope, X-ray photoelectron spectroscopy, ultraviolet visible (UV-vis) diffuse reflectance spectra, fourier transform infrared, photoluminescence and transient photocurrent analysis. The carbon dioxide (CO2) photoreduction activities under ultraviolet visible (UV-vis) light irradiation were significantly enhanced when gold (Au) was loaded on the surface of CN. 2Au-CN catalyst with Au to CN mole ratio of 2% showed the best catalytic activity. After 2 h UV-vis light irradiation, the methane (CH4) yield over the 2Au-CN catalyst was 9.1 times higher than that over the pure CN. The CH4 selectivity also greatly improved for the 2Au-CN compared to the CN. The deposited Au nanoparticles facilitated the separation of electron-hole pairs on the CN surface. Moreover, the surface plasmon resonance effect of Au further promoted the generation of hot electrons and visible light absorption. Therefore, Au loading significantly improved CO2 photoreduction performance of CN under UV-vis light irradiation.

Iron-Induced Activation of Ordered Mesoporous Nickel Cobalt Oxide Electrocatalyst for the Oxygen Evolution Reaction.

PubMed

Deng, Xiaohui; Öztürk, Secil; Weidenthaler, Claudia; Tüysüz, Harun

2017-06-28

Herein, ordered mesoporous nickel cobalt oxides prepared by the nanocasting route are reported as highly active oxygen evolution reaction (OER) catalysts. By using the ordered mesoporous structure as a model system and afterward elevating the optimal catalysts composition, it is shown that, with a simple electrochemical activation step, the performance of nickel cobalt oxide can be significantly enhanced. The electrochemical impedance spectroscopy results indicated that charge transfer resistance increases for Co 3 O 4 spinel after an activation process, while this value drops for NiO and especially for CoNi mixed oxide significantly, which confirms the improvement of oxygen evolution kinetics. The catalyst with the optimal composition (Co/Ni 4/1) reaches a current density of 10 mA/cm 2 with an overpotential of a mere 336 mV and a Tafel slope of 36 mV/dec, outperforming benchmarked and other reported Ni/Co-based OER electrocatalysts. The catalyst also demonstrates outstanding durability for 14 h and maintained the ordered mesoporous structure. The cyclic voltammograms along with the electrochemical measurements in Fe-free KOH electrolyte suggest that the activity boost is attributed to the generation of surface Ni(OH) 2 species that incorporate Fe impurities from the electrolyte. The incorporation of Fe into the structure is also confirmed by inductively coupled plasma optical emission spectrometry.

Operando investigation of Au-MnO x thin films with improved activity for the oxygen evolution reaction

DOE PAGES

Frydendal, Rasmus; Seitz, Linsey C.; Sokaras, Dimosthenis; ...

2017-01-20

The electrochemical splitting of water holds great potential as a method for producing clean fuels by storing electricity from intermittent energy sources. The efficiency of such a process would be greatly facilitated by incorporating more active catalysts based on abundant materials for the oxygen evolution reaction. Manganese oxides are promising as catalysts for this reaction. Recent reports show that their activity can be drastically enhanced when modified with gold. Herein, we investigate highly active mixed Au-MnO x thin films for the oxygen evolution reaction, which exhibit more than five times improvement over pure MnO x. These films are characterized withmore » operando X-ray Absorption Spectroscopy, which reveal that Mn assumes a higher oxidation state under reaction conditions when Au is present. As a result, the magnitude of the enhancement is correlated to the size of the Au domains, where larger domains are the more beneficial.« less

Intrinsic selectivity and structure sensitivity of Rhodium catalysts for C 2+ oxygenate production [On the intrinsic selectivity and structure sensitivity of Rhodium catalysts for C 2+ oxygenate production

DOE PAGES

Yang, Nuoya; Medford, Andrew J.; Liu, Xinyan; ...

2016-01-31

Synthesis gas (CO + H 2) conversion is a promising route to converting coal, natural gas, or biomass into synthetic liquid fuels. Rhodium has long been studied as it is the only elemental catalyst that has demonstrated selectivity to ethanol and other C 2+ oxygenates. However, the fundamentals of syngas conversion over rhodium are still debated. In this work a microkinetic model is developed for conversion of CO and H 2 into methane, ethanol, and acetaldehyde on the Rh (211) and (111) surfaces, chosen to describe steps and close-packed facets on catalyst particles. The model is based on DFT calculationsmore » using the BEEF-vdW functional. The mean-field kinetic model includes lateral adsorbate–adsorbate interactions, and the BEEF-vdW error estimation ensemble is used to propagate error from the DFT calculations to the predicted rates. The model shows the Rh(211) surface to be ~6 orders of magnitude more active than the Rh(111) surface, but highly selective toward methane, while the Rh(111) surface is intrinsically selective toward acetaldehyde. A variety of Rh/SiO 2 catalysts are synthesized, tested for catalytic oxygenate production, and characterized using TEM. The experimental results indicate that the Rh(111) surface is intrinsically selective toward acetaldehyde, and a strong inverse correlation between catalytic activity and oxygenate selectivity is observed. Furthermore, iron impurities are shown to play a key role in modulating the selectivity of Rh/SiO 2 catalysts toward ethanol. The experimental observations are consistent with the structure-sensitivity predicted from theory. As a result, this work provides an improved atomic-scale understanding and new insight into the mechanism, active site, and intrinsic selectivity of syngas conversion over rhodium catalysts and may also guide rational design of alloy catalysts made from more abundant elements.« less

A New Bioinspired Perchlorate Reduction Catalyst with Significantly Enhanced Stability via Rational Tuning of Rhenium Coordination Chemistry and Heterogeneous Reaction Pathway.

PubMed

Liu, Jinyong; Han, Mengwei; Wu, Dimao; Chen, Xi; Choe, Jong Kwon; Werth, Charles J; Strathmann, Timothy J

2016-06-07

Rapid reduction of aqueous ClO4(-) to Cl(-) by H2 has been realized by a heterogeneous Re(hoz)2-Pd/C catalyst integrating Re(O)(hoz)2Cl complex (hoz = oxazolinyl-phenolato bidentate ligand) and Pd nanoparticles on carbon support, but ClOx(-) intermediates formed during reactions with concentrated ClO4(-) promote irreversible Re complex decomposition and catalyst deactivation. The original catalyst design mimics the microbial ClO4(-) reductase, which integrates Mo(MGD)2 complex (MGD = molybdopterin guanine dinucleotide) for oxygen atom transfer (OAT). Perchlorate-reducing microorganisms employ a separate enzyme, chlorite dismutase, to prevent accumulation of the destructive ClO2(-) intermediate. The structural intricacy of MGD ligand and the two-enzyme mechanism for microbial ClO4(-) reduction inspired us to improve catalyst stability by rationally tuning Re ligand structure and adding a ClOx(-) scavenger. Two new Re complexes, Re(O)(htz)2Cl and Re(O)(hoz)(htz)Cl (htz = thiazolinyl-phenolato bidentate ligand), significantly mitigate Re complex decomposition by slightly lowering the OAT activity when immobilized in Pd/C. Further stability enhancement is then obtained by switching the nanoparticles from Pd to Rh, which exhibits high reactivity with ClOx(-) intermediates and thus prevents their deactivating reaction with the Re complex. Compared to Re(hoz)2-Pd/C, the new Re(hoz)(htz)-Rh/C catalyst exhibits similar ClO4(-) reduction activity but superior stability, evidenced by a decrease of Re leaching from 37% to 0.25% and stability of surface Re speciation following the treatment of a concentrated "challenge" solution containing 1000 ppm of ClO4(-). This work demonstrates the pivotal roles of coordination chemistry control and tuning of individual catalyst components for achieving both high activity and stability in environmental catalyst applications.

Intrinsic selectivity and structure sensitivity of Rhodium catalysts for C 2+ oxygenate production [On the intrinsic selectivity and structure sensitivity of Rhodium catalysts for C 2+ oxygenate production

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Nuoya; Medford, Andrew J.; Liu, Xinyan

Synthesis gas (CO + H 2) conversion is a promising route to converting coal, natural gas, or biomass into synthetic liquid fuels. Rhodium has long been studied as it is the only elemental catalyst that has demonstrated selectivity to ethanol and other C 2+ oxygenates. However, the fundamentals of syngas conversion over rhodium are still debated. In this work a microkinetic model is developed for conversion of CO and H 2 into methane, ethanol, and acetaldehyde on the Rh (211) and (111) surfaces, chosen to describe steps and close-packed facets on catalyst particles. The model is based on DFT calculationsmore » using the BEEF-vdW functional. The mean-field kinetic model includes lateral adsorbate–adsorbate interactions, and the BEEF-vdW error estimation ensemble is used to propagate error from the DFT calculations to the predicted rates. The model shows the Rh(211) surface to be ~6 orders of magnitude more active than the Rh(111) surface, but highly selective toward methane, while the Rh(111) surface is intrinsically selective toward acetaldehyde. A variety of Rh/SiO 2 catalysts are synthesized, tested for catalytic oxygenate production, and characterized using TEM. The experimental results indicate that the Rh(111) surface is intrinsically selective toward acetaldehyde, and a strong inverse correlation between catalytic activity and oxygenate selectivity is observed. Furthermore, iron impurities are shown to play a key role in modulating the selectivity of Rh/SiO 2 catalysts toward ethanol. The experimental observations are consistent with the structure-sensitivity predicted from theory. As a result, this work provides an improved atomic-scale understanding and new insight into the mechanism, active site, and intrinsic selectivity of syngas conversion over rhodium catalysts and may also guide rational design of alloy catalysts made from more abundant elements.« less

Unsupported Pt-Ni Aerogels with Enhanced High Current Performance and Durability in Fuel Cell Cathodes.

PubMed

Henning, Sebastian; Ishikawa, Hiroshi; Kühn, Laura; Herranz, Juan; Müller, Elisabeth; Eychmüller, Alexander; Schmidt, Thomas J

2017-08-28

Highly active and durable oxygen reduction catalysts are needed to reduce the costs and enhance the service life of polymer electrolyte fuel cells (PEFCs). This can be accomplished by alloying Pt with a transition metal (for example Ni) and by eliminating the corrodible, carbon-based catalyst support. However, materials combining both approaches have seldom been implemented in PEFC cathodes. In this work, an unsupported Pt-Ni alloy nanochain ensemble (aerogel) demonstrates high current PEFC performance commensurate with that of a carbon-supported benchmark (Pt/C) following optimization of the aerogel's catalyst layer (CL) structure. The latter is accomplished using a soluble filler to shift the CL's pore size distribution towards larger pores which improves reactant and product transport. Chiefly, the optimized PEFC aerogel cathodes display a circa 2.5-fold larger surface-specific ORR activity than Pt/C and maintain 90 % of the initial activity after an accelerated stress test (vs. 40 % for Pt/C). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

One-Pot Process for Hydrodeoxygenation of Lignin to Alkanes Using Ru-Based Bimetallic and Bifunctional Catalysts Supported on Zeolite Y.

PubMed

Wang, Hongliang; Ruan, Hao; Feng, Maoqi; Qin, Yuling; Job, Heather; Luo, Langli; Wang, Chongmin; Engelhard, Mark H; Kuhn, Erik; Chen, Xiaowen; Tucker, Melvin P; Yang, Bin

2017-04-22

The synthesis of high-efficiency and low-cost catalysts for hydrodeoxygenation (HDO) of waste lignin to advanced biofuels is crucial for enhancing current biorefinery processes. Inexpensive transition metals, including Fe, Ni, Cu, and Zn, were severally co-loaded with Ru on HY zeolite to form bimetallic and bifunctional catalysts. These catalysts were subsequently tested for HDO conversion of softwood lignin and several lignin model compounds. Results indicated that the inexpensive earth-abundant metals could modulate the hydrogenolysis activity of Ru and decrease the yield of low-molecular-weight gaseous products. Among these catalysts, Ru-Cu/HY showed the best HDO performance, affording the highest selectivity to hydrocarbon products. The improved catalytic performance of Ru-Cu/HY was probably a result of the following three factors: (1) high total and strong acid sites, (2) good dispersion of metal species and limited segregation, and (3) high adsorption capacity for polar fractions, including hydroxyl groups and ether bonds. Moreover, all bifunctional catalysts proved to be superior over the combination catalysts of Ru/Al 2 O 3 and HY zeolite. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

One-pot process for hydrodeoxygenation of lignin to alkanes using Ru-based bimetallic and bifunctional catalysts supported on zeolite Y

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hongliang; Ruan, Hao; Feng, Maoqi

2017-02-22

Here, the synthesis of high-efficiency and low-cost catalysts for hydrodeoxygenation (HDO) of waste lignin to advanced biofuels is crucial for enhancing current biorefinery processes. Inexpensive transition metals, including Fe, Ni, Cu, and Zn, were severally co-loaded with Ru on HY zeolite to form bimetallic and bifunctional catalysts. These catalysts were subsequently tested for HDO conversion of softwood lignin and several lignin model compounds. Results indicated that the inexpensive earth-abundant metals could modulate the hydrogenolysis activity of Ru and decrease the yield of low-molecular-weight gaseous products. Among these catalysts, Ru-Cu/HY showed the best HDO performance, affording the highest selectivity to hydrocarbonmore » products. The improved catalytic performance of Ru-Cu/HY was probably a result of the following three factors: (1) high total and strong acid sites, (2) good dispersion of metal species and limited segregation, and (3) high adsorption capacity for polar fractions, including hydroxyl groups and ether bonds. Moreover, all bifunctional catalysts proved to be superior over the combination catalysts of Ru/Al 2O 3 and HY zeolite.« less

The Influence of Ziegler-Natta and Metallocene Catalysts on Polyolefin Structure, Properties, and Processing Ability

PubMed Central

Shamiri, Ahmad; Chakrabarti, Mohammed H.; Jahan, Shah; Hussain, Mohd Azlan; Kaminsky, Walter; Aravind, Purushothaman V.; Yehye, Wageeh A.

2014-01-01

50 years ago, Karl Ziegler and Giulio Natta were awarded the Nobel Prize for their discovery of the catalytic polymerization of ethylene and propylene using titanium compounds and aluminum-alkyls as co-catalysts. Polyolefins have grown to become one of the biggest of all produced polymers. New metallocene/methylaluminoxane (MAO) catalysts open the possibility to synthesize polymers with highly defined microstructure, tacticity, and steroregularity, as well as long-chain branched, or blocky copolymers with excellent properties. This improvement in polymerization is possible due to the single active sites available on the metallocene catalysts in contrast to their traditional counterparts. Moreover, these catalysts, half titanocenes/MAO, zirconocenes, and other single site catalysts can control various important parameters, such as co-monomer distribution, molecular weight, molecular weight distribution, molecular architecture, stereo-specificity, degree of linearity, and branching of the polymer. However, in most cases research in this area has reduced academia as olefin polymerization has seen significant advancements in the industries. Therefore, this paper aims to further motivate interest in polyolefin research in academia by highlighting promising and open areas for the future. PMID:28788120

Integrating Semiconducting Catalyst of ReS2 Nanosheets into P-silicon Photocathode toward Enhanced Solar Water Reduction.

PubMed

Zhao, Heng; Dai, Zhengyi; Xu, Xiaoyong; Pan, Jing; Hu, Jingguo

2018-06-22

Loading the electro-catalysts at the semiconductor-electrolyte interface is one of promising strategies to develop photoelectrochemical (PEC) water splitting cells. However, the assembly of compatible and synergistic heterojunction between the semiconductor and the selected catalyst remains challenging. Here, we report a hierarchical p-Si/ReS2 heterojunction photocathode fabricated through uniform growth vertically standing ReS2 nanosheets (NSs) on planar p-Si substrate for solar-driven hydrogen evolution reaction (HER). The laden ReS2 NSs not only serve as a high-activity HER catalyst but also render a suitable electronic band coupled with p-Si into a Ⅱ-type heterojunction, which facilitates the photo-induced charge production, separation and utilization. As a result, the assembled p-Si/ReS2 photocathode exhibits a 23-fold-increased photocurrent density at 0 VRHE and a 35-fold-enhanced photoconversion efficiency compared to pure p-Si counterpart. The bifunctional ReS2 as catalyst and semiconductor enables multi effects in improving light harvesting, charge separation and catalytic kinetics, highlighting the potential of semiconducting catalysts integrated into solar water splitting devices.

The physical chemistry and materials science behind sinter-resistant catalysts.

PubMed

Dai, Yunqian; Lu, Ping; Cao, Zhenming; Campbell, Charles T; Xia, Younan

2018-06-18

Catalyst sintering, a main cause of the loss of catalytic activity and/or selectivity at high reaction temperatures, is a major concern and grand challenge in the general area of heterogeneous catalysis. Although all heterogeneous catalysts are inevitably subjected to sintering during their operation, the immediate and drastic consequences can be mitigated by carefully engineering the catalytic particles and their interactions with the supports. In this tutorial review, we highlight recent progress in understanding the physical chemistry and materials science involved in sintering, including the discussion of advanced techniques, such as in situ microscopy and spectroscopy, for investigating the sintering process and its rate. We also discuss strategies for the design and rational fabrication of sinter-resistant catalysts. Finally, we showcase recent success in improving the thermal stability and thus sinter resistance of supported catalytic systems.

Role of structural H 2O in TiO 2 nanotubes in enhancing Pt/C direct ethanol fuel cell anode electro-catalysts

NASA Astrophysics Data System (ADS)

Song, Huanqiao; Qiu, Xinping; Guo, Daojun; Li, Fushen

TiO 2 nanotubes (TNTs) with different structural water were obtained by heat treatment under different temperatures. The role of the structural water in TNTs co-catalyzing ethanol oxidation with Pt/C catalyst was studied systematically. Electrochemical studies using cyclic voltammetry and CO stripping voltammetry indicated that more structural water in TNTs was favorable for improving the tolerance of Pt/C to poisoning species; while chronoamperometry curves and repeated cyclic voltammograms showed that slightly less structural water in TNTs actually led to higher catalytic activity and better stability of Pt/C catalysts for ethanol oxidation. This strange result has been analyzed and was ascribed to the appropriate balance of bi-functional mechanism and ethanol transfer in the catalyst layer with less structural water.

Pt Nanostructures/N-Doped Carbon hybrid, an Efficient Catalyst for Hydrogen Evolution/Oxidation Reactions: Enhancing its Base Media Activity through Bifunctionality of the Catalyst.

PubMed

Barman, Sudip; Kundu, Manas; Bhowmik, Tanmay; Mishra, Ranjit

2018-06-04

Design and synthesis of active catalyst for HER/HOR are important for the development of hydrogen based renewable technologies. We report synthesis of Pt nanostructures-N-doped carbon hybrid (Pt-(PtO2)-NSs/C) for HER/HOR applications. The HER activity of this Pt-(PtOx)-NSs/C catalyst is 4 and 6.5 times better than commercial Pt/C in acid and base. The catalyst exhibits a current density of 10 mA/cm2 at overpotentials of 5 and 51 mV with tafel slopes of 29 and 64mV/dec in in 0.5 M H2SO4 and 0.5 M KOH. This catalyst also showed superior HOR activity at all pH values. The HER/HOR activity of Pt-(PtOx)-NSs/C and PtOx-free Pt-Nanostructures/C (PtNSs/C) catalysts are comparable in acid. The presence of PtOx in Pt-(PtOx)-NSs/C makes this Pt-catalyst more HER/HOR active in base media. The activity of Pt-(PtOx)NSs/C catalyst is 5 fold higher than that of PtNSs/C catalyst in basic medium although their activity is comparable in acid. Hydrogen binding energy and oxophilicity are the two equivalent descriptors for HER/HOR in basic media. We propose a bi-functional mechanism for the enhanced alkaline HER/HOR activity of Pt(PtOx)-NSs/C catalyst. In bi-functional Pt-(PtOx)-NSs/C catalyst, PtOx provide an active site for OH- adsorption to form OHads which reacts with hydrogen intermediate (Hads), present at neighbouring Pt sites to form H2O leading to enhancement of HOR activity in basic medium This work may provide opportunity to develop catalysts for various renewable energy technologies. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Evolution of a Fourth Generation Catalyst for the Amination and Thioetherification of Aryl Halides

PubMed Central

Hartwig, John F.

2010-01-01

Conspectus Synthetic methods to form the carbon-nitrogen bonds in aromatic amines are fundamental enough to be considered part of introductory organic courses. Arylamines are important because they are common precursors to or substructures within active pharmaceutical ingredients and herbicides produced on ton scales, as well as conducting polymers and layers of organic light-emitting diodes produced on small scale. For many years, this class of compound was prepared from classical methods, such as nitration, reduction and reductive alkylation, copper-mediated chemistry at high temperatures, addition to benzyne intermediates, or direct nucleophilic substitution on particularly electron-poor aromatic or heteroaromatic halides. During the past decade, these methods to form aromatic amines have been largely supplanted by palladium-catalyzed coupling reactions of amines with aryl halides. The scope and efficiency of the palladium-catalyzed processes has gradually improved with successive generations of catalysts to the point of being useful for the synthesis of both milligrams and kilograms of product. This Account describes the conceptual basis and utility of our latest, “fourth-generation” catalyst for the coupling of amines and related reagents with aryl halides. The introductory sections of this account describe the progression of catalyst development from the first-generation to current systems and the motivation for selection of the components of the fourth-generation catalyst. This progression began with catalysts containing palladium and sterically hindered monodentate aromatic phosphines used initially for coupling of tin amides with haloarenes in the first work on C-N coupling. A second generation of catalysts was then developed based on the combination of palladium and aromatic bisphosphines. These systems were then followed by third-generation systems catalysts on the combination of palladium and a sterically hindered alkylmonophosphine or N-heterocyclic carbene. During the past five years, we have studied a fourth-generation catalyst for these reactions containing ligands that combine the chelating properties of the second-generation systems with the steric hindrance and strong electron donation of the third-generation systems. This combination has created a catalyst that couples aryl chlorides, bromides and iodides with primary amines, N-H imines, and hydrazones in high yield, with broad scope, high functional group tolerance, nearly perfect selectivity for monoarylation, and the lowest levels of palladium that have been used for C-N coupling. This catalyst is based on palladium and a sterically hindered version of the Josiphos family of ligands that possesses a ferrocenyl-1-ethylbackbone, a hindered di-tert-butylphosphino group, and a hindered dicyclohexylphosphino group. This latest generation of catalyst not only improves the coupling of primary amines and related nucleophiles, but it has dramatically improved the coupling of thiols with haloarenes to form C-S bonds. This catalyst system couples both aliphatic and aromatic thiols with chloroarenes with much greater scope, functional group tolerance, and turnover numbers than had been observed previously. The effects of structural features of the Josiphos ligand on catalyst activity have been revealed by examining the reactivity of catalysts generated from ligands lacking one or more of the structural elements of the most active catalyst. These modified ligands lack the relative stereochemistry of the ferrocenyl-1-ethyl backbone, the strong electron donation of the dialkylphosphino groups, the steric demands of the alkylphosphine groups, or the stability of the ferrocenyl unit. This set of studies showed that each one of these structural features contributed to the high reactivity and selectivity of the catalyst containing the hindered, bidentate Josiphos ligand. Finally, a series of studies on the effect of electronic properties on the rates of reductive elimination have recently distinguished between the effect of the properties of the M-N σ-bond and the nitrogen electron pair on the rate of reductive elimination. These studies have shown that the effect of substituents attached to the metal-bound nitrogen or carbon atoms on the rate of reductive elimination are similar. Because the amido ligands contain an electron pair, while the alkyl ligands do not, we have concluded that the major electronic effect is transmitted through the σ-bond. In other words, we have concluded that the electronic effect on the metal-nitrogen σ bond dominates an electronic effect on the nitrogen electron pair. PMID:18681463

One-Pot Process for Hydrodeoxygenation of Lignin to Alkanes Using Ru-Based Bimetallic and Bifunctional Catalysts Supported on Zeolite Y

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hongliang; Ruan, Hao; Feng, Maoqi

2017-03-16

The synthesis of high-efficiency and low-cost multifunctional catalysts for hydrodeoxygenation (HDO) of waste lignin into advanced biofuels is crucial for enhancing current biorefinery processes. Inexpensive transition metals, including Fe, Ni, Cu, Zn, were severally co-loaded with Ru on HY zeolite to form bimetallic and bifunctional catalysts. These catalysts were subsequently tested for HDO conversion of softwood lignin and several lignin model compounds. Results indicated that the inexpensive earth abundant metals could modulate the hydrogenolysis activity of Ru and decrease the yield of low molecular weight gaseous side-products. Among all the prepared catalysts, Ru-Cu/HY showed the best HDO performance, giving themore » highest selectivity to hydrocarbon products. The improved catalytic performance of Ru-Cu/HY was probably due to the following three factors: (1) high total and strong acid sites, (2) good dispersion of metal species and limited segregation, (3) high adsorption capacity for polar fractions, including hydroxyl groups and ether bonds. Moreover, all the bifunctional catalysts were proven to be superior over the combination catalysts of Ru/Al2O3 and HY zeolite, and this could be attributed to the “intimacy criterion”. The practical use of the designed catalysts would be promising in lignin valorization.« less

Catalyst design with atomic layer deposition

DOE PAGES

O'Neill, Brandon J.; Jackson, David H. K.; Lee, Jechan; ...

2015-02-06

Atomic layer deposition (ALD) has emerged as an interesting tool for the atomically precise design and synthesis of catalytic materials. Herein, we discuss examples in which the atomic precision has been used to elucidate reaction mechanisms and catalyst structure-property relationships by creating materials with a controlled distribution of size, composition, and active site. We highlight ways ALD has been utilized to design catalysts with improved activity, selectivity, and stability under a variety of conditions (e.g., high temperature, gas and liquid phase, and corrosive environments). In addition, due to the flexibility and control of structure and composition, ALD can create myriadmore » catalytic structures (e.g., high surface area oxides, metal nanoparticles, bimetallic nanoparticles, bifunctional catalysts, controlled microenvironments, etc.) that consequently possess applicability for a wide range of chemical reactions (e.g., CO 2 conversion, electrocatalysis, photocatalytic and thermal water splitting, methane conversion, ethane and propane dehydrogenation, and biomass conversion). Lastly, the outlook for ALD-derived catalytic materials is discussed, with emphasis on the pending challenges as well as areas of significant potential for building scientific insight and achieving practical impacts.« less

Catalyst design with atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

O'Neill, Brandon J.; Jackson, David H. K.; Lee, Jechan

Atomic layer deposition (ALD) has emerged as an interesting tool for the atomically precise design and synthesis of catalytic materials. Herein, we discuss examples in which the atomic precision has been used to elucidate reaction mechanisms and catalyst structure-property relationships by creating materials with a controlled distribution of size, composition, and active site. We highlight ways ALD has been utilized to design catalysts with improved activity, selectivity, and stability under a variety of conditions (e.g., high temperature, gas and liquid phase, and corrosive environments). In addition, due to the flexibility and control of structure and composition, ALD can create myriadmore » catalytic structures (e.g., high surface area oxides, metal nanoparticles, bimetallic nanoparticles, bifunctional catalysts, controlled microenvironments, etc.) that consequently possess applicability for a wide range of chemical reactions (e.g., CO 2 conversion, electrocatalysis, photocatalytic and thermal water splitting, methane conversion, ethane and propane dehydrogenation, and biomass conversion). Lastly, the outlook for ALD-derived catalytic materials is discussed, with emphasis on the pending challenges as well as areas of significant potential for building scientific insight and achieving practical impacts.« less

Cobalt Fischer-Tropsch catalysts having improved selectivity

DOEpatents

Miller, James G.; Rabo, Jule A.

1989-01-01

A cobalt Fischer-Tropsch catalyst having an improved steam treated, acid extracted LZ-210 support is taught. The new catalyst system demonstrates improved product selectivity at Fischer-Tropsch reaction conditions evidenced by lower methane production, higher C.sub.5.sup.+ yield and increased olefin production.

Cobalt-Doped Perovskite-Type Oxide LaMnO3 as Bifunctional Oxygen Catalysts for Hybrid Lithium-Oxygen Batteries.

PubMed

Liu, Xiao; Gong, Hao; Wang, Tao; Guo, Hu; Song, Li; Xia, Wei; Gao, Bin; Jiang, Zhongyi; Feng, Linfei; He, Jianping

2018-03-02

Perovskite-type oxides based on rare-earth metals containing lanthanum manganate are promising catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolyte. Perovskite-type LaMnO 3 shows excellent ORR performance, but poor OER activity. To improve the OER performance of LaMnO 3 , the element cobalt is doped into perovskite-type LaMnO 3 through a sol-gel method followed by a calcination process. To assess electrocatalytic activities for the ORR and OER, a series of LaMn 1-x Co x O 3 (x=0, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5) perovskite oxides were synthesized. The results indicate that the amount of doped cobalt has a significant effect on the catalytic performance of LaMn 1-x Co x O 3 . If x=0.3, LaMn 0.7 Co 0.3 O 3 not only shows a tolerable electrocatalytic activity for the ORR, but also exhibits a great improvement (>200 mV) on the catalytic activity for the OER; this indicates that the doping of cobalt is an effective approach to improve the OER performance of LaMnO 3 . Furthermore, the results demonstrate that LaMn 0.7 Co 0.3 O 3 is a promising cost-effective bifunctional catalyst with high performance in the ORR and OER for application in hybrid Li-O 2 batteries. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

ATTRITION RESISTANT IRON-BASED FISCHER-TROPSCH CATALYSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

James G. Goodwin, Jr.; James J. Spivey; K. Jothimurugesan

1999-03-29

The Fischer-Tropsch (F-T) reaction provides a way of converting coal-derived synthesis gas (CO+H{sub 2}) to liquid fuels. Since the reaction is highly exothermic, one of the major problems in control of the reaction is heat removal. Recent work has shown that the use of slurry bubble column reactors (SBCRs) can largely solve this problem. Iron-based (Fe) catalysts are preferred catalysts for F-T when using low CO/H2 ratio synthesis gases derived from modern coal gasifiers. This is because in addition to reasonable F-T activity, the F-T catalysts also possess high water gas shift (WGS) activity. However, a serious problem with themore » use of Fe catalysts in a SBCR is their tendency to undergo attrition. This can cause fouling/plugging of downstream filters and equipment, making the separation of catalyst from the oil/wax product very difficult if not impossible, and results in a steady loss of catalyst from the reactor. The objectives of this research are to develop a better understanding of the parameters affecting attrition resistance of Fe F-T catalysts suitable for use in SBCRs and to incorporate this understanding into the design of novel Fe catalysts having superior attrition resistance. Catalyst preparations will be based on the use of spray drying and will be scalable using commercially available equipment. The research will employ among other measurements, attrition testing and F-T synthesis, including long duration slurry reactor runs in order to ascertain the degree of success of the various preparations. The goal is to develop an Fe catalyst which can be used in a SBCR having only an internal filter for separation of the catalyst from the liquid product, without sacrificing F-T activity and selectivity. The effect of silica addition via coprecipitation and as a binder to a doubly promoted Fischer-Tropsch synthesis iron catalyst (100 Fe/5 Cu/4.2 K) was studied. The catalysts were prepared by coprecipitation, followed by binder addition and drying in a 1 m diameter, 2 m tall spray dryer. The binder silica content was varied from 0 to 20 wt %. A catalyst with 12 wt % binder silica was found to have the highest attrition resistance. F-T reaction studies over 100 hours in a fixed-bed reactor showed that this catalyst maintained around 95 % CO conversion with a methane selectivity of less than 7 wt % and a C5 + selectivity of greater than 73 wt %. The effect of adding precipitated silica from 0 to 20 parts by weight to this catalyst (containing 12 wt % binder silica) was also studied. Addition of precipitated silica was found to be detrimental to attrition resistance and resulted in increased methane and reduced wax formation. An HPR series of proprietary catalysts was prepared to further improve the attrition resistance. Based on the experience gained, a proprietary HPR-43 catalyst has been successfully spray dried in 500 g quantity. This catalyst showed 95 % CO conversion over 125 h and had less than 4 % methane selectivity. Its attrition resistance was one of the highest among the catalyst tested.« less

Comparison of iridium- and ruthenium-based, Pt-surface-enriched, nanosize catalysts for the oxygen-reduction reaction

NASA Astrophysics Data System (ADS)

Kaplan, D.; Goor, M.; Alon, M.; Tsizin, S.; Burstein, L.; Rosenberg, Y.; Popov, I.; Peled, E.

2016-02-01

Pt-surface-enriched nanosize catalysts (Pt-SENS catalysts) with ruthenium and iridium cores, supported on XC72, were synthesized and characterized. The structure and composition of the catalysts are determined by Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS), Scanning Transmission Electron Microscopy (STEM) and X-Ray Diffraction (XRD). Electrochemical characterization tests, including oxygen-reduction-catalysis activity and durability studies of catalysts are performed with the use of cyclic-voltammetry and rotating-disk-electrode (RDE) techniques at room temperature. The ORR activity of the homemade catalysts is also compared to ORR activity of commercial 50%Pt/C catalyst. It is determined that the Ir-based catalyst (Pt/Ir/XC72) shows higher ORR activity in terms of A g-1 of Pt (at 0.85 V vs. RHE) than the Ru-based catalyst (Pt/Ru/XC72) and the commercial 50%Pt/C. The Ru-based catalyst shows similar ORR activity in terms of A g-1 of Pt, to that of the commercial 50%Pt/C, but with much lower durability.

Ruthenium-cobalt nanoalloys encapsulated in nitrogen-doped graphene as active electrocatalysts for producing hydrogen in alkaline media

NASA Astrophysics Data System (ADS)

Su, Jianwei; Yang, Yang; Xia, Guoliang; Chen, Jitang; Jiang, Peng; Chen, Qianwang

2017-04-01

The scalable production of hydrogen could conveniently be realized by alkaline water electrolysis. Currently, the major challenge confronting hydrogen evolution reaction (HER) is lacking inexpensive alternatives to platinum-based electrocatalysts. Here we report a high-efficient and stable electrocatalyst composed of ruthenium and cobalt bimetallic nanoalloy encapsulated in nitrogen-doped graphene layers. The catalysts display remarkable performance with low overpotentials of only 28 and 218 mV at 10 and 100 mA cm-2, respectively, and excellent stability of 10,000 cycles. Ruthenium is the cheapest platinum-group metal and its amount in the catalyst is only 3.58 wt.%, showing the catalyst high activity at a very competitive price. Density functional theory calculations reveal that the introduction of ruthenium atoms into cobalt core can improve the efficiency of electron transfer from alloy core to graphene shell, beneficial for enhancing carbon-hydrogen bond, thereby lowing ΔGH* of HER.

Methane Oxidation to Methanol Catalyzed by Cu-Oxo Clusters Stabilized in NU-1000 Metal–Organic Framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ikuno, Takaaki; Zheng, Jian; Vjunov, Aleksei

The catalyzed conversion of shale gas-derived light hydrocarbons, e.g. methane to methanol, for further application as automotive fuels and/or bulk chemicals is especially attractive in light of improved methods of hydrocarbon extraction. MOF based catalysts have previously been demonstrated to be active for a range of catalytic reactions. In this work we used Cu-NU1000 as a methane-to-methanol oxidation catalyst. In addition to product studies, in-situ X-ray Absorption Spectroscopic (XAS) experiments are performed under catalytic conditions in order to follow the modification of the Cu-species and directly probe the structure/activity properties of the Cu-NU1000 system. The insights reported herein serve asmore » a first look at metal-organic framework materials as catalysts for methane oxidation and be the basis for development of the subsequent generations of materials.« less

Directing Reaction Pathways through Controlled Reactant Binding at Pd-TiO2 Interfaces.

PubMed

Zhang, Jing; Wang, Bingwen; Nikolla, Eranda; Medlin, J Will

2017-06-01

Recent efforts to design selective catalysts for multi-step reactions, such as hydrodeoxygenation (HDO), have emphasized the preparation of active sites at the interface between two materials having different properties. However, achieving precise control over interfacial properties, and thus reaction selectivity, has remained a challenge. Here, we encapsulated Pd nanoparticles (NPs) with TiO 2 films of regulated porosity to gain a new level of control over catalyst performance, resulting in essentially 100 % HDO selectivity for two biomass-derived alcohols. This catalyst also showed exceptional reaction specificity in HDO of furfural and m-cresol. In addition to improving HDO activity by maximizing the interfacial contact between the metal and metal oxide sites, encapsulation by the nanoporous oxide film provided a significant selectivity boost by restricting the accessible conformations of aromatics on the surface. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mass-produced multi-walled carbon nanotubes as catalyst supports for direct methanol fuel cells.

PubMed

Jang, In Young; Park, Ki Chul; Jung, Yong Chae; Lee, Sun Hyung; Song, Sung Moo; Muramatsu, Hiroyuki; Kim, Yong Jung; Endo, Morinobu

2011-01-01

Commercially mass-produced multi-walled carbon nanotubes, i.e., VGNF (Showa Denko Co.), were applied to support materials for platinum-ruthenium (PtRu) nanoparticles as anode catalysts for direct methanol fuel cells. The original VGNFs are composed of high-crystalline graphitic shells, which hinder the favorable surface deposition of the PtRu nanoparticles that are formed via borohydride reduction. The chemical treatment of VGNFs with potassium hydroxide (KOH), however, enables highly dispersed and dense deposition of PtRu nanoparticles on the VGNF surface. This capability becomes more remarkable depending on the KOH amount. The electrochemical evaluation of the PtRu-deposited VGNF catalysts showed enhanced active surface areas and methanol oxidation, due to the high dispersion and dense deposition of the PtRu nanoparticles. The improvement of the surface deposition states of the PtRu nanoparticles was significantly due to the high surface area and mesorporous surface structure of the KOH-activated VGNFs.

Water-gas-shift over metal-free nanocrystalline ceria: An experimental and theoretical study

DOE PAGES

Guild, Curtis J.; Vovchok, Dimitriy; Kriz, David A.; ...

2017-01-23

A tandem experimental and theoretical investigation of a mesoporous ceria catalyst reveals the properties of the metal oxide are conducive for activity typically ascribed to metals, suggesting reduced Ce 3+ and oxygen vacancies are responsible for the inherent bi-functionality of CO oxidation and dissociation of water required for facilitating the production of H 2. The degree of reduction of the ceria, specifically the (1 0 0) face, is found to significantly influence the binding of reagents, suggesting reduced surfaces harbor the necessary reactive sites. The metal-free catalysis of the reaction is significant for catalyst design considerations, and the suite ofmore » in situ analyses provides a comprehensive study of the dynamic nature of the high surface area catalyst system. Finally, this study postulates feasible improvements in catalytic activity may redirect the purpose of the water-gas shift reaction from CO purification to primary hydrogen production.« less

Water-gas-shift over metal-free nanocrystalline ceria: An experimental and theoretical study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guild, Curtis J.; Vovchok, Dimitriy; Kriz, David A.

A tandem experimental and theoretical investigation of a mesoporous ceria catalyst reveals the properties of the metal oxide are conducive for activity typically ascribed to metals, suggesting reduced Ce 3+ and oxygen vacancies are responsible for the inherent bi-functionality of CO oxidation and dissociation of water required for facilitating the production of H 2. The degree of reduction of the ceria, specifically the (1 0 0) face, is found to significantly influence the binding of reagents, suggesting reduced surfaces harbor the necessary reactive sites. The metal-free catalysis of the reaction is significant for catalyst design considerations, and the suite ofmore » in situ analyses provides a comprehensive study of the dynamic nature of the high surface area catalyst system. Finally, this study postulates feasible improvements in catalytic activity may redirect the purpose of the water-gas shift reaction from CO purification to primary hydrogen production.« less

Heterogeneous biomimetic catalysis using iron porphyrin for cyclohexane oxidation promoted by chitosan

NASA Astrophysics Data System (ADS)

Huang, Guan; Liu, Yao; Cai, Jing Li; Chen, Xiang Feng; Zhao, Shu Kai; Guo, Yong An; Wei, Su Juan; Li, Xu

2017-04-01

This study investigates how ligands modulate metalloporphyrin activity with the goal of producing a practical biomimetic catalyst for use in the chemical industry. We immobilized iron porphyrinate [iron-tetrakis-(4-sulfonatophenyl)-porphyrin; Fe(III) (TPPS)] on powdered chitosan (pd-CTS) to form an immobilized catalyst Fe(III) (TPPS)/pd-CTS, which was characterized using modern spectroscopic techniques and used for catalytic oxidation of cyclohexane with O2. Amino coordination to iron porphyrin in Fe(III) (TPPS)/pd-CTS altered the electron cloud density around the iron cation, probably by reducing the activation energy of Fe(III) (TPPS) and raising the reactivity of the iron ion catalytic center, thereby improving the catalytic efficiency. One milligram of Fe(III) (TPPS) catalyst can be reused three times for the oxidation reaction to yield an average of 22.9 mol% of cyclohexanone and cyclohexanol.

Hydrocracking of Jatropha Oil over non-sulfided PTA-NiMo/ZSM-5 Catalyst

PubMed Central

Yang, Xiaosong; Liu, Jing; Fan, Kai; Rong, Long

2017-01-01

The PTA-NiMo/ZSM-5 catalyst impregnated with phosphotungstic acid (PTA) was designed for the transformation of Jatropha oil into benzene, toluene, and xylenes (BTX) aromatics. The produced catalyst was characterized by N2 adsorption-desorption, powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and the temperature-programmed desorption of ammonia (NH3-TPD). The catalytic performance was evaluated by gas chromatography (GC). The liquid products were 70 wt% of the feed oil, and the majority of the liquid products were BTX. The aromatization activity of the catalyst was improved by the addition of PTA and the hierarchical process. The favorable PTA amount was 20 wt% and the yield of BTX was 59 wt% at 380 °C, 3 MPa, H2/oil (v/v) = 1000 and LHSV = 1 h−1 over the PTA20-NiMo/HZ0.5 catalyst (PTA 20 wt%) without sulfurization. PMID:28134313

Highly selective plasma-activated copper catalysts for carbon dioxide reduction to ethylene

DOE PAGES

Mistry, Hemma; Varela, Ana Sofia; Bonifacio, Cecile S.; ...

2016-06-30

There is an urgent need to develop technologies that use renewable energy to convert waste products such as carbon dioxide into hydrocarbon fuels. Carbon dioxide can be electrochemically reduced to hydrocarbons over copper catalysts, although higher efficiency is required. We have developed oxidized copper catalysts displaying lower overpotentials for carbon dioxide electroreduction and record selectivity towards ethylene (60%) through facile and tunable plasma treatments. Herein we provide insight into the improved performance of these catalysts by combining electrochemical measurements with microscopic and spectroscopic characterization techniques. Operando X-ray absorption spectroscopy and cross-sectional scanning transmission electron microscopy show that copper oxides aremore » surprisingly resistant to reduction and copper + species remain on the surface during the reaction. Furthermore, our results demonstrate that the roughness of oxide-derived copper catalysts plays only a partial role in determining the catalytic performance, while the presence of copper + is key for lowering the onset potential and enhancing ethylene selectivity.« less

Realization of Both High-Performance and Enhanced Durability of Fuel Cells: Pt-Exoskeleton Structure Electrocatalysts.

PubMed

Kim, Ok-Hee; Cho, Yoon-Hwan; Jeon, Tae-Yeol; Kim, Jung Won; Cho, Yong-Hun; Sung, Yung-Eun

2015-07-01

Core-shell structure nanoparticles have been the subject of many studies over the past few years and continue to be studied as electrocatalysts for fuel cells. Therefore, many excellent core-shell catalysts have been fabricated, but few studies have reported the real application of these catalysts in a practical device actual application. In this paper, we demonstrate the use of platinum (Pt)-exoskeleton structure nanoparticles as cathode catalysts with high stability and remarkable Pt mass activity and report the outstanding performance of these materials when used in membrane-electrode assemblies (MEAs) within a polymer electrolyte membrane fuel cell. The stability and degradation characteristics of these materials were also investigated in single cells in an accelerated degradation test using load cycling, which is similar to the drive cycle of a polymer electrolyte membrane fuel cell used in vehicles. The MEAs with Pt-exoskeleton structure catalysts showed enhanced performance throughout the single cell test and exhibited improved degradation ability that differed from that of a commercial Pt/C catalyst.

Cyclic alkyl amino carbene (CAAC) ruthenium complexes as remarkably active catalysts for ethenolysis

DOE PAGES

Marx, Vanessa M.; Sullivan, Alexandra H.; Melaimi, Mohand; ...

2014-12-17

In this paper, an expanded family of ruthenium-based metathesis catalysts bearing cyclic alkyl amino carbene (CAAC) ligands was prepared. These catalysts exhibited exceptional activity in the ethenolysis of the seed-oil derivative methyl oleate. In many cases, catalyst turnover numbers (TONs) of more than 100,000 were achieved, at a catalyst loading of only 3 ppm. Remarkably, the most active catalyst system was able to achieve a TON of 340 000, at a catalyst loading of only 1 ppm. Finally, this is the first time a series of metathesis catalysts has exhibited such high performance in cross-metathesis reactions employing ethylene gas, withmore » activities sufficient to render ethenolysis applicable to the industrial-scale production of linear α-olefins (LAOs) and other terminal-olefin products.« less

Promotional effect of Al2O3 on WO3/CeO2-ZrO2 monolithic catalyst for selective catalytic reduction of nitrogen oxides with ammonia after hydrothermal aging treatment

NASA Astrophysics Data System (ADS)

Xu, Haidi; Liu, Shuang; Wang, Yun; Lin, Qingjin; Lin, Chenlu; Lan, Li; Wang, Qin; Chen, Yaoqiang

2018-01-01

Hydrothermal stability of catalysts for selective catalytic reduction of NOx with NH3 (NH3-SCR) has always been recognized as a challenge in development of candidate catalysts for applications in diesel engine emissions. In this study, Al2O3 was introduced into CeO2-ZrO2 to improve the NH3-SCR activity of WO3/CeO2-ZrO2 after hydrothermal aging (HA) treatment at 800 °C for 12 h. The activity results indicated that the NH3-SCR activity of WO3/CeO2-ZrO2-HA was obviously improved in the whole reaction temperature range after doping Al2O3 into CeO2-ZrO2, for example, the average and maximum NOx conversion were separately increased by ca. 20% and 25% after HA treatment. XRD, Raman, TEM and EDX results revealed that the introduction of Al2O3 inhibited the sintering and agglomeration of CeO2-ZrO2 and WO3 and the formation of Ce2(WO4)3 after HA treatment. Accordingly, WO3/CeO2-ZrO2-Al2O3-HA showed remarkably improved structural stability and reducibility, increased surface acidity, and facilitated the reactivity between adsorbed NH3 and nitrate species, which together contributed to its better catalytic performance after hydrothermal aging treatment.

Improved catalysts for carbon and coal gasification

DOEpatents

McKee, D.W.; Spiro, C.L.; Kosky, P.G.

1984-05-25

This invention relates to improved catalysts for carbon and coal gasification and improved processes for catalytic coal gasification for the production of methane. The catalyst is composed of at least two alkali metal salts and a particulate carbonaceous substrate or carrier is used. 10 figures, 2 tables.

An investigation into support cooperativity for the deoxygenation of guaiacol over nanoparticle Ni and Rh 2P

DOE PAGES

Griffin, Michael B.; Baddour, Frederick G.; Habas, Susan E.; ...

2017-06-06

Here, the production of hydrocarbon fuels from biomass pyrolysis requires the development of effective deoxygenation catalysts, and insight into how the properties of the support influence performance is critical for catalyst design. In this report, nanoparticles of Ni and Rh 2P were synthesized using solution-phase techniques and dispersed on high surface area supports. The supports included a relatively inert material (C), an acidic reducible metal-oxide (TiO 2), an acidic irreducible metal-oxide (Al 2O 3), and a basic irreducible metal-oxide (MgO). The eight active phase/support combinations were investigated for the deoxygenation of guaiacol, a pyrolysis vapor model compound, under ex situmore » catalytic fast pyrolysis conditions (350 °C, 0.44 MPa H 2). Compared to the baseline performance of the C-supported catalysts, Ni/TiO 2 and Rh 2P/TiO 2 exhibited higher guaiacol conversion and lower O : C ratios for C 5+ products, highlighting the enhanced activity and greater selectivity to deoxygenated products derived from the use of an acidic reducible metal-oxide support. The Al 2O 3-supported catalysts also exhibited higher conversion than the C-supported catalysts and promoted alkylation reactions, which improve carbon efficiency and increase the carbon number of the C 5+ products. However, Ni/Al 2O 3 and Rh 2P/Al 2O 3 were less selective towards deoxygenated products than the C-supported catalysts. The MgO-supported catalyst exhibited lower conversion and decreased yield of deoxygenated products compared to the C-supported catalysts. The results reported here suggest that basic metal-oxide supports may inhibit deoxygenation of phenolics under CFP conditions. Contrastingly, support acidity and reducibility were demonstrated to promote conversion and selectivity to deoxygenated products, respectively.« less

The role of electronic coupling between substrate and 2D MoS2 nanosheets in electrocatalytic production of hydrogen.

PubMed

Voiry, Damien; Fullon, Raymond; Yang, Jieun; de Carvalho Castro E Silva, Cecilia; Kappera, Rajesh; Bozkurt, Ibrahim; Kaplan, Daniel; Lagos, Maureen J; Batson, Philip E; Gupta, Gautam; Mohite, Aditya D; Dong, Liang; Er, Dequan; Shenoy, Vivek B; Asefa, Tewodros; Chhowalla, Manish

2016-09-01

The excellent catalytic activity of metallic MoS2 edges for the hydrogen evolution reaction (HER) has led to substantial efforts towards increasing the edge concentration. The 2H basal plane is less active for the HER because it is less conducting and therefore possesses less efficient charge transfer kinetics. Here we show that the activity of the 2H basal planes of monolayer MoS2 nanosheets can be made comparable to state-of-the-art catalytic properties of metallic edges and the 1T phase by improving the electrical coupling between the substrate and the catalyst so that electron injection from the electrode and transport to the catalyst active site is facilitated. Phase-engineered low-resistance contacts on monolayer 2H-phase MoS2 basal plane lead to higher efficiency of charge injection in the nanosheets so that its intrinsic activity towards the HER can be measured. We demonstrate that onset potentials and Tafel slopes of ∼-0.1 V and ∼50 mV per decade can be achieved from 2H-phase catalysts where only the basal plane is exposed. We show that efficient charge injection and the presence of naturally occurring sulfur vacancies are responsible for the observed increase in catalytic activity of the 2H basal plane. Our results provide new insights into the role of contact resistance and charge transport on the performance of two-dimensional MoS2 nanosheet catalysts for the HER.

Ultrathin layered double hydroxide nanosheets with Ni(III) active species obtained by exfoliation for highly efficient ethanol electrooxidation

PubMed Central

Xu, Liang; Wang, Zhe; Chen, Xu; Qu, Zongkai; Li, Feng; Yang, Wensheng

2018-01-01

The development of non-precious metal electrocatalysts for renewable energy conversion and storage is compelling but greatly challenging due to low activity of the existing catalysts. Herein, the ultrathin NiAl-layered double hydroxide nanosheets (NiAl-LDH-NSs) are prepared by simple liquid-exfoliation of bulk NiAl-LDHs and first used as ethanol electrooxidation catalysts. The ultrathin two-dimensional (2D) structure ensures that the LDH nanosheets expose a greater number of active sites. More importantly, much Ni(III) active species (NiOOH) in the ultrathin nanosheets are formed by the exfoliation process, which play an authentic catalytic role in the ethanol oxidation reaction (EOR). The presence of NiOOH remarkably improves the reactivity and electrical conductivity of LDH nanosheets. These synergistic effects lead to strikingly more than 30 times enhanced EOR activity of NiAl-LDH-NSs compared to bulk NiAl-LDHs. The obtained electrocatalytic activity is also much better than those of most Ni- and LDH-based EOR catalysts reported to date. In addition, the ultrathin NiAl-LDH-NS electrocatalyst also exhibits good long-term stability (maintain 81.8% of the original value after 10000 s). This study not only provides a highly competitive EOR catalyst, but also opens new avenues toward the design of highly efficient electrode materials that have various potential applications in supercapacitor, Ni-MH battery and other electrocatalytic systems. PMID:29622818

Advancing Fenton and photo-Fenton water treatment through the catalyst design.

PubMed

Vorontsov, Alexander V

2018-04-20

The review is devoted to modern Fenton, photo-Fenton, as well as Fenton-like and photo-Fenton-like reactions with participation of iron species in liquid phase and as heterogeneous catalysts. Mechanisms of these reactions were considered that include hydroxyl radical and oxoferryl species as the reactive intermediates. The barriers in the way of application of these reactions to wastewater treatment were discussed. The following fundamental problems need further research efforts: inclusion of more mechanism steps and quantum calculations of all rate constants lacking in the literature, checking the outer sphere electron transfer contribution, determination of the causes for the key changes in the homogeneous Fenton reaction mechanism with a change in the reagents concentration. The key advances for Fenton reactions implementation for the water treatment are related to tremendous hydrodynamical effects on the catalytic activity, design of ligands for high rate and completeness of mineralization in short time, and design of highly active heterogeneous catalysts. While both homogeneous and heterogeneous Fenton and photo-Fenton systems are open for further improvements, heterogeneous photo-Fenton systems are most promising for practical applications because of the inherent higher catalyst stability. Modern methods of quantum chemistry are expected to play a continuously increasing role in development of such catalysts. Copyright © 2018 Elsevier B.V. All rights reserved.

Efficient decomposition of formaldehyde at room temperature over Pt/honeycomb ceramics with ultra-low Pt content.

PubMed

Nie, Longhui; Zheng, Yingqiu; Yu, Jiaguo

2014-09-14

Pt/honeycomb ceramic (Pt/HC) catalysts with ultra-low Pt content (0.005-0.055 wt%) were for the first time prepared by an impregnation of honeycomb ceramics with Pt precursor and NaBH4-reduction combined method. The microstructures, morphologies and textural properties of the resulting samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The obtained Pt/HC catalysts were used for catalytic oxidative decomposition of formaldehyde (HCHO) at room temperature. It was found that the as-prepared Pt/HC catalysts can efficiently decompose HCHO in air into CO2 and H2O at room temperature. The catalytic activity of the Pt/HC catalysts increases with increasing the Pt loading in the range of 0.005-0.013 wt%, and the further increase of the Pt loading does not obviously improve catalytic activity. From the viewpoint of cost and catalytic performance, 0.013 wt% Pt loading is the optimal Pt loading amount, and the Pt/HC catalyst with 0.013 wt% Pt loading also exhibited good catalytic stability. Considering practical applications, this work will provide new insights into the low-cost and large-scale fabrication of advanced catalytic materials for indoor air purification.

An iron-iron hydrogenase mimic with appended electron reservoir for efficient proton reduction in aqueous media

PubMed Central

Becker, René; Amirjalayer, Saeed; Li, Ping; Woutersen, Sander; Reek, Joost N. H.

2016-01-01

The transition from a fossil-based economy to a hydrogen-based economy requires cheap and abundant, yet stable and efficient, hydrogen production catalysts. Nature shows the potential of iron-based catalysts such as the iron-iron hydrogenase (H2ase) enzyme, which catalyzes hydrogen evolution at rates similar to platinum with low overpotential. However, existing synthetic H2ase mimics generally suffer from low efficiency and oxygen sensitivity and generally operate in organic solvents. We report on a synthetic H2ase mimic that contains a redox-active phosphole ligand as an electron reservoir, a feature that is also crucial for the working of the natural enzyme. Using a combination of (spectro)electrochemistry and time-resolved infrared spectroscopy, we elucidate the unique redox behavior of the catalyst. We find that the electron reservoir actively partakes in the reduction of protons and that its electron-rich redox states are stabilized through ligand protonation. In dilute sulfuric acid, the catalyst has a turnover frequency of 7.0 × 104 s−1 at an overpotential of 0.66 V. This catalyst is tolerant to the presence of oxygen, thereby paving the way for a new generation of synthetic H2ase mimics that combine the benefits of the enzyme with synthetic versatility and improved stability. PMID:26844297

High-Valent Organometallic Copper and Palladium in Catalysis

PubMed Central

Hickman, Amanda J.; Sanford, Melanie S.

2015-01-01

Preface Copper and palladium catalysts are critically important for numerous commercial chemical processes. Improvements in the activity, selectivity, and scope of these catalysts have the potential to dramatically reduce the environmental impact and increase the sustainability of chemical reactions. One rapidly emerging strategy to achieve these goals is to exploit “high-valent” copper and palladium intermediates in catalysis. This review describes exciting recent advances involving both the fundamental chemistry and the applications of these high-valent metal complexes in numerous synthetically useful catalytic transformations. PMID:22498623

Synthesis of hierarchical porous δ-MnO2 nanoboxes as an efficient catalyst for rechargeable Li-O2 batteries

NASA Astrophysics Data System (ADS)

Zhang, Jian; Luan, Yanping; Lyu, Zhiyang; Wang, Liangjun; Xu, Leilei; Yuan, Kaidi; Pan, Feng; Lai, Min; Liu, Zhaolin; Chen, Wei

2015-09-01

A rechargeable lithium-oxygen (Li-O2) battery with a remarkably high theoretical energy storage capacity has attracted enormous research attention. However, the poor oxygen reduction and oxygen evolution reaction (ORR and OER) activities in discharge and charge processes cause low energy efficiency, poor electrolyte stability and short cycle life. This requires the development of efficient cathode catalysts to dramatically improve the Li-O2 battery performances. MnO2-based materials are recognized as efficient and low-cost catalysts for a Li-O2 battery cathode. Here, we report a controllable approach to synthesize hierarchical porous δ-MnO2 nanoboxes by using Prussian blue analogues as the precursors. The obtained products possess hierarchical pore size and an extremely large surface area (249.3 m2 g-1), which would favour oxygen transportation and provide more catalytically active sites to promote ORR and OER as the Li-O2 battery cathode. The battery shows enhanced discharge capacity (4368 mA h g-1@0.08 mA cm-2), reduced overpotential (270 mV), improved rate performance and excellent cycle stability (248 cycles@500 mA h g-1 and 112 cycles@1000 mA h g-1), in comparison with the battery with a VX-72 carbon cathode. The superb performance of the hierarchical porous δ-MnO2 nanoboxes, together with a convenient fabrication method, presents an alternative to develop advanced cathode catalysts for the Li-O2 battery.A rechargeable lithium-oxygen (Li-O2) battery with a remarkably high theoretical energy storage capacity has attracted enormous research attention. However, the poor oxygen reduction and oxygen evolution reaction (ORR and OER) activities in discharge and charge processes cause low energy efficiency, poor electrolyte stability and short cycle life. This requires the development of efficient cathode catalysts to dramatically improve the Li-O2 battery performances. MnO2-based materials are recognized as efficient and low-cost catalysts for a Li-O2 battery cathode. Here, we report a controllable approach to synthesize hierarchical porous δ-MnO2 nanoboxes by using Prussian blue analogues as the precursors. The obtained products possess hierarchical pore size and an extremely large surface area (249.3 m2 g-1), which would favour oxygen transportation and provide more catalytically active sites to promote ORR and OER as the Li-O2 battery cathode. The battery shows enhanced discharge capacity (4368 mA h g-1@0.08 mA cm-2), reduced overpotential (270 mV), improved rate performance and excellent cycle stability (248 cycles@500 mA h g-1 and 112 cycles@1000 mA h g-1), in comparison with the battery with a VX-72 carbon cathode. The superb performance of the hierarchical porous δ-MnO2 nanoboxes, together with a convenient fabrication method, presents an alternative to develop advanced cathode catalysts for the Li-O2 battery. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02983j

Effect of Particle Size and Operating Conditions on Pt 3Co PEMFC Cathode Catalyst Durability

DOE PAGES

Gummalla, Mallika; Ball, Sarah; Condit, David; ...

2015-05-29

The initial performance and decay trends of polymer electrolyte membrane fuel cells (PEMFC) cathodes with Pt 3Co catalysts of three mean particle sizes (4.9 nm, 8.1 nm, and 14.8 nm) with identical Pt loadings are compared. Even though the cathode based on 4.9 nm catalyst exhibited the highest initial electrochemical surface area (ECA) and mass activity, the cathode based on 8.1 nm catalyst showed better initial performance at high currents. Owing to the low mass activity of the large particles, the initial performance of the 14.8 nm Pt3Co-based electrode was the lowest. The performance decay rate of the electrodes withmore » the smallest Pt 3Co particle size was the highest and that of the largest Pt 3Co particle size was lowest. Interestingly, with increasing number of decay cycles (0.6 to 1.0 V, 50 mV/s), the relative improvement in performance of the cathode based on 8.1 nm Pt 3Co over the 4.9 nm Pt 3Co increased, owing to better stability of the 8.1 nm catalyst. The electron microprobe analysis (EMPA) of the decayed membrane-electrode assembly (MEA) showed that the amount of Co in the membrane was lower for the larger particles, and the platinum loss into the membrane also decreased with increasing particle size. This suggests that the higher initial performance at high currents with 8.1 nm Pt 3Co could be due to lower contamination of the ionomer in the electrode. Furthermore, lower loss of Co from the catalyst with increased particle size could be one of the factors contributing to the stability of ECA and mass activity of electrodes with larger cathode catalyst particles. To delineate the impact of particle size and alloy effects, these results are compared with prior work from our research group on size effects of pure platinum catalysts. The impact of PEMFC operating conditions, including upper potential, relative humidity, and temperature on the alloy catalyst decay trends, along with the EMPA analysis of the decayed MEAs, are reported.« less

Pt skin on AuCu intermetallic substrate: a strategy to maximize Pt utilization for fuel cells.

PubMed

Wang, Gongwei; Huang, Bing; Xiao, Li; Ren, Zhandong; Chen, Hao; Wang, Deli; Abruña, Héctor D; Lu, Juntao; Zhuang, Lin

2014-07-09

The dependence on Pt catalysts has been a major issue of proton-exchange membrane (PEM) fuel cells. Strategies to maximize the Pt utilization in catalysts include two main approaches: to put Pt atoms only at the catalyst surface and to further enhance the surface-specific catalytic activity (SA) of Pt. Thus far there has been no practical design that combines these two features into one single catalyst. Here we report a combined computational and experimental study on the design and implementation of Pt-skin catalysts with significantly improved SA toward the oxygen reduction reaction (ORR). Through screening, using density functional theory (DFT) calculations, a Pt-skin structure on AuCu(111) substrate, consisting of 1.5 monolayers of Pt, is found to have an appropriately weakened oxygen affinity, in comparison to that on Pt(111), which would be ideal for ORR catalysis. Such a structure is then realized by substituting the Cu atoms in three surface layers of AuCu intermetallic nanoparticles (AuCu iNPs) with Pt. The resulting Pt-skinned catalyst (denoted as Pt(S)AuCu iNPs) has been characterized in depth using synchrotron XRD, XPS, HRTEM, and HAADF-STEM/EDX, such that the Pt-skin structure is unambiguously identified. The thickness of the Pt skin was determined to be less than two atomic layers. Finally the catalytic activity of Pt(S)AuCu iNPs toward the ORR was measured via rotating disk electrode (RDE) voltammetry through which it was established that the SA was more than 2 times that of a commercial Pt/C catalyst. Taking into account the ultralow Pt loading in Pt(S)AuCu iNPs, the mass-specific catalytic activity (MA) was determined to be 0.56 A/mg(Pt)@0.9 V, a value that is well beyond the DOE 2017 target for ORR catalysts (0.44 A/mg(Pt)@0.9 V). These findings provide a strategic design and a realizable approach to high-performance and Pt-efficient catalysts for fuel cells.

Comparison of preparation methods for ceria catalyst and the effect of surface and bulk sulfates on its activity toward NH3-SCR.

PubMed

Chang, Huazhen; Ma, Lei; Yang, Shijian; Li, Junhua; Chen, Liang; Wang, Wei; Hao, Jiming

2013-11-15

A series of CeO2 catalysts prepared with sulfate (S) and nitrate (N) precursors by hydrothermal (H) and precipitation (P) methods were investigated in selective catalytic reduction of NOx by NH3 (NH3-SCR). The catalytic activity of CeO2 was significantly affected by the preparation methods and the precursor type. CeO2-SH, which was prepared by hydrothermal method with cerium (IV) sulfate as a precursor, showed excellent SCR activity and high N2 selectivity in the temperature range of 230-450 °C. Based on the results obtained by temperature-programmed reduction (H2-TPR), transmission infrared spectra (IR) and thermal gravimetric analysis (TGA), the excellent performance of CeO2-SH was correlated with the surface sulfate species formed in the hydrothermal reaction. These results indicated that sulfate species bind with Ce(4+) on the CeO2-SH catalyst, and the specific sulfate species, such as Ce(SO4)2 or CeOSO4, were formed. The adsorption of NH3 was promoted by these sulfate species, and the probability of immediate oxidation of NH3 to N2O on Ce(4+) was reduced. Accordingly, the selective oxidation of NH3 was enhanced, which contributed to the high N2 selectivity in the SCR reaction. However, the location of sulfate on the CeO2-SP catalyst was different. Plenty of sulfate species were likely deposited on CeO2-SP surface, covering the active sites for NO oxidation, which resulted in poor SCR activity in the test temperature range. Moreover, the resistance to alkali metals, such as Na and K, was improved over the CeO2-SH catalyst. Copyright © 2013 Elsevier B.V. All rights reserved.

Enhancement of activity and sulfur resistance of CeO2 supported on TiO2-SiO2 for the selective catalytic reduction of NO by NH3.

PubMed

Liu, Caixia; Chen, Liang; Li, Junhua; Ma, Lei; Arandiyan, Hamidreza; Du, Yu; Xu, Jiayu; Hao, Jiming

2012-06-05

A series of novel metal-oxide-supported CeO(2) catalysts were prepared via the wet impregnation method, and their NH(3)-SCR activities were investigated. The Ce/TiO(2)-SiO(2) catalyst with a Ti/Si mass ratio of 3/1 exhibited superior NH(3)-SCR activity and high N(2) selectivity in the temperature range of 250-450 °C. The characterization results revealed that the activity enhancement was correlated with the properties of the support material. Cerium was highly dispersed on the TiO(2)-SiO(2) binary metal oxide support, and the interaction of Ti and Si resulted in greater conversion of Ce(4+) to Ce(3+) on the surface of the catalyst compared to that on the single metal oxide supports. As a result of in the increased number of acid sites on Ce/TiO(2)-SiO(2) that resulted from the addition of SiO(2), the NH(3) adsorption capacity was significantly improved. All of these factors played significant roles in the high SCR activity. More importantly, Ce/TiO(2)-SiO(2) exhibited strong resistance to SO(2) and H(2)O poisoning. After the addition of SiO(2), the number of Lewis-acid sites was not decreased, but the number of Brønsted-acid sites on the TiO(2)-SiO(2) carrier was increased. The introduction of SiO(2) further weakened the alkalinity over the surface of the Ce/TiO(2)-SiO(2) catalyst, which resulted in sulfate not easily accumulating on the surface of the Ce/TiO(2)-SiO(2) catalyst in comparison with Ce/TiO(2).

Insight into the role of the promoters Pt, Ru and B in inhibiting the deactivation of Co catalysts in Fischer-Tropsch synthesis

NASA Astrophysics Data System (ADS)

Zhang, Riguang; Liu, Hongxia; Li, Qiaohong; Wang, Baojun; Ling, Lixia; Li, Debao

2018-09-01

In order to probe into the roles of the promoters Pt, Ru and B in inhibiting the deactivation of Co catalysts in FTS reactions, the adsorption ability of neighboring surface C and subsurface C atom around the promoters (Pt, Ru and B), and the mechanisms of surface C diffusion, accumulation, hydrogenation and penetration are examined by density functional theory calculations over the promoters Pt, Ru and B-modified Co catalysts, as well as the pure Co catalysts. Our results clearly show that compared to Co catalysts, both PtCo and RuCo bimetallic catalysts promote surface C hydrogenation, and inhibit surface C diffusion, accumulation and penetration, and therefore the ability of resistance toward deactivation and the stability of Co-based catalysts are enhanced; the promoter B cannot effectively improve the ability of resistance toward deactivation. Thus, the sequence for resistance toward deactivation of Co-based catalyst is BCo < Co < PtCo < RuCo. Moreover, the activation free energy of surface C accumulation to C2 species increases with the increasing of surface C adsorption free energy, namely, the adsorption characteristic of surface C species well represent the surface carbon deposition. Our results not only give an explanation for reported experiment that the Pt, Ru and B-modified Co catalysts exhibit ability of resistance toward deactivation in FTS at a molecular level, but also provide a clue for the design of efficient Co-based catalysts in FTS reactions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

The LZ-105-6, a medium pore molecular sieve, similar in structure to ZSM-5, is the most active catalyst we have tested so far for the conversion of propylene. At optimal conditions, it converted 90% of the feed versus 63% found with UCC-104. However, the test carried out in the Berty reactor showed that this catalyst has inferior selectivity to C/sub 5//sup +/ (89%) relative to UCC-104 (96%). The lower C/sub 5//sup +/ yield with LZ-105 follows from the increased conversion of the propylene to saturated C/sub 3/-C/sub 4/ hydrocarbons. A Task 2 catalyst was prepared by the physical mixture of themore » reference Fischer-Tropsch catalyst used above and the large pore UCC-101. This catalyst, in contrast to the reference catalyst, did not produce the excess C/sub 20//sup +/ products. Here, the hydrocarbons were isomerized and the pour points of all condensed samples were below room temperature. Conditions were adjusted to obtain excellent selectivity to gasoline, 50 wt. %, and total motor fuel, 70 wt. %. The high selectivity was achieved with this catalyst, however, at a relatively low activity level. Importantly, the product distribution of two runs showed signs of a carbon number cut off (shape selective effect). Thus, this experiment demonstrated the efficiency of UCC-101 as SSC component in that it isomerized the hydrocarbons formed on the MC resulting in substantial improvement of the motor fuel products, and it also seemed to show a cut-off at the end of the motor fuel boiling range (C/sub 20/).« less

DEVELOPMENT OF ATTRITION RESISTANT IRON-BASED FISCHER-TROPSCH CATALYSTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adeyinka A. Adeyiga

2003-12-01

Fischer-Tropsch (FT) synthesis to convert syngas (CO + H{sub 2}) derived from natural gas or coal to liquid fuels and wax is a well-established technology. For low H{sub 2} to CO ratio syngas produced from CO{sub 2} reforming of natural gas or from gasification of coal, the use of Fe catalysts is attractive because of their high water gas shift activity in addition to their high FT activity. Fe catalysts are also attractive due to their low cost and low methane selectivity. Because of the highly exothermic nature of the FT reaction, there has been a recent move away frommore » fixed-bed reactors toward the development of slurry bubble column reactors (SBCRs) that employ 30 to 90 {micro}m catalyst particles suspended in a waxy liquid for efficient heat removal. However, the use of Fe FT catalysts in an SBCR has been problematic due to severe catalyst attrition resulting in fines that plug the filter employed to separate the catalyst from the waxy product. Fe catalysts can undergo attrition in SBCRs not only due to vigorous movement and collisions but also due to phase changes that occur during activation and reaction. The objectives of this research were to develop a better understanding of the parameters affecting attrition of Fe F-T catalysts suitable for use in SBCRs and to incorporate this understanding into the design of novel Fe catalysts having superior attrition resistance. The catalysts were prepared by co-precipitation, followed by binder addition and spray drying at 250 C in a 1 m diameter, 2 m tall spray dryer. The binder silica content was varied from 0 to 20 wt %. The results show that use of small amounts of precipitated SiO{sub 2} alone in spray-dried Fe catalysts can result in good attrition resistance. All catalysts investigated with SiO{sub 2} wt% {le} 12 produced fines less than 10 wt% during the jet cup attrition test, making them suitable for long-term use in a slurry bubble column reactor. Thus, concentration rather than type of SiO{sub 2} incorporated into catalyst has a more critical impact on catalyst attrition resistance of spray-dried Fe catalysts. Lower amounts of SiO{sub 2} added to a catalyst give higher particle densities and therefore higher attrition resistances. In order to produce a suitable SBCR catalyst, however, the amount of SiO{sub 2} added has to be optimized to provide adequate surface area, particle density, and attrition resistance. Two of the catalysts with precipitated and binder silica were tested in Texas A&M University's CSTR (Autoclave Engineers). Spray-dried catalysts with compositions 100 Fe/5 Cu/4.2 K/11 (P) SiO{sub 2} and 100 Fe/5 Cu/4.2 K/1.1 (B) SiO{sub 2} have excellent selectivity characteristics (low methane and high C{sub 5}{sup +} yields), but their productivity and stability (deactivation rate) need to be improved. Mechanical integrity (attrition strength) of these two catalysts was markedly dependent upon their morphological features. The attrition strength of the catalyst made out of largely spherical particles (1.1 (B) SiO{sub 2}) was considerably higher than that of the catalyst consisting of irregularly shaped particles (11 (P) SiO{sub 2}).« less

Balancing activity, stability and conductivity of nanoporous core-shell iridium/iridium oxide oxygen evolution catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Yong-Tae; Lopes, Pietro Papa; Park, Shin-Ae

The selection of oxide materials for catalyzing the Oxygen Evolution Reaction in acid-based electrolyzers must be guided by the proper balance between activity, stability and conductivity – a challenging mission of great importance for delivering affordable and environmentally friendly hydrogen. Here we report that the highly conductive nanoporous architecture of an iridium oxide shell on a metallic iridium core, formed through the fast dealloying of osmium from an Ir25Os75 alloy, exhibits an exceptional balance between oxygen evolution activity and stability as quantified by the Activity-Stability FactorASF. Based on this metric, the nanoporous Ir/IrO2 morphology of dealloyed Ir25Os75 shows a factormore » of ~30 improvement ASFrelative to conventional Ir-based oxide materials and a ~8 times improvement over dealloyed Ir25Os75 nanoparticles due to optimized stability and conductivity, respectively. We propose that the Activity-Stability FactorASF is the key “metric” for determining the technological relevance of oxide-based anodic water electrolyzer catalysts.« less

Application of BiFeO3-based on nickel foam composites with a highly efficient catalytic activity and easily recyclable in Fenton-like process under microwave irradiation

NASA Astrophysics Data System (ADS)

Li, Shuo; Zhang, Guangshan; Zheng, Heshan; Zheng, Yongjie; Wang, Peng

2018-05-01

In this study, BiFeO3 (BFO) powders decorated on nickel foam (NF) with a high catalytic activity are prepared via a one-step microwave-assisted hydrothermal method. The factors that influence the degradation of bisphenol A (BPA) with BFO/NFs as catalysts are optimized to improve the catalytic activity in a microwave-enhanced Fenton-like process. BFO/NF exhibit a superior catalytic activity with a high BPA removal ratio (98.4%) and TOC removal ratio (69.5%) within 5 min. Results indicate that NF significantly affect the improvement of the catalytic activity of BFO because it served as a source of hydroxyl radicals (•OH) during degradation. The amount of •OH generated by BFO/NF is approximately 1.65-fold higher than that by pure BFO. After six reaction cycles, the stability and reusability of •OH remain high. These findings provide new insights into the synthesis of composites on heterogeneous catalysts with high efficiency and easy recyclability for water treatment applications.

Synthesis of a highly dispersed CuO catalyst on CoAl-HT for the epoxidation of styrene.

PubMed

Hu, Rui; Yang, Pengfei; Pan, Yongning; Li, Yunpeng; He, Yufei; Feng, Junting; Li, Dianqing

2017-10-10

A highly dispersed CuO catalyst was prepared by the deposition-precipitation method and evaluated for the catalytic epoxidation of styrene with tert-butyl hydroperoxide (TBHP) as the oxidant under solvent acetonitrile conditions. Compared with MgAl hydrotalcite (MgAl-HT)-, MgO-, TiO 2 -, C-, and MCM-22-supported catalysts, CuO/CoAl-HT exhibited preferable activity and selectivity towards styrene oxide (72% selectivity at 99.5% styrene conversion) due to its high dispersion of CuO and surface area of Cu. The improved dispersion of CuO/CoAl-HT could be ascribed to the nature of HT support, especially the synergistic effect of acidic and basic sites on the surface, which facilitated the formation of highly dispersed CuO species. A structure-performance relationship study indicated that copper(ii) in CuO was the active site for the epoxidation and oxidation of styrene, and that Cu II of rich electronic density favored the improvement of selectivity of styrene oxide. Based on these results, a reaction mechanism was proposed. Moreover, the preferred catalytic performance of CuO/CoAl-HT could be maintained in five reused cycles.

Selective hydrogenation of phenol to cyclohexanone over Pd@CN (N-doped porous carbon): Role of catalyst reduction method

NASA Astrophysics Data System (ADS)

Hu, Shuo; Yang, Guangxin; Jiang, Hong; Liu, Yefei; Chen, Rizhi

2018-03-01

Selective phenol hydrogenation is a green and sustainable technology to produce cyclohexanone. The work focused on investigating the role of catalyst reduction method in the liquid-phase phenol hydrogenation to cyclohexanone over Pd@CN (N-doped porous carbon). A series of reduction methods including flowing hydrogen reduction, in-situ reaction reduction and liquid-phase reduction were designed and performed. The results highlighted that the reduction method significantly affected the catalytic performance of Pd@CN in the liquid-phase hydrogenation of phenol to cyclohexanone, and the liquid-phase reduction with the addition of appropriate amount of phenol was highly efficient to improve the catalytic activity of Pd@CN. The influence mechanism was explored by a series of characterizations. The results of TEM, XPS and CO chemisorption confirmed that the reduction method mainly affected the size, surface composition and dispersion of Pd in the CN material. The addition of phenol during the liquid-phase reduction could inhibit the aggregation of Pd NPs and promote the reduction of Pd (2+), and then improved the catalytic activity of Pd@CN. The work would aid the development of high-performance Pd@CN catalysts for selective phenol hydrogenation.

Technology for advanced liquefaction processes: Coal/waste coprocessing studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cugini, A.V.; Rothenberger, K.S.; Ciocco, M.V.

1995-12-31

The efforts in this project are directed toward three areas: (1) novel catalyst (supported and unsupported) research and development, (2) study and optimization of major operating parameters (specifically pressure), and (3) coal/waste coprocessing. The novel catalyst research and development activity has involved testing supported catalysts, dispersed catalysts, and use of catalyst testing units to investigate the effects of operating parameters (the second area) with both supported and unsupported catalysts. Several supported catalysts were tested in a simulated first stage coal liquefaction application at 404{degrees}C during this performance period. A Ni-Mo hydrous titanate catalyst on an Amocat support prepared by Sandiamore » National laboratories was tested. Other baseline experiments using AO-60 and Amocat, both Ni-Mo/Al{sub 2}O{sub 3} supported catalysts, were also made. These experiments were short duration (approximately 12 days) and monitored the initial activity of the catalysts. The results of these tests indicate that the Sandia catalyst performed as well as the commercially prepared catalysts. Future tests are planned with other Sandia preparations. The dispersed catalysts tested include sulfated iron oxide, Bayferrox iron oxide (iron oxide from Miles, Inc.), and Bailey iron oxide (micronized iron oxide from Bailey, Inc.). The effects of space velocity, temperature, and solvent-to-coal ratio on coal liquefaction activity with the dispersed catalysts were investigated. A comparison of the coal liquefaction activity of these catalysts relative to iron catalysts tested earlier, including FeOOH-impregnated coal, was made. These studies are discussed.« less

Unravelling Site-Specific Photo-Reactions of Ethanol on Rutile TiO2(110)

PubMed Central

Hansen, Jonas Ø.; Bebensee, Regine; Martinez, Umberto; Porsgaard, Soeren; Lira, Estephania; Wei, Yinying; Lammich, Lutz; Li, Zheshen; Idriss, Hicham; Besenbacher, Flemming; Hammer, Bjørk; Wendt, Stefan

2016-01-01

Finding the active sites of catalysts and photo-catalysts is crucial for an improved fundamental understanding and the development of efficient catalytic systems. Here we have studied the photo-activated dehydrogenation of ethanol on reduced and oxidized rutile TiO2(110) in ultrahigh vacuum conditions. Utilizing scanning tunnelling microscopy, various spectroscopic techniques and theoretical calculations we found that the photo-reaction proceeds most efficiently when the reactants are adsorbed on regular Ti surface sites, whereas species that are strongly adsorbed at surface defects such as O vacancies and step edges show little reaction under reducing conditions. We propose that regular Ti surface sites are the most active sites in photo-reactions on TiO2. PMID:26915303

Self-assembly of cobalt-centered metal organic framework and multiwalled carbon nanotubes hybrids as a highly active and corrosion-resistant bifunctional oxygen catalyst

NASA Astrophysics Data System (ADS)

Fang, Yiyun; Li, Xinzhe; Li, Feng; Lin, Xiaoqing; Tian, Min; Long, Xuefeng; An, Xingcai; Fu, Yan; Jin, Jun; Ma, Jiantai

2016-09-01

Metal organic frameworks (MOF) derived carbonaceous materials have emerged as promising bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts for electrochemical energy conversion and storage. But previous attempts to overcome the poor electrical conductivity of MOFs hybrids involve a harsh high-template pyrolytic process to in situ form carbon, which suffer from extremely complex operation and inevitable carbon corrosion at high positive potentials when OER is operated. Herein, a self-assembly approach is presented to synthesize a non-precious metal-based, high active and strong durable Co-MOF@CNTs bifunctional catalyst for OER and ORR. CNTs not only improve the transportation of the electrons but also can sustain the harsh oxidative environment of OER without carbon corrosion. Meanwhile, the unique 3D hierarchical structure offers a large surface area and stable anchoring sites for active centers and CNTs, which enables the superior durability of hybrid. Moreover, a synergistic catalysis of Co(II), organic ligands and CNTs will enhance the bifunctional electrocatalytic performance. Impressively, the hybrid exhibits comparable OER and ORR catalytic activity to RuO2 and 20 wt% Pt/C catalysts and superior stability. This facile and versatile strategy to fabricating MOF-based hybrids may be extended to other electrode materials for fuel cell and water splitting applications.

Carefully designed oxygen-containing functional groups and defects of porous carbon spheres with UV-O3 treatment and their enhanced catalytic performance

NASA Astrophysics Data System (ADS)

Han, Weiliang; Huang, Xiaosheng; Lu, Gongxuan; Tang, Zhicheng

2018-04-01

In this paper, the support surface properties (surface oxygen-containing functional groups and structure defects) of porous carbon spheres (PCSs) were carefully designed by as UV assisted O3 technology. CO catalytic oxidation reactions performed over the supported Pd-Ce catalysts on modified porous carbon spheres. Results illustrated that the Pd-Ce/PCSs catalysts exhibited high CO catalytic activity, which were increased at first, and then decreased with UV assistant-O3 treatment time. The Pd-Ce/PCSs-30 catalyst exhibited superior activity and T100 was only 15 °C. Moreover, the Pd-Ce/PCSs-30 catalyst obtained an excellent stability, and 100% CO conversion could be maintained as the time on stream evolutes up to 16h in the presence of H2O in the feed. Based on characterization results, there were two main factors: (a) the surface area and pore volume were decreased with UV-O3 treatment, leading to the enhancement of Pd-Ce particle size, and the decrease of Pd-Ce nanoparticle dispersion and mass transfer efficiency, as well as the decrease of catalytic activity of Pd-Ce/PCSs, (b) the surface oxygen content and defect sites of PCSs were raised by UV-O3 treatment, which could improve surface loading of Pd, Ce and enhance Pdsbnd Osbnd Ce bonding interactions, thereby increasing the activity of Pd-Ce/PCSs.

TiO2 and Al2O3 promoted Pt/C nanocomposites as low temperature fuel cell catalysts for electro oxidation of methanol in acidic media

NASA Astrophysics Data System (ADS)

Naeem, Rabia; Ahmed, Riaz; Shahid Ansari, Muhammad

2014-06-01

Carbon corrosion and platinum dissolution are the two major catalyst layer degradation problems in polymer electrolyte membrane fuel cells (PEMFC). Ceramic addition can reduce the corrosion of carbon and increase the stability of catalysts. Pt/TiO2, Pt/TiO2-C, Pt/Al2O3 and Pt/Al2O3-C catalysts were synthesized and characterized. Electrochemical surface area of Pt/TiO2-C and Pt/Al2O3-C nanocomposite catalysts was much higher than the Pt/TiO2 and Pt/Al2O3 catalysts. Peak current, specific activity and mass activity of the catalysts was also determined by cyclic voltammetry and were much higher for the carbon nanocomposites. Exchange current densities were determined from Tafel plots. Heterogeneous rates of reaction of electro oxidation of methanol were determined for all the catalysts and were substantially higher for titania catalysts as compared to alumina added catalysts. Mass activity of Pt/TiO2-C was much higher than mass activity of Pt/Al2O3-C. Stability studies showed that addition of ceramics have increased the catalytic activity and durability of the catalysts considerably.

Protic ionic liquid modified electrocatalyst enables robust anode under cell reversal condition

NASA Astrophysics Data System (ADS)

Zhu, Zhengyu; Yan, Xiaocong; Tang, Haolin; Cai, Haopeng; Pan, Mu; Zhang, Haining; Luo, Jiangshui

2017-05-01

Pt/C has been commercially used as anode electrocatalyst for fuel cells but generally exhibits limited durability under conditions of fuel starvation and subsequent cell reversal. Herein we report an improved scaffold concept to simultaneously stabilize the catalyst against particle growth and reduce the adverse effects of cell reversal by modifying Pt/C with suitable protic ionic liquids (PILs). The modified Pt/C catalysts show enhanced cell reversal tolerance because of their high activity towards oxygen evolution reaction (OER), up to 300 mV lower overpotential compared to the unmodified Pt/C. Moreover, the PIL modified catalysts show better resistance to the loss of electrochemical surface area (ECSA) under simulated cell reversal conditions. The results indicate that modification of Pt/C catalysts with PILs is a promising strategy to enhance the stability and durability of electrocatalysts in fuel cell applications with the risk of frequent fuel starvation events, such as automotive fuel cells.

Active site formation mechanism of carbon-based oxygen reduction catalysts derived from a hyperbranched iron phthalocyanine polymer.

PubMed

Hiraike, Yusuke; Saito, Makoto; Niwa, Hideharu; Kobayashi, Masaki; Harada, Yoshihisa; Oshima, Masaharu; Kim, Jaehong; Nabae, Yuta; Kakimoto, Masa-Aki

2015-01-01

Carbon-based cathode catalysts derived from a hyperbranched iron phthalocyanine polymer (HB-FePc) were characterized, and their active-site formation mechanism was studied by synchrotron-based spectroscopy. The properties of the HB-FePc catalyst are compared with those of a catalyst with high oxygen reduction reaction (ORR) activity synthesized from a mixture of iron phthalocyanine and phenolic resin (FePc/PhRs). Electrochemical measurements demonstrate that the HB-FePc catalyst does not lose its ORR activity up to 900°C, whereas that of the FePc/PhRs catalyst decreases above 700°C. Hard X-ray photoemission spectra reveal that the HB-FePc catalysts retain more nitrogen components than the FePc/PhRs catalysts between pyrolysis temperatures of 600°C and 800°C. This is because the linked structure of the HB-FePc precursor has high thermostability against nitrogen desorption. Consequently, effective doping of active nitrogen species into the sp (2) carbon network of the HB-FePc catalysts may occur up to 900°C.

Activation of catalysts for synthesizing methanol from synthesis gas

DOEpatents

Blum, David B.; Gelbein, Abraham P.

1985-01-01

A method for activating a methanol synthesis catalyst is disclosed. In this method, the catalyst is slurried in an inert liquid and is activated by a reducing gas stream. The activation step occurs in-situ. That is, it is conducted in the same reactor as is the subsequent step of synthesizing methanol from a methanol gas stream catalyzed by the activated catalyst still dispersed in a slurry.

Preparation of MoO2/g-C3N4 composites with a high surface area and its application in deep desulfurization from model oil

NASA Astrophysics Data System (ADS)

Hou, Liang-pei; Zhao, Rong-xiang; Li, Xiu-ping; Gao, Xiao-han

2018-03-01

A series of catalysts of composition X-MoO2/g-C3N4 (X = 0, 0.5, 1, 3, 5 wt.%) were successfully synthesized by calcination of a mixture of (NH4)6Mo7O24·4H2O and g-C3N4. Oxidative desulfurization experiments were conducted using X-MoO2/g-C3N4 as a catalyst, H2O2 as an oxidant, and ionic liquids (ILs) as extraction agents. Catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), and Brunauer-Emmett-Teller analysis (BET). Characterization results suggested that MoO2 was present in the catalyst and its crystallinity improved with increased Mo-loading. The catalysts had a larger specific surface area due to the presence of MoO2 dispersed on g-C3N4. Experimental results showed that 3%-MoO2/g-C3N4 had the highest catalytic activity among all the catalysts tested. A desulfurization rate of 96.0% was achieved under optimal conditions. Through gas chromatography-mass spectrometry (GC-MS) analysis, it was shown that dibenzothoiphene sulfone was the sole product of the oxidation desulfurization reaction. An apparent activation energy of 61.1 kJ/mol was estimated based on Arrhenius equation. The activity of 3%-MoO2/g-C3N4 slightly decreased after six runs. A possible mechanism for the reaction has been proposed.

Application of a mixed metal oxide catalyst to a metallic substrate

NASA Technical Reports Server (NTRS)

Sevener, Kathleen M. (Inventor); Lohner, Kevin A. (Inventor); Mays, Jeffrey A. (Inventor); Wisner, Daniel L. (Inventor)

2009-01-01

A method for applying a mixed metal oxide catalyst to a metallic substrate for the creation of a robust, high temperature catalyst system for use in decomposing propellants, particularly hydrogen peroxide propellants, for use in propulsion systems. The method begins by forming a prepared substrate material consisting of a metallic inner substrate and a bound layer of a noble metal intermediate. Alternatively, a bound ceramic coating, or frit, may be introduced between the metallic inner substrate and noble metal intermediate when the metallic substrate is oxidation resistant. A high-activity catalyst slurry is applied to the surface of the prepared substrate and dried to remove the organic solvent. The catalyst layer is then heat treated to bind the catalyst layer to the surface. The bound catalyst layer is then activated using an activation treatment and calcinations to form the high-activity catalyst system.

PdCo supported on multiwalled carbon nanotubes as an anode catalyst in a microfluidic formic acid fuel cell

NASA Astrophysics Data System (ADS)

Morales-Acosta, D.; Morales-Acosta, M. D.; Godinez, L. A.; Álvarez-Contreras, L.; Duron-Torres, S. M.; Ledesma-García, J.; Arriaga, L. G.

This work reports the synthesis of Pd-based alloys of Co and their evaluation as anode materials in a microfluidic formic acid fuel cell (μFAFC). The catalysts were prepared using the impregnation method followed by thermal treatment. The synthesized catalysts contain 22 wt.% Pd on multiwalled carbon nanotubes (Pd/MWCNT) and its alloys with two Co atomic percent in the sample with 4 at.% Co (PdCo1/MWCNT) and 10 at.% Co (PdCo2/MWCNT). The role of the alloying element was determined by XRD and XPS techniques. Both catalysts were evaluated as anode materials in a μFAFC operating with different concentrations of HCOOH (0.1 and 0.5 M), and the results were compared to those obtained with Pd/MWCNT. A better performance was obtained for the cell using PdCo1/MWCNT (1.75 mW cm -2) compared to Pd/MWCNT (0.85 mW cm -2) in the presence of 0.5 M HCOOH. By means of external electrode measurements, it was also possible to observe shifts in the formic acid oxidation potential due to a fuel concentration increment (ca. 0.05 V for both PdCo1/MWCNT and PdCo2/MWCNT catalysts and 0.23 V for Pd/MWCNT) that was attributed to deactivation of the catalyst material. The maximum current densities obtained were 8 mA cm -2 and 5.2 mA cm -2 for PdCo2/MWCNT and Pd/MWCNT, respectively. In this way, the addition of Co to the Pd catalyst was shown to improve the tolerance of intermediates produced during formic acid oxidation that tend to poison Pd, thus improving the catalytic activity and stability of the cell.

Evolving artificial metalloenzymes via random mutagenesis

NASA Astrophysics Data System (ADS)

Yang, Hao; Swartz, Alan M.; Park, Hyun June; Srivastava, Poonam; Ellis-Guardiola, Ken; Upp, David M.; Lee, Gihoon; Belsare, Ketaki; Gu, Yifan; Zhang, Chen; Moellering, Raymond E.; Lewis, Jared C.

2018-03-01

Random mutagenesis has the potential to optimize the efficiency and selectivity of protein catalysts without requiring detailed knowledge of protein structure; however, introducing synthetic metal cofactors complicates the expression and screening of enzyme libraries, and activity arising from free cofactor must be eliminated. Here we report an efficient platform to create and screen libraries of artificial metalloenzymes (ArMs) via random mutagenesis, which we use to evolve highly selective dirhodium cyclopropanases. Error-prone PCR and combinatorial codon mutagenesis enabled multiplexed analysis of random mutations, including at sites distal to the putative ArM active site that are difficult to identify using targeted mutagenesis approaches. Variants that exhibited significantly improved selectivity for each of the cyclopropane product enantiomers were identified, and higher activity than previously reported ArM cyclopropanases obtained via targeted mutagenesis was also observed. This improved selectivity carried over to other dirhodium-catalysed transformations, including N-H, S-H and Si-H insertion, demonstrating that ArMs evolved for one reaction can serve as starting points to evolve catalysts for others.

New electrocatalysts for unitized regenerative fuel cell: Pt-Ir alloy deposited on the proton exchange membrane surface by impregnation-reduction method.

PubMed

Wan, Chieh-Hao; Wu, Chun-Lin; Lin, Meng-Tsun; Shih, Chihhsiong

2010-07-01

In this paper, a modified technique to prepare Pt-Ir catalyst layer on the proton exchange membrane (PEM) surface using the impregnation-reduction (IR) method is proposed to improve the electrocatalytic activity as well as the life cycle of the bifunctional oxygen electrode (BOE). The resulted electrocatalysts were characterized by the Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Electron Probe Micro-Analysis (EPMA), and Transmission Electron Microscope (TEM). The electrocatalytic properties of the Pt-Ir layer on PEM surface for the oxygen reduction and water oxidation reactions as well as the life cycle of MEA were investigated. Experimental results showed that the Ir particles were dispersed densely in the platinum layer through the modified IR technique. The atomic ratio of Pt over Ir elements was 9:1, and the resulted thickness of the obtained Pt-Ir catalyst layer was about 1.0 microm. The Pt-Ir catalyst layer was composed of Pt layer doped with Ir nano-particles comprising nano Pt-Ir alloy phase. The large surface area of Ir core with Pt shell particles and the presence of nano Pt-Ir alloy phase led to a higher electrocatalytic activity of BOE. Due to the good binding between the Nafion membrane and the Pt-Ir alloy catalyst, as well as the composite structure of the resulted Pt-Ir, the life cycle of Unitized Regenerative Fuel Cell (URFC) is improved through this novel BOE.

Comparison of designed and randomly generated catalysts for simple chemical reactions.

PubMed

Kipnis, Yakov; Baker, David

2012-09-01

There has been recent success in designing enzymes for simple chemical reactions using a two-step protocol. In the first step, a geometric matching algorithm is used to identify naturally occurring protein scaffolds at which predefined idealized active sites can be realized. In the second step, the residues surrounding the transition state model are optimized to increase transition state binding affinity and to bolster the primary catalytic side chains. To improve the design methodology, we investigated how the set of solutions identified by the design calculations relate to the overall set of solutions for two different chemical reactions. Using a TIM barrel scaffold in which catalytically active Kemp eliminase and retroaldolase designs were obtained previously, we carried out activity screens of random libraries made to be compositionally similar to active designs. A small number of active catalysts were found in screens of 10³ variants for each of the two reactions, which differ from the computational designs in that they reuse charged residues already present in the native scaffold. The results suggest that computational design considerably increases the frequency of catalyst generation for active sites involving newly introduced catalytic residues, highlighting the importance of interaction cooperativity in enzyme active sites. Copyright © 2012 The Protein Society.

[Catalytic combustion of soot on combined oxide catalysts].

PubMed

He, Xu-wen; Yu, Jun-jie; Kang, Shou-fang; Hao, Zheng-ping; Hu, Chun

2005-01-01

Combined oxide catalysts are prepared for catalytic combustion of soot and regeneration from diesel emissions. Thermo-gravimetric analysis(TGA) and temperature programmed oxidation(TPO)are used to evaluate the activity of catalysts under the influence of composition,atomic ration, H2O, calcinations temperature and mass ration between catalysts and soot. Results show that Cu-Mo-O had high activity among double metal oxide catalysts. Among multicomponent metal oxide catalysts, Cu-K-Mo-O had high activity when atomic ratio Cu: K: Mo = 1:1:2 and mass ration between catalysts and soot equals 5: 1. Under this condition, soot ignition temperature of Cu-K-Mo-O catalyst was 327 degrees C. H2O addition and calcinations temperature had little influence on it,which is one kind of compatible catalyst for soot control and catalytic regeneration from diesel emissions.

Preparation, Characterization, and Catalytic Activity of MoCo/USY Catalyst on Hydrodeoxygenation Reaction of Anisole

NASA Astrophysics Data System (ADS)

Nugrahaningtyas, K. D.; Suharbiansah, R. S. R.; Rahmawati, F.

2018-03-01

This research aims to prepare, characterize, and study the catalytic activity of Molybdenum (Mo) and Cobalt (Co) metal with supporting material Ultra Stable Y-Zeolite (USY), to produce catalysts with activity in hydrotreatment reaction and in order to eliminate impurities compounds that containing unwanted groups heteroatoms. The bimetallic catalysts MoCo/USY were prepared by wet impregnation method with weight variation of Co metal 0%, 2%, 4%, 6%, 8%, and Mo metal 8% (w/w), respectively. Activation method of the catalyst included calcination, oxidation, reduction and the crystallinity was characterized using X-ray diffraction (XRD), the acidity of the catalyst was analyzed using Fourier Transform Infrared Spectroscopy (FT-IR) and gravimetry method, minerals present in the catalyst was analyzed using X-Ray Fluorescence (XRF), and surface of the catalyst was analyzed using Surface Area Analyzer (SAA). Catalytic activity test (benzene yield product) of MoCo/USY on hydrodeoxigenation reaction of anisole aimed to determine the effect of Mo-Co/USY for catalytic activity in the reaction hydrodeoxigenation (HDO) anisole. Based on characterization and test of catalytic activity, it is known that catalytic of MoCo/USY 2% (catalyst B) shows best activities with acidity of 10.209 mmol/g, specific area of catalyst of 426.295 m2/g, pore average of 14.135 Å, total pore volume 0.318 cc/g, and total yield of HDO products 6.06%.

Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.

The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100)more » and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.« less

Integrating carbon nanotube forests into polysilicon MEMS: Growth kinetics, mechanisms, and adhesion

DOE PAGES

Ubnoske, Stephen M.; Radauscher, Erich J.; Meshot, Eric R.; ...

2016-11-19

The growth of carbon nanotubes (CNTs) on polycrystalline silicon substrates was studied to improve the design of CNT field emission sources for microelectromechanical systems (MEMS) applications and vacuum microelectronic devices (VMDs). Microwave plasma-enhanced chemical vapor deposition (PECVD) was used for CNT growth, resulting in CNTs that incorporate the catalyst particle at their base. The kinetics of CNT growth on polysilicon were compared to growth on Si (100) using the model of Deal and Grove, finding activation energies of 1.61 and 1.54 eV for the nucleation phase of growth and 1.90 and 3.69 eV for the diffusion-limited phase on Si (100)more » and polysilicon, respectively. Diffusivity values for growth on polysilicon were notably lower than the corresponding values on Si (100) and the growth process became diffusion-limited earlier. Evidence favors a surface diffusion growth mechanism involving diffusion of carbon precursor species along the length of the CNT forest to the catalyst at the base. Explanations for the differences in activation energies and diffusivities were elucidated by SEM analysis of the catalyst nanoparticle arrays and through wide-angle X-ray scattering (WAXS) of CNT forests. As a result, methods are presented to improve adhesion of CNT films during operation as field emitters, resulting in a 2.5× improvement.« less

Alloy catalysts for fuel cell-based alcohol sensors

NASA Astrophysics Data System (ADS)

Ghavidel, Mohammadreza Zamanzad

Direct ethanol fuel cells (DEFCs) are attractive from both economic and environmental standpoints for generating renewable energy and powering vehicles and portable electronic devices. There is a great interest recently in developing DEFC systems. The cost and performance of the DEFCs are mainly controlled by the Pt-base catalysts used at each electrode. In addition to energy conversion, DEFC technology is commonly employed in the fuel-cell based breath alcohol sensors (BrAS). BrAS is a device commonly used to measure blood alcohol concentration (BAC) and enforce drinking and driving laws. The BrAS is non-invasive and has a fast respond time. However, one of the most important drawback of the commercially available BrAS is the very high loading of Pt employed. One well-known and cost effective method to reduce the Pt loading is developing Pt-alloy catalysts. Recent studies have shown that Pt-transition metal alloy catalysts enhanced the electroactivity while decreasing the required loadings of the Pt catalysts. In this thesis, carbon supported Pt-Mn and Pt-Cu electrocatalysts were synthesized by different methods and the effects of heat treatment and structural modification on the ethanol oxidation reaction (EOR) activity, oxygen reduction reaction (ORR) activity and durability of these samples were thoroughly studied. Finally, the selected Pt-Mn and Pt-Cu samples with the highest EOR activity were examined in a prototype BrAS system and compared to the Pt/C and Pt 3Sn/C commercial electrocatalysts. Studies on the Pt-Mn catalysts produced with and without additives indicate that adding trisodium citrate (SC) to the impregnation solution improved the particle dispersion, decreased particle sizes and reduced the time required for heat treatment. Further studies show that the optimum weight ratio of SC to the metal loading in the impregnation solution was 2:1 and optimum results achieved at pH lower than 4. In addition, powder X-ray diffraction (XRD) analyses indicate that the optimum heat treatment temperature was 700 °C where a uniform ordered PtMn intermetallic phase was formed. Although the electrochemical active surface area (ECSA) decreased due to the heat treatment, the EOR activity of Pt-Mn samples was improved. Moreover, it was shown that the heat-treated samples prepared in the presence of SC showed superior the EOR activity compared to the samples made without SC. The Pt-Cu/C alloys were produced by three different methods: impregnation, impregnation in the presence of sodium citrate and microwave assisted polyol methods. These studies showed that the polyol method was the optimum method to produce the Pt-Cu alloy. The XRD analysis indicates that the heat treatment at 700 °C developed catalysts rich in the PtCu and PtCu3 ordered phases. The highest EOR activity was measured for the Pt-Cu/C-POL (sample made by the polyol method) and heat treated at 700 °C for 1h. Comparing the EOR activity of the Pt-Cu and Pt-Mn samples also demonstrates that the heat treated Pt-Cu/C-POL sample showed higher EOR activity compared to the Pt-Mn samples. These results indicate that the benefits of thermally treating alloy nanoparticles could outweigh any activity losses that may occur due to the particle size growth and the ECSA loss. Besides, accelerated stress tests (ASTs) illustrate that the heat treatment improved the durability of the Pt-Mn and Pt-Cu samples. The durability and EOR activity of the heat treated Pt-Mn and Pt-Cu samples was similar or better than commercial samples. On the other hand, the ORR activity of Pt-Mn and Pt-Cu after the heat treatment was slightly lower than the commercial samples but the ORR activity loss can be compensated by the economic benefits from using the lower Pt loading. Finally, studying the alcohol sensing characteristic of different samples shows that the heat treated Pt-Mn and Pt-Cu catalysts could be used for the ethanol sensing. Additionally, among the different commercial samples tested for ethanol sensing, Pt-Sn/C showed the highest sensitivity but with slightly higher standard deviation. Further studies on the Pt- Cu/C and Pt-Mn/C samples indicate that the heat treatment improved the sensitivity of these samples and the highest normalized sensitivity among all the samples belonged to the Pt- Cu/C-POL (sample produced by polyol method) and heat treated at 700 °C. It can be concluded that the heat treated Pt-Mn and Pt-Cu samples could be used as an alternative to replace Pt black in commercial sensors which would dramatically decrease the Pt loading. This could reduce the price and increase the sensitivity of commercial alcohol sensors.

Evaluation of mechanical properties in metal wire mesh supported selective catalytic reduction (SCR) catalyst structures

NASA Astrophysics Data System (ADS)

Rajath, S.; Siddaraju, C.; Nandakishora, Y.; Roy, Sukumar

2018-04-01

The objective of this research is to evaluate certain specific mechanical properties of certain stainless steel wire mesh supported Selective catalytic reduction catalysts structures wherein the physical properties of the metal wire mesh and also its surface treatments played vital role thereby influencing the mechanical properties. As the adhesion between the stainless steel wire mesh and the catalyst material determines the bond strength and the erosion resistance of catalyst structures, surface modifications of the metal- wire mesh structure in order to facilitate the interface bonding is therefore very important to realize enhanced level of mechanical properties. One way to enhance such adhesion properties, the stainless steel wire mesh is treated with the various acids, i.e., chromic acid, phosphoric acid including certain mineral acids and combination of all those in various molar ratios that could generate surface active groups on metal surface that promotes good interface structure between the metal- wire mesh and metal oxide-based catalyst material and then the stainless steel wire mesh is dipped in the glass powder slurry containing some amount of organic binder. As a result of which the said catalyst material adheres to the metal-wire mesh surface more effectively that improves the erosion profile of supported catalysts structure including bond strength.

Hierarchical nanostructured hollow spherical carbon with mesoporous shell as a unique cathode catalyst support in proton exchange membrane fuel cell.

PubMed

Fang, Baizeng; Kim, Jung Ho; Kim, Minsik; Kim, Minwoo; Yu, Jong-Sung

2009-03-07

Hierarchical nanostructured spherical carbon with hollow macroporous core in combination with mesoporous shell has been explored to support Pt cathode catalyst with high metal loading in proton exchange membrane fuel cell (PEMFC). The hollow core-mesoporous shell carbon (HCMSC) has unique structural characteristics such as large specific surface area and mesoporous volume, ensuring uniform dispersion of the supported high loading (60 wt%) Pt nanoparticles with small particle size, and well-developed three-dimensionally interconnected hierarchical porosity network, facilitating fast mass transport. The HCMSC-supported Pt(60 wt%) cathode catalyst has demonstrated markedly enhanced catalytic activity toward oxygen reduction and greatly improved PEMFC polarization performance compared with carbon black Vulcan XC-72 (VC)-supported ones. Furthermore, the HCMSC-supported Pt(40 wt%) or Pt(60 wt%) outperforms the HCMSC-supported Pt(20 wt%) even at a low catalyst loading of 0.2 mg Pt cm(-2) in the cathode, which is completely different from the VC-supported Pt catalysts. The capability of supporting high loading Pt is supposed to accelerate the commercialization of PEMFC due to the anticipated significant reduction in the amount of catalyst support required, diffusion layer thickness and fabricating cost of the supported Pt catalyst electrode.

Production of hydrogen using nanocrystalline protein-templated catalysts on m13 phage.

PubMed

Neltner, Brian; Peddie, Brian; Xu, Alex; Doenlen, William; Durand, Keith; Yun, Dong Soo; Speakman, Scott; Peterson, Andrew; Belcher, Angela

2010-06-22

For decades, ethanol has been in use as a fuel for the storage of solar energy in an energy-dense, liquid form. Over the past decade, the ability to reform ethanol into hydrogen gas suitable for a fuel cell has drawn interest as a way to increase the efficiency of both vehicles and stand-alone power generators. Here we report the use of extremely small nanocrystalline materials to enhance the performance of 1% Rh/10% Ni@CeO(2) catalysts in the oxidative steam reforming of ethanol with a ratio of 1.7:1:10:11 (air/EtOH/water/argon) into hydrogen gas, achieving 100% conversion of ethanol at only 300 degrees C with 60% H(2) in the product stream and less than 0.5% CO. Additionally, nanocrystalline 10% Ni@CeO(2) was shown to achieve 100% conversion of ethanol at 400 degrees C with 73% H(2), 2% CO, and 2% CH(4) in the product stream. Finally, we demonstrate the use of biological templating on M13 to improve the resistance of this catalyst to deactivation over 52 h tests at high flow rates (120 000 h(-1) GHSV) at 450 degrees C. This study suggests that the use of highly nanocrystalline, biotemplated catalysts to improve activity and stability is a promising route to significant gains over traditional catalyst manufacture methods.

Fischer–Tropsch Synthesis: Characterization Rb Promoted Iron Catalyst

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarkar,A.; Jacobs, G.; Ji, Y.

Rubidium promoted iron Fischer-Tropsch synthesis (FTS) catalysts were prepared with two Rb/Fe atomic ratios (1.44/100 and 5/100) using rubidium nitrate and rubidium carbonate as rubidium precursors. Results of catalytic activity and deactivation studies in a CSTR revealed that rubidium promoted catalysts result in a steady conversion with a lower deactivation rate than that of the corresponding unpromoted catalyst although the initial activity of the promoted catalyst was almost half that of the unpromoted catalyst. Rubidium promotion results in lower methane production, and higher CO2, alkene and 1-alkene fraction in FTS products. M{umlt o}ssbauer spectroscopic measurements of CO activated and workingmore » catalyst samples indicated that the composition of the iron carbide phase formed after carbidization was -Fe5 C2 for both promoted and unpromoted catalysts. However, in the case of the rubidium promoted catalyst, '-Fe2.2C became the predominant carbidic phase as FTS continued and the overall catalyst composition remained carbidic in nature. In contrast, the carbide content of the unpromoted catalyst was found to decline very quickly as a function of synthesis time. Results of XANES and EXAFS measurements suggested that rubidium was present in the oxidized state and that the compound most prevalent in the active catalyst samples closely resembled that of rubidium carbonate.« less

Influence of surface oxygenated groups on the formation of active Cu species and the catalytic activity of Cu/AC catalyst for the synthesis of dimethyl carbonate

NASA Astrophysics Data System (ADS)

Zhang, Guoqiang; Li, Zhong; Zheng, Huayan; Hao, Zhiqiang; Wang, Xia; Wang, Jiajun

2016-12-01

Activated carbon (AC) supported Cu catalysts are employed to study the influence of surface oxygenated groups on the formation of active Cu species and the catalytic activity of Cu/AC catalyst for oxidative carbonylation of methanol to dimethyl carbonate (DMC). The AC supports are thermal treated under different temperatures in order to adjust the levels of surface oxygenated groups. The AC supports are characterized by BET, TPD-MS and XRD, and the Cu/AC catalysts are characterized by BET, XRD, TEM, XPS, AAS, CH3OH-TPD and N2O chemisorption. The results show that as the treatment temperature is below 800 °C, the BET surface area of the corresponding AC supports are nearly unchanged and close to that of the original AC (1529.6 m2/g). But as the thermal treatment temperature is elevated from 1000 to 1600 °C, the BET surface area of AC supports gradually decreases from 1407.6 to 972.2 m2/g. After loading of Cu, the BET surface area of copper catalysts is in the range of 834.4 to 1545.3 m2/g, which is slightly less than that of the respective supports. When AC is thermal treated at 400 and 600 °C, the unstable carboxylic acid and anhydrides groups are selectively removed, which has weakened the mobility and agglomeration of Cu species during the calcination process, and thus improve the Cu species dispersion over AC support. But as the treatment temperature is elevated from 600 °C to 1200 °C, the Cu species dispersion begins to decline suggesting further removal of stable surface oxygenated groups is unfavorable for Cu species dispersion. Moreover, higher thermal treatment temperature (above 1200 °C) promotes the graphitization degree of AC and leds to the decrease of Cu loading on AC support. Meanwhile, the removal of surface oxygenated groups by thermal treatment is conducive to the formation of more π-sites, and thus promote the reduction of Cu2+ to Cu+ and Cu0 as active centers. The specific surface area of (Cu+ + Cu0) is improved by thermal treatment of AC, however, the space time yield of DMC on unit specific surface area of (Cu+ + Cu0) is in the range of 23.1-49.1 mg h-1 m-2, which is much less than that (77.6 mg h-1 m-2) of the original catalyst. The possible reason is that the removal of surface oxygenated groups results in AC support transforms from hydrophilicity to hydrophobicity, which is detrimental for the adsorption of CH3OH resulting in the decreased local concentration of CH3OH on active Cu species.

The production of high efficiency Ziegler-Natta catalyst with dual active sites nature using cyclohexyl chloride as promoter with super activity and produced superior polyethylene with controllable molecular weight distribution.

PubMed

Seifali Abbas-Abadi, Mehrdad

2017-01-01

In the previous studies, the several halocarbons (HC) were tested as promoters for a Ti-based Ziegler-Natta (ZN) catalyst at different polymerization conditions. The Results showed that chloro cyclohexane has the best operation in catalyst activity, polymer particle size growth, hydrogen responsibility and wax reduction too. For the first time in this study, the effect of Al/Ti ratio on the optimum HC/Ti ratio has been considered and the results showed that the optimum HC/Ti ratio depends on the Al/Ti ratio directly. In the optimum HC/Ti ratio, the catalyst activity and hydrogen responsibility ratio of the catalyst increase up to 125 and 55% respectively. The acceptable growth of polymer powder up to 46%, lower flow rate ratio (FRR) up to 19% and decrease of wax amount up to 12%, completed the promotion results. Furthermore, in the next part of this study and as key note, a little dose of halocarbon was used in the catalyst preparation to produce the special catalysts with dual active sites. In the catalyst preparation, the concentration of each active sites depends on the halocarbon amount and it can control the molecular weight distribution of the produced polyethylene; because each active sites have different response to hydrogen. The halocarbon based catalysts showed the remarkable effect on the catalyst activity, the molecular weight and especially molecular weight distribution (MWD). The flow rate ratio and MWD could be increased up to 77 and 88% respectively as the main result of halocarbon addition during the catalyst preparation.

The production of high efficiency Ziegler–Natta catalyst with dual active sites nature using cyclohexyl chloride as promoter with super activity and produced superior polyethylene with controllable molecular weight distribution

PubMed Central

Seifali Abbas-Abadi, Mehrdad

2017-01-01

Abstract In the previous studies, the several halocarbons (HC) were tested as promoters for a Ti-based Ziegler–Natta (ZN) catalyst at different polymerization conditions. The Results showed that chloro cyclohexane has the best operation in catalyst activity, polymer particle size growth, hydrogen responsibility and wax reduction too. For the first time in this study, the effect of Al/Ti ratio on the optimum HC/Ti ratio has been considered and the results showed that the optimum HC/Ti ratio depends on the Al/Ti ratio directly. In the optimum HC/Ti ratio, the catalyst activity and hydrogen responsibility ratio of the catalyst increase up to 125 and 55% respectively. The acceptable growth of polymer powder up to 46%, lower flow rate ratio (FRR) up to 19% and decrease of wax amount up to 12%, completed the promotion results. Furthermore, in the next part of this study and as key note, a little dose of halocarbon was used in the catalyst preparation to produce the special catalysts with dual active sites. In the catalyst preparation, the concentration of each active sites depends on the halocarbon amount and it can control the molecular weight distribution of the produced polyethylene; because each active sites have different response to hydrogen. The halocarbon based catalysts showed the remarkable effect on the catalyst activity, the molecular weight and especially molecular weight distribution (MWD). The flow rate ratio and MWD could be increased up to 77 and 88% respectively as the main result of halocarbon addition during the catalyst preparation. PMID:29491824

TePtFe Nanotubes as High-Performing Bifunctional Electrocatalysts for the Oxygen Reduction Reaction and Hydrogen Evolution Reaction.

PubMed

Li, Wenqiang; Amiinu, Ibrahim Saana; Ye, Bei; Wang, Zhe; Zhu, Jiawei; Kou, Zongkui; Mu, Shichun

2018-04-25

Currently, a multicomponent platinum-based alloy has been applied as a promising electrocatalyst to improve catalysis and lower the usage of the noble metal platinum. Herein, a tellurium nanowire (NW)-derived ternary TePtFe nanotube (NT) electrocatalyst has been prepared by the Kirkendall effect. The TePtFe NT formed consists of small single-crystal nanoparticles and voids with an open-end and hollow structure. The TePtFe NT electrocatalyst presents an impressive catalytic activity and stability for both the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Its ORR specific activity and mass activity are 8.5 and 2.4 times, respectively, improved relative to those of commercial platinum catalysts. It is also impressive that, for the HER, a very low overpotential of 28.1 mV at 10 mA cm -2 can be achieved; this is lower than that of platinum (51.8 mV) catalysts in 0.1 m HClO 4 , and the activity is improved, even after 5000 cycles. This work reveals that TePtFe NTs can be employed as nanocatalysts with an impressive catalytic activity and stability for application in fuel cells and hydrogen production. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electronic π-Delocalization Boosts Catalytic Water Oxidation by Cu(II) Molecular Catalysts Heterogenized on Graphene Sheets.

PubMed

Garrido-Barros, Pablo; Gimbert-Suriñach, Carolina; Moonshiram, Dooshaye; Picón, Antonio; Monge, Pere; Batista, Victor S; Llobet, Antoni

2017-09-20

A molecular water oxidation catalyst based on the copper complex of general formula [(L py )Cu II ] 2- , 2 2- , (L py is 4-pyrenyl-1,2-phenylenebis(oxamidate) ligand) has been rationally designed and prepared to support a more extended π-conjugation through its structure in contrast with its homologue, the [(L)Cu II ] 2- water oxidation catalyst, 1 2- (L is o-phenylenebis(oxamidate)). The catalytic performance of both catalysts has been comparatively studied in homogeneous phase and in heterogeneous phase by π-stacking anchorage to graphene-based electrodes. In the homogeneous system, the electronic perturbation provided by the pyrene functionality translates into a 150 mV lower overpotential for 2 2- with respect to 1 2- and an impressive increase in the k cat from 6 to 128 s -1 . Upon anchorage, π-stacking interactions with the graphene sheets provide further π-delocalization that improves the catalytic performance of both catalysts. In this sense, 2 2- turned out to be the most active catalyst due to the double influence of both the pyrene and the graphene, displaying an overpotential of 538 mV, a k cat of 540 s -1 and producing more than 5300 TONs.

Catalytic combustion of methane over commercial catalysts in presence of ammonia and hydrogen sulphide.

PubMed

Hurtado, Paloma; Ordóñez, Salvador; Vega, Aurelio; Díez, Fernando V

2004-05-01

The performance of different commercially available catalysts (supported Pd, Pt, Rh, bimetallic Pd-Pt, and Cr-Cu-Ti oxide catalyst) for the oxidation of methane, alone and in presence of ammonia and hydrogen sulphide is studied in this work. Catalysts performance was evaluated both in terms of activity and resistance to poisoning. The main conclusions are that supported Pd and Rh, present the highest activities for methane oxidation, both alone and in presence of ammonia, whereas they are severely poisoned in presence of H2S. Pt and Cr-Cu-Ti are less active but more sulphur resistant, but their activity is lower than the residual activity of sulphur-deactivated Pd and Rh catalysts. The Pd-Pt catalyst exhibits low activity and it is quickly deactivated in presence of hydrogen sulphide.

Fischer-Tropsch activity for non-promoted cobalt-on-alumina catalysts

DOEpatents

Singleton, Alan H.; Oukaci, Rachid; Goodwin, James G.

2001-01-01

Cobalt catalysts, and processes employing these inventive catalysts, for hydrocarbon synthesis. The inventive catalyst comprises cobalt on an alumina support and is not promoted with any noble or near noble metals. In one aspect of the invention, the alumina support preferably includes a dopant in an amount effective for increasing the activity of the inventive catalyst. The dopant is preferably a titanium dopant. In another aspect of the invention, the cobalt catalyst is preferably reduced in the presence of hydrogen at a water vapor partial pressure effective to increase the activity of the cobalt catalyst for hydrocarbon synthesis. The water vapor partial pressure is preferably in the range of from 0 to about 0.1 atmospheres.

Phillips CO-oxidation catalyts for long-lived CO2 lasers: Activity and initial characterization studies

NASA Technical Reports Server (NTRS)

Kolts, J. H.; Elliott, D. J.; Pennella, F.

1990-01-01

Four different catalysts have been developed specifically for use in sealed carbon dioxide lasers. The catalysts have been designed to be low dusting, stable to shock and vibration, have high activity at low temperatures and have long active lifetimes. Measured global CO oxidation rates range from 1.4 to 2.2 cc CO converted per minute per gram of catalyst at ambient temperature. The catalysts also retain substantial activity at temperatures as low as -35 C. The Phillips laser catalysts are prepared in a variety of different shapes to meet the different pressure drop and gas flow profiles present in the many different styles of lasers. Each catalyst has been tested in sealed TEA lasers and has been shown to substantially increase the sealed life of the laser. Activity measurements made on the precious metal catalysts which were prepared with and without activity promoters showed that the promoter materials increase catalyst CO oxidation activity at least an order of magnitude at ambient temperature. Initial studies using H2 and CO chemisorption, X ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS) have shown that the activity promoters do not significantly affect the precious metal crystallite size or the electronic structure around the precious metal. In addition, the formation or lack of formation of solid solutions between the precious metal and promoters has also been shown not to affect the activity of the promoted catalyst.

Pt/SnO2-based CO-oxidation catalysts for long-life closed-cycle CO2 lasers

NASA Technical Reports Server (NTRS)

Schryer, David R.; Upchurch, Billy T.; Hess, Robert V.; Wood, George M.; Sidney, Barry D.; Miller, Irvin M.; Brown, Kenneth G.; Vannorman, John D.; Schryer, Jacqueline; Brown, David R.

1990-01-01

Noble-metal/tin-oxide based catalysts such as Pt/SnO2 have been shown to be good catalysts for the efficient oxidation of CO at or near room temperature. These catalysts require a reductive pretreatment and traces of hydrogen or water to exhibit their full activity. Addition of Palladium enhances the activity of these catalysts with about 15 to 20 percent Pt, 4 percent Pd, and the balance SnO2 being an optimum composition. Unfortunately, these catalysts presently exhibit significant decay due in part to CO2 retention, probably as a bicarbonate. Research on minimizing the decay in activity of these catalysts is currently in progress. A proposed mechanism of CO oxidation on Pt/SnO2-based catalysts has been developed and is discussed.

Study of Pt-Rh/CeO2-ZrO2-MxOy (M = Y, La)/Al2O3 three-way catalysts

NASA Astrophysics Data System (ADS)

Jiaxiu, Guo; Zhonghua, Shi; Dongdong, Wu; Huaqiang, Yin; Maochu, Gong; Yaoqiang, Chen

2013-05-01

CeO2-ZrO2-MxOy (M = Y; La) mixed oxides, prepared by co-precipitation method and characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Raman spectra (RM) and oxygen pulse reaction, were comparatively investigated to elucidate the combinational effects of Y and/or La oxide promoters on the catalytic activity and anti-aging performance of monolithic cordierite honeycomb catalysts with low Pt and Rh content. The catalytic activities, water-gas shift (WGS) and steam reforming reaction (SR) were studied under a simulated gas mixture. The catalysts were also characterized by H2-temperature-programmed reduction (H2-TPR) and O2-temperature-programmed desorption (O2-TPD). The results showed that the prepared CeO2-ZrO2-MxOy oxides have a face-centered cubic fluorite structure and are nanosize. La3+ ions can significantly improve thermal stability and efficiently retard CeO2-ZrO2 crystal sintering and growth. Doped CeO2-ZrO2 with Y3+ and La3+ has 105 and 60 m2/g surface area and 460 and 390 μmol/g OSC before and after aging. The T50 of fresh Pt-Rh/CZYL/LA is 170 °C for CO, 222 °C for C3H8 and 189 °C for NO, and shift to 205, 262 and 228 °C after hydrothermal aging, which are better than those of Pt-Rh/CZY/LA or Pt-Rh/CZL/LA. WGS and SR are relate to the OSC of oxygen storage materials and absorbed oxygen species on the catalyst surface and affect the three-way catalytic activities of catalysts. The reductive property of noble metals and the dissociatively adsorbed O2 on the surface of catalysts are closely related to the catalytic activities.

The Influence of the Anionic Counter-Ion on the Activity of Ammonium Substituted Hoveyda-Type Olefin Metathesis Catalysts in Aqueous Media

NASA Astrophysics Data System (ADS)

Gułajski, Łukasz; Grela, Karol

Polar olefin metathesis catalysts, bearing an ammonium group are presented. The electron withdrawing ammonium group not only activates the catalysts electronically, but at the same time makes the catalysts more hydrophilic. Catalysts can be therefore efficiently used not only in traditional media, such as methylene chloride and toluene, but also in technical-grade alcohols, alcohol— water mixtures and in neat water. Finally, in this overview the influence of the anionic counter-ion on the activity of ammonium substituted Hoveyda-type olefin metathesis catalysts in aqueous media is presented.

Beneficial Role of Copper in the Enhancement of Durability of Ordered Intermetallic PtFeCu Catalyst for Electrocatalytic Oxygen Reduction.

PubMed

Arumugam, Balamurugan; Tamaki, Takanori; Yamaguchi, Takeo

2015-08-05

Design of Pt alloy catalysts with enhanced activity and durability is a key challenge for polymer electrolyte membrane fuel cells. In the present work, we compare the durability of the ordered intermetallic face-centered tetragonal (fct) PtFeCu catalyst for the oxygen reduction reaction (ORR) relative to its counterpart bimetallic catalysts, i.e., the ordered intermetallic fct-PtFe catalyst and the commercial catalyst from Tanaka Kikinzoku Kogyo, TKK-PtC. Although both fct catalysts initially exhibited an ordered structure and mass activity approximately 2.5 times higher than that of TKK-Pt/C, the presence of Cu at the ordered intermetallic fct-PtFeCu catalyst led to a significant enhancement in durability compared to that of the ordered intermetallic fct-PtFe catalyst. The ordered intermetallic fct-PtFeCu catalyst retained more than 70% of its mass activity and electrochemically active surface area (ECSA) over 10 000 durability cycles carried out at 60 °C. In contrast, the ordered intermetallic fct-PtFe catalyst maintained only about 40% of its activity. The temperature of the durability experiment is also shown to be important: the catalyst was more severely degraded at 60 °C than at room temperature. To obtain insight into the observed enhancement in durability of fct-PtFeCu catalyst, a postmortem analysis of the ordered intermetallic fct-PtFeCu catalyst was carried out using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) line scan. The STEM-EDX line scans of the ordered intermetallic fct-PtFeCu catalyst over 10 000 durability cycles showed a smaller degree of Fe and Cu dissolution from the catalyst. Conversely, large dissolution of Fe was identified in the ordered intermetallic fct-PtFe catalyst, indicating a lesser retention of Fe that causes the destruction of ordered structure and gives rise to poor durability. The enhancement in the durability of the ordered intermetallic fct-PtFeCu catalyst is ascribed to the synergistic effects of Cu presence and the ordered structure of catalyst.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Yongchun; Hensley, Alyssa; McEwen, Jean-Sabin

Catalytic fast pyrolysis is the most promising approach for biofuel production, due to its simple process and versatility to handle lignocellulosic biomass feedstocks with varying and complex compositions. Compared with in situ catalytic fast pyrolysis, ex situ catalytic pyrolysis has the flexibility of optimizing the pyrolysis step and catalytic process individually to improve the quality of pyrolysis oil (stability, oxygen content, acid number, etc.) and to maximize the carbon efficiency in the conversion of biomass to pyrolysis oil. Hydrodeoxygenation is one of the key catalytic functions in ex situ catalytic fast pyrolysis. Recently, Fe-based catalysts have been reported to exhibitmore » superior catalytic properties in hydrodeoxygenation of model compounds in pyrolysis oil, which potentially makes the ex situ pyrolysis of biomass commercially viable due to the abundance and low cost of Fe. Here, we briefly summarize the recent progress on Fe-based catalysts for hydrodeoxygenation of biomass, and provide perspectives on how to further improve Fe-based catalysts (activity and stability) for their potential applications in the emerging area of biomass conversion.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Teng; Lin, Zhaoyang; Chiu, Chin-Yi

Metallic nanoparticles are emerging as an exciting class of heterogeneous catalysts with the potential advantages of exceptional activity, stability, recyclability, and easier separation than homogeneous catalysts. The traditional colloid nanoparticle syntheses usually involve strong surface binding ligands that could passivate the surface active sites and result in poor catalytic activity. The subsequent removal of surface ligands could reactivate the surface but often leads to metal ion leaching and/or severe Ostwald ripening with diminished catalytic activity or poor stability. Molecular ligand engineering represents a powerful strategy for the design of homogeneous molecular catalysts but is insufficiently explored for nanoparticle catalysts tomore » date. We report a systematic investigation on molecular ligand modulation of palladium (Pd) nanoparticle catalysts. Our studies show that β-functional groups of butyric acid ligand on Pd nanoparticles can significantly modulate the catalytic reaction process to modify the catalytic activity and stability for important aerobic reactions. With a β-hydroxybutyric acid ligand, the Pd nanoparticle catalysts exhibit exceptional catalytic activity and stability with an unsaturated turnover number (TON) >3000 for dehydrogenative oxidation of cyclohexenone to phenol, greatly exceeding that of homogeneous Pd(II) catalysts (TON, ~30). This study presents a systematic investigation of molecular ligand modulation of nanoparticle catalysts and could open up a new pathway toward the design and construction of highly efficient and robust heterogeneous catalysts through molecular ligand engineering.« less

In-situ activation of CuO/ZnO/Al.sub.2 O.sub.3 catalysts in the liquid phase

DOEpatents

Brown, Dennis M.; Hsiung, Thomas H.; Rao, Pradip; Roberts, George W.

1989-01-01

The present invention relates to a method of activation of a CuO/ZnO/Al.sub.2 O.sub.3 catalyst slurried in a chemically inert liquid. Successful activation of the catalyst requires the use of a process in which the temperature of the system at any time is not allowed to exceed a certain critical value, which is a function of the specific hydrogen uptake of the catalyst at that same time. This process is especially critical for activating highly concentrated catalyst slurries, typically 25 to 50 wt %. Activation of slurries of CuO/ZnO/Al.sub.2 O.sub.3 catalyst is useful in carrying out the liquid phase methanol or the liquid phase shift reactions.

Catalysts for oxidation of mercury in flue gas

DOEpatents

Granite, Evan J [Wexford, PA; Pennline, Henry W [Bethel Park, PA

2010-08-17

Two new classes of catalysts for the removal of heavy metal contaminants, especially mercury (Hg) from effluent gases. Both of these classes of catalysts are excellent absorbers of HCl and Cl.sub.2 present in effluent gases. This adsorption of oxidizing agents aids in the oxidation of heavy metal contaminants. The catalysts remove mercury by oxidizing the Hg into mercury (II) moieties. For one class of catalysts, the active component is selected from the group consisting of iridium (Ir) and iridum-platinum (Ir/Pt) alloys. The Ir and Ir/Pt alloy catalysts are especially corrosion resistant. For the other class of catalyst, the active component is partially combusted coal or "Thief" carbon impregnated with Cl.sub.2. Untreated Thief carbon catalyst can be self-activating in the presence of effluent gas streams. The Thief carbon catalyst is disposable by means of capture from the effluent gas stream in a particulate collection device (PCD).

Non-noble electrocatalysts for alkaline fuel cells

NASA Technical Reports Server (NTRS)

Sarangapani, S.; Lessner, P.; Manoukian, M.; Giner, J.

1989-01-01

Carbons activated with macrocyclics have attracted increasing attention as alternative electrocatalysts for oxygen reduction. Initial activity of these catalysts is good, but performance declines rapidly. Pyrolyzing the macrocyclic on the carbon support leads to enhanced stability and the catalysts retain good activity. The approach described is designed to develop bulk doped catalysts with similar structures to pyrolyzed macrocyclic catalysts. The transition metal and coordinated ligands are dispersed throughout the bulk of the conductive carbon skeleton. Two approaches to realizing this concept are being pursued, both involving the doping of carbon precursors. In one approach, the precursor is a solid phase carbon-containing ion-exchange resin. The precursor is doped with a transition metal and/or nitrogen, and the resulting mixture is pyrolyzed. In the other approach, the precursor is a gas-phase hydrocarbon. This is introduced with a transition metal species and nitrogen species into a reactor and pyrolyzed. Several studies have been conducted to determine if there is a synergistic effect between the transition metal and nitrogen and the effect of different methods of introducing the metal-nitrogen (M-N) coordination on performance. One approach was to introduce the metal and nitrogen separately, for example, by sequentially doping FeCl3 and NH4OH into the resin. Catalysts were prepared from an undoped ion-exchange resin, a resin doped only with N, a resin doped only with Fe, and a resin doped with both Fe and N. Introduction of nitrogen alone has no beneficial effect on the performance of the catalysts. The introduction of the Fe alone significantly improves the performance in both the high and low current density regions. When both Fe and N are introduced, the performance at lower current densities (catalytic activity) is increased beyond that of the Fe-doped carbon, but the performance at higher current densities is similar to the carbon containing only Fe. Catalysts prepared from resins-Fe(bipy)3SO4 precursors have performance that is only slightly less then CoTMPP adsorbed and pyroloyzed on Vulcan XC-72. Their performance is much better than carbons which have had the N and Fe introduced separately.

Activity Tests of Macro-Meso Porous Catalysts over Metal Foam Plate for Steam Reforming of Bio-Ethanol.

PubMed

Park, No-Kuk; Jeong, Yong Han; Kang, Misook; Lee, Tae Jin

2018-09-01

The catalytic activity of a macro-mesoporous catalyst coated on a metal foam plate in the reforming of bio-ethanol to synthesis gas was investigated. The catalysts were prepared by coating a support with a noble metal and transition metal. The catalytic activity for the production of synthetic gas by the reforming of bio-ethanol was compared according to the support material, reaction temperature, and steam/carbon ratio. The catalysts coated on the metal foams were prepared using a template method, in which macro-pores and meso-pores were formed by mixing polymer beads. In particular, the thermodynamic equilibrium composition of bio-ethanol reforming with the reaction temperature and steam/carbon ratio to produce synthetic gas was examined using the HSC (Enthalpy-Entropy-Heat capacity) chemistry program in this study. The composition of hydrogen and carbon monoxide in the reformate gas produced by steam reforming over the Rh/Ni-Ce-Zr/Al2O3-based pellet type catalysts and metal foam catalysts that had been coated with the Rh/Al-Ce-Zr-based catalysts was investigated by experimental activity tests. The activity of the metal foam catalyst was higher than that of the pellet type catalyst.

Catalytic properties of a CoMo/Al[sub 2]O[sub 3] catalyst presulfided with alkyl polysulfides: Comparison with conventional sulfiding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gestel, J. van; Leglise, J.; Duchet, J.C.

1994-02-01

A CoMo/Al[sub 2]O[sub 3] hydrotreating catalyst has been sulfided in different ways: (i) by conventional in situ sulfiding in a high-pressure reactor with a H[sub 2]S/H[sub 2] or dimethyldisulfide (DMDS)/H[sub 2] mixture at 350[degrees]C and 4 MPa; or (ii) by a preliminary presulfidation with di-tert-nonyl or di-tert-dodecyl pentasulfides followed by one of the above conventional in situ sulfidations. The presulfidation was performed in two steps: impregnation of the oxidic catalyst with the polysulfide and then thermal treatment under flowing nitrogen at 130[degrees]C. The catalysts were evaluated for their catalytic properties at 280-350[degrees]C and 4 MPa for the simultaneous hydrodesulfurization ofmore » thiophene and hydrogenation of cyclohexene. Compared to H[sub 2]S/H[sub 2], in situ DMDS/H[sub 2] sulfiding of the CoMo/Al[sub 2]O[sub 3] catalyst enhanced the C-S hydrogenolysis at 280[degrees]C but not the hydrogenation; however, the apparent activation energy for hydrogenation was markedly increased. The presulfidation with the polysulfides following by H[sub 2]S/H[sub 2] sulfidation yielded improved activities at 280[degrees]C for both hydrogenation and C-S bond breakage and did not influence the apparent activation energies. The highest activities were obtained by combining presulfiding and DMDS/H[sub 2] sulfidation. These results are discussed in terms of the genesis of the supported sulfide phase with various sulfur species. 40 refs., 2 figs., 2 tabs.« less

Highly active and efficient catalysts for alkoxycarbonylation of alkenes

PubMed Central

Dong, Kaiwu; Fang, Xianjie; Gülak, Samet; Franke, Robert; Spannenberg, Anke; Neumann, Helfried; Jackstell, Ralf; Beller, Matthias

2017-01-01

Carbonylation reactions of alkenes constitute the most important industrial processes in homogeneous catalysis. Despite the tremendous progress in this transformation, the development of advanced catalyst systems to improve their activity and widen the range of feedstocks continues to be essential for new practical applications. Herein a palladium catalyst based on 1,2-bis((tert-butyl(pyridin-2-yl)phosphanyl)methyl)benzene L3 (pytbpx) is rationally designed and synthesized. Application of this system allows a general alkoxycarbonylation of sterically hindered and demanding olefins including all kinds of tetra-, tri- and 1,1-disubstituted alkenes as well as natural products and pharmaceuticals to the desired esters in excellent yield. Industrially relevant bulk ethylene is functionalized with high activity (TON: >1,425,000; TOF: 44,000 h−1 for initial 18 h) and selectivity (>99%). Given its generality and efficiency, we expect this catalytic system to immediately impact both the chemical industry and research laboratories by providing a practical synthetic tool for the transformation of nearly any alkene into a versatile ester product. PMID:28120947

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pihl, Josh A.; Toops, Todd J.; Fisher, Galen B.

Lean gasoline engines running on ethanol/gasoline blends and equipped with a silver/alumina catalyst for selective catalytic reduction (SCR) of NO by ethanol provide a pathway to reduced petroleum consumption through both increased biofuel utilization and improved engine efficiency relative to the current stoichiometric gasoline engines that dominate the U.S. light duty vehicle fleet. A pre-commercial silver/alumina catalyst demonstrated high NO x conversions over a moderate temperature window with both neat ethanol and ethanol/gasoline blends containing at least 50% ethanol. Selectivity to NH 3 increases with HC dosing and ethanol content in gasoline blends, but appears to saturate at around 45%.more » NO 2 and acetaldehyde behave like intermediates in the ethanol SCR of NO. NH 3 SCR of NO x does not appear to play a major role in the ethanol SCR reaction mechanism. Ethanol is responsible for the low temperature SCR activity observed with the ethanol/gasoline blends. In conclusion, the gasoline HCs do not deactivate the catalyst ethanol SCR activity, but they also do not appear to be significantly activated by the presence of ethanol.« less

Covalent Attachment of the Water-insoluble Ni(P Cy 2 N Phe 2 ) 2 Electrocatalyst to Electrodes Showing Reversible Catalysis in Aqueous Solution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rodríguez-Maciá, Patricia; Priyadarshani, Nilusha; Dutta, Arnab

Hydrogenases are a diverse group of metalloenzymes which catalyze the reversible conversion between molecular hydrogen and protons at high rates. The catalytic activity of these enzymes does not require overpotential because their active site has been evolutionarily optimized to operate fast and efficiently. These enzymes have inspired the development of molecular catalysts, which have dramatically improved in efficiency in recent years, to the point that some synthetic catalysts even outperform hydrogenases under certain conditions. In this work, we use a reversible noble-metal-free homogeneous catalyst, the [Ni(PCy2NPhe2)2]2+ complex, and we covalently immobilize it on a functionalized highly oriented pyrolytic graphite “edge”more » (HOPGe) electrode surface. This catalyst is not water soluble, but once it is surface-confined on the electrode, it maintains its catalytic properties in aqueous solutions, showing reversibility for H2 oxidation/reduction. Immobilization of the [Ni(PCy2NPhe2)2]2+ complex onto a multi-walled carbon nanotubes coated electrode leads to even higher catalytic current densities and enhanced stability.« less

Electrocatalysts for Hydrogen Evolution in Alkaline Electrolytes: Mechanisms, Challenges, and Prospective Solutions.

PubMed

Mahmood, Nasir; Yao, Yunduo; Zhang, Jing-Wen; Pan, Lun; Zhang, Xiangwen; Zou, Ji-Jun

2018-02-01

Hydrogen evolution reaction (HER) in alkaline medium is currently a point of focus for sustainable development of hydrogen as an alternative clean fuel for various energy systems, but suffers from sluggish reaction kinetics due to additional water dissociation step. So, the state-of-the-art catalysts performing well in acidic media lose considerable catalytic performance in alkaline media. This review summarizes the recent developments to overcome the kinetics issues of alkaline HER, synthesis of materials with modified morphologies, and electronic structures to tune the active sites and their applications as efficient catalysts for HER. It first explains the fundamentals and electrochemistry of HER and then outlines the requirements for an efficient and stable catalyst in alkaline medium. The challenges with alkaline HER and limitation with the electrocatalysts along with prospective solutions are then highlighted. It further describes the synthesis methods of advanced nanostructures based on carbon, noble, and inexpensive metals and their heterogeneous structures. These heterogeneous structures provide some ideal systems for analyzing the role of structure and synergy on alkaline HER catalysis. At the end, it provides the concluding remarks and future perspectives that can be helpful for tuning the catalysts active-sites with improved electrochemical efficiencies in future.

Homogeneous Molecular Catalysis of Electrochemical Reactions: Catalyst Benchmarking and Optimization Strategies.

PubMed

Costentin, Cyrille; Savéant, Jean-Michel

2017-06-21

Modern energy challenges currently trigger an intense interest in catalysis of redox reactions-electrochemical and photochemical-particularly those involving small molecules such as water, hydrogen, oxygen, proton, carbon dioxide. A continuously increasing number of molecular catalysts of these reactions, mostly transition metal complexes, have been proposed, rendering necessary procedures for their rational benchmarking and fueling the quest for leading principles that could inspire the design of improved catalysts. The search of "volcano plots" correlating catalysis kinetics to the stability of the key intermediate is a popular approach to the question in catalysis by surface-active sites, with as foremost example the electrochemical reduction of aqueous proton on metal surfaces. We discussed here for the first time, on theoretical and experimental grounds, the pertinence of such an approach in the field of molecular catalysis. This is the occasion to insist on the virtue of careful mechanism assignments. Particular emphasis is put on the interest of expressing the catalysts' intrinsic kinetic properties by means of catalytic Tafel plots, which relate kinetics and overpotential. We also underscore that the principle and strategies put forward for the catalytic activation of the above-mentioned small molecules are general as illustrated by catalytic applications out of this particular field.

High Performance and Cost-Effective Direct Methanol Fuel Cells: Fe-N-C Methanol-Tolerant Oxygen Reduction Reaction Catalysts.

PubMed

Sebastián, David; Serov, Alexey; Artyushkova, Kateryna; Gordon, Jonathan; Atanassov, Plamen; Aricò, Antonino S; Baglio, Vincenzo

2016-08-09

Direct methanol fuel cells (DMFCs) offer great advantages for the supply of power with high efficiency and large energy density. The search for a cost-effective, active, stable and methanol-tolerant catalyst for the oxygen reduction reaction (ORR) is still a great challenge. In this work, platinum group metal-free (PGM-free) catalysts based on Fe-N-C are investigated in acidic medium. Post-treatment of the catalyst improves the ORR activity compared with previously published PGM-free formulations and shows an excellent tolerance to the presence of methanol. The feasibility for application in DMFC under a wide range of operating conditions is demonstrated, with a maximum power density of approximately 50 mW cm(-2) and a negligible methanol crossover effect on the performance. A review of the most recent PGM-free cathode formulations for DMFC indicates that this formulation leads to the highest performance at a low membrane-electrode assembly (MEA) cost. Moreover, a 100 h durability test in DMFC shows suitable applicability, with a similar performance-time behavior compared to common MEAs based on Pt cathodes. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Exceptionally High Efficient Co-Co2P@N, P-Codoped Carbon Hybrid Catalyst for Visible Light-Driven CO2-to-CO Conversion.

PubMed

Fu, Wen Gan

2018-05-02

Artificial photosynthesis has attracted wide attention, particularly the development of efficient solar light-driven methods to reduce CO2 to form energy-rich carbon-based products. Because CO2 reduction is an uphill process with a large energy barrier, suitable catalysts are necessary to achieve this transformation. In addition, CO2 adsorption on a catalyst and proton transfer to CO2 are two important factors for the conversion reaction，and catalysts with high surface area and more active sites are required to improve the efficiency of CO2 reduction. Here, we report a visible light-driven system for CO2-to-CO conversion that consists of a heterogeneous hybrid catalyst of Co and Co2P nanoparticles embedded in carbon nanolayers codoped with N and P (Co-Co2P@NPC) and a homogeneous Ru(II)-based complex photosensitizer. The average generation rate of CO of the system was up to 35,000 μmol h-1 g-1 with selectivity of 79.1% in 3 h. Linear CO production at an exceptionally high rate of 63,000 μmol h-1 g-1 was observed in the first hour of reaction. Inspired by this highly active catalyst, we also synthesized Co@NC and Co2P@NPC materials and explored their structure, morphology, and catalytic properties for CO2 photoreduction. The results showed that the nanoparticle size, partially adsorbed H2O molecules on the catalyst surface, and the hybrid nature of the systems influenced their photocatalytic CO2 reduction performance. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Application of a Re-Pd bimetallic catalyst for treatment of perchlorate in waste ion-exchange regenerant brine.

PubMed

Liu, Jinyong; Choe, Jong Kwon; Sasnow, Zachary; Werth, Charles J; Strathmann, Timothy J

2013-01-01

Concentrated sodium chloride (NaCl) brines are often used to regenerate ion-exchange (IX) resins applied to treat drinking water sources contaminated with perchlorate (ClO(4)(-)), generating large volumes of contaminated waste brine. Chemical and biological processes for ClO(4)(-) reduction are often inhibited severely by high salt levels, making it difficult to recycle waste brines. Recent work demonstrated that novel rhenium-palladium bimetallic catalysts on activated carbon support (Re-Pd/C) can efficiently reduce ClO(4)(-) to chloride (Cl(-)) under acidic conditions, and here the applicability of the process for treating waste IX brines was examined. Experiments conducted in synthetic NaCl-only brine (6-12 wt%) showed higher Re-Pd/C catalyst activity than in comparable freshwater solutions, but the rate constant for ClO(4)(-) reduction measured in a real IX waste brine was found to be 65 times lower than in the synthetic NaCl brine. Through a series of experiments, co-contamination of the IX waste brine by excess NO(3)(-) (which the catalyst reduces principally to NH(4)(+)) was found to be the primary cause for deactivation of the Re-Pd/C catalyst, most likely by altering the immobilized Re component. Pre-treatment of NO(3)(-) using a different bimetallic catalyst (In-Pd/Al(2)O(3)) improved selectivity for N(2) over NH(4)(+) and enabled facile ClO(4)(-) reduction by the Re-Pd/C catalyst. Thus, sequential catalytic treatment may be a promising strategy for enabling reuse of waste IX brine containing NO(3)(-) and ClO(4)(-). Copyright © 2012 Elsevier Ltd. All rights reserved.

Preparation of metal/zeolite catalysts: Formation of palladium aquocomplexes in the precursor of palladium-mordenite catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1993-09-01

Previous research has revealed that the catalytic performance of metal/zeolite catalysts can be significantly modified by exposing the catalyst precursor to H[sub 2]O vapor during the period after calcination, but before reduction. For bimetallic PdCo/NaY catalysts used for CO hydrogenation, the selectivity was changed from predominant production of oxygenates to predominant production of higher hydrocarbons. For Pt/H-mordenite catalysts, this water treatment has been reported to improve the alkane isomerization activity. Although it is certain that Lewis sites are transformed to Bronsted sites by reaction with H[sub 2]O, the activity of the catalyst is affected most when the water is addedmore » after calcination, when the noble metal is present as ligand-free ions. This observation led to the hypothesis that complexation of transition metal ions with water might be instrumental for the observed effects. In zeolites containing cages, such as Y, the formation of metal-ligand complex ions appears to incite their migration from small to large cages. In cageless zeolites such as mordenite, however, it is not clear, a priori, whether hydration of transition metal ions will increase or decrease their reducibility and whether it will ultimately result in higher or lower metal dispersion. The authors have therefore undertaken research to clarify these issues. Palladium supported in H-mordenite (Pd/HMor) or Na-mordenite (Pd/Na-Mor) has been tested using methylcyclopentane as a probe reaction; temperature-programmed reduction (TPR), desorption (TPD), and extended X-ray absorption fine structure (EXAFS) spectroscopy have been used to characterize the effects of water treatment on the samples.« less

Communicating catalysts

NASA Astrophysics Data System (ADS)

Weckhuysen, Bert M.

2018-06-01

The beauty and activity of enzymes inspire chemists to tailor new and better non-biological catalysts. Now, a study reveals that the active sites within heterogeneous catalysts actively cooperate in a fashion phenomenologically similar to, but mechanistically distinct, from enzymes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Partridge Jr, William P.; Choi, Jae-Soon

By directly resolving spatial and temporal species distributions within operating honeycomb monolith catalysts, spatially resolved capillary inlet mass spectrometry (SpaciMS) provides a uniquely enabling perspective for advancing automotive catalysis. Specifically, the ability to follow the spatiotemporal evolution of reactions throughout the catalyst is a significant advantage over inlet-and-effluent-limited analysis. Intracatalyst resolution elucidates numerous catalyst details including the network and sequence of reactions, clarifying reaction pathways; the relative rates of different reactions and impacts of operating conditions and catalyst state; and reaction dynamics and intermediate species that exist only within the catalyst. These details provide a better understanding of how themore » catalyst functions and have basic and practical benefits; e.g., catalyst system design; strategies for on-road catalyst state assessment, control, and on-board diagnostics; and creating robust and accurate predictive catalyst models. Moreover, such spatiotemporally distributed data provide for critical model assessment, and identification of improvement opportunities that might not be apparent from effluent assessment; i.e., while an incorrectly formulated model may provide correct effluent predictions, one that can accurately predict the spatiotemporal evolution of reactions along the catalyst channels will be more robust, accurate, and reliable. In such ways, intracatalyst diagnostics comprehensively enable improved design and development tools, and faster and lower-cost development of more efficient and durable automotive catalyst systems. Beyond these direct contributions, SpaciMS has spawned and been applied to enable other analytical techniques for resolving transient distributed intracatalyst performance. This chapter focuses on SpaciMS applications and associated catalyst insights and improvements, with specific sections related to lean NOx traps, selective catalytic reduction catalysts, oxidation catalysts, and particulate filters. The objective is to promote broader use and development of intracatalyst analytical methods, and thereby expand the insights resulting from this detailed perspective for advancing automotive catalyst technologies.« less

Local Platinum Environments in a Solid Analogue of the Molecular Periana Catalyst

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soorholtz, Mario; Jones, Louis C.; Samuelis, Dominik

2016-02-16

Combining advantages of homogeneous and heterogeneous catalysis by incorporating active species on a solid support is often an effective strategy for improving overall catalyst performance, although the influences of the support are generally challenging to establish, especially at a molecular level. In this paper, we report the local compositions, and structures of platinum species incorporated into covalent triazine framework (Pt-CTF) materials, a solid analogue of the molecular Periana catalyst, Pt(bpym)Cl 2, both of which are active for the selective oxidation of methane in the presence of concentrated sulfuric acid. By using a combination of solid-state 195Pt nuclear magnetic resonance (NMR)more » spectroscopy, aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), important similarities and differences are observed between the Pt-CTF and Periana catalysts, which are likely related to their respective macroscopic reaction properties. In particular, wide-line solid-state 195Pt NMR spectra enable direct measurement, identification, and quantification of distinct platinum species in as-synthesized and used Pt-CTF catalysts. The results indicate that locally ordered and disordered Pt sites are present in as-synthesized Pt-CTF, with the former being similar to one of the two crystallographically distinct Pt sites in crystalline Pt(bpym)Cl 2. A distribution of relatively disordered Pt moieties is also present in the used catalyst, among which are the principal active sites. Similarly XAS shows good agreement between the measured data of Pt-CTF and a theoretical model based on Pt(bpym)Cl 2. Analyses of the absorption spectra of Pt-CTF used for methane oxidation suggests ligand exchange, as predicted for the molecular catalyst. XPS analyses of Pt(bpym)Cl 2, Pt-CTF, as well as the unmodified ligands, further corroborate platinum coordination by pyridinic N atoms. Aberration-corrected high-angle annular dark-field STEM proves that Pt atoms are distributed within Pt-CTF before and after catalysis. Finally, the overall results establish the close similarities of Pt-CTF and the molecular Periana catalyst Pt(bpym)Cl 2, along with differences that account for their respective properties.« less

Effect of TiO2, ZrO2, and TiO2-ZrO2 on the performance of CuO-ZnO catalyst for CO2 hydrogenation to methanol

NASA Astrophysics Data System (ADS)

Xiao, Jie; Mao, Dongsen; Guo, Xiaoming; Yu, Jun

2015-05-01

The influence of TiO2, ZrO2, and TiO2-ZrO2 mixed oxide on the catalytic performance of CuO-ZnO catalyst in the methanol synthesis from CO2 hydrogenation was studied. The catalysts were prepared by oxalate co-precipitation method and characterized by TGA, N2 adsorption, XRD, reactive N2O adsorption, XPS, H2-TPR, H2-TPD, and CO2-TPD techniques. Characterization results reveal that all the additives improve the CuO dispersion in the catalyst body and increase the Cu surface area and adsorption capacities of CO2 and H2. The results of catalytic test reveal that the additives increase both the CO2 conversion and methanol selectivity, and TiO2-ZrO2 mixed oxide is more effective than single components of TiO2 or ZrO2. Moreover, the activity of methanol synthesis is correlated directly with CO2 adsorption capacity over the catalysts.

Polyoxometalate electrocatalysts based on earth-abundant metals for efficient water oxidation in acidic media

NASA Astrophysics Data System (ADS)

Blasco-Ahicart, Marta; Soriano-López, Joaquín; Carbó, Jorge J.; Poblet, Josep M.; Galan-Mascaros, J. R.

2018-01-01

Water splitting is a promising approach to the efficient and cost-effective production of renewable fuels, but water oxidation remains a bottleneck in its technological development because it largely relies on noble-metal catalysts. Although inexpensive transition-metal oxides are competitive water oxidation catalysts in alkaline media, they cannot compete with noble metals in acidic media, in which hydrogen production is easier and faster. Here, we report a water oxidation catalyst based on earth-abundant metals that performs well in acidic conditions. Specifically, we report the enhanced catalytic activity of insoluble salts of polyoxometalates with caesium or barium counter-cations for oxygen evolution. In particular, the barium salt of a cobalt-phosphotungstate polyanion outperforms the state-of-the-art IrO2 catalyst even at pH < 1, with an overpotential of 189 mV at 1 mA cm-2. In addition, we find that a carbon-paste conducting support with a hydrocarbon binder can improve the stability of metal-oxide catalysts in acidic media by providing a hydrophobic environment.

Enhanced performance of CO oxidation over Pt/CuCrOx catalyst in the presence of CO2 and H2O

NASA Astrophysics Data System (ADS)

Deng, Yun; Wang, Ting; Zhu, Li; Jia, Ai-Pin; Lu, Ji-Qing; Luo, Meng-Fei

2018-06-01

A Pt catalyst supported on CuO-CrOx composite oxide (Pt/CuCrOx) was prepared and tested for CO oxidation in the presence of CO2 and H2O. It was found that the catalyst was stable in the realistic reaction conditions and the catalytic activity was improved in the presence of CO2 and H2O compared to that in dry condition. Kinetic investigation and temperature - programmed desorption of CO results revealed that the addition of CO2 in the feed resulted in the competitive adsorption of CO/CO2 and the formation of surface carbonate species, which consequently deactivated the catalyst. In contrast, although the presence of H2O also inhibited the adsorption of CO, the possible formation of surface hydroxyl groups may trigger a new and more facile reaction route for CO oxidation, which could explain the promoting effect of H2O. Therefore, the current findings makes the catalyst promising in CO oxidation under realistic reaction conditions.

Improvement of sulfur resistance of Pd/Ce-Zr-Al-O catalysts for CO oxidation

NASA Astrophysics Data System (ADS)

Shin, Haebin; Baek, Minsung; Ro, Youngsoo; Song, Changyeol; Lee, Kwan-Young; Song, In Kyu

2018-01-01

Two kinds of mesoporous ceria-zirconia-alumina supports were prepared by a single-step epoxide-driven sol-gel method (SGCZA) and by a co-precipitation method (PCZA). Palladium catalysts supported on these materials were then prepared by a wet impregnation method (Pd/SGCZA and Pd/PCZA). The prepared catalysts were applied to the CO oxidation reaction before and after sulfur aging. XRD and N2 adsorption-desorption analyses revealed that these two catalysts retained different physicochemical properties. Pd/SGCZA had higher surface area and larger pore volume than Pd/PCZA before and after sulfur aging. TPR (Temperature-programmed reduction), CO chemisorption, FT-IR, and XPS analyses showed that the catalysts were differently influenced by sulfur species. Pd/SGCZA formed less sulfate and retained higher palladium dispersion than Pd/PCZA after sulfur aging. In the CO oxidation, Pd/PCZA showed better activity than Pd/SGCZA before sulfur aging. However, Pd/SGCZA showed higher CO conversion than Pd/PCZA after sulfur aging. We concluded that Pd/SGCZA was less poisoned by sulfur species than Pd/PCZA.

The Role of Lewis and Brønsted Acid Sites in NO Reduction with NH3 on Sulfur Modified TiO2-Supported V2O5 Catalyst

NASA Astrophysics Data System (ADS)

Zhao, Wei; Dou, Shengping; Zhong, Qin; Wu, Licheng; Wang, Qian; Wang, Aijian

2017-12-01

V2O5/S-doped TiO2 was prepared by the sol-gel and impregnation methods. The adsorption of NO, NH3, and O2 over the catalyst was studied by in situ DRIFTS spectroscopy to elucidate the reaction mechanism of the low-temperature selective catalytic reduction of NO with NH3. Exposing the catalyst to O2 and NO, three types of nitrates species appeared on the surface. The introduction of S to TiO2 could generate large amounts of acid sites for ammonia adsorption on the catalyst, which was believed to be an important role in the SCR reaction and hereby improved the catalytic activity. The results indicated two possible SCR reaction pathways for catalyst. One was that NO was absorbed to form nitrite species, which could react with NH3 on Lewis acid sites, producing N2 and H2O. Another way was that NH3 was adsorbed, then reacted with gas phase NO (E-R) and nitrite intermediates on the surface (L-H).

Study of Catalyst Variation Effect in Glycerol Conversion Process to Hydrogen Gas by Steam Reforming

NASA Astrophysics Data System (ADS)

Widayat; Hartono, R.; Elizabeth, E.; Annisa, A. N.

2018-04-01

Along with the economic development, needs of energy being increase too. Hydrogen as alternative energy has many usages. Besides that, hydrogen is one source of energy that is a clean fuel, but process production of hydrogen from natural gas as a raw material has been used for a long time. Therefore, there is need new invention to produce hydrogen from the others raw material. Glycerol, a byproduct of biodiesel production, is a compound which can be used as a raw material for hydrogen production. By using glycerol as a raw material of hydrogen production, we can get added value of glycerol as well as an energy source solution. The process production of hydrogen by steam reforming is a thermochemical process with efficiency 70%. This process needs contribution of catalyst to improve its efficiency and selectivity of the process. In this study will be examined the effect variation of catalyst for glycerol conversion process to hydrogen by steam reforming. The method for catalyst preparation was variation of catalyst impregnation composition, catalyst calcined with difference concentration of hydrochloric acid and calcined with difference hydrochloric acid ratio. After that, all of catalyst which have been prepared, used for steam reforming process for hydrogen production from glycerol as a raw material. From the study, the highest yield of hydrogen gas showed in the process production by natural zeolite catalyst with 1:15 Hydrochloric acid ratio was 42.28%. Hydrogen yield for 2M calcined natural zeolite catalyst was 38.37%, for ZSM-5 catalyst was 15.83%, for 0.5M calcined natural zeolite was 13.09% and for ultrasonic natural zeolite was 11.43%. The lowest yield of hydrogen gas showed in catalyst 2Zn/ZSM-5 with 11.22%. This result showed that hydrogen yield product was affected by catalyst variation because of the catalyst has difference characteristic and difference catalytic activity after the catalyst preparation process.

Pt/SnO2-based CO-oxidation catalysts for CO2 lasers

NASA Technical Reports Server (NTRS)

Upchurch, Billy T.; Schryer, David R.; Hess, Robert V.; Brown, Kenneth G.; Van Norman, John D.

1990-01-01

The activity of Pt/SnO2-based CO-oxidation catalysts has been maximized by optimizing pretreatment conditions and catalyst formulation. The role of H2O in activating these catalysts and of CO2 retention in deactivating them has been determined as has the interaction of these catalysts with rare-isotope C(0-18) and (O-18)2.

Linking morphology with activity through the lifetime of pretreated PtNi nanostructured thin film catalysts

DOE PAGES

Cullen, David A.; Lopez-Haro, Miguel; Bayle-Guillemaud, Pascale; ...

2015-04-10

In this study, the nanoscale morphology of highly active Pt 3Ni 7 nanostructured thin film fuel cell catalysts is linked with catalyst surface area and activity following catalyst pretreatments, conditioning and potential cycling. The significant role of fuel cell conditioning on the structure and composition of these extended surface catalysts is demonstrated by high resolution imaging, elemental mapping and tomography. The dissolution of Ni during fuel cell conditioning leads to highly complex, porous structures which were visualized in 3D by electron tomography. Quantification of the rendered surfaces following catalyst pretreatment, conditioning, and cycling shows the important role pore structure playsmore » in surface area, activity, and durability.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xing, Rong; Dagle, Vanessa Lebarbier; Flake, Matthew

In this study we examine feasibility for steam reforming the mixed oxygenate aqueous fraction derived from mildly hydrotreated fast pyrolysis bio-oils. Catalysts selective towards hydrogen formation and resistant to carbon formation utilizing feeds with relatively low steam-to-carbon (S/C) ratios are desired. Rh (5 wt%), Pt (5 wt%), Ru (5 wt%), Ir (5 wt%), Ni (15 wt%), and Co (15 wt%) metals supported on MgAl 2O 4 were evaluated for catalytic performance at 500°C and 1 atm using a complex feed mixture comprising of acids, polyols, cycloalkanes, and phenolic compounds. The Rh catalyst was found to be the most active andmore » resistant to carbon formation. The Ni and Co catalysts were found to be more active than the other noble metal catalysts investigated (Pt, Ru, and Ir). However, Ni was found to form significantly more carbon (coke) on the catalyst surface. Furthermore, Co was found to be the most selective towards H 2 formation. Evaluating the effect of temperature on stability for the Rh catalyst we found that catalyst stability was best when operated at 500°C as compared to the higher temperatures investigated (700, 800°C). When operating at 700°C significantly more graphitic formation was observed on the spent catalyst surface. Operating at 800°C resulted in reactor plugging as a result of thermal decomposition of the reactants. Thus, a concept analogous to the petroleum industries’ use of a pre-reformer, operated at approximately 500°C for steam reforming of the heavier naphtha components, followed by a high temperature methane reforming operated in the 600-850°C temperature range, could be applied in the case of steam reforming biomass derived oxygenates. Moreover, stability evaluations were performed over the Rh, Ni, and Co catalysts at 500°C and 1 atm, under similar initial conversions, reveal the Co catalyst to be the most stable and selective towards H 2 production. Conversion and selectivity to CH 4 over Co remained relatively stable at approximately 80% and 1.2%, respectively. By contrast, the Rh and Ni catalysts CH 4 selectivity’s were approximately 7-8%. Thus suggesting that a Co type catalyst may be more suitable for the steam reforming of biomass derived oxygenates as compared to the more conventional Ni and Rh type steam reforming catalysts. However, deposition of carbon on the surface was observed. High resolution TEM on the spent catalysts revealed the formation of graphitic carbon on the Rh catalyst, and filamentous carbon formation was observed on both the Ni and Co catalysts, albeit less pronounced on Co. Thus there is certainly opportunity for improvement in Co catalyst design and/or with process optimization.« less

Spectroscopic insights into the nature of active sites in iron–nitrogen–carbon electrocatalysts for oxygen reduction in acid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jia, Qingying; Ramaswamy, Nagappan; Tylus, Urszula

Developing efficient and inexpensive catalysts for the sluggish oxygen reduction reaction (ORR) constitutes one of the grand challenges in the fabrication of commercially viable fuel cell devices and metal–air batteries for future energy applications. Despite recent achievements in designing advanced Pt-based and Pt-free catalysts, current progress primarily involves an empirical approach of trial-and-error combination of precursors and synthesis conditions, which limits further progress. Rational design of catalyst materials requires proper understanding of the mechanistic origin of the ORR and the underlying surface properties under operating conditions that govern catalytic activity. Herein, several different groups of iron-based catalysts synthesized via differentmore » methods and/or precursors were systematically studied by combining multiple spectroscopic techniques under ex situ and in situ conditions in an effort to obtain a comprehensive understanding of the synthesis-products correlations, nature of active sites, and the reaction mechanisms. These catalysts include original macrocycles, macrocycle-pyrolyzed catalysts, and Fe-N–C catalysts synthesized from individual Fe, N, and C precursors including polymer-based catalysts, metal organic framework (MOF)-based catalysts, and sacrificial support method (SSM)-based catalysts. The latter group of catalysts is most promising as not only they exhibit exceptional ORR activity and/or durability, but also the final products are controllable. We show that the high activity observed for most pyrolyzed Fe-based catalysts can mainly be attributed to a single active site: non-planar Fe–N 4 moiety embedded in distorted carbon matrix characterized by a high potential for the Fe 2+/3+ redox transition in acidic electrolyte/environment. The high intrinsic ORR activity, or turnover frequency (TOF), of this site is shown to be accounted for by redox catalysis mechanism that highlights the dominant role of the site-blocking effect. Moreover, a highly active MOF-based catalyst without Fe–N moieties was developed, and the active sites were identified as nitrogen-doped carbon fibers with embedded iron particles that are not directly involved in the oxygen reduction pathway. The high ORR activity and durability of catalysts involving this second site, as demonstrated in fuel cell, are attributed to the high density of active sites and the elimination or reduction of Fenton-type processes. The latter are initiated by hydrogen peroxide but are known to be accelerated by iron ions exposed to the surface, resulting in the formation of damaging free-radicals.« less

Catalytic systems used for polymerization, biomass conversion, and enhancing diffusion

NASA Astrophysics Data System (ADS)

Pong, Frances

A significant amount of research has been dedicated towards the study and improvement of catalysts. A better understanding of how catalysts work can lead to developing more cost-efficient catalytic systems for a variety of applications. My research is focuses on catalytic systems used in three different fields, which are (i) organometallic polymerization catalysts, (ii) molecular motors and (iii) biomass conversion. Researchers have long studied and modified organometallic catalysts for use in the direct co- and homopolymerization of monomers with polar functional groups. The ability to add polar moieties to polymers, which can potentially yield materials with a wider range of physical properties, is highly desirable. In this study (i), a series of naphthoxyimine palladium(II) catalysts -- in which the naphthyl backbone had been functionalized with different moieties -- were synthesized and systematically studied to determine the ligand structure's impact on catalytic activity. The study showed that slight modifications of the naphthyl backbone led to significant changes in the polymer's molecular weight and polydispersity index. The catalysts were also displayed some ability to co-polymerize ethylene and functionalized norbornene. These positive results suggest that further exploration of naphthoxyimine palladium (II) catalysts may be fundamentally interesting. The effect of active, motile particles at the nanoscale has been vigorously researched during the past decade. By understanding how such active suspensions behave, researchers can gain new insights which can potentially provide new applications in many fields. Here (ii) the momentum transfer of active catalysts (Grubbs' 2nd generation catalyst with a hydrodynamic radius of 6A) to their immediate surroundings is observed in an organic suspension. This phenomenon, which has been coined "enhanced diffusion," has not been well studied at the angstrom scale until now. Diffusion-NMR spectroscopy surprisingly revealed that these angstrom sized catalysts nearly double the speed of diffusion of passive molecular tracers in their immediate surroundings. This result is particularly intriguing because in this size regime, the viscosity of the surroundings is expected to completely overcome the inertial forces of these catalysts. This study has prompted further diffusion-NMR studies of molecular catalysts and enzymes as molecular motors. Catalytic systems play a crucial role in the conversion of renewable biomasses into energy and useful materials. This field of research has become increasingly important and lucrative as fossil fuel sources continue to decline/destabilize in the face of increased worldwide demand for more resources. In this work (iii), the efficacy of a hydrogen-pressurized, biphasic catalytic system to convert linear sugar polyols to iodoalkanes was examined. These iodoalkanes can easily be converted to 1-alkenes which can then be used for the synthesis of low density polyethylene. The results indicated that the system products were relatively pure and that the catalytic layer had a degree of recyclability, hinting that such a system may be viable for industrial use.

Autothermal reforming catalyst having perovskite structure

DOEpatents

Krumpel, Michael [Naperville, IL; Liu, Di-Jia [Naperville, IL

2009-03-24

The invention addressed two critical issues in fuel processing for fuel cell application, i.e. catalyst cost and operating stability. The existing state-of-the-art fuel reforming catalyst uses Rh and platinum supported over refractory oxide which add significant cost to the fuel cell system. Supported metals agglomerate under elevated temperature during reforming and decrease the catalyst activity. The catalyst is a perovskite oxide or a Ruddlesden-Popper type oxide containing rare-earth elements, catalytically active firs row transition metal elements, and stabilizing elements, such that the catalyst is a single phase in high temperature oxidizing conditions and maintains a primarily perovskite or Ruddlesden-Popper structure under high temperature reducing conditions. The catalyst can also contain alkaline earth dopants, which enhance the catalytic activity of the catalyst, but do not compromise the stability of the perovskite structure.

The synergistic effect of phase heterojunction and surface heterojunction to improve photocatalytic activity of VO •-TiO2: the co-catalytic effect of H3PW12O40

NASA Astrophysics Data System (ADS)

Li, Haiyan; Cai, Shengnan; Yang, Pengfei; Bai, Yan; Dang, Dongbin

2018-06-01

With nanotube titanic acid (abbreviated as NTA) and the 12-tungstophosphoric acid (H3PW12O40• xH2O, denoted as HPW) as start materials, respectively, according to a simple hydrothermal process in acid medium, we successfully prepared HPW modified VO •-TiO2 composite photocatalysts. During heat treatment companied by the transformation of NTA to TiO2, a kind of single-electron-trapped oxygen vacancy (VO •) could be formed contributing to the visible light absorption of catalysts. The morphology, phase and chemical structure, optical and electronic properties, and so on of the produced catalysts with various HPW loadings are characterized. The size range of synthesized photocatalyst nanoparticles are about 10 50 nm. Taking aqueous rhodamine B (RhB) dye as model pollutant, we carried out photocatalytic activity test of the achieved catalysts, revealing that the hybrid photocatalysts display significantly enhanced visible light-driven ( λ ≥ 420 nm) photocatalytic activity for degradation of RhB. Among various catalysts, HPWN-0.1-120 composite with nominal loading of 0.1 g HPW and heat treatment temperature of 120 °C possesses the highest photocatalytic performance in visible light, which is closely related to the co-effect of phase heterojunction of rutile/anatase, surface heterojunction of anatase/HPW, and oxygen vacancy (VO •). The two types of heterojunction promote greatly the separation efficiency of photoelectrons and photoholes and oxygen vacancy lures response of catalysts to visible light.

Composite tin and zinc oxide nanocrystalline particles for enhanced charge separation in sensitized degradation of dyes.

PubMed

Bandara, J; Tennakone, K; Jayatilaka, P P B

2002-10-01

Composite ZnO/SnO2 catalyst has been studied for the sensitized degradation of dyes e.g. Eosin Y (2', 4', 5', 7'-tetrabromofluorescein disodium salt) in relation to efficient charge separation properties of the catalyst. Improved photocatalytic activity was observed in the case of ZnO/SnO2 composite catalyst compared to the catalytic activity of ZnO, SnO2 or TiO2 powder. The suppression of charge recombination in the composite ZnO/SnO2 catalyst led to higher catalytic activity for the degradation of Eosin Y. Degradation of Eosin follows concomitant formation of CO2 and formation of CO2 followed a pseudo-first-order rate. Photoelectrochemical cells constructed using SnO2, ZnO, ZnO/SnO2 sensitized with Eosin Y showed V(oc) of 175, 306, 512 mV/cm2 and I(sc) of 50, 70, 200 microA/cm2 respectively. A higher irreversible degradation of Eosin Y and higher V(oc) observed on composite ZnO/SnO2 than ZnO and SnO2 separately can be considered as a proof of enhanced charge separation of ZnO/SnO2 catalyst. Eosin Y showed a higher emission decreases on ZnO/SnO2 composite than on individual ZnO, SnO2 or TiO2 indicating dominance of the charge injection process. Photoinjected electrons are tunneled from ZnO to SnO2 particles accumulating injected electrons in the conduction bands allowing wider separation of excited carriers.

Al-doped TiO{sub 2} mesoporous material supported Pd with enhanced catalytic activity for complete oxidation of ethanol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Jing, E-mail: mlczjsls123@163.com; Mu, Wentao, E-mail: mwt15035687833@163.com; Su, Liqing, E-mail: suliqing0163@163.com

Pd catalysts supported on Al-doped TiO{sub 2} mesoporous materials were evaluated in complete oxidation of ethanol. The catalysts synthesized by wet impregnation based on evaporation-induced self-assembly were characterized by X-ray diffraction, measurement of pore structure, XPS, FT-IR, temperature programmed reduction and TEM. Characteristic results showed that the aluminium was doped into the lattice of mesoporous anatase TiO{sub 2} to form Al-O-Ti defect structure. Catalytic results revealed that Al-doped catalysts were much more active than the pristine one, especially at low temperature (≤200 °C). This should be ascribed to the introduction of aluminium ions that suppressed the strong metal-support interaction andmore » increased the active sites of Pd oxides, enhanced the stabilized anatase TiO{sub 2}, improved well dispersed high valence palladium species with high reducibility and enriched chemisorption oxygen. - Graphical abstract: Al-doped Pd/TiO{sub 2} exhibited optimal catalytic performance for ethanol oxidation and CO{sub 2} yield by the suppression of SMSI. - Highlights: • Palladium catalysts supported on Al-doped TiO{sub 2} mesoporous materials were studied. • The introduction of Al can enhance anatase stabilization and increase defect TiO{sub 2}. • The Pd/Al-TiO{sub 2} catalysts show higher ethanol conversion and CO{sub 2} yield than Pd/TiO{sub 2}. • The influence of Al on SMSI and catalytic performance were evaluated by TPR and XPS.« less

Efficient Removal of Methane over Cobalt-Monoxide-Doped AuPd Nanocatalysts.

PubMed

Xie, Shaohua; Liu, Yuxi; Deng, Jiguang; Zang, Simiao; Zhang, Zhenhua; Arandiyan, Hamidreza; Dai, Hongxing

2017-02-21

To overcome deactivation of Pd-based catalysts at high temperatures, we herein design a novel pathway by introducing a certain amount of CoO to the supported Au-Pd alloy nanoparticles (NPs) to generate high-performance Au-Pd-xCoO/three-dimensionally ordered macroporous (3DOM) Co 3 O 4 (x is the Co/Pd molar ratio) catalysts. The doping of CoO induced the formation of PdO-CoO active sites, which was beneficial for the improvement in adsorption and activation of CH 4 and catalytic performance. The Au-Pd-0.40CoO/3DOM Co 3 O 4 sample performed the best (T 90% = 341 °C at a space velocity of 20 000 mL g -1 h -1 ). Deactivation of the 3DOM Co 3 O 4 -supported Au-Pd, Pd-CoO, and Au-Pd-xCoO nanocatalysts resulting from water vapor addition was due to the formation and accumulation of hydroxyl on the catalyst surface, whereas deactivation of the Pd-CoO/3DOM Co 3 O 4 catalyst at high temperatures (680-800 °C) might be due to decomposition of the PdO y active phase into aggregated Pd 0 NPs. The Au-Pd-xCoO/3DOM Co 3 O 4 nanocatalysts exhibited better thermal stability and water tolerance ability compared to the 3DOM Co 3 O 4 -supported Au-Pd and Pd-CoO nanocatalysts. We believe that the supported Au-Pd-xCoO nanomaterials are promising catalysts in practical applications for organic combustion.

Using polyfurfuryl alcohol to improve the hydrothermal stability of mesoporous oxides for reactions in the aqueous phase

USDA-ARS?s Scientific Manuscript database

Hydrodeoxygenation (HDO) of bio-oils derived from the pyrolysis of woody biomass is required to improve the stability and heating value of the liquid hydrocarbon products. Since pyrolysis produces bio-oils having up to 30 vol% water, HDO catalysts must not only be active and selective, but also sta...