Effect of calcination temperature on formaldehyde oxidation performance of Pt/TiO2 nanofiber composite at room temperature

NASA Astrophysics Data System (ADS)

Xu, Feiyan; Le, Yao; Cheng, Bei; Jiang, Chuanjia

2017-12-01

Catalytic oxidation at room temperature over well-designed catalysts is an environmentally friendly method for the abatement of indoor formaldehyde (HCHO) pollution. Herein, nanocomposites of platinum (Pt) and titanium dioxide (TiO2) nanofibers with various phase compositions were prepared by calcining the electrospun TiO2 precursors at different temperatures and subsequently depositing Pt nanoparticles (NPs) on the TiO2 through a NaBH4-reduction process. The phase compositions and structures of Pt/TiO2 can be easily controlled by varying the calcination temperature. The Pt/TiO2 nanocomposites showed a phase-dependent activity towards the catalytic HCHO oxidation. Pt/TiO2 containing pure rutile phase showed enhanced activity with a turnover frequency (TOF) of 16.6 min-1 (for a calcination temperature of 800 °C) as compared to those containing the anatase phase or mixed phases. Density functional theory calculation shows that TiO2 nanofibers with pure rutile phase have stronger adsorption ability to Pt atoms than anatase phase, which favors the reduction of Pt over rutile phase TiO2, leading to higher contents of metallic Pt in the nanocomposite. In addition, the Pt/TiO2 with rutile phase possesses more abundant oxygen vacancies, which is conducive to the activation of adsorbed oxygen. Consequently, the Pt/rutile-TiO2 nanocomposite exhibited better catalytic activity towards HCHO oxidation at room temperature.

pH-Responsive Mercaptoundecanoic Acid Functionalized Gold Nanoparticles and Applications in Catalysis

PubMed Central

Ansar, Siyam M.; Chakraborty, Saptarshi

2018-01-01

Mercaptoundecanoic acid (MUA) functionalized gold nanoparticles (AuNP-MUA) were synthesized and demonstrated to possess pH-triggered aggregation and re-dispersion, as well as the capability of phase transfer between aqueous and organic phases in response to changes in pH. The pH of aggregation for AuNP-MUA is consistent with the pKa of MUA (pH ~4) in solution, while AuNP-MUA phase transition between aqueous and organic phases occurs at pH ~9. The ion pair formation between the amine group in octadecylamine (ODA), the carboxylate group in MUA, and the hydrophobic alkyl chain of ODA facilitates the phase transfer of AuNP-MUA into an organic medium. The AuNP-MUA were investigated as a reusable catalyst in the catalytic reduction of 4-nitrophenol by borohydride—a model reaction for AuNPs. It was determined that 100% MUA surface coverage completely inhibits the catalytic activity of AuNPs. Decreasing the surface coverage was shown to increase catalytic activity, but this decrease also leads to decreased colloidal stability, recoverability, and reusability in subsequent reactions. At 60% MUA surface coverage, colloidal stability and catalytic activity were achieved, but the surface coverage was insufficient to enable redispersion following pH-induced recovery. A balance between AuNP colloidal stability, recoverability, and catalytic activity with reusability was achieved at 90% MUA surface coverage. The AuNP-MUA catalyst can also be recovered at different pH ranges depending on the recovery method employed. At pH ~4, protonation of the MUA results in reduced surface charge and aggregation. At pH ~9, ODA will form an ion-pair with the MUA and induce phase transfer into an immiscible organic phase. Both the pH-triggered aggregation/re-dispersion and aqueous/organic phase transfer methods were employed for catalyst recovery and reuse in subsequent reactions. The ability to recover and reuse the AuNP-MUA catalyst by two different methods and different pH regimes is significant, based on the fact that nanoparticle-catalyzed reactions may occur under different pH conditions. PMID:29772775

Catalytic conversion of syngas to mixed alcohols over Zn-Mn promoted Cu-Fe based catalyst

DOE PAGES

Lu, Yongwu; Yu, Fei; Hu, Jin; ...

2012-04-12

Zn-Mn promoted Cu-Fe based catalyst was synthesized by the co-precipitation method. Mixed alcohols synthesis from syngas was studied in a half-inch tubular reactor system after the catalyst was reduced. Zn-Mn promoted Cu-Fe based catalyst was characterized by SEM-EDS, TEM, XRD, and XPS. The liquid phase products (alcohol phase and hydrocarbon phase) were analyzed by GC-MS and the gas phase products were analyzed by GC. The results showed that Zn-Mn promoted Cu-Fe based catalyst had high catalytic activity and high alcohol selectivity. The maximal CO conversion rate was 72%, and the yield of alcohol and hydrocarbons were also very high. Cumore » (111) was the active site for mixed alcohols synthesis, Fe 2C (101) was the active site for olefin and paraffin synthesis. The reaction mechanism of mixed alcohols synthesis from syngas over Zn-Mn promoted Cu-Fe based catalyst was proposed. Here, Zn-Mn promoted Cu-Fe based catalyst can be regarded as a potential candidate for catalytic conversion of biomass-derived syngas to mixed alcohols.« less

Catalytic conversion of light alkanes. Final report, January 1, 1990--October 31, 1994

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

NONE

During the course of the first three years of the Cooperative Agreement (Phase I-III), we uncovered a family of metal perhaloporphyrin complexes which had unprecedented activity for the selective air-oxidation of fight alkanes to alcohols. The reactivity of fight hydrocarbon substrates with air or oxygen was in the order: isobutane>propane>ethane>methane, in accord with their homolytic bond dissociation energies. Isobutane was so reactive that the proof-of concept stage of a process for producing tert-butyl alcohol from isobutane was begun (Phase V). It was proposed that as more active catalytic systems were developed (Phases IV, VI), propane, then ethane and finally methanemore » oxidations will move into this stage (Phases VII through IX). As of this writing, however, the program has been terminated during the later stages of Phases V and VI so that further work is not anticipated. We made excellent progress during 1994 in generating a class of less costly new materials which have the potential for high catalytic activity. New routes were developed for replacing costly perfluorophenyl groups in the meso-position of metalloporphyrin catalysts with far less expensive and lower molecular weight perfluoromethyl groups.« less

A spontaneous change in the oxidation states of Pd/WO3 toward an active phase during catalytic cycles of CO oxidation

NASA Astrophysics Data System (ADS)

Jeon, Byungwook; Kim, Ansoon; Lee, Young-Ahn; Seo, Hyungtak; Kim, Yu Kwon

2017-11-01

CO oxidation over Pd/WO3 films prepared on a glass substrate has been examined at the substrate temperature of 150 - 250 °C and pressures less than 1 Torr with a stoichiometric mixture of CO and O2. Under the given reaction condition, the chemical states of the Pd/WO3 film gradually change into the most catalytically active form with the highest saturation reaction rate regardless of the initial oxidation states. The measured CO oxidation rate over the Pd/WO3 is strongly dependent on the chemical states of Pd and W. Either metallic Pd or fully oxidized PdO phase is not as catalytically active as the active form with mixed metallic Pd and thin PdO layers supported on WO3 with partially reduced W5+ state which is spontaneously obtained during the catalytic reaction cycles. Our results indicate that the facile oxygen transfer between Pd and WO3 layers not only facilitate the spontaneous changes into the active form, but also act as a promotional role in CO oxidation over the Pd layer.

Process for forming a homogeneous oxide solid phase of catalytically active material

DOEpatents

Perry, Dale L.; Russo, Richard E.; Mao, Xianglei

1995-01-01

A process is disclosed for forming a homogeneous oxide solid phase reaction product of catalytically active material comprising one or more alkali metals, one or more alkaline earth metals, and one or more Group VIII transition metals. The process comprises reacting together one or more alkali metal oxides and/or salts, one or more alkaline earth metal oxides and/or salts, one or more Group VIII transition metal oxides and/or salts, capable of forming a catalytically active reaction product, in the optional presence of an additional source of oxygen, using a laser beam to ablate from a target such metal compound reactants in the form of a vapor in a deposition chamber, resulting in the deposition, on a heated substrate in the chamber, of the desired oxide phase reaction product. The resulting product may be formed in variable, but reproducible, stoichiometric ratios. The homogeneous oxide solid phase product is useful as a catalyst, and can be produced in many physical forms, including thin films, particulate forms, coatings on catalyst support structures, and coatings on structures used in reaction apparatus in which the reaction product of the invention will serve as a catalyst.

Synthesis of a Ni2P/Ni12P5 bi-phase nanocomposite for the efficient catalytic reduction of 4-nitrophenol based on the unique n-n heterojunction effects.

PubMed

Tian, Feng-Yu; Hou, Dongfang; Zhang, Wei-Min; Qiao, Xiu-Qing; Li, Dong-Sheng

2017-10-24

A novel heterostructure catalyst of Ni 2 P/Ni 12 P 5 has been fabricated through a simple solvothermal method by modifying the molar ratio of the initial raw materials. The products are characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), nitrogen adsorption and X-ray photoelectron spectroscopy (XPS). It is found that the two phases, Ni 2 P and Ni 12 P 5 , are interlaced with one another in the as-formed nanocomposite, resulting in more interfaces. The bi-phase catalyst exhibits a markedly enhanced catalytic activity in the reduction of 4-nitrophenol, as compared to that of single Ni 2 P or Ni 12 P 5 . The enhanced catalytic activity can be attributed to the unique n-n series effects, which result in the increased ease of electron transfer over the Ni 2 P/Ni 12 P 5 bi-phase catalyst.

Effect of Ni-Co Ternary Molten Salt Catalysts on Coal Catalytic Pyrolysis Process

NASA Astrophysics Data System (ADS)

Cui, Xin; Qi, Cong; Li, Liang; Li, Yimin; Li, Song

2017-08-01

In order to facilitate efficient and clean utilization of coal, a series of Ni-Co ternary molten salt crystals are explored and the catalytic pyrolysis mechanism of Datong coal is investigated. The reaction mechanisms of coal are achieved by thermal gravimetric analyzer (TGA), and a reactive kinetic model is constructed. The microcosmic structure and macerals are observed by scanning electron microscope (SEM). The catalytic effects of ternary molten salt crystals at different stages of pyrolysis are analyzed. The experimental results show that Ni-Co ternary molten salt catalysts have the capability to bring down activation energy required by pyrolytic reactions at its initial phase. Also, the catalysts exert a preferable catalytic action on macromolecular structure decomposition and free radical polycondensation reactions. Furthermore, the high-temperature condensation polymerization is driven to decompose further with a faster reaction rate by the additions of Ni-Co ternary molten salt crystal catalysts. According to pyrolysis kinetic research, the addition of catalysts can effectively decrease the activation energy needed in each phase of pyrolysis reaction.

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.

Spark plasma sintering synthesis of Ni1-xZnxFe2O4 ferrites: Mössbauer and catalytic study

NASA Astrophysics Data System (ADS)

Velinov, Nikolay; Manova, Elina; Tsoncheva, Tanya; Estournès, Claude; Paneva, Daniela; Tenchev, Krassimir; Petkova, Vilma; Koleva, Kremena; Kunev, Boris; Mitov, Ivan

2012-08-01

Nickel-zinc ferrite nanoparticles, Ni1-xZnxFe2O4 (x = 0, 0.2, 0.5, 0.8, 1.0) were prepared by combination of chemical precipitation and spark plasma sintering (SPS) techniques and conventional thermal treatment of the obtained precursors. The phase composition and structural properties of the obtained materials were investigated by X-ray diffraction and Mössbauer spectroscopy and their catalytic activity in methanol decomposition was tested. A strong effect of reaction medium leading to the transformation of ferrites to a complex mixture of different iron containing phases was detected. A tendency of formation of Fe-carbide was found for the samples synthesized by SPS, while predominantly iron-nickel alloys ware registered in TS obtained samples. The catalytic activity and selectivity in methanol decomposition to CO and methane depended on the current phase composition of the obtained ferrites, which was formed by the influence of the reaction medium.

Cobalt- and iron-based nanoparticles hosted in SBA-15 mesoporous silica and activated carbon from biomass: Effect of modification procedure

NASA Astrophysics Data System (ADS)

Tsoncheva, Tanya; Genova, Izabela; Paneva, Daniela; Dimitrov, Momtchil; Tsyntsarski, Boyko; Velinov, Nicolay; Ivanova, Radostina; Issa, Gloria; Kovacheva, Daniela; Budinova, Temenujka; Mitov, Ivan; Petrov, Narzislav

2015-10-01

Ordered mesoporous silica of SBA-15 type and activated carbon, prepared from waste biomass (peach stones), are used as host matrix of nanosized iron and cobalt particles. The effect of preparation procedure on the state of loaded nanoparticles is in the focus of investigation. The obtained materials are characterized by Boehm method, low temperature physisorption of nitrogen, XRD, UV-Vis, FTIR, Mossbauer spectroscopy and temperature programmed reduction with hydrogen. The catalytic behaviour of the samples is tested in methanol decomposition. The dispersion, oxidative state and catalytic behaviour of loaded cobalt and iron nanoparticles are successfully tuned both by the nature of porous support and the metal precursor used during the samples preparation. Facile effect of active phase deposition from aqueous solution of nitrate precursors is assumed for activated carbon support. For the silica based materials the catalytic activity could be significantly improved when cobalt acetylacetonate is used during the modification. The complex effect of pore topology and surface functionality of different supports on the active phase formation is discussed.

Spatially resolved observation of crystal-face-dependent catalysis by single turnover counting

NASA Astrophysics Data System (ADS)

Roeffaers, Maarten B. J.; Sels, Bert F.; Uji-I, Hiroshi; de Schryver, Frans C.; Jacobs, Pierre A.; de Vos, Dirk E.; Hofkens, Johan

2006-02-01

Catalytic processes on surfaces have long been studied by probing model reactions on single-crystal metal surfaces under high vacuum conditions. Yet the vast majority of industrial heterogeneous catalysis occurs at ambient or elevated pressures using complex materials with crystal faces, edges and defects differing in their catalytic activity. Clearly, if new or improved catalysts are to be rationally designed, we require quantitative correlations between surface features and catalytic activity-ideally obtained under realistic reaction conditions. Transmission electron microscopy and scanning tunnelling microscopy have allowed in situ characterization of catalyst surfaces with atomic resolution, but are limited by the need for low-pressure conditions and conductive surfaces, respectively. Sum frequency generation spectroscopy can identify vibrations of adsorbed reactants and products in both gaseous and condensed phases, but so far lacks sensitivity down to the single molecule level. Here we adapt real-time monitoring of the chemical transformation of individual organic molecules by fluorescence microscopy to monitor reactions catalysed by crystals of a layered double hydroxide immersed in reagent solution. By using a wide field microscope, we are able to map the spatial distribution of catalytic activity over the entire crystal by counting single turnover events. We find that ester hydrolysis proceeds on the lateral {1010} crystal faces, while transesterification occurs on the entire outer crystal surface. Because the method operates at ambient temperature and pressure and in a condensed phase, it can be applied to the growing number of liquid-phase industrial organic transformations to localize catalytic activity on and in inorganic solids. An exciting opportunity is the use of probe molecules with different size and functionality, which should provide insight into shape-selective or structure-sensitive catalysis and thus help with the rational design of new or more productive heterogeneous catalysts.

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.

Hydrogenation of 4-nitrophenol to 4-aminophenol at room temperature: Boosting palladium nanocrystals efficiency by coupling with copper via liquid phase pulsed laser ablation

NASA Astrophysics Data System (ADS)

Park, Hanbit; Reddy, D. Amaranatha; Kim, Yujin; Lee, Seunghee; Ma, Rory; Lim, Manho; Kim, Tae Kyu

2017-04-01

Ultra-dispersed bimetallic nanomaterials have attracted much attention in the hydrogenation of highly toxic aromatic nitro compounds to aromatic amines owing to their high stability, superior activity, reusability, and unique optical and electronic properties, as compared to monometalic nanocrystals. However, the lack of facile and economically controllable strategies of producing highly pure ultra-dispersed bimetallic nanocatalysts limits their practical industrial applications. Considering the above obstacles, we present a simple and effective strategy for the formation of bimetallic (PdCu) nanocrystals by liquid phase pulsed laser ablation using a bulk Pd metal plate submerged in CuCl2 solutions with different concentrations, in contrast to the complex and costly experimental methods used previously. The microstructural and optical properties of the synthesized nanocrystals indicate that the obtained bimetallic nanostructures are highly pure and monodispersed. Moreover, bimetallic PdCu nanostructures show a higher catalytic activity than monometallic Pd nanocrystals for the hydrogenation of 4-nitrophenol to 4-aminophenol at room temperature, also exhibiting high stability for up to four recycles. The mechanism of the enhanced catalytic activity and stability of bimetallic nanocrystals is discussed in detail. Finally, we believe that the presented design strategy and utilization of bimetallic nanocrystals for catalytic applications enables the development of novel bimetallic nanostructures by liquid phase pulsed laser ablation and their catalytic application for environmental remediation.

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.

Catalytic conversion of light alkanes: Quarterly report, January 1-March 31, 1992

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

Biscardi, J.; Bowden, P.T.; Durante, V.A.

The first Quarterly Report of 1992 on the Catalytic Conversion of Light Alkanes reviews the work done between January 1. 1992 and March 31, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products which can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon transportation fuel. During the past quarter we have continued to design, prepare, characterize and test novel catalysts for the mildmore » selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. We continue to investigate three molecular environments for the active catalytic species that we are trying to generate: electron-deficient porphryinic macrocycles (PHASE I), polyoxometallates (PHASE II), and regular oxidic lattices including zeolites and related structures as well as other molecular surface structures having metal oxo groups (PHASE III).« less

Catalytic dehydrogenation of alcohol over solid-state molybdenum sulfide clusters with an octahedral metal framework

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

Kamiguchi, Satoshi, E-mail: kamigu@riken.jp; Organometallic Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako City, Saitama 351-0198; Okumura, Kazu

Graphical abstract: - Highlights: • Solid-state molybdenum sulfide clusters catalyzed the dehydrogenation of alcohol. • The dehydrogenation proceeded without the addition of any oxidants. • The catalytic activity developed when the cluster was activated at 300–500 °C in H{sub 2}. • The Lewis-acidic molybdenum atom and basic sulfur ligand were catalytically active. • The clusters function as bifunctional acid–base catalysts. - Abstract: Solid-state molybdenum sulfide clusters with an octahedral metal framework, the superconducting Chevrel phases, are applied to catalysis. A copper salt of a nonstoichiometric sulfur-deficient cluster, Cu{sub x}Mo{sub 6}S{sub 8–δ} (x = 2.94 and δ ≈ 0.3), is storedmore » in air for more than 90 days. When the oxygenated cluster is thermally activated in a hydrogen stream above 300 °C, catalytic activity for the dehydrogenation of primary alcohols to aldehydes and secondary alcohols to ketones develops. The addition of pyridine or benzoic acid decreases the dehydrogenation activity, indicating that both a Lewis-acidic coordinatively unsaturated molybdenum atom and a basic sulfur ligand synergistically act as the catalytic active sites.« less

Catalytic Gas-Phase Production of Lactide from Renewable Alkyl Lactates.

PubMed

De Clercq, Rik; Dusselier, Michiel; Makshina, Ekaterina; Sels, Bert F

2018-03-12

A new route to lactide, which is a key building block of the bioplastic polylactic acid, is proposed involving a continuous catalytic gas-phase transesterification of renewable alkyl lactates in a scalable fixed-bed setup. Supported TiO 2 /SiO 2 catalysts are highly selective to lactide, with only minimal lactide racemization. The solvent-free process allows for easy product separation and recycling of unconverted alkyl lactates and recyclable lactyl intermediates. The catalytic activity of TiO 2 /SiO 2 catalysts was strongly correlated to their optical properties by DR UV/Vis spectroscopy. Catalysts with high band-gap energy of the supported TiO 2 phase, indicative of a high surface spreading of isolated Ti centers, show the highest turnover frequency per Ti site. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuning Catalytic Performance through a Single or Sequential Post-Synthesis Reaction(s) in a Gas Phase

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

Shan, Junjun; Zhang, Shiran; Choksi, Tej

2016-12-05

Catalytic performance of a bimetallic catalyst is determined by geometric structure and electronic state of the surface or even the near-surface region of the catalyst. Here we report that single and sequential postsynthesis reactions of an as-synthesized bimetallic nanoparticle catalyst in one or more gas phases can tailor surface chemistry and structure of the catalyst in a gas phase, by which catalytic performance of this bimetallic catalyst can be tuned. Pt–Cu regular nanocube (Pt–Cu RNC) and concave nanocube (Pt–Cu CNC) are chosen as models of bimetallic catalysts. Surface chemistry and catalyst structure under different reaction conditions and during catalysis weremore » explored in gas phase of one or two reactants with ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy. The newly formed surface structures of Pt–Cu RNC and Pt–Cu CNC catalysts strongly depend on the reactive gas(es) used in the postsynthesis reaction(s). A reaction of Pt–Cu RNC-as synthesized with H2 at 200 °C generates a near-surface alloy consisting of a Pt skin layer, a Cu-rich subsurface, and a Pt-rich deep layer. This near-surface alloy of Pt–Cu RNC-as synthesized-H2 exhibits a much higher catalytic activity in CO oxidation in terms of a low activation barrier of 39 ± 4 kJ/mol in contrast to 128 ± 7 kJ/mol of Pt–Cu RNC-as synthesized. Here the significant decrease of activation barrier demonstrates a method to tune catalytic performances of as-synthesized bimetallic catalysts. A further reaction of Pt–Cu RNC-as synthesized-H2 with CO forms a Pt–Cu alloy surface, which exhibits quite different catalytic performance in CO oxidation. It suggests the capability of generating a different surface by using another gas. The capability of tuning surface chemistry and structure of bimetallic catalysts was also demonstrated in restructuring of Pt–Cu CNC-as synthesized.« less

Effect of composition and calcination temperature of ceria-zirconia-alumina mixed oxides on catalytic performances of ethanol conversion

NASA Astrophysics Data System (ADS)

Chuklina, S. G.; Maslenkova, S. A.; Pylinina, A. I.; Podzorova, L. I.; Ilyicheva, A. A.

2017-02-01

In the present study, we investigated the effect of preparation method, phase composition and calcination temperature of the (Ce-TZP) - Al2O3 mixed oxides on their structural features and catalytic performance in ethanol conversion. Ceria-zirconia-alumina mixed oxides with different (Ce+Zr)/Al atomic ratios were prepared via sol-gel method. Catalytic activity and selectivity were investigated for ethanol conversion to acetaldehyde, ethylene and diethyl ether.

Rhenium doping induced structural transformation in mono-layered MoS2 with improved catalytic activity for hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Shi, Wenwu; Wang, Zhiguo; Qing Fu, Yong

2017-10-01

This paper reports a new design methodology to improve catalytic activities of catalysts based on 2D transition metal dichalcogenides through elemental doping which induces structural transformations. Effects of rhenium (Re) doping on structural stability/phase transformation and catalytic activity of mono-layered trigonal prismatic (2H) MoS2 were investigated using density functional theory as one example. Results show that 2H-Mo1-x Re x S2 transforms into 1T‧-Mo1-x Re x S2MoS2 as the value of x is larger than 0.4, and the transfer of the electron from Re to Mo is identified as the main reason for this structural transformation. The 1T‧-Mo1-x Re x S2 shows a good catalytic activity for the hydrogen evolution reaction when 0.75  ⩽  x  ⩽  0.94.

Catalytic conversion of methane to methanol using Cu-zeolites.

PubMed

Alayon, Evalyn Mae C; Nachtegaal, Maarten; Ranocchiari, Marco; van Bokhoven, Jeroen A

2012-01-01

The conversion of methane to value-added liquid chemicals is a promising answer to the imminent demand for fuels and chemical synthesis materials in the advent of a dwindling petroleum supply. Current technology requires high energy input for the synthesis gas production, and is characterized by low overall selectivity, which calls for alternative reaction routes. The limitation to achieve high selectivity is the high C-H bond strength of methane. High-temperature reaction systems favor gas-phase radical reactions and total oxidation. This suggests that the catalysts for methane activation should be active at low temperatures. The enzymatic-inspired metal-exchanged zeolite systems apparently fulfill this need, however, methanol yield is low and a catalytic process cannot yet be established. Homogeneous and heterogeneous catalytic systems have been described which stabilize the intermediate formed after the first C-H activation. The understanding of the reaction mechanism and the determination of the active metal sites are important for formulating strategies for the upgrade of methane conversion catalytic technologies.

Dramatically different kinetics and mechanism at solid/liquid and solid/gas interfaces for catalytic isopropanol oxidation over size-controlled platinum nanoparticles.

PubMed

Wang, Hailiang; Sapi, Andras; Thompson, Christopher M; Liu, Fudong; Zherebetskyy, Danylo; Krier, James M; Carl, Lindsay M; Cai, Xiaojun; Wang, Lin-Wang; Somorjai, Gabor A

2014-07-23

We synthesize platinum nanoparticles with controlled average sizes of 2, 4, 6, and 8 nm and use them as model catalysts to study isopropanol oxidation to acetone in both the liquid and gas phases at 60 °C. The reaction at the solid/liquid interface is 2 orders of magnitude slower than that at the solid/gas interface, while catalytic activity increases with the size of platinum nanoparticles for both the liquid-phase and gas-phase reactions. The activation energy of the gas-phase reaction decreases with the platinum nanoparticle size and is in general much higher than that of the liquid-phase reaction which is largely insensitive to the size of catalyst nanoparticles. Water substantially promotes isopropanol oxidation in the liquid phase. However, it inhibits the reaction in the gas phase. The kinetic results suggest different mechanisms between the liquid-phase and gas-phase reactions, correlating well with different orientations of IPA species at the solid/liquid interface vs the solid/gas interface as probed by sum frequency generation vibrational spectroscopy under reaction conditions and simulated by computational calculations.

Novel Co(II) phthalocyanines of extended periphery and their water-soluble derivatives. Synthesis, spectral properties and catalytic activity

NASA Astrophysics Data System (ADS)

Filippova, Anna; Vashurin, Artur; Znoyko, Serafima; Kuzmin, Ilya; Razumov, Mikhail; Chernova, Alena; Shaposhnikov, Gennady; Koifman, Oscar

2017-12-01

Novel complexes of cobalt and copper with substituted phthalocyanines were synthesized and characterized. Their water-soluble derivatives were obtained by sulfonation under mild conditions and structurally proved. Aggregation equilibrium in water mediums was shown and influence of geometrical and electron parameters of macroheterocycle peripheral substituents on these processes was established. Catalytic activity upon liquid-phase oxidation of N,N-diethylcarbamodithiolate to thiuram E was studied. Kinetic parameters of substrate oxidation in presence of cobalt phthalocyanines were considered.

Removal of gas phase low-concentration toluene over Mn, Ag and Ce modified HZSM-5 catalysts by periodical operation of adsorption and non-thermal plasma regeneration.

PubMed

Wang, Wenzheng; Wang, Honglei; Zhu, Tianle; Fan, Xing

2015-07-15

Ag/HZSM-5, Mn/HZSM-5, Ce/HZSM-5, Ag-Mn/HZSM-5 and Ce-Mn/HZSM-5 were prepared by impregnation method. Both their adsorption capacity and catalytic activity were investigated for the removal of gas phase low-concentration toluene by periodical operation of adsorption and non-thermal plasma regeneration. Results show that catalysts loaded with Ag (Ag/HZSM-5 and Ag-Mn/HZSM-5) had larger adsorption capacity for toluene than the other catalysts. And Ag-Mn/HZSM-5 displayed the best catalytic performance for both toluene oxidation by non-thermal plasma and byproducts suppression. On the other hand, the deactivated catalyst can be fully regenerated by calcining in air stream when its adsorption capacity and catalytic activity of the Ag-Mn/HZSM-5 catalyst was found to be decreased after 10 cycles of periodical adsorption and non-thermal regeneration. Copyright © 2015. Published by Elsevier B.V.

Preparation of improved catalytic materials for water purification

NASA Astrophysics Data System (ADS)

Cherkezova-Zheleva, Z.; Paneva, D.; Tsvetkov, M.; Kunev, B.; Milanova, M.; Petrov, N.; Mitov, I.

2014-04-01

The aim of presented paper was to study preparation of catalytic materials for water purification. Iron oxide (Fe3O4) samples supported on activated carbon were prepared by wet impregnation method and low temperature heating in an inert atmosphere. The as-prepared, activated and samples after catalytic test were characterized by Mössbauer spectroscopy and X-ray diffraction. The obtained X-ray diffraction patterns of prepared samples show broad and low-intensity peaks of magnetite phase and the characteristic peaks of the activated carbon. The average crystallite size of magnetite particles was calculated below 20 nm. The registered Mössbauer spectra of prepared materials show a superposition of doublet lines or doublet and sextet components. The calculated hyperfine parameters after spectra evaluation reveal the presence of magnetite phase with nanosize particles. Relaxation phenomena were registered in both cases, i.e. superparamagnetism or collective magnetic excitation behavior, respectively. Low temperature Mössbauer spectra confirm this observation. Application of materials as photo-Fenton catalysts for organic pollutions degradation was studied. It was obtained high adsorption degree of dye, extremely high reaction rate and fast dye degradation. Photocatalytic behaviour of a more active sample was enhanced using mechanochemical activation (MCA). The nanometric size and high dispersion of photocatalyst particles influence both the adsorption and degradation mechanism of reaction. The results showed that all studied photocatalysts effectively decompose the organic pollutants under UV light irradiation. Partial oxidation of samples after catalytic tests was registered. Combination of magnetic particles with high photocatalytic activity meets both the requirements of photocatalytic degradation of water contaminants and that of recovery for cyclic utilization of material.

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.

Catalytic decomposition of toxic chemicals over metal-promoted carbon nanotubes.

PubMed

Li, Lili; Han, Changxiu; Han, Xinyu; Zhou, Yixiao; Yang, Li; Zhang, Baogui; Hu, Jianli

2011-01-15

Effective decomposition of toxic gaseous compounds is important for pollution control at many chemical manufacturing plants. This study explores catalytic decomposition of phosphine (PH(3)) using novel metal-promoted carbon nanotubes (CNTs). The cerium-promoted Co/CNTs catalysts (CoCe/CNTs) are synthesized by means of coimpregnation method and reduced by three different methods (H(2), KBH(4), NaH(2)PO(2)·H(2)O/KBH(4)). The morphology, structure, and composition of the catalysts are characterized using a number of analytical instrumentations including high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, BET surface area measurement, and inductively coupled plasma. The activity of the catalysts in PH(3) decomposition reaction is measured and correlated with their surface and structural properties. The characterization results show that the CoCe/CNTs catalyst reduced by H(2) possesses small particles and is shown thermally stable in PH(3) decomposition reaction. The activities of these catalysts are compared and are shown in the following sequence: CoCe/CNTs > Co/CNTs > CoCeBP/CNTs> CoCeB/CNTs. The difference in reduction method results in the formation of different active phases during the PH(3) decomposition reaction. After a catalytic activity test, only the CoP phase is formed on CoCe/CNTs and Co/CNTs catalysts, whereas multiphases CoP, Co(2)P, and Co phases are formed on CoCeBP/CNTs and CoCeB/CNTs. Results show that the CoP phase is formed predominantly on the CoCe/CNTs and Co/CNTs catalysts and is found to likely be the most active phase for this reaction. Furthermore, the CoCe/CNTs catalyst exhibits not only highest activity but also long-term stability in PH(3) decomposition reaction. When operated in a fixed-bed reactor at 360 °C, single-pass PH(3) conversion of about 99.8% can be achieved.

Asymmetric Fluorination of α-Branched Cyclohexanones Enabled by a Combination of Chiral Anion Phase-Transfer Catalysis and Enamine Catalysis using Protected Amino Acids

PubMed Central

2015-01-01

We report a study involving the successful merger of two separate chiral catalytic cycles: a chiral anion phase-transfer catalysis cycle to activate Selectfluor and an enamine activation cycle, using a protected amino acid as organocatalyst. We have demonstrated the viability of this approach with the direct asymmetric fluorination of α-substituted cyclohexanones to generate quaternary fluorine-containing stereocenters. With these two chiral catalytic cycles operating together in a matched sense, high enantioselectivites can be achieved, and we envisage that this dual catalysis method has the potential to be more broadly applicable, given the breadth of enamine catalysis. It also represents a rare example of chiral enamine catalysis operating successfully on α-branched ketones, substrates commonly inert to this activation mode. PMID:24684209

PdHx entrapped in covalent triazine framework modulates selectivity in glycerol oxidation [Modulation of palladium activity and stability by a covalent triazine framework

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

Chan-Thaw, Carine E.; Villa, Alberto; Wang, Di

The confinement of a Pd nanoparticle within a nitrogen-containing covalent triazine framework (CTF) material was investigated to understand if the highly tunable CTF chemistry mediates the Pd catalytic properties through an ensemble effect with the CTF nitrogen atoms or a confinement effect within the CTF pores. The results surprisingly demonstrate that the CTF stabilizes the formation of 2.6 nm PdHx particles within the pores. These PdHx particles are very active for the liquid phase oxidation of glycerol due to the in situ formation of H2O2 which catalytically promotes the initial C-C cleavage. In addition the confined particles are stable overmore » many catalytic cycles whereas nanoparticles trapped outside of the pores loose activity rapidly. These results indicate that there is the potential to tune the CTF chemistry to significantly modify the chemistry of the catalytic metals.« less

PdHx entrapped in covalent triazine framework modulates selectivity in glycerol oxidation [Modulation of palladium activity and stability by a covalent triazine framework

DOE PAGES

Chan-Thaw, Carine E.; Villa, Alberto; Wang, Di; ...

2015-06-25

The confinement of a Pd nanoparticle within a nitrogen-containing covalent triazine framework (CTF) material was investigated to understand if the highly tunable CTF chemistry mediates the Pd catalytic properties through an ensemble effect with the CTF nitrogen atoms or a confinement effect within the CTF pores. The results surprisingly demonstrate that the CTF stabilizes the formation of 2.6 nm PdHx particles within the pores. These PdHx particles are very active for the liquid phase oxidation of glycerol due to the in situ formation of H2O2 which catalytically promotes the initial C-C cleavage. In addition the confined particles are stable overmore » many catalytic cycles whereas nanoparticles trapped outside of the pores loose activity rapidly. These results indicate that there is the potential to tune the CTF chemistry to significantly modify the chemistry of the catalytic metals.« less

Purification of Active Myrosinase from Plants by Aqueous Two-Phase Counter-Current Chromatography

PubMed Central

Wade, Kristina L.; Ito, Yoichiro; Ramarathnam, Aarthi; Holtzclaw, W. David; Fahey, Jed W.

2014-01-01

Introduction Myrosinase (thioglucoside glucohydrolase; E.C. 3.2.1.147), is a plant enzyme of increasing interest and importance to the biomedical community. Myrosinase catalyses the formation of isothiocyanates such as sulforaphane (frombroccoli) and 4-(α-l-rhamnopyranosyloxy)benzyl isothiocyanate (from moringa), which are potent inducers of the cytoprotective phase-2 response in humans, by hydrolysis of their abundant glucosinolate (β-thioglucoside N-hydroxysulphate) precursors. Objective To develop an aqueous two-phase counter-current chromatography (CCC) system for the rapid, three-step purification of catalytically active myrosinase. Methods A high-concentration potassium phosphate and polyethylene glycol biphasic aqueous two-phase system (ATPS) is used with a newly developed CCC configuration that utilises spiral-wound, flat-twisted tubing (with an ovoid cross-section). Results Making the initial crude plant extract directly in the ATPS and injecting only the lower phase permitted highly selective partitioning of the myrosinase complex before a short chromatography on a spiral disk CCC. Optimum phase retention and separation of myrosinase from other plant proteins afforded a 60-fold purification. Conclusion Catalytically active myrosinase is purified from 3-day broccoli sprouts, 7-day daikon sprouts, mustard seeds and the leaves of field-grown moringa trees, in a CCC system that is predictably scalable. PMID:25130502

Purification of active myrosinase from plants by aqueous two-phase counter-current chromatography.

PubMed

Wade, Kristina L; Ito, Yoichiro; Ramarathnam, Aarthi; Holtzclaw, W David; Fahey, Jed W

2015-01-01

Myrosinase (thioglucoside glucohydrolase; E.C. 3.2.1.147), is a plant enzyme of increasing interest and importance to the biomedical community. Myrosinase catalyses the formation of isothiocyanates such as sulforaphane (from broccoli) and 4-(α-l-rhamnopyranosyloxy)benzyl isothiocyanate (from moringa), which are potent inducers of the cytoprotective phase-2 response in humans, by hydrolysis of their abundant glucosinolate (β-thioglucoside N-hydroxysulphate) precursors. To develop an aqueous two-phase counter-current chromatography (CCC) system for the rapid, three-step purification of catalytically active myrosinase. A high-concentration potassium phosphate and polyethylene glycol biphasic aqueous two-phase system (ATPS) is used with a newly developed CCC configuration that utilises spiral-wound, flat-twisted tubing (with an ovoid cross-section). Making the initial crude plant extract directly in the ATPS and injecting only the lower phase permitted highly selective partitioning of the myrosinase complex before a short chromatography on a spiral disk CCC. Optimum phase retention and separation of myrosinase from other plant proteins afforded a 60-fold purification. Catalytically active myrosinase is purified from 3-day broccoli sprouts, 7-day daikon sprouts, mustard seeds and the leaves of field-grown moringa trees, in a CCC system that is predictably scalable. Copyright © 2014 John Wiley & Sons, Ltd.

Synthesis and characterization of NiFe{sub 2}O{sub 4}–Pd magnetically recyclable catalyst for hydrogenation reaction

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

Karaoğlu, E., E-mail: ekaraoglu@fatih.edu.tr; Özel, U.; Caner, C.

2012-12-15

Graphical abstract: Display Omitted Highlights: ► Novel superparamagnetic NiFe{sub 2}O{sub 4}–Pd magnetically recyclable catalyst was fabricated through co-precipitation. ► It could be reused several times without significant loss in catalytic activity for hydrogenation reaction. ► No further modification of the NiFe{sub 2}O{sub 4}–Pd magnetically recyclable catalyst is necessary for utilization as catalyst. -- Abstract: Herein we report the fabrication and characterization magnetically recyclable catalysts of NiFe{sub 2}O{sub 4}–Pd nanocomposite as highly effective catalysts for reduction reactions in liquid phase. The reduction Pd{sup 2+} was accomplished with polyethylene glycol 400 (PEG-400) instead of sodium borohydride (NaBH{sub 4}) and NiFe{sub 2}O{sub 4}more » nanoparticles was prepared by sonochemically using FeCI{sub 3}·6H{sub 2}O and NiCl{sub 2}. The chemical characterization of the product was done with X-ray diffractometry, Infrared spectroscopy, transmission electron microscopy, UV–Vis spectroscopy, thermal gravimetry and inductively coupled plasma. Thus formed NiFe{sub 2}O{sub 4}–Pd MRCs showed a very high activity in reduction reactions of 4-nitro aniline and 1,3-dinitrobenzene in liquid phase. It was found out that the catalytic activity of NiFe{sub 2}O{sub 4}–Pd MRCs on the reduction of 4-nitro aniline and 1,3-dinitrobenzene in liquid phase are between 99–93% and 98–93%, respectively. Magnetic character of this system allowed recovery and multiple use without significant loss of its catalytic activity. It is found that NiFe{sub 2}O{sub 4}–Pd MRCs showed very efficient catalytic activity and multiple usability.« less

Kinetic analysis of butyrylcholinesterase-catalyzed hydrolysis of acetanilides.

PubMed

Masson, Patrick; Froment, Marie-Thérèse; Gillon, Emilie; Nachon, Florian; Darvesh, Sultan; Schopfer, Lawrence M

2007-09-01

The aryl-acylamidase (AAA) activity of butyrylcholinesterase (BuChE) has been known for a long time. However, the kinetic mechanism of aryl-acylamide hydrolysis by BuChE has not been investigated. Therefore, the catalytic properties of human BuChE and its peripheral site mutant (D70G) toward neutral and charged aryl-acylamides were determined. Three neutral (o-nitroacetanilide, m-nitroacetanilide, o-nitrophenyltrifluoroacetamide) and one positively charged (3-(acetamido) N,N,N-trimethylanilinium, ATMA) acetanilides were studied. Hydrolysis of ATMA by wild-type and D70G enzymes showed a long transient phase preceding the steady state. The induction phase was characterized by a hysteretic "burst". This reflects the existence of two enzyme states in slow equilibrium with different catalytic properties. Steady-state parameters for hydrolysis of the three acetanilides were compared to catalytic parameters for hydrolysis of esters giving the same acetyl intermediate. Wild-type BuChE showed substrate activation while D70G displayed a Michaelian behavior with ATMA as with positively charged esters. Owing to the low affinity of BuChE for amide substrates, the hydrolysis kinetics of neutral amides was first order. Acylation was the rate-determining step for hydrolysis of aryl-acetylamide substrates. Slow acylation of the enzyme, relative to that by esters may, in part, be due suboptimal fit of the aryl-acylamides in the active center of BuChE. The hypothesis that AAA and esterase active sites of BuChE are non-identical was tested with mutant BuChE. It was found that mutations on the catalytic serine, S198C and S198D, led to complete loss of both activities. The silent variant (FS117) had neither esterase nor AAA activity. Mutation in the peripheral site (D70G) had the same effect on esterase and AAA activities. Echothiophate inhibited both activities identically. It was concluded that the active sites for esterase and AAA activities are identical, i.e. S198. This excludes any other residue present in the gorge for being the catalytic nucleophile pole.

Systematic Identification of Promoters for Methane Oxidation Catalysts Using Size- and Composition-Controlled Pd-Based Bimetallic Nanocrystals.

PubMed

Willis, Joshua J; Goodman, Emmett D; Wu, Liheng; Riscoe, Andrew R; Martins, Pedro; Tassone, Christopher J; Cargnello, Matteo

2017-08-30

Promoters enhance the performance of catalytic active phases by increasing rates, stability, and/or selectivity. The process of identifying promoters is in most cases empirical and relies on testing a broad range of catalysts prepared with the random deposition of active and promoter phases, typically with no fine control over their localization. This issue is particularly relevant in supported bimetallic systems, where two metals are codeposited onto high-surface area materials. We here report the use of colloidal bimetallic nanocrystals to produce catalysts where the active and promoter phases are colocalized to a fine extent. This strategy enables a systematic approach to study the promotional effects of several transition metals on palladium catalysts for methane oxidation. In order to achieve these goals, we demonstrate a single synthetic protocol to obtain uniform palladium-based bimetallic nanocrystals (PdM, M = V, Mn, Fe, Co, Ni, Zn, Sn, and potentially extendable to other metal combinations) with a wide variety of compositions and sizes based on high-temperature thermal decomposition of readily available precursors. Once the nanocrystals are supported onto oxide materials, thermal treatments in air cause segregation of the base metal oxide phase in close proximity to the Pd phase. We demonstrate that some metals (Fe, Co, and Sn) inhibit the sintering of the active Pd metal phase, while others (Ni and Zn) increase its intrinsic activity compared to a monometallic Pd catalyst. This procedure can be generalized to systematically investigate the promotional effects of metal and metal oxide phases for a variety of active metal-promoter combinations and catalytic reactions.

Identification of a Catalytically Highly Active Surface Phase for CO Oxidation over PtRh Nanoparticles under Operando Reaction Conditions

NASA Astrophysics Data System (ADS)

Hejral, U.; Franz, D.; Volkov, S.; Francoual, S.; Strempfer, J.; Stierle, A.

2018-03-01

Pt-Rh alloy nanoparticles on oxide supports are widely employed in heterogeneous catalysis with applications ranging from automotive exhaust control to energy conversion. To improve catalyst performance, an atomic-scale correlation of the nanoparticle surface structure with its catalytic activity under industrially relevant operando conditions is essential. Here, we present x-ray diffraction data sensitive to the nanoparticle surface structure combined with in situ mass spectrometry during near ambient pressure CO oxidation. We identify the formation of ultrathin surface oxides by detecting x-ray diffraction signals from particular nanoparticle facets and correlate their evolution with the sample's enhanced catalytic activity. Our approach opens the door for an in-depth characterization of well-defined, oxide-supported nanoparticle based catalysts under operando conditions with unprecedented atomic-scale resolution.

Synergetic effect at the interfaces of solution processed MoS2-WS2 composite for hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Kim, Seong Ku; Song, Wooseok; Ji, Seulgi; Lim, Yi Rang; Lee, Young Bum; Myung, Sung; Lim, Jongsun; An, Ki-Seok; Lee, Sun Sook

2017-12-01

Recently, the importance of developing an effective catalyst for hydrogen evolution reaction is emphasized because hydrogen fueled energy conversion processes are gaining attention as the next generation energy production method. We propose a transition metal dichalcogenide composite catalyst based on molybdenum disulfide (MoS2) and tungsten disulfide (WS2) on reduced graphene oxide coated nickel (rGO-Ni) foams. The composite exhibited enhanced catalytic activity with observed on-set potential of ∼275 mV at -10 mA/cm2 and Tafel slope of 54.1 mV/dec when the composition of the composite was 50%MoS2-50%WS2. The composite catalyst demonstrated high-stability up to 300 cycles. In order to understand the enhanced catalytic activity, X-ray photoelectron spectroscopy compositional analysis was utilized. We propose that the enhancement of catalytic activities exhibited by the composited samples were achieved due to introduction of new type of interface between MoS2 and WS2 grains, regional transition of 2H phase MoS2 and WS2 to 1T phase, and formation of excess sulfur which depended directly on the composition.

Research and Development in support of the Surface Chemistry Branch. Volume 1

DTIC Science & Technology

1988-06-01

reactions could occur in the melt and/or gas phase-and (2) formation of HCN from RDX pyrolysis followed by hydrolysis with atmospheric/RDX decomposition ...interest is the development of electrochemically active transition metal complexes for the catalytic conversion/ decomposition of dissolved gases, such...impregnated charcoals for the collection and catalytic decomposition of toxic vapors (2), and the evaluation of Navy shipboard environments (3). For the

Enzyme Inquiry

ERIC Educational Resources Information Center

Rushton, Gregory T.; Dias, Michael; McDurmon, Grant

2008-01-01

In this article, the authors describe a two-phase inquiry lesson in which students explore the catalytic activity of amylase on starch (Rungruangsa and Panijpan 1979). In the first phase, students' prior knowledge about the reaction is assessed through a set of directed prompts and small-group discussion, then challenged or reinforced as students…

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

Rimoldi, Martino; Nakamura, Akitake; Vermeulen, Nicolaas A.

An iridium pincer complex has been immobilised in the metal–organic frameworkNU-1000. The stable Ir-pincer modifiedNU-1000is catalytically active in the hydrogenation of alkenes in condensed phase and under flow conditions.

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

Rimoldi, Martino; Nakamura, Akitake; Vermeulen, Nicolaas A.

An iridium pincer complex has been immobilised in the metal–organic framework NU-1000. The stable Ir-pincer modified NU-1000 is catalytically active in the hydrogenation of alkenes in condensed phase and under flow conditions.

Porous metallosilicates for heterogeneous, liquid-phase catalysis: perspectives and pertaining challenges

PubMed Central

Padovan, Daniele; Tarantino, Giulia

2018-01-01

Porous silicates containing dilute amounts of tri-, tetra- and penta-valent metal sites, such as TS-1, Sn-β and Fe-ZSM-5, have recently emerged as state of the art catalysts for a variety of sustainable chemical transformations. In contrast with their aluminosilicate cousins, which are widely employed throughout the refinery industry for gas-phase catalytic transformations, such metallosilicates have exhibited unprecedented levels of performance for a variety of liquid-phase catalytic processes, including the conversion of biomass to chemicals, and sustainable oxidation technologies with H2O2. However, despite their unique levels of performance for these new types of chemical transformations, increased utilization of these promising materials is complicated by several factors. For example, their utilization in a liquid, and often polar, medium hinders process intensification (scale-up, catalyst deactivation). Moreover, such materials do not generally exhibit the active-site homogeneity of conventional aluminosilicates, and they typically possess a wide variety of active-site ensembles, only some of which may be directly involved in the catalytic chemistry of interest. Consequently, mechanistic understanding of these catalysts remains relatively low, and competitive reactions are commonly observed. Accordingly, unified approaches towards developing more active, selective and stable porous metallosilicates have not yet been achieved. Drawing on some of the most recent literature in the field, the purpose of this mini review is both to highlight the breakthroughs made with regard to the use of porous metallosilicates as heterogeneous catalysts for liquid-phase processing, and to highlight the pertaining challenges that we, and others, aim to overcome during the forthcoming years. PMID:29515849

Porous metallosilicates for heterogeneous, liquid-phase catalysis: perspectives and pertaining challenges

NASA Astrophysics Data System (ADS)

Hammond, Ceri; Padovan, Daniele; Tarantino, Giulia

2018-02-01

Porous silicates containing dilute amounts of tri-, tetra- and penta-valent metal sites, such as TS-1, Sn-β and Fe-ZSM-5, have recently emerged as state of the art catalysts for a variety of sustainable chemical transformations. In contrast with their aluminosilicate cousins, which are widely employed throughout the refinery industry for gas-phase catalytic transformations, such metallosilicates have exhibited unprecedented levels of performance for a variety of liquid-phase catalytic processes, including the conversion of biomass to chemicals, and sustainable oxidation technologies with H2O2. However, despite their unique levels of performance for these new types of chemical transformations, increased utilization of these promising materials is complicated by several factors. For example, their utilization in a liquid, and often polar, medium hinders process intensification (scale-up, catalyst deactivation). Moreover, such materials do not generally exhibit the active-site homogeneity of conventional aluminosilicates, and they typically possess a wide variety of active-site ensembles, only some of which may be directly involved in the catalytic chemistry of interest. Consequently, mechanistic understanding of these catalysts remains relatively low, and competitive reactions are commonly observed. Accordingly, unified approaches towards developing more active, selective and stable porous metallosilicates have not yet been achieved. Drawing on some of the most recent literature in the field, the purpose of this mini review is both to highlight the breakthroughs made with regard to the use of porous metallosilicates as heterogeneous catalysts for liquid-phase processing, and to highlight the pertaining challenges that we, and others, aim to overcome during the forthcoming years.

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.

Synthesis and catalytic performance of ZSM-5/MCM-41 composite molecular sieve from palygorskite

NASA Astrophysics Data System (ADS)

Jiang, Jinlong; Wu, Mei; Yang, Yong; Duanmu, Chuansong; Chen, Jing; Gu, Xu

2017-10-01

ZSM-5/MCM-41 composite molecular sieve has been hydrothermally synthesized through a two-step crystallization process using palygorskite (PAL) as silicon and aluminum source. The products were characterized by various means and their catalytic properties for acetalization of cyclohexanone and esterification of acetic acid and n-butanol were also investigated. In the first step ZSM-5 zeolite could be formed from the acid-treated PAL after hydrothermal treatment using tetrapropylammonium bromide as template. XRD patterns, N2 adsorption and desorption data, and TEM images show that the composite obtained in the secondary step had a well-ordered mesoporous MCM-41 phase and a microporous ZSM-5 zeolite phase. Compared with ZSM-5, ZSM-5/MCM-41 composite possessed more total acid amount, weak acid sites and large pore structure due to the formation of MCM-41 and exhibited higher catalytic activity for the acetalization and esterification reaction.

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.

Catalytic and electrocatalytic oxidation of ethanol over palladium-based nanoalloy catalysts.

PubMed

Yin, Jun; Shan, Shiyao; Ng, Mei Shan; Yang, Lefu; Mott, Derrick; Fang, Weiqin; Kang, Ning; Luo, Jin; Zhong, Chuan-Jian

2013-07-23

The control of the nanoscale composition and structure of alloy catalysts plays an important role in heterogeneous catalysis. This paper describes novel findings of an investigation for Pd-based nanoalloy catalysts (PdCo and PdCu) for ethanol oxidation reaction (EOR) in gas phase and alkaline electrolyte. Although the PdCo catalyst exhibits a mass activity similar to Pd, the PdCu catalyst is shown to display a much higher mass activity than Pd for the electrocatalytic EOR in alkaline electrolyte. This finding is consistent with the finding on the surface enrichment of Pd on the alloyed PdCu surface, in contrast to the surface enrichment of Co in the alloyed PdCo surface. The viability of C-C bond cleavage was also probed for the PdCu catalysts in both gas-phase and electrolyte-phase EOR. In the gas-phase reaction, although the catalytic conversion rate for CO2 product is higher over Pd than PdCu, the nanoalloy PdCu catalyst appears to suppress the formation of acetic acid, which is a significant portion of the product in the case of pure Pd catalyst. In the alkaline electrolyte, CO2 was detected from the gas phase above the electrolyte upon acid treatment following the electrolysis, along with traces of aldehyde and acetic acid. An analysis of the electrochemical properties indicates that the oxophilicity of the base metal alloyed with Pd, in addition to the surface enrichment of metals, may have played an important role in the observed difference of the catalytic and electrocatalytic activities. In comparison with Pd alloyed with Co, the results for Pd alloyed with Cu showed a more significant positive shift of the reduction potential of the oxygenated Pd species on the surface. These findings have important implications for further fine-tuning of the Pd nanoalloys in terms of base metal composition toward highly active and selective catalysts for EOR.

pH Triggered Recovery and Reuse of Thiolated Poly(acrylic acid) Functionalized Gold Nanoparticles with Applications in Colloidal Catalysis.

PubMed

Ansar, Siyam M; Fellows, Benjamin; Mispireta, Patrick; Mefford, O Thompson; Kitchens, Christopher L

2017-08-08

Thiolated poly(acrylic acid) (PAA-SH) functionalized gold nanoparticles were explored as a colloidal catalyst with potential application as a recoverable catalyst where the PAA provides pH-responsive dispersibility and phase transfer capability between aqueous and organic media. This system demonstrates complete nanoparticle recovery and redispersion over multiple reaction cycles without changes in nanoparticle morphology or reduction in conversion. The catalytic activity (rate constant) was reduced in subsequent reactions when recovery by aggregation was employed, despite unobservable changes in morphology or dispersibility. When colloidal catalyst recovery employed a pH induced phase transfer between two immiscible solvents, the catalytic activity of the recovered nanoparticles was unchanged over four cycles, maintaining the original rate constant and 100% conversion. The ability to recover and reuse colloidal catalysts by aggregation/redispersion and phase transfer methods that occur at low and high pH, respectively, could be used for different gold nanoparticle catalyzed reactions that occur at different pH conditions.

Vapor-phase catalytic oxidesulfurization (ODS) of organosulfur compounds over supported metal oxide catalysts

NASA Astrophysics Data System (ADS)

Choi, Sukwon

Sulfur in transportation fuels remains a leading source of SOx emissions from vehicle engines and is a major source of air pollution. The very low levels of sulfur globally mandated for transportation fuels in the near future cannot be achieved by current practices of hydrodesulfurization (HDS) for sulfur removal, which operate under severe conditions (high T, P) and use valuable H2. Novel vapor-phase catalytic oxidesulfurization (ODS) processes of selectively oxidizing various organosulfur compounds (carbonyl sulfide, carbon disulfide, methanethiol, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), thiophene, 2,5-dimenthylthiophene) typically found in various industrial streams (e.g., petroleum refining, pulp and paper) into valuable chemical intermediates (H 2CO, CO, H2, maleic anhydride and concentrated SO2) has been extensively studied. This research has primarily focused on establishing the fundamental kinetics and mechanisms of these selective oxidation reactions over well-defined supported metal oxide catalysts. The selective oxidation reactions of COS + O2 → CO + SO2; 2CS2 + 5O2 → 2CO + 4SO2; CH3SH + 2O 2 → H2CO + SO2 + H2O; C4 H4S + 3O2 → C4H2O 3 + H2O + SO2; were studied. Raman spectroscopy revealed that the supported metal oxide phases were 100% dispersed on the oxide substrate. All the catalysts were highly active and selective for the oxidesulfurization of carbonyl sulfide, carbon disulfide, methanethiol, and thiophene between 290--330°C, 230--270°C, 350--400°C, and 250--400°C, respectively and did not deactivate. The TOFs (turnover frequency, normalized activity per active catalytic site) for all ODS reactions over supported vanadia catalysts, only containing molecularly dispersed surface vanadia species, varied within one order of magnitude and revealed the V-O-Support bridging bond was involved in the critical rate-determining kinetic steps. The surface reaction mechanism for each reaction was revealed by in situ IR (infrared) and temperature programmed surface reaction-mass spectroscopy (TPSR-MS). The systematic investigation of vapor-phase oxidesulfurization (ODS) reactions of organosulfur compounds over catalytic supported metal oxides revealed the facile S-O exchange mechanisms allow for the efficient removal of sulfur while producing value-added chemicals and represents the discovery of a new series of catalytic reactions.

Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol over Nitrogen-Doped Carbon-Supported Iron Catalysts.

PubMed

Li, Jiang; Liu, Jun-Ling; Zhou, Hong-Jun; Fu, Yao

2016-06-08

Iron-based heterogeneous catalysts, which were generally prepared by pyrolysis of iron complexes on supports at elevated temperature, were found to be capable of catalyzing the transfer hydrogenation of furfural (FF) to furfuryl alcohol (FFA). The effects of metal precursor, nitrogen precursor, pyrolysis temperature, and support on catalytic performance were examined thoroughly, and a comprehensive study of the reaction parameters was also performed. The highest selectivity of FFA reached 83.0 % with a FF conversion of 91.6 % under the optimal reaction condition. Catalyst characterization suggested that iron cations coordinated by pyridinic nitrogen functionalities were responsible for the enhanced catalytic activity. The iron catalyst could be recycled without significant loss of catalytic activity for five runs, and the destruction of the nitrogen-iron species, the presence of crystallized Fe2 O3 phase, and the pore structure change were the main reasons for catalyst deactivation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preparation of immobilized coating Fenton-like catalyst for high efficient degradation of phenol.

PubMed

Wang, Jiankang; Yao, Zhongping; Wang, Yajing; Xia, Qixing; Chu, Huiya; Jiang, Zhaohua

2017-05-01

In this study, solid acid amorphous Fe 3 O 4 /SiO 2 ceramic coating decorated with sulfur on Q235 carbon steel as Fenton-like catalyst for phenol degradation was successfully prepared by plasma electrolytic oxidation (PEO) in silicate electrolyte containing Na 2 S 2 O 8 as sulfur source. The surface morphology and phase composition were characterized by SEM, EDS, XRD and XPS analyses. NH 3 -TPD was used to evaluate surface acidity of PEO coating. The results indicated that sulfur decorated amorphous Fe 3 O 4 /SiO 2 ceramic coatings with porous structure and higher acid strength had the similar pore size and the surface became more and more uneven with the increase of Na 2 S 2 O 8 in the silicate electrolyte. The Fenton-like catalytic activity of sulfur decorated PEO coatings was also evaluated. In contrast to negligible catalytic activity of sulfur undecorated PEO coating, catalytic activity of sulfur decorated PEO coating was excellent and PEO coating prepared with 3.0 g Na 2 S 2 O 8 had the highest catalytic activity which could degrade 99% of phenol within 8 min under circumneutral pH. The outstanding performance of sulfur decorated PEO coating was attributed to strong acidic microenvironment and more Fe 2+ on the surface. The strong acid sites played a key factor in determining catalytic activity of catalyst. In conclusion, rapid phenol removal under circumneutral pH and easier separation endowed it potential application in wastewater treatment. In addition, this strategy of preparing immobilized solid acid coating could provide guidance for designing Fenton-like catalyst with excellent catalytic activity and easier separation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Perovskite oxides: Oxygen electrocatalysis and bulk structure

NASA Technical Reports Server (NTRS)

Carbonio, R. E.; Fierro, C.; Tryk, D.; Scherson, D.; Yeager, Ernest

1987-01-01

Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

Perovskite-type oxides - Oxygen electrocatalysis and bulk structure

NASA Technical Reports Server (NTRS)

Carbonio, R. E.; Fierro, C.; Tryk, D.; Scherson, D.; Yeager, E.

1988-01-01

Perovskite type oxides were considered for use as oxygen reduction and generation electrocatalysts in alkaline electrolytes. Perovskite stability and electrocatalytic activity are studied along with possible relationships of the latter with the bulk solid state properties. A series of compounds of the type LaFe(x)Ni1(-x)O3 was used as a model system to gain information on the possible relationships between surface catalytic activity and bulk structure. Hydrogen peroxide decomposition rate constants were measured for these compounds. Ex situ Mossbauer effect spectroscopy (MES), and magnetic susceptibility measurements were used to study the solid state properties. X ray photoelectron spectroscopy (XPS) was used to examine the surface. MES has indicated the presence of a paramagnetic to magnetically ordered phase transition for values of x between 0.4 and 0.5. A correlation was found between the values of the MES isomer shift and the catalytic activity for peroxide decomposition. Thus, the catalytic activity can be correlated to the d-electron density for the transition metal cations.

Synthesis of ternary oxide for efficient photo catalytic conversion of CO2

NASA Astrophysics Data System (ADS)

Wan, Lijuan

2018-01-01

Zn2GeO4 Nan rods were prepared by solution phase route. The morphology and structure of the as-prepared products were characterized by scanning electron microscopy (SEM) and Bruner-Emmett-Teller (BET) surface area measurements. The results revealed that Zn2GeO4 Nan rods with higher surface area have higher photo catalytic activity in photo reduction of CO2 than Zn2GeO4 prepared through solid-state reaction.

Mn-Ce-Co complex oxide nanoparticles: hydrothermal synthesis and their catalytic subcritical oxidation of 4,4'-Dibromobiphenyl.

PubMed

Chen, Jinyang; Xu, Tianjiao; Ding, Junying; Ji, Yimei; Ni, Pei; Li, Zhilian

2012-10-15

In situ transformation of 4,4'-Dibromobiphenyl (4,4'-DBB) in water was observed with hydrothermal diamond anvil cell (HDAC) up to 633 K. It shows that 4,4'-DBB dissolves in water to form a homogenous phase at the temperature of 588 K and thus subcritical water oxidation of 4,4'-DBB higher than the temperature can be a homogenous phase. To accelerate the oxidative degradation, some Mn-Ce-Co complex oxide nanoparticles of about 100 nm were prepared by co-precipitation hydrothermal method. The nanoparticles show enough stability and catalytic activity for oxidative degradation of 4,4'-DBB in subcritical water. The catalytic activation increases with some Co doping and as for the complex oxides of Mn(1)Ce(1), Mn(0.9)Ce(1)Co(0.1), Mn(0.5)Ce(1)Co(0.5), Mn(0.1)Ce(1)Co(0.9), and Co(1)Ce(1), the Mn(0.9)Ce(1)Co(0.1) presents the best activation. The main intermediate products of degradation are benzoic acid and phenol. The apparent activation energy (E(a)) is 35.92 with 5% Mn(0.9)Ce(1)Co(0.1) as catalyst and 46.69 kJ/mol with no catalyst about the chemical oxygen demand (COD). Copyright © 2012 Elsevier B.V. All rights reserved.

ROLE OF TUNGSTEN IN THE AQUEOUS PHASE HYDRODEOXYGENATION OF ETHYLENE GLYCOL ON TUNGSTATED ZIRCONIA SUPPORTED PALLADIUM

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

Marin-Flores, Oscar G.; Karim, Ayman M.; Wang, Yong

2014-11-15

The focus of the present work was specifically on the elucidation of the role played by tungsten on the catalytic activity and selectivity of tungstated zirconia supported palladium (Pd-mWZ) for the aqueous phase hydrodeoxygenation (APHDO) of ethylene glycol (EG). Zirconia supported palladium (Pd-mZ) was used as reference. The catalysts were prepared via incipient wet impregnation and characterized using X-ray diffraction (XRD), temperature-programmed reduction (TPR), CO pulse chemisorption, CO-DRIFTS, ammonia temperature-programmed desorption (NH3-TPD) and pyridine adsorption. The presence of W results in larger Pd particles on supported Pd catalysts, i.e., 0.9 and 6.1 nm Pd particles are for Pd-mZ and Pd-mWZ,more » respectively. For comparison purposes, the activity of the catalytic materials used in this work was obtained using a well-defined set of operating conditions. The catalytic activity measurements show that the overall intrinsic activity of Pd particles on mWZ is 1.9 times higher than on mZ. APHDO process appears to be highly favored on Pd-mWZ whereas Pd-mZ exhibits a higher selectivity for reforming. This difference in terms of selectivity seems to be related to the high concentration of Brønsted acid sites and electron-deficient Pd species present on Pd-mWZ.« less

Comparing the catalytic oxidation of ethanol at the solid-gas and solid-liquid interfaces over size-controlled Pt nanoparticles: striking differences in kinetics and mechanism.

PubMed

Sapi, Andras; Liu, Fudong; Cai, Xiaojun; Thompson, Christopher M; Wang, Hailiang; An, Kwangjin; Krier, James M; Somorjai, Gabor A

2014-11-12

Pt nanoparticles with controlled size (2, 4, and 6 nm) are synthesized and tested in ethanol oxidation by molecular oxygen at 60 °C to acetaldehyde and carbon dioxide both in the gas and liquid phases. The turnover frequency of the reaction is ∼80 times faster, and the activation energy is ∼5 times higher at the gas-solid interface compared to the liquid-solid interface. The catalytic activity is highly dependent on the size of the Pt nanoparticles; however, the selectivity is not size sensitive. Acetaldehyde is the main product in both media, while twice as much carbon dioxide was observed in the gas phase compared to the liquid phase. Added water boosts the reaction in the liquid phase; however, it acts as an inhibitor in the gas phase. The more water vapor was added, the more carbon dioxide was formed in the gas phase, while the selectivity was not affected by the concentration of the water in the liquid phase. The differences in the reaction kinetics of the solid-gas and solid-liquid interfaces can be attributed to the molecular orientation deviation of the ethanol molecules on the Pt surface in the gas and liquid phases as evidenced by sum frequency generation vibrational spectroscopy.

Synthesis of Densely Packaged, Ultrasmall Pt02 Clusters within a Thioether-Functionalized MOF: Catalytic Activity in Industrial Reactions at Low Temperature.

PubMed

Mon, Marta; Rivero-Crespo, Miguel A; Ferrando-Soria, Jesús; Vidal-Moya, Alejandro; Boronat, Mercedes; Leyva-Pérez, Antonio; Corma, Avelino; Hernández-Garrido, Juan C; López-Haro, Miguel; Calvino, José J; Ragazzon, Giulio; Credi, Alberto; Armentano, Donatella; Pardo, Emilio

2018-05-22

The gram-scale synthesis, stabilization, and characterization of well-defined ultrasmall subnanometric catalytic clusters on solids is a challenge. The chemical synthesis and X-ray snapshots of Pt 0 2 clusters, homogenously distributed and densely packaged within the channels of a metal-organic framework, is presented. This hybrid material catalyzes efficiently, and even more importantly from an economic and environmental viewpoint, at low temperature (25 to 140 °C), energetically costly industrial reactions in the gas phase such as HCN production, CO 2 methanation, and alkene hydrogenations. These results open the way for the design of precisely defined catalytically active ultrasmall metal clusters in solids for technically easier, cheaper, and dramatically less-dangerous industrial reactions. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

NO—CO—O2 Reaction on a Metal Catalytic Surface using Eley—Rideal Mechanism

NASA Astrophysics Data System (ADS)

Waqar, Ahmad

2008-10-01

Interactions among the reacting species NO, CO and O2 on metal catalytic surfaces are studied by means of Monte Carlo simulation using the Eley-Rideal (ER) mechanism. The study of this three-component system is important for understanding of the reaction kinetics by varying the relative ratios of the reactants. It is found that contrary to the conventional Langmuir-Hinshelwood (LH) thermal mechanism in which two irreversible phase transitions are obtained between active states and poisoned states, a single phase transition is observed when the ER mechanism is combined with the LH mechanism. The phase diagrams of the surface coverage and the steady state production of CO2, N2 and N2 O are evaluated as a function of the partial pressures of the reactants in the gas phase. The continuous production of CO2 starts as soon as the CO pressure is switched on and the second order phase transition at the first critical point is eliminated, which is in agreement with the experimental findings.

The Catalytic and Non-catalytic Functions of the Brahma Chromatin-Remodeling Protein Collaborate to Fine-Tune Circadian Transcription in Drosophila

PubMed Central

Kwok, Rosanna S.; Li, Ying H.; Lei, Anna J.; Edery, Isaac; Chiu, Joanna C.

2015-01-01

Daily rhythms in gene expression play a critical role in the progression of circadian clocks, and are under regulation by transcription factor binding, histone modifications, RNA polymerase II (RNAPII) recruitment and elongation, and post-transcriptional mechanisms. Although previous studies have shown that clock-controlled genes exhibit rhythmic chromatin modifications, less is known about the functions performed by chromatin remodelers in animal clockwork. Here we have identified the Brahma (Brm) complex as a regulator of the Drosophila clock. In Drosophila, CLOCK (CLK) is the master transcriptional activator driving cyclical gene expression by participating in an auto-inhibitory feedback loop that involves stimulating the expression of the main negative regulators, period (per) and timeless (tim). BRM functions catalytically to increase nucleosome density at the promoters of per and tim, creating an overall restrictive chromatin landscape to limit transcriptional output during the active phase of cycling gene expression. In addition, the non-catalytic function of BRM regulates the level and binding of CLK to target promoters and maintains transient RNAPII stalling at the per promoter, likely by recruiting repressive and pausing factors. By disentangling its catalytic versus non-catalytic functions at the promoters of CLK target genes, we uncovered a multi-leveled mechanism in which BRM fine-tunes circadian transcription. PMID:26132408

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.

A metal–organic framework immobilised iridium pincer complex

DOE PAGES

Rimoldi, Martino; Nakamura, Akitake; Vermeulen, Nicolaas A.; ...

2016-05-10

An iridium pincer complex has been immobilised in the metal–organic framework NU-1000. The stable Ir-pincer modified NU-1000 is catalytically active in the hydrogenation of alkenes in condensed phase and under flow conditions.

[State of Fungal Lipases of Rhizopus microsporus, Penicillium sp. and Oospora lactis in Border Layers Water-Solid Phase and Factors Affecting Catalytic Properties of Enzymes].

PubMed

Khasanov, Kh T; Davranov, K; Rakhimov, M M

2015-01-01

We demonstrated that a change in the catalytic activity of fungal lipases synthesized by Rhizopus microsporus, Penicillium sp. and Oospora lactis and their ability to absorb on different sorbents depended on the nature of groups on the solid phase surface in the model systems water: lipid and water: solid phase. Thus, the stability of Penicillium sp. lipases increased 85% in the presence ofsorsilen or DEAE-cellulose, and 55% of their initial activity respectively was preserved. In the presence of silica gel and CM-cellulose, a decreased rate of lipid hydrolysis by Pseudomonas sp. enzymes was observed in water medium, and the hydrolysis rate increased by 2.4 and 1.5 times respectively in the presence of aminoaerosil and polykefamid. In an aqueous-alcohol medium, aminoaerosil and polykefamid decreased the rate of substrate hydrolysis by more than 30 times. The addition of aerosil to aqueous and aqueous-alcohol media resulted in an increase in the hydrolysis rate by 1.2-1.3 times. Sorsilen stabilized Penicillium sp. lipase activity at 40, 45, 50 and 55 degrees C. Either stabilization or inactivation of lipases was observed depending on the pH of the medium and the nature of chemical groups localized on the surface of solid phase. The synthetizing activity of lipases also changed depending on the conditions.

Synergistic Interaction within Bifunctional Ruthenium Nanoparticle/SILP Catalysts for the Selective Hydrodeoxygenation of Phenols.

PubMed

Luska, Kylie L; Migowski, Pedro; El Sayed, Sami; Leitner, Walter

2015-12-21

Ruthenium nanoparticles immobilized on acid-functionalized supported ionic liquid phases (Ru NPs@SILPs) act as efficient bifunctional catalysts in the hydrodeoxygenation of phenolic substrates under batch and continuous flow conditions. A synergistic interaction between the metal sites and acid groups within the bifunctional catalyst leads to enhanced catalytic activities for the overall transformation as compared to the individual steps catalyzed by the separate catalytic functionalities. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Influence of dopant substitution mechanism on catalytic properties within hierarchical architectures

PubMed Central

Newland, Stephanie H.; Sinkler, Wharton; Mezza, Thomas; Bare, Simon R.

2016-01-01

A range of hierarchically porous (HP) AlPO-5 catalysts, with isomorphously substituted transition metal ions, have been synthesized using an organosilane as a soft template. By employing a range of structural and spectroscopic characterization protocols, the properties of the dopant-substituted species within the HP architectures have been carefully evaluated. The resulting nature of the active site is shown to have a direct impact on the ensuing catalytic properties in the liquid-phase Beckmann rearrangement of cyclic ketones. PMID:27493563

Influence of dopant substitution mechanism on catalytic properties within hierarchical architectures

NASA Astrophysics Data System (ADS)

Newland, Stephanie H.; Sinkler, Wharton; Mezza, Thomas; Bare, Simon R.; Raja, Robert

2016-07-01

A range of hierarchically porous (HP) AlPO-5 catalysts, with isomorphously substituted transition metal ions, have been synthesized using an organosilane as a soft template. By employing a range of structural and spectroscopic characterization protocols, the properties of the dopant-substituted species within the HP architectures have been carefully evaluated. The resulting nature of the active site is shown to have a direct impact on the ensuing catalytic properties in the liquid-phase Beckmann rearrangement of cyclic ketones.

Hierarchical Porous Interlocked Polymeric Microcapsules: Sulfonic Acid Functionalization as Acid Catalysts

NASA Astrophysics Data System (ADS)

Wang, Xiaomei; Gu, Jinyan; Tian, Lei; Zhang, Xu

2017-03-01

Owing to their unique structural and surface properties, mesoporous microspheres are widely applied in the catalytic field. Generally, increasing the surface area of the specific active phase of the catalyst is a good method, which can achieve a higher catalytic activity through the fabrication of the corresponding catalytic microspheres with the smaller size and hollow structure. However, one of the major challenges in the use of hollow microspheres (microcapsules) as catalysts is their chemical and structural stability. Herein, the grape-like hypercrosslinked polystyrene hierarchical porous interlocked microcapsule (HPIM-HCL-PS) is fabricated by SiO2 colloidal crystals templates, whose structure is the combination of open mouthed structure, mesoporous nanostructure and interlocked architecture. Numerous microcapsules assembling together and forming the roughly grape-like microcapsule aggregates can enhance the structural stability and recyclability of these microcapsules. After undergoing the sulfonation, the sulfonated HPIM-HCL-PS is served as recyclable acid catalyst for condensation reaction between benzaldehyde and ethylene glycol (TOF = 793 h-1), moreover, exhibits superior activity, selectivity and recyclability.

The mechanisms of hydrothermal deconstruction of lignocellulose: New insights from thermal–analytical and complementary studies

PubMed Central

Ibbett, Roger; Gaddipati, Sanyasi; Davies, Scott; Hill, Sandra; Tucker, Greg

2011-01-01

Differential Scanning Calorimetry, Dynamic Mechanical Thermal Analysis, gravimetric and chemical techniques have been used to study hydrothermal reactions of straw biomass. Exothermic degradation initiates above 195 °C, due to breakdown of the xylose ring from hemicellulose, which may be similar to reactions occurring during the early stage pyrolysis of dry biomass, though activated at lower temperature through water mediation. The temperature and magnitude of the exotherm reduce with increasing acid concentration, suggesting a reduction in activation energy and a change in the balance of reaction pathways. The presence of xylan oligomers in auto-catalytic hydrolysates is believed to be due to a low rate constant rather than a specific reaction mechanism. The loss of the lignin glass transition indicates that the lignin phase is reorganised under high temperature auto-catalytic conditions, but remains partially intact under lower temperature acid-catalytic conditions. This shows that lignin degradation reactions are activated thermally but are not effectively catalysed by aqueous acid. PMID:21763128

Nanophase-separated Ni3Nb as an automobile exhaust catalyst.

PubMed

Tanabe, Toyokazu; Imai, Tsubasa; Tokunaga, Tomoharu; Arai, Shigeo; Yamamoto, Yuta; Ueda, Shigenori; Ramesh, Gubbala V; Nagao, Satoshi; Hirata, Hirohito; Matsumoto, Shin-Ichi; Fujita, Takeshi; Abe, Hideki

2017-05-01

Catalytic remediation of automobile exhaust has relied on precious metals (PMs) including platinum (Pt). Herein, we report that an intermetallic phase of Ni and niobium (Nb) ( i.e. , Ni 3 Nb) exhibits a significantly higher activity than that of Pt for the remediation of the most toxic gas in exhaust ( i.e. , nitrogen monoxide (NO)) in the presence of carbon monoxide (CO). When subjected to the exhaust-remediation atmosphere, Ni 3 Nb spontaneously evolves into a catalytically active nanophase-separated structure consisting of filamentous Ni networks (thickness < 10 nm) that are incorporated in a niobium oxide matrix ( i.e. , NbO x ( x < 5/2)). The exposure of the filamentous Ni promotes NO dissociation, CO oxidation and N 2 generation, and the NbO x matrix absorbs excessive nitrogen adatoms to retain the active Ni 0 sites at the metal/oxide interface. Furthermore, the NbO x matrix immobilizes the filamentous Ni at elevated temperatures to produce long-term and stable catalytic performance over hundreds of hours.

One-step fabrication of large-area ultrathin MoS2 nanofilms with high catalytic activity for photovoltaic devices.

PubMed

Liang, Jia; Li, Jia; Zhu, Hongfei; Han, Yuxiang; Wang, Yanrong; Wang, Caixing; Jin, Zhong; Zhang, Gengmin; Liu, Jie

2016-09-21

Here we report a facile one-step solution-phase process to directly grow ultrathin MoS2 nanofilms on a transparent conductive glass as a novel high-performance counter electrode for dye-sensitized solar cells. After an appropriate reaction time, the entire surface of the conductive glass substrate was uniformly covered by ultrathin MoS2 nanofilms with a thickness of only several stacked layers. Electrochemical impedance spectroscopy and cyclic voltammetry reveal that the MoS2 nanofilms possess excellent catalytic activity towards tri-iodide reduction. When used in dye-sensitized solar cells, the MoS2 nanofilms show an impressive energy conversion efficiency of 8.3%, which is higher than that of a Pt-based electrode and very promising to be a desirable alternative counter electrode. Considering their ultrathin thickness, superior catalytic activity, simple preparation process and low cost, the as-prepared MoS2 nanofilms with high photovoltaic performance are expected to be widely employed in dye-sensitized solar cells.

Ethylene Glycol Quenching of Nitrogenase Catalysis: An Electron Paramagnetic Resonance Spectroscopic Study of Nitrogenase Turnover States and CO Bonding.

PubMed

Hales, Brian J

2015-07-14

Most hydrophilic organic solvents inhibit enzymatic activity. Nitrogenase is shown to be approximately 3 times more sensitive to organic inhibition than most other soluble enzymes. Ethylene glycol (EG) is demonstrated to rapidly inhibit nitrogenase activity without uncoupling ATP hydrolysis. Our data suggest the mechanism of inhibition is EG's blocking of binding of MgATP to the nitrogenase Fe protein. EG quenching allows, for the first time, the observation of the relaxation of the intermediate reaction states at room temperature. Electron paramagnetic resonance (EPR) spectroscopy is used to monitor the room-temperature decay of the nitrogenase turnover states following EG quenching of catalytic activity. The return of the intermediate states to the resting state occurs in multiple phases over 2 h. During the initial stage, nitrogenase still possesses the ability to generate CO-induced EPR signals even though catalytic activity has ceased. During the last phase of relaxation, the one-electron reduced state of the MoFe protein (E1) relaxes to the resting state (E0) in a slow first-order reaction.

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

Camacho-Bunquin, Jeffrey; Shou, Heng; Aich, Payoli

An integrated atomic layer deposition-catalysis (I-ALD-CAT) tool was developed, combining an ALD manifold with a plug-flow reactor system for the synthesis of supported catalytic materials by ALD and immediate evaluation of catalyst reactivity using gas-phase probe reactions. The I-ALD-CAT system can deliver gaseous reagents comprised of 12 different metal ALD precursors, 4 oxidizing or reducing agents, and 4 catalytic reaction feeds to either of the two plug-flow reactors. The system can employ reactor pressures and temperatures in the range of 10-3–1 bar and 300–1000 K, respectively. The instrument is also equipped with a gas chromatograph and a mass spectrometer unitmore » for the detection and quantification of volatile species from ALD and catalytic reactions. In this report, we demonstrate the use of the I-ALD-CAT tool for the ALD of platinum active sites and Al2O3 overcoats, and evaluation of catalyst propylene hydrogenation activity.« less

Catalytic Ethanol Dehydration to Ethylene over Nanocrystalline χ- and γ-Al2O3 Catalysts.

PubMed

Janlamool, Jakrapan; Jongsomjit, Bunjerd

2017-01-01

The study is aimed to investigate the combination of nanocrystalline γ- and χ- alumina that displays the attractive chemical and physical properties for the catalytic dehydration of ethanol. The correlation between the acid density and ethanol conversion was observed. The high acid density apparently results in high catalytic activity, especially for the equally mixed γ- and χ- phase alumina (G50C50). In order to obtain a better understanding on how different catalysts would affect the ethylene yield, one of the most powerful techniques such as X-ray photoelectron spectroscopy (XPS) was performed. Hence, the different O 1s surface atoms can be identified and divided into three types including lattice oxygen (O, 530.7 eV), surface hydroxyl (OH, 532.1 eV) and lattice water (H 2 O, 532.9 eV). It was remarkably found that the large amount of O 1s surface atoms in lattice water can result in increased ethylene yield. In summary, the appearance of metastable χ-alumina structure exhibited better catalytic activity and ethylene yield than γ- alumina. Thus, the introduction of metastable χ- alumina structure into γ- alumina enhanced catalytic activity and ethylene yield. As the result, it was found that the G50C50 catalyst exhibits the ethylene yield (80%) at the lowest reaction temperature ca. 250°C among other catalysts.

Zeolite-encapsulated Co(II), Mn(II), Cu(II) and Cr(III) salen complexes as catalysts for efficient selective oxidation of benzyl alcohol

NASA Astrophysics Data System (ADS)

Li, F. H.; Bi, H.; Huang, D. X.; Zhang, M.; Song, Y. B.

2018-01-01

Co(II), Mn(II), Cu(II) and Cr(III) salen type complexes were synthesized in situ in Y zeolite by the reaction of ion-exchanged metal ions with the flexible ligand molecules that had diffused into the cavities. Data of characterization indicates the formation of metal salen complexes in the pores without affecting the zeolite framework structure, the absence of any extraneous species and the geometry of encapsulated complexes. The catalytic activity results show that Cosalcyen Y exhibited higher catalytic activity in the water phase selective oxidation of benzyl alcohol, which could be attributed to their geometry and the steric environment of the metal actives sites.

Boosted surface acidity in TiO2 and Al2O3-TiO2 nanotubes as catalytic supports

NASA Astrophysics Data System (ADS)

Camposeco, R.; Castillo, S.; Mejía-Centeno, Isidro; Navarrete, J.; Nava, N.

2015-11-01

In this study, titanate nanotubes (NT) and titanate nanotubes with alumina (NT-Al) were studied as solid acid catalytic supports to show the relationship between the kind of acidity and catalytic activity. The supports were characterized by XRD, TEM, FTIR, XPS, and tested in the SCR-NO with NH3. It was found that the amount of Brönsted acid sites was maintained and the Lewis acid sites were significantly affected by the addition of alumina (1, 3, 5 and 10 wt.%); such acidity was higher than that of the titanate nanotubes (NT) by two-fold. To confirm the formation of titanate nanotubes and titanate nanotubes with alumina, transmission electron microscopy (TEM) was used. X-ray diffraction (XRD) revealed the formation of the H2Ti4O9·H2O phase. All NT and NT-Al supports presented catalytic activity to remove NO with NH3 under lean conditions, confirming the presence of an important amount of Brönsted and Lewis acid sites in both NT and NT-Al supports.

Effect of calcination temperature of a copper ferrite synthesized by a sol-gel method on its structural characteristics and performance as Fenton catalyst to remove gallic acid from water.

PubMed

López-Ramón, María V; Álvarez, Miguel A; Moreno-Castilla, Carlos; Fontecha-Cámara, María A; Yebra-Rodríguez, África; Bailón-García, Esther

2018-02-01

A copper ferrite synthesized by a sol-gel combustion method was calcined at different temperatures up to 800°C, determining changes in its structural characteristics and magnetic measurements and studying its catalytic performance in gallic acid removal by Fenton reaction. The main objective was to study the effect of the calcination temperature of copper ferrite on its crystalline phase formation and transformation, activity and metal ion leaching. The cubic-to-tetragonal transformation of the spinel occurred via its reaction with the CuO phase, displacing Fe 3+ ions in B (octahedral) sites out of the spinel structure by the following reaction: 2Fe 3+ B +3CuO→Fe 2 O 3 +3Cu 2+ B . The catalysts showed superparamagnetic or substantial superparamagnetic behaviour. At higher calcination temperatures, catalyst activity was lower, and Cu ion leaching was markedly decreased. There was no Fe ion leaching with any catalyst. The as-prepared catalyst showed better catalytic performance than a commercial copper ferrite. Leached Cu ions acted as homogeneous catalysts, and their contribution to the overall removal mechanism was examined. Cu 2 O present in the as-prepared catalysts made only a small contribution to their activity. Finally, the reutilization of various catalysts was studied by performing different catalytic cycles. Copyright © 2017 Elsevier Inc. All rights reserved.

CONTROL OF INDUSTRIAL VOC (VOLATILE ORGANIC COMPOUND) EMISSIONS BY CATALYTIC INCINERATION. VOLUME 8. CATALYTIC INCINERATOR PERFORMANCE AT INDUSTRIAL SITE C-6

EPA Science Inventory

The report is part of a two-phase EPA effort to assess the performance, suitability, and costs of various technologies to control emissions of volatile organic compounds (VOCs). In Phase 1, information was assembled from the literature on the use and cost of using catalytic incin...

CONTROL OF INDUSTRIAL VOC (VOLATILE ORGANIC COMPOUND) EMISSIONS BY CATALYTIC INCINERATION. VOLUME 1. ASSESSMENT OF CATALYTIC INCINERATION AND COMPETING CONTROLS

EPA Science Inventory

The report is part of a two-phase EPA effort to assess the performance, suitability, and costs of various technologies to control emissions of volatile organic compounds (VOCs). In Phase 1, information was assembled from the literature on the use and cost of using catalytic incin...

CONTROL OF INDUSTRIAL VOC (VOLATILE ORGANIC COMPOUND) EMISSIONS BY CATALYTIC INCINERATION. VOLUME 7. CATALYTIC INCINERATOR PERFORMANCE AT INDUSTRIAL SITE C-5

EPA Science Inventory

The report is part of a two-phase EPA effort to assess the performance, suitability, and costs of various technologies to control emissions of volatile organic compounds (VOCs). In Phase 1, information was assembled from the literature on the use and cost of using catalytic incin...

CONTROL OF INDUSTRIAL VOC (VOLATILE ORGANIC COMPOUND) EMISSIONS BY CATALYTIC INCINERATION. VOLUME 5. CATALYTIC INCINERATOR PERFORMANCE AT INDUSTRIAL SITE C-3

EPA Science Inventory

The report is part of a two-phase EPA effort to assess the performance, suitability, and costs of various technologies to control emissions of volatile organic compounds (VOCs). In Phase 1, information was assembled from the literature on the use and cost of using catalytic incin...

Gas phase oxidation downstream of a catalytic combustor

NASA Technical Reports Server (NTRS)

Tien, J. S.; Anderson, D. N.

1979-01-01

Effect of the length available for gas-phase reactions downstream of the catalytic reactor on the emission of CO and unburned hydrocarbons was investigated. A premixed, prevaporized propane/air feed to a 12/cm/diameter catalytic/reactor test section was used. The catalytic reactor was made of four 2.5 cm long monolithic catalyst elements. Four water cooled gas sampling probes were located at positions between 0 and 22 cm downstream of the catalytic reactor. Measurements of unburned hydrocarbon, CO, and CO2 were made. Tests were performed with an inlet air temperature of 800 K, a reference velocity of 10 m/s, pressures of 3 and 600,000 Pa, and fuel air equivalence ratios of 0.14 to 0.24. For very lean mixtures, hydrocarbon emissions were high and CO continued to be formed downstream of the catalytic reactor. At the highest equivalence ratios tested, hydrocarbon levels were much lower and CO was oxidized to CO2 in the gas phase downstream. To achieve acceptable emissions, a downstream region several times longer than the catalytic reactor could be required.

Controlled synthesis of α-MnO{sub 2} nanowires and their catalytic performance for toluene combustion

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

Cheng, Gao; Yu, Lin, E-mail: gych@gdut.edu.cn; Lan, Bang

Highlights: • One-dimensional α-MnO{sub 2} nanowires were prepared by a facile hydrothermal route. • Shape and crystal phase of the products were controlled by tuning reaction conditions. • A possible formation mechanism of the α-MnO{sub 2} nanowires was discussed. • The α-MnO{sub 2} nanowires showed great catalytic activity for toluene combustion. - Abstract: α-MnO{sub 2} nanowires with a length about 6–10 μm and an average diameter of 20 nm were synthesized through a facile hydrothermal process without any templates or surfactants. The products were characterized by X-ray powder diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, hydrogenmore » temperature-programmed reduction techniques, X-ray photoelectron spectroscopy and surface area analysis. The effects of the hydrothermal temperature and the concentration of CH{sub 3}COOH on the crystal phase and morphology of the final products were studied in detail. The hydrothermal temperature and the concentration of CH{sub 3}COOH play crucial roles in determining the crystal phase and morphology of the products. The possible formation mechanism of the α-MnO{sub 2} nanowires was investigated and discussed. Additionally, the as-prepared α-MnO{sub 2} nanowires showed higher catalytic activity for toluene combustion than the commercial MnO{sub 2}, suggesting their potential applications in the elimination of volatile organic compounds.« less

Density Functional Theory Study of Oxygen Reduction Activity on Ultrathin Platinum Nanotubes

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

Matanovic, Ivana; Kent, Paul; Garzon, Fernando

2012-07-13

The structure, stability, and catalytic activity of a number of single- and double-wall platinum (n,m) nanotubes ranging in diameter from 0.3 to 2.0 nm were studied using plane-wave based density functional theory in the gas phase and water environment. The change in the catalytic activity toward the oxygen reduction reaction (ORR) with the size and chirality of the nanotube was studied by calculating equilibrium adsorption potentials for ORR intermediates and by constructing free energy diagrams in the ORR dissociative mechanism network. In addition, the stability of the platinum nanotubes is investigated in terms of electrochemical dissolution potentials and by determiningmore » the most stable state of the material as a function of pH and potential, as represented in Pourbaix diagrams. Our results show that the catalytic activity and the stability toward electrochemical dissolution depend greatly on the diameter and chirality of the nanotube. On the basis of the estimated overpotentials for ORR, we conclude that smaller, approximately 0.5 nm in diameter single-wall platinum nanotubes consistently show a huge, up to 400 mV larger overpotential than platinum, indicating very poor catalytic activity toward ORR. This is the result of substantial structural changes induced by the adsorption of any chemical species on these tubes. Single-wall n = m platinum nanotubes with a diameter larger than 1 nm have smaller ORR overpotentials than bulk platinum for up to 180 mV and thus show improved catalytic activity relative to bulk. We also predict that these nanotubes can endure the highest cell potentials but dissolution potentials are still for 110 mV lower than for the bulk, indicating a possible corrosion problem.« less

Novel Attrition-Resistant Fischer Tropsch Catalyst

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

Weast, Logan, E.; Staats, William, R.

2009-05-01

There is a strong national interest in the Fischer-Tropsch synthesis process because it offers the possibility of making liquid hydrocarbon fuels from reformed natural gas or coal and biomass gasification products. This project explored a new approach that had been developed to produce active, attrition-resistant Fischer-Tropsch catalysts that are based on glass-ceramic materials and technology. This novel approach represented a promising solution to the problem of reducing or eliminating catalyst attrition and maximizing catalytic activity, thus reducing costs. The technical objective of the Phase I work was to demonstrate that glass-ceramic based catalytic materials for Fischer-Tropsch synthesis have resistance tomore » catalytic deactivation and reduction of particle size superior to traditional supported Fischer-Tropsch catalyst materials. Additionally, these novel glass-ceramic-based materials were expected to exhibit catalytic activity similar to the traditional materials. If successfully developed, the attrition-resistant Fischer-Tropsch catalyst materials would be expected to result in significant technical, economic, and social benefits for both producers and public consumers of Fischer-Tropsch products such as liquid fuels from coal or biomass gasification. This program demonstrated the anticipated high attrition resistance of the glass-ceramic materials. However, the observed catalytic activity of the materials was not sufficient to justify further development at this time. Additional testing documented that a lack of pore volume in the glass-ceramic materials limited the amount of surface area available for catalysis and consequently limited catalytic activity. However, previous work on glass-ceramic catalysts to promote other reactions demonstrated that commercial levels of activity can be achieved, at least for those reactions. Therefore, we recommend that glass-ceramic materials be considered again as potential Fischer-Tropsch catalysts if it can be demonstrated that materials with adequate pore volume can be produced. During the attrition resistance tests, it was learned that the glass-ceramic materials are very abrasive. Attention should be paid in any further developmental efforts to the potential for these hard, abrasive materials to damage reactors.« less

Metal-organic cooperative catalysis in C-H and C-C bond activation and its concurrent recovery.

PubMed

Park, Young Jun; Park, Jung-Woo; Jun, Chul-Ho

2008-02-01

The development of an efficient catalytic activation (cleavage) system for C-H and C-C bonds is an important challenge in organic synthesis, because these bonds comprise a variety of organic molecules such as natural products, petroleum oils, and polymers on the earth. Among many elegant approaches utilizing transition metals to activate C-H and C-C bonds facilely, chelation-assisted protocols based on the coordinating ability of an organic moiety have attracted great attention, though they have often suffered from the need for an intact coordinating group in a substrate. In this Account, we describe our entire efforts to activate C-H or C-C bonds adjacent to carbonyl groups by employing a new concept of metal-organic cooperative catalysis (MOCC), which enables the temporal installation of a 2-aminopyridyl group into common aldehydes or ketones in a catalytic way. Consequently, a series of new catalytic reactions such as alcohol hydroacylation, oxo-ester synthesis, C-C triple bond cleavage, hydrative dimerization of alkynes, and skeletal rearrangements of cyclic ketones was realized through MOCC. In particular, in the quest for an optimized MOCC system composed of a Wilkinson's catalyst (Ph 3P) 3RhCl and an organic catalyst (2-amino-3-picoline), surprising efficiency enhancements could be achieved when benzoic acid and aniline were introduced as promoters for the aldimine formation process. Furthermore, a notable accomplishment of C-C bond activation has been made using 2-amino-3-picoline as a temporary chelating auxiliary in the reactions of unstrained ketones with various terminal olefins and Wilkinson's catalyst. In the case of seven-membered cyclic ketones, an interesting ring contraction to five- or six-membered ones takes place through skeletal rearrangements initiated by the C-C bond activation of MOCC. On the other hand, the fundamental advances of these catalytic systems into recyclable processes could be achieved by immobilizing both metal and organic components using a hydrogen-bonded self-assembled system as a catalyst support. This catalyst-recovery system provides a homogeneous phase at high temperature during the reaction and a heterogeneous phase at room temperature after the reaction. The product could be separated conveniently from the self-assembly support system by decanting the upper layer. The immobilized catalysts of both 2-aminopyridine and rhodium metal species sustained high catalytic activity for up to the eight catalytic reactions. In conclusion, the successful incorporation of an organocatalytic cycle into a transition metal catalyzed reaction led us to find MOCC for C-H and C-C bond activation. In addition, the hydrogen-bonded self-assembled support has been developed for an efficient and effective recovery system of homogeneous catalysts and could be successful in immobilizing both metal and organic catalysts.

Local reaction kinetics by imaging☆

PubMed Central

Suchorski, Yuri; Rupprechter, Günther

2016-01-01

In the present contribution we present an overview of our recent studies using the “kinetics by imaging” approach for CO oxidation on heterogeneous model systems. The method is based on the correlation of the PEEM image intensity with catalytic activity: scaled down to the μm-sized surface regions, such correlation allows simultaneous local kinetic measurements on differently oriented individual domains of a polycrystalline metal-foil, including the construction of local kinetic phase diagrams. This allows spatially- and component-resolved kinetic studies and, e.g., a direct comparison of inherent catalytic properties of Pt(hkl)- and Pd(hkl)-domains or supported μm-sized Pd-powder agglomerates, studies of the local catalytic ignition and the role of defects and grain boundaries in the local reaction kinetics. PMID:26865736

An evaluation of the vapor phase catalytic ammonia removal process for use in a Mars transit vehicle.

PubMed

Flynn, M; Borchers, B

1998-01-01

This article describes the design specification of the Vapor Phase Catalytic Ammonia Removal (VPCAR) process and the relative benefits of its utilization in a Mars Transit Vehicle application. The VPCAR process is a wastewater treatment technology that combines distillation with high-temperature catalytic oxidation of volatile impurities such as ammonia and organic compounds.

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

Zhu, Yuanyuan; Sushko, Peter V.; Melzer, Daniel

A novel pathway of increasing the surface density of catalytically active oxygen radical sites on a MoVTeNb oxide (M1 phase) catalyst during alkane oxidative dehydrogenation is reported. The novel sites form when a fraction of Te4+ is reduced and emitted from the M1 crystals under catalytic operating conditions, without compromising structural integrity of the catalyst framework. Density functional theory calculations show this Te reduction induces multiple inter-related electron transfers, and the associated cooperative effects lead to the formation of O- radicals. The in situ observations identify complex dynamic changes in the catalyst on an atomistic level, highlighting a new waymore » to tailor structure and dynamics for highly active catalysts.« less

Development of Vapor-Phase Catalytic Ammonia Removal System

NASA Technical Reports Server (NTRS)

Flynn, Michael; Fisher, John; Kiss, Mark; Borchers, Bruce; Tleimat, Badawi; Tleimat, Maher; Quinn, Gregory; Fort, James; Nalette, Tim; Baker, Gale;

Thermal behavior and catalytic activity in naphthalene destruction of Ce-, Zr- and Mn-containing oxide layers on titanium

NASA Astrophysics Data System (ADS)

Vasilyeva, Marina S.; Rudnev, Vladimir S.; Wiedenmann, Florian; Wybornov, Svetlana; Yarovaya, Tatyana P.; Jiang, Xin

2011-11-01

The present paper is devoted to studies of the composition and surface structure, including those after annealing at high temperatures, and catalytic activity in the reaction of naphthalene destruction of Ce-, Zr- and Mn-containing oxide layers on titanium obtained by means of the plasma electrolytic oxidation (PEO) method. The composition and structure of the obtained systems were investigated using the methods of X-ray phase and energy dispersive analysis and scanning electron microscopy (SEM). It was demonstrated that Ce- and Zr- containing structures had relatively high thermal stability: their element and phase compositions and surface structure underwent virtually no changes after annealing in the temperature range 600-800 °C. Annealing of Ce- and Zr-containing coatings in the temperature range 850-900 °C resulted in substantial changes of their surface composition and structure: a relatively homogeneous and porous surface becomes coated by large pole-like crystals. The catalytic studies showed rather high activity of Ce- and Zr-containing coatings in the reaction of naphthalene destruction at temperatures up to 850 °C. Mn-containing structures of the type MnOx + SiO2 + TiO2/Ti have a well-developed surface coated by “nano-whiskers”. The phase composition and surface structure of manganese-containing layers changes dramatically in the course of thermal treatment. After annealing above 600 °C nano-whiskers vanish with formation of molten structures on the surface. The Mn-containing oxide systems demonstrated lower conversion degrees than the Ce- and Zr-containing coatings, which can be attributed to substantial surface modification and formation of molten manganese silicates at high temperatures.

A new three-phase heterocrystal catalysts and their superior treatment efficiency for tetracycline

NASA Astrophysics Data System (ADS)

Wang, Feng-Rui; Sun, Hui-Ping; Wang, Yan; Liu, Jin-Ku; Fang, Yi; Wang, Jian-Dong

An easy recyclable and interesting Ag3PO4@Pt@TiO2 (APTP) three-phase heterocrystal chains were self-assembled by the cohesive action and chemical construction of polyvinylpyrrolidone (PVP). We found that a new electron-hole transmission path has been built via the rematch of the band structure of Ag3PO4, Pt and TiO2 which extends the light absorption and promoted the electron-hole separation to treat the antibiotic residues in the water. Based on the thorough investigations, a new catalytic material was provided for antibiotics degradation. The catalytic activity of APTP toward the degradation of tetracycline solution was enhanced by 166.67% and the stability increased remarkably compared with pure Ag3PO4 through the integration of different functional components.

2D and 3D imaging of the gas phase close to an operating model catalyst by planar laser induced fluorescence

NASA Astrophysics Data System (ADS)

Blomberg, Sara; Zhou, Jianfeng; Gustafson, Johan; Zetterberg, Johan; Lundgren, Edvin

2016-11-01

In recent years, efforts have been made in catalysis related surface science studies to explore the possibilities to perform experiments at conditions closer to those of a technical catalyst, in particular at increased pressures. Techniques such as high pressure scanning tunneling/atomic force microscopy (HPSTM/AFM), near ambient pressure x-ray photoemission spectroscopy (NAPXPS), surface x-ray diffraction (SXRD) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) at semi-realistic conditions have been used to study the surface structure of model catalysts under reaction conditions, combined with simultaneous mass spectrometry (MS). These studies have provided an increased understanding of the surface dynamics and the structure of the active phase of surfaces and nano particles as a reaction occurs, providing novel information on the structure/activity relationship. However, the surface structure detected during the reaction is sensitive to the composition of the gas phase close to the catalyst surface. Therefore, the catalytic activity of the sample itself will act as a gas-source or gas-sink, and will affect the surface structure, which in turn may complicate the assignment of the active phase. For this reason, we have applied planar laser induced fluorescence (PLIF) to the gas phase in the vicinity of an active model catalysts. Our measurements demonstrate that the gas composition differs significantly close to the catalyst and at the position of the MS, which indeed should have a profound effect on the surface structure. However, PLIF applied to catalytic reactions presents several beneficial properties in addition to investigate the effect of the catalyst on the effective gas composition close to the model catalyst. The high spatial and temporal resolution of PLIF provides a unique tool to visualize the on-set of catalytic reactions and to compare different model catalysts in the same reactive environment. The technique can be applied to a large number of molecules thanks to the technical development of lasers and detectors over the last decades, and is a complementary and visual alternative to traditional MS to be used in environments difficult to asses with MS. In this article we will review general considerations when performing PLIF experiments, our experimental set-up for PLIF and discuss relevant examples of PLIF applied to catalysis.

Influence of the physico-chemical properties of CeO 2-ZrO 2 mixed oxides on the catalytic oxidation of NO to NO 2

NASA Astrophysics Data System (ADS)

Atribak, Idriss; Guillén-Hurtado, Noelia; Bueno-López, Agustín; García-García, Avelina

2010-10-01

Commercial and home-made Ce-Zr catalysts prepared by co-precipitation were characterised by XRD, Raman spectroscopy, N 2 adsorption at -196 °C and XPS, and were tested for NO oxidation to NO 2. Among the different physico-chemical properties characterised, the surface composition seems to be the most relevant one in order to explain the NO oxidation capacity of these Ce-Zr catalysts. As a general trend, Ce-Zr catalysts with a cerium-rich surface, that is, high XPS-measured Ce/Zr atomic surface ratios, are more active than those with a Zr-enriched surface. The decrease in catalytic activity of the Ce-Zr mixed oxided upon calcinations at 800 °C with regard to 500 °C is mainly attributed to the decrease in Ce/Zr surface ratio, that is, to the surface segregation of Zr. The phase composition (cubic or t'' for Ce-rich compositions) seems not to be a direct effect on the catalytic activity for NO oxidation in the range of compositions tested. However, the formation of a proper solid solution prevents important surface segregation of Zr upon calcinations at high temperature. The effect of the BET surface area in the catalytic activity for NO oxidation of Ce-Zr mixed oxides is minor in comparison with the effect of the Ce/Zr surface ratio.

CO oxidation on gold-supported iron oxides: New insights into strong oxide–metal interactions

DOE PAGES

Yu, Liang; Liu, Yun; Yang, Fan; ...

2015-07-14

Very active FeO x–Au catalysts for CO oxidation are obtained after depositing nanoparticles of FeO, Fe 3O 4, and Fe 2O 3 on a Au(111) substrate. Neither FeO nor Fe 2O 3 is stable under the reaction conditions. Under an environment of CO/O 2, they undergo oxidation (FeO) or reduction (Fe 2O 3) to yield nanoparticles of Fe 3O 4 that are not formed in a bulk phase. Using a combined experimental and theoretical approach, we show a strong oxide–metal interaction (SOMI) between Fe 3O 4 nanostructures and Au(111), which gives the oxide special properties, allows the formation of anmore » active phase, and provides a unique interface to facilitate a catalytic reaction. This work highlights the important role that the SOMI can play in enhancing the catalytic performance of the oxide component in metal–oxide catalysts.« less

A multifunctional biphasic water splitting catalyst tailored for integration with high-performance semiconductor photoanodes

NASA Astrophysics Data System (ADS)

Yang, Jinhui; Cooper, Jason K.; Toma, Francesca M.; Walczak, Karl A.; Favaro, Marco; Beeman, Jeffrey W.; Hess, Lucas H.; Wang, Cheng; Zhu, Chenhui; Gul, Sheraz; Yano, Junko; Kisielowski, Christian; Schwartzberg, Adam; Sharp, Ian D.

2017-03-01

Artificial photosystems are advanced by the development of conformal catalytic materials that promote desired chemical transformations, while also maintaining stability and minimizing parasitic light absorption for integration on surfaces of semiconductor light absorbers. Here, we demonstrate that multifunctional, nanoscale catalysts that enable high-performance photoelectrochemical energy conversion can be engineered by plasma-enhanced atomic layer deposition. The collective properties of tailored Co3O4/Co(OH)2 thin films simultaneously provide high activity for water splitting, permit efficient interfacial charge transport from semiconductor substrates, and enhance durability of chemically sensitive interfaces. These films comprise compact and continuous nanocrystalline Co3O4 spinel that is impervious to phase transformation and impermeable to ions, thereby providing effective protection of the underlying substrate. Moreover, a secondary phase of structurally disordered and chemically labile Co(OH)2 is introduced to ensure a high concentration of catalytically active sites. Application of this coating to photovoltaic p+n-Si junctions yields best reported performance characteristics for crystalline Si photoanodes.

Multi-component Fe–Ni hydroxide nanocatalyst for oxygen evolution and methanol oxidation reactions under alkaline conditions

DOE PAGES

Candelaria, Stephanie L.; Bedford, Nicholas M.; Woehl, Taylor J.; ...

2016-11-29

Here, iron-incorporated nickel-based materials show promise as catalysts for the oxygen evolution reac-tion (OER) half-reaction of water electrolysis. Nickel has also exhibited high catalytic activity for methanol oxidation, particularly when in the form of a bimetallic catalyst. In this work, bimetallic iron-nickel nanoparticles were synthesized using a multi-step procedure in water under ambient conditions. When compared to monometallic iron and nickel nanoparticles, Fe-Ni nanoparticles show enhanced catalytic activity for both OER and methanol oxidation under alkaline conditions. At 1 mA/cm 2, the overpotential for monometallic iron and nickel nanoparticles was 421 mV and 476 mV, respectively, while the bimetallic Fe-Nimore » nanoparticles had a greatly reduced overpotential of 256 mV. At 10 mA/cm 2, bimetallic Fe-Ni nanoparticles had an overpotential of 311 mV. Spec-troscopy characterization suggests that the primary phase of nickel in Fe-Ni nanoparticles is the more disordered alpha phase of nickel hydroxide.« less

Size-dependent ROS production by palladium and nickel nanoparticles in cellular and acellular environments - An indication for the catalytic nature of their interactions.

PubMed

Neubauer, Nicole; Palomaeki, Jaana; Karisola, Piia; Alenius, Harri; Kasper, Gerhard

2015-01-01

Palladium and nickel nanoparticles with variable but narrowly defined primary particle sizes in the range of 4-27 nm were investigated toward their catalytic activity and their ability to produce reactive oxygen species (ROS). The agglomerate size in the gas phase was between 50 and 150 nm, after transfer into solution probably larger. The catalytic activity was measured on the basis of CO oxidation to CO2. The formation of ROS was determined after transferring the particles into phosphate buffered saline (PBS), via the 2',7'-dichlorofluorescein method in a cell-free environment and with THP-1 cells. Activities were normalized with regard to catalyst surface area to enable a meaningful comparison of size effects. The solubility was measured for both materials and found to be 2 µg/ml for Ni and below the detection limit of 0.8 µg/ml for Pd. In the concentration range of about 4-250 µg/ml both materials induced a significant production of ROS in both acellular and cellular environments, with palladium being more active than nickel by several orders of magnitude. On an equal surface area concentration basis, both acellular and cellular ROS production showed a pronounced dependence on the primary particle size, with a maximum in the vicinity of 12 nm. The surface-specific catalytic activity also had a maximum at that size range. The correlation of these size effects is both surprising and - in combination with the poor solubility of palladium and nickel in PBS solution - a strong argument in favor of a particulate, catalytic mechanism for ROS production.

Transient Catalytic Combustor Model With Detailed Gas and Surface Chemistry

NASA Technical Reports Server (NTRS)

Struk, Peter M.; Dietrich, Daniel L.; Mellish, Benjamin P.; Miller, Fletcher J.; Tien, James S.

2005-01-01

In this work, we numerically investigate the transient combustion of a premixed gas mixture in a narrow, perfectly-insulated, catalytic channel which can represent an interior channel of a catalytic monolith. The model assumes a quasi-steady gas-phase and a transient, thermally thin solid phase. The gas phase is one-dimensional, but it does account for heat and mass transfer in a direction perpendicular to the flow via appropriate heat and mass transfer coefficients. The model neglects axial conduction in both the gas and in the solid. The model includes both detailed gas-phase reactions and catalytic surface reactions. The reactants modeled so far include lean mixtures of dry CO and CO/H2 mixtures, with pure oxygen as the oxidizer. The results include transient computations of light-off and system response to inlet condition variations. In some cases, the model predicts two different steady-state solutions depending on whether the channel is initially hot or cold. Additionally, the model suggests that the catalytic ignition of CO/O2 mixtures is extremely sensitive to small variations of inlet equivalence ratios and parts per million levels of H2.

Characterization and profiling of hepatic cytochromes P450 and phase II xenobiotic-metabolizing enzymes in beluga whales (Delphinapterus leucas) from the St. Lawrence River Estuary and the Canadian Arctic.

PubMed

McKinney, Melissa A; Arukwe, Augustine; De Guise, Sylvain; Martineau, Daniel; Béland, Pierre; Dallaire, André; Lair, Stéphane; Lebeuf, Michel; Letcher, Robert J

2004-07-30

Cytochromes P450 (CYP, phase I) and conjugating (phase II) enzymes can be induced by and influence the toxicokinetics (metabolism) and toxicity of xenobiotic contaminants in exposed organisms. Beluga whale (Delphinapterus leucas) from the endangered St. Lawrence (SL) River Estuary population exhibit deleterious health effects and various severe pathologies that have been associated with contaminant exposure. In contrast, such effects (e.g. reproductive and immunological impairment) are generally less frequent in less exposed populations in the Canadian Arctic (CA). In the present study, opportunistic sampling resulted in the collection immediately after death of liver tissue from a single female neonate SL beluga (SL6) and male and female CA beluga (n=10) from the Arviat region of western Hudson Bay, in addition to sampling of stranded carcasses of male and female SL beluga (n=5) at least 12 h postmortem. We immunologically characterized cross-reactive proteins of hepatic microsomal CYP1A, CYP2B, CYP3A, CYP2E, epoxide hydrolase (EH) and uridine diphosphoglucuronosyl transferase (UDPGT) isozymes. Cross-reactive proteins were found in all SL and CA beluga using anti-rat CYP1A1, anti-rainbow trout CYP3A, anti-human CYP2E1, anti-rabbit EH and anti-human UDPGT1A1 polyclonal antibodies (Abs), whereas faintly cross-reactive CYP2B proteins were only found in SL6 and the CA samples using an anti-rabbit CYP2B1 Ab. In corresponding catalytic activity assessments, only SL6 and all CA beluga microsomal samples exhibited CYP1A-mediated 7-ethoxyresorufin O-deethylase (EROD) activity (51-260 pmol/mg/min), CYP3A-mediated activity (113-899 pmol/mg/min) based on the formation of 6beta-hydroxytestosterone using a testosterone hydroxylase assay, and UDPGT activity (830-4956 pmol/mg/min) based on 1-naphthylglucuronide formation. The marginal cross-reactivity with the anti-CYP2B1 Ab and lack of catalytically measurable hydroxytestosterone isomers associated with CYP2B-type activity in all the SL and CA animals is suggestive of low CYP2B-type enzyme expression in beluga. The absence of measurable total P450 enzyme levels and catalytic activities in samples from the stranded SL belugas suggested catalytically inactive enzymes as a consequence of tissue degradation related due to the time delay of sample collection after death. However, all SL and CA animals demonstrated similar, immunologically cross-reactive phase I and II hepatic enzyme profiles, which is suggestive of the importance of metabolism in the toxicokinetics and fate of xenobiotics in animals from both populations Copyright 2004 Elsevier B.V.

Selective synthesis of vitamin K3 over mesoporous NbSBA-15 catalysts synthesized by an efficient hydrothermal method.

PubMed

Selvaraj, M; Park, D-W; Kim, I; Kawi, S; Ha, C S

2012-08-28

Well hexagonally ordered NbSBA-15 catalysts synthesized by an efficient hydrothermal method were used, for the first time, for the selective synthesis of vitamin K(3) by liquid-phase oxidation of 2-methyl-1-naphthol (2MN1-OH) under various reaction conditions. The recyclable NbSBA-15 catalysts were also reused to find their catalytic activities. To investigate the leaching of non-framework niobium species on the surface of silica networks, the results of original and recyclable NbSBA-15 catalysts were correlated and compared. To find an optimum condition for the selective synthesis of vitamin K(3), the washed NbSBA-15(2.2pH) was extensively used in this reaction with various reaction parameters such as temperature, time and ratios of reactant (2M1N-OH to H(2)O(2)), and the obtained results were also demonstrated. Additionally, the liquid-phase oxidation of 2M1N-OH was carried out with different solvents to find the best solvent with a good catalytic activity. Based on the all catalytic studies, the vitamin K(3) selectivity (97.3%) is higher in NbSBA-15(2.2pH) than that of other NbSBA-15 catalysts, and the NbSBA-15(2.2pH) is found to be a highly active and eco-friendly heterogeneous catalyst for the selective synthesis of vitamin K(3).

Preparation and characterization of nanostructured metal oxides for application to biomass upgrading Polar (111) metal oxide surfaces for pyrolysis oil upgrading and lignin depolymerization

NASA Astrophysics Data System (ADS)

Finch, Kenneth

2013-01-01

Pyrolysis oil, or bio-oil, is one of the most promising methods to upgrade a variety of biomass to transportation fuels. Moving toward a more "green" catalytic process requires heterogeneous catalysis over homogeneous catalysis to avoid extraction solvent waste. Nanoscale catalysts are showing great promise due to their high surface area and unusual surfaces. Base catalyzed condensation reactions occur much quicker than acid catalyzed condensation reactions. However, MgO is slightly soluble in water and is susceptible to degradation by acidic environments, similar to those found in fast-pyrolysis oil. Magnesium oxide (111) has a highly active Lewis base surface, which can catalyze Claisen-Schmidt condensation reactions in the organic phase. It has been shown previously that carbon coating a catalyst, such as a metal oxide, provides integrity while leaving the catalytic activity intact. Here, carbon-coated MgO(111) will be discussed with regards to synthesis, characterization and application to bio-oil upgrading through model compounds. Raman spectroscopy and HR-TEM are used to characterize the thickness and carbon-bonding environment of the carbon coating. Propanal self-condensation reactions have been conducted in the aqueous phase with varying amounts of acetic acid present. Quantitative analysis by gas chromatography was completed to determine the catalytic activity of CC-MgO(111). ICP-OES analysis has been conducted to measure the magnesium concentration in the product solution and give insight into the leaching of the catalyst into the reaction solution.

Chemical imaging of Fischer-Tropsch catalysts under operating conditions

PubMed Central

Price, Stephen W. T.; Martin, David J.; Parsons, Aaron D.; Sławiński, Wojciech A.; Vamvakeros, Antonios; Keylock, Stephen J.; Beale, Andrew M.; Mosselmans, J. Frederick W.

2017-01-01

Although we often understand empirically what constitutes an active catalyst, there is still much to be understood fundamentally about how catalytic performance is influenced by formulation. Catalysts are often designed to have a microstructure and nanostructure that can influence performance but that is rarely considered when correlating structure with function. Fischer-Tropsch synthesis (FTS) is a well-known and potentially sustainable technology for converting synthetic natural gas (“syngas”: CO + H2) into functional hydrocarbons, such as sulfur- and aromatic-free fuel and high-value wax products. FTS catalysts typically contain Co or Fe nanoparticles, which are often optimized in terms of size/composition for a particular catalytic performance. We use a novel, “multimodal” tomographic approach to studying active Co-based catalysts under operando conditions, revealing how a simple parameter, such as the order of addition of metal precursors and promoters, affects the spatial distribution of the elements as well as their physicochemical properties, that is, crystalline phase and crystallite size during catalyst activation and operation. We show in particular how the order of addition affects the crystallinity of the TiO2 anatase phase, which in turn leads to the formation of highly intergrown cubic close-packed/hexagonal close-packed Co nanoparticles that are very reactive, exhibiting high CO conversion. This work highlights the importance of operando microtomography to understand the evolution of chemical species and their spatial distribution before any concrete understanding of impact on catalytic performance can be realized. PMID:28345057

Synthesis of three-dimensional reduced graphene oxide layer supported cobalt nanocrystals and their high catalytic activity in F-T CO2 hydrogenation.

PubMed

He, Fei; Niu, Na; Qu, Fengyu; Wei, Shuquan; Chen, Yujin; Gai, Shili; Gao, Peng; Wang, Yan; Yang, Piaoping

2013-09-21

The reduced graphene oxide (rGO) supported cobalt nanocrystals have been synthesized through an in situ crystal growth method using Co(acac)2 under solvothermal conditions by using DMF as the solvent. By carefully controlling the reaction temperature, the phase transition of the cobalt nanocrystals from the cubic phase to the hexagonal phase has been achieved. Moreover, the microscopic structure and morphology as well as the reduction process of the composite have been investigated in detail. It is found that oxygen-containing functional groups on the graphene oxide (GO) can greatly influence the formation process of the Co nanocrystals by binding the Co(2+) cations dissociated from the Co(acac)2 in the initial reaction solution at 220 °C, leading to the 3D reticular structure of the composite. Furthermore, this is the first attempt to use a Co/rGO composite as the catalyst in the F-T CO2 hydrogenation process. The catalysis testing results reveal that the as-synthesized 3D structured composite exhibits ideal catalytic activity and good stability, which may greatly extend the scope of applications for this kind of graphene-based metal hybrid material.

Liquid-Phase Catalytic Transfer Hydrogenation of Furfural over Homogeneous Lewis Acid-Ru/C Catalysts.

PubMed

Panagiotopoulou, Paraskevi; Martin, Nickolas; Vlachos, Dionisios G

2015-06-22

The catalytic performance of homogeneous Lewis acid catalysts and their interaction with Ru/C catalyst are studied in the catalytic transfer hydrogenation of furfural by using 2-propanol as a solvent and hydrogen donor. We find that Lewis acid catalysts hydrogenate the furfural to furfuryl alcohol, which is then etherified with 2-propanol. The catalytic activity is correlated with an empirical scale of Lewis acid strength and exhibits a volcano behavior. Lanthanides are the most active, with DyCl3 giving complete furfural conversion and a 97 % yield of furfuryl alcohol at 180 °C after 3 h. The combination of Lewis acid and Ru/C catalysts results in synergy for the stronger Lewis acid catalysts, with a significant increase in the furfural conversion and methyl furan yield. Optimum results are obtained by using Ru/C combined with VCl3 , AlCl3 , SnCl4 , YbCl3 , and RuCl3 . Our results indicate that the combination of Lewis acid/metal catalysts is a general strategy for performing tandem reactions in the upgrade of furans. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Camacho-Bunquin, Jeffrey; Shou, Heng; Marshall, Christopher L.

An integrated atomic layer deposition synthesis-catalysis (I-ALD-CAT) tool was developed. It combines an ALD manifold in-line with a plug-flow reactor system for the synthesis of supported catalytic materials by ALD and immediate evaluation of catalyst reactivity using gas-phase probe reactions. The I-ALD-CAT delivery system consists of 12 different metal ALD precursor channels, 4 oxidizing or reducing agents, and 4 catalytic reaction feeds to either of the two plug-flow reactors. The system can employ reactor pressures and temperatures in the range of 10{sup −3} to 1 bar and 300–1000 K, respectively. The instrument is also equipped with a gas chromatograph andmore » a mass spectrometer unit for the detection and quantification of volatile species from ALD and catalytic reactions. In this report, we demonstrate the use of the I-ALD-CAT tool for the synthesis of platinum active sites and Al{sub 2}O{sub 3} overcoats, and evaluation of catalyst propylene hydrogenation activity.« less

Visualizing the chain-flipping mechanism in fatty-acid biosynthesis

DOE PAGES

Beld, Joris; Cang, Hu; Burkart, Michael D.

2014-10-29

The acyl carrier protein (ACP) from fatty acid synthases sequesters elongating products within its hydrophobic core, but this dynamic mechanism remains poorly understood. In this paper, we exploited solvatochromic pantetheine probes attached to ACP that fluoresce when sequestered. The addition of a catalytic partner lures the cargo out of the ACP and into the active site of the enzyme, thus enhancing fluorescence to reveal the elusive chain-flipping mechanism. This activity was confirmed by the use of a dual solvatochromic cross-linking probe and solution-phase NMR spectroscopy. Finally, the chain-flipping mechanism was visualized by single-molecule fluorescence techniques, thus demonstrating specificity between themore » Escherichia coli ACP and its ketoacyl synthase catalytic partner KASII.« less

A novel approach of solid waste management via aromatization using multiphase catalytic pyrolysis of waste polyethylene.

PubMed

Gaurh, Pramendra; Pramanik, Hiralal

2018-01-01

A new and innovative approach was adopted to increase the yield of aromatics like, benzene, toluene and xylene (BTX) in the catalytic pyrolysis of waste polyethylene (PE). The BTX content was significantly increased due to effective interaction between catalystZSM-5 and target molecules i.e., lower paraffins within the reactor. The thermal and catalytic pyrolysis both were performed in a specially designed semi-batch reactor at the temperature range of 500 °C-800 °C. Catalytic pyrolysis were performed in three different phases within the reactor batch by batch systematically, keeping the catalyst in A type- vapor phase, B type- liquid phase and C type- vapor and liquid phase (multiphase), respectively. Total aromatics (BTX) of 6.54 wt% was obtained for thermal pyrolysis at a temperature of 700 °C. In contrary, for the catalytic pyrolysis A, B and C types reactor arrangement, the aromatic (BTX) contents were progressively increased, nearly 6 times from 6.54 wt% (thermal pyrolysis) to 35.06 wt% for C-type/multiphase (liquid and vapor phase). The pyrolysis oil were characterized using GC-FID, FT-IR, ASTM distillation and carbon residue test to evaluate its end use and aromatic content. Copyright © 2017 Elsevier Ltd. All rights reserved.

Systematic study on the influence of the morphology of α-MoO{sub 3} in the selective oxidation of propylene

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

Schuh, Kirsten; Kleist, Wolfgang; Høj, Martin

2015-08-15

A variety of morphologically different α-MoO{sub 3} samples were prepared by hydrothermal synthesis and applied in the selective oxidation of propylene. Their catalytic performance was compared to α-MoO{sub 3} prepared by flame spray pyrolysis (FSP) and a classical synthesis route. Hydrothermal synthesis from ammonium heptamolybdate (AHM) and nitric acid at pH 1–2 led to ammonium containing molybdenum oxide phases that were completely transformed into α-MoO{sub 3} after calcination at 550 °C. A one-step synthesis of α-MoO{sub 3} rods was possible starting from MoO{sub 3}·2H{sub 2}O with acetic acid or nitric acid and from AHM with nitric acid at 180 °C.more » Particularly, if nitric acid was used during synthesis, the rod-like morphology of the samples could be stabilized during calcination at 550 °C and the following catalytic activity tests, which was beneficial for the catalytic performance in propylene oxidation. Characterization studies using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy showed that those samples, which retained their rod-like morphology during the activity tests, yielded the highest propylene conversion. - Graphical abstract: Hydrothermal synthesis from MoO{sub 3}·2H{sub 2}O in the presence of HNO{sub 3} led to rod-shaped particles which mainly expose (1 0 0) facets which are the most active surfaces. - Highlights: • Hydrothermal synthesis of MoO3 resulted in either rod or slab shaped particles depending on pH. • At pH<0 rods stable towards calcination and catalytic activity testing were formed. • Rod shaped particles had significantly higher activity than slab shaped ones. • The rod shaped particles mainly expose the (1 0 0) facets which are the most active surfaces. • Total surface area is not main determining factor for catalytic activity.« less

Exploiting basic principles to control the selectivity of the vapor phase catalytic oxidative cross-coupling of primary alcohols over nanoporous gold catalysts

DOE PAGES

Wang, Lu-Cun; Stowers, Kara J.; Zugic, Branko; ...

2015-05-20

It is important to achieve high selectivity for high volume chemical synthesis in order to lower energy consumption through reduction in waste. Here, we report the selective synthesis of methyl esters—methyl acetate and methyl butyrate—through catalytic O 2-assisted cross-coupling of methanol with ethanol or 1-butanol using activated, support-free nanoporous gold (npAu). Both well-controlled studies on ingots in UHV and experiments under ambient pressure catalytic conditions on both ingots and microspherical hollow shell catalysts reveal guiding principles for controlling selectivity. Under UHV conditions, the ester products of the cross-coupling of methanol with both ethanol and 1-butanol evolve near room temperature inmore » temperature-programmed reaction studies, indicating that the reactions occur facilely. Furthermore, under steady-state catalytic operation, high stable activity was observed for cross-coupling in flowing gaseous reactant mixtures at atmospheric pressure and 423 K with negligible combustion. Optimum selectivity for cross-coupling is obtained in methanol-rich mixtures due to a combination of two factors: (1) the relative coverage of the respective alkoxys and (2) the relative facility of their β-H elimination. The relative coverage of the alkoxys is governed by van der Waal’s interactions between the alkyl groups and the surface; here, we demonstrate the importance of these weak interactions in a steady-state catalytic process.« less

Gas-Phase Dimerization of Ethylene under Mild Conditions Catalyzed by MOF Materials Containing (bpy)Ni II Complexes

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

Madrahimov, Sherzod T.; Gallagher, James R.; Zhang, Guanghui

2015-10-09

NU-1000-(bpy)Ni-II, a highly porous MOF material possessing well-defined (bpy)Ni-II moieties, was prepared through solvent-assisted ligand incorporation (SALI). Treatment with Et2AlCl affords a single-site catalyst with excellent catalytic activity for ethylene dimerization (intrinsic activity for butenes that is up to an order of magnitude higher than the corresponding (bpy)NiCl2 homogeneous analogue) and stability (can be reused at least three times). The high porosity of this catalyst results in outstanding levels of activity at ambient temperature in gas-phase ethylene dimerization reactions, both under batch and continuous flow conditions.

Preparation, Characterization and Photocatalytic Activity of Ag/TiO2 Nanoparticle Semiconductor Catalysts

NASA Astrophysics Data System (ADS)

Zhang, Yaoyao; Li, Mengyao; Guo, Yinli

2018-01-01

A series of Ag-doped TiO2 powder photocatalysts were prepared by the sol-gel method. The phase structure and morphology of the samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The persistent organic pollutant sodium pentachlorophenol ate (PCP-Na) was selected as the target pollutant, and the photocatalytic property of the material Ag/TiO2 was evaluated by PCP-Na degradation rate. It was found that the calcination at 450 °C was conducive to form the anatase structure with high catalytic activity, and the catalytic activity was higher when the silver mole fraction of Ag/TiO2 was 0.50%. The influence of Ag/TiO2 dosage, hydrogen peroxide volume, silver mole fraction and PCP-Na initial concentration was investigated by the single factor experiment.

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.

Structural analysis of nickel doped cerium oxide catalysts for fuel reforming in solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Cavendish, Rio

As world energy demands increase, research into more efficient energy production methods has become imperative. Heterogeneous catalysis and nanoscience are used to promote chemical transformations important for energy production. These concepts are important in solid oxide fuel cells (SOFCs) which have attracted attention because of their potential to provide an efficient and environmentally favorable power generation system. The SOFC is also fuel-flexible with the ability to run directly on many fuels other than hydrogen. Internal fuel reforming directly in the anode of the SOFC would greatly reduce the cost and complexity of the device. Methane is the simplest hydrocarbon and a main component in natural gas, making it useful when testing catalysts on the laboratory scale. Nickel (Ni) and gadolinium (Gd) doped ceria (CeO 2) catalysts for potential use in the SOFC anode were synthesized with a spray drying method and tested for catalytic performance using partial oxidation of methane and steam reforming. The relationships between catalytic performance and structure were then investigated using X-ray diffraction, transmission electron microscopy, and environmental transmission electron microscopy. The possibility of solid solutions, segregated phases, and surface layers of Ni were explored. Results for a 10 at.% Ni in CeO2 catalyst reveal a poor catalytic behavior while a 20 at.% Ni in CeO2 catalyst is shown to have superior activity. The inclusion of both 10 at.% Gd and 10 at.% Ni in CeO2 enhances the catalytic performance. Analysis of the presence of Ni in all 3 samples reveals Ni heterogeneity and little evidence for extensive solid solution doping. Ni is found in small domains throughout CeO2 particles. In the 20 at.% Ni sample a segregated, catalytically active NiO phase is observed. Overall, it is found that significant interaction between Ni and CeO2 occurs that could affect the synthesis and functionality of the SOFC anode.

Effect of urea deproteinization on catalytic hydrogenation of natural rubber latex

NASA Astrophysics Data System (ADS)

Cifriadi, A.; Chalid, M.; Puspitasari, S.

2017-07-01

Natural rubber is unsaturated biopolymer which has low resistance to heat, oxygen, and ozone. Chemical modification of natural rubber by catalytic hydrogenation can improve its oxidative property. In this study, the catalytic hydrogenation of natural rubber was investigated in latex phase after reduction of protein content with urea. Hydrogenation of deproteinized natural rubber latex was performed by using diimide which generated insitu from hydrazine hydrate/hydrogen peroxide and catalyst (boric acid, cupric sulfate and cupric acetate) at 70°C for 5 h. The hydrogenation system was stabilized with sodium dodecyl sulphate. The hydrogenation of deproteinized natural rubber (HDPNR) was confirmed by FTIR analysis. The result indicated that cupric sulphate was extremely active catalyst which was showed by the elimination of C=C transmittance bands at 1660 cm-1 on HDPNR spectra and highest degree of hydrogenation. Furthermore, urea deproteinization increased possibility of side reactions during catalytic hydrogenation as seen on the reduction of gel content compared to undeproteinized natural rubber.

Synchrotron EXAFS and XANES spectroscopy studies of transition aluminas doped with La and Cr for catalytic applications

NASA Astrophysics Data System (ADS)

Glazoff, Michael V.

2016-04-01

Transition aluminas doped with Cr find widespread application in the dehydrogenation catalysis industry, while La-stabilized transition aluminas are used extensively for high-temperature application as catalytic supports (Wefers and Misra in Oxides and hydroxides of aluminum, Alcoa Laboratories, Pittsburgh, 1987). In this work, detailed synchrotron XAFS spectroscopy studies were conducted to shed light upon the atomic mechanisms of surface and subsurface reconstructions and/or catalytic support stabilization of doped aluminas. It was demonstrated that in four transition aluminas doped with Cr, it is the atoms which are mostly in the state of oxidation Cr3+ and enter nanoparticles of Cr-bearing phases (Cr2O3 in the case of gamma- and chi-alumina). In the transition series aluminas: "gamma- chi- theta- eta-alumina," the change of properties (in particular, the dramatic increase in dehydrogenation catalytic activity and catalyst longevity and the coloration of samples) takes place because of the reduction in the average size of Cr clusters and their appearance on the Al2O3 surface, probably responsible for change in catalytic activity. It was demonstrated that in the samples of gamma-alumina doped with La any substantial change in the local coordination of the La atoms takes place only upon heating up to 1400 °C. This makes the La-stabilized gamma-alumina a perfect catalytic support for the numerous applications, e.g., catalytic three-way conversion of automobile exhaust gases. This change manifested itself in the form of increased La-O bond lengths and the La coordination number (from 8 to 12). Furthermore, it was demonstrated that the local environment of La in this new La-bearing phase cannot be explained in terms of the LaAlO3 formation. The absence of the La atoms in the second coordination sphere favors monoatomic distribution of La atoms on grain boundaries, proving that only very small amount of this rare earth material is required to achieve full stabilization. It is inferred that the tendency of La atoms to get surrounded by oxygen atoms, and also the impossibility of going into the alumina bulk, could be a major reason of the increased thermal stability of gamma-alumina doped with lanthanum.

Nickel/ruthenium catalyst and method for aqueous phase reactions

DOEpatents

Elliott, D.C.; Sealock, J.L.

1998-09-29

A method of hydrogenation is described using a catalyst in the form of a plurality of porous particles wherein each particle is a support having nickel metal catalytic phase or reduced nickel deposited thereon in a first dispersed phase and an additional ruthenium metal deposited onto the support in a second dispersed phase. The additional ruthenium metal is effective in retarding or reducing agglomeration or sintering of the nickel metal catalytic phase thereby increasing the life time of the catalyst during hydrogenation reactions. 2 figs.

Nickel/ruthenium catalyst and method for aqueous phase reactions

DOEpatents

Elliott, Douglas C.; Sealock, John L.

1998-01-01

A method of hydrogenation using a catalyst in the form of a plurality of porous particles wherein each particle is a support having nickel metal catalytic phase or reduced nickel deposited thereon in a first dispersed phase and an additional ruthenium metal deposited onto the support in a second dispersed phase. The additional ruthenium metal is effective in retarding or reducing agglomeration or sintering of the nickel metal catalytic phase thereby increasing the life time of the catalyst during hydrogenation reactions.

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.

Vapor Phase Catalytic Ammonia Reduction

NASA Technical Reports Server (NTRS)

Flynn, Michael T.; Harper, Lynn D. (Technical Monitor)

1994-01-01

This paper discusses the development of a Vapor Phase Catalytic Ammonia Reduction (VPCAR) teststand and the results of an experimental program designed to evaluate the potential of the technology as a water purification process. In the experimental program the technology is evaluated based upon product water purity, water recovery rate, and power consumption. The experimental work demonstrates that the technology produces high purity product water and attains high water recovery rates at a relatively high specific power consumption. The experimental program was conducted in 3 phases. In phase I an Igepon(TM) soap and water mixture was used to evaluate the performance of an innovative Wiped-Film Rotating-Disk evaporator and associated demister. In phase II a phenol-water solution was used to evaluate the performance of the high temperature catalytic oxidation reactor. In phase III a urine analog was used to evaluate the performance of the combined distillation/oxidation functions of the processor.

Liquid phase catalytic hydrodebromination of tetrabromobisphenol A on supported Pd catalysts

NASA Astrophysics Data System (ADS)

Wu, Ke; Zheng, Mengjia; Han, Yuxiang; Xu, Zhaoyi; Zheng, Shourong

2016-07-01

Tetrabromobisphenol A (TBBPA) is a widely used brominated flame retardant and reductive debromination is an effective method for the abatement of TBBPA pollution. In this study, Pd catalysts supported on TiO2, CeO2, Al2O3 and SiO2 were prepared by the impregnation (the resulting catalyst denoted as im-Pd/support), deposition-precipitation (the resulting catalyst denoted as dp-Pd/support), and photo-deposition (the resulting catalyst denoted as pd-Pd/support) methods. The catalysts were characterized by N2 adsorption-desorption isotherm, X-ray diffraction, transmission electron microscopy, measurement of zeta potential, CO chemisorption, and X-ray photoelectron spectroscopy. The results showed that at an identical Pd loading amount (2.0 wt.%) Pd particle size in dp-Pd/TiO2 was much smaller than those in im-Pd/TiO2 and pd-Pd/TiO2. Pd particle size of the dp-Pd/TiO2 catalyst increased with Pd loading amount. Additionally, Pd particles in the dp-Pd/TiO2 catalysts were positively charged due to the strong metal-support interaction, whereas the cationization effect was gradually attenuated with the increase of Pd loading amount. For the liquid phase catalytic hydrodebromination (HDB) of TBBPA, tri-bromobisphenol A (tri-BBPA), di-bromobisphenol A (di-BBPA), and mono-bromobisphenol A (mono-BBPA) were identified as the intermediate products, indicative of a stepwise debromination process. The catalytic HDB of TBBPA followed the Langmuir-Hinshelwood model, reflecting an adsorption enhanced catalysis mechanism. At an identical Pd loading amount, the Pd catalyst supported on TiO2 exhibited a much higher catalytic activity than those on other supports. Furthermore, dp-Pd/TiO2 was found to be more active than im-Pd/TiO2 and pd-Pd/TiO2.

Metastability of the atomic structures of size-selected gold nanoparticles

NASA Astrophysics Data System (ADS)

Wells, Dawn M.; Rossi, Giulia; Ferrando, Riccardo; Palmer, Richard E.

2015-04-01

All nanostructures are metastable - but some are more metastable than others. Here we employ aberration-corrected electron microscopy and atomistic computer simulations to demonstrate the hierarchy of metastability in deposited, size-selected gold nanoparticles (clusters), an archetypal class of nanomaterials well known for the catalytic activity which only appears on the nanometer-scale. We show that the atomic structures presented by ``magic number'' Au561, Au742 and Au923 clusters are ``locked''. They are in fact determined by the solidification which occurs from the liquid state early in their growth (by assembly from atoms in the gas phase) followed by template growth. It is quite likely that transitions from a locked, metastable configuration to a more stable (but still metastable) structure, as observed here under the electron beam, will occur during catalytic reactions, for example.All nanostructures are metastable - but some are more metastable than others. Here we employ aberration-corrected electron microscopy and atomistic computer simulations to demonstrate the hierarchy of metastability in deposited, size-selected gold nanoparticles (clusters), an archetypal class of nanomaterials well known for the catalytic activity which only appears on the nanometer-scale. We show that the atomic structures presented by ``magic number'' Au561, Au742 and Au923 clusters are ``locked''. They are in fact determined by the solidification which occurs from the liquid state early in their growth (by assembly from atoms in the gas phase) followed by template growth. It is quite likely that transitions from a locked, metastable configuration to a more stable (but still metastable) structure, as observed here under the electron beam, will occur during catalytic reactions, for example. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05811a

The assembly and properties of protobiological structures - The beginnings of cellular peptide synthesis

NASA Technical Reports Server (NTRS)

Fox, S. W.; Nakashima, T.

1980-01-01

New data indicate that lysine-rich proteinoids have the ability to catalyze the synthesis of peptide bonds from a variety of amino acids and ATP. This capacity is evident in aqueous solution, in suspension of phase-separated complexes of lysine-rich proteinoid with acidic proteinoids, and in suspension of phase-separated particles composed of lysine-rich proteinoids with polynucleotides. Since the proteinoid complexes can contain other catalytic activities, including ability to catalyze internucleotide bond formation, it is inferred that the first protocells on earth already had a number of biological types of activity.

Catalytic Ignition and Upstream Reaction Propagation in a Platinum Tube

NASA Technical Reports Server (NTRS)

Struk, P. M.; Dietrich, D. L.; Mellish, B. P.; Miller, F. J.; T'ien, J. S.

2007-01-01

A challenge for catalytic combustion in monolithic reactors at elevated temperatures is the start-up or "light-off" from a cold initial condition. In this work, we demonstrate a concept called "back-end catalytic ignition that potentially can be utilized in the light-off of catalytic monoliths. An external downstream flame or Joule heating raises the temperature of a small portion of the catalyst near the outlet initiating a localized catalytic reaction that propagates upstream heating the entire channel. This work uses a transient numerical model to demonstrate "back-end" ignition within a single channel which can characterize the overall performance of a monolith. The paper presents comparisons to an experiment using a single non-adiabatic channel but the concept can be extended to the adiabatic monolith case. In the model, the time scales associated with solid heat-up are typically several orders of magnitude larger than the gas-phase and chemical kinetic time-scales. Therefore, the model assumes a quasi-steady gas-phase with respect to a transient solid. The gas phase is one-dimensional. Appropriate correlations, however, account for heat and mass transfer in a direction perpendicular to the flow. The thermally-thin solid includes axial conduction. The gas phase, however, does not include axial conduction due to the high Peclet number flows. The model includes both detailed gas-phase and catalytic surface reactions. The experiment utilizes a pure platinum circular channel oriented horizontally though which a CO/O2 mixture (equivalence ratios ranging from 0.6 to 0.9) flows at 2 m/s.

Probing the Adsorption of Carbon Monoxide on Transition Metal Clusters Using IR Action Spectroscopy

NASA Astrophysics Data System (ADS)

Lapoutre, Vivike J. F.; Oomens, Jos; Bakker, Joost M.

2012-06-01

The discovery of enhanced catalytic activity of small gold clusters has led to a great interest in size-dependent catalytic properties of metal clusters. To obtain a better understanding of the catalytic mechanisms it is essential to know the structures of these clusters and the nature of their interaction with reactant molecules. We have studied the structure of gas-phase niobium clusters with a carbon monoxide adsorbed using IR action spectroscopy. We present size-selective IR spectra obtained via IR multiple photon spectroscopy monitoring either photodetachment or photodissociation depending on the charge state. The combination of these spectra with DFT calculations allows for the structural determination of the adsorption product. M. Haruta et al., Journal of Catalysis 115 301-309 (1989). M. Haertelt et al., The Journal of Physical Chemistry Letters 2 1720-1724 (2011)

Bicarbonate-induced activation of H₂O₂ for metal-free oxidative desulfurization.

PubMed

Bokare, Alok D; Choi, Wonyong

2016-03-05

Efficient oxidative desulfurization (ODS) of model oil containing dibenzothiophene (DBT) and aromatic thiophenic derivatives has been achieved at room temperature using hydrogen peroxide activation by inorganic bicarbonate (HCO3(-)). Using in-situ formation of peroxymonocarbonate as oxidant, the transformation of main model substrate DBT to corresponding DBT-sulfone was easily accomplished in biphasic reaction conditions. In the presence of water-acetonitrile polar phase, increasing the water content upto 50% decreased the extraction capacity more than 3 times, but ∼ 90% DBT oxidation was still achieved. The oxidizing capacity of bicarbonate catalyst was maintained during repeated ODS cycles, but DBT removal efficiency was critically dependent on the extraction capacity of the polar phase. Under heterogeneous reaction conditions, bicarbonate-modified ion-exchange resin achieved similar ODS activity compared to the homogeneous catalytic system. Additionally, the efficient formation of peroxymonocarbonate using gaseous CO2 precursor in alkaline conditions was also utilized for DBT oxidation. The present study proposes the NaHCO3/H2O2 catalytic system as an efficient and cheap metal-free alternative for the oxidative removal of aromatic sulfur compounds from fuel oil. Copyright © 2015 Elsevier B.V. All rights reserved.

Multi-Phase Field Models and Microstructural Evolution with Applications in Fuel Cell Technology

NASA Astrophysics Data System (ADS)

Davis, Ryan Scott

The solid oxide fuel cell (SOFC) has shown tremendous potential as an efficient energy conversion device that may be instrumental in the transition to renewable resources. However, commercialization is hindered by many degradation mechanisms that plague long term stability. In this dissertation, computation methods are used to explore the relationship between the microstructure of the fuel cell anode and performance critical metrics. The phase field method and standard modeling procedures are introduced using a classic model of spinodal decomposition. This is further developed into a complete, multi-phase modeling framework designed for the complex microstructural evolution of SOFC anode systems. High-temperature coarsening of the metallic phase in the state-of-the-art SOFC cermet anode is investigated using our phase field model. A systematic study into the effects of interface properties on microstructural evolution is accomplished by altering the contact angle between constituent phases. It is found that metrics of catalytic activity and conductivity display undesirable minima near the contact angle of conventional SOFC materials. These results suggest that tailoring the interface properties of the constituent phases could lead to a significant increase in the performance and lifetime of SOFCs. Supported-metal catalyst systems are investigated in the first detailed study of their long-term stability and application to SOFC anode design. Porous support structures are numerically sintered to mimic specific fabrication techniques, and these structures are then infiltrated with a nanoscale catalyst phase ranging from 2% to 21% loading. Initially, these systems exhibit enhanced potential for catalytic activity relative to conventional cells. However, extended evolution results in severe degradation, and we show that Ostwald ripening and particle migration are key kinetic processes. Strong geometric heterogeneity in the support structure via a novel approach to nanopore formation is proposed as a potential solution for catalyst stabilization.

Role of Arginine 293 and Glutamine 288 in Communication between Catalytic and Allosteric Sites in Yeast Ribonucleotide Reductase

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

Ahmad, Md. Faiz; Kaushal, Prem Singh; Wan, Qun

2012-11-01

Ribonucleotide reductases (RRs) catalyze the rate-limiting step of de novo deoxynucleotide (dNTP) synthesis. Eukaryotic RRs consist of two proteins, RR1 ({alpha}) that contains the catalytic site and RR2 ({beta}) that houses a diferric-tyrosyl radical essential for ribonucleoside diphosphate reduction. Biochemical analysis has been combined with isothermal titration calorimetry (ITC), X-ray crystallography and yeast genetics to elucidate the roles of two loop 2 mutations R293A and Q288A in Saccharomyces cerevisiae RR1 (ScRR1). These mutations, R293A and Q288A, cause lethality and severe S phase defects, respectively, in cells that use ScRR1 as the sole source of RR1 activity. Compared to the wild-typemore » enzyme activity, R293A and Q288A mutants show 4% and 15%, respectively, for ADP reduction, whereas they are 20% and 23%, respectively, for CDP reduction. ITC data showed that R293A ScRR1 is unable to bind ADP and binds CDP with 2-fold lower affinity compared to wild-type ScRR1. With the Q288A ScRR1 mutant, there is a 6-fold loss of affinity for ADP binding and a 2-fold loss of affinity for CDP compared to the wild type. X-ray structures of R293A ScRR1 complexed with dGTP and AMPPNP-CDP [AMPPNP, adenosine 5-({beta},{gamma}-imido)triphosphate tetralithium salt] reveal that ADP is not bound at the catalytic site, and CDP binds farther from the catalytic site compared to wild type. Our in vivo functional analyses demonstrated that R293A cannot support mitotic growth, whereas Q288A can, albeit with a severe S phase defect. Taken together, our structure, activity, ITC and in vivo data reveal that the arginine 293 and glutamine 288 residues of ScRR1 are crucial in facilitating ADP and CDP substrate selection.« less

Comparative study on catalytic hydrodehalogenation of halogenated aromatic compounds over Pd/C and Raney Ni catalysts

NASA Astrophysics Data System (ADS)

Ma, Xuanxuan; Liu, Sujing; Liu, Ying; Gu, Guodong; Xia, Chuanhai

2016-04-01

Catalytic hydrodehalogenation (HDH) has proved to be an efficient approach to dispose halogenated aromatic compounds (HACs). Liquid-phase HDH of single and mixed halobenzenes/4-halophenols with H2 over 5% Pd/C and Raney Ni catalyst are investigated and compared. For liquid-phase HDH of single HACs, hydrogenolytic scission reactivity of C-X bonds decreases in order of C-Br > C-Cl > C-I > C-F over Pd/C catalyst, and in order of C-I > C-Br > C-Cl > C-F over Raney Ni catalyst. To clarify the reason why hydrogenolytic scission reactivity of C-X bonds over Pd/C and Raney Ni catalysts exhibits different trends, liquid-phase HDH of mixed HACs over Pd/C and Raney Ni catalysts were studied, and catalysts are characterized by SEM, EDX, and XRD techniques. It was found that the high adsorption of iodoarenes on Pd/C catalyst caused the HDH reactivity of iodoarenes to be lower than that of chloroarenes and bromoarenes in the HDH of single HACs. Moreover, the adsorption of in situ produced iodine ion (I-) to catalyst surface would result in the decline of catalytic activity, which might be the main reason why the HDH reactivity of HACs in the presence of NaI is rather low.

Structure Characterization and Catalytic Properties of Cr2O3 Doped with MgO Supported on MgF2

NASA Astrophysics Data System (ADS)

Goslar, J.; Wojciechowska, M.; Zieliński, M.; Tomska-Foralewska, I.; Przystajko, W.

2006-08-01

A characterization of double oxide systems containing Cr2O3 doped with MgO and supported on MgF2 was carried out. The catalysts were prepared by impregnation and co-impregnation methods and characterized by the Brunauer-Emmett-Teller method, EPR, and temperature programmed reduction. The results proved the interactions between supported oxides and the presence of spinel-like phase after treatment at 400 ºC. Magnesium oxide clearly influences the catalytic activity as well as selectivity of chromium catalysts supported on MgF2. The MgO-Cr2O3/MgF2 systems were active and selective in the reaction of CO oxidation at the room temperature and in the dehydrogenation of cyclohexene.

Process for upgrading wax from Fischer-Tropsch synthesis

DOEpatents

Derr, Jr., W. Rodman; Garwood, William E.; Kuo, James C.; Leib, Tiberiu M.; Nace, Donald M.; Tabak, Samuel A.

1987-01-01

The waxy liquid phase of an oil suspension of Fischer-Tropsch catalyst containing dissolved wax is separated out and the wax is converted by hydrocracking, dewaxing or by catalytic cracking with a low activity catalyst to provide a highly olefinic product which may be further converted to premium quality gasoline and/or distillate fuel.

A multifunctional biphasic water splitting catalyst tailored for integration with high-performance semiconductor photoanodes

DOE PAGES

Yang, Jinhui; Cooper, Jason K.; Toma, Francesca M.; ...

2016-11-07

Artificial photosystems are advanced by the development of conformal catalytic materials that promote desired chemical transformations, while also maintaining stability and minimizing parasitic light absorption for integration on surfaces of semiconductor light absorbers. We demonstrate that multifunctional, nanoscale catalysts that enable high-performance photoelectrochemical energy conversion can be engineered by plasma-enhanced atomic layer deposition. The collective properties of tailored Co 3 O 4 /Co(OH) 2 thin films simultaneously provide high activity for water splitting, permit efficient interfacial charge transport from semiconductor substrates, and enhance durability of chemically sensitive interfaces. Furthermore, these films comprise compact and continuous nanocrystalline Co 3 O 4more » spinel that is impervious to phase transformation and impermeable to ions, thereby providing effective protection of the underlying substrate. Moreover, a secondary phase of structurally disordered and chemically labile Co(OH) 2 is introduced to ensure a high concentration of catalytically active sites. Application of this coating to photovoltaic p + n-Si junctions yields best reported performance characteristics for crystalline Si photoanodes.« less

Hydrogenation of succinic acid to 1,4-butanediol over rhenium catalyst supported on copper-containing mesoporous carbon.

PubMed

Hong, Ung Gi; Park, Hai Woong; Lee, Joongwon; Hwang, Sunhwan; Kwak, Jimin; Yi, Jongheop; Song, In Kyu

2013-11-01

Copper-containing mesoporous carbon (Cu-MC) was prepared by a single-step surfactant-templating method. For comparison, copper-impregnated mesoporous carbon (Cu/MC) was also prepared by a surfactant-templating method and a subsequent impregnation method. Rhenium catalysts supported on copper-containing mesoporous carbon and copper-impregnated mesoporous carbon (Re/Cu-MC and Re/Cu/MC, respectively) were then prepared by an incipient wetness method, and they were applied to the liquid-phase hydrogenation of succinic acid to 1,4-butanediol (BDO). It was observed that copper in the Re/Cu-MC catalyst was well incorporated into carbon framework, resulting in higher surface area and larger pore volume than those of Re/Cu/MC catalyst. Therefore, Re/Cu-MC catalyst showed higher copper dispersion than Re/Cu/MC catalyst, although both catalysts retained the same amounts of copper and rhenium. In the liquid-phase hydrogenation of succinic acid to BDO, Re/Cu-MC catalyst showed a better catalytic activity than Re/Cu/MC catalyst. Fine dispersion of copper in the Re/Cu-MC catalyst was responsible for its enhanced catalytic activity.

Conversion of CH4/CO2 to syngas over Ni-Co/Al2O3-ZrO2 nanocatalyst synthesized via plasma assisted co-impregnation method: Surface properties and catalytic performance

NASA Astrophysics Data System (ADS)

Rahemi, Nader; Haghighi, Mohammad; Akbar Babaluo, Ali; Fallah Jafari, Mahdi; Khorram, Sirous

2013-09-01

Ni/Al2O3 catalyst promoted by Co and ZrO2 was prepared by co-impregnation method and treated with glow discharge plasma. The catalytic activity of the synthesized nanocatalysts has been tested toward conversion of CH4/CO2 to syngas. The physicochemical characterizations like XRD, EDX, FESEM, TEM, BET, FTIR, and XPS show that plasma treatment results in smaller particle size, more surface concentration, and uniform morphology. The dispersion of nickel in plasma-treated nanocatalyst was also significantly improved, which was helpful for controlling the ensemble size of active phase atoms on the support surface. Improved physicochemical properties caused 20%-30% enhancement in activity of plasma-treated nanocatalyst that means to achieve the same H2 or CO yield, the plasma-treated nanocatalyst needed about 100 °C lower reaction temperature. The H2/CO ratio got closer to 1 at higher temperatures and finally at 850 °C H2/CO = 1 is attained for plasma-treated nanocatalyst. Plasma-treated nanocatalyst due to smaller Ni particles and strong interaction between active phase and support has lower tendency to keep carbon species on its structure and hence excellent stability can be observed for this catalyst.

Atomically Precise Growth of Catalytically Active Cobalt Sulfide on Flat Surfaces and within a Metal–Organic Framework via Atomic Layer Deposition

DOE PAGES

Peters, Aaron W.; Li, Zhanyong; Farha, Omar K.; ...

2015-08-04

Atomic layer deposition (ALD) has been employed as a new synthetic route to thin films of cobalt sulfide on silicon and fluorine-doped tin oxide platforms. The self-limiting nature of the stepwise synthesis is established through growth rate studies at different pulse times and temperatures. Additionally, characterization of the materials by X-ray diffraction and X-ray photoelectron spectroscopy indicates that the crystalline phase of these films has the composition Co 9S 8. The nodes of the metal–organic framework (MOF) NU-1000 were then selectively functionalized with cobalt sulfide via ALD in MOFs (AIM). Spectroscopic techniques confirm uniform deposition of cobalt sulfide throughout themore » crystallites, with no loss in crystallinity or porosity. The resulting material, CoS-AIM, is catalytically active for selective hydrogenation of m-nitrophenol to m-aminophenol, and outperforms the analogous oxide AIM material (CoO-AIM) as well as an amorphous CoS x reference material. Here, these results reveal AIM to be an effective method of incorporating high surface area and catalytically active cobalt sulfide in metal–organic frameworks.« less

Loss of maintenance DNA methylation results in abnormal DNA origin firing during DNA replication

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

Haruta, Mayumi; Shimada, Midori, E-mail: midorism@med.nagoya-cu.ac.jp; Nishiyama, Atsuya

The mammalian maintenance methyltransferase DNMT1 [DNA (cytosine-5-)-methyltransferase 1] mediates the inheritance of the DNA methylation pattern during replication. Previous studies have shown that depletion of DNMT1 causes a severe growth defect and apoptosis in differentiated cells. However, the detailed mechanisms behind this phenomenon remain poorly understood. Here we show that conditional ablation of Dnmt1 in murine embryonic fibroblasts (MEFs) resulted in an aberrant DNA replication program showing an accumulation of late-S phase replication and causing severely defective growth. Furthermore, we found that the catalytic activity and replication focus targeting sequence of DNMT1 are required for a proper DNA replication program.more » Taken together, our findings suggest that the maintenance of DNA methylation by DNMT1 plays a critical role in proper regulation of DNA replication in mammalian cells. - Highlights: • DNMT1 depletion results in an abnormal DNA replication program. • Aberrant DNA replication is independent of the DNA damage checkpoint in DNMT1cKO. • DNMT1 catalytic activity and RFT domain are required for proper DNA replication. • DNMT1 catalytic activity and RFT domain are required for cell proliferation.« less

Nanophase-separated Ni3Nb as an automobile exhaust catalyst† †Electronic supplementary information (ESI) available: Demonstration procedure, experimental and characterization details. See DOI: 10.1039/c6sc05473k Click here for additional data file. Click here for additional data file.

PubMed Central

Tanabe, Toyokazu; Imai, Tsubasa; Tokunaga, Tomoharu; Arai, Shigeo; Yamamoto, Yuta; Ueda, Shigenori; Ramesh, Gubbala V.; Nagao, Satoshi; Hirata, Hirohito; Matsumoto, Shin-ichi

2017-01-01

Catalytic remediation of automobile exhaust has relied on precious metals (PMs) including platinum (Pt). Herein, we report that an intermetallic phase of Ni and niobium (Nb) (i.e., Ni3Nb) exhibits a significantly higher activity than that of Pt for the remediation of the most toxic gas in exhaust (i.e., nitrogen monoxide (NO)) in the presence of carbon monoxide (CO). When subjected to the exhaust-remediation atmosphere, Ni3Nb spontaneously evolves into a catalytically active nanophase-separated structure consisting of filamentous Ni networks (thickness < 10 nm) that are incorporated in a niobium oxide matrix (i.e., NbOx (x < 5/2)). The exposure of the filamentous Ni promotes NO dissociation, CO oxidation and N2 generation, and the NbOx matrix absorbs excessive nitrogen adatoms to retain the active Ni0 sites at the metal/oxide interface. Furthermore, the NbOx matrix immobilizes the filamentous Ni at elevated temperatures to produce long-term and stable catalytic performance over hundreds of hours. PMID:28507707

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.

Reforming Biomass Derived Pyrolysis Bio-oil Aqueous Phase to Fuels

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

Mukarakate, Calvin; Evans, Robert J.; Deutch, Steve

Fast pyrolysis and catalytic fast pyrolysis (CFP) of biomass produce a liquid product stream comprised of various classes of organic compounds having different molecule size and polarity. This liquid, either spontaneously in the case of catalytic fast pyrolysis or by water addition for the non-catalytic process separates into a non-polar organic-rich fraction and a highly polar water-rich fraction. The organic fraction can be used as a blendstock or feedstock for further processing in a refinery while, in the CFP process design, the aqueous phase is currently sent to wastewater treatment, which results in a loss of residual biogenic carbon presentmore » in this stream. Our work focuses on the catalytic conversion of the biogenic carbon in pyrolysis aqueous phase streams to produce hydrocarbons using a vertical micro-reactor coupled to a molecular beam mass spectrometer (MBMS). Furthermore, the MBMS provides real-time analysis of products while also tracking catalyst deactivation. The catalyst used in this work was HZSM-5, which upgraded the oxygenated organics in the aqueous fraction to fuels comprising small olefins and aromatic hydrocarbons. During processing the aqueous bio-oil fraction the HZSM-5 catalyst exhibited higher activity and coke resistance than those observed in similar experiments using biomass or whole bio-oils. Reduced coking is likely due to ejection of coke precursors from the catalyst pores that was enhanced by excess process water available for steam stripping. The water reacted with coke precursors to form phenol, methylated phenols, naphthol, and methylated naphthols. Conversion data shows that up to 40 wt% of the carbon in the feed stream is recovered as hydrocarbons.« less

Reforming Biomass Derived Pyrolysis Bio-oil Aqueous Phase to Fuels

DOE PAGES

Mukarakate, Calvin; Evans, Robert J.; Deutch, Steve; ...

2017-01-07

Fast pyrolysis and catalytic fast pyrolysis (CFP) of biomass produce a liquid product stream comprised of various classes of organic compounds having different molecule size and polarity. This liquid, either spontaneously in the case of catalytic fast pyrolysis or by water addition for the non-catalytic process separates into a non-polar organic-rich fraction and a highly polar water-rich fraction. The organic fraction can be used as a blendstock or feedstock for further processing in a refinery while, in the CFP process design, the aqueous phase is currently sent to wastewater treatment, which results in a loss of residual biogenic carbon presentmore » in this stream. Our work focuses on the catalytic conversion of the biogenic carbon in pyrolysis aqueous phase streams to produce hydrocarbons using a vertical micro-reactor coupled to a molecular beam mass spectrometer (MBMS). Furthermore, the MBMS provides real-time analysis of products while also tracking catalyst deactivation. The catalyst used in this work was HZSM-5, which upgraded the oxygenated organics in the aqueous fraction to fuels comprising small olefins and aromatic hydrocarbons. During processing the aqueous bio-oil fraction the HZSM-5 catalyst exhibited higher activity and coke resistance than those observed in similar experiments using biomass or whole bio-oils. Reduced coking is likely due to ejection of coke precursors from the catalyst pores that was enhanced by excess process water available for steam stripping. The water reacted with coke precursors to form phenol, methylated phenols, naphthol, and methylated naphthols. Conversion data shows that up to 40 wt% of the carbon in the feed stream is recovered as hydrocarbons.« less

The effect of catalyst length and downstream reactor distance on catalytic combustor performance

NASA Technical Reports Server (NTRS)

Anderson, D.

1980-01-01

A study was made to determine the effects on catalytic combustor performance which resulted from independently varying the length of a catalytic reactor and the length available for gas-phase reactions downstream of the catalyst. Monolithic combustion catalysts from three manufacturers were tested in a combustion test rig with no. 2 diesel fuel. Catalytic reactor lengths of 2.5 and 5.4 cm, and downstream gas-phase reaction distances of 7.3, 12.4, 17.5, and 22.5 cm were evaluated. Measurements of carbon monoxide, unburned hydrocarbons, nitrogen oxides, and pressure drop were made. The catalytic-reactor pressure drop was less than 1 percent of the upstream total pressure for all test configurations and test conditions. Nitrogen oxides and unburned hydrocarbons emissions were less than 0.25 g NO2/kg fuel and 0.6 g HC/kg fuel, respectively. The minimum operating temperature (defined as the adiabatic combustion temperature required to obtain carbon monoxide emissions below a reference level of 13.6 g CO/kg fuel) ranged from 1230 K to 1500 K for the various conditions and configurations tested. The minimum operating temperature decreased with increasing total (catalytic-reactor-plus-downstream-gas-phase-reactor-zone) residence time but was independent of the relative times spent in each region when the catalytic-reactor residence time was greater than or equal to 1.4 ms.

Sintering of catalytic nanoparticles: particle migration or Ostwald ripening?

PubMed

Hansen, Thomas W; Delariva, Andrew T; Challa, Sivakumar R; Datye, Abhaya K

2013-08-20

Metal nanoparticles contain the active sites in heterogeneous catalysts, which are important for many industrial applications including the production of clean fuels, chemicals and pharmaceuticals, and the cleanup of exhaust from automobiles and stationary power plants. Sintering, or thermal deactivation, is an important mechanism for the loss of catalyst activity. This is especially true for high temperature catalytic processes, such as steam reforming, automotive exhaust treatment, or catalytic combustion. With dwindling supplies of precious metals and increasing demand, fundamental understanding of catalyst sintering is very important for achieving clean energy and a clean environment, and for efficient chemical conversion processes with atom selectivity. Scientists have proposed two mechanisms for sintering of nanoparticles: particle migration and coalescence (PMC) and Ostwald ripening (OR). PMC involves the mobility of particles in a Brownian-like motion on the support surface, with subsequent coalescence leading to nanoparticle growth. In contrast, OR involves the migration of adatoms or mobile molecular species, driven by differences in free energy and local adatom concentrations on the support surface. In this Account, we divide the process of sintering into three phases. Phase I involves rapid loss in catalyst activity (or surface area), phase II is where sintering slows down, and phase III is where the catalyst may reach a stable performance. Much of the previous work is based on inferences from catalysts that were observed before and after long term treatments. While the general phenomena can be captured correctly, the mechanisms cannot be determined. Advancements in the techniques of in situ TEM allow us to observe catalysts at elevated temperatures under working conditions. We review recent evidence obtained via in situ methods to determine the relative importance of PMC and OR in each of these phases of catalyst sintering. The evidence suggests that, in phase I, OR is responsible for the rapid loss of activity that occurs when particles are very small. Surprisingly, very little PMC is observed in this phase. Instead, the rapid loss of activity is caused by the disappearance of the smallest particles. These findings are in good agreement with representative atomistic simulations of sintering. In phase II, sintering slows down since the smallest particles have disappeared. We now see a combination of PMC and OR, but do not fully understand the relative contribution of each of these processes to the overall rates of sintering. In phase III, the particles have grown large and other parasitic phenomena, such as support restructuring, can become important, especially at high temperatures. Examining the evolution of particle size and surface area with time, we do not see a stable or equilibrium state, especially for catalysts operating at elevated temperatures. In conclusion, the recent literature, especially on in situ studies, shows that OR is the dominant process causing the growth of nanoparticle size. Consequently, this leads to the loss of surface area and activity. While particle migration could be controlled through suitable structuring of catalyst supports, it is more difficult to control the mobility of atomically dispersed species. These insights into the mechanisms of sintering could help to develop sinter-resistant catalysts, with the ultimate goal of designing catalysts that are self-healing.

Catalytic wet oxidation: mathematical modeling of multicompound destruction.

PubMed

Yang, J; Hand, D W; Hokanson, D R; Crittenden, J C; Oman, E J

2003-01-01

A mathematical model of a three-phase catalytic reactor, CatReac, was developed for analysis and optimization of a catalytic oxidation reactor that is used in the International Space Station potable water processor. The packed-bed catalytic reactor, known as the volatile reactor assembly (VRA), is operated as a three-phase reactor and contains a proprietary catalyst, a pure-oxygen gas phase, and the contaminated water. The contaminated water being fed to the VRA primarily consists of acetic acid, acetone, ethanol, 1-propanol, 2-propanol, and propionic acid ranging in concentration from 1 to 10 mg/L. The Langmuir-Hinshelwood Hougen-Watson (L-H) (Hougen, 1943) expression was used to describe the surface reaction rate for these compounds. Single and multicompound short-column experiments were used to determine the L-H rate parameters and calibrate the model. The model was able to predict steady-state multicomponent effluent profiles for short and full-scale reactor experiments.

[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.

Synthesis and characterization of supported polysugar-stabilized palladium nanoparticle catalysts for enhanced hydrodechlorination of trichloroethylene

NASA Astrophysics Data System (ADS)

Bacik, Deborah B.; Zhang, Man; Zhao, Dongye; Roberts, Christopher B.; Seehra, Mohinar S.; Singh, Vivek; Shah, Naresh

2012-07-01

Palladium (Pd) nanoparticle catalysts were successfully synthesized within an aqueous phase using sodium carboxymethyl cellulose (CMC) as a capping ligand which offers a green alternative to conventional nanoparticle synthesis techniques. The CMC-stabilized Pd nanoparticles were subsequently dispersed within support materials using the incipient wetness impregnation technique for utilization in heterogeneous catalyst systems. The unsupported and supported (both calcined and uncalcined) Pd nanoparticle catalysts were characterized using transmission electron microscopy, energy dispersive x-ray spectrometry, x-ray diffraction, and Brunauer-Emmett-Teller surface area measurement and their catalytic activity toward the hydrodechlorination of trichloroethylene (TCE) in aqueous media was examined using homogeneous and heterogeneous catalyst systems, respectively. The unsupported Pd nanoparticles showed considerable activity toward the degradation of TCE, as demonstrated by the reaction kinetics. Although the supported Pd nanoparticle catalysts had a lower catalytic activity than the unsupported particles that were homogeneously dispersed in the aqueous solutions, the supported catalysts retained sufficient activity toward the degradation of TCE. In addition, the use of the hydrophilic Al2O3 support material induced a mass transfer resistance to TCE that affected the initial hydrodechlorination rate. This paper demonstrates that supported Pd catalysts can be applied to the heterogeneous catalytic hydrodechlorination of TCE.

Liquid-phase chemical hydrogen storage: catalytic hydrogen generation under ambient conditions.

PubMed

Jiang, Hai-Long; Singh, Sanjay Kumar; Yan, Jun-Min; Zhang, Xin-Bo; Xu, Qiang

2010-05-25

There is a demand for a sufficient and sustainable energy supply. Hence, the search for applicable hydrogen storage materials is extremely important owing to the diversified merits of hydrogen energy. Lithium and sodium borohydride, ammonia borane, hydrazine, and formic acid have been extensively investigated as promising hydrogen storage materials based on their relatively high hydrogen content. Significant advances, such as hydrogen generation temperatures and reaction kinetics, have been made in the catalytic hydrolysis of aqueous lithium and sodium borohydride and ammonia borane as well as in the catalytic decomposition of hydrous hydrazine and formic acid. In this Minireview we briefly survey the research progresses in catalytic hydrogen generation from these liquid-phase chemical hydrogen storage materials.

Combined effects Na and SO2 in flue gas on Mn-Ce/TiO2 catalyst for low temperature selective catalytic reduction of NO by NH3 simulated by Na2SO4 doping

NASA Astrophysics Data System (ADS)

Zhou, Aiyi; Yu, Danqing; Yang, Liu; Sheng, Zhongyi

2016-08-01

A series of Mn-Ce/TiO2 catalysts were synthesized through an impregnation method and used for low temperature selective catalytic reduction (SCR) of NOx with ammonia (NH3). Na2SO4 was added into the catalyst to simulate the combined effects of alkali metal and SO2 in the flue gas. Experimental results showed that Na2SO4 had strong and fluctuant influence on the activity of Mn-Ce/TiO2, because the effect of Na2SO4 included pore occlusion and sulfation effect simultaneously. When Na2SO4 loading content increased from 0 to 1 wt.%, the SCR activities of Na2SO4-doped catalysts decreased greatly. With further increasing amount of Na2SO4, however, the catalytic activity increased gradually. XRD results showed that Na2SO4 doping could induce the crystallization of MnOx phases, which were also confirmed by TEM and SEM results. BET results showed that the surface areas decreased and a new bimodal mesoporous structure formed gradually with the increasing amount of Na2SO4. XPS results indicated that part of Ce4+ and Mn3+ were transferred to Ce3+ and Mn4+ due to the sulfation after Na2SO4 deposition on the surface of the catalysts. When the doped amounts of Na2SO4 increased, NH3-TPD results showed that the Lewis acid sites decreased and the Brønsted acid sites of Mn-Ce/TiO2 increased quickly, which could be considered as another reason for the observed changes in the catalytic activity. The decreased Mn and Ce atomic concentration, the changes of their oxidative states, and the variation in acidic properties on the surface of Na2SO4-doped catalysts could be the reasons for the fluctuant changes of the catalytic activity.

NiSe-Ni0.85 Se Heterostructure Nanoflake Arrays on Carbon Paper as Efficient Electrocatalysts for Overall Water Splitting.

PubMed

Chen, Yajie; Ren, Zhiyu; Fu, Huiying; Zhang, Xin; Tian, Guohui; Fu, Honggang

2018-06-01

Fabricating cost-effective, bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in basic media is critical for renewable energy generation. Here, NiSe/CP, Ni 0.85 Se/CP, and NiSe-Ni 0.85 Se/CP heterostructure catalysts with different phase constitutions are successfully prepared through in situ selenylation of a NiO nanoflake array oriented on carbon paper (CP) by tuning the original Ni/Se molar ratio of the raw materials. The relationship between the crystal phase component and electrocatalytic activity is systematically studied. Benefiting from the synergetic effect of the intrinsic metallic state, facile charge transport, abundant catalytic active sites, and multiple electrolyte transmission paths, the optimized NiSe-Ni 0.85 Se/CP exhibits a remarkably higher catalytic activity for both the HER and OER than single-phase NiSe/CP and Ni 0.85 Se/CP. A current density of 10 mA cm -2 at 1.62 V and a high stability can be obtained by using NiSe-Ni 0.85 Se/CP as both the cathode and anode for overall water splitting under alkaline conditions. Density functional theory calculations confirm that H and OH - can be more easily adsorbed on NiSe-Ni 0.85 Se than on NiSe and Ni 0.85 Se. This study paves the way for enhancing the overall water splitting performance of nickel selenides by fabricating heterophase junctions using nickel selenides with different phases. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enantioselective syntheses of aeruginosin 298-A and its analogues using a catalytic asymmetric phase-transfer reaction and epoxidation.

PubMed

Ohshima, Takashi; Gnanadesikan, Vijay; Shibuguchi, Tomoyuki; Fukuta, Yuhei; Nemoto, Tetsuhiro; Shibasaki, Masakatsu

2003-09-17

We developed a versatile synthetic process for aeruginosin 298-A as well as several attractive analogues, in which all stereocenters were controlled by a catalytic asymmetric phase-transfer reaction and epoxidation. Furthermore, drastic counteranion effects in phase-transfer catalysis were observed for the first time, making it possible to three-dimensionally fine-tune the catalyst (ketal part, aromatic part, and counteranion).

The Structure of Carbonic Anhydrase IX Is Adapted for Low-pH Catalysis.

PubMed

Mahon, Brian P; Bhatt, Avni; Socorro, Lilien; Driscoll, Jenna M; Okoh, Cynthia; Lomelino, Carrie L; Mboge, Mam Y; Kurian, Justin J; Tu, Chingkuang; Agbandje-McKenna, Mavis; Frost, Susan C; McKenna, Robert

2016-08-23

Human carbonic anhydrase IX (hCA IX) expression in many cancers is associated with hypoxic tumors and poor patient outcome. Inhibitors of hCA IX have been used as anticancer agents with some entering Phase I clinical trials. hCA IX is transmembrane protein whose catalytic domain faces the extracellular tumor milieu, which is typically associated with an acidic microenvironment. Here, we show that the catalytic domain of hCA IX (hCA IX-c) exhibits the necessary biochemical and biophysical properties that allow for low pH stability and activity. Furthermore, the unfolding process of hCA IX-c appears to be reversible, and its catalytic efficiency is thought to be correlated directly with its stability between pH 3.0 and 8.0 but not above pH 8.0. To rationalize this, we determined the X-ray crystal structure of hCA IX-c to 1.6 Å resolution. Insights from this study suggest an understanding of hCA IX-c stability and activity in low-pH tumor microenvironments and may be applicable to determining pH-related effects on enzymes.

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

An Adaptor Domain-Mediated Auto-Catalytic Interfacial Kinase Reaction

PubMed Central

Liao, Xiaoli; Su, Jing; Mrksich, Milan

2010-01-01

This paper describes a model system for studying the auto-catalytic phosphorylation of an immobilized substrate by a kinase enzyme. This work uses self-assembled monolayers (SAMs) of alkanethiolates on gold to present the peptide substrate on a planar surface. Treatment of the monolayer with Abl kinase results in phosphorylation of the substrate. The phosphorylated peptide then serves as a ligand for the SH2 adaptor domain of the kinase and thereby directs the kinase activity to nearby peptide substrates. This directed reaction is intramolecular and proceeds with a faster rate than does the initial, intermolecular reaction, making this an auto-catalytic process. The kinetic non-linearity gives rise to properties that have no counterpart in the corresponding homogeneous phase reaction: in one example, the rate for phosphorylation of a mixture of two peptides is faster than the sum of the rates for phosphorylation of each peptide when presented alone. This work highlights the use of an adaptor domain in modulating the activity of a kinase enzyme for an immobilized substrate and offers a new approach for studying biochemical reactions in spatially inhomogeneous settings. PMID:19821459

Avalanching strain dynamics during the hydriding phase transformation in individual palladium nanoparticles

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

Ulvestad, A.; Welland, M. J.; Collins, S. S. E.

2015-12-11

Phase transitions in reactive environments are crucially important in energy and information storage, catalysis and sensors. Nanostructuring active particles can yield faster charging/ discharging kinetics, increased lifespan and record catalytic activities. However, establishing the causal link between structure and function is challenging for nanoparticles, as ensemble measurements convolve intrinsic single-particle properties with sample diversity. Here we study the hydriding phase transformation in individual palladium nanocubes in situ using coherent X-ray diffractive imaging. The phase transformation dynamics, which involve the nucleation and propagation of a hydrogen-rich region, are dependent on absolute time (aging) and involve intermittent dynamics (avalanching). A hydrogen-rich surfacemore » layer dominates the crystal strain in the hydrogen-poor phase, while strain inversion occurs at the cube corners in the hydrogen-rich phase. A three-dimensional phase-field model is used to interpret the experimental results. In conclusion, our experimental and theoretical approach provides a general framework for designing and optimizing phase transformations for single nanocrystals in reactive environments.« less

Avalanching strain dynamics during the hydriding phase transformation in individual palladium nanoparticles

NASA Astrophysics Data System (ADS)

Ulvestad, A.; Welland, M. J.; Collins, S. S. E.; Harder, R.; Maxey, E.; Wingert, J.; Singer, A.; Hy, S.; Mulvaney, P.; Zapol, P.; Shpyrko, O. G.

2015-12-01

Phase transitions in reactive environments are crucially important in energy and information storage, catalysis and sensors. Nanostructuring active particles can yield faster charging/discharging kinetics, increased lifespan and record catalytic activities. However, establishing the causal link between structure and function is challenging for nanoparticles, as ensemble measurements convolve intrinsic single-particle properties with sample diversity. Here we study the hydriding phase transformation in individual palladium nanocubes in situ using coherent X-ray diffractive imaging. The phase transformation dynamics, which involve the nucleation and propagation of a hydrogen-rich region, are dependent on absolute time (aging) and involve intermittent dynamics (avalanching). A hydrogen-rich surface layer dominates the crystal strain in the hydrogen-poor phase, while strain inversion occurs at the cube corners in the hydrogen-rich phase. A three-dimensional phase-field model is used to interpret the experimental results. Our experimental and theoretical approach provides a general framework for designing and optimizing phase transformations for single nanocrystals in reactive environments.

Avalanching strain dynamics during the hydriding phase transformation in individual palladium nanoparticles

PubMed Central

Ulvestad, A.; Welland, M. J.; Collins, S. S. E.; Harder, R.; Maxey, E.; Wingert, J.; Singer, A.; Hy, S.; Mulvaney, P.; Zapol, P.; Shpyrko, O. G.

2015-01-01

Phase transitions in reactive environments are crucially important in energy and information storage, catalysis and sensors. Nanostructuring active particles can yield faster charging/discharging kinetics, increased lifespan and record catalytic activities. However, establishing the causal link between structure and function is challenging for nanoparticles, as ensemble measurements convolve intrinsic single-particle properties with sample diversity. Here we study the hydriding phase transformation in individual palladium nanocubes in situ using coherent X-ray diffractive imaging. The phase transformation dynamics, which involve the nucleation and propagation of a hydrogen-rich region, are dependent on absolute time (aging) and involve intermittent dynamics (avalanching). A hydrogen-rich surface layer dominates the crystal strain in the hydrogen-poor phase, while strain inversion occurs at the cube corners in the hydrogen-rich phase. A three-dimensional phase-field model is used to interpret the experimental results. Our experimental and theoretical approach provides a general framework for designing and optimizing phase transformations for single nanocrystals in reactive environments. PMID:26655832

Comparative study of activated carbon, natural zeolite, and green sand supports for CuOX and ZnO sites as ozone decomposition catalyst

NASA Astrophysics Data System (ADS)

Azhariyah, A. S.; Pradyasti, A.; Dianty, A. G.; Bismo, S.

2018-03-01

This research was based on ozone decomposition in industrial environment. Ozone is harmful to human. Therefore, catalysts were made as a mask filter to decompose ozone. Comparison studies of catalyst supports were done using Granular Activated Carbon (GAC), Natural Zeolite (NZ), and Green Sand (GS). GAC showed the highest catalytic activity compared to other supports with conversion of 98%. Meanwhile, the conversion using NZ was only 77% and GS had been just 27%. GAC had the highest catalytic activity because it had the largest pore volume, which is 0.478 cm3/g. So GAC was used as catalyst supports. To have a higher conversion in ozone decomposition, GAC was impregnated with metal oxide as the active site of the catalyst. Active site comparison was made using CuOX and ZnO as the active site. Morphology, composition, and crystal phase were analyzed using SEM-EDX, XRF, and XRD methods. Mask filter, which contained catalysts for ozone decomposition, was tested using a fixed bed reactor at room temperature and atmospheric pressure. The result of conversion was analyzed using iodometric method. CuOX/GAC and ZnO/GAC 2%-w showed the highest catalytic activity and conversion reached 100%. From the durability test, CuOX/GAC 2%-w was better than ZnO/GAC 2%-w because the conversion of ozone to oxygen reached 100% with the lowest conversion was 70% for over eight hours.

Support effects in catalysis studied by in-situ sum frequency generation vibrational spectroscopy and in-situ x-ray spectroscopies

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

Kennedy, Griffin John

Here, kinetic measurements are paired with in-situ spectroscopic characterization tools to investigate colloidally based, supported Pt catalytic model systems in order to elucidate the mechanisms by which metal and support work in tandem to dictate activity and selectivity. The results demonstrate oxide support materials, while inactive in absence of Pt nanoparticles, possess unique active sites for the selective conversion of gas phase molecules when paired with an active metal catalyst.

Catalytic transformation of carbon dioxide and methane into syngas over ruthenium and platinum supported hydroxyapatites

NASA Astrophysics Data System (ADS)

Rêgo De Vasconcelos, Bruna; Zhao, Lulu; Sharrock, Patrick; Nzihou, Ange; Pham Minh, Doan

2016-12-01

This work focused on the catalytic transformation of methane (CH4) and carbon dioxide (CO2) into syngas (mixture of CO and H2). Ruthenium- and platinum-based catalysts were prepared using hydroxyapatite (HAP) as catalyst support. Different methods for metal deposition were used including incipient wetness impregnation (IWI), excess liquid phase impregnation (LIM), and cationic exchange (CEX). Metal particle size varied in large range from less than 1 nm to dozens nm. All catalysts were active at 400-700 °C but only Pt catalyst prepared by IWI method (Pt/HAP IWI) was found stable. The catalytic performance of Pt/HAP IWI could be comparable with the literature data on noble metal-based catalysts, prepared on metal oxide supports. For the first time, water was experimentally quantified as a by-product of the reaction. This helped to correctly buckle the mass balance of the process.

Nanoscale zero-valent iron incorporated with nanomagnetic diatomite for catalytic degradation of methylene blue in heterogeneous Fenton system.

PubMed

Zha, Yiming; Zhou, Ziqing; He, Haibo; Wang, Tianlin; Luo, Liqiang

2016-01-01

Nanoscale zero-valent iron (nZVI) incorporated with nanomagnetic diatomite (DE) composite material was prepared for catalytic degradation of methylene blue (MB) in heterogeneous Fenton system. The material was constructed by two facile steps: Fe3O4 magnetic nanoparticles were supported on DE by chemical co-precipitation method, after which nZVI was incorporated into magnetic DE by liquid-phase chemical reduction strategy. The as-prepared catalyst was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, magnetic properties measurement and nitrogen adsorption-desorption isotherm measurement. The novel nZVI@Fe3O4-diatomite nanocomposites showed a distinct catalytic activity and a desirable effect for degradation of MB. MB could be completely decolorized within 8 min and the removal efficiency of total organic carbon could reach to 90% after reaction for 1 h.

Study of the dynamics of the MoO2-Mo2C system for catalytic partial oxidation reactions

NASA Astrophysics Data System (ADS)

Cuba Torres, Christian Martin

On a global scale, the energy demand is largely supplied by the combustion of non-renewable fossil fuels. However, their rapid depletion coupled with environmental and sustainability concerns are the main drivers to seek for alternative energetic strategies. To this end, the sustainable generation of hydrogen from renewable resources such as biodiesel would represent an attractive alternative solution to fossil fuels. Furthermore, hydrogen's lower environmental impact and greater independence from foreign control make it a strong contender for solving this global problem. Among a wide variety of methods for hydrogen production, the catalytic partial oxidation offers numerous advantages for compact and mobile fuel processing systems. For this reaction, the present work explores the versatility of the Mo--O--C catalytic system under different synthesis methods and reforming conditions using methyl oleate as a surrogate biodiesel. MoO2 exhibits good catalytic activity and exhibits high coke-resistance even under reforming conditions where long-chain oxygenated compounds are prone to form coke. Moreover, the lattice oxygen present in MoO2 promotes the Mars-Van Krevelen mechanism. Also, it is introduced a novel beta-Mo2C synthesis by the in-situ formation method that does not utilize external H2 inputs. Herein, the MoO 2/Mo2C system maintains high catalytic activity for partial oxidation while the lattice oxygen serves as a carbon buffer for preventing coke formation. This unique feature allows for longer operation reforming times despite slightly lower catalytic activity compared to the catalysts prepared by the traditional temperature-programmed reaction method. Moreover, it is demonstrated by a pulse reaction technique that during the phase transformation of MoO2 to beta-Mo2C, the formation of Mo metal as an intermediate is not responsible for the sintering of the material wrongly assumed by the temperature-programmed method.

Nanoscale effects of silica particle supports on the formation and properties of TiO2 nanocatalysts

NASA Astrophysics Data System (ADS)

Li, Aize; Jin, Yuhui; Muggli, Darrin; Pierce, David T.; Aranwela, Hemantha; Marasinghe, Gaya K.; Knutson, Theodore; Brockman, Greg; Zhao, Julia Xiaojun

2013-06-01

Small TiO2 crystals in the anatase phase are in high demand as photocatalysts. Stable TiO2 crystals in the anatase phase were obtained using a silica nanoparticle as a support. The focus of this study was to investigate the nanoscale effect of the silica support on the formation and properties of small anatase crystals. The experiments were carried out using powder X-ray diffraction, differential thermal analysis, transmission electron microscopy, and energy dispersion spectroscopy. The results showed that the size of the silica support played a crucial role in crystallization of TiO2 and regulation of TiO2 properties, including phase transition, crystal size, thermodynamic property and catalytic activity. A nanoscale curvature model of the spherical silica support was proposed to explain these size effects. Finally, the developed TiO2 catalysts were applied to the oxidation of methanol using a high-throughput photochemical reactor. The size effect of the silica supports on the TiO2 catalytic efficiency was demonstrated using this system.

Identification of N-Terminal Lobe Motifs that Determine the Kinase Activity of the Catalytic Domains and Regulatory Strategies of Src and Csk Protein Tyrosine Kinases†

PubMed Central

Huang, Kezhen; Wang, Yue-Hao; Brown, Alex; Sun, Gongqin

2009-01-01

Csk and Src protein tyrosine kinases are structurally homologous, but use opposite regulatory strategies. The isolated catalytic domain of Csk is intrinsically inactive and is activated by interactions with the regulatory SH3 and SH2 domains, while the isolated catalytic domain of Src is intrinsically active and is suppressed by interactions with the regulatory SH3 and SH2 domains. The structural basis for why one isolated catalytic domain is intrinsically active while the other is inactive is not clear. In this current study, we identify the structural elements in the N-terminal lobe of the catalytic domain that render the Src catalytic domain active. These structural elements include the α-helix C region, a β-turn between the β-4 and β-5 strands, and an Arg residue at the beginning of the catalytic domain. These three motifs interact with each other to activate the Src catalytic domain, but the equivalent motifs in Csk directly interact with the regulatory domains that are important for Csk activation. The Src motifs can be grafted to the Csk catalytic domain to obtain an active Csk catalytic domain. These results, together with available Src and Csk tertiary structures, reveal an important structural switch that determines the kinase activity of a catalytic domain and dictates the regulatory strategy of a kinase. PMID:19244618

A Highly Active Magnetically Recoverable Nano Ferrite-Glutathione-Copper (Nano-FGT-Cu) Catalyst for Huisgen 1, 3-Dipolar Cycloadditions

EPA Science Inventory

A homogeneous catalyst, where the catalyst is in the same phase as the reactants, is generally accepted by chemists.1 One attractive property is that all catalytic sites are accessible because the catalyst is generally a soluble metal complex where it is possible to tune the chem...

Process for upgrading wax from Fischer-Tropsch synthesis

DOEpatents

Derr, W.R. Jr.; Garwood, W.E.; Kuo, J.C.; Leib, T.M.; Nace, D.M.; Tabak, S.A.

1987-08-04

The waxy liquid phase of an oil suspension of Fischer-Tropsch catalyst containing dissolved wax is separated out and the wax is converted by hydrocracking, dewaxing or by catalytic cracking with a low activity catalyst to provide a highly olefinic product which may be further converted to premium quality gasoline and/or distillate fuel. 2 figs.

Efficient Decarbonylation of Furfural to Furan Catalyzed by Zirconia-Supported Palladium Clusters with Low Atomicity.

PubMed

Ishida, Tamao; Kume, Kurumi; Kinjo, Kota; Honma, Tetsuo; Nakada, Kengo; Ohashi, Hironori; Yokoyama, Takushi; Hamasaki, Akiyuki; Murayama, Haruno; Izawa, Yusuke; Utsunomiya, Masaru; Tokunaga, Makoto

2016-12-20

Decarbonylation of furfural to furan was efficiently catalyzed by ZrO 2 -supported Pd clusters in the liquid phase under a N 2 atmosphere without additives. Although Pd/C and Pd/Al 2 O 3 have frequently been used for decarbonylation, Pd/ZrO 2 exhibited superior catalytic performance compared with these conventional catalysts. Transmission electron microscopy and X-ray absorption fine structure measurements revealed that the size of the Pd particles decreased with an increase in the specific surface area of ZrO 2 . ZrO 2 with a high surface area immobilized Pd as clusters consisting of several (three to five) Pd atoms, whereas Pd aggregated to form nanoparticles on other supports such as carbon and Al 2 O 3 despite their high surface areas. The catalytic activity of Pd/ZrO 2 was enhanced with a decrease in particle size, and the smallest Pd/ZrO 2 was the most active catalyst for decarbonylation. When CeO 2 was used as the support, a decrease in Pd particle size with an increase in surface area was also observed. Single Pd atoms were deposited on CeO 2 with a high surface area, with a strong interaction through the formation of a Pd-O-Ce bond, which led to a lower catalytic activity than that of Pd/ZrO 2 . This result suggests that zero-valent small Pd clusters consisting of more than one Pd atom are the active species for the decarbonylation reaction. Recycling tests proved that Pd/ZrO 2 maintained its catalytic activity until its sixth use. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

On the Origin of the Catalytic power of Caboxypetidase A and Other Metalloenzymes

PubMed Central

Kilshtain, Alexandra Vardi; Warshel, Arieh

2009-01-01

Zinc metalloenzymes play a major role in key biological processes and Carboxypeptidase-A (CPA) is a major prototype of such enzymes. The present work quantifies the energetics of the catalytic reaction of CPA and its mutants using the EVB approach. The simulations allow us to quantify the origin of the catalytic power of this enzyme and to examine different mechanistic alternatives. The first step of the analysis used experimental information to determine the activation energy of each assumed mechanism of the reference reaction without the enzyme. The next step of the analysis involved EVB simulations of the reference reaction and then a calibration of the simulations by forcing them to reproduce the energetics of the reference reaction, in each assumed mechanism. The calibrated EVB was then used in systematic simulations of the catalytic reaction in the protein environment, without changing any parameter. The simulations reproduced the observed rate enhancement in two feasible general acid-general base mechanisms (GAGB-1 and GAGB-2), although the calculations with the GAGB-2 mechanism underestimated the catalytic effect in some treatments. We also reproduced the catalytic effect in the R127A mutant. The mutation calculations indicate that the GAGB-2 mechanism is significantly less likely than the GAGB-1 mechanism. It is also found, that the enzyme loses all its catalytic effect without the metal. This and earlier studies show that the catalytic effect of the metal is not some constant electrostatic effect, that can be assessed from gas phase studies, but a reflection of the dielectric effect of the specific environment. PMID:19480013

An Evaluation of the Vapor Phase Catalytic Ammonia Removal Process for Use in a Mars Transit Vehicle

NASA Technical Reports Server (NTRS)

Flynn, Michael; Borchers, Bruce

1998-01-01

An experimental program has been developed to evaluate the potential of the Vapor Phase Catalytic Ammonia Reduction (VPCAR) technology for use as a Mars Transit Vehicle water purification system. Design modifications which will be required to ensure proper operation of the VPCAR system in reduced gravity are also evaluated. The VPCAR system is an integrated wastewater treatment technology that combines a distillation process with high temperature catalytic oxidation. The distillation portion of the system utilizes a vapor compression distillation process to provide an energy efficient phase change separation. This portion of the system removes any inorganic salts and large molecular weight, organic contaminates, i.e., non-volatile, from the product water stream and concentrates these contaminates into a byproduct stream. To oxidize the volatile organic compounds and ammonia, a vapor phase, high temperature catalytic oxidizer is used. This catalytic system converts these compounds along with the aqueous product into CO2, H2O, and N2O. A secondary catalytic bed can then be used to reduce the N2O to nitrogen and oxygen (although not evaluated in this study). This paper describes the design specification of the VPCAR process, the relative benefits of its utilization in a Mars Transit Vehicle, and the design modification which will be required to ensure its proper operation in reduced gravity. In addition, the results of an experimental evaluation of the processors is presented. This evaluation presents the processors performance based upon product water purity, water recovery rates, and power.

Catalyst material and method of making

DOEpatents

Matson, Dean W.; Fulton, John L.; Linehan, John C.; Bean, Roger M.; Brewer, Thomas D.; Werpy, Todd A.; Darab, John G.

1997-01-01

The material of the present invention is a mixture of catalytically active material and carrier materials, which may be catalytically active themselves. Hence, the material of the present invention provides a catalyst particle that has catalytically active material throughout its bulk volume as well as on its surface. The presence of the catalytically active material throughout the bulk volume is achieved by chemical combination of catalytically active materials with carrier materials prior to or simultaneously with crystallite formation.

Catalyst material and method of making

DOEpatents

Matson, D.W.; Fulton, J.L.; Linehan, J.C.; Bean, R.M.; Brewer, T.D.; Werpy, T.A.; Darab, J.G.

1997-07-29

The material of the present invention is a mixture of catalytically active material and carrier materials, which may be catalytically active themselves. Hence, the material of the present invention provides a catalyst particle that has catalytically active material throughout its bulk volume as well as on its surface. The presence of the catalytically active material throughout the bulk volume is achieved by chemical combination of catalytically active materials with carrier materials prior to or simultaneously with crystallite formation. 7 figs.

Synthesis-atomic structure-properties relationships in metallic nanoparticles by total scattering experiments and 3D computer simulations: case of Pt-Ru nanoalloy catalysts

NASA Astrophysics Data System (ADS)

Prasai, Binay; Ren, Yang; Shan, Shiyao; Zhao, Yinguang; Cronk, Hannah; Luo, Jin; Zhong, Chuan-Jian; Petkov, Valeri

2015-04-01

An approach to determining the 3D atomic structure of metallic nanoparticles (NPs) in fine detail and using the unique knowledge obtained for rationalizing their synthesis and properties targeted for optimization is described and exemplified on Pt-Ru alloy NPs of importance to the development of devices for clean energy conversion such as fuel cells. In particular, PtxRu100-x alloy NPs, where x = 31, 49 and 75, are synthesized by wet chemistry and activated catalytically by a post-synthesis treatment involving heating under controlled N2-H2 atmosphere. So-activated NPs are evaluated as catalysts for gas-phase CO oxidation and ethanol electro-oxidation reactions taking place in fuel cells. Both as-synthesized and activated NPs are characterized structurally by total scattering experiments involving high-energy synchrotron X-ray diffraction coupled to atomic pair distribution functions (PDFs) analysis. 3D structure models both for as-synthesized and activated NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modelling Sutton-Chen method. Models are refined against the experimental PDF data by reverse Monte Carlo simulations and analysed in terms of prime structural characteristics such as metal-to-metal bond lengths, bond angles and first coordination numbers for Pt and Ru atoms. Analysis indicates that, though of a similar type, the atomic structure of as-synthesized and respective activated NPs differ in several details of importance to NP catalytic properties. Structural characteristics of activated NPs and data for their catalytic activity are compared side by side and strong evidence found that electronic effects, indicated by significant changes in Pt-Pt and Ru-Ru metal bond lengths at NP surface, and practically unrecognized so far atomic ensemble effects, indicated by distinct stacking of atomic layers near NP surface and prevalence of particular configurations of Pt and Ru atoms in these layers, contribute to the observed enhancement of the catalytic activity of PtxRu100-x alloy NPs at x ~ 50. Implications of so-established relationships between the atomic structure and catalytic activity of Pt-Ru alloy NPs on efforts aimed at improving further the latter by tuning-up the former are discussed and the usefulness of detailed NP structure studies to advancing science and technology of metallic NPs - exemplified.An approach to determining the 3D atomic structure of metallic nanoparticles (NPs) in fine detail and using the unique knowledge obtained for rationalizing their synthesis and properties targeted for optimization is described and exemplified on Pt-Ru alloy NPs of importance to the development of devices for clean energy conversion such as fuel cells. In particular, PtxRu100-x alloy NPs, where x = 31, 49 and 75, are synthesized by wet chemistry and activated catalytically by a post-synthesis treatment involving heating under controlled N2-H2 atmosphere. So-activated NPs are evaluated as catalysts for gas-phase CO oxidation and ethanol electro-oxidation reactions taking place in fuel cells. Both as-synthesized and activated NPs are characterized structurally by total scattering experiments involving high-energy synchrotron X-ray diffraction coupled to atomic pair distribution functions (PDFs) analysis. 3D structure models both for as-synthesized and activated NPs are built by molecular dynamics simulations based on the archetypal for current theoretical modelling Sutton-Chen method. Models are refined against the experimental PDF data by reverse Monte Carlo simulations and analysed in terms of prime structural characteristics such as metal-to-metal bond lengths, bond angles and first coordination numbers for Pt and Ru atoms. Analysis indicates that, though of a similar type, the atomic structure of as-synthesized and respective activated NPs differ in several details of importance to NP catalytic properties. Structural characteristics of activated NPs and data for their catalytic activity are compared side by side and strong evidence found that electronic effects, indicated by significant changes in Pt-Pt and Ru-Ru metal bond lengths at NP surface, and practically unrecognized so far atomic ensemble effects, indicated by distinct stacking of atomic layers near NP surface and prevalence of particular configurations of Pt and Ru atoms in these layers, contribute to the observed enhancement of the catalytic activity of PtxRu100-x alloy NPs at x ~ 50. Implications of so-established relationships between the atomic structure and catalytic activity of Pt-Ru alloy NPs on efforts aimed at improving further the latter by tuning-up the former are discussed and the usefulness of detailed NP structure studies to advancing science and technology of metallic NPs - exemplified. Electronic supplementary information (ESI) available: XRD patterns, TEM and 3D structure modelling methodology. See DOI: 10.1039/c5nr00800j

Application of Mössbauer spectroscopy in industrial heterogeneous catalysis: effect of oxidant on FePO4 material phase transformations in direct methanol synthesis from methane

NASA Astrophysics Data System (ADS)

Dasireddy, Venkata D. B. C.; Khan, Faiza B.; Hanzel, Darko; Bharuth-Ram, Krish; Likozar, Blaž

2017-11-01

The effect of the FePO4 material phase transformation in the direct selective oxidation of methane to methanol was studied using various oxidants, i.e. O2, H2O and N2O. The phases of the heterogeneous catalyst applied, before and after the reactions, were characterized by M¨ossbauer spectroscopy. The main reaction products were methanol, carbon monoxide and carbon dioxide, whereas formaldehyde was produced in rather minute amounts. The Mössbauer spectra showed the change of the initial catalyst material, FePO4 (tridymite-like phase (tdm)), to the reduced metal form, iron(II) pyrophosphate, Fe2P2O7, and thereafter, the material phase change was governed by the oxidation with individual oxidizing species.Mössbauer spectroscopy measurements applied along with X-ray diffraction (XRD) studies on fresh, reduced and spent catalytic materials demonstrated a transformation of the catalyst to a mixture of phases which depended on operating process conditions. Generally, activity was low and should be a subject of further material optimization and engineering, while the selectivity towards methanol at low temperatures applied was adequate. The proceeding redox mechanism should thus play a key role in catalytic material design, while the advantage of iron-based heterogeneous catalysts primarily lies in them being comparably inexpensive and comprising non-critical raw materials only.

Understanding the Oxygen Evolution Reaction Mechanism on CoO x using Operando Ambient-Pressure X-ray Photoelectron Spectroscopy

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

Favaro, Marco; Yang, Jinhui; Nappini, Silvia

Photoelectrochemical water splitting is a promising approach for renewable production of hydrogen from solar energy and requires interfacing advanced water-splitting catalysts with semiconductors. Understanding the mechanism of function of such electrocatalysts at the atomic scale and under realistic working conditions is a challenging, yet important, task for advancing efficient and stable function. This is particularly true for the case of oxygen evolution catalysts and, here, we study a highly active Co 3O 4/Co(OH) 2 biphasic electrocatalyst on Si by means of operando ambient-pressure X-ray photoelectron spectroscopy performed at the solid/liquid electrified interface. Spectral simulation and multiplet fitting reveal that themore » catalyst undergoes chemical-structural transformations as a function of the applied anodic potential, with complete conversion of the Co(OH) 2 and partial conversion of the spinel Co 3O 4 phases to CoO(OH) under precatalytic electrochemical conditions. Furthermore, we observe new spectral features in both Co 2p and O 1s core-level regions to emerge under oxygen evolution reaction conditions on CoO(OH). The operando photoelectron spectra support assignment of these newly observed features to highly active Co 4+ centers under catalytic conditions. Comparison of these results to those from a pure phase spinel Co 3O 4 catalyst supports this interpretation and reveals that the presence of Co(OH) 2 enhances catalytic activity by promoting transformations to CoO(OH). The direct investigation of electrified interfaces presented in this work can be extended to different materials under realistic catalytic conditions, thereby providing a powerful tool for mechanism discovery and an enabling capability for catalyst design.« less

Understanding the Oxygen Evolution Reaction Mechanism on CoO x using Operando Ambient-Pressure X-ray Photoelectron Spectroscopy

DOE PAGES

Favaro, Marco; Yang, Jinhui; Nappini, Silvia; ...

2017-06-09

Photoelectrochemical water splitting is a promising approach for renewable production of hydrogen from solar energy and requires interfacing advanced water-splitting catalysts with semiconductors. Understanding the mechanism of function of such electrocatalysts at the atomic scale and under realistic working conditions is a challenging, yet important, task for advancing efficient and stable function. This is particularly true for the case of oxygen evolution catalysts and, here, we study a highly active Co 3O 4/Co(OH) 2 biphasic electrocatalyst on Si by means of operando ambient-pressure X-ray photoelectron spectroscopy performed at the solid/liquid electrified interface. Spectral simulation and multiplet fitting reveal that themore » catalyst undergoes chemical-structural transformations as a function of the applied anodic potential, with complete conversion of the Co(OH) 2 and partial conversion of the spinel Co 3O 4 phases to CoO(OH) under precatalytic electrochemical conditions. Furthermore, we observe new spectral features in both Co 2p and O 1s core-level regions to emerge under oxygen evolution reaction conditions on CoO(OH). The operando photoelectron spectra support assignment of these newly observed features to highly active Co 4+ centers under catalytic conditions. Comparison of these results to those from a pure phase spinel Co 3O 4 catalyst supports this interpretation and reveals that the presence of Co(OH) 2 enhances catalytic activity by promoting transformations to CoO(OH). The direct investigation of electrified interfaces presented in this work can be extended to different materials under realistic catalytic conditions, thereby providing a powerful tool for mechanism discovery and an enabling capability for catalyst design.« less

Methylene Blue Inhibits Caspases by Oxidation of the Catalytic Cysteine.

PubMed

Pakavathkumar, Prateep; Sharma, Gyanesh; Kaushal, Vikas; Foveau, Bénédicte; LeBlanc, Andrea C

2015-09-24

Methylene blue, currently in phase 3 clinical trials against Alzheimer Disease, disaggregates the Tau protein of neurofibrillary tangles by oxidizing specific cysteine residues. Here, we investigated if methylene blue can inhibit caspases via the oxidation of their active site cysteine. Methylene blue, and derivatives, azure A and azure B competitively inhibited recombinant Caspase-6 (Casp6), and inhibited Casp6 activity in transfected human colon carcinoma cells and in serum-deprived primary human neuron cultures. Methylene blue also inhibited recombinant Casp1 and Casp3. Furthermore, methylene blue inhibited Casp3 activity in an acute mouse model of liver toxicity. Mass spectrometry confirmed methylene blue and azure B oxidation of the catalytic Cys163 cysteine of Casp6. Together, these results show a novel inhibitory mechanism of caspases via sulfenation of the active site cysteine. These results indicate that methylene blue or its derivatives could (1) have an additional effect against Alzheimer Disease by inhibiting brain caspase activity, (2) be used as a drug to prevent caspase activation in other conditions, and (3) predispose chronically treated individuals to cancer via the inhibition of caspases.

Methylene Blue Inhibits Caspases by Oxidation of the Catalytic Cysteine

PubMed Central

Pakavathkumar, Prateep; Sharma, Gyanesh; Kaushal, Vikas; Foveau, Bénédicte; LeBlanc, Andrea C.

2015-01-01

Methylene blue, currently in phase 3 clinical trials against Alzheimer Disease, disaggregates the Tau protein of neurofibrillary tangles by oxidizing specific cysteine residues. Here, we investigated if methylene blue can inhibit caspases via the oxidation of their active site cysteine. Methylene blue, and derivatives, azure A and azure B competitively inhibited recombinant Caspase-6 (Casp6), and inhibited Casp6 activity in transfected human colon carcinoma cells and in serum-deprived primary human neuron cultures. Methylene blue also inhibited recombinant Casp1 and Casp3. Furthermore, methylene blue inhibited Casp3 activity in an acute mouse model of liver toxicity. Mass spectrometry confirmed methylene blue and azure B oxidation of the catalytic Cys163 cysteine of Casp6. Together, these results show a novel inhibitory mechanism of caspases via sulfenation of the active site cysteine. These results indicate that methylene blue or its derivatives could (1) have an additional effect against Alzheimer Disease by inhibiting brain caspase activity, (2) be used as a drug to prevent caspase activation in other conditions, and (3) predispose chronically treated individuals to cancer via the inhibition of caspases. PMID:26400108

Synthesis and catalytic activity of polysaccharide templated nanocrystalline sulfated zirconia

NASA Astrophysics Data System (ADS)

Sherly, K. B.; Rakesh, K.

2014-01-01

Nanoscaled materials are of great interest due to their unique enhanced optical, electrical and magnetic properties. Sulfate-promoted zirconia has been shown to exhibit super acidic behavior and high activity for acid catalyzed reactions. Nanocrystalline zirconia was prepared in the presence of polysaccharide template by interaction between ZrOCl2ṡ8H2O and chitosan template. The interaction was carried out in aqueous phase, followed by the removal of templates by calcination at optimum temperature and sulfation. The structural and textural features were characterized by powder XRD, TG, SEM and TEM. XRD patterns showed the peaks of the diffractogram were in agreement with the theoretical data of zirconia with the catalytically active tetragonal phase and average crystalline size of the particles was found to be 9 nm, which was confirmed by TEM. TPD using ammonia as probe, FTIR and BET surface area analysis were used for analyzing surface features like acidity and porosity. The BET surface area analysis showed the sample had moderately high surface area. FTIR was used to find the type species attached to the surface of zirconia. UV-DRS found the band gap of the zirconia was found to be 2.8 eV. The benzylation of o-xylene was carried out batchwise in atmospheric pressure and 433K temperature using sulfated zirconia as catalyst.

The performances of proto-type Ni/MH secondary batteries using Zr-based hydrogen storage alloys and filamentary type Ni

NASA Astrophysics Data System (ADS)

Lee, Sang-Min; Lee, Ho; Kim, Jin-Ho; Lee, Paul S.; Lee, Jai-Young

2001-04-01

For the purpose of developing a Zr-based Laves phase alloy with higher capacity and better performance for electrochemical application, extensive work has been carried out. After careful alloy design of ZrMn2-based hydrogen storage alloys through varying their stoichiometry by means of substituting or adding alloying elements, the Zr0.9Ti0.1(Mn0.7V0.5Ni1.4)0.92 with high capacity (392 mAh/g at the 0.25C) and improved performance (comparable to that of commercialized AB5 type alloy) was developed. Another endeavor was made to improve the poor activation property and the low rate capability of the developed Zr-based Laves phase alloy for commercialization. The combination method of hot-immersion and slow-charging was introduced. It was found that electrode activation was greatly improved after hot immersion at 80°C for 12h followed by charging at 0.05C. The effects of this method are discussed in comparison with other activation methods. The combination method was successfully applied to the formation process of 80 Ah Ni/MH cells. A series of systematic investigations has been rendered to analyze the inner cell pressure characteristics of a sealed type Ni-MH battery. It was found that the increase of inner cell pressure in the sealed type Ni/MH battery of the above-mentioned Zr-Ti-Mn-V-Ni alloy was mainly due to the accumulation of oxygen gas during charge/discharge cycling. The fact identified that the surface catalytic activity was affected more dominantly by the oxygen recombination reaction than the reaction surface area was also identified. In order to improve the surface catalytic activity of a Zr-Ti-Mn-V-Ni alloy, which is closely related to the inner pressure behavior in a sealed cell, the electrode was fabricated by mixing the alloy with Cu powder and a filamentary type of Ni and replacing 75% of the carbon black with them; thus, the inner cell pressure rarely increases with cycles due to the active gas recombination reaction. Measurements of the surface area of the electrode and the surface catalytic activity showed that the surface catalytic activity for the oxygen recombination reaction was greatly improved by the addition of Cu powder and the filamentary type of Ni. Finally, we have collaborated with Hyundai Motors Company on fabrication of the 80Ah cells for Electric Vehicles and evaluated the cell performance.

Catalytic Activity and Impedance Behavior of Screen-Printed Nickel Oxide as Efficient Water Oxidation Catalysts.

PubMed

Singh, Archana; Fekete, Monika; Gengenbach, Thomas; Simonov, Alexandr N; Hocking, Rosalie K; Chang, Shery L Y; Rothmann, Mathias; Powar, Satvasheel; Fu, Dongchuan; Hu, Zheng; Wu, Qiang; Cheng, Yi-Bing; Bach, Udo; Spiccia, Leone

2015-12-21

We report that films screen printed from nickel oxide (NiO) nanoparticles and microballs are efficient electrocatalysts for water oxidation under near-neutral and alkaline conditions. Investigations of the composition and structure of the screen-printed films by X-ray diffraction, X-ray absorption spectroscopy, and scanning electron microscopy confirmed that the material was present as the cubic NiO phase. Comparison of the catalytic activity of the microball films to that of films fabricated by using NiO nanoparticles, under similar experimental conditions, revealed that the microball films outperform nanoparticle films of similar thickness owing to a more porous structure and higher surface area. A thinner, less-resistive NiO nanoparticle film, however, was found to have higher activity per Ni atom. Anodization in borate buffer significantly improved the activity of all three films. X-ray photoelectron spectroscopy showed that during anodization, a mixed nickel oxyhydroxide phase formed on the surface of all films, which could account for the improved activity. Impedance spectroscopy revealed that surface traps contribute significantly to the resistance of the NiO films. On anodization, the trap state resistance of all films was reduced, which led to significant improvements in activity. In 1.00 m NaOH, both the microball and nanoparticle films exhibit high long-term stability and produce a stable current density of approximately 30 mA cm(-2) at 600 mV overpotential. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Facile preparation of highly-dispersed cobalt-silicon mixed oxide nanosphere and its catalytic application in cyclohexane selective oxidation

PubMed Central

2011-01-01

Highly dispersed cobalt-silicon mixed oxide [Co-SiO2] nanosphere was successfully prepared with a modified reverse-phase microemulsion method. This material was characterized in detail by X-ray diffraction, transmission electron microscopy, Fourier transform infrared, ultraviolet-visible diffuse reflectance spectra, X-ray absorption spectroscopy near-edge structure, and N2 adsorption-desorption measurements. High valence state cobalt could be easily obtained without calcination, which is fascinating for the catalytic application for its strong oxidation ability. In the selective oxidation of cyclohexane, Co-SiO2 acted as an efficient catalyst, and good activity could be obtained under mild conditions. PMID:22067075

Synthesis of three-dimensional reduced graphene oxide layer supported cobalt nanocrystals and their high catalytic activity in F-T CO2 hydrogenation

NASA Astrophysics Data System (ADS)

He, Fei; Niu, Na; Qu, Fengyu; Wei, Shuquan; Chen, Yujin; Gai, Shili; Gao, Peng; Wang, Yan; Yang, Piaoping

2013-08-01

The reduced graphene oxide (rGO) supported cobalt nanocrystals have been synthesized through an in situ crystal growth method using Co(acac)2 under solvothermal conditions by using DMF as the solvent. By carefully controlling the reaction temperature, the phase transition of the cobalt nanocrystals from the cubic phase to the hexagonal phase has been achieved. Moreover, the microscopic structure and morphology as well as the reduction process of the composite have been investigated in detail. It is found that oxygen-containing functional groups on the graphene oxide (GO) can greatly influence the formation process of the Co nanocrystals by binding the Co2+ cations dissociated from the Co(acac)2 in the initial reaction solution at 220 °C, leading to the 3D reticular structure of the composite. Furthermore, this is the first attempt to use a Co/rGO composite as the catalyst in the F-T CO2 hydrogenation process. The catalysis testing results reveal that the as-synthesized 3D structured composite exhibits ideal catalytic activity and good stability, which may greatly extend the scope of applications for this kind of graphene-based metal hybrid material.The reduced graphene oxide (rGO) supported cobalt nanocrystals have been synthesized through an in situ crystal growth method using Co(acac)2 under solvothermal conditions by using DMF as the solvent. By carefully controlling the reaction temperature, the phase transition of the cobalt nanocrystals from the cubic phase to the hexagonal phase has been achieved. Moreover, the microscopic structure and morphology as well as the reduction process of the composite have been investigated in detail. It is found that oxygen-containing functional groups on the graphene oxide (GO) can greatly influence the formation process of the Co nanocrystals by binding the Co2+ cations dissociated from the Co(acac)2 in the initial reaction solution at 220 °C, leading to the 3D reticular structure of the composite. Furthermore, this is the first attempt to use a Co/rGO composite as the catalyst in the F-T CO2 hydrogenation process. The catalysis testing results reveal that the as-synthesized 3D structured composite exhibits ideal catalytic activity and good stability, which may greatly extend the scope of applications for this kind of graphene-based metal hybrid material. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03038e

Hydrothermal synthesis of TiO2/WO3 compositions and their photocatalytic activity

NASA Astrophysics Data System (ADS)

Pyachin, Sergey A.; Karpovich, Natalia F.; Zaitsev, Alexey V.; Makarevich, Konstantin S.; Burkov, Alexander A.; Ustinov, Alexander Yu.

2016-11-01

Photocatalytic activity, optical properties, thermal stability, phase patterns and morphology of nano-size TiO2/WO3 compositions obtained from organic precursors through hydrothermal synthesis have been studied. It has been shown that doping of anatase nanoparticles with tungsten W+6 results in particle diameter reduction from 35 to 10 nm; decrease in width of the band gap from 3.15 eV to 2.91 eV and increase in temperature of phase transition of anatase to rutile up to 980oC. Catalytic activity of TiO2/WO3 (4 mol.%) composition under photochemical methylene blue (MB) oxidation by simulated solar light exceeds that of undoped anatase (obtained in the same way) 6-fold.

One molecule of ionic liquid and tert-alcohol on a polystyrene-support as catalysts for efficient nucleophilic substitution including fluorination.

PubMed

Shinde, Sandip S; Patil, Sunil N

2014-12-07

The tert-alcohol and ionic liquid solvents in one molecule [mim-(t)OH][OMs] was immobilized on polystyrene and reported to be a highly efficient catalyst in aliphatic nucleophilic substitution using alkali metal salts. Herein, we investigated the catalytic activity of a new structurally modified polymer-supported tert-alcohol functionalized imidazolium salt catalyst in nucleophilic substitution of 2-(3-methanesulfonyloxypropyoxy)naphthalene as a model substrate with various metal nucleophiles. The tert-alcohol moiety of the ionic liquid with a hexyl chain distance from polystyrene had a better catalytic activity compared to the other resin which lacked an alkyl linker and tert-alcohol moiety. We found that the maximum [mim-(t)OH][OMs] loading had the best catalytic efficacy among the tested polystyrene-based ionic liquids (PSILs) in nucleophilic fluorination. The catalytic efficiency of the PS[him-(t)OH][OMs] as a phase transfer catalyst (PTC) was determined by carrying out various nucleophilic substitutions using the corresponding alkali metal salts from the third to sixth periodic in CH3CN or tert-BuOH media. The scope of this protocol with primary and secondary polar substrates containing many heteroatoms is also reported. This PS[him-(t)OH][OMs] catalyst not only enhances the reactivity of alkali metal salts and reduces the formation of by-products but also affords high yield with easy isolation.

Low Concentration Fe-Doped Alumina Catalysts Using Sol-Gel and Impregnation Methods: The Synthesis, Characterization and Catalytic Performance during the Combustion of Trichloroethylene.

PubMed

Maldonado, Carolina Solis; De la Rosa, Javier Rivera; Lucio-Ortiz, Carlos J; Hernández-Ramírez, Aracely; Barraza, Felipe F Castillón; Valente, Jaime S

2014-03-12

The role of iron in two modes of integration into alumina catalysts was studied at 0.39 wt% Fe and tested in trichloroethylene combustion. One modified alumina was synthesized using the sol-gel method with Fe added in situ during hydrolysis; another modification was performed using calcined alumina, prepared using the sol-gel method and impregnated with Fe. Several characterization techniques were used to study the level of Fe modification in the γ-Al₂O₃ phase formed and to correlate the catalytic properties during trichloroethylene (TCE) combustion. The introduction of Fe in situ during the sol-gel process influenced the crystallite size, and three iron species were generated, namely, magnetite, maghemite and hematite. The impregnated Fe-alumina formed hematite and maghemite, which were highly dispersed on the γ-Al₂O 3 surface. The X-ray photoelectron spectra (XPS), FT-IR and Mössbauer spectroscopy analyses revealed how Fe interacted with the γ-Al₂O₃ lattice in both catalysts. The impregnated Fe-catalyst showed the best catalytic performance compared to the catalyst that was Fe-doped in situ by the sol-gel method; both had better catalytic activity than pure alumina. This difference in activity was correlated with the accessibility of the reactants to the hematite iron species on the surface. The chlorine poisoning for all three catalysts was less than 1.8%.

Calcium-doped ceria/titanate tabular functional nanocomposite by layer-by-layer coating method

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

Liu, Xiang W., E-mail: lxwluck@gmail.co; Devaraju, M.K.; Yin, Shu

2010-07-15

Ca-doped ceria (CDC)/tabular titanate (K{sub 0.8}Li{sub 0.27}Ti{sub 1.73}O{sub 4}, TT) UV-shielding functional nanocomposite with fairly uniform CDC coating layers was prepared through a polyelectrolyte-associated layer-by-layer (LbL) coating method. TT with lepidocrocite-like layered structure was used as the substrate, poly (diallyldimethylammonium chloride) (PDDA) was used as a coupling agent, CDC nanoparticles were used as the main UV-shielding component. CDC/TT nanocomposites with various coating layers of CDC were obtained through a multistep coating process. The phases were studied by X-ray diffraction. The morphology and coating quality were studied by scanning electron microscopy and element mapping of energy dispersive X-ray analysis. The oxidationmore » catalytic activity, UV-shielding ability and using comfort were characterized by Rancimat test, UV-vis spectra and dynamic friction test, respectively. CDC/TT nanocomposites with low oxidation catalytic activity, high UV-shielding ability and good using comfort were finally obtained. - Graphical abstract: Through the control of surface charge of particles calcium-doped ceria/titanate composites with low oxidation catalytic activity, higher UV-shielding ability and excellent comfort was obtained by a facile layer-by-layer coating method.« less

Lamellar zirconium phosphates to host metals for catalytic purposes.

PubMed

Ballesteros-Plata, Daniel; Infantes-Molina, Antonia; Rodríguez-Aguado, Elena; Braos-García, Pilar; Rodríguez-Castellón, Enrique

2018-02-27

In the present study a porous lamellar zirconium phosphate heterostructure (PPH) formed from zirconium(iv) phosphate expanded with silica galleries (P/Zr molar ratio equal to 2 and (Si + Zr)/P equal to 3) was prepared to host noble metals. Textural and structural characterization of PPH-noble metal materials was carried out in order to elucidate the location and dispersion of the metallic particles and the properties of the resulting material to be used in catalytic processes. In the present paper, their activity in the catalytic hydrodeoxygenation (HDO) reaction of dibenzofuran (DBF) was evaluated. X-ray diffraction (XRD), solid state nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) evidenced that the structure of the pillared zirconium phosphate material was not modified by the incorporation of Pt and Pd. Moreover, transmission electron microscopy (TEM) showed a different dispersion of the noble metal. The acidity of the resulting PPH-noble metal materials also changed, although in all cases the acidity was of weak nature, and the incorporation of noble metals affected Brønsted acid sites as observed from 31 P NMR spectra. In general, the textural, structural and acidic properties of the resulting materials suggest that PPH can be considered a good candidate to be used as a catalytic support. Thus, the catalytic results of the PPH-noble metal samples indicated that the Pd sample showed a stable behavior probably ascribed to a high dispersion of the active phase. However, the Pt sample suffered from fast deactivation. The selectivity to the reaction products was strongly dependent on the noble metal employed.

Synthesis, characterization of double perovskite Ca{sub 2}MSbO{sub 6} (M = Dy, Fe, Cr, Al) materials via sol–gel auto-combustion and their catalytic properties

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

Feraru, S.; Samoila, P.; Borhan, A.I.

2013-10-15

Double perovskite-type oxide Ca{sub 2}MSbO{sub 6} materials, where M = Dy, Fe, Cr, and Al, were prepared by using the sol–gel auto-combustion method. The role of different B-site cations on their synthesis, structures, morphologies and catalytic properties was investigated. The progress of double-perovskite type structure formation and the disappearance of the organic phases were monitored by infrared absorption spectroscopy (FTIR). Double perovskite oxide structures were evaluated using X-ray diffraction (XRD), while the microstructure of obtained compounds was studied using scanning electron microscopy (SEM). Also, BET surface areas were measured at the liquid nitrogen temperature by nitrogen adsorption. Catalytic properties ofmore » the obtained compounds were evaluated by test reaction of hydrogen peroxide decomposition. - Highlights: • Ca{sub 2}MSbO{sub 6} double perovskites were obtained by sol–gel auto-combustion method. • Ca{sub 2}MSbO{sub 6} (M = Dy, Fe, Cr and Al) as catalysts in H{sub 2}O{sub 2} decomposition • Strong relationship between particles' shape, BET area and catalytic performance • Ca{sub 2}FeSbO{sub 6} spherical grains show superior catalytic activity.« less

Production of Ethylene through Ethanol Dehydration on SBA-15 Catalysts Synthesized by Sol-gel and One-step Hydrothermal Methods.

PubMed

Autthanit, Chaowat; Jongsomjit, Bunjerd

2018-02-01

The present work deals with the catalytic performance of SBA-15 supported catalysts in the gas phase catalytic dehydration of ethanol in the temperature range of 200 to 400°C. The SBA-15 support was incorporated on a zirconium (Zr) and bimetal of zirconium and lanthanum (Zr-La) prepared by sol-gel (SG) and hydrothermal (HT) methods. The catalysts were characterized by means of N 2 physisorption, SEM/EDX, and NH 3 -TPD. The experimental results demonstrated that the Zr-La/SBA-15-HT exhibited the highest catalytic activity. Ethanol conversion and ethylene selectivity were found to increase with increased reaction temperature. The best catalytic results were achieved for Zr-La/SBA-15-HT indicating values of ethanol conversion and ethylene yield of ca. 84% and 80%, respectively at 400°C. The most important parameter influencing their catalytic properties appears to be the interaction between metal and support depending on different methods. The metal dispersion inside the siliceous matrix of SBA-15 has a direct influence on their surface acidity. Meanwhile, the performance of these SBA-15 supported catalysts in ethanol dehydration is also related with the alteration of surface acidity caused by the introduction of Zr and Zr-La.

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

Mihaela Grigore; Richard Sakurovs; David French

Gasification of coke contributes to its degradation in the blast furnace. In this study, the effect of gasification on the inherent catalytic minerals in cokes and their reciprocal influence on gasification are investigated. The catalytic mineral phases identified in the cokes used in this study were metallic iron, iron sulfides, and iron oxides. Metallic iron and pyrrhotite were rapidly oxidized during gasification to iron oxide. The catalysts had a strong influence on the apparent rates at the initial stages of reaction. As gasification proceeds, their effect on the reaction rate diminishes as a result of reducing the surface contact betweenmore » catalyst and carbon matrix because of carbon consumption around the catalyst particles; with extended burnout the reactivity of the coke becomes increasingly dependent on surface area. The reaction rate in the initial stages was also influenced by the particle size of the catalytic minerals; for a given catalytic iron level, the cokes whose catalytic minerals were more finely dispersed had a higher apparent reaction rate than cokes containing larger catalytic particles. Iron, sodium, and potassium in the amorphous phase did not appear to affect the reaction rate. 40 refs., 16 figs., 6 tabs.« less

Ionizable side chains at catalytic active sites of enzymes.

PubMed

Jimenez-Morales, David; Liang, Jie; Eisenberg, Bob

2012-05-01

Catalytic active sites of enzymes of known structure can be well defined by a modern program of computational geometry. The CASTp program was used to define and measure the volume of the catalytic active sites of 573 enzymes in the Catalytic Site Atlas database. The active sites are identified as catalytic because the amino acids they contain are known to participate in the chemical reaction catalyzed by the enzyme. Acid and base side chains are reliable markers of catalytic active sites. The catalytic active sites have 4 acid and 5 base side chains, in an average volume of 1,072 Å(3). The number density of acid side chains is 8.3 M (in chemical units); the number density of basic side chains is 10.6 M. The catalytic active site of these enzymes is an unusual electrostatic and steric environment in which side chains and reactants are crowded together in a mixture more like an ionic liquid than an ideal infinitely dilute solution. The electrostatics and crowding of reactants and side chains seems likely to be important for catalytic function. In three types of analogous ion channels, simulation of crowded charges accounts for the main properties of selectivity measured in a wide range of solutions and concentrations. It seems wise to use mathematics designed to study interacting complex fluids when making models of the catalytic active sites of enzymes.

Ionizable Side Chains at Catalytic Active Sites of Enzymes

PubMed Central

Jimenez-Morales, David; Liang, Jie

2012-01-01

Catalytic active sites of enzymes of known structure can be well defined by a modern program of computational geometry. The CASTp program was used to define and measure the volume of the catalytic active sites of 573 enzymes in the Catalytic Site Atlas database. The active sites are identified as catalytic because the amino acids they contain are known to participate in the chemical reaction catalyzed by the enzyme. Acid and base side chains are reliable markers of catalytic active sites. The catalytic active sites have 4 acid and 5 base side chains, in an average volume of 1072 Å3. The number density of acid side chains is 8.3 M (in chemical units); the number density of basic side chains is 10.6 M. The catalytic active site of these enzymes is an unusual electrostatic and steric environment in which side chains and reactants are crowded together in a mixture more like an ionic liquid than an ideal infinitely dilute solution. The electrostatics and crowding of reactants and side chains seems likely to be important for catalytic function. In three types of analogous ion channels, simulation of crowded charges accounts for the main properties of selectivity measured in a wide range of solutions and concentrations. It seems wise to use mathematics designed to study interacting complex fluids when making models of the catalytic active sites of enzymes. PMID:22484856

Catalytic diversity in self-propagating peptide assemblies

NASA Astrophysics Data System (ADS)

Omosun, Tolulope O.; Hsieh, Ming-Chien; Childers, W. Seth; Das, Dibyendu; Mehta, Anil K.; Anthony, Neil R.; Pan, Ting; Grover, Martha A.; Berland, Keith M.; Lynn, David G.

2017-08-01

The protein-only infectious agents known as prions exist within cellular matrices as populations of assembled polypeptide phases ranging from particles to amyloid fibres. These phases appear to undergo Darwinian-like selection and propagation, yet remarkably little is known about their accessible chemical and biological functions. Here we construct simple peptides that assemble into well-defined amyloid phases and define paracrystalline surfaces able to catalyse specific enantioselective chemical reactions. Structural adjustments of individual amino acid residues predictably control both the assembled crystalline order and their accessible catalytic repertoire. Notably, the density and proximity of the extended arrays of enantioselective catalytic sites achieve template-directed polymerization of new polymers. These diverse amyloid templates can now be extended as dynamic self-propagating templates for the construction of even more complex functional materials.

Manganese-cerium oxide catalysts prepared by non-thermal plasma for NO oxidation: Effect of O2 in discharge atmosphere

NASA Astrophysics Data System (ADS)

Liu, Lu; Zheng, Chenghang; Wu, Shenghao; Gao, Xiang; Ni, Mingjiang; Cen, Kefa

2017-09-01

Non-thermal plasma with different O2 concentration in discharge atmosphere was applied to synthesize manganese and cerium mixed-oxides catalysts, which were compared in NO oxidation activity. Discharge atmosphere displayed a crucial influence on the performance of the catalysts prepared by plasma. Relatively low O2 concentration in discharge atmosphere allows synthesizing manganese-cerium oxides catalysts in a moderate environment and therefore is favorable for better physicochemical properties which lead to superior catalytic behavior. The best catalyst was obtained by treatment with 10% O2/N2 plasma and presented over 80% NO conversion in the temperature range of 275-325 °C, whereas catalyst prepared in pure O2 discharge atmosphere had the same activity with a catalyst prepared by calcinations. A correlation between the surface properties of the plasma prepared catalysts and its catalytic activity in NO oxidation is proposed. The amount of the surface adsorbed oxygen has an obvious linear correlation with the amount of Ce3+, the H2 consumption at low temperatures and the catalytic performance. The superior catalytic performance is mainly attributed to the stronger interaction between manganese oxides and ceria, and the formation of poorly crystallized Mn-O-Ce phase in the catalyst which resulted from the slow decomposition of nitrates and organics during plasma treatment. Catalysts prepared in relatively low O2 concentration have large specific surface area and is abundant in Ce3+ species and active oxygen species. The study suggests that plasma treatment with proper discharge gas components is a promising method to prepare effective manganese- cerium oxides catalyst for NO oxidation.

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.

Switchable Hydrolase Based on Reversible Formation of Supramolecular Catalytic Site Using a Self-Assembling Peptide.

PubMed

Zhang, Chunqiu; Shafi, Ramim; Lampel, Ayala; MacPherson, Douglas; Pappas, Charalampos G; Narang, Vishal; Wang, Tong; Maldarelli, Charles; Ulijn, Rein V

2017-11-13

The reversible regulation of catalytic activity is a feature found in natural enzymes which is not commonly observed in artificial catalytic systems. Here, we fabricate an artificial hydrolase with pH-switchable activity, achieved by introducing a catalytic histidine residue at the terminus of a pH-responsive peptide. The peptide exhibits a conformational transition from random coil to β-sheet by changing the pH from acidic to alkaline. The β-sheet self-assembles to form long fibrils with the hydrophobic edge and histidine residues extending in an ordered array as the catalytic microenvironment, which shows significant esterase activity. Catalytic activity can be reversible switched by pH-induced assembly/disassembly of the fibrils into random coils. At higher concentrations, the peptide forms a hydrogel which is also catalytically active and maintains its reversible (de-)activation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Patterned self-assembled monolayers for nanoscale lithography and the control of catalytically produced electroosmosis

NASA Astrophysics Data System (ADS)

Subramanian, Shyamala

This thesis explores two applications of self-assembled monolayers (SAMs) (a) for developing novel molecular assembly based nanolithography techniques and (b) for tailoring zeta-potential of surfaces towards achieving directional control of catalytically induced fluid flow. The first half of the thesis develops the process of molecular ruler lithography using sacrificial host structures. This is a novel hybrid nanolithography technique which combines chemical self-assembly with conventional fabrication methods for improving the resolution of existing lithography tools to sub-50 nm. Previous work related to molecular ruler lithography have shown the use of thiol-SAMs, placed one on top of the other like a molecular resist, for scaling down feature sizes. In this thesis various engineering solutions for improving the reproducibility, yield, nanoscale roughness and overall manufacturability of the process are introduced. This is achieved by introducing a sacrificial inert layer underneath the gold parent structure. This bilayer sacrificial host allows for preferential, easy and quick removal of the parent structures, isolates the parent metal from the underlying substrate and improves reproducibility of the lift-off process. Also it opens avenues for fabrication of high aspect ratio features. Also molecular layer vapor deposition method is developed for building the multilayer molecular resist via vapor phase to reduce contaminations and yield issues associated with solution phase deposition. The smallest isolated metal features produced using this process were 40 nm in width. The second half of the thesis describes application of thiol-SAMs to tailor surface properties of gold, specifically the surface charge or zeta potential. Previous work has demonstrated that the direction of movement of fluid in the vicinity of a catalytically active bimetallic junction placed in a solution of dilute hydrogen peroxide depends on the charge of the gold surface. SAMs with different end-group functionality impart different surface zeta potential to the gold surface. Zeta-potential engineering via patterning various end-group functionalized SAMs on gold surface to control direction of catalytically induced electroosmotic fluid flow is demonstrated for the first time. This work also describes the application of catalytic power to produce controlled rotational motion. Gold gears-like structures made using conventional microfabrication techniques and propelled by catalytic power are shown to rotate at speeds of 1 rotation/sec in a dilute solution of hydrogen peroxide. Fabrication of a force sensor for detection and measurement of catalytic forces is also introduced. The force sensor, with sensitivity in the piconewton range, consists of a microcantilever with a catalytically active silver post patterned on the tip. Changes in cantilever displacement and resonance frequency due to the catalytic force were monitored as a function of concentration of hydrogen peroxide. Overall, this thesis integrates SAM deposition and patterning techniques with conventional fabrication methods to engineer and control nanoscale structures and devices. Possible future device designs are described including CMOS devices having channel width defined using molecular ruler lithography with sacrificial hosts, drug delivery device based on AFM force sensor and channeless pumps powered by catalytic reactions with SAM controlled electroosmotic fluid flow.

The chemical and catalytic properties of nanocrystalline metal oxides prepared through modified sol-gel synthesis

NASA Astrophysics Data System (ADS)

Carnes, Corrie Leigh

The goal of this research was to synthesize, characterize and study the chemical properties of nanocrystalline metal oxides. Nanocrystalline (NC) ZnO, CuO, NiO, Al2O3, and the binary Al2O 3/MgO and ZnO/CuO were prepared through modified sol gel methods. These NC metal oxides were studied in comparison to the commercial (CM) metal oxides. The samples were characterized by XRD, TGA, FTIR, BET, and TEM. The NC samples were all accompanied by a significant increase in surface area and decrease in crystallite size. Several chemical reactions were studied to compare the NC samples to the CM samples. One of the reactions involved a high temperature reaction between carbon tetrachloride and the oxide to form carbon dioxide and the corresponding metal chloride. A similar high temperature reaction was conducted between the metal oxide and hydrogen sulfide to form water and the corresponding metal sulfide. A room temperature gas phase adsorption was studied where SO2 was adsorbed onto the oxide. A liquid phase adsorption conducted at room temperature was the destructive adsorption of paraoxon (a toxic insecticide). In all reactions the NC samples exhibited greater activity, destroying or adsorbing a larger amount of the toxins compared to the CM samples. To better study surface area effects catalytic reactions were also studied. The catalysis of methanol was studied over the nanocrystalline ZnO, CuO, NiO, and ZnO/CuO samples in comparison to their commercial counterparts. In most cases the NC samples proved to be more active catalysts, having higher percent conversions and turnover numbers. A second catalytic reaction was also studied, this reaction was investigated to look at the support effects. The catalysis of cyclopropane to propane was studied over Pt and Co catalysts. These catalysts were supported onto NC and CM alumina by impregnation. By observing differences in the catalytic behavior, support effects have become apparent.

Platinum-Modulated Cobalt Nanocatalysts for Low-Temperature Aqueous-Phase Fischer Tropsch Synthesis

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

Wang, Hang; Zhou, Wu; Liu, JinXun

2013-01-01

Fischer Tropsch synthesis (FTS) is an important catalytic process for liquid fuel generation, which converts coal/shale gas/biomass-derived syngas (a mixture of CO and H2) to oil. While FTS is thermodynamically favored at low temperature, it is desirable to develop a new catalytic system that could allow working at a relatively low reaction temperature. In this article, we present a one-step hydrogenation reduction route for the synthesis of Pt Co nanoparticles (NPs) which were found to be excellent catalysts for aqueous-phase FTS at 433 K. Coupling with atomic-resolution scanning transmission electron microscopy (STEM) and theoretical calculations, the outstanding activity is rationalizedmore » by the formation of Co overlayer structures on Pt NPs or Pt Co alloy NPs. The improved energetics and kinetics from the change of the transition states imposed by the lattice mismatch between the two metals are concluded to be the key factors responsible for the dramatically improved FTS performance.« less

Dynamic Oxygen on Surface: Catalytic Intermediate and Coking Barrier in the Modeled CO 2 Reforming of CH 4 on Ni (111)

DOE PAGES

Yuan, Kaidi; Zhong, Jian-Qiang; Zhou, Xiong; ...

2016-06-08

We identify Ni-O phases as important intermediates in a model dry (CO 2) reforming of methane catalyzed by Ni (111), based on results from in operando near ambient X-ray photoelectron spectroscopy (NAP-XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). We find that under a CO 2 or CO 2-CH 4 atmosphere, the Ni-O phases exist as p(2×2) structured chemisorbed oxygen (Chem-O), epitaxial NiO (111), or oxygen-rich Ni xO y (x2O 3), depending on the chemical potential. The growth rates of the Ni-O phases have a negative correlation with temperature from 600 K to 900 K, proving thatmore » their dynamic concentrations in the reaction are not limited by CO 2 activation, but by their thermal stability. Between 300 K and 800 K (1:1 CH 4 and CO 2 mixture), oxidation by CO 2is dominant, resulting in a fully Ni-O covered surface. Between 800 K and 900 K, a partially oxidized Ni (111) exists which could greatly facilitate the effective conversion of CH 4. As CH 4 is activation-limited and dissociates mainly on metallic nickel, the released carbon species can quickly react with the adjacent oxygen (Ni-O phases) to form CO. After combining with carbon and releasing CO molecules, the Ni-O phases can be further regenerated through oxidation by CO 2. In this way, the Ni-O phases participate in the catalytic process, acting as an intermediate in addition to the previously reported Ni-C phases. We also reveal the carbon phobic property of the Ni-O phases, which links to the intrinsic coking resistance of the catalysts. The low dynamic coverage of surface oxygen at higher temperatures (>900 K) is inferred to be an underlying factor causing carbon aggregation. Therefore solutions based on Ni-O stabilization are proposed in developing coking resisting catalysts.« less

Uranium oxide catalysts: environmental applications for treatment of chlorinated organic waste from nuclear industry.

PubMed

Lazareva, Svetlana; Ismagilov, Zinfer; Kuznetsov, Vadim; Shikina, Nadezhda; Kerzhentsev, Mikhail

2018-02-05

Huge amounts of nuclear waste, including depleted uranium, significantly contribute to the adverse environmental situation throughout the world. An approach to the effective use of uranium oxides in catalysts for the deep oxidation of chlorine-containing hydrocarbons is suggested. Investigation of the catalytic activity of the synthesized supported uranium oxide catalysts doped with Cr, Mn and Co transition metals in the chlorobenzene oxidation showed that these catalysts are comparable with conventional commercial ones. Physicochemical properties of the catalysts were studied by X-ray diffraction, temperature-programmed reduction with hydrogen (H 2 -TPR), and Fourier transform infrared spectroscopy. The higher activity of Mn- and Co-containing uranium oxide catalysts in the H 2 -TPR and oxidation of chlorobenzene in comparison with non-uranium catalysts may be related to the formation of a new disperse phase represented by uranates. The study of chlorobenzene adsorption revealed that the surface oxygen is involved in the catalytic process.

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

Yip, Wingkip; Dong, Jianguo,; Yang, Shang Fa

Tomato ACC synthase is inactivated by its substrate SAM, with the moiety of aminobutyrate being covalently linked to ACC synthase during the catalytic reactions. A partial purified ACC synthase (the catalytic activity 100 {mu}mol/h{center dot}mg protein) from pellets of apple extract was incubated with (3,4{sup 14}C) SAM. Only one radioactive peak was revealed in a C-4 reverse phase HPLC and one radioactive band on SDS-PAGE with an M.W. of 48 kDa. Apple ACC synthase in native form is resistant to V8, {alpha}-chromtrypsin and carboxylpeptidase A digestion, but effectively inactivated by trypsin and ficin, as demonstrated by both the activity assaymore » and SAM labeling. The radioactive protein cut from the SDS-PAGE was injected to three mice, two of the mice showed responses to the protein in western blot analysis. The antibodies from mice is currently under characterization.« less

Calcium Modulation of Plant Plasma Membrane-Bound Atpase Activities

NASA Technical Reports Server (NTRS)

Caldwell, C.

1983-01-01

The kinetic properties of barley enzyme are discussed and compared with those of other plants. Possibilities for calcium transport in the plasma membrane by proton pump and ATPase-dependent calcium pumps are explored. Topics covered include the ph phase of the enzyme; high affinity of barley for calcium; temperature dependence, activation enthalpy, and the types of ATPase catalytic sites. Attention is given to lipids which are both screened and bound by calcium. Studies show that barley has a calmodulin activated ATPase that is found in the presence of magnesium and calcium.

Catalytic activity in lithium-treated core–shell MoO x/MoS 2 nanowires

DOE PAGES

Cummins, Dustin R.; Martinez, Ulises; Kappera, Rajesh; ...

2015-09-22

Significant interest has grown in the development of earth-abundant and efficient catalytic materials for hydrogen generation. Layered transition metal dichalcogenides present opportunities for efficient electrocatalytic systems. Here, we report the modification of 1D MoO x/MoS 2 core–shell nanostructures by lithium intercalation and the corresponding changes in morphology, structure, and mechanism of H 2 evolution. The 1D nanowires exhibit significant improvement in H 2 evolution properties after lithiation, reducing the hydrogen evolution reaction (HER) onset potential by ~50 mV and increasing the generated current density by ~600%. The high electrochemical activity in the nanowires results from disruption of MoS 2 layersmore » in the outer shell, leading to increased activity and concentration of defect sites. This is in contrast to the typical mechanism of improved catalysis following lithium exfoliation, i.e., crystal phase transformation. As a result, these structural changes are verified by a combination of Raman and X-ray photoelectron spectroscopy (XPS).« less

Heterogeneous Catalysts for VOC Oxidation from Red Mud and Bagasse Ash Carbon

NASA Astrophysics Data System (ADS)

Pande, Gaurav

A range of VOC oxidation catalysts have been prepared in this study from agricultural and industrial waste as the starting point. The aim is to prepare catalysts with non-noble metal oxides as the active catalytic component (iron in red mud). The same active component was also supported on activated carbon obtained from unburned carbon in bagasse ash. Red mud which is an aluminum industry waste and rich in different phases of iron as oxide and hydroxide is used as the source for the catalytically active species. It is our aim to enhance the catalytic performance of red mud which though high in iron concentration has a low surface area and may not have the properties of an ideal catalyst by itself. In one of the attempts to enhance the catalytic performance, we have tried to leach red mud for which we have explored a range of leaching acids for effecting the leaching most efficiently and then precipitated the iron from the leachate as its hydroxide by precipitating with alkali solution followed by drying and calcination to give high surface area metal oxide material. Extensive surface characterization and VOC oxidation catalytic testing were performed for these solids. In a step to further enhance the catalytic activity towards oxidation, copper was introduced by taking another industrial waste from the copper tubing industry viz. the pickling acid. Copper has a more favourable redox potential making it catalytically more effective than iron. To make the mixed metal oxide, red mud leachate was mixed with the pickling acid in a pre-decided ratio before precipitating with alkali solution followed by drying and calcination as was done with the red mud leachate. The results from these experiments are encouraging. The temperature programmed reduction (TPR) of the solids show that the precipitate of red mud leachates show hydrogen uptake peak at a lower temperature than for just the calcined red mud. This could be due to the greatly enhanced surface area of the prepared solids. The highest surface area of 311 m2/g was for the sample prepared from oxalic acid and l-ascorbic acid as the leaching acid; as received red mud has a surface area of 11.5 m2/g. This sample showed better catalytic performance than the ones made from hydrochloric acid as the leaching acid in spite of a similar increase in surface area. High temperature XRD shows the reason for this difference in catalytic properties could be due to both the solids reducing in a different way to give different phases though they are both derived from red mud as the starting material. Also, the sample prepared with oxalic acid leachate had higher surface iron concentration. For the best catalyst (oxalic acid derived) the light off temperature is about 300 °C for toluene oxidation. For solids prepared from red mud leachate for iron source and pickling acid for copper source, it was seen that the TPR gave hydrogen absorption at temperatures even lower than that for red mud leachate precipitates. In another set of experiments, iron oxide impregnated on activated carbon supports were prepared. Activated carbon is known for its adsorption properties which could give a better access of the impregnated metal oxide catalyst to perform the catalytic oxidation on the adsorbed substrate. Unburned carbon in bagasse ash which is a sugar industry agricultural waste was used to get the activated carbon. This material was separated from the ash and further modified to enhance the activity and increase the porosity. To this effect steam activation was performed. To impart thermal stability for oxidation reaction, the carbon was impregnated by phosphoric acid at activated at high temperatures in inert atmosphere. These carbons were thermally stable due to the surface C--O--P groups. Toluene adsorption studies were also performed for both the steam activated as well as phosphoric acid activated carbon and it was found that the steam activated carbons with less surface oxygen had reasonable adsorption attributes. For iron impregnation onto the prepared bagasse ash carbons, two different methods of impregnation viz. incipient wetness method as well as impregnation by precipitation of the red mud leachate by adding alkali to a slurry of carbon and leachate (Pratt method) was used. It was found that impregnation by precipitation led to better butanol oxidation performing catalyst than the one prepared by impregnating by incipient wetness method. The best performing catalyst amongst the iron impregnated on carbon types was found to give 100% butanol conversion at 200 °C. It was also observed that red mud leachate precipitated catalyst performed well for toluene oxidation and not for butanol oxidation while carbon supported iron oxide catalysts worked better for butanol oxidation than for toluene oxidation.

Photothermal Catalyst Engineering: Hydrogenation of Gaseous CO2 with High Activity and Tailored Selectivity

PubMed Central

Jia, Jia; Wang, Hong; Lu, Zhuole; O'Brien, Paul G.; Ghoussoub, Mireille; Duchesne, Paul; Zheng, Ziqi; Li, Peicheng; Qiao, Qiao; Wang, Lu; Gu, Alan; Jelle, Abdinoor A.; Dong, Yuchan; Wang, Qiang; Ghuman, Kulbir Kaur; Wood, Thomas; Qian, Chenxi; Shao, Yue; Qiu, Chenyue; Ye, Miaomiao; Zhu, Yimei; Lu, Zheng‐Hong; Zhang, Peng; Helmy, Amr S.; Singh, Chandra Veer; Kherani, Nazir P.; Perovic, Doug D.

2017-01-01

Abstract This study has designed and implemented a library of hetero‐nanostructured catalysts, denoted as Pd@Nb2O5, comprised of size‐controlled Pd nanocrystals interfaced with Nb2O5 nanorods. This study also demonstrates that the catalytic activity and selectivity of CO2 reduction to CO and CH4 products can be systematically tailored by varying the size of the Pd nanocrystals supported on the Nb2O5 nanorods. Using large Pd nanocrystals, this study achieves CO and CH4 production rates as high as 0.75 and 0.11 mol h−1 gPd −1, respectively. By contrast, using small Pd nanocrystals, a CO production rate surpassing 18.8 mol h−1 gPd −1 is observed with 99.5% CO selectivity. These performance metrics establish a new milestone in the champion league of catalytic nanomaterials that can enable solar‐powered gas‐phase heterogeneous CO2 reduction. The remarkable control over the catalytic performance of Pd@Nb2O5 is demonstrated to stem from a combination of photothermal, electronic and size effects, which is rationally tunable through nanochemistry. PMID:29051865

Platinum clusters with precise numbers of atoms for preparative-scale catalysis.

PubMed

Imaoka, Takane; Akanuma, Yuki; Haruta, Naoki; Tsuchiya, Shogo; Ishihara, Kentaro; Okayasu, Takeshi; Chun, Wang-Jae; Takahashi, Masaki; Yamamoto, Kimihisa

2017-09-25

Subnanometer noble metal clusters have enormous potential, mainly for catalytic applications. Because a difference of only one atom may cause significant changes in their reactivity, a preparation method with atomic-level precision is essential. Although such a precision with enough scalability has been achieved by gas-phase synthesis, large-scale preparation is still at the frontier, hampering practical applications. We now show the atom-precise and fully scalable synthesis of platinum clusters on a milligram scale from tiara-like platinum complexes with various ring numbers (n = 5-13). Low-temperature calcination of the complexes on a carbon support under hydrogen stream affords monodispersed platinum clusters, whose atomicity is equivalent to that of the precursor complex. One of the clusters (Pt 10 ) exhibits high catalytic activity in the hydrogenation of styrene compared to that of the other clusters. This method opens an avenue for the application of these clusters to preparative-scale catalysis.The catalytic activity of a noble metal nanocluster is tied to its atomicity. Here, the authors report an atom-precise, fully scalable synthesis of platinum clusters from molecular ring precursors, and show that a variation of only one atom can dramatically change a cluster's reactivity.

Photothermal Catalyst Engineering: Hydrogenation of Gaseous CO 2 with High Activity and Tailored Selectivity

DOE PAGES

Jia, Jia; Wang, Hong; Lu, Zhuole; ...

2017-07-25

This study has designed and implemented a library of hetero-nanostructured catalysts, denoted as Pd@Nb 2O 5, comprised of size-controlled Pd nanocrystals interfaced with Nb 2O 5 nanorods. This study also demonstrates that the catalytic activity and selectivity of CO 2 reduction to CO and CH 4 products can be systematically tailored by varying the size of the Pd nanocrystals supported on the Nb 2O 5 nanorods. Using large Pd nanocrystals, this study achieves CO and CH 4 production rates as high as 0.75 and 0.11 mol h –1 gPd –1, respectively. By contrast, using small Pd nanocrystals, a CO productionmore » rate surpassing 18.8 mol h –1 gPd –1 is observed with 99.5% CO selectivity. These performance metrics establish a new milestone in the champion league of catalytic nanomaterials that can enable solar-powered gas-phase heterogeneous CO 2 reduction. In conclusion, the remarkable control over the catalytic performance of Pd@Nb 2O 5 is demonstrated to stem from a combination of photothermal, electronic and size effects, which is rationally tunable through nanochemistry.« less

Size, shape, and compositional effects on the order-disorder phase transitions in Au-Cu and Pt-M (M = Fe, Co, and Ni) nanocluster alloys.

PubMed

Kaatz, Forrest H; Bultheel, Adhemar

2018-08-24

Au-Cu and Pt-M (M = Fe, Co, and Ni) nanocluster alloys are currently being investigated world-wide by many researchers for their interesting catalytic and nanophase properties. The low temperature behavior of the phase diagrams is not well understood for alloys with nanometer sizes and shapes. We consider two models for low temperature ordering in the phase diagrams of Au-Cu and Pt-M nanocluster alloys. These models are valid for sizes ∼5 nm and approach bulk values for sizes ∼20 nm. We study the phase transitions in nanoclusters with cubic, octahedral, and cuboctahedral shapes, covering the compositions of interest. These models are based on studying the melting temperatures in nanoclusters using the regular solution, mixing model for alloys. From our data, experiments on nanocubes about 5 nm in size, of stoichiometric AuCu and PtM composition, could help differentiate between the models. Dispersion data shows that for the three shapes considered, octahedra have the highest percentage of surface atoms for the same relative diameter. We summarize the effects of structural ordering on the catalytic activity and suggest a method to avoid sintering during annealing of Pt-M alloys.

The new insight into the structure-activity relation of Pd/CeO2-ZrO2-Nd2O3 catalysts by Raman, in situ DRIFTS and XRD Rietveld analysis.

PubMed

Yang, X; Yang, L; Lin, J; Zhou, R

2016-01-28

Pd/CeO2-ZrO2-Nd2O3 (CZN) catalysts with different CeO2/ZrO2 molar ratios were synthesized and have been characterized by multiple techniques, e.g. XRD in combination with Rietveld refinement, UV-Raman, XPS and in situ DRIFTS. The XRD pattern of CZN with CeO2/ZrO2 molar ratios ≥1/2 can be indexed satisfactorily to the fluorite structure with a space group Fm3̄m, while the XRD patterns of CZ12 only display diffraction peaks of the tetragonal phase (S.G. P42/nmc). Nd addition can effectively stabilize the cubic structure of the CZN support and increase the enrichment of defect sites on the surface, which may be related to the better catalytic activity of Pd/CZN12 catalysts compared with Pd/CZ12. The presence of moderate ZrO2 can increase the concentration of O* active species, leading to accelerate the formation of nitrate species and thus enhance the catalytic activity of NOx and HC elimination. The Pd-dispersion decreases with the increasing Zr content, leading to the decreased CO catalytic activity, especially for the aged catalysts. The change regularity of the OSC value is almost the same with the in situ dynamic operational window, demonstrating that the in situ dynamic operational window is basically affected by the OSC value.

Trends in Selective Hydrogen Peroxide Production on Transition Metal Surfaces from First Principles

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

Rankin, Rees B.; Greeley, Jeffrey P.

2012-10-19

We present a comprehensive, Density Functional Theory-based analysis of the direct synthesis of hydrogen peroxide, H2O2, on twelve transition metal surfaces. We determine the full thermodynamics and selected kinetics of the reaction network on these metals, and we analyze these energetics with simple, microkinetically motivated rate theories to assess the activity and selectivity of hydrogen peroxide production on the surfaces of interest. By further exploiting Brønsted-Evans-Polanyi relationships and scaling relationships between the binding energies of different adsorbates, we express the results in the form of a two dimensional contour volcano plot, with the activity and selectivity being determined as functionsmore » of two independent descriptors, the atomic hydrogen and oxygen adsorption free energies. We identify both a region of maximum predicted catalytic activity, which is near Pt and Pd in descriptor space, and a region of selective hydrogen peroxide production, which includes Au. The optimal catalysts represent a compromise between activity and selectivity and are predicted to fall approximately between Au and Pd in descriptor space, providing a compact explanation for the experimentally known performance of Au-Pd alloys for hydrogen peroxide synthesis, and suggesting a target for future computational screening efforts to identify improved direct hydrogen peroxide synthesis catalysts. Related methods of combining activity and selectivity analysis into a single volcano plot may be applicable to, and useful for, other aqueous phase heterogeneous catalytic reactions where selectivity is a key catalytic criterion.« less

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.

Electrons to Reactors Multiscale Modeling: Catalytic CO Oxidation over RuO 2

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

Sutton, Jonathan E.; Lorenzi, Juan M.; Krogel, Jaron T.

First-principles kinetic Monte Carlo (1p-kMC) simulations for CO oxidation on two RuO 2 facets, RuO 2(110) and RuO 2(111), were coupled to the computational fluid dynamics (CFD) simulations package MFIX, and reactor-scale simulations were then performed. 1p-kMC coupled with CFD has recently been shown as a feasible method for translating molecular scale mechanistic knowledge to the reactor scale, enabling comparisons to in situ and online experimental measurements. Only a few studies with such coupling have been published. This work incorporates multiple catalytic surface facets into the scale-coupled simulation, and three possibilities were investigated: the two possibilities of each facet individuallymore » being the dominant phase in the reactor, and also the possibility that both facets were present on the catalyst particles in the ratio predicted by an ab initio thermodynamics-based Wulff construction. When lateral interactions between adsorbates were included in the 1p-kMC simulations, the two surfaces, RuO 2(110) and RuO 2(111), were found to be of similar order-of-magnitude in activity for the pressure range of 1 × 10 –4 bar to 1 bar, with the RuO 2(110) surface-termination showing more simulated activity than the RuO 2(111) surface-termination. Coupling between the 1p-kMC and CFD was achieved with a lookup table generated by the error-based modified Shepard interpolation scheme. Isothermal reactor scale simulations were performed and compared to two separate experimental studies, conducted with reactant partial pressures of ≤0.1 bar. Simulations without an isothermality restriction were also conducted and showed that the simulated temperature gradient across the catalytic reactor bed is <0.5 K, which validated the use of the isothermality restriction for investigating the reactor-scale phenomenological temperature dependences. The approach with the Wulff construction based reactor simulations reproduced a trend similar to one experimental data set relatively well, with the (110) surface being more active at higher temperaures; in contrast, for the other experimental data set, our reactor simulations achieve surprisingly and perhaps fortuitously good agreement with the activity and phenomenological pressure dependence when it is assumed that the (111) facet is the only active facet present. Lastly, the active phase of catalytic CO oxidation over RuO 2 remains unsettled, but the present study presents proof of principle (and progress) toward more accurate multiscale modeling from electrons to reactors and new simulation results.« less

Electrons to Reactors Multiscale Modeling: Catalytic CO Oxidation over RuO 2

DOE PAGES

Sutton, Jonathan E.; Lorenzi, Juan M.; Krogel, Jaron T.; ...

2018-04-20

First-principles kinetic Monte Carlo (1p-kMC) simulations for CO oxidation on two RuO 2 facets, RuO 2(110) and RuO 2(111), were coupled to the computational fluid dynamics (CFD) simulations package MFIX, and reactor-scale simulations were then performed. 1p-kMC coupled with CFD has recently been shown as a feasible method for translating molecular scale mechanistic knowledge to the reactor scale, enabling comparisons to in situ and online experimental measurements. Only a few studies with such coupling have been published. This work incorporates multiple catalytic surface facets into the scale-coupled simulation, and three possibilities were investigated: the two possibilities of each facet individuallymore » being the dominant phase in the reactor, and also the possibility that both facets were present on the catalyst particles in the ratio predicted by an ab initio thermodynamics-based Wulff construction. When lateral interactions between adsorbates were included in the 1p-kMC simulations, the two surfaces, RuO 2(110) and RuO 2(111), were found to be of similar order-of-magnitude in activity for the pressure range of 1 × 10 –4 bar to 1 bar, with the RuO 2(110) surface-termination showing more simulated activity than the RuO 2(111) surface-termination. Coupling between the 1p-kMC and CFD was achieved with a lookup table generated by the error-based modified Shepard interpolation scheme. Isothermal reactor scale simulations were performed and compared to two separate experimental studies, conducted with reactant partial pressures of ≤0.1 bar. Simulations without an isothermality restriction were also conducted and showed that the simulated temperature gradient across the catalytic reactor bed is <0.5 K, which validated the use of the isothermality restriction for investigating the reactor-scale phenomenological temperature dependences. The approach with the Wulff construction based reactor simulations reproduced a trend similar to one experimental data set relatively well, with the (110) surface being more active at higher temperaures; in contrast, for the other experimental data set, our reactor simulations achieve surprisingly and perhaps fortuitously good agreement with the activity and phenomenological pressure dependence when it is assumed that the (111) facet is the only active facet present. Lastly, the active phase of catalytic CO oxidation over RuO 2 remains unsettled, but the present study presents proof of principle (and progress) toward more accurate multiscale modeling from electrons to reactors and new simulation results.« less

Size-dependent effects in supported highly dispersed Fe2O3 catalysts, doped with Pt and Pd

NASA Astrophysics Data System (ADS)

Cherkezova-Zheleva, Zara; Shopska, Maya; Mitov, Ivan; Kadinov, Georgi

2010-06-01

Series of Fe and Fe-Me (Me = Pt or Pd) catalyst supported on γ-Al2O3, TiO2 (anatase) or diatomite were prepared by the incipient wetness impregnation method. The metal loading was 8 wt.% Fe and 0.7 wt.% noble metal. The preparation and pretreatment conditions of all studied samples were kept to be the same. X-ray diffraction, Moessbauer spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed reduction are used for characterization of the supports and the samples at different steps during their treatment and catalytic tests. The catalytic activity of the samples was tested in the reaction of total benzene oxidation. The physicochemical and catalytic properties of the obtained materials are compared with respect of the different chemical composition, dispersion of used carriers and of the supported phases. Samples with the same composition prepared by mechanical mixing are studied as catalysts for comparison and for clearing up the presence of size-dependent effect, also.

Conversion of CO2 into cyclic carbonates by a Co(ii) metal-organic framework and the improvement of catalytic activity via nanocrystallization.

PubMed

Ji, Xiao-He; Zhu, Ning-Ning; Ma, Jian-Gong; Cheng, Peng

2018-02-06

The Co(ii) metal-organic framework (MOF) {[Co(μ 3 -L)(H 2 O)]·0.5H 2 O} n (1, H 2 L = thiazolidine 2,4-dicarboxylic acid) with rich Lewis acid sites was used as a catalyst for the conversion of CO 2 and propylene oxide into propylene carbonate with a yield of up to 98% under 50 °C and 1 atm. 1 exhibited excellent reusability, which could be regenerated easily for at least five runs without a decrease in the yield. Importantly, we synthesized two types of nano-crystals (N1 and N2) of 1 with polyvinylpyrrolidone (PVP) and hexadecyltrimethylammonium bromide (CTAB) as surfactants, respectively, and investigated their catalytic properties in comparison with that of 1 in the powder phase. A significant enhancement in both catalytic efficiency and product yield was observed when 1 was nano-crystallized. This is the first investigation about the relationship between the morphology and the catalytic parameters of MOFs. The results showed a strategy for efficiently applying MOFs as catalysts towards CO 2 conversion, which could also be used in other MOF-catalyzed processes.

Catalytic methods using molecular oxygen for treatment of PMMS and ECLSS waste streams, volume 2

NASA Technical Reports Server (NTRS)

Akse, James R.

1992-01-01

Catalytic oxidation has proven to be an effective addition to the baseline sorption, ion exchange water reclamation technology which will be used on Space Station Freedom (SSF). Low molecular weight, polar organics such as alcohols, aldehydes, ketones, amides, and thiocarbamides which are poorly removed by the baseline multifiltration (MF) technology can be oxidized to carbon dioxide at low temperature (121 C). The catalytic oxidation process by itself can reduce the Total Organic Carbon (TOC) to below 500 ppb for solutions designed to model these waste waters. Individual challenges by selected contaminants have shown only moderate selectivity towards particular organic species. The combined technology is applicable to the more complex waste water generated in the Process Materials Management System (PMMS) and Environmental Control and Life Support System (ECLSS) aboard SSF. During the phase 3 Core Module Integrated Facility (CMIF) water recovery tests at NASA MSFC, real hygiene waste water and humidity condensate were processed to meet potable specifications by the combined technology. A kinetic study of catalytic oxidation demonstrates that the Langmuir-Hinshelwood rate equation for heterogeneous catalysts accurately represent the kinetic behavior. From this relationship, activation energy and rate constants for acetone were determined.

Active biopolymers in green non-conventional media: a sustainable tool for developing clean chemical processes.

PubMed

Lozano, Pedro; Bernal, Juana M; Nieto, Susana; Gomez, Celia; Garcia-Verdugo, Eduardo; Luis, Santiago V

2015-12-21

The greenness of chemical processes turns around two main axes: the selectivity of catalytic transformations, and the separation of pure products. The transfer of the exquisite catalytic efficiency shown by enzymes in nature to chemical processes is an important challenge. By using appropriate reaction systems, the combination of biopolymers with supercritical carbon dioxide (scCO2) and ionic liquids (ILs) resulted in synergetic and outstanding platforms for developing (multi)catalytic green chemical processes, even under flow conditions. The stabilization of biocatalysts, together with the design of straightforward approaches for separation of pure products including the full recovery and reuse of enzymes/ILs systems, are essential elements for developing clean chemical processes. By understanding structure-function relationships of biopolymers in ILs, as well as for ILs themselves (e.g. sponge-like ionic liquids, SLILs; supported ionic liquids-like phases, SILLPs, etc.), several integral green chemical processes of (bio)catalytic transformation and pure product separation are pointed out (e.g. the biocatalytic production of biodiesel in SLILs, etc.). Other developments based on DNA/ILs systems, as pathfinder studies for further technological applications in the near future, are also considered.

RuO2 supported NaY zeolite catalysts: Effect of preparation methods on catalytic performance during aerobic oxidation of benzyl alcohol

NASA Astrophysics Data System (ADS)

Jung, Dasom; Lee, Sunwoo; Na, Kyungsu

2017-10-01

The effects of preparation method for RuO2 supported zeolite catalysts on the catalytic consequences during the aerobic oxidation of benzyl alcohol to benzaldehyde were investigated. Three preparation methods, i.e., (i) simultaneous crystallization of the zeolite framework in the presence of RuCl3 (Ru(SC)/NaY), (ii) post ion-exchange with RuCl3 on the zeolite framework (Ru(IE)/NaY), and (iii) post support of preformed Ru metal nanoparticles on the zeolite surface (Ru(PS)/NaY), were used to construct three different RuO2 supported NaY zeolite catalysts. The catalyst performance was investigated as functions of the reaction time and temperature, in correlation with the structural changes of the catalysts, as analyzed by X-ray diffraction (XRD). The results revealed that the catalytic consequences were dramatically affected by the preparation methods. Although similar conversion was achieved with all three catalysts, the turnover frequency (TOF) differed. The Ru(PS)/NaY catalyst exhibited the highest TOF (33-48 h-1), whereas the other catalysts produced much lower TOFs (9-12 h-1). The Ru(PS)/NaY catalyst also had the highest activation energy (Ea) of 48.39 kJ mol-1, whereas the Ru(SC)/NaY and Ru(IE)/NaY catalysts had Ea values of 18.58 and 24.11 kJ mol-1, respectively. Notably, the Ru(PS)/NaY catalyst yielded a significantly higher pre-exponential factor of 5.22 × 105 h-1, which is about 5 orders of magnitude larger than that of the Ru(SC)/NaY catalyst (7.15 × 100 h-1). This suggests that collision between benzyl alcohol and molecular oxygen was very intensive on the Ru(PS)/NaY catalyst, which explains the higher TOF of the Ru(PS)/NaY catalyst relative to the others in spite of the higher Ea value of the former. In terms of recyclability, the pristine crystallinity of the zeolite framework was maintained in the Ru(SC)/NaY catalyst and the RuO2 phase exhibited an insignificant loss of the initial activity up to three catalytic cycles, whereas Ru(PS)/NaY showed slight loss of activity and Ru(IE)/NaY showed a significant loss of activity due to the disappearance of the RuO2 phase.

Many-body dynamics of chemically propelled nanomotors

NASA Astrophysics Data System (ADS)

Colberg, Peter H.; Kapral, Raymond

2017-08-01

The collective behavior of chemically propelled sphere-dimer motors made from linked catalytic and noncatalytic spheres in a quasi-two-dimensional confined geometry is studied using a coarse-grained microscopic dynamical model. Chemical reactions at the catalytic spheres that convert fuel to product generate forces that couple to solvent degrees of freedom as a consequence of momentum conservation in the microscopic dynamics. The collective behavior of the many-body system is influenced by direct intermolecular interactions among the motors, chemotactic effects due to chemical gradients, hydrodynamic coupling, and thermal noise. Segregation into high and low density phases and globally homogeneous states with strong fluctuations are investigated as functions of the motor characteristics. Factors contributing to this behavior are discussed in the context of active Brownian models.

Surfactant-mediated assembly of crystalline mesoporous aluminas: Synthesis, characterization, and application in hydrodesulfurization

NASA Astrophysics Data System (ADS)

Hicks, Randall Wayne

Aluminas are utilized in many industrial applications, including as adsorbents, abrasives, ceramics, catalysts, and catalyst supports. Many different phases of aluminas exist, but due to its favorable combination of surface and textural properties, the most important phase is gamma-alumina. Surface areas and pore volumes of conventional aluminas are typically less than 250 m 2/g and 0.5 cc/g, respectively. Performance in catalytic applications is limited in part by these properties. As has been shown in silica chemistry, the use of surfactants to aid in the assembly of a mesostructure leads to improvement in textural properties. Similar advances are anticipated in alumina chemistry, but to date, little progress has been made in this area. Since the disclosure of mesostructured aluminas in 1996, all but a couple of subsequent reports have described compositions of mesostructured aluminas with amorphous walls. This limits their thermal and hydrothermal stability, and thus their potential use in catalytic applications. The present work describes the synthesis of the first members of a new family of crystalline mesostructured aluminas prepared from the hydrolysis of aluminum sec-butoxide in the presence of either polyethylene oxide (PEO) or amine surfactants as porogens. Members of this family exhibiting the gamma-Al 2O3 phase, denoted MSU-gamma aluminas, have surface areas, pore sizes, and pore volumes in excess of 400 m2/g, 15 nm, and 1.5 cc/g, respectively. In addition, forms of these aluminas have expressed thermal and hydrothermal stability. Mesostructured boehmites, MSU-B aluminas, have also been obtained using similar synthetic methods. In the synthesis of either alumina, the key step is the formation of an MSU-S/B surfactant-boehmite precursor, which is converted to the desired final product through calcination. To demonstrate their usefulness, MSU-gamma aluminas have been utilized as catalyst supports in dibenzothiophene hydrodesulfurization reactions. Conversions and selectivities superior to that of a commercial catalyst have been achieved. Their success in this capacity can be traced to the stability of the gamma-Al 2O3 phase, the ability to effectively disperse the active catalytic component, and increased accessibility to the active sites.

A Facile Molecular Precursor Route to Metal Phosphide Nanoparticles and Their Evaluation as Hydrodeoxygenation Catalysts

DOE PAGES

Habas, Susan E.; Baddour, Frederick G.; Ruddy, Daniel A.; ...

2015-11-05

Metal phosphides have been identified as a promising class of materials for the catalytic upgrading of bio-oils, which are renewable and potentially inexpensive sources for liquid fuels. Herein, we report the facile synthesis of a series of solid, phase-pure metal phosphide nanoparticles (NPs) (Ni 2P, Rh 2P, and Pd 3P) utilizing commercially available, air-stable metal–phosphine complexes in a one-pot reaction. This single-source molecular precursor route provides an alternative method to access metal phosphide NPs with controlled phases and without the formation of metal NP intermediates that can lead to hollow particles. The formation of the Ni 2P NPs was shownmore » to proceed through an amorphous Ni–P intermediate, leading to the desired NP morphology and metal-rich phase. This low-temperature, rapid route to well-defined metal NPs is expected to have broad applicability to a variety of readily available or easily synthesized metal–phosphine complexes with high decomposition temperatures. Hydrodeoxygenation of acetic acid, an abundant bio-oil component, was performed to investigate H 2 activation and deoxygenation pathways under conditions that are relevant to ex situ catalytic fast pyrolysis (high temperatures, low pressures, and near-stoichiometric H 2 concentrations). The catalytic performance of the silica-supported metal phosphide NPs was compared to the analogous incipient wetness (IW) metal and metal phosphide catalysts over the range 200–500 °C. Decarbonylation was the primary pathway for H 2 incorporation in the presence of all of the catalysts except NP-Pd 3P, which exhibited minimal productive activity, and IW-Ni, which evolved H 2. The highly controlled NP-Ni2P and NP-Rh2P catalysts, which were stable under these conditions, behaved comparably to the IW-metal phosphides, with a slight shift to higher product onset temperatures, likely due to the presence of surface ligands. Most importantly, the NP-Ni 2P catalyst exhibited H 2 activation and incorporation, in contrast to IW-Ni, indicating that the behavior of the metal phosphide is significantly different from that of the parent metal, and more closely resembles that of noble metal catalysts.« less

Improving biomass pyrolysis economics by integrating vapor and liquid phase upgrading

DOE PAGES

Iisa, Kristiina; Robichaud, David J.; Watson, Michael J.; ...

2017-11-24

Partial deoxygenation of bio-oil by catalytic fast pyrolysis with subsequent coupling and hydrotreating can lead to improved economics and will aid commercial deployment of pyrolytic conversion of biomass technologies. Biomass pyrolysis efficiently depolymerizes and deconstructs solid plant matter into carbonaceous molecules that, upon catalytic upgrading, can be used for fuels and chemicals. Upgrading strategies include catalytic deoxygenation of the vapors before they are condensed (in situ and ex situ catalytic fast pyrolysis), or hydrotreating following condensation of the bio-oil. In general, deoxygenation carbon efficiencies, one of the most important cost drivers, are typically higher for hydrotreating when compared to catalyticmore » fast pyrolysis alone. However, using catalytic fast pyrolysis as the primary conversion step can benefit the entire process chain by: (1) reducing the reactivity of the bio-oil, thereby mitigating issues with aging and transport and eliminating need for multi-stage hydroprocessing configurations; (2) producing a bio-oil that can be fractionated through distillation, which could lead to more efficient use of hydrogen during hydrotreating and facilitate integration in existing petroleum refineries; and (3) allowing for the separation of the aqueous phase. In this perspective, we investigate in detail a combination of these approaches, where some oxygen is removed during catalytic fast pyrolysis and the remainder removed by downstream hydrotreating, accompanied by carbon–carbon coupling reactions in either the vapor or liquid phase to maximize carbon efficiency toward value-driven products (e.g. fuels or chemicals). The economic impact of partial deoxygenation by catalytic fast pyrolysis will be explored in the context of an integrated two-stage process. In conclusion, improving the overall pyrolysis-based biorefinery economics by inclusion of production of high-value co-products will be examined.« less

Improving biomass pyrolysis economics by integrating vapor and liquid phase upgrading

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

Iisa, Kristiina; Robichaud, David J.; Watson, Michael J.

Partial deoxygenation of bio-oil by catalytic fast pyrolysis with subsequent coupling and hydrotreating can lead to improved economics and will aid commercial deployment of pyrolytic conversion of biomass technologies. Biomass pyrolysis efficiently depolymerizes and deconstructs solid plant matter into carbonaceous molecules that, upon catalytic upgrading, can be used for fuels and chemicals. Upgrading strategies include catalytic deoxygenation of the vapors before they are condensed (in situ and ex situ catalytic fast pyrolysis), or hydrotreating following condensation of the bio-oil. In general, deoxygenation carbon efficiencies, one of the most important cost drivers, are typically higher for hydrotreating when compared to catalyticmore » fast pyrolysis alone. However, using catalytic fast pyrolysis as the primary conversion step can benefit the entire process chain by: (1) reducing the reactivity of the bio-oil, thereby mitigating issues with aging and transport and eliminating need for multi-stage hydroprocessing configurations; (2) producing a bio-oil that can be fractionated through distillation, which could lead to more efficient use of hydrogen during hydrotreating and facilitate integration in existing petroleum refineries; and (3) allowing for the separation of the aqueous phase. In this perspective, we investigate in detail a combination of these approaches, where some oxygen is removed during catalytic fast pyrolysis and the remainder removed by downstream hydrotreating, accompanied by carbon–carbon coupling reactions in either the vapor or liquid phase to maximize carbon efficiency toward value-driven products (e.g. fuels or chemicals). The economic impact of partial deoxygenation by catalytic fast pyrolysis will be explored in the context of an integrated two-stage process. In conclusion, improving the overall pyrolysis-based biorefinery economics by inclusion of production of high-value co-products will be examined.« less

Mixed ionic and electronic conducting ceramic membranes for hydrocarbon processing

DOEpatents

Van Calcar, Pamela; Mackay, Richard; Sammells, Anthony F.

2002-01-01

The invention relates to mixed phase materials for the preparation of catalytic membranes which exhibit ionic and electronic conduction and which exhibit improved mechanical strength compared to single phase ionic and electronic conducting materials. The mixed phase materials are useful for forming gas impermeable membranes either as dense ceramic membranes or as dense thin films coated onto porous substrates. The membranes and materials of this invention are useful in catalytic membrane reactors in a variety of applications including synthesis gas production. One or more crystalline second phases are present in the mixed phase material at a level sufficient to enhance the mechanical strength of the mixture to provide membranes for practical application in CMRs.

Synergetic photocatalytic effect between 1 T@2H-MoS2 and plasmon resonance induced by Ag quantum dots

NASA Astrophysics Data System (ADS)

Liu, Haiyang; Wu, Rong; Tian, Lie; Kong, Yangyang; Sun, Yanfei

2018-07-01

Semiconductor phase transitions and plasma noble metal quantum dots (QDs) for visible-light-driven photocatalysts have attracted significant research interest. In this study, novel microwave hydrothermal and photo-reduction methods are proposed to synthesise a visible-light-driven plasma photocatalytic 1T@2H-MoS2/Ag composite. Photoelectrochemical results show that the introduction of the 1T phase and Ag significantly enhances the light response range and charge separation. The 1T phase can act as a co-catalyst to provide a high electron concentration. Ag QDs can effectively improve the light absorption and catalytic effect. The synergistic effect between the 1T@2H-MoS2 microspheres and localised surface plasmon resonance of the Ag QDs can effectively enhance the photocatalytic activity of 1T@2H-MoS2/Ag. The developed 1T@2H-MoS2/Ag composite is superior, not only with respect to a visible-light photocatalytic degradation of conventional dyes, but also in the photocatalytic reduction of Cr(VI). Compared with 2H-MoS2, the catalytic efficiency of 1T@2H-MoS2/Ag for Cr(VI) and MB is increased by 81% and 41%, respectively. This study demonstrates that the introduction of 1T-MoS2 and Ag QDs can significantly enhance the catalytic properties of 2H-MoS2. The microwave and photo-reduction technologies can be employed as green, safe, simple, and rapid methods for the synthesis of noble metal plasma composites.

Synergetic photocatalytic effect between 1 T@2H-MoS2 and plasmon resonance induced by Ag quantum dots.

PubMed

Liu, Haiyang; Wu, Rong; Tian, Lie; Kong, Yangyang; Sun, Yanfei

2018-07-13

Semiconductor phase transitions and plasma noble metal quantum dots (QDs) for visible-light-driven photocatalysts have attracted significant research interest. In this study, novel microwave hydrothermal and photo-reduction methods are proposed to synthesise a visible-light-driven plasma photocatalytic 1T@2H-MoS 2 /Ag composite. Photoelectrochemical results show that the introduction of the 1T phase and Ag significantly enhances the light response range and charge separation. The 1T phase can act as a co-catalyst to provide a high electron concentration. Ag QDs can effectively improve the light absorption and catalytic effect. The synergistic effect between the 1T@2H-MoS 2 microspheres and localised surface plasmon resonance of the Ag QDs can effectively enhance the photocatalytic activity of 1T@2H-MoS 2 /Ag. The developed 1T@2H-MoS 2 /Ag composite is superior, not only with respect to a visible-light photocatalytic degradation of conventional dyes, but also in the photocatalytic reduction of Cr(VI). Compared with 2H-MoS 2 , the catalytic efficiency of 1T@2H-MoS 2 /Ag for Cr(VI) and MB is increased by 81% and 41%, respectively. This study demonstrates that the introduction of 1T-MoS 2 and Ag QDs can significantly enhance the catalytic properties of 2H-MoS 2 . The microwave and photo-reduction technologies can be employed as green, safe, simple, and rapid methods for the synthesis of noble metal plasma composites.

Copper cluster size effect in methanol synthesis from CO 2

DOE PAGES

Yang, Bing; Liu, Cong; Halder, Avik; ...

2017-05-08

Here, size-selected Cu n catalysts ( n = 3, 4, 20) were synthesized on Al 2O 3 thin films using mass-selected cluster deposition. A systematic study of size and support effects was carried out for CO 2 hydrogenation at atmospheric pressure using a combination of in situ grazing incidence X-ray absorption spectroscopy, catalytic activity measurement, and first-principles calculations. The catalytic activity for methanol synthesis is found to strongly vary as a function of the cluster size; the Cu 4/Al 2O 3 catalyst shows the highest turnover rate for CH 3OH production. With only one atom less than Cu 4, Cumore » 3 showed less than 50% activity. Density functional theory calculations predict that the activities of the gas-phase Cu clusters increase as the cluster size decreases; however, the stronger charge transfer interaction with Al 2O 3 support for Cu 3 than for Cu 4 leads to remarkably reduced binding strength between the adsorbed intermediates and supported Cu 3, which subsequently results in a less favorable energetic pathway to transform carbon dioxide to methanol.« less

Ruthenium on rutile catalyst, catalytic system, and method for aqueous phase hydrogenations

DOEpatents

Elliot, Douglas C.; Werpy, Todd A.; Wang, Yong; Frye, Jr., John G.

2001-01-01

An essentially nickel- and rhenium-free catalyst is described comprising ruthenium on a titania support where the titania is greater than 75% rutile. A catalytic system containing a nickel-free catalyst comprising ruthenium on a titania support where the titania is greater than 75% rutile, and a method using this catalyst in the hydrogenation of an organic compound in the aqueous phase is also described.

Fast preparation of Bi{sub 2}GeO{sub 5} nanoflakes via a microwave-hydrothermal process and enhanced photocatalytic activity after loading with Ag nanoparticles

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

Li, Zhao-Qian; Lin, Xin-Shan; Zhang, Lei

2012-09-15

Highlights: ► Bi{sub 2}GeO{sub 5} nanoflakes were successfully synthesized via a microwave-assisted solution-phase approach. ► Ag nanoparticles were deposited on the Bi{sub 2}GeO{sub 5} nanoflakes by a photoreduction procedure. ► Catalytic activity of the Ag/Bi{sub 2}GeO{sub 5} nanocomposite in the photo-degradation of rhodamine B (RhB) was much higher than that of pure Bi{sub 2}GeO{sub 5}. -- Abstract: In this work, a facile and rapid microwave-assisted hydrothermal route has been developed to prepare Bi{sub 2}GeO{sub 5} nanoflakes. Ag nanoparticles were subsequently deposited on the Bi{sub 2}GeO{sub 5} nanoflakes by a photoreduction procedure. The phases and morphologies of the products were characterizedmore » by powder X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and UV–vis diffuse reflectance spectroscopy. Photocatalytic experiments indicate that such Ag/Bi{sub 2}GeO{sub 5} nanocomposite possesses higher photocatalytic activity for RhB degradation under UV light irradiation in comparison to pure Bi{sub 2}GeO{sub 5}. The amount of Ag in the nanocomposite affects the catalytic activity, and 3 wt% Ag showed the highest photodegradation efficiency. Moreover, the catalyst remains active after four consecutive tests. The present study provides a new strategy to design composite materials with enhanced photocatalytic activity.« less

Assessment of the Vapor Phase Catalytic Ammonia Removal (VPCAR) Technology at the MSFC ECLS Test Facility

NASA Technical Reports Server (NTRS)

Tomes, Kristin; Long, David; Carter, Layne; Flynn, Michael

2007-01-01

The Vapor Phase Catalytic Ammonia. Removal (VPCAR) technology has been previously discussed as a viable option for. the Exploration Water Recovery System. This technology integrates a phase change process with catalytic oxidation in the vapor phase to produce potable water from exploration mission wastewaters. A developmental prototype VPCAR was designed, built and tested under funding provided by a National Research. Announcement (NRA) project. The core technology, a Wiped Film Rotating Device (WFRD) was provided by Water Reuse Technologies under the NRA, whereas Hamilton Sundstrand Space Systems International performed the hardware integration and acceptance test. of the system. Personnel at the-Ames Research Center performed initial systems test of the VPCAR using ersatz solutions. To assess the viability of this hardware for Exploration. Life Support (ELS) applications, the hardware has been modified and tested at the MSFC ECLS Test facility. This paper summarizes the hardware modifications and test results and provides an assessment of this technology for the ELS application.

Hydrogenation-controlled phase transition on two-dimensional transition metal dichalcogenides and their unique physical and catalytic properties.

PubMed

Qu, Yuanju; Pan, Hui; Kwok, Chi Tat

2016-09-30

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have been widely used from nanodevices to energy harvesting/storage because of their tunable physical and chemical properties. In this work, we systematically investigate the effects of hydrogenation on the structural, electronic, magnetic, and catalytic properties of 33 TMDs based on first-principles calculations. We find that the stable phases of TMD monolayers can transit from 1T to 2H phase or vice versa upon the hydrogenation. We show that the hydrogenation can switch their magnetic and electronic states accompanying with the phase transition. The hydrogenation can tune the magnetic states of TMDs among non-, ferro, para-, and antiferro-magnetism and their electronic states among semiconductor, metal, and half-metal. We further show that, out of 33 TMD monolayers, 2H-TiS 2 has impressive catalytic ability comparable to Pt in hydrogen evolution reaction in a wide range of hydrogen coverages. Our findings would shed the light on the multi-functional applications of TMDs.

Catalytic decomposition of toxic chemicals over iron group metals supported on carbon nanotubes.

PubMed

Li, Lili; Chen, Can; Chen, Long; Zhu, Zixue; Hu, Jianli

2014-03-18

This study explores catalytic decomposition of phosphine (PH3) using iron group metals (Co, Ni) and metal oxides (Fe2O3, Co(3)O4, NiO) supported on carbon nanotubes (CNTs). The catalysts are synthesized by means of a deposition-precipitation method. The morphology, structure, and composition of the catalysts are characterized using a number of analytical instrumentations, including high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, BET surface area measurement, and inductively coupled plasma. The activity of the catalysts in the PH3 decomposition reaction is measured and correlated with their surface and structural properties. The characterization results show that phosphidation occurs on the catalyst surface, and the resulting metal phosphides act as an active phase in the PH3 decomposition reaction. Cobalt phosphide, CoP, is formed on Co/CNTs and Co(3)O4/CNTs, whereas iron phosphide, FeP, is formed on Fe2O3/CNTs. In contrast, phosphorus-rich phosphide NiP2 is formed on Ni/CNTs and NiO/CNTs. The initial activities of the catalysts are shown in the following sequence: Ni/CNTs > Co/CNTs > Co(3)O4/CNTs >NiO/CNTs > Fe2O3/CNTs, whereas activities of metal phosphides are shown in the following order: CoP > NiP2 > FeP. The catalytic activity of metal phosphides is attributed to their electronic properties. Cobalt phosphide formed on Co/CNTs and Co(3)O4/CNTs exhibits not only the highest activity, but also long-term stability in the PH3 decomposition reaction.

Photochemical water oxidation by crystalline polymorphs of manganese oxides: structural requirements for catalysis.

PubMed

Robinson, David M; Go, Yong Bok; Mui, Michelle; Gardner, Graeme; Zhang, Zhijuan; Mastrogiovanni, Daniel; Garfunkel, Eric; Li, Jing; Greenblatt, Martha; Dismukes, G Charles

2013-03-06

Manganese oxides occur naturally as minerals in at least 30 different crystal structures, providing a rigorous test system to explore the significance of atomic positions on the catalytic efficiency of water oxidation. In this study, we chose to systematically compare eight synthetic oxide structures containing Mn(III) and Mn(IV) only, with particular emphasis on the five known structural polymorphs of MnO2. We have adapted literature synthesis methods to obtain pure polymorphs and validated their homogeneity and crystallinity by powder X-ray diffraction and both transmission and scanning electron microscopies. Measurement of water oxidation rate by oxygen evolution in aqueous solution was conducted with dispersed nanoparticulate manganese oxides and a standard ruthenium dye photo-oxidant system. No Ru was absorbed on the catalyst surface as observed by XPS and EDX. The post reaction atomic structure was completely preserved with no amorphization, as observed by HRTEM. Catalytic activities, normalized to surface area (BET), decrease in the series Mn2O3 > Mn3O4 ≫ λ-MnO2, where the latter is derived from spinel LiMn2O4 following partial Li(+) removal. No catalytic activity is observed from LiMn2O4 and four of the MnO2 polymorphs, in contrast to some literature reports with polydispersed manganese oxides and electro-deposited films. Catalytic activity within the eight examined Mn oxides was found exclusively for (distorted) cubic phases, Mn2O3 (bixbyite), Mn3O4 (hausmannite), and λ-MnO2 (spinel), all containing Mn(III) possessing longer Mn-O bonds between edge-sharing MnO6 octahedra. Electronically degenerate Mn(III) has antibonding electronic configuration e(g)(1) which imparts lattice distortions due to the Jahn-Teller effect that are hypothesized to contribute to structural flexibility important for catalytic turnover in water oxidation at the surface.

Synthesis and catalytic activity of polysaccharide templated nanocrystalline sulfated zirconia

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

Sherly, K. B.; Rakesh, K.

Nanoscaled materials are of great interest due to their unique enhanced optical, electrical and magnetic properties. Sulfate-promoted zirconia has been shown to exhibit super acidic behavior and high activity for acid catalyzed reactions. Nanocrystalline zirconia was prepared in the presence of polysaccharide template by interaction between ZrOCl{sub 2}⋅8H{sub 2}O and chitosan template. The interaction was carried out in aqueous phase, followed by the removal of templates by calcination at optimum temperature and sulfation. The structural and textural features were characterized by powder XRD, TG, SEM and TEM. XRD patterns showed the peaks of the diffractogram were in agreement with themore » theoretical data of zirconia with the catalytically active tetragonal phase and average crystalline size of the particles was found to be 9 nm, which was confirmed by TEM. TPD using ammonia as probe, FTIR and BET surface area analysis were used for analyzing surface features like acidity and porosity. The BET surface area analysis showed the sample had moderately high surface area. FTIR was used to find the type species attached to the surface of zirconia. UV-DRS found the band gap of the zirconia was found to be 2.8 eV. The benzylation of o-xylene was carried out batchwise in atmospheric pressure and 433K temperature using sulfated zirconia as catalyst.« less

Low Concentration Fe-Doped Alumina Catalysts Using Sol-Gel and Impregnation Methods: The Synthesis, Characterization and Catalytic Performance during the Combustion of Trichloroethylene

PubMed Central

Maldonado, Carolina Solis; De la Rosa, Javier Rivera; Lucio-Ortiz, Carlos J.; Hernández-Ramírez, Aracely; Castillón Barraza, Felipe F.; Valente, Jaime S.

2014-01-01

The role of iron in two modes of integration into alumina catalysts was studied at 0.39 wt% Fe and tested in trichloroethylene combustion. One modified alumina was synthesized using the sol-gel method with Fe added in situ during hydrolysis; another modification was performed using calcined alumina, prepared using the sol-gel method and impregnated with Fe. Several characterization techniques were used to study the level of Fe modification in the γ-Al2O3 phase formed and to correlate the catalytic properties during trichloroethylene (TCE) combustion. The introduction of Fe in situ during the sol-gel process influenced the crystallite size, and three iron species were generated, namely, magnetite, maghemite and hematite. The impregnated Fe-alumina formed hematite and maghemite, which were highly dispersed on the γ-Al2O3 surface. The X-ray photoelectron spectra (XPS), FT-IR and Mössbauer spectroscopy analyses revealed how Fe interacted with the γ-Al2O3 lattice in both catalysts. The impregnated Fe-catalyst showed the best catalytic performance compared to the catalyst that was Fe-doped in situ by the sol-gel method; both had better catalytic activity than pure alumina. This difference in activity was correlated with the accessibility of the reactants to the hematite iron species on the surface. The chlorine poisoning for all three catalysts was less than 1.8%. PMID:28788556

Effect of A-site deficiency in LaMn{sub 0.9}Co{sub 0.1}O{sub 3} perovskites on their catalytic performance for soot combustion

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

Dinamarca, Robinson; Garcia, Ximena; Jimenez, Romel

Highlights: • A-site defective perovskites increases the oxidation state of the B-cation. • Not always non-stoichiometric perovskites exhibit higher catalytic activity in soot combustion. • The highly symmetric cubic crystalline structure diminishes the redox properties of perovskites. - Abstract: The influence of lanthanum stoichiometry in Ag-doped (La{sub 1-x}Ag{sub x}Mn{sub 0.9}Co{sub 0.1}O{sub 3}) and A-site deficient (La{sub 1-x}Mn{sub 0.9}Co{sub 0.1}O{sub 3-δ}) perovskites with x equal to 10, 20 and 30 at.% has been investigated in catalysts for soot combustion. The catalysts were prepared by the amorphous citrate method and characterized by XRD, nitrogen adsorption, XPS, O{sub 2}-TPD and TPR. The formationmore » of a rhombohedral excess-oxygen perovskite for Ag-doped and a cubic perovskite structure for an A-site deficient series is confirmed. The efficient catalytic performance of the larger Ag-doped perovskite structure is attributed to the rhombohedral crystalline structure, Ag{sub 2}O segregated phases and the redox pair Mn{sup 4+}/Mn{sup 3+}. A poor catalytic activity for soot combustion was observed with A-site deficient perovskites, despite the increase in the redox pair Mn{sup 4+}/Mn{sup 3+}, which is attributed to the cubic crystalline structure.« less

Low-temperature cluster catalysis.

PubMed

Judai, Ken; Abbet, Stéphane; Wörz, Anke S; Heiz, Ulrich; Henry, Claude R

2004-03-10

Free and supported metal clusters reveal unique chemical and physical properties, which vary as a function of size as each cluster possesses a characteristic electron confinement. Several previous experimental results showed that the outcome of a given chemical reaction can be controlled by tuning the cluster size. However, none of the examples indicate that clusters prepared in the gas phase and then deposited on a support material are indeed catalytically active over several reaction cycles nor that their catalytic properties remain constant during such a catalytic process. In this work we report turn-over frequencies (TOF) for Pd(n) (n = 4, 8, 30) clusters using pulsed molecular beam experiments. The obtained results illustrate that the catalytic reactivity for the NO reduction by CO (CO + NO --> 1/2N(2) + CO(2)) is indeed a function of cluster size and that the measured TOF remain constant at a given temperature. More interestingly, the temperature of maximal reactivity is at least 100 K lower than observed for palladium nanoparticles or single crystals. One reason for this surprising observation is the character of the binding sites of these small clusters: N(2) forms already at relatively low temperatures (400 and 450 K) and therefore poisoning by adsorbed nitrogen adatoms is prevented. Thus, small clusters not only open the possibility of tuning a catalytic process by changing cluster size, but also of catalyzing chemical reactions at low temperatures.

Catalytic decomposition of hydrogen peroxide and 4-chlorophenol in the presence of modified activated carbons.

PubMed

Huang, Hsu-Hui; Lu, Ming-Chun; Chen, Jong-Nan; Lee, Cheng-Te

2003-06-01

The objective of this research was to examine the heterogeneous catalytic decomposition of H(2)O(2) and 4-chlorophenol (4-CP) in the presence of activated carbons modified with chemical pretreatments. The decomposition of H(2)O(2) was suppressed significantly by the change of surface properties including the decreased pH(pzc) modified with oxidizing agent and the reduced active sites occupied by the adsorption of 4-CP. The apparent reaction rate of H(2)O(2) decomposition was dominated by the intrinsic reaction rates on the surface of activated carbon rather than the mass transfer rate of H(2)O(2) to the solid surface. By the detection of chloride ion in suspension, the reduction of 4-CP was not only attributed to the advanced adsorption but also the degradation of 4-CP. The catalytic activity toward 4-CP for the activated carbon followed the inverse sequence of the activity toward H(2)O(2), suggesting that acidic surface functional group could retard the H(2)O(2) loss and reduce the effect of surface scavenging resulting in the increase of the 4-CP degradation efficiency. Few effective radicals were expected to react with 4-CP for the strong effect of surface scavenging, which could explain why the degradation rate of 4-CP observed in this study was so slow and the dechlorination efficiency was independent of the 4-CP concentration in aqueous phase. Results show that the combination of H(2)O(2) and granular activated carbon (GAC) did increase the total removal of 4-CP than that by single GAC adsorption.

Sol-Gel Process for Making Pt-Ru Fuel-Cell Catalysts

NASA Technical Reports Server (NTRS)

Narayanan, Sekharipuram; Valdez, Thomas; Kumta, Prashant; Kim, Y.

2005-01-01

A sol-gel process has been developed as a superior alternative to a prior process for making platinum-ruthenium alloy catalysts for electro-oxidation of methanol in fuel cells. The starting materials in the prior process are chloride salts of platinum and ruthenium. The process involves multiple steps, is time-consuming, and yields a Pt-Ru product that has relatively low specific surface area and contains some chloride residue. Low specific surface area translates to incomplete utilization of the catalytic activity that might otherwise be available, while chloride residue further reduces catalytic activity ("poisons" the catalyst). In contrast, the sol-gel process involves fewer steps and less time, does not leave chloride residue, and yields a product of greater specific area and, hence, greater catalytic activity. In this sol-gel process (see figure), the starting materials are platinum(II) acetylacetonate [Pt(C5H7O2)2, also denoted Pt-acac] and ruthenium(III) acetylacetonate [Ru(C5H7O2)3, also denoted Ru-acac]. First, Pt-acac and Ru-acac are dissolved in acetone at the desired concentrations (typically, 0.00338 moles of each salt per 100 mL of acetone) at a temperature of 50 C. A solution of 25 percent tetramethylammonium hydroxide [(CH3)4NOH, also denoted TMAH] in methanol is added to the Pt-acac/Ruacac/ acetone solution to act as a high-molecular-weight hydrolyzing agent. The addition of the TMAH counteracts the undesired tendency of Pt-acac and Ru-acac to precipitate as separate phases during the subsequent evaporation of the solvent, thereby helping to yield a desired homogeneous amorphous gel. The solution is stirred for 10 minutes, then the solvent is evaporated until the solution becomes viscous, eventually transforming into a gel. The viscous gel is dried in air at a temperature of 170 C for about 10 hours. The dried gel is crushed to make a powder that is the immediate precursor of the final catalytic product. The precursor powder is converted to the final product in a controlled-atmosphere heat treatment. Desirably, the final product is a phase-pure (Pt phase only) Pt-Ru powder with a high specific surface area. The conditions of the controlled- atmosphere heat are critical for obtaining the aforementioned desired properties. A typical heat treatment that yields best results for a catalytic alloy of equimolar amounts of Pt and Ru consists of at least two cycles of heating to a temperature of 300 C and holding at 300 C for several hours, all carried out in an atmosphere of 1 percent O2 and 99 percent N2. The resulting powder consists of crystallites with typical linear dimensions of <10 nm. Tests have shown that the powder is highly effective in catalyzing the electro-oxidation of methanol.

Catalytic distillation water recovery subsystem

NASA Technical Reports Server (NTRS)

Budininkas, P.; Rasouli, F.

1985-01-01

An integrated engineering breadboard subsystem for the recovery of potable water from untreated urine based on the vapor phase catalytic ammonia removal was designed, fabricated and tested. Unlike other evaporative methods, this process catalytically oxidizes ammonia and volatile hydrocarbons vaporizing with water to innocuous products; therefore, no pretreatment of urine is required. Since the subsystem is fabricated from commercially available components, its volume, weight and power requirements are not optimized; however, it is suitable for zero-g operation. The testing program consists of parametric tests, one month of daily tests and a continuous test of 168 hours duration. The recovered water is clear, odorless, low in ammonia and organic carbon, and requires only an adjustment of its pH to meet potable water standards. The obtained data indicate that the vapor phase catalytic ammonia removal process, if further developed, would also be competitive with other water recovery systems in weight, volume and power requirements.

Thermodynamic Stability of Molybdenum Oxycarbides Formed from Orthorhombic Mo 2 C in Oxygen-Rich Environments

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

Likith, S. R. J.; Farberow, C. A.; Manna, S.

Molybdenum carbide (Mo 2C) nanoparticles and thin films are particularly suitable catalysts for catalytic fast pyrolysis (CFP) as they are effective for deoxygenation and can catalyze certain reactions that typically occur on noble metals. Oxygen deposited during deoxygenation reactions may alter the carbide structure, leading to the formation of oxycarbides, which can determine changes in catalytic activity or selectivity. Despite emerging spectroscopic evidence of bulk oxycarbides, so far there have been no reports of their precise atomic structure or their relative stability with respect to orthorhombic Mo 2C. This knowledge is essential for assessing the catalytic properties of molybdenum (oxy)carbidesmore » for CFP. In this article, we use density functional theory (DFT) calculations to (a) describe the thermodynamic stability of surface and subsurface configurations of oxygen and carbon atoms for a commonly studied Mo-terminated surface of orthorhombic Mo 2C and (b) determine atomic structures for oxycarbides with a Mo:C ratio of 2:1. The surface calculations suggest that oxygen atoms are not stable under the top Mo layer of the Mo 2C(100) surface. Coupling DFT calculations with a polymorph sampling method, we determine (Mo 2C) xO y oxycarbide structures for a wide range of oxygen compositions. Oxycarbides with lower oxygen content (y/x = 2) adopt layered structures reminiscent of the parent carbide phase, with flat Mo layers separated by layers of oxygen and carbon; for higher oxygen content, our results suggest the formation of amorphous phases, as the atomic layers lose their planarity with increasing oxygen content. We characterize the oxidation states of Mo in the oxycarbide structures determined computationally, and simulate their X-ray diffraction (XRD) patterns in order to facilitate comparisons with experiments. Our study may provide a platform for large-scale investigations of the catalytic properties of oxycarbides and their surfaces and for tailoring the catalytic properties for different desired reactions.« less

Thermodynamic Stability of Molybdenum Oxycarbides Formed from Orthorhombic Mo 2 C in Oxygen-Rich Environments

DOE PAGES

Likith, S. R. J.; Farberow, C. A.; Manna, S.; ...

2017-12-20

Molybdenum carbide (Mo 2C) nanoparticles and thin films are particularly suitable catalysts for catalytic fast pyrolysis (CFP) as they are effective for deoxygenation and can catalyze certain reactions that typically occur on noble metals. Oxygen deposited during deoxygenation reactions may alter the carbide structure, leading to the formation of oxycarbides, which can determine changes in catalytic activity or selectivity. Despite emerging spectroscopic evidence of bulk oxycarbides, so far there have been no reports of their precise atomic structure or their relative stability with respect to orthorhombic Mo 2C. This knowledge is essential for assessing the catalytic properties of molybdenum (oxy)carbidesmore » for CFP. In this article, we use density functional theory (DFT) calculations to (a) describe the thermodynamic stability of surface and subsurface configurations of oxygen and carbon atoms for a commonly studied Mo-terminated surface of orthorhombic Mo 2C and (b) determine atomic structures for oxycarbides with a Mo:C ratio of 2:1. The surface calculations suggest that oxygen atoms are not stable under the top Mo layer of the Mo 2C(100) surface. Coupling DFT calculations with a polymorph sampling method, we determine (Mo 2C) xO y oxycarbide structures for a wide range of oxygen compositions. Oxycarbides with lower oxygen content (y/x = 2) adopt layered structures reminiscent of the parent carbide phase, with flat Mo layers separated by layers of oxygen and carbon; for higher oxygen content, our results suggest the formation of amorphous phases, as the atomic layers lose their planarity with increasing oxygen content. We characterize the oxidation states of Mo in the oxycarbide structures determined computationally, and simulate their X-ray diffraction (XRD) patterns in order to facilitate comparisons with experiments. Our study may provide a platform for large-scale investigations of the catalytic properties of oxycarbides and their surfaces and for tailoring the catalytic properties for different desired reactions.« less

Effects of copper-precursors on the catalytic activity of Cu/graphene catalysts for the selective catalytic oxidation of ammonia

NASA Astrophysics Data System (ADS)

Li, Jingying; Tang, Xiaolong; Yi, Honghong; Yu, Qingjun; Gao, Fengyu; Zhang, Runcao; Li, Chenlu; Chu, Chao

2017-08-01

Different copper-precursors were used to prepare Cu/graphene catalysts by an impregnation method. XRD, Raman spectra, TEM, BET, XPS, H2-TPR, NH3-TPD, DRIFTS and catalytic activity test were used to characterize and study the effect of precursors on the catalytic activity of Cu/graphene catalysts for NH3-SCO reaction. The large specific surface area of Cu/graphene catalysts and high dispersion of the metal particles on the graphene caused the well catalytic activity of NH3-SCO reaction. Compared to Cu/GE(AC), Cu/GE(N) showed better catalytic performance, and the complete NH3 removal efficiency was obtained at 250 °C with N2 selectivity of 85%. The copper-precursors had influence on the distribution of surface Cu species and further affected the catalytic activity of Cu/GE catalysts. The more amount of surface Cu species and highly dispersed CuO particles on the graphene surface formed by using copper nitrate as precursor could significantly improve the reducibility of catalysts and enhance NH3 adsorption, thereby improving the catalytic activity of Cu/graphene catalyst.

Regulation of Catalytic and Non-catalytic Functions of the Drosophila Ste20 Kinase Slik by Activation Segment Phosphorylation.

PubMed

Panneton, Vincent; Nath, Apurba; Sader, Fadi; Delaunay, Nathalie; Pelletier, Ariane; Maier, Dominic; Oh, Karen; Hipfner, David R

2015-08-21

Protein kinases carry out important functions in cells both by phosphorylating substrates and by means of regulated non-catalytic activities. Such non-catalytic functions have been ascribed to many kinases, including some members of the Ste20 family. The Drosophila Ste20 kinase Slik phosphorylates and activates Moesin in developing epithelial tissues to promote epithelial tissue integrity. It also functions non-catalytically to promote epithelial cell proliferation and tissue growth. We carried out a structure-function analysis to determine how these two distinct activities of Slik are controlled. We find that the conserved C-terminal coiled-coil domain of Slik, which is necessary and sufficient for apical localization of the kinase in epithelial cells, is not required for Moesin phosphorylation but is critical for the growth-promoting function of Slik. Slik is auto- and trans-phosphorylated in vivo. Phosphorylation of at least two of three conserved sites in the activation segment is required for both efficient catalytic activity and non-catalytic signaling. Slik function is thus dependent upon proper localization of the kinase via the C-terminal coiled-coil domain and activation via activation segment phosphorylation, which enhances both phosphorylation of substrates like Moesin and engagement of effectors of its non-catalytic growth-promoting activity. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Zircon Supported Copper Catalysts for the Steam Reforming of Methanol

NASA Astrophysics Data System (ADS)

Widiastri, M.; Fendy, Marsih, I. N.

2008-03-01

Steam reforming of methanol (SRM) is known as one of the most favorable catalytic processes for producing hydrogen. Current research on zirconia, ZrO2 supported copper catalyst revealed that CuO/ZrO2 as an active catalyst for the SRM. Zircon, ZrSiO4 is available from the by-product of tin mining. In the work presented here, the catalytic properties of CuO/ZrSiO4 with various copper oxide compositions ranging from 2.70% (catalyst I), 4.12% (catalyst II), and 7.12%-mass (catalyst III), synthesized by an incipient wetness impregnation technique, were investigated to methanol conversion, selectivity towards CO formation, and effect of ZnO addition (7.83%CuO/8.01%ZnO/ZrSiO4 = catalyst V). The catalytic activity was obtained using a fixed bed reactor and the zircon supported catalyst activity was compared to those of CuO/ZnO/Al2O3 catalyst (catalyst IV) and commercial Kujang LTSC catalyst. An X-ray powder diffraction (XRD) analysis was done to identify the abundant phases of the catalysts. The catalysts topography and particle diameter were measured with scanning electron microscopy (SEM) and composition of the catalysts was measured by SEM-EDX, scanning electron microscope-energy dispersive using X-ray analysis. The results of this research provide information on the possibility of using zircon (ZrSiO4) as solid support for SRM catalysts.

Analysis of in vitro evolution reveals the underlying distribution of catalytic activity among random sequences.

PubMed

Pressman, Abe; Moretti, Janina E; Campbell, Gregory W; Müller, Ulrich F; Chen, Irene A

2017-08-21

The emergence of catalytic RNA is believed to have been a key event during the origin of life. Understanding how catalytic activity is distributed across random sequences is fundamental to estimating the probability that catalytic sequences would emerge. Here, we analyze the in vitro evolution of triphosphorylating ribozymes and translate their fitnesses into absolute estimates of catalytic activity for hundreds of ribozyme families. The analysis efficiently identified highly active ribozymes and estimated catalytic activity with good accuracy. The evolutionary dynamics follow Fisher's Fundamental Theorem of Natural Selection and a corollary, permitting retrospective inference of the distribution of fitness and activity in the random sequence pool for the first time. The frequency distribution of rate constants appears to be log-normal, with a surprisingly steep dropoff at higher activity, consistent with a mechanism for the emergence of activity as the product of many independent contributions. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

Synthesis, characterization and inhibitory activities of (4-N3[3,5-3H]Phe10)PKI(6-22)amide and its precursors: photoaffinity labeling peptides for the active site of cyclic AMP-dependent protein kinase.

PubMed

Katz, B M; Lundquist, L J; Walsh, D A; Glass, D B

1989-06-01

PKI(6-22)amide is a 17 residue peptide corresponding to the active portion of the heat-stable inhibitor of cAMP-dependent protein kinase. The peptide is a potent (Ki = 1.6 nM), competitive inhibitor of the enzyme. The photoreactive peptide analog (4-azidophenylalanine10)PKI(6-22)amide was synthesized in both its non-radiolabeled and tritiated forms by chemical modification of precursor peptides that were prepared by stepwise solid-phase synthesis. (4-Amino[3,5-3H]phenylalanine10)PKI(6-22)amide, the precursor for the radiolabeled arylazide peptide, was obtained by catalytic reduction of the corresponding peptide containing the 3,5-diiodo-4-aminophenylalanine residue at position 10. The purified PKI peptides were analyzed by HPLC, amino acid analysis, and u.v. spectra. In the dark, (4-azidophenylalanine10)PKI(6-22)amide inhibited the catalytic subunit of cAMP-dependent protein kinase with a Ki value of 2.8 nM. The photoreactivity of the arylazide peptide was demonstrated by time-dependent u.v. spectral changes on exposure to light. Photolysis of the catalytic subunit (4-azido[3,5-3H]phenylalanine10)PKI(6-22)amide complex resulted in specific covalent labeling of the enzyme. The data indicate that this peptide is a useful photoaffinity labeling reagent for the active site of the protein kinase.

Crystal Structural Effect of AuCu Alloy Nanoparticles on Catalytic CO Oxidation

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

Zhan, Wangcheng; Wang, Jinglin; Wang, Haifeng

2017-06-07

Controlling the physical and chemical properties of alloy nanoparticles (NPs) is an important approach to optimize NP catalysis. Unlike other tuning knobs, such as size, shape, and composition, crystal structure has received limited attention and not been well understood for its role in catalysis. This deficiency is mainly due to the difficulty in synthesis and fine-tuning of the NPs’ crystal structure. Here, Exemplifying by AuCu alloy NPs with face centered cubic (fcc) and face centered tetragonal (fct) structure, we demonstrate a remarkable difference in phase segregation and catalytic performance depending on the crystal structure. During the thermal treatment in air,more » the Cu component in fcc-AuCu alloy NPs segregates more easily onto the alloy surface as compared to that in fct-AuCu alloy NPs. As a result, after annealing at 250 °C in air for 1 h, the fcc- and fct-AuCu alloy NPs are phase transferred into Au/CuO and AuCu/CuO core/shell structures, respectively. More importantly, this variation in heterostructures introduces a significant difference in CO adsorption on two catalysts, leading to a largely enhanced catalytic activity of AuCu/CuO NP catalyst for CO oxidation. Furthermore, the same concept can be extended to other alloy NPs, making it possible to fine-tune NP catalysis for many different chemical reactions.« less

Enhanced magneto-optical and photo-catalytic properties of transition metal cobalt (Co2+ ions) doped spinel MgFe2O4 ferrite nanocomposites

NASA Astrophysics Data System (ADS)

Abraham, A. Godlyn; Manikandan, A.; Manikandan, E.; Vadivel, S.; Jaganathan, S. K.; Baykal, A.; Renganathan, P. Sri

2018-04-01

In this study, spinel magnesium cobalt ferrite (CoxMg1-xFe2O4: x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) nanocomposites were synthesized successfully by modified sol-gel combustion method. Magnesium nitrate, cobalt nitrate and iron nitrate were used as the source of divalent (Mg2+ and Co2+) and trivalent (Fe3+) cations, respectively and urea were used as the reducing (fuel) agent. The effects of cobalt ions on morphology, structural, optical, magnetic and photo-catalytic properties of spinel CoxMg1-xFe2O4 nanocomposites were investigated. Various characterization methods, including X-ray powder diffraction (XRD), high resolution scanning electron microscope (HR-SEM), transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transforms infrared (FT-IR) spectroscopy, vibrating sample magnetometer (VSM) and photo-catalytic degradation (PCD) activity were used to study the phase purity, microstructure, particle size, elemental composition, functional group determination, band gap calculation, magnetic properties and degradation efficiency of nanoparticles, respectively. The observed results showed that the final products consists cubic spinel phase with sphere-like nanoparticles morphologies. Furthermore, spinel Co0.6Mg0.4Fe2O4 nanocomposite showed highest PCD efficiency (98.55%) than other composition of ferrite nanoparticles.

Biomimetic CO2 capture using a highly thermostable bacterial α-carbonic anhydrase immobilized on a polyurethane foam.

PubMed

Migliardini, Fortunato; De Luca, Viviana; Carginale, Vincenzo; Rossi, Mosè; Corbo, Pasquale; Supuran, Claudiu T; Capasso, Clemente

2014-02-01

The biomimetic approach represents an interesting strategy for carbon dioxide (CO2) capture, offering advantages over other methods, due to its specificity for CO2 and its eco-compatibility, as it allows concentration of CO2 from other gases, and its conversion to water soluble ions. This approach uses microorganisms capable of fixing CO2 through metabolic pathways or via the use of an enzyme, such as carbonic anhydrase (CA, EC 4.2.1.1). Recently, our group cloned and purified a novel bacterial α-CA, named SspCA, from the thermophilic bacteria, Sulfurihydrogenibium yellowstonense YO3AOP1 living in hot springs at temperatures of up to 110 °C. This enzyme showed an exceptional thermal stability, retaining its high catalytic activity for the CO2 hydration reaction even after being heated at 70 °C for several hours. In the present paper, the SspCA was immobilized within a polyurethane (PU) foam. The immobilized enzyme was found to be catalytically active and showed a long-term stability. A bioreactor containing the "PU-immobilized enzyme" (PU-SspCA) as shredded foam was used for experimental tests aimed to verify the CO2 capture capability in conditions close to those of a power plant application. In this bioreactor, a gas phase, containing CO2, was put into contact with a liquid phase under conditions, where CO2 contained in the gas phase was absorbed and efficiently converted into bicarbonate by the extremo-α-CA.

Converting sugars to sugar alcohols by aqueous phase catalytic hydrogenation

DOEpatents

Elliott, Douglas C [Richland, WA; Werpy, Todd A [West Richland, WA; Wang, Yong [Richland, WA; Frye, Jr., John G.

2003-05-27

The present invention provides a method of converting sugars to their corresponding sugar alcohols by catalytic hydrogenation in the aqueous phase. It has been found that surprisingly superior results can be obtained by utilizing a relatively low temperature (less than 120.degree. C.), selected hydrogenation conditions, and a hydrothermally stable catalyst. These results include excellent sugar conversion to the desired sugar alcohol, in combination with long life under hydrothermal conditions.

Method and apparatus for thermal management of vehicle exhaust systems

DOEpatents

Benson, David K.; Potter, Thomas F.

1995-01-01

A catalytic converter is surrounded by variable conductance insulation for maintaining the operating temperature of the catalytic converter at an optimum level, for inhibiting heat loss when raising catalytic converter temperature to light-off temperature, for storing excess heat to maintain or accelerate reaching light-off temperature, and for conducting excess heat away from the catalytic converter after reaching light-off temperature. The variable conductance insulation includes vacuum gas control and metal-to-metal thermal shunt mechanisms. Radial and axial shielding inhibits radiation and convection heat loss. Thermal storage media includes phase change material, and heat exchanger chambers and fluids carry heat to and from the catalytic converter.

Hydrogen production from bio-fuels using precious metal catalysts

NASA Astrophysics Data System (ADS)

Pasel, Joachim; Wohlrab, Sebastian; Rotov, Mikhail; Löhken, Katrin; Peters, Ralf; Stolten, Detlef

2017-11-01

Fuel cell systems with integrated autothermal reforming unit require active and robust catalysts for H2 production. Thus, an experimental screening of catalysts for autothermal reforming of commercial biodiesel fuel was performed. Catalysts consisted of a monolithic cordierite substrate, an oxide support (γ-Al2O3) and Pt, Ru, Ni, PtRh and PtRu as active phase. Experiments were run by widely varying the O2/C and H2O/C molar ratios at different gas hourly space velocities. Fresh and aged catalysts were characterized by temperature programmed methods and thermogravimetry to find correlations with catalytic activity and stability.

Highly Efficient Gas-Phase Oxidation of Renewable Furfural to Maleic Anhydride over Plate Vanadium Phosphorus Oxide Catalyst.

PubMed

Li, Xiukai; Ko, Jogie; Zhang, Yugen

2018-02-09

Maleic anhydride (MAnh) and its acids are critical intermediates in chemical industry. The synthesis of maleic anhydride from renewable furfural is one of the most sought after processes in the field of sustainable chemistry. In this study, a plate vanadium phosphorus oxide (VPO) catalyst synthesized by a hydrothermal method with glucose as a green reducing agent catalyzes furfural oxidation to MAnh in the gas phase. The plate catalyst-denoted as VPO HT -has a preferentially exposed (200) crystal plane and exhibited dramatically enhanced activity, selectivity and stability as compared to conventional VPO catalysts and other state-of-the-art catalytic systems. At 360 °C reaction temperature with air as an oxidant, about 90 % yield of MAnh was obtained at 10 vol % of furfural in the feed, a furfural concentration value that is much higher than those (<2 vol %) reported for other catalytic systems. The catalyst showed good long-term stability and there was no decrease in activity or selectivity for MAnh during the time-on-stream of 25 h. The high efficiency and catalyst stability indicate the great potential of this system for the synthesis of maleic anhydride from renewable furfural. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Surface Structure Dependent Electrocatalytic Activity of Co3O4 Anchored on Graphene Sheets toward Oxygen Reduction Reaction

PubMed Central

Xiao, Junwu; Kuang, Qin; Yang, Shihe; Xiao, Fei; Wang, Shuai; Guo, Lin

2013-01-01

Catalytic activity is primarily a surface phenomenon, however, little is known about Co3O4 nanocrystals in terms of the relationship between the oxygen reduction reaction (ORR) catalytic activity and surface structure, especially when dispersed on a highly conducting support to improve the electrical conductivity and so to enhance the catalytic activity. Herein, we report a controllable synthesis of Co3O4 nanorods (NR), nanocubes (NC) and nano-octahedrons (OC) with the different exposed nanocrystalline surfaces ({110}, {100}, and {111}), uniformly anchored on graphene sheets, which has allowed us to investigate the effects of the surface structure on the ORR activity. Results show that the catalytically active sites for ORR should be the surface Co2+ ions, whereas the surface Co3+ ions catalyze CO oxidation, and the catalytic ability is closely related to the density of the catalytically active sites. These results underscore the importance of morphological control in the design of highly efficient ORR catalysts. PMID:23892418

Transient Numerical Modeling of Catalytic Channels

NASA Technical Reports Server (NTRS)

Struk, Peter M.; Dietrich, Daniel L.; Miller, Fletcher J.; T'ien, James S.

2007-01-01

This paper presents a transient model of catalytic combustion suitable for isolated channels and monolith reactors. The model is a lumped two-phase (gas and solid) model where the gas phase is quasi-steady relative to the transient solid. Axial diffusion is neglected in the gas phase; lateral diffusion, however, is accounted for using transfer coefficients. The solid phase includes axial heat conduction and external heat loss due to convection and radiation. The combustion process utilizes detailed gas and surface reaction models. The gas-phase model becomes a system of stiff ordinary differential equations while the solid phase reduces, after discretization, into a system of stiff ordinary differential-algebraic equations. The time evolution of the system came from alternating integrations of the quasi-steady gas and transient solid. This work outlines the numerical model and presents some sensitivity studies on important parameters including internal transfer coefficients, catalytic surface site density, and external heat-loss (if applicable). The model is compared to two experiments using CO fuel: (1) steady-state conversion through an isothermal platinum (Pt) tube and (2) transient propagation of a catalytic reaction inside a small Pt tube. The model requires internal mass-transfer resistance to match the experiments at lower residence times. Under mass-transport limited conditions, the model reasonably predicted exit conversion using global mass-transfer coefficients. Near light-off, the model results did not match the experiment precisely even after adjustment of mass-transfer coefficients. Agreement improved for the first case after adjusting the surface kinetics such that the net rate of CO adsorption increased compared to O2. The CO / O2 surface mechanism came from a sub-set of reactions in a popular CH4 / O2 mechanism. For the second case, predictions improved for lean conditions with increased external heat loss or adjustment of the kinetics as in the first case. Finally, the results show that different initial surface-species distribution leads to different steady-states under certain conditions. These results demonstrate the utility of a lumped two-phase model of a transient catalytic combustor with detailed chemistry.

Kinetic study on the catalytic performance of Rh/TiO/sub 2/ reduced at different temperatures in the CO-H/sub 2/ reaction

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

Fujitsu, H.; Ikeyama, N.; Mochida, I.

1986-08-01

Catalytic CO-H/sub 2/ reaction on Rh/TiO/sub 2/ reduced at 200, 400, and 500/sup 0/C (Cat-200, -400, -500) for 2 h was kinetically studied at 250/sup 0/C using a circulating reactor and Fourier transform-infrared (FT-IR) spectroscopy to determine how Cat-400 exhibited the highest activity. The rate equation distinguished the best catalyst with zero and first orders in CO and H/sub 2/, respectively, from other catalysts with negative order in CO. The adsorption ability of the catalyst at 200/sup 0/C was comparable to that of Cat-200, and two to three times larger than that of Cat-500, although the ability of Cat-200 wasmore » much larger at room temperature. Carbon monoxide adsorbed on the catalysts reversibly as well as irreversibly. IR spectroscopy revealed that the major form of irreversibly adsorbed CO was linear on Cat-200, whereas similar amounts of linear and bridge forms were observed on Cat-400 and Cat-500. These latter forms were highly reactive against hydrogen molecules when no carbon monoxide was present in the gas phase. Based on these results, the highest activity of Cat-400 is ascribed to rhodium metal modified by properly reduced TiO/sub 2/ to show the appropriate adsorption ability of carbon monoxide which least retards the activation of hydrogen according to first-order kinetics. Typical strong metal-support interaction decreases the catalytic activity by decreasing the active sites and strengthening the CO adsorption too much.« less

Reactivity and Characterization of Solid State Hydrodesulfurization Catalysts.

NASA Astrophysics Data System (ADS)

Lindner, James Henry

1990-01-01

The identification of the phase responsible for hydrodesulfurization (HDS) activity has been the subject of extensive research. In this study, model solid state catalysts prepared from elemental starting materials were synthesized, characterized, and then used to desulfurize thiophene at temperatures ranging from 200-400 ^circC and a pressure of one atmosphere. The results of this work indicate that an increased HDS activity can be correlated with the presence of a poorly crystalline molybdenum sulfide-like phase detected by XRD, HREM, or AEM. The formation of this sulfur-deficient, non-stoichiometric phase could be accomplished by either removing sulfur directly from the catalyst synthesis mixture to yield a non-stoichiometric MoS_{ rm 2-x} moiety, or by introducing a transition metal promoter such as Fe, Co, Ni, or Cu into the system. The promoter atoms induced structural changes in the molybdenum sulfide edge planes by effectively scavenging sulfur during catalyst synthesis to form promoter sulfide species, which enhanced the formation of a non-stoichiometric, highly active molybdenum sulfide. This morphological effect was the primary function of the promoter in this system. All model catalysts displayed similar structure in the (0002) basal plane of MoS_2; however, only the catalytically active samples showed a high concentration of defects and disorder in the (1010), (1011), and (1012) edge planes. The HREM images obtained from these edge planes and their correlation with HDS activity dramatically illustrated the importance of the often-discussed edge plane structure of MoS_2 and its significance on HDS catalysis. Normalization of the HDS activities for the solid state models and a commercial catalyst with O_2 or CO chemisorption uptakes suggested that a similarity may exist between the catalytically active sites of these materials. In-situ XPS revealed that increasing promoter atom concentrations resulted in a more complete reduction of the promoter atom; but this shift to lower binding energies could not necessarily be correlated with activity. However, it was observed that the more active catalysts all exhibited the ability to dissociate H_2 and remove oxygen from their surface. This H_2 spillover or activation may also influence catalyst performance.

Different Device Architectures for Bulk-Heterojunction Solar Cells

NASA Astrophysics Data System (ADS)

Adam, Getachew; Munkhbat, Battulga; Denk, Patrick; Ulbricht, Christoph; Hrelescu, Calin; Scharber, Markus

2016-08-01

Titania is the most widely studied photocatalyst. In it’s mixed-phase configuration (anatase-rutile form) -as manifested in the commercially available P25 Degussa material- titania was previously found to exhibit the best photocatalytic properties reported for the pure system. A great deal of published research by various workers in the field have not fully explained the underlying mechanism for the observed behavior of mixed-phase titania photocatalysts. One of the prevalent hypothesis in the literature that is tested in this work involves the presence of small, active clusters of interwoven anatase and rutile crystallites or “catalytic “hot-spots””. Therefore, non-woven nanofibrous mats of titania were produced and upon calcination the mats consisted of nanostructured fibers with different anatase-rutile ratios. By assessing the photocatalytic and photoelectrochemical properties of these samples the optimized photocatalyst was determined. This consisted of TiO2 nanostructures annealed at 500˚C with an anatase /rutile content of 90/10. Since the performance of this material exceeded that of P25 complete structural characterization was employed to understand the catalytic mechanism involved. It was determined that the dominant factors controlling the photocatalytic behavior of the titania system are the relative particle size of the different phases of titania and the growth of rutile laths on anatase grains which allow for rapid electron transfer between the two phases. This explains how to optimize the response of the pure system.

Optimized nanostructured TiO2 photocatalysts

NASA Astrophysics Data System (ADS)

Topcu, Selda; Jodhani, Gagan; Gouma, Pelagia

2016-07-01

Titania is the most widely studied photocatalyst. In it’s mixed-phase configuration (anatase-rutile form) -as manifested in the commercially available P25 Degussa material- titania was previously found to exhibit the best photocatalytic properties reported for the pure system. A great deal of published research by various workers in the field have not fully explained the underlying mechanism for the observed behavior of mixed-phase titania photocatalysts. One of the prevalent hypothesis in the literature that is tested in this work involves the presence of small, active clusters of interwoven anatase and rutile crystallites or “catalytic “hot-spots””. Therefore, non-woven nanofibrous mats of titania were produced and upon calcination the mats consisted of nanostructured fibers with different anatase-rutile ratios. By assessing the photocatalytic and photoelectrochemical properties of these samples the optimized photocatalyst was determined. This consisted of TiO2 nanostructures annealed at 500˚C with an anatase /rutile content of 90/10. Since the performance of this material exceeded that of P25 complete structural characterization was employed to understand the catalytic mechanism involved. It was determined that the dominant factors controlling the photocatalytic behavior of the titania system are the relative particle size of the different phases of titania and the growth of rutile laths on anatase grains which allow for rapid electron transfer between the two phases. This explains how to optimize the response of the pure system.

Cell Partition in Two Polymer Aqueous Phases

NASA Technical Reports Server (NTRS)

Harris, J. M.

1985-01-01

Partition of biological cells in two phase aqueous polymer systems is recognized as a powerful separation technique which is limited by gravity. The synthesis of new, selective polymer ligand conjugates to be used in affinity partition separations is of interest. The two most commonly used polymers in two phase partitioning are dextran and polyethylene glycol. A thorough review of the chemistry of these polymers was begun, particularly in the area of protein attachment. Preliminary studies indicate the importance in affinity partitioning of minimizing gravity induced randomizing forces in the phase separation process. The PEG-protein conjugates that were prepared appear to be ideally suited for achieving high quality purifications in a microgravity environment. An interesting spin-off of this synthetic work was the observation of catalytic activity for certain of our polymer derivatives.

Enzymatic oxidation of ethanol in the gaseous phase.

PubMed

Barzana, E; Karel, M; Klibanov, A M

1989-11-01

The enzymatic conversion of gaseous substrates represents a novel concept in bioprocessing. A critical parameter in such systems is the water activity, A(w) The present article reports the effect of A(w) on the catalytic performance of alcohol oxidase acting on ethanol vapors. Enzyme activity in the gas-phase reaction increases several orders of magnitude, whereas the thermostability decreases drastically when A(w) is increased from 0.11 to 0.97. The enzyme is active on gaseous substrates even at hydration levels below the monolayer coverage. Enhanced thermostability at lower hydrations results in an increase in the optimum temperature of the gas-phase reaction catalyzed by alcohol oxidase. The apparent activation energy decreases as A(w) increases, approaching the value obtained for the enzyme in aqueous solution. The formation of a pread-sorbed ethanol phase on the surface of the support is not a prerequisite for the reaction, suggesting that the reaction occurs by direct interaction of the gaseous substrate with the enzyme. The gas-phase reaction follows Michaelis-Menten kinetics, with a K(m) value almost 100 times lower than that in aqueous solution. Based on vapor-liquid equilibrium data and observed K(m) values, it is postulated that during the gas-phase reaction the ethanol on the enzyme establishes an equilibrium with the ethanol vapor similar to that between ethanol in water and ethanol in the gas phase.

A recyclable and highly active Co{sub 3}O{sub 4} nanoparticles/titanate nanowire catalyst for organic dyes degradation with peroxymonosulfate

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

Chen, Zhili; Chen, Shihua; Li, Yonghe

2014-09-15

Sodium ions of TNWs were exchanged with hydrogen ions, and this protocol was very suitable for capturing high density of cobalt ions. Meanwhile, the fabricated Co{sub 3}O{sub 4}/TNWs nano-material presented a highly catalytic and stable activity for dye degradation. - Highlights: • Co{sub 3}O{sub 4} nanoparticles were deposited on the pretreated TNWs surface. • The TNWs treated by hydrogen ions captures higher density of cobalt ions. • The Co{sub 3}O{sub 4}/TNWs catalyst possesses highly efficiency for dyes degradation with oxone. - Abstract: In this paper, we reported a recyclable and highly active porous catalyst of titanate nanowires (TNWs) coated withmore » well-distributed Co{sub 3}O{sub 4} nanoparticles (NPs) (Co{sub 3}O{sub 4}/TNWs). Sodium ions of TNWs were exchanged with hydrogen ions in the dilute nitric acid, and this protocol was very suitable for capturing cobalt ions. X-ray diffraction (XRD) demonstrated the existence of Co{sub 3}O{sub 4} phase with unique lattice planes, such as (2 2 0), (3 1 1) and (5 1 1). Electron microscopes (FE-SEM and TEM) indicated that the Co{sub 3}O{sub 4} NPs with an average diameter of 22 ± 3 nm were coated uniformly on TNWs surface (average diameter: 37 ± 5.5 nm), and the Co{sub 3}O{sub 4} NPs mainly exposed their (2 2 0) and (2 2 2) active planes. XPS analysis confirms the formation of Co{sub 3}O{sub 4} phase by the presence of Co 2p peaks at 780.1 eV (2p 3/2) and 795.5 eV (2p 1/2). Methylene blue (MB) and other organic dyes (rhodamine B (RhB) and methyl orange (MO)) were chosen as target compounds for catalytic degradation under indoor scattering light. Compared to the original Co{sub 3}O{sub 4}/TNWs catalyst, the catalytic efficiency of nanoscaled catalyst with oxone for MB was about 15 times higher, and the MB solution (10 mg L{sup −1}) was completely degraded within 8 min. The catalytic activity of recycled catalyst used in the sixth run still remained very active, and the degradation time for MB was only 16 min. The nanosized catalyst also had a high activity for dyes of RhB (10 mg L{sup −1}) and MO (10 mg L{sup −1}), as the degradation efficiencies of RhB and MO after 10 min of contact time were about 90.2% and 92.6%, respectively.« less

Coated mesh photocatalytic reactor for air treatment applications: comparative study of support materials.

PubMed

Passalía, Claudio; Nocetti, Emanuel; Alfano, Orlando; Brandi, Rodolfo

2017-03-01

An experimental comparative study of different meshes as support materials for photocatalytic applications in gas phase is presented. The photocatalytic oxidation of dichloromethane in air was addressed employing different coated meshes in a laboratory-scale, continuous reactor. Two fiberglass meshes and a stainless steel mesh were studied regarding the catalyst load, adherence, and catalytic activity. Titanium dioxide photocatalyst was immobilized on the meshes by dip-coating cycles. Results indicate the feasibility of the dichloromethane elimination in the three cases. When the number of coating cycles was doubled, the achieved conversion levels were increased twofold for stainless steel and threefold for the fiberglass meshes. One of the fiberglass meshes (FG2) showed the highest reactivity per mass of catalyst and per catalytic surface area.

Nanoporous Gold as a Platform for a Building Block Catalyst

DOE PAGES

Wittstock, Arne; Wichmann, Andre; Baeumer, Marcus

2012-09-25

The porous bulk materials are of great interest in catalysis because they can be employed in heterogeneous gas and liquid phase catalysis, electrocatalysis, and in electrocatalytic sensing. Nanoporous gold gained considerable attraction in this context because it is the prime example of a corrosion-derived nanoporous bulk metal. Moreover, the material was shown to be a very active and selective Au type catalyst for a variety of oxidation reactions. In leveraging the functionalization of the surface of the material with various additives, its catalytic applications can be extended and tuned. In this review, we will summarize recent developments in using nanoporousmore » gold as the platform for the development of high performance catalytic materials by adding metals, metal oxides, and molecular functionalities as building blocks.« less

Catalytic reaction processes revealed by scanning probe microscopy. [corrected].

PubMed

Jiang, Peng; Bao, Xinhe; Salmeron, Miquel

2015-05-19

Heterogeneous catalysis is of great importance for modern society. About 80% of the chemicals are produced by catalytic reactions. Green energy production and utilization as well as environmental protection also need efficient catalysts. Understanding the reaction mechanisms is crucial to improve the existing catalysts and develop new ones with better activity, selectivity, and stability. Three components are involved in one catalytic reaction: reactant, product, and catalyst. The catalytic reaction process consists of a series of elementary steps: adsorption, diffusion, reaction, and desorption. During reaction, the catalyst surface can change at the atomic level, with roughening, sintering, and segregation processes occurring dynamically in response to the reaction conditions. Therefore, it is imperative to obtain atomic-scale information for understanding catalytic reactions. Scanning probe microscopy (SPM) is a very appropriate tool for catalytic research at the atomic scale because of its unique atomic-resolution capability. A distinguishing feature of SPM, compared to other surface characterization techniques, such as X-ray photoelectron spectroscopy, is that there is no intrinsic limitation for SPM to work under realistic reaction conditions (usually high temperature and high pressure). Therefore, since it was introduced in 1981, scanning tunneling microscopy (STM) has been widely used to investigate the adsorption, diffusion, reaction, and desorption processes on solid catalyst surfaces at the atomic level. STM can also monitor dynamic changes of catalyst surfaces during reactions. These invaluable microscopic insights have not only deepened the understanding of catalytic processes, but also provided important guidance for the development of new catalysts. This Account will focus on elementary reaction processes revealed by SPM. First, we will demonstrate the power of SPM to investigate the adsorption and diffusion process of reactants on catalyst surfaces at the atomic level. Then the dynamic processes, including surface reconstruction, roughening, sintering, and phase separation, studied by SPM will be discussed. Furthermore, SPM provides valuable insights toward identifying the active sites and understanding the reaction mechanisms. We also illustrate here how both ultrahigh vacuum STM and high pressure STM provide valuable information, expanding the understanding provided by traditional surface science. We conclude with highlighting remarkable recent progress in noncontact atomic force microscopy (NC-AFM) and inelastic electron tunneling spectroscopy (IETS), and their impact on single-chemical-bond level characterization for catalytic reaction processes in the future.

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

A comparative theoretical study of the catalytic activities of Au2(-) and AuAg(-) dimers for CO oxidation.

PubMed

Liu, Peng; Song, Ke; Zhang, Dongju; Liu, Chengbu

2012-05-01

The detailed mechanisms of catalytic CO oxidation over Au(2)(-) and AuAg(-) dimers, which represent the simplest models for monometal Au and bimetallic Au-Ag nanoparticles, have been studied by performing density functional theory calculations. It is found that both Au(2)(-) and AuAg(-) dimers catalyze the reaction according to the similar mono-center Eley-Rideal mechanism. The catalytic reaction is of the multi-channel and multi-step characteristic, which can proceed along four possible pathways via two or three elementary steps. In AuAg(-), the Au site is more active than the Ag site, and the calculated energy barrier values for the rate-determining step of the Au-site catalytic reaction are remarkably smaller than those for both the Ag-site catalytic reaction and the Au(2)(-) catalytic reaction. The better catalytic activity of bimetallic AuAg(-) dimer is attributed to the synergistic effect between Au and Ag atom. The present results provide valuable information for understanding the higher catalytic activity of Au-Ag nanoparticles and nanoalloys for low-temperature CO oxidation than either pure metallic catalyst.

Predicting Catalytic Activity of Nanoparticles by a DFT-Aided Machine-Learning Algorithm.

PubMed

Jinnouchi, Ryosuke; Asahi, Ryoji

2017-09-07

Catalytic activities are often dominated by a few specific surface sites, and designing active sites is the key to realize high-performance heterogeneous catalysts. The great triumphs of modern surface science lead to reproduce catalytic reaction rates by modeling the arrangement of surface atoms with well-defined single-crystal surfaces. However, this method has limitations in the case for highly inhomogeneous atomic configurations such as on alloy nanoparticles with atomic-scale defects, where the arrangement cannot be decomposed into single crystals. Here, we propose a universal machine-learning scheme using a local similarity kernel, which allows interrogation of catalytic activities based on local atomic configurations. We then apply it to direct NO decomposition on RhAu alloy nanoparticles. The proposed method can efficiently predict energetics of catalytic reactions on nanoparticles using DFT data on single crystals, and its combination with kinetic analysis can provide detailed information on structures of active sites and size- and composition-dependent catalytic activities.

Chemical catalysis of nitrate reduction by iron (II)

NASA Astrophysics Data System (ADS)

Ottley, C. J.; Davison, W.; Edmunds, W. M.

1997-05-01

Experiments have been conducted to investigate the chemical reduction of nitrate under conditions relevant to the often low organic carbon environment of groundwaters. At pH 8 and 20 ± 2°C, in the presence of Cu(II), NO 3- was chemically reduced by Fe(II) to NH 4+ with an average stoichiometric liberation of 8 protons. The rate of the reaction systematically increased with pH in the range pH 7-8.5. The half-life for nitrate reduction, t 1/2, was inversely related to the total molar copper concentration, [Cu T], by the equation log t 1/2 = -1.35 log [Cu T] -2.616, for all measured values of t 1/2 from 23 min to 15 days. At the Cu(II) concentrations used of 7 × 10 -6 -10 -3 M, Cu was present mainly as a solid phase, either adsorbed to the surfaces of precipitated iron oxides or as a saturated solid. It is this solid phase copper rather than CU 2+ in solution which is catalytically active. Neither magnetite, which was formed as a product of the reaction, nor freshly prepared lepidocrocite catalysed the reaction, but goethite did. Although traces of oxygen accelerated the reaction, at higher partial pressures (>0.01 atm) the reduction of nitrate was inhibited, probably due to competition between NO 3- and O 2 for Fe(II). Appreciable catalytic effects were also observed for solid phase forms of Ag(I), Cd(H), Ni(H), Hg(II), and Pb(II). Mn(II) enhanced the rate slightly, and there was evidence for slow abiotic reduction in the absence of any added metal catalysts. These results suggest that the chemical reduction of nitrate at catalytic concentrations and temperatures appropriate to groundwater conditions is feasible on a timescale of months to years.

Molecular Self-Assembly Strategy for Generating Catalytic Hybrid Polypeptides

PubMed Central

Ikezoe, Yasuhiro; Pike, Douglas H.; Nanda, Vikas; Matsui, Hiroshi

2016-01-01

Recently, catalytic peptides were introduced that mimicked protease activities and showed promising selectivity of products even in organic solvents where protease cannot perform well. However, their catalytic efficiency was extremely low compared to natural enzyme counterparts presumably due to the lack of stable tertiary fold. We hypothesized that assembling these peptides along with simple hydrophobic pockets, mimicking enzyme active sites, could enhance the catalytic activity. Here we fused the sequence of catalytic peptide CP4, capable of protease and esterase-like activities, into a short amyloidogenic peptide fragment of Aβ. When the fused CP4-Aβ construct assembled into antiparallel β-sheets and amyloid fibrils, a 4.0-fold increase in the hydrolysis rate of p-nitrophenyl acetate (p-NPA) compared to neat CP4 peptide was observed. The enhanced catalytic activity of CP4-Aβ assembly could be explained both by pre-organization of a catalytically competent Ser-His-acid triad and hydrophobic stabilization of a bound substrate between the triad and p-NPA, indicating that a design strategy for self-assembled peptides is important to accomplish the desired functionality. PMID:27116246

Molecular self-assembly strategy for generating catalytic hybrid polypeptides

DOE PAGES

Maeda, Yoshiaki; Fang, Justin; Ikezoe, Yasuhiro; ...

2016-04-26

Recently, catalytic peptides were introduced that mimicked protease activities and showed promising selectivity of products even in organic solvents where protease cannot perform well. However, their catalytic efficiency was extremely low compared to natural enzyme counterparts presumably due to the lack of stable tertiary fold. We hypothesized that assembling these peptides along with simple hydrophobic pockets, mimicking enzyme active sites, could enhance the catalytic activity. Here we fused the sequence of catalytic peptide CP4, capable of protease and esterase-like activities, into a short amyloidogenic peptide fragment of Aβ. When the fused CP4-Aβ construct assembled into antiparallel β- sheets and amyloidmore » fibrils, a 4.0-fold increase in the hydrolysis rate of p-nitrophenyl acetate (p-NPA) compared to neat CP4 peptide was observed. Furthermore, the enhanced catalytic activity of CP4-Aβ assembly could be explained both by pre-organization of a catalytically competent Ser-His-acid triad and hydrophobic stabilization of a bound substrate between the triad and p-NPA, indicating that a design strategy for self-assembled peptides is important to accomplish the desired functionality.« less

NOVEL NANOPARTICULATE CATALYSTS FOR IMPROVED VOC TREATMENT DEVICES - PHASE I

EPA Science Inventory

Catalytic oxidation of VOCs is increasingly used for treatment of large-volume emissions at relatively dilute VOC levels. The best performing catalytic oxidation devices for attainment of very high VOC destruction levels employ precious metal catalysts, the costs of which a...

Cu@C nanoporous composites containing little copper oxides derived from dimethyl imidazole modified MOF199 as electrocatalysts for hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Wei, Xuedong; Li, Na; Zhang, Xianming

2017-12-01

It remains a huge challenge to develop non precious electrocatalysts with high activity to substitute commercial Pt catalysts for hydrogen evolution reactions (HER). Here, the C-Cu-DI and C-Cu materials with the copper based nanoporous carbon structures were synthesized by carbonizing MOF199 and DI-MOF199. The composite structure and HER electrocatalytic properties of the C-Cu-DI and C-Cu materials are studied. The results show that C-Cu-DI and C-Cu samples exhibit good catalytic activity. And C-Cu-DI sample through the addition of Dimethyl imidazole(DI) in the DI-MOF199 precursor has higher electrocatalytic activity than the C-Cu sample. The superior catalytic activity is attributed to the special composite structure of nanoscale deposition particles on the framework with plenty of nano pores and nano copper and few copper oxidation particles distributed or wrapped into the amorphous porous carbon phase. The nano copper and few copper oxidation particles in the C-Cu and C-Cu-DI catalysts maybe provide the more effective catalytic activity sites. The C-Cu-DI composite with large size spherical hollow deposition particles has higher conductivity, better BET surface area and reasonable micro-meso-macro porous distribution, so the overpotentials at the current density of 1 mA cm-2 and 10 mA cm-2 are respectively 270 mV and 390 mV vs. RHE. Although the HER activity has a big gap with commercial platinum catalyst, this study can provide an important experimental exploration for the design of copper based non noble metal/nano porous carbon composite HER electrocatalyst.

Surface chemistry characterization of hydrodesulfurization and methanol synthesis model nanocatalysts

NASA Astrophysics Data System (ADS)

Komarneni, Mallikharjuna Rao

Surface science investigations of model catalysts have contributed significantly to heterogeneous catalysis over the past several decades. The unique properties of nanomaterials are being exploited in catalysis for the development of highly active and selective catalysts. Surface science investigations of model catalysts such as inorganic fullerene-like (IF) nanoparticles (NP), inorganic nanotubes (INT), and the oxide-supported nanoclusters are included in this dissertation. Thermal desorption spectroscopy and molecular beam scattering were respectively utilized to study the adsorption kinetics and dynamics of gas phase molecules on catalyst surfaces. In addition, ambient pressure kinetics experiments were performed to characterize the catalytic activity of hydrodesulfurization (HDS) nanocatalysts. The nanocatalysts were characterized with a variety of techniques, including Auger electron spectroscopy, x-ray photoelectron spectroscopy, electron microscopy, and x-ray diffraction. The adsorption kinetics studies of thiophene on novel HDS catalysts provided the first evidence for the presence of different adsorption sites on INT-WS2. Additionally, the adsorption sites on IF-MoS2 NP and silica-supported Mo clusters (Mo/silica) were characterized. Furthermore, the C-S bond activation energy of thiophene on Mo/silica was determined. These studies finally led to the fabrication of Ni/Co coated INT-WS2, which showed good catalytic activity towards HDS of thiophene. The studies of methanol synthesis catalysts include the adsorption kinetics and dynamics studies of CO and CO2 on Cu/silica and silica-supported EBL-fabricated Cu/CuOx nanoclusters. The adsorption dynamics of CO on Cu/silica are modeled within the frame work of the capture zone model (CZM), and the active sites of the silica-supported Au/Cu catalysts are successfully mapped. Studies on EBL model catalysts identify the rims of the CuOx nanoclusters as catalytically active sites. This observation has implications for new methanol catalyst design.

Structurally ordered Pt–Zn/C series nanoparticles as efficient anode catalysts for formic acid electrooxidation

DOE PAGES

Zhu, Jing; Zheng, Xin; Wang, Jie; ...

2015-09-15

Controlling the size, composition, and structure of bimetallic nanoparticles is of particular interest in the field of electrocatalysts for fuel cells. In the present work, structurally ordered nanoparticles with intermetallic phases of Pt 3Zn and PtZn have been successfully synthesized via an impregnation reduction method, followed by post heat-treatment. The Pt 3Zn and PtZn ordered intermetallic nanoparticles are well dispersed on a carbon support with ultrasmall mean particle sizes of ~5 nm and ~3 nm in diameter, respectively, which are credited to the evaporation of the zinc element at high temperature. These catalysts are less susceptible to CO poisoning relativemore » to Pt/C and exhibited enhanced catalytic activity and stability toward formic acid electrooxidation. The mass activities of the as-prepared catalysts were approximately 2 to 3 times that of commercial Pt at 0.5 V (vs. RHE). As a result, this facile synthetic strategy is scalable for mass production of catalytic materials.« less

Templated Assembly of a Functional Ordered Protein Macromolecular Framework from P22 Virus-like Particles.

PubMed

McCoy, Kimberly; Uchida, Masaki; Lee, Byeongdu; Douglas, Trevor

2018-04-24

Bottom-up construction of mesoscale materials using biologically derived nanoscale building blocks enables engineering of desired physical properties using green production methods. Virus-like particles (VLPs) are exceptional building blocks due to their monodispersed sizes, geometric shapes, production ease, proteinaceous composition, and our ability to independently functionalize the interior and exterior interfaces. Here a VLP, derived from bacteriophage P22, is used as a building block for the fabrication of a protein macromolecular framework (PMF), a tightly linked 3D network of functional protein cages that exhibit long-range order and catalytic activity. Assembly of PMFs was electrostatically templated, using amine-terminated dendrimers, then locked into place with a ditopic cementing protein that binds to P22. Long-range order is preserved on removal of the dendrimer, leaving a framework material composed completely of protein. Encapsulation of β-glucosidase enzymes inside of P22 VLPs results in formation of stable, condensed-phase materials with high local concentration of enzymes generating catalytically active PMFs.

Gold nanoparticles supported on magnesium oxide for CO oxidation

NASA Astrophysics Data System (ADS)

Carabineiro, Sónia Ac; Bogdanchikova, Nina; Pestryakov, Alexey; Tavares, Pedro B.; Fernandes, Lisete Sg; Figueiredo, José L.

2011-06-01

Au was loaded (1 wt%) on a commercial MgO support by three different methods: double impregnation, liquid-phase reductive deposition and ultrasonication. Samples were characterised by adsorption of N2 at -96°C, temperature-programmed reduction, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction. Upon loading with Au, MgO changed into Mg(OH)2 (the hydroxide was most likely formed by reaction with water, in which the gold precursor was dissolved). The size range for gold nanoparticles was 2-12 nm for the DIM method and 3-15 nm for LPRD and US. The average size of gold particles was 5.4 nm for DIM and larger than 6.5 for the other methods. CO oxidation was used as a test reaction to compare the catalytic activity. The best results were obtained with the DIM method, followed by LPRD and US. This can be explained in terms of the nanoparticle size, well known to determine the catalytic activity of gold catalysts.

Recovery of rare metal compounds from nickel-metal hydride battery waste and their application to CH4 dry reforming catalyst.

PubMed

Kanamori, Tomohiro; Matsuda, Motohide; Miyake, Michihiro

2009-09-30

The recovery of valuable components such as nickel from nickel-metal hydride (Ni-MH) battery waste by chemical processes and their applications to CH(4) dry reforming catalysts were investigated. Three types of compound, identified by XRD analysis as NiO, CeO(2) and LaCoO(3) phases, were successfully separated from the waste by a series of chemical processes at room temperature using aqueous solutions of HCl, NaOH and NH(3), and Ni component of approximately 70% in Ni-MH battery waste was recovered. The separated NiO, CeO(2) and LaCoO(3) showed catalytic activities for CH(4) dry reforming. In particular, the separated NiO easily reduced to Ni(0) at an initial stage, and exhibited excellent catalytic activity in terms of CH(4) conversion and stability. Furthermore, it was found that the resulting Ni from separated NiO exhibited an anomalous catalysis from the comparison with that from regent NiO.

A facile in situ self-assembly strategy for large-scale fabrication of CHS@MOF yolk/shell structure and its catalytic application in a flow system.

PubMed

Gao, Hongyi; Luan, Yi; Chaikittikul, Kullapat; Dong, Wenjun; Li, Jie; Zhang, Xiaowei; Jia, Dandan; Yang, Mu; Wang, Ge

2015-03-04

A hierarchical yolk/shell copper hydroxysulfates@MOF (CHS@MOF, where MOF = metal-organic frameworks) structure was fabricated from a homogeneous yolk/shell CHS template composed of an active shell and a stabilized core via a facile self-template strategy at room temperature. The active shell of the template served as the source of metal ion and was in situ transformed into a well-defined MOF crystal shell, and the relatively stabilized core retained its own nature during the formation of the MOF shell. The strategy of in situ transformation of CHS shell to MOF shell avoided the self-nucleation of MOF in the solution and complex multistep procedures. Furthermore, a flow reaction system using CHS@MOF as self-supported stationary-phase catalyst was developed, which demonstrated excellent catalytic performance for aldehyde acetalization with ethanol, and high yields and selectivities were achieved under mild conditions.

MOF-Templated Fabrication of Hollow Co4N@N-Doped Carbon Porous Nanocages with Superior Catalytic Activity.

PubMed

Sheng, Jianping; Wang, Liqiang; Deng, Liu; Zhang, Min; He, Haichuan; Zeng, Ke; Tang, Feiying; Liu, You-Nian

2018-02-28

Metallic Co 4 N catalysts have been considered as one of the most promising non-noble materials for heterogeneous catalysis because of their high electrical conductivity, great magnetic property, and high intrinsic activity. However, the metastable properties seriously limit their applications for heterogeneous water phase catalysis. In this work, a novel Co-metal-organic framework (MOF)-derived hollow porous nanocages (PNCs) composed of metallic Co 4 N and N-doped carbon (NC) were synthesized for the first time. This hollow three-dimensional (3D) PNC catalyst was synthesized by taking advantage of Co-MOF as a precursor for fabricating 3D hollow Co 3 O 4 @C PNCs, along with the NH 3 treatment of Co-oxide frames to promote the in situ conversion of Co-MOF to Co 4 N@NC PNCs, benefiting from the high intrinsic activity and electron conductivity of the metallic Co 4 N phase and the good permeability of the hollow porous nanostructure as well as the efficient doping of N into the carbon layer. Besides, the covalent bridge between the active Co 4 N surface and PNC shells also provides facile pathways for electron and mass transport. The obtained Co 4 N@NC PNCs exhibit excellent catalytic activity and stability for 4-nitrophenol reduction in terms of low activation energy (E a = 23.53 kJ mol -1 ), high turnover frequency (52.01 × 10 20 molecule g -1 min -1 ), and high apparent rate constant (k app = 2.106 min -1 ). Furthermore, its magnetic property and stable configuration account for the excellent recyclability of the catalyst. It is hoped that our finding could pave the way for the construction of other hollow transition metal-based nitride@NC PNC catalysts for wide applications.

Voltage-dependent motion of the catalytic region of voltage-sensing phosphatase monitored by a fluorescent amino acid

PubMed Central

Sakata, Souhei; Jinno, Yuka; Kawanabe, Akira; Okamura, Yasushi

2016-01-01

The cytoplasmic region of voltage-sensing phosphatase (VSP) derives the voltage dependence of its catalytic activity from coupling to a voltage sensor homologous to that of voltage-gated ion channels. To assess the conformational changes in the cytoplasmic region upon activation of the voltage sensor, we genetically incorporated a fluorescent unnatural amino acid, 3-(6-acetylnaphthalen-2-ylamino)-2-aminopropanoic acid (Anap), into the catalytic region of Ciona intestinalis VSP (Ci-VSP). Measurements of Anap fluorescence under voltage clamp in Xenopus oocytes revealed that the catalytic region assumes distinct conformations dependent on the degree of voltage-sensor activation. FRET analysis showed that the catalytic region remains situated beneath the plasma membrane, irrespective of the voltage level. Moreover, Anap fluorescence from a membrane-facing loop in the C2 domain showed a pattern reflecting substrate turnover. These results indicate that the voltage sensor regulates Ci-VSP catalytic activity by causing conformational changes in the entire catalytic region, without changing their distance from the plasma membrane. PMID:27330112

Voltage-dependent motion of the catalytic region of voltage-sensing phosphatase monitored by a fluorescent amino acid.

PubMed

Sakata, Souhei; Jinno, Yuka; Kawanabe, Akira; Okamura, Yasushi

2016-07-05

The cytoplasmic region of voltage-sensing phosphatase (VSP) derives the voltage dependence of its catalytic activity from coupling to a voltage sensor homologous to that of voltage-gated ion channels. To assess the conformational changes in the cytoplasmic region upon activation of the voltage sensor, we genetically incorporated a fluorescent unnatural amino acid, 3-(6-acetylnaphthalen-2-ylamino)-2-aminopropanoic acid (Anap), into the catalytic region of Ciona intestinalis VSP (Ci-VSP). Measurements of Anap fluorescence under voltage clamp in Xenopus oocytes revealed that the catalytic region assumes distinct conformations dependent on the degree of voltage-sensor activation. FRET analysis showed that the catalytic region remains situated beneath the plasma membrane, irrespective of the voltage level. Moreover, Anap fluorescence from a membrane-facing loop in the C2 domain showed a pattern reflecting substrate turnover. These results indicate that the voltage sensor regulates Ci-VSP catalytic activity by causing conformational changes in the entire catalytic region, without changing their distance from the plasma membrane.

Method and apparatus for thermal management of vehicle exhaust systems

DOEpatents

Benson, D.K.; Potter, T.F.

1995-12-26

A catalytic converter is surrounded by variable conductance insulation for maintaining the operating temperature of the catalytic converter at an optimum level, for inhibiting heat loss when raising catalytic converter temperature to light-off temperature, for storing excess heat to maintain or accelerate reaching light-off temperature, and for conducting excess heat away from the catalytic converter after reaching light-off temperature. The variable conductance insulation includes vacuum gas control and metal-to-metal thermal shunt mechanisms. Radial and axial shielding inhibits radiation and convection heat loss. Thermal storage media includes phase change material, and heat exchanger chambers and fluids carry heat to and from the catalytic converter. 7 figs.

N1-Alkylated 3,4-dihydropyrimidine-2(1H)-ones: Convenient one-pot selective synthesis and evaluation of their calcium channel blocking activity.

PubMed

Singh, Kamaljit; Arora, Divya; Poremsky, Elizabeth; Lowery, Jazmyne; Moreland, Robert S

2009-05-01

It has been found that selective N1-alkylation of 3,4-dihydropyrimidine-2(1H)-ones can be achieved under solvent-less, mild phase transfer catalytic (PTC) conditions with tetrabutylammonium hydrogen sulfate and 50% aqueous NaOH as the catalyst and base, respectively. The procedure is tolerant to substitutional variation at key diversity points on the pyrimidinone moiety.

Isotopic Exchange of Deuterium Between Hydrogen and Water in Vapor Phase. Report No. 56; INTERCAMBIO ISOTOPICO DE DEUTERIO ENTRE EL HIDROGENO Y EL AGUA EN FASE VAPOR. INFORME NO. 56

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

Baran, W.J.; Cretella, R.F.

1961-01-01

The design is described of a device for the measurement of catalytic activities of the isotopic exchange reaction, H/sub 2/O (v) + HD in equilibrium HDO (v) + H/sub 2/, and to determine experimentally the kinetics for the interpretation of the results for the optimum conditions for the reaction. (tr- auth)

Formation of alcohol conversion catalysts

DOEpatents

Wachs, Israel E.; Cai, Yeping

2001-01-01

The method of the present invention involves a composition containing an intimate mixture of (a) metal oxide support particles and (b) a catalytically active metal oxide from Groups VA, VIA, or VIIA, its method of manufacture, and its method of use for converting alcohols to aldehydes. During the conversion process, catalytically active metal oxide from the discrete catalytic metal oxide particles migrates to the oxide support particles and forms a monolayer of catalytically active metal oxide on the oxide support particle to form a catalyst composition having a higher specific activity than the admixed particle composition.

Substitution scanning identifies a novel, catalytically active ibrutinib-resistant BTK cysteine 481 to threonine (C481T) variant

PubMed Central

Hamasy, A; Wang, Q; Blomberg, K E M; Mohammad, D K; Yu, L; Vihinen, M; Berglöf, A; Smith, C I E

2017-01-01

Irreversible Bruton tyrosine kinase (BTK) inhibitors, ibrutinib and acalabrutinib have demonstrated remarkable clinical responses in multiple B-cell malignancies. Acquired resistance has been identified in a sub-population of patients in which mutations affecting BTK predominantly substitute cysteine 481 in the kinase domain for catalytically active serine, thereby ablating covalent binding of inhibitors. Activating substitutions in the BTK substrate phospholipase Cγ2 (PLCγ2) instead confers resistance independent of BTK. Herein, we generated all six possible amino acid substitutions due to single nucleotide alterations for the cysteine 481 codon, in addition to threonine, requiring two nucleotide substitutions, and performed functional analysis. Replacement by arginine, phenylalanine, tryptophan or tyrosine completely inactivated the catalytic activity, whereas substitution with glycine caused severe impairment. BTK with threonine replacement was catalytically active, similar to substitution with serine. We identify three potential ibrutinib resistance scenarios for cysteine 481 replacement: (1) Serine, being catalytically active and therefore predominating among patients. (2) Threonine, also being catalytically active, but predicted to be scarce, because two nucleotide changes are needed. (3) As BTK variants replaced with other residues are catalytically inactive, they presumably need compensatory mutations, therefore being very scarce. Glycine and tryptophan variants were not yet reported but likely also provide resistance. PMID:27282255

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 °C. Part 9: reference procedure for the measurement of catalytic concentration of alkaline phosphatase International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Scientific Division, Committee on Reference Systems of Enzymes (C-RSE) (1)).

PubMed

Schumann, Gerhard; Klauke, Rainer; Canalias, Francesca; Bossert-Reuther, Steffen; Franck, Paul F H; Gella, F-Javier; Jørgensen, Poul J; Kang, Dongchon; Lessinger, Jean-Marc; Panteghini, Mauro; Ceriotti, Ferruccio

2011-09-01

Abstract This paper is the ninth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 °C and the certification of reference preparations. Other parts deal with: Part 1. The concept of reference procedures for the measurement of catalytic activity concentrations of enzymes; Part 2. Reference procedure for the measurement of catalytic concentration of creatine kinase; Part 3. Reference procedure for the measurement of catalytic concentration of lactate dehydrogenase; Part 4. Reference procedure for the measurement of catalytic concentration of alanine aminotransferase; Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase; Part 6. Reference procedure for the measurement of catalytic concentration of γ-glutamyltransferase; Part 7. Certification of four reference materials for the determination of enzymatic activity of γ-glutamyltransferase, lactate dehydrogenase, alanine aminotransferase and creatine kinase at 37 °C; Part 8. Reference procedure for the measurement of catalytic concentration of α-amylase. The procedure described here is derived from the previously described 30 °C IFCC reference method. Differences are tabulated and commented on in Appendix 1.

Inhibition of tafel kinetics for electrolytic hydrogen evolution on isolated micron scale electrocatalysts on semiconductor interfaces

DOE PAGES

Coridan, Robert H.; Schichtl, Zebulon G.; Sun, Tao; ...

2016-08-30

Semiconductor-liquid junctions are ubiquitous in photoelectrochemical approaches for solar-to-fuels energy conversion. Electrocatalysts are added to the interface to improve catalytic efficiency, but they can also impair the photovoltage-generating energetics of the electrode without appropriate microscopic organization of catalytically active area on the surface. This balance is more complicated when gas products are evolved, like hydrogen on water splitting electrodes. Discrete catalysts can be blocked by the gas liquid-solid boundary of a bubble stuck to the surface. Here, we study the kinetics of hydrogen evolution on semiconductor electrodes fabricated with an isolated, micronscale platinum electrocatalyst pad. Movies of in operando bubblemore » evolution were recorded with synchrotron-based high-speed x-ray phase-contrast imaging in a compatible electrochemical cell. The self-limited growth of a bubble residing on the isolated electrocatalyst was measured by tracking the evolution of the gas-liquid boundary through the sequence of images in the movie. As a result, the effect of pad size on the catalytic currents and the issues with reactant transport can be inferred from these dynamics.« less

Inhibition of tafel kinetics for electrolytic hydrogen evolution on isolated micron scale electrocatalysts on semiconductor interfaces

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

Coridan, Robert H.; Schichtl, Zebulon G.; Sun, Tao

Semiconductor-liquid junctions are ubiquitous in photoelectrochemical approaches for solar-to-fuels energy conversion. Electrocatalysts are added to the interface to improve catalytic efficiency, but they can also impair the photovoltage-generating energetics of the electrode without appropriate microscopic organization of catalytically active area on the surface. This balance is more complicated when gas products are evolved, like hydrogen on water splitting electrodes. Discrete catalysts can be blocked by the gas liquid-solid boundary of a bubble stuck to the surface. Here, we study the kinetics of hydrogen evolution on semiconductor electrodes fabricated with an isolated, micronscale platinum electrocatalyst pad. Movies of in operando bubblemore » evolution were recorded with synchrotron-based high-speed x-ray phase-contrast imaging in a compatible electrochemical cell. The self-limited growth of a bubble residing on the isolated electrocatalyst was measured by tracking the evolution of the gas-liquid boundary through the sequence of images in the movie. As a result, the effect of pad size on the catalytic currents and the issues with reactant transport can be inferred from these dynamics.« less

HYBRID SNCR-SCR TECHNOLOGIES FOR NOX CONTROL: MODELING AND EXPERIMENT

EPA Science Inventory

The hybrid process of homogeneous gas-phase selective non-catalytic reduction (SNCR) followed by selective catalytic reduction (SCR) of nitric oxide (NO) was investigated through experimentation and modeling. Measurements, using NO-doped flue gas from a gas-fired 29 kW test combu...

Shp2–Mitogen-Activated Protein Kinase Signaling Drives Proliferation during Zebrafish Embryo Caudal Fin Fold Regeneration

PubMed Central

Hale, Alexander James

2017-01-01

ABSTRACT Regeneration of the zebrafish caudal fin following amputation occurs through wound healing, followed by formation of a blastema, which produces cells to replace the lost tissue in the final phase of regenerative outgrowth. We show that ptpn11a−/− ptpn11b−/− zebrafish embryos, lacking functional Shp2, fail to regenerate their caudal fin folds. Rescue experiments indicated that Shp2a has a functional signaling role, requiring its catalytic activity and SH2 domains but not the two C-terminal tyrosine phosphorylation sites. Surprisingly, expression of Shp2a variants with increased and reduced catalytic activity, respectively, rescued caudal fin fold regeneration to similar extents. Expression of mmp9 and junbb, indicative of formation of the wound epidermis and distal blastema, respectively, suggested that these processes occurred in ptpn11a−/− ptpn11b−/− zebrafish embryos. However, cell proliferation and MAPK phosphorylation were reduced. Pharmacological inhibition of MEK1 in wild-type zebrafish embryos phenocopied loss of Shp2. Our results suggest an essential role for Shp2a–mitogen-activated protein kinase (MAPK) signaling in promoting cell proliferation during zebrafish embryo caudal fin fold regeneration. PMID:29203641

Effect of Precursors on the Synthesis of CuO Nanoparticles Under Microwave for Photocatalytic Activity Towards Methylene Blue and Rhodamine B Dyes.

PubMed

Sanjini, N S; Winston, B; Velmathi, S

2017-01-01

Copper oxide nanoparticles have been successfully synthesized by microwave assisted precipitation method. Different precursors like copper chloride, copper nitrate and copper sulphate were used for synthesis of CuO nanoparticles with different shape, size and catalytic activity. Sodium hydroxide acts as a capping agent and ethanol as solvent for the synthesis. The XRD study was conducted to confirm the single phase monoclinic structure of as-synthesized and annealed CuO nano particles. The morphology of the as-synthesized and annealed CuO samples was analyzed by high resolution field emission scanning electron microscope. Fourier transform infrared spectroscopy was done for all the synthesized CuO nanoparticles for functional group characterization. The wide band gap and photocatalytic activity were studied by UV-Visible spectroscopy. The photocatalytic degradation of Methylene blue (MB) and Rhodamine B (RhB) dyes in aqueous solution were investigated under UV light (254 nm). In all the cases annealed samples showed good catalytic activity compared to as-synthesized CuO nanoparticles. The CuO nanoparticles from CuCl2 precursor act as excellent photocatalyst for both MB and RhB compared to CuNO₃ and CuSO₄.

Role of regulatory subunits and protein kinase inhibitor (PKI) in determining nuclear localization and activity of the catalytic subunit of protein kinase A.

PubMed

Wiley, J C; Wailes, L A; Idzerda, R L; McKnight, G S

1999-03-05

Regulation of protein kinase A by subcellular localization may be critical to target catalytic subunits to specific substrates. We employed epitope-tagged catalytic subunit to correlate subcellular localization and gene-inducing activity in the presence of regulatory subunit or protein kinase inhibitor (PKI). Transiently expressed catalytic subunit distributed throughout the cell and induced gene expression. Co-expression of regulatory subunit or PKI blocked gene induction and prevented nuclear accumulation. A mutant PKI lacking the nuclear export signal blocked gene induction but not nuclear accumulation, demonstrating that nuclear export is not essential to inhibit gene induction. When the catalytic subunit was targeted to the nucleus with a nuclear localization signal, it was not sequestered in the cytoplasm by regulatory subunit, although its activity was completely inhibited. PKI redistributed the nuclear catalytic subunit to the cytoplasm and blocked gene induction, demonstrating that the nuclear export signal of PKI can override a strong nuclear localization signal. With increasing PKI, the export process appeared to saturate, resulting in the return of catalytic subunit to the nucleus. These results demonstrate that both the regulatory subunit and PKI are able to completely inhibit the gene-inducing activity of the catalytic subunit even when the catalytic subunit is forced to concentrate in the nuclear compartment.

A Finite-Rate-Catalytic Model For Hypersonic Flows Informed By Molecular Dynamics

NASA Astrophysics Data System (ADS)

Schwartzentruber, T. E.; Valentini, P.; Norman, P.; Sorensen, C.

2011-05-01

The implementation of a finite-rate catalytic (FRC) wall boundary condition within a general 3D unstructured CFD solver is described. A set of one-step gas-surface chemical equations and atomistic parameters that deter- mine the reaction rates must be prescribed as input to the model. The chemical rate equations are solved at each wall face in the CFD simulation and result in a net production of species at the wall. In order for a finite- rate gas-surface reaction model to be consistent at equilibrium, it is determined that not all forward and back- ward rates can be specified arbitrarily. Provided that the forward rates for each surface recombination are as- signed, the backward rates must be determined using equilibrium constants that are consistent with the gas- phase chemistry model and thermodynamics. Reactive molecular dynamics (MD) simulations are performed us- ing the ReaxFFSiO potential to investigate oxygen-silica interactions. β-quartz and amorphous SiO2 surfaces are accommodated to a high temperature gas via MD simulation and reach a steady-state surface coverage. In addition to stable surface reconstructions a number of active sites are observed on which recombination occurs. Single collision MD simulations are performed where gas-phase oxygen atoms interact with the most dominant active site. Probabilities of recombination are found to have an exponential trend with gas-surface system temperature. The MD simulations are used to determine the activation energy for Eley-Rideal recombination of oxygen on a specific silica active site which is an important input parameter for the FRC model.

Room-Temperature Wet Chemical Synthesis of Au NPs/TiH2/Nanocarved Ti Self-Supported Electrocatalysts for Highly Efficient H2 Generation.

PubMed

Amin, Mohammed A; Fadlallah, Sahar A; Alosaimi, Ghaida S; Ahmed, Emad M; Mostafa, Nasser Y; Roussel, Pascal; Szunerits, Sabine; Boukherroub, Rabah

2017-09-06

Self-supported electrocatalysts are a new class of materials exhibiting high catalytic performance for various electrochemical processes and can be directly equipped in energy conversion devices. We present here, for the first time, sparse Au NPs self-supported on etched Ti (nanocarved Ti substrate self-supported with TiH 2 ) as promising catalysts for the electrochemical generation of hydrogen (H 2 ) in KOH solutions. Cleaned, as-polished Ti substrates were etched in highly concentrated sulfuric acid solutions without and with 0.1 M NH 4 F at room temperature for 15 min. These two etching processes yielded a thin layer of TiH 2 (the corrosion product of the etching process) self-supported on nanocarved Ti substrates with different morphologies. While F - -free etching process led to formation of parallel channels (average width: 200 nm), where each channel consists of an array of rounded cavities (average width: 150 nm), etching in the presence of F - yielded Ti surface carved with nanogrooves (average width: 100 nm) in parallel orientation. Au NPs were then grown in situ (self-supported) on such etched surfaces via immersion in a standard gold solution at room temperature without using stabilizers or reducing agents, producing Au NPs/TiH 2 /nanostructured Ti catalysts. These materials were characterized by scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), grazing incidence X-ray diffraction (GIXRD), and X-ray photoelectron spectroscopy (XPS). GIXRD confirmed the formation of Au 2 Ti phase, thus referring to strong chemical interaction between the supported Au NPs and the substrate surface (also evidenced from XPS) as well as a titanium hydride phase of chemical composition TiH 2 . Electrochemical measurements in 0.1 M KOH solution revealed outstanding hydrogen evolution reaction (HER) electrocatalytic activity for our synthesized catalysts, with Au NPs/TiH 2 /nanogrooved Ti catalyst being the best one among them. It exhibited fast kinetics for the HER with onset potentials as low as -22 mV vs. RHE, high exchange current density of 0.7 mA cm -2 , and a Tafel slope of 113 mV dec -1 . These HER electrochemical kinetic parameters are very close to those measured here for a commercial Pt/C catalyst (onset potential: -20 mV, Tafel slope: 110 mV dec -1 , and exchange current density: 0.75 mA cm -2 ). The high catalytic activity of these materials was attributed to the catalytic impacts of both TiH 2 phase and self-supported Au NPs (active sites for the catalytic reduction of water to H 2 ), in addition to their nanostructured features which provide a large-surface area for the HER.

Evaluation of Silica-Supported Metal and Metal Phosphide Nanoparticle Catalysts for the Hydrodeoxygenation of Guaiacol Under Ex Situ Catalytic Fast Pyrolysis Conditions

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

Griffin, Michael B.; Baddour, Frederick G.; Habas, Susan E.

A series of metal and metal phosphide catalysts were investigated for the hydrodeoxygenation of guaiacol under ex situ catalytic fast pyrolysis (CFP) conditions (350 °C, 0.5 MPa, 12 H 2:1 guaiacol, weight hourly space velocity 5 h $-$1). Ligand-capped Ni, Pt, Rh, Ni 2P, and Rh 2P nanoparticles (NPs) were prepared using solution-phase synthesis techniques and dispersed on a silica support. For the metal phosphide NP-catalysts, a synthetic route that relies on the decomposition of a single molecular precursor was employed. The reactivity of the NP-catalysts was compared to a series of reference materials including Ni/SiO 2 and Pt/SiO 2more » prepared using incipient wetness (IW) impregnation and a commercial (com) Pt/SiO 2 catalyst. The NP-Ni/SiO 2 catalyst exhibited the largest reduction in the oxygen mol% of the organic phase and outperformed the IW-Ni/SiO 2 material. Although it was less active for guaiacol conversion than NP-Ni/SiO 2, NP-Rh2P/SiO 2 demonstrated the largest production of completely deoxygenated products and the highest selectivity to anisole, benzene, and cyclohexane, suggesting that it is a promising catalyst for deoxygenation of aryl-OH bonds. Finally, the com-Pt/SiO 2 and IW-Pt/SiO 2 catalyst exhibited the highest normalized rate of guaiacol conversion per m 2 and per gram of active phase, respectively, but did not produce any completely deoxygenated products.« less

Reverse micelle synthesis of nanoscale metal containing catalysts

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

Darab, J.G.; Fulton, J.L.; Linehan, J.C.

1993-03-01

The need for morphological control during the synthesis of catalyst precursor powders is generally accepted to be important. In the liquefaction of coal, for example, iron-bearing catalyst precursor particles containing individual crystallites with diameters in the 1-100 nanometer range are believed to achieve good dispersion through out the coal-solvent slurry during liquefaction 2 runs and to undergo chemical transformations to catalytically active iron sulfide phases. The production of the nanoscale powders described here employs the confining spherical microdomains comprising the aqueous phase of a modified reverse micelle (MRM) microemulsion system as nanoscale reaction vessels in which polymerization, electrochemical reduction andmore » precipitation of solvated salts can occur. The goal is to take advantage of the confining nature of micelles to kinetically hinder transformation processes which readily occur in bulk aqueous solution in order to control the morphology and phase of the resulting powder. We have prepared a variety of metal, alloy, and metal- and mixed metal-oxide nanoscale powders from appropriate MRM systems. Examples of nanoscale powders produced include Co, Mo-Co, Ni{sub 3}Fe, Ni, and various oxides and oxyhydroxides of iron. Here, we discuss the preparation and characterization of nickel metal (with a nickel oxide surface layer) and iron oxyhydroxide MRM nanoscale powders. We have used extended x-ray absorption fine structure (EXAFS) spectroscopy to study the chemical polymerization process in situ, x-ray diffraction (XRD), scanning and transmission electron microcroscopies (SEM and TEM), elemental analysis and structural modelling to characterize the nanoscale powders produced. The catalytic activity of these powders is currently being studied.« less

Evaluation of Silica-Supported Metal and Metal Phosphide Nanoparticle Catalysts for the Hydrodeoxygenation of Guaiacol Under Ex Situ Catalytic Fast Pyrolysis Conditions

DOE PAGES

Griffin, Michael B.; Baddour, Frederick G.; Habas, Susan E.; ...

2015-09-30

A series of metal and metal phosphide catalysts were investigated for the hydrodeoxygenation of guaiacol under ex situ catalytic fast pyrolysis (CFP) conditions (350 °C, 0.5 MPa, 12 H 2:1 guaiacol, weight hourly space velocity 5 h $-$1). Ligand-capped Ni, Pt, Rh, Ni 2P, and Rh 2P nanoparticles (NPs) were prepared using solution-phase synthesis techniques and dispersed on a silica support. For the metal phosphide NP-catalysts, a synthetic route that relies on the decomposition of a single molecular precursor was employed. The reactivity of the NP-catalysts was compared to a series of reference materials including Ni/SiO 2 and Pt/SiO 2more » prepared using incipient wetness (IW) impregnation and a commercial (com) Pt/SiO 2 catalyst. The NP-Ni/SiO 2 catalyst exhibited the largest reduction in the oxygen mol% of the organic phase and outperformed the IW-Ni/SiO 2 material. Although it was less active for guaiacol conversion than NP-Ni/SiO 2, NP-Rh2P/SiO 2 demonstrated the largest production of completely deoxygenated products and the highest selectivity to anisole, benzene, and cyclohexane, suggesting that it is a promising catalyst for deoxygenation of aryl-OH bonds. Finally, the com-Pt/SiO 2 and IW-Pt/SiO 2 catalyst exhibited the highest normalized rate of guaiacol conversion per m 2 and per gram of active phase, respectively, but did not produce any completely deoxygenated products.« less

The irreversible formation of palladium carbide during hydrogenation of 1-pentyne over silica-supported palladium nanoparticles: in situ Pd K and L3 edge XAS.

PubMed

Tew, Min Wei; Nachtegaal, Maarten; Janousch, Markus; Huthwelker, Thomas; van Bokhoven, Jeroen A

2012-04-28

The catalytically active phase of silica-supported palladium catalysts in the selective and non-selective hydrogenation of 1-pentyne was determined using in situ X-ray absorption spectroscopy at the Pd K and L(3) edges. Upon exposure to alkyne, a palladium carbide-like phase rapidly forms, which prevents hydrogen to diffuse into the bulk of the nano-sized particles. Both selective and non-selective hydrogenation occur over carbided particles. The palladium carbide-like phase is stable under reaction conditions and only partially decomposes under high hydrogen partial pressure. Non-selective hydrogenation to pentane is not indicative of hydride formation. The palladium carbide phase was detected in the EXAFS analysis and the K edge XANES showed representative features. This journal is © the Owner Societies 2012

Activated carbon fiber composite material and method of making

DOEpatents

Burchell, Timothy D.; Weaver, Charles E.; Chilcoat, Bill R.; Derbyshire, Frank; Jagtoyen, Marit

2000-01-01

An activated carbon fiber composite for separation and purification, or catalytic processing of fluids is described. The activated composite comprises carbon fibers rigidly bonded to form an open, permeable, rigid monolith capable of being formed to near-net-shape. Separation and purification of gases are effected by means of a controlled pore structure that is developed in the carbon fibers contained in the composite. The open, permeable structure allows the free flow of gases through the monolith accompanied by high rates of adsorption. By modification of the pore structure and bulk density the composite can be rendered suitable for applications such as gas storage, catalysis, and liquid phase processing.

Activated carbon fiber composite material and method of making

DOEpatents

Burchell, Timothy D.; Weaver, Charles E.; Chilcoat, Bill R.; Derbyshire, Frank; Jagtoyen, Marit

2001-01-01

An activated carbon fiber composite for separation and purification, or catalytic processing of fluids is described. The activated composite comprises carbon fibers rigidly bonded to form an open, permeable, rigid monolith capable of being formed to near-net-shape. Separation and purification of gases are effected by means of a controlled pore structure that is developed in the carbon fibers contained in the composite. The open, permeable structure allows the free flow of gases through the monolith accompanied by high rates of adsorption. By modification of the pore structure and bulk density the composite can be rendered suitable for applications such as gas storage, catalysis, and liquid phase processing.

Continuous-flow processes for the catalytic partial hydrogenation reaction of alkynes

PubMed Central

Moreno-Marrodan, Carmen; Liguori, Francesca

2017-01-01

The catalytic partial hydrogenation of substituted alkynes to alkenes is a process of high importance in the manufacture of several market chemicals. The present paper shortly reviews the heterogeneous catalytic systems engineered for this reaction under continuous flow and in the liquid phase. The main contributions appeared in the literature from 1997 up to August 2016 are discussed in terms of reactor design. A comparison with batch and industrial processes is provided whenever possible. PMID:28503209

All the catalytic active sites of MoS 2 for hydrogen evolution

DOE PAGES

Li, Guoqing; Zhang, Du; Qiao, Qiao; ...

2016-11-29

MoS 2 presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS 2, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. Here, the intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated tomore » be 7.5 s –1 (65–75 mV/dec), 3.2 s –1 (65–85 mV/dec), and 0.1 s –1 (120–160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7–10%, and the number of sulfur vacancies in high crystalline quality MoS 2 is higher than that in low crystalline quality MoS 2, which may be related with the proximity of different local crystalline structures to the vacancies.« less

Boosting the catalytic performance of MoSx cocatalysts over CdS nanoparticles for photocatalytic H2 evolution by Co doping via a facile photochemical route

NASA Astrophysics Data System (ADS)

Lei, Yonggang; Hou, Jianhua; Wang, Fang; Ma, Xiaohua; Jin, Zhiliang; Xu, Jing; Min, Shixiong

2017-10-01

Low-crystalline or amorphous molybdenum sulfides (MoSx), bearing abundant unsaturated active sites, have been identified as efficient catalysts for electrocatalytic and photocatalytic H2 evolution reactions, however, their intrinsic activity is still low and need to be further improved for large-scale applications. In this paper, we report that low-crystalline MoSx doped with Co (Co-MoSx) as efficient cocatalysts could be loaded on CdS nanoparticles through a facile and controllable photochemical reduction method and showed high performances in catalyzing H2 evolution under visible light irradiation (≥420 nm). The photochemical loading of Co-MoSx was accomplished by using an in-situ formed molecular complex precursor and photogenerated electrons on CdS as reductants under mild conditions. The optimized CdS/Co-MoSx (Co:Mo = 1:4, 2 mol% loading) photocatalyst exhibited a catalytic H2 evolution rate of 535 μmol h-1, which is 1.8 times higher than that of CdS/MoSx, and an apparent quantum efficiency (AQE) of 23.5% was achieved over CdS/Co-MoSx photocatalyst at 420 nm. Co-MoSx catalyst also shows a long-term stability without noticeable activity degradation. Notably, Co-MoSx cocatalyst was found more efficient than that of noble metals in catalyzing photocatalytic H2 evolution on CdS. The formation of CoMoS phase, the enhanced electrocatalytic activity as well as reduced electron transfer resistance due to the doping effects of Co ions, account for the enhanced catalytic activity of this Co-MoSx cocatalyst.

Nanostructured manganese oxides as highly active water oxidation catalysts: a boost from manganese precursor chemistry.

PubMed

Menezes, Prashanth W; Indra, Arindam; Littlewood, Patrick; Schwarze, Michael; Göbel, Caren; Schomäcker, Reinhard; Driess, Matthias

2014-08-01

We present a facile synthesis of bioinspired manganese oxides for chemical and photocatalytic water oxidation, starting from a reliable and versatile manganese(II) oxalate single-source precursor (SSP) accessible through an inverse micellar molecular approach. Strikingly, thermal decomposition of the latter precursor in various environments (air, nitrogen, and vacuum) led to the three different mineral phases of bixbyite (Mn2 O3 ), hausmannite (Mn3 O4 ), and manganosite (MnO). Initial chemical water oxidation experiments using ceric ammonium nitrate (CAN) gave the maximum catalytic activity for Mn2 O3 and MnO whereas Mn3 O4 had a limited activity. The substantial increase in the catalytic activity of MnO in chemical water oxidation was demonstrated by the fact that a phase transformation occurs at the surface from nanocrystalline MnO into an amorphous MnOx (1

Low-temperature carbon monoxide oxidation over zirconia-supported CuO-CeO2 catalysts: Effect of zirconia support properties

NASA Astrophysics Data System (ADS)

Moretti, Elisa; Molina, Antonia Infantes; Sponchia, Gabriele; Talon, Aldo; Frattini, Romana; Rodriguez-Castellon, Enrique; Storaro, Loretta

2017-05-01

A study was conducted to investigate the effect of the preparation route of ZrO2 in CuO-CeO2/ZrO2 catalysts for the oxidation of carbon monoxide at low temperature (COX). Four ZrO2 supports were synthetized via either type sol-gel methodology or precipitation. The final Cu-Ce-Zr oxide catalysts were prepared by incipient wetness co-impregnation with copper and cerium solutions (with a loading of 6 wt% of CuO and 20 wt% of CeO2). The catalyst crystalline phases, texture and active species reducibility were determined by XRD, N2 physisorption at -196 °C and H2-TPR, respectively; meanwhile the surface composition and copper-cerium electronic states were studied by XPS. The catalytic activity was evaluated in the oxidation of CO to CO2, in the 40-215 °C temperature range. Catalytic results evidenced that the samples prepared by a sol-gel methodology showed, after the impregnation, a severe decrease of specific surface area and pore volume attributable to a wide degree of pore blockage caused by the presence of metal oxide particles and a collapse of the structure partially burying the active sites. A simple co-impregnation of a zirconia support, obtained through facile and fast precipitation, provided instead a catalyst with very good redox properties and high dispersion of the active phases, which completely oxidizes CO in the range 115-215 °C with T50 of 65 °C. This higher observed activity was ascribed to the formation of a larger fraction of highly dispersed and easily reducible Cu species and ceria nanocrystallites, mainly present as Ce(IV), with an average size of 5 nm.

Enhanced catalyst activity by decorating of Au on Ag@Cu2O nanoshell

NASA Astrophysics Data System (ADS)

Chen, Lei; Liu, Maomao; Zhao, Yue; Kou, Qiangwei; Wang, Yaxin; Liu, Yang; Zhang, Yongjun; Yang, Jinghai; Jung, Young Mee

2018-03-01

We successfully synthesized Au-decorated Ag@Cu2O heterostructures via a simple galvanic replacement method. As the Au precursor concentration increased, the density of the Au nanoparticles (NPs) on the Ag@Cu2O surface increased, which changed the catalytic activity of the Ag@Cu2O-Au structure. The combination of Au, Ag, and Cu2O exhibited excellent catalytic properties, which can further effect on the catalyst activity of the Ag@Cu2O-Au structure. In addition, the proposed Ag@Cu2O-Au nanocomposite was used to transform the organic, toxic pollutant, 4-nitrophenol (4-NP), into its nontoxic and medicinally important amino derivative via a catalytic reduction to optimize the material performance. The proposed Au-decorated Ag@Cu2O exhibited excellent catalytic activity, and the catalytic reduction time greatly decreased (5 min). Thus, three novel properties of Ag@Cu2O-Au, i.e., charge redistribution and transfer, adsorption, and catalytic reduction of organic pollutants, were ascertained for water remediation. The proposed catalytic properties have potential applications for photocatalysis and localized surface plasmon resonance (LSPR)- and peroxidase-like catalysis.

Development and characterization of silica and titania based nano structured materials for the removal of indoor and outdoor air pollutants

NASA Astrophysics Data System (ADS)

Peiris, Thelge Manindu Nirasha

Solar energy driven catalytic systems have gained popularity in environmental remediation recently. Various photocatalytic systems have been reported in this regard and most of the photocatalysts are based on well-known semiconducting material, Titanium Dioxide, while some are based on other materials such as Silicon Dioxide and various Zeolites. However, in titania based photocatalysts, titania is actively involved in the catalytic mechanism by absorbing light and generating exitons. Because of this vast popularity of titania in the field of photocatalysis it is believed that photocatalysis mainly occurs via non-localized mechanisms and semiconductors are extremely important. Even though it is still rare, photocatalysis could be localized and possible without use of a semiconductor as well. Thus, to support localized photocatalytic systems, and to compare the activity to titania based systems, degradation of organic air pollutants by nanostructured silica, titania and mixed silica titania systems were studied. New materials were prepared using two different approaches, precipitation technique (xerogel) and aerogel preparation technique. The prepared xerogel samples were doped with both metal (silver) and non-metals (carbon and sulfur) and aerogel samples were loaded with Chromium, Cobalt and Vanadium separately, in order to achieve visible light photocatalytic activity. Characterization studies of the materials were carried out using Nova BET analysis, DR UV-vis spectrometry, powder X-ray diffraction, X-ray photoelectron Spectroscopy, FT-IR spectroscopy, Transmission Electron Microscopy, etc. Kinetics of the catalytic activities was studied using a Shimadzu GCMS-QP 5000 instrument using a closed glass reactor. All the experiments were carried out in gaseous phase using acetaldehyde as the model pollutant. Kinetic results suggest that chromium doped silica systems are good UV and visible light active photocatalysts. This is a good example for a localized photocatalytic activity. In contrast, our xerogel system shows comparatively high visible light photocatalytic activity for the titania based system, showing the importance of non-localized nature of photocatalysis. The Cobalt doped silica system shows interesting dark catalytic activity towards acetaldehyde and several other pollutants. Thus, in summary, based on the different activities we observed during our studies these materials could be successfully used to improve the quality of both indoor and outdoor air.

Top-Down and Bottom-Up Approaches in Engineering 1 T Phase Molybdenum Disulfide (MoS2 ): Towards Highly Catalytically Active Materials.

PubMed

Chua, Chun Kiang; Loo, Adeline Huiling; Pumera, Martin

2016-09-26

The metallic 1 T phase of MoS2 has been widely identified to be responsible for the improved performances of MoS2 in applications including hydrogen evolution reactions and electrochemical supercapacitors. To this aim, various synthetic methods have been reported to obtain 1 T phase-rich MoS2 . Here, the aim is to evaluate the efficiencies of the bottom-up (hydrothermal reaction) and top-down (chemical exfoliation) approaches in producing 1 T phase MoS2 . It is established in this study that the 1 T phase MoS2 produced through the bottom-up approach contains a high proportion of 1 T phase and demonstrates excellent electrochemical and electrical properties. Its performance in the hydrogen evolution reaction and electrochemical supercapacitors also surpassed that of 1 T phase MoS2 produced through a top-down approach. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cavitational synthesis of nanostructured inorganic materials for enhanced heterogeneous catalysis

NASA Astrophysics Data System (ADS)

Krausz, Ivo Michael

The synthesis of nanostructured inorganic materials by hydrodynamic cavitation processing was investigated. The goal of this work was to develop a general synthesis technique for nanostructured materials with a control over crystallite size in the 1--20 nm range. Materials with crystallite sizes in this range have shown enhanced catalytic activity compared to materials with larger crystallite sizes. Several supported and unsupported inorganic materials were studied to understand the effects of cavitation on crystallite size. Cavitation processing of calcium fluoride resulted in more spherical particles, attached to one another by melted necks. This work produced the first evidence of shock wave heating of nanostructured materials by hydrodynamic cavitation processing. Hydrodynamic cavitation synthesis of various catalytic support materials indicated that their phase composition and purity could be controlled by adjustment of the processing parameters. Zirconia/alumina supports synthesized using hydro-dynamic cavitation and calcined to 1368 K retained a high purity cubic zirconia phase, whereas classically prepared samples showed a phase transformation to monoclinic zirconia. Similarly, the synthesis of alumina resulted in materials with varying Bohmite and Bayerite contents as a function of the process parameters. High temperature calcination resulted in stable alumina supports with varying amounts of delta-, and theta-alumina. Synthesis studies of palladium and silver showed modest variations in crystallite size as a function of cavitation process parameters. Calcination resulted in larger grain materials, indicating a disappearance of intergrain boundaries. Based on these results, a new synthesis method was studied involving controlled agglomeration of small silver crystallites by hydrodynamic cavitation processing, followed by deposition on alumina. The optimal pH, concentration, and processing time for controlling the silver crystallite size in the cavitation equipment were determined using a statistical design of experiments approach. Three series of alumina supported silver catalysts were prepared, with silver weight loadings of 1%, 2%, and 5%. Variation of cavitation processing time between 1--64 min allowed the systematic control of silver crystallite size in the range of 3--19 nm. The preferred oxidation of CO in hydrogen (PROX) was chosen as a catalytic test reaction, because of its increasing importance for fuel cell applications. It was found that the catalytic activity was significantly increased for silver crystallite sizes below 5 nm. This work is the first experimental evidence of independent crystallite size control by hydrodynamic cavitation for alumina supported silver catalysts. The synthesis method involving controlled agglomeration and calcination is a general synthesis procedure that can be used to synthesize a wide range of novel catalysts and advanced materials.

Catalytic method for synthesizing hydrocarbons

DOEpatents

Sapienza, R.S.; Sansone, M.J.; Slegeir, W.A.R.

A method for synthesizing hydrocarbons from carbon monoxide and hydrogen by contacting said gases with a slurry of a catalyst composed of palladium or platinum and cobalt supported on a solid phase is disclosed. The catalyst is prepared by heating a heterogeneous component of the palladium or platinum deposited on the solid support in a solution of cobalt carbonyl or precursors thereof. The catalyst exhibits excellent activity, stability in air, and produces highly desirable product fractions even with dilute gaseous reactants.

Catalytic method for synthesizing hydrocarbons

DOEpatents

Sapienza, Richard S.; Sansone, Michael J.; Slegeir, William A. R.

1984-01-01

A method for synthesizing hydrocarbons from carbon monoxide and hydrogen by contacting said gases with a slurry of a catalyst composed of palladium or platinum and cobalt supported on a solid phase is disclosed. The catalyst is prepared by heating a heterogeneous component of the palladium or platinum deposited on the solid support in a solution of cobalt carbonyl or precursors thereof. The catalyst exhibits excellent activity, stability in air, and produces highly desirable product fractions even with dilute gaseous reactants.

Dodecahedral W@WC Composite as Efficient Catalyst for Hydrogen Evolution and Nitrobenzene Reduction Reactions.

PubMed

Chen, Zhao-Yang; Duan, Long-Fa; Sheng, Tian; Lin, Xiao; Chen, Ya-Feng; Chu, You-Qun; Sun, Shi-Gang; Lin, Wen-Feng

2017-06-21

Core-shell composites with strong phase-phase contact could provide an incentive for catalytic activity. A simple, yet efficient, H 2 O-mediated method has been developed to synthesize a mesoscopic core-shell W@WC architecture with a dodecahedral microstructure, via a one-pot reaction. The H 2 O plays an important role in the resistance of carbon diffusion, resulting in the formation of the W core and W-terminated WC shell. Density functional theory (DFT) calculations reveal that adding W as core reduced the oxygen adsorption energy and provided the W-terminated WC surface. The W@WC exhibits significant electrocatalytic activities toward hydrogen evolution and nitrobenzene electroreduction reactions, which are comparable to those found for commercial Pt/C, and substantially higher than those found for meso- and nano-WC materials. The experimental results were explained by DFT calculations based on the energy profiles in the hydrogen evolution reactions over WC, W@WC, and Pt model surfaces. The W@WC also shows a high thermal stability and thus may serve as a promising more economical alternative to Pt catalysts in these important energy conversion and environmental protection applications. The current approach can also be extended or adapted to various metals and carbides, allowing for the design and fabrication of a wide range of catalytic and other multifunctional composites.

Simultaneous introduction of various palladium active sites into MOF via one-pot synthesis: Pd@[Cu3-xPdx(BTC)2]n.

PubMed

Zhang, Wenhua; Chen, Zhihao; Al-Naji, Majd; Guo, Penghu; Cwik, Stefan; Halbherr, Olesia; Wang, Yuemin; Muhler, Martin; Wilde, Nicole; Gläser, Roger; Fischer, Roland A

2016-10-14

Simultaneous incorporation of palladium within Pd-Pd and/or Pd-Cu paddlewheels as framework-nodes and Pd nanoparticle (NP) dispersion into MOF have been achieved for the first time via one-pot synthesis. In particular, the framework substitution of Cu(2+) by Pd(2+) as well as the pore loading with PdNPs have been confirmed and characterized by XPS. The obtained solids featuring such multiple Pd-sites show enhanced catalytic activity in the aqueous-phase hydrogenation of p-nitrophenol (PNP) with NaBH4 to p-aminophenol (PAP).

Substituting Tyr138 in the active site loop of human phenylalanine hydroxylase affects catalysis and substrate activation.

PubMed

Leandro, João; Stokka, Anne J; Teigen, Knut; Andersen, Ole A; Flatmark, Torgeir

2017-07-01

Mammalian phenylalanine hydroxylase (PAH) is a key enzyme in l-phenylalanine (l-Phe) metabolism and is active as a homotetramer. Biochemical and biophysical work has demonstrated that it cycles between two states with a variably low and a high activity, and that the substrate l-Phe is the key player in this transition. X-ray structures of the catalytic domain have shown mobility of a partially intrinsically disordered Tyr 138 -loop to the active site in the presence of l-Phe. The mechanism by which the loop dynamics are coupled to substrate binding at the active site in tetrameric PAH is not fully understood. We have here conducted functional studies of four Tyr 138 point mutants. A high linear correlation ( r 2 = 0.99) was observed between their effects on the catalytic efficiency of the catalytic domain dimers and the corresponding effect on the catalytic efficiency of substrate-activated full-length tetramers. In the tetramers, a correlation ( r 2 = 0.96) was also observed between the increase in catalytic efficiency (activation) and the global conformational change (surface plasmon resonance signal response) at the same l-Phe concentration. The new data support a similar functional importance of the Tyr 138 -loop in the catalytic domain and the full-length enzyme homotetramer.

Correction: Towards the rationalization of catalytic activity values by means of local hyper-softness on the catalytic site: a criticism about the use of net electric charges.

PubMed

Martínez-Araya, Jorge Ignacio; Grand, André; Glossman-Mitnik, Daniel

2016-01-28

Correction for 'Towards the rationalization of catalytic activity values by means of local hyper-softness on the catalytic site: a criticism about the use of net electric charges' by Jorge Ignacio Martínez-Araya et al., Phys. Chem. Chem. Phys., 2015, DOI: 10.1039/c5cp03822g.

Advanced Life Support Water Recycling Technologies Case Studies: Vapor Phase Catalytic Ammonia Removal and Direct Osmotic Concentration

NASA Technical Reports Server (NTRS)

Flynn, Michael

2004-01-01

Design for microgravity has traditionally not been well integrated early on into the development of advanced life support (ALS) technologies. NASA currently has a many ALS technologies that are currently being developed to high technology readiness levels but have not been formally evaluated for microgravity compatibility. Two examples of such technologies are the Vapor Phase Catalytic Ammonia Removal Technology and the Direct Osmotic Concentration Technology. This presentation will cover the design of theses two systems and will identify potential microgravity issues.

Nanostructures nucleation in carbon-metal gaseous phase: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Galiullina, G. M.; Orekhov, N. D.; Stegailov, V. V.

2018-01-01

We perform nonequilibrium molecular dynamics simulation of carbon nanoclusters nucleation and early stages of growth from the gaseous phase. We analyze the catalytic effect of iron atoms on the nucleation kinetics and structure of the resultant nanoparticles. Reactive Force Field (ReaxFF) is used in the simulations for the description of bond formation and dissociation during the nucleation process at the nanoscale. The catalytic effect of iron reveals itself even on nanosecond simulation times: iron atoms accelerate the process of clustering but result in less graphitized carbon structures.

Catalytic Oxidation of Methane into Methanol over Copper-Exchanged Zeolites with Oxygen at Low Temperature

PubMed Central

2016-01-01

The direct catalytic conversion of methane to liquid oxygenated compounds, such as methanol or dimethyl ether, at low temperature using molecular oxygen is a grand challenge in C–H activation that has never been met with synthetic, heterogeneous catalysts. We report the first demonstration of direct, catalytic oxidation of methane into methanol with molecular oxygen over copper-exchanged zeolites at low reaction temperatures (483–498 K). Reaction kinetics studies show sustained catalytic activity and high selectivity for a variety of commercially available zeolite topologies under mild conditions (e.g., 483 K and atmospheric pressure). Transient and steady state measurements with isotopically labeled molecules confirm catalytic turnover. The catalytic rates and apparent activation energies are affected by the zeolite topology, with caged-based zeolites (e.g., Cu-SSZ-13) showing the highest rates. Although the reaction rates are low, the discovery of catalytic sites in copper-exchanged zeolites will accelerate the development of strategies to directly oxidize methane into methanol under mild conditions. PMID:27413787

The surface plasmon-induced hot carrier effect on the catalytic activity of CO oxidation on a Cu2O/hexoctahedral Au inverse catalyst.

PubMed

Lee, Si Woo; Hong, Jong Wook; Lee, Hyunhwa; Wi, Dae Han; Kim, Sun Mi; Han, Sang Woo; Park, Jeong Young

2018-06-14

The intrinsic correlation between an enhancement of catalytic activity and the flow of hot electrons generated at metal-oxide interfaces suggests an intriguing way to control catalytic reactions and is a significant subject in heterogeneous catalysis. Here, we show surface plasmon-induced catalytic enhancement by the peculiar nanocatalyst design of hexoctahedral (HOH) Au nanocrystals (NCs) with Cu2O clusters. We found that this inverse catalyst comprising a reactive oxide for the catalytic portion and a metal as the source of electrons by localized surface plasmon resonance (localized SPR) exhibits a change in catalytic activity by direct hot electron transfer or plasmon-induced resonance energy transfer (PIRET) when exposed to light. We prepared two types of inverse catalysts, Cu2O at the vertex sites of HOH Au NCs (Cu2O/Au vertex site) and a HOH Au NC-Cu2O core-shell structure (HOH Au@Cu2O), to test the structural effect on surface plasmons. Under broadband light illumination, the Cu2O/Au vertex site catalyst showed 30-90% higher catalytic activity and the HOH Au@Cu2O catalyst showed 10-30% higher catalytic activity than when in the dark. Embedding thin SiO2 layers between the HOH Au NCs and the Cu2O verified that the dominant mechanism for the catalytic enhancement is direct hot electron transfer from the HOH Au to the Cu2O. Finite-difference time domain calculations show that a much stronger electric field was formed on the vertex sites after growing the Cu2O on the HOH Au NCs. These results imply that the catalytic activity is enhanced when hot electrons, created from photon absorption on the HOH Au metal and amplified by the presence of surface plasmons, are transferred to the reactive Cu2O.

Charge neutralization in the active site of the catalytic trimer of aspartate transcarbamoylase promotes diverse structural changes.

PubMed

Endrizzi, James A; Beernink, Peter T

2017-11-01

A classical model for allosteric regulation of enzyme activity posits an equilibrium between inactive and active conformations. An alternative view is that allosteric activation is achieved by increasing the potential for conformational changes that are essential for catalysis. In the present study, substitution of a basic residue in the active site of the catalytic (C) trimer of aspartate transcarbamoylase with a non-polar residue results in large interdomain hinge changes in the three chains of the trimer. One conformation is more open than the chains in both the wild-type C trimer and the catalytic chains in the holoenzyme, the second is closed similar to the bisubstrate-analog bound conformation and the third hinge angle is intermediate to the other two. The active-site 240s loop conformation is very different between the most open and closed chains, and is disordered in the third chain, as in the holoenzyme. We hypothesize that binding of anionic substrates may promote similar structural changes. Further, the ability of the three catalytic chains in the trimer to access the open and closed active-site conformations simultaneously suggests a cyclic catalytic mechanism, in which at least one of the chains is in an open conformation suitable for substrate binding whereas another chain is closed for catalytic turnover. Based on the many conformations observed for the chains in the isolated catalytic trimer to date, we propose that allosteric activation of the holoenzyme occurs by release of quaternary constraint into an ensemble of active-site conformations. © 2017 The Protein Society.

Preparation of Cu@Cu₂O Nanocatalysts by Reduction of HKUST-1 for Oxidation Reaction of Catechol.

PubMed

Jang, Seongwan; Yoon, Chohye; Lee, Jae Myung; Park, Sungkyun; Park, Kang Hyun

2016-11-02

HKUST-1, a copper-based metal organic framework (MOF), has been investigated as a catalyst in various reactions. However, the HKUST-1 shows low catalytic activity in the oxidation of catechol. Therefore, we synthesized Fe₃O₄@HKUST-1 by layer-by layer assembly strategy and Cu@Cu₂O by reduction of HKUST-1 for enhancement of catalytic activity. Cu@Cu₂O nanoparticles exhibited highly effective catalytic activity in oxidation of 3,5-di- tert -butylcatechol. Through this method, MOF can maintain the original core-shell structure and be used in various other reactions with enhanced catalytic activity.

Aqueous phase hydrogenation of phenol catalyzed by Pd and PdAg on ZrO 2

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

Resende, Karen A.; Hori, Carla E.; Noronha, Fabio B.

The impact of particle size of ZrO 2-supported Pd and of alloying with Ag was explored for hydrogenation of phenol in aqueous phase. Kinetic assessments were performed in a batch reactor, on monometallic Pd/ZrO 2 samples with different Pd loadings (0.5%, 1% and 2%), as well as on a 1% PdAg/ZrO 2 sample. The catalytic activity normalized to accessible Pd (turnover frequency, TOF) increased with the particle size of Pd. Reaction orders in phenol and H 2 and lower activation energies suggest that smaller particles bind the reacting substrates more strongly, leading to higher surface coverages by phenol. But, surprisingly,more » smaller Pd particles exhibited lower TOFs. The lower activity of the small Pd particles is attributed to lower activation entropies for the strongly bound species. Furthermore, the presence of Ag increased the catalyst activity by decreasing the apparent energy of activation and increasing the coverages of phenol and H 2, without negatively affecting the activation entropy.« less

Aqueous phase hydrogenation of phenol catalyzed by Pd and PdAg on ZrO 2

DOE PAGES

Resende, Karen A.; Hori, Carla E.; Noronha, Fabio B.; ...

2017-08-05

The impact of particle size of ZrO 2-supported Pd and of alloying with Ag was explored for hydrogenation of phenol in aqueous phase. Kinetic assessments were performed in a batch reactor, on monometallic Pd/ZrO 2 samples with different Pd loadings (0.5%, 1% and 2%), as well as on a 1% PdAg/ZrO 2 sample. The catalytic activity normalized to accessible Pd (turnover frequency, TOF) increased with the particle size of Pd. Reaction orders in phenol and H 2 and lower activation energies suggest that smaller particles bind the reacting substrates more strongly, leading to higher surface coverages by phenol. But, surprisingly,more » smaller Pd particles exhibited lower TOFs. The lower activity of the small Pd particles is attributed to lower activation entropies for the strongly bound species. Furthermore, the presence of Ag increased the catalyst activity by decreasing the apparent energy of activation and increasing the coverages of phenol and H 2, without negatively affecting the activation entropy.« less

Influence of hot carriers on catalytic reaction; Pt nanoparticles on GaN substrates under light irradiation.

PubMed

Kim, Sun Mi; Park, Dahee; Yuk, Youngji; Kim, Sang Hoon; Park, Jeong Young

2013-01-01

We report the hot carrier-driven catalytic activity of two-dimensional arrays of Pt nanoparticles on GaN substrate under light irradiation. In order to elucidate the effect of a hot carrier in a catalytic chemical reaction, the CO oxidation reaction was carried out on Pt nanoparticles on p- and n-type GaN under light irradiation. Metal catalysts composed of Pt nanoparticles were prepared using two different preparation methods: the one-pot polyol reduction and are plasma deposition methods. Under light irradiation, the catalytic activity of the Pt nanoparticles supported on GaN exhibited a distinct change depending on the doping type. The catalytic activity of the Pt nanoparticles on the n-doped GaN wafer decreased by 8-28% under light irradiation, compared to no irradiation (i.e., in the dark), while the Pt nanoparticles on the p-doped GaN wafer increased by 11-33% under light irradiation, compared to no irradiation. The catalytic activity increased on the smaller Pt nanoparticles, compared to the larger nanoparticles, presumably due to the mean free path of hot carriers. Based on these results, we conclude that the flow of hot carriers generated at the Pt-GaN interface during light irradiation is responsible for the change in catalytic activity on the Pt nanoparticles.

Preparation and characterization of a supported system of Ni2P/Ni12P5 nanoparticles and their use as the active phase in chemoselective hydrogenation of acetophenone

NASA Astrophysics Data System (ADS)

Costa, Dolly C.; Soldati, Analía L.; Pecchi, Gina; Bengoa, José Fernando; Marchetti, Sergio Gustavo; Vetere, Virginia

2018-05-01

Ni2P/Ni12P5 nanoparticles were obtained by thermal decomposition of nickel organometallic salt at low temperature. The use of different characterization techniques allowed us to determine that this process produced a mixture of two nickel phosphide phases: Ni2P and Ni12P5. These nickel phosphides nanoparticles, supported on mesoporous silica, showed activity and high selectivity for producing the hydrogenation of the acetophenone carbonyl group to obtain 1-phenylethanol. This is a first report that demonstrates the ability of supported Ni2P/Ni12P5 nanoparticles to produce the chemoselective hydrogenation of acetophenone. We attribute these special catalytic properties to the particular geometry of the Ni–P sites on the surface of the nanoparticles. This is an interesting result because the nickel phosphides have a wide composition range (from Ni3P to NiP3), with different crystallographic structures, therefore we think that different phases could be active and selective to hydrogenate many important molecules with more than one functional group.

Kinetic study of hydroxytyrosol oxidation and its related compounds by Red Globe grape polyphenol oxidase.

PubMed

García-García, María Inmaculada; Hernández-García, Samanta; Sánchez-Ferrer, Álvaro; García-Carmona, Francisco

2013-06-26

Red Globe grape polyphenol oxidase, partially purified using phase partitioning with Triton-X114, was used to study the oxidation of hydroxytytosol (HT) and its related compounds tyrosol (TS), tyrosol acetate (TSA), and hydroxytyrosol acetate (HTA). The enzyme showed activity toward both monophenols (monophenolase activity) and o-diphenols (diphenolase activity) with a pH optimum (pH 6.5) that was independent of the phenol used. However, the optimal temperature for diphenolase activity was substrate-dependent, with a broad optimum of 25-65 °C for HT, compared with the maximum obtained for HTA (40 °C). Monophenolase activity showed the typical lag period, which was modulated by pH, substrate and enzyme concentrations, and the presence of catalytic amounts of o-diphenols. When the catalytic power (Vmax/K(M)) was determined for both activities, higher values were observed for o-diphenols than for monophenols: 9-fold higher for the HT/TS pair and 4-fold higher for HTA/TSA pair. Surprisingly, this ratio was equally higher for TSA (2.2-fold) compared with that of TS, whereas no such effect was observed for o-diphenols. This higher efficiency of TSA could be related to its greater hydrophobicity. Acetyl modification of these phenols not only changes the kinetic parameters of the enzyme but also affects their antioxidant activity (ORAC-FL assays), which is lower in HTA than in HT.

The protein cofactor allows the sequence of an RNase P ribozyme to diversify by maintaining the catalytically active structure of the enzyme.

PubMed Central

Kim, J J; Kilani, A F; Zhan, X; Altman, S; Liu, F

1997-01-01

To study the effect proteins have on the catalysis and evolution of RNA enzymes, we simulated evolution of RNase P catalytic M1 RNA in vitro, in the presence and absence of its C5 protein cofactor. In the presence of C5, functional M1 sequence variants (not catalytically active in the absence of C5) were selected in addition to those identical to M1. C5 maintains the catalytically active structure of the variants and allows for an enhanced spectrum of M1 molecules to function in the context of a ribonucleoprotein (RNP) complex. The generation of an RNP enzyme, requiring both RNA and protein components, from a catalytically active RNA molecule has implications for how modern RNP complexes evolved from ancestral RNAs. PMID:9174096

The role of surface generated radicals in catalytic combustion

NASA Technical Reports Server (NTRS)

Santavicca, D. A.; Stein, Y.; Royce, B. S. H.

1985-01-01

Experiments were conducted to better understand the role of catalytic surface reactions in determining the ignition characteristics of practical catalytic combustors. Hydrocarbon concentrations, carbon monoxide and carbon dioxide concentrations, hydroxyl radical concentrations, and gas temperature were measured at the exit of a platinum coated, stacked plate, catalytic combustor during the ignition of lean propane-air mixtures. The substrate temperature profile was also measured during the ignition transient. Ignition was initiated by suddenly turning on the fuel and the time to reach steady state was of the order of 10 minutes. The gas phase reaction, showed no pronounced effect due to the catalytic surface reactions, except the absence of a hydroxyl radical overshoot. It is found that the transient ignition measurements are valuable in understanding the steady state performance characteristics.

Solid strong base K-Pt/NaY zeolite nano-catalytic system for completed elimination of formaldehyde at room temperature

NASA Astrophysics Data System (ADS)

Song, Shaoqing; Wu, Xi; Lu, Changhai; Wen, Meicheng; Le, Zhanggao; Jiang, Shujuan

2018-06-01

Solid strong base nano-catalytic system of K-modification NaY zeolite supported 0.08% Pt (K-Pt/NaY) were constructed for eliminating HCHO at room temperature. In the catalytic process, activation energy over K-Pt/NaY nano-catalytic system was greatly decreased along with the enhanced reaction rate. Characterization and catalytic tests revealed the surface electron structure of K-Pt/NaY was improved, as reflected by the enhanced HCHO adsorption capability, high sbnd OH concentration, and low-temperature reducibility. Therefore, the optimal K-Pt/NaY showed high catalytic efficiency and strong H2O tolerance for HCHO elimination by directly promoting the reaction between active sbnd OH and formate species. These results may suggest a new way for probing the advanced solid strong base nano-catalytic system for the catalytic elimination of indoor HCHO.

Easy solid-phase synthesis of pH-insensitive heterogeneous CNTs/FeS Fenton-like catalyst for the removal of antibiotics from aqueous solution.

PubMed

Ma, Jie; Yang, Mingxuan; Yu, Fei; Chen, Junhong

2015-04-15

We report a facile solid method to synthesize efficient carbon-based Fenton-like catalyst (CNTs/FeS) using as-prepared carbon nanotubes (APCNTs), which makes full use of the iron nanoparticles in APCNTs without needless purification. Furthermore, the CNTs/FeS was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric (TG) and other analysis techniques, and then the CNTs/FeS was used as a Fenton-like catalyst for removing ciprofloxacin from aqueous solution. Response Surface Methodology (RSM) was applied to find the effect of the reaction parameter and the optimum operating condition. Results shows the catalytic reaction had better suitability than previous studies in a wide range of pH values (pH 3-8) and the Fenton-like catalyst CNTs/FeS exhibits good catalytic activity for removing of antibiotic, which be attributed to the synergistic effect of adsorption-advanced oxidation and significantly improves efficiency of advanced oxidation. More importantly, the CNTs/FeS catalyst exhibit good regeneration performance and retains a high catalytic capacity (>75%) even after four reaction cycles. The catalytic mechanism were also studied further, the removal mechanism of ciprofloxacin by a CNTs/FeS heterogeneous Fenton-like process primarily involves three removal pathways occurring simultaneously: (a) adsorption removal by CNTs, (b) Fenton-like degradation catalyzed by FeS, (c) catalytic degradation by CNTs catalyst. And these actions also have synergistic effects for ciprofloxacin removal. Copyright © 2014 Elsevier Inc. All rights reserved.

Mussel-Inspired Polydopamine Functionalized Plasmonic Nanocomposites for Single-Particle Catalysis.

PubMed

Wang, Jun-Gang; Hua, Xin; Li, Meng; Long, Yi-Tao

2017-01-25

Polydopamine functionalized plasmonic nanocomposites with well-distributed catalytically active small gold nanoislands around large gold core were fabricated without using any chemical reductant or surfactant. The optical properties, surface molecular structures, and ensemble catalytic activity of the gold nanocomposites were investigated by time-of-flight secondary ion mass spectrometry and UV-vis spectroscopy, respectively. Moreover, the considerable catalytic activity of the nanocomposites toward 4-nitrophenol reduction was real time monitored by dark-field spectroscopy techniques at the single-nanoparticle level avoiding averaging effects in bulk systems. According to the obtained plasmonic signals from individual nanocomposites, the electron charging and discharging rates for these nanocomposites during the catalytic process were calculated. Our results offer new insights into the design and synthesis of plasmonic nanocomposites for future catalytic applications as well as a further mechanistic understanding of the electron transfer during the catalytic process at the single-nanoparticle level.

Synthesis and catalytic activity of the metastable phase of gold phosphide

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

Fernando, Deshani; Nigro, Toni A. E.; Dyer, I. D.

Recently, transition metal phosphides have found new applications as catalysts for the hydrogen evolution reaction that has generated an impetus to synthesize these materials at the nanoscale. In this work, Au2P3 was synthesized utilizing the high temperature decomposition of tri-n-octylphosphine as a source of elemental phosphorous. Gold nanorods were used as morphological templates with the aim of controlling the shape and size of the resulting gold phosphide particles. We demonstrate that the surface capping ligand of the gold nanoparticle precursors can influence the purity and extent to which the gold phosphide phase will form. Gold nanorods functionalized with 1-dodecanethiol undergomore » digestive ripening to produce discrete spherical particles that exhibit reduced reactivity towards phosphorous, resulting in low yields of the gold phosphide. In contrast, gold phosphide was obtained as a phase pure product when cetyltrimethylammonium bromide functionalized gold nanorods are used instead. The Au2P3 nanoparticles exhibited higher activity than polycrystalline gold towards the hydrogen evolution reaction.« less

Antarctic stratospheric chemistry of chlorine nitrate, hydrogen chloride, and ice - Release of active chlorine

NASA Technical Reports Server (NTRS)

Molina, Mario J.; Tso, Tai-Ly; Molina, Luisa T.; Wang, Frank C.-Y.

1987-01-01

The reaction rate between atmospheric hydrogen chloride (HCl) and chlorine nitrate (ClONO2) is greatly enhanced in the presence of ice particles; HCl dissolves readily into ice, and the collisional reaction probability for ClONO2 on the surface of ice with HCl in the mole fraction range from about 0.003 to 0.010 is in the range from about 0.05 to 0.1 for temperatures near 200 K. Chlorine is released into the gas phase on a time scale of at most a few milliseconds, whereas nitric acid (HNO3), the other product, remains in the condensed phase. This reaction could play an important role in explaining the observed depletion of ozone over Antarctica; it releases photolytically active chlorine from its most abundant reservoir species, and it promotes the formation of HNO3 and thus removes nitrogen dioxide from the gas phase. Hence it establishes the necessary conditions for the efficient catalytic destruction of ozone by halogenated free radicals.

Structural determinants of APOBEC3B non-catalytic domain for molecular assembly and catalytic regulation

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

Xiao, Xiao; Yang, Hanjing; Arutiunian, Vagan

The catalytic activity of human cytidine deaminase APOBEC3B (A3B) has been correlated with kataegic mutational patterns within multiple cancer types. The molecular basis of how the N-terminal non-catalytic CD1 regulates the catalytic activity and consequently, biological function of A3B remains relatively unknown. Here, we report the crystal structure of a soluble human A3B-CD1 variant and delineate several structural elements of CD1 involved in molecular assembly, nucleic acid interactions and catalytic regulation of A3B. We show that (i) A3B expressed in human cells exists in hypoactive high-molecular-weight (HMW) complexes, which can be activated without apparent dissociation into low-molecular-weight (LMW) species aftermore » RNase A treatment. (ii) Multiple surface hydrophobic residues of CD1 mediate the HMW complex assembly and affect the catalytic activity, including one tryptophan residue W127 that likely acts through regulating nucleic acid binding. (iii) One of the highly positively charged surfaces on CD1 is involved in RNA-dependent attenuation of A3B catalysis. (iv) Surface hydrophobic residues of CD1 are involved in heterogeneous nuclear ribonucleoproteins (hnRNPs) binding to A3B. The structural and biochemical insights described here suggest that unique structural features on CD1 regulate the molecular assembly and catalytic activity of A3B through distinct mechanisms.« less

Role of non-metallic atoms in enhancing the catalytic activity of nickel-based compounds for hydrogen evolution reaction† †Electronic supplementary information (ESI) available: Experimental details, structure and morphology characterization, electrochemical characterizations, supplementary figures and data. See DOI: 10.1039/c7sc04851c

PubMed Central

Zheng, Xingqun; Peng, Lishan; Yang, Na; Yang, Yanjun; Li, Jing; Wang, Jianchuan

2018-01-01

The transition-metal compounds (MX) have gained wide attention as hydrogen evolution reaction (HER) electrocatalysts; however, the interaction between the non-metallic atom (X) and the metal atom (M) in MX, and the role of X in the enhanced catalytic activity of MX, are still ambiguous. In this work, we constructed a simple model [X/Ni(100)] to decipher the contribution of X towards enhancing the catalytic activity of NiX, which allows us to accurately predict the trend in HER catalytic activity of NiX based on the easily accessible physico-chemical characteristics of X. Theoretical calculations showed that the electronegativity (χX) and the principle quantum number (nX) of X are two important descriptors for evaluating and predicting the HER catalytic activity of NiX catalysts effectively. X atoms in the VIA group can enhance the HER activity of X/Ni(100) more significantly than those in the second period due to the large χX or nX. At a relatively low X coverage, the S/Ni(100) possesses the best HER activity among all of the discussed X/Ni(100) models, and the optimum surface S : Ni atomic ratio is about 22–33%. Further experiments demonstrated that the Ni–Ni3S2 catalyst with a surface S : Ni atomic ratio of 28.9% exhibits the best catalytic activity and lowest charge transfer resistance. The trend in catalytic activity of NiX with differing X offers a new possible strategy to exploit MX materials and design new active catalysts rationally. PMID:29675227

Protein kinase CK2 inhibitors: a patent review.

PubMed

Cozza, Giorgio; Pinna, Lorenzo A; Moro, Stefano

2012-09-01

CK2 is a pleiotropic, ubiquitous and constitutively active protein kinase, localized in both cytosolic and nuclear compartments, where it catalyzes the phosphorylation of hundreds of proteins. CK2 is generally described as a tetramer composed of two catalytic (α and/or α') and two regulatory subunits (β), however, the free α/α' subunits are catalytically active by themselves. CK2 plays a key role in several physiological and pathological processes and has been connected to many neoplastic, inflammatory, autoimmune and infectious disorders. In the last 20 years, several inhibitors of CK2 have been discovered though only one of these, CX-4945, has recently entered into Phase II clinical trials as potential anticancer drug. The main objective of the present review is to describe the development of CK2 activity modulators over the years according to the timeline of their patent registration. CK2 was discovered in 1954, but the first patent on CK2 modulators was deposited only 50 years later, in 2004. However, in the last 5 years an increasing number of patents on CK2 inhibitors have been registered, reflecting an increased interest in this kind of drug candidates and their possible therapeutic applications.

Efficient Dual-Site Carbon Monoxide Electro-Catalysts via Interfacial Nano-Engineering.

PubMed

Liu, Zhen; Huang, Zhongyuan; Cheng, Feifei; Guo, Zhanhu; Wang, Guangdi; Chen, Xu; Wang, Zhe

2016-09-21

Durable, highly efficient, and economic sound electrocatalysts for CO electrooxidation (COE) are the emerging key for wide variety of energy solutions, especially fuel cells and rechargeable metal-air batteries. Herein, we report the novel system of nickel-aluminum double layered hydroxide (NiAl-LDH) nanoplates on carbon nanotubes (CNTs) network. The formulation of such complexes system was to be induced through the assistance of gold nanoparticles in order to form dual-metal active sites so as to create a extended Au/NiO two phase zone. Bis (trifluoromethylsulfonyl)imide (NTf2) anion of ionic liquid electrolyte was selected to enhance the CO/O2 adsorption and to facilitate electro-catalyzed oxidation of Ni (OH)2 to NiOOH by increasing the electrophilicity of catalytic interface. The resulting neutral catalytic system exhibited ultra-high electrocatalytic activity and stability for CO electrooxidation than commercial and other reported precious metal catalysts. The turnover frequency (TOF) of the LDH-Au/CNTs COE catalyst was much higher than the previous reported other similar electrocatalysts, even close to the activity of solid-gas chemical catalysts at high temperature. Moreover, in the long-term durability testing, the negligible variation of current density remains exsisting after 1000 electrochemistry cycles.

Efficient Dual-Site Carbon Monoxide Electro-Catalysts via Interfacial Nano-Engineering

PubMed Central

Liu, Zhen; Huang, Zhongyuan; Cheng, Feifei; Guo, Zhanhu; Wang, Guangdi; Chen, Xu; Wang, Zhe

2016-01-01

Durable, highly efficient, and economic sound electrocatalysts for CO electrooxidation (COE) are the emerging key for wide variety of energy solutions, especially fuel cells and rechargeable metal−air batteries. Herein, we report the novel system of nickel−aluminum double layered hydroxide (NiAl-LDH) nanoplates on carbon nanotubes (CNTs) network. The formulation of such complexes system was to be induced through the assistance of gold nanoparticles in order to form dual-metal active sites so as to create a extended Au/NiO two phase zone. Bis (trifluoromethylsulfonyl)imide (NTf2) anion of ionic liquid electrolyte was selected to enhance the CO/O2 adsorption and to facilitate electro-catalyzed oxidation of Ni (OH)2 to NiOOH by increasing the electrophilicity of catalytic interface. The resulting neutral catalytic system exhibited ultra-high electrocatalytic activity and stability for CO electrooxidation than commercial and other reported precious metal catalysts. The turnover frequency (TOF) of the LDH-Au/CNTs COE catalyst was much higher than the previous reported other similar electrocatalysts, even close to the activity of solid-gas chemical catalysts at high temperature. Moreover, in the long-term durability testing, the negligible variation of current density remains exsisting after 1000 electrochemistry cycles. PMID:27650532

Efficient Dual-Site Carbon Monoxide Electro-Catalysts via Interfacial Nano-Engineering

NASA Astrophysics Data System (ADS)

Liu, Zhen; Huang, Zhongyuan; Cheng, Feifei; Guo, Zhanhu; Wang, Guangdi; Chen, Xu; Wang, Zhe

2016-09-01

Durable, highly efficient, and economic sound electrocatalysts for CO electrooxidation (COE) are the emerging key for wide variety of energy solutions, especially fuel cells and rechargeable metal-air batteries. Herein, we report the novel system of nickel-aluminum double layered hydroxide (NiAl-LDH) nanoplates on carbon nanotubes (CNTs) network. The formulation of such complexes system was to be induced through the assistance of gold nanoparticles in order to form dual-metal active sites so as to create a extended Au/NiO two phase zone. Bis (trifluoromethylsulfonyl)imide (NTf2) anion of ionic liquid electrolyte was selected to enhance the CO/O2 adsorption and to facilitate electro-catalyzed oxidation of Ni (OH)2 to NiOOH by increasing the electrophilicity of catalytic interface. The resulting neutral catalytic system exhibited ultra-high electrocatalytic activity and stability for CO electrooxidation than commercial and other reported precious metal catalysts. The turnover frequency (TOF) of the LDH-Au/CNTs COE catalyst was much higher than the previous reported other similar electrocatalysts, even close to the activity of solid-gas chemical catalysts at high temperature. Moreover, in the long-term durability testing, the negligible variation of current density remains exsisting after 1000 electrochemistry cycles.

Malonate-bound structure of the glycerophosphodiesterase from Enterobacter aerogenes (GpdQ) and characterization of the native Fe[superscript 2+] metal-ion preference

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

Jackson, Colin J.; Hadler, Kieran S.; Carr, Paul D.

2011-09-28

The structure of a malonate-bound form of the glycerophosphodiesterase from Enterobacter aerogenes, GpdQ, has been refined at a resolution of 2.2 {angstrom} to a final R factor of 17.1%. The structure was originally solved to 2.9 {angstrom} resolution using SAD phases from Zn{sup 2+} metal ions introduced into the active site of the apoenzyme [Jackson et al. (2007), J. Mol. Biol. 367, 1047-1062]. However, the 2.9 {angstrom} resolution was insufficient to discern significant details of the architecture of the binuclear metal centre that constitutes the active site. Furthermore, kinetic analysis revealed that the enzyme lost a significant amount of activitymore » in the presence of Zn2+, suggesting that it is unlikely to be a catalytically relevant metal ion. In this communication, a higher resolution structure of GpdQ is presented in which malonate is visibly coordinated in the active site and analysis of the native metal-ion preference is presented using atomic absorption spectroscopy and anomalous scattering. Catalytic implications of the structure and its Fe{sup 2+} metal-ion preference are discussed.« less

Malonate-bound structure of the glycerophosphodiesterase from Enterobacter aerogenes (GpdQ) and characterization of the native Fe[supscript 2+] metal-ion preference

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

Jackson, Colin J.; Hadler, Kieran S.; Carr, Paul D.

2010-09-20

The structure of a malonate-bound form of the glycerophosphodiesterase from Enterobacter aerogenes, GpdQ, has been refined at a resolution of 2.2 {angstrom} to a final R factor of 17.1%. The structure was originally solved to 2.9 {angstrom} resolution using SAD phases from Zn{sup 2+} metal ions introduced into the active site of the apoenzyme [Jackson et al. (2007), J. Mol. Biol. 367, 1047-1062]. However, the 2.9 {angstrom} resolution was insufficient to discern significant details of the architecture of the binuclear metal centre that constitutes the active site. Furthermore, kinetic analysis revealed that the enzyme lost a significant amount of activitymore » in the presence of Zn{sup 2+}, suggesting that it is unlikely to be a catalytically relevant metal ion. In this communication, a higher resolution structure of GpdQ is presented in which malonate is visibly coordinated in the active site and analysis of the native metal-ion preference is presented using atomic absorption spectroscopy and anomalous scattering. Catalytic implications of the structure and its Fe{sup 2+} metal-ion preference are discussed.« less

Nanostructured Silica-Titania Hybrid using Dendritic Fibrous Nanosilica as a Photocatalyst.

PubMed

Bayal, Nisha; Singh, Rustam; Polshettiwar, Vivek

2017-05-22

A new method has been developed to fabricate active TiO 2 photocatalysts by tuning the morphology of the catalyst support. A sustainable solution-phase TiO 2 deposition on dendritic fibrous nanosilica (DFNS) protocol is developed, which is better than the complex and expensive atomic layer deposition technique. In general, catalytic activity decreases with an increased TiO 2 loading on conventional mesoporous silica because of the loss of the surface area caused by the blocking of pores. Notably, in the case of the dendritic fibrous nanosilica KCC-1 as a support, because of its open fibrous morphology, even at the highest TiO 2 loading, a relatively large amount of surface area remained intact. This improved the accessibility of active sites, which increased the catalytic performance of the KCC-1/TiO 2 photocatalyst. KCC-1-supported TiO 2 is a superior photocatalyst in terms of H 2 generation (26.4 mmol gTiO2 -1  h -1 ) under UV light. This study may provide a new direction for photocatalyst development through the morphology control of the support. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dehydration, Dehydrogenation, and Condensation of Alcohols on Supported Oxide Catalysts Based on Cyclic (WO3)3 and (MoO3)3 Clusters

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

Rousseau, Roger J.; Dixon, David A.; Kay, Bruce D.

2014-01-01

Supported early transition metal oxides have important applications in numerous catalytic reactions. In this article we review preparation and activity of well-defined model WO3 and MoO3 catalysts prepared via deposition of cyclic gas-phase (WO3)3 and (MoO3)3 clusters generated by sublimation of WO3 and MoO3 powders. Conversion of small aliphatic alcohols to alkenes, aldehydes/ketons, and ethers is employed to probe the structure-activity relationships on model WO3 and MoO3 catalysts ranging from unsupported (WO3)3 and (MoO3)3 clusters embedded in alcohol matrices, to (WO3)3 clusters supported on surfaces of other oxides, and epitaxial and nanoporous WO3 films. Detailed theoretical calculations reveal the underlyingmore » reaction mechanisms and provide insight into the origin of the differences in the WO3 and MoO3 reactivity. For the range of interrogated (WO3)3 they further shed light into the role structure and binding of (WO3)3 clusters with the support play in determining their catalytic activity.« less

Phase 1 remediation of jet fuel contaminated soil and groundwater at JFK International Airport using dual phase extraction and bioventing

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

Roth, R.; Bianco, P. Rizzo, M.; Pressly, N.

1995-12-31

Soil and groundwater contaminated with jet fuel at Terminal One of the JFK International Airport in New York have been remediated using dual phase extraction (DPE) and bioventing. Two areas were remediated using 51 DPE wells and 20 air sparging/air injection wells. The total area remediated by the DPE wells is estimated to be 4.8 acres. Groundwater was extracted to recover nonaqueous phase and aqueous phase jet fuel from the shallow aquifer and treated above ground by the following processes; oil/water separation, iron-oxidation, flocculation, sedimentation, filtration, air stripping and liquid-phase granular activated carbon (LPGAC) adsorption. The extracted vapors were treatedmore » by vapor-phase granular activated carbon (VPGAC) adsorption in one area, and catalytic oxidation and VPGAC adsorption in another area. After 6 months of remediation, approximately 5,490 lbs. of volatile organic compounds (VOCs) were removed by soil vapor extraction (SVE), 109,650 lbs. of petroleum hydrocarbons were removed from the extracted groundwater, and 60,550 lbs. of petroleum hydrocarbons were biologically oxidized by subsurface microorganisms. Of these three mechanisms, the rate of petroleum hydrocarbon removal was the highest for biological oxidation in one area and by groundwater extraction in another area.« less

Surface chemistry and catalytic properties of VOX/Ti-MCM-41 catalysts for dibenzothiophene oxidation in a biphasic system

NASA Astrophysics Data System (ADS)

González, J.; Chen, L. F.; Wang, J. A.; Manríquez, Ma.; Limas, R.; Schachat, P.; Navarrete, J.; Contreras, J. L.

2016-08-01

A series of vanadium oxide supported on Ti-MCM-41 catalysts was synthesized via the incipient impregnation method by varying the vanadia loading from 5 wt% to 10, 15, 20 and 25 wt%. These catalysts were characterized by a variety of advanced techniques for investigating their crystalline structure, textural properties, and surface chemistry information including surface acidity, reducibility, vanadium oxidation states, and morphological features. The catalytic activities of the catalysts were evaluated in a biphasic reaction system for oxidative desulfurization (ODS) of a model diesel containing 300 ppm of dibenzothiophene (DBT) where acetonitrile was used as extraction solvent and H2O2 as oxidant. ODS activity was found to be proportional to the V5+/(V4+ + V5+) values of the catalysts, indicating that the surface vanadium pentoxide (V2O5) was the active phase. Reaction temperature would influence significantly the ODS efficiency; high temperature, i.e., 80 °C, would lead to low ODS reaction due to the partial decomposition of oxidant. All the catalysts contained both Lewis and Brønsted acid sites but the former was predominant. The catalysts with low vanadia loading (5 or 10 wt%V2O5) had many Lewis acid sites and could strongly adsorb DBT molecule via the electron donation/acceptance action which resulted in an inhibition for the reaction of DBT with the surface peroxometallic species. The catalyst with high vanadia loading (25wt%V2O5/Ti-MCM-41) showed the highest catalytic activity and could remove 99.9% of DBT at 60 °C within 60 min.

Impact of Zeolite Aging in Hot Liquid Water on Activity for Acid-Catalyzed Dehydration of Alcohols.

PubMed

Vjunov, Aleksei; Derewinski, Miroslaw A; Fulton, John L; Camaioni, Donald M; Lercher, Johannes A

2015-08-19

The location and stability of Brønsted acid sites catalytically active in zeolites during aqueous phase dehydration of alcohols were studied on the example of cyclohexanol. The catalytically active hydronium ions originate from Brønsted acid sites (BAS) of the zeolite that are formed by framework tetrahedral Si atom substitution by Al. Al K-edge extended X-ray absorption fine structure (EXAFS) and (27)Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopies in combination with density functional theory (DFT) calculations are used to determine the distribution of tetrahedral Al sites (Al T-sites) both qualitatively and quantitatively for both parent and HBEA catalysts aged in water prior to catalytic testing. The aging procedure leads to partial degradation of the zeolite framework evidenced from the decrease of material crystallinity (XRD) as well as sorption capacity (BET). With the exception of one commercial zeolite sample, which had the highest concentration of framework silanol-defects, there is no evidence of Al coordination modification after aging in water. The catalyst weight-normalized dehydration rate correlated best with the sum of strong and weak Brønsted acidic protons both able to generate the hydrated hydronium ions. All hydronium ions were equally active for the acid-catalyzed reactions in water. Zeolite aging in hot water prior to catalysis decreased the weight normalized dehydration reaction rate compared to that of the parent HBEA, which is attributed to the reduced concentration of accessible Brønsted acid sites. Sites are hypothesized to be blocked due to reprecipitation of silica dissolved during framework hydrolysis in the aging procedure.

Application of silica-supported Fe-Cu nanoparticles in the selective hydrogenation of p-dinitrobenzene to p-phenylenediamine

NASA Astrophysics Data System (ADS)

Shesterkina, A. A.; Shuvalova, E. V.; Kirichenko, O. A.; Strelkova, A. A.; Nissenbaum, V. D.; Kapustin, G. I.; Kustov, L. M.

2017-02-01

Supported bimetallic Fe-Cu/SiO2 materials are synthesized, and their catalytic activity in hydrogenation of dinitrobenzene to phenylenediamine at 145-180°C and 1.3 MPa hydrogen pressure is studied for the first time. The best results (89% selectivity toward p-phenylenediamine at complete conversion of p-dinitrobenzene) are obtained for the sample synthesized via co-deposition with subsequent calcination at 300°C. The sample contains 7% iron and 3% copper. The formation of separate phases of metal oxides (for the catalysts prepared by impregnation) and mixed bimetallic oxide phases (in case of co-deposition procedure) in calcined samples is revealed via thermoprogrammed reduction with hydrogen.

Catalytic Gas-Phase Glycerol Processing over SiO2-, Cu-, Ni- and Fe- Supported Au Nanoparticles

PubMed Central

Kapkowski, Maciej; Siudyga, Tomasz; Sitko, Rafal; Lelątko, Józef; Szade, Jacek; Balin, Katarzyna; Klimontko, Joanna; Bartczak, Piotr; Polanski, Jaroslaw

2015-01-01

In this study, we investigated different metal pairings of Au nanoparticles (NPs) as potential catalysts for glycerol dehydration for the first time. All of the systems preferred the formation of hydroxyacetone (HYNE). Although the bimetallics that were tested, i.e., Au NPs supported on Ni, Fe and Cu appeared to be more active than the Au/SiO2 system, only Cu supported Au NPs gave high conversion (ca. 63%) and selectivity (ca. 70%) to HYNE. PMID:26580400

High-density defects on PdAg nanowire networks as catalytic hot spots for efficient dehydrogenation of formic acid and reduction of nitrate.

PubMed

Liu, Hu; Yu, Yongsheng; Yang, Weiwei; Lei, Wenjuan; Gao, Manyi; Guo, Shaojun

2017-07-13

Controlling the surface defects of nanocrystals is a new way of tuning/boosting their catalytic properties. Herein, we report networked PdAg nanowires (NWs) with high-density defects as catalytic hot spots for efficient catalytic dehydrogenation of formic acid (FA) and catalytic reduction of nitrates. The networked PdAg NWs exhibit composition-dependent catalytic activity for the dehydrogenation reaction of FA without any additive, with Pd 5 Ag 5 NWs exhibiting the highest activity. They also show good durability, reflected by the retention of their initial activity during the dehydrogenation reaction of FA even after five cycles. Their initial TOF is 419 h -1 at 60 °C in water solution, much higher than those of the most Pd-based catalysts with a support. Moreover, they can efficiently reduce nitrates to alleviate nitrate pollution in water (conversion yield >99%). This strategy opens up a new green synthetic technique to design support-free heterogeneous catalysts with high-density defects as catalytic hot spots for efficient dehydrogenation catalysis of FA to meet the requirement of fuel cell applications and catalytic reduction of nitrates in water polluted with nitrates.

The photo-oxidation of automobile emissions: measurements of the transformation products and their mutagenic activity

NASA Astrophysics Data System (ADS)

Kleindienst, Tadeusz E.; Smith, David F.; Hudgens, Edward E.; Snow, Richard F.; Perry, Erica; Claxton, Larry D.; Bufalini, Joseph J.; Black, Francis M.; Cupitt, Larry T.

Dilute mixtures of automobile emissions (comprising 50% exhaust and 50% surrogate evaporative emissions) were irradiated in a 22.7 m 3 smog chamber and tested for mutagenic activity by using a variant of the Ames test. The exhaust was taken from a single vehicle, a 1977 Ford Mustang equipped with a catalytic converter. Irradiated and nonirradiated gas-phase emissions were used in exposures of the bacteria, Salmonella typhimurium, strains TA100 and TA98. A single set of vehicular operating conditions was used to perform multiple exposures. The mutagenic activities of extracts from the particulate phase were also measured with the standard plate incorporation assay. (In most experiments only direct-acting mutagenic compounds were measured.) The gas-phase data for TA100 and TA98 showed increased activity for the irradiated emissions when compared to the nonirradiated mixture, which exhibited negligible activity with respect to the control values. The particulate phase for both the irradiated and nonirradiated mixtures showed negligible activity when results were compared to the control values for both strains. However, the experimental conditions limited the amount of extractable mass which could be collected in the particulate phase. The measured activities from the gas phase and particulate phase were converted to the number of revertants per cubic meter of effluent (i.e. the mutagenic density) to compare the contributions of each of these phases to the total mutagenic activity for each strain. Under the experimental conditions of this study, the mutagenic density of the gas-phase component of the irradiated mixture contributed approximately two orders of magnitude more of the total TA100 activity than did the particulate phase. For TA98 the gas-phase component contributed approximately one order of magnitude more. However, caution must be exercised in extrapolating these results to urban atmospheres heavily impacted by automotive emissions, because the bacterial mutagenicity assay was used as a screening method, and additional assays using mammalian systems have not yet been conducted. In addition, only limited number of conditions were able to be tested. The significance and limitations of the results are discussed.

Catalytic wet air oxidation of bisphenol A solution in a batch-recycle trickle-bed reactor over titanate nanotube-based catalysts.

PubMed

Kaplan, Renata; Erjavec, Boštjan; Senila, Marin; Pintar, Albin

2014-10-01

Catalytic wet air oxidation (CWAO) is classified as an advanced oxidation process, which proved to be highly efficient for the removal of emerging organic pollutant bisphenol A (BPA) from water. In this study, BPA was successfully removed in a batch-recycle trickle-bed reactor over bare titanate nanotube-based catalysts at very short space time of 0.6 min gCAT g(-1). The as-prepared titanate nanotubes, which underwent heat treatment at 600 °C, showed high activity for the removal of aqueous BPA. Liquid-phase recycling (5- or 10-fold recycle) enabled complete BPA conversion already at 200 °C, together with high conversion of total organic carbon (TOC), i.e., 73 and 98 %, respectively. The catalyst was chemically stable in the given range of operating conditions for 189 h on stream.

Sinter-Resistant Platinum Catalyst Supported by Metal-Organic Framework

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

Kim, In Soo; Li, Zhanyong; Zheng, Jian

Installed on the zirconia nodes of a metal-organic framework (MOF) NU-1000 via targeted vapor-phase synthesis. The catalytic Pt clusters, site-isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 degrees C. In situ IR spectroscopy reveals the presence of both single atoms and few-atom clusters that depend upon synthesis conditions. Operando X-ray absorption spectroscopy and Xray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novelmore » catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size-selected clusters, including noble metals, on a high surface area support.« less

Novel Catalysis by Gold: A Modern Alchemy

NASA Astrophysics Data System (ADS)

Haruta, Masatake

Gold has long been neglected as a catalyst because of its chemical inertness. However, when gold is deposited as nanoparticles on carbon and polymer materials as well as on base metal oxides and hydroxides, it exhibits unique catalytic properties for many reactions such as CO oxidation at a temperature as low as 200 K, gas phase direct epoxidation of propylene, and aerobic oxidation of glucose to gluconic acid. The structure-catalytic activity correlations are discussed with emphasis on the contact structure, support selection, and the size control of gold particles. Gold clusters with diameters smaller than 2 nm are expected to exhibit novel properties in catalysis, optics, and electronics depending on the size (number of atoms), shape, and the electronic and chemical interaction with the support materials. The above achievements and attempts can be regarded as a modern alchemy that creates valuables by means of the noblest element with little practical use.

Photochemical route for accessing amorphous metal oxide materials for water oxidation catalysis.

PubMed

Smith, Rodney D L; Prévot, Mathieu S; Fagan, Randal D; Zhang, Zhipan; Sedach, Pavel A; Siu, Man Kit Jack; Trudel, Simon; Berlinguette, Curtis P

2013-04-05

Large-scale electrolysis of water for hydrogen generation requires better catalysts to lower the kinetic barriers associated with the oxygen evolution reaction (OER). Although most OER catalysts are based on crystalline mixed-metal oxides, high activities can also be achieved with amorphous phases. Methods for producing amorphous materials, however, are not typically amenable to mixed-metal compositions. We demonstrate that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis. The films contain a homogeneous distribution of metals with compositions that can be accurately controlled. The catalytic properties of amorphous iron oxide prepared with this technique are superior to those of hematite, whereas the catalytic properties of a-Fe(100-y-z)Co(y)Ni(z)O(x) are comparable to those of noble metal oxide catalysts currently used in commercial electrolyzers.

Palladium nanoparticles deposited on silanized halloysite nanotubes: synthesis, characterization and enhanced catalytic property

NASA Astrophysics Data System (ADS)

Zhang, Yi; He, Xi; Ouyang, Jing; Yang, Huaming

2013-10-01

Palladium (Pd) nanoparticles were deposited on the surface of halloysite nanotubes (HNTs) modified with γ-aminopropyltriethoxysilane (APTES) to produce Pd/NH2-HNTs nanocomposites. The results indicated that Pd nanoparticles were densely immobilized onto NH2-HNTs with an average diameter of ~ 3 nm. The Pd distribution on the surface of silanized HNTs showed much more uniform, and the Pd nanoparticle size became smaller compared with those directly deposited onto HNTs without silanization. Systematic characterization demonstrated that APTES were chemically bonded onto HNTs, and further confirmed the bond formation between Pd and -NH2 groups, which could ensure the firm deposit of Pd nanoparticles on the surface of silanized HNTs. The as-synthesized Pd/NH2-HNTs exhibited an excellent catalytic activity in the liquid-phase hydrogenation of styrene to ethylbenzene with full conversion within 30 min. The mechanism of the deposit of Pd nanoparticles on silanized HNTs was also investigated.

Dehydration of glycerol over niobia-supported silicotungstic acid catalysts.

PubMed

Lee, Young Yi; Ok, Hye Jeong; Moon, Dong Ju; Kim, Jong Ho; Park, Nam Cook; Kim, Young Chul

2013-01-01

Liquid-phase dehydration of glycerol to acrolein over nanosized niobia-supported silicotungstic acid catalysts was performed to investigate the effect of the silicotungstic acid loading on the catalytic performance of the catalysts. The catalysts were prepared by following an impregnation method with different HSiW loadings in the range of 10-50 wt%. The prepared catalysts were characterized by N2 physisorption, XRD, FT-IR, TPD of ammonia, and TGA. Dehydration of glycerol was conducted in an autoclave reactor under the conditions of controlled reaction temperatures under corresponding pressure. Increasing HSiW loading rapidly increased the acidity of HSiW/Nb205 catalyst and rate of glycerol conversion, but acrolein selectivity decreased due to enhanced deactivation of the catalyst by carbon deposit. Consequently, it was confirmed that catalytic activity for the dehydration of glycerol to acrolein was dependant on the acidity of catalyst and can be controlled by HSiW loading.

A molecular approach to self-supported cobalt-substituted ZnO materials as remarkably stable electrocatalysts for water oxidation.

PubMed

Pfrommer, Johannes; Lublow, Michael; Azarpira, Anahita; Göbel, Caren; Lücke, Marcel; Steigert, Alexander; Pogrzeba, Martin; Menezes, Prashanth W; Fischer, Anna; Schedel-Niedrig, Thomas; Driess, Matthias

2014-05-12

In regard to earth-abundant cobalt water oxidation catalysts, very recent findings show the reorganization of the materials to amorphous active phases under catalytic conditions. To further understand this concept, a unique cobalt-substituted crystalline zinc oxide (Co:ZnO) precatalyst has been synthesized by low-temperature solvolysis of molecular heterobimetallic Co(4-x)Zn(x) O4 (x = 1-3) precursors in benzylamine. Its electrophoretic deposition onto fluorinated tin oxide electrodes leads after oxidative conditioning to an amorphous self-supported water-oxidation electrocatalyst, which was observed by HR-TEM on FIB lamellas of the EPD layers. The Co-rich hydroxide-oxidic electrocatalyst performs at very low overpotentials (512 mV at pH 7; 330 mV at pH 12), while chronoamperometry shows a stable catalytic current over several hours. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

High-throughput investigation of catalysts for JP-8 fuel cracking to liquefied petroleum gas.

PubMed

Bedenbaugh, John E; Kim, Sungtak; Sasmaz, Erdem; Lauterbach, Jochen

2013-09-09

Portable power technologies for military applications necessitate the production of fuels similar to LPG from existing feedstocks. Catalytic cracking of military jet fuel to form a mixture of C₂-C₄ hydrocarbons was investigated using high-throughput experimentation. Cracking experiments were performed in a gas-phase, 16-sample high-throughput reactor. Zeolite ZSM-5 catalysts with low Si/Al ratios (≤25) demonstrated the highest production of C₂-C₄ hydrocarbons at moderate reaction temperatures (623-823 K). ZSM-5 catalysts were optimized for JP-8 cracking activity to LPG through varying reaction temperature and framework Si/Al ratio. The reducing atmosphere required during catalytic cracking resulted in coking of the catalyst and a commensurate decrease in conversion rate. Rare earth metal promoters for ZSM-5 catalysts were screened to reduce coking deactivation rates, while noble metal promoters reduced onset temperatures for coke burnoff regeneration.

Investigation of holdup and axial dispersion of liquid phase in a catalytic exchange column using radiotracer technique.

PubMed

Kumar, Rajesh; Pant, H J; Goswami, Sunil; Sharma, V K; Dash, A; Mishra, S; Bhanja, K; Mohan, Sadhana; Mahajani, S M

2017-03-01

Holdup and axial dispersion of liquid phase in a catalytic exchange column were investigated by measuring residence time distributions (RTD) using a radiotracer technique. RTD experiments were independently carried out with two different types of packings i.e. hydrophobic water-repellent supported platinum catalyst and a mixture (50% (v/v)) of hydrophobic catalyst and a hydrophillic wettable packing were used in the column. Mean residence times and hold-ups of the liquid phase were estimated at different operating conditions. Axial dispersion model (ADM) and axial dispersion with exchange model (ADEM) were used to simulate the measured RTD data. Both the models were found equally suitable to describe the measured data. The degree of axial mixing was estimated in terms of Peclet number (Pe) and Bodenstein number (Bo). Based on the obtained parameters of the ADM, correlations for total liquid hold-up (H T ) and axial mixing in terms of Bo were proposed for design and scale up of the full-scale catalytic exchange column. Copyright © 2016 Elsevier Ltd. All rights reserved.

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

McInnis, Brittney; Mitchell, Jessica; Marcus, Stevan, E-mail: smarcus@bama.ua.edu

Research highlights: {yields} cAMP deficiency induces phosphorylation of PKA catalytic subunit (Pka1) in S. pombe. {yields} Pka1 phosphorylation is further induced by physiological stresses. {yields} Pka1 phosphorylation is not induced in cells lacking the PKA regulatory subunit. {yields} Results suggest that cAMP-independent Pka1 phosphorylation is stimulatory in nature. -- Abstract: In the fission yeast, Schizosaccharomyces pombe, cyclic AMP (cAMP)-dependent protein kinase (PKA) is not essential for viability under normal culturing conditions, making this organism attractive for investigating mechanisms of PKA regulation. Here we show that S. pombe cells carrying a deletion in the adenylate cyclase gene, cyr1, express markedly highermore » levels of the PKA catalytic subunit, Pka1, than wild type cells. Significantly, in cyr1{Delta} cells, but not wild type cells, a substantial proportion of Pka1 protein is hyperphosphorylated. Pka1 hyperphosphorylation is strongly induced in cyr1{Delta} cells, and to varying degrees in wild type cells, by both glucose starvation and stationary phase stresses, which are associated with reduced cAMP-dependent PKA activity, and by KCl stress, the cellular adaptation to which is dependent on PKA activity. Interestingly, hyperphosphorylation of Pka1 was not detected in either cyr1{sup +} or cyr1{Delta} S. pombe strains carrying a deletion in the PKA regulatory subunit gene, cgs1, under any of the tested conditions. Our results demonstrate the existence of a cAMP-independent mechanism of PKA catalytic subunit phosphorylation, which we propose could serve as a mechanism for inducing or maintaining specific PKA functions under conditions in which its cAMP-dependent activity is downregulated.« less

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%.

Continuous monitoring of enzymatic activity within native electrophoresis gels: Application to mitochondrial oxidative phosphorylation complexes

PubMed Central

Covian, Raul; Chess, David; Balaban, Robert S.

2012-01-01

Native gel electrophoresis allows the separation of very small amounts of protein complexes while retaining aspects of their activity. In-gel enzymatic assays are usually performed by using reaction-dependent deposition of chromophores or light scattering precipitates quantified at fixed time points after gel removal and fixation, limiting the ability to analyze enzyme reaction kinetics. Herein, we describe a custom reaction chamber with reaction media recirculation and filtering and an imaging system that permits the continuous monitoring of in-gel enzymatic activity even in the presence of turbidity. Images were continuously collected using time-lapse high resolution digital imaging, and processing routines were developed to obtain kinetic traces of the in-gel activities and analyze reaction time courses. This system also permitted the evaluation of enzymatic activity topology within the protein bands of the gel. This approach was used to analyze the reaction kinetics of two mitochondrial complexes in native gels. Complex IV kinetics showed a short initial linear phase where catalytic rates could be calculated, whereas Complex V activity revealed a significant lag phase followed by two linear phases. The utility of monitoring the entire kinetic behavior of these reactions in native gels, as well as the general application of this approach, is discussed. PMID:22975200

Continuous monitoring of enzymatic activity within native electrophoresis gels: application to mitochondrial oxidative phosphorylation complexes.

PubMed

Covian, Raul; Chess, David; Balaban, Robert S

2012-12-01

Native gel electrophoresis allows the separation of very small amounts of protein complexes while retaining aspects of their activity. In-gel enzymatic assays are usually performed by using reaction-dependent deposition of chromophores or light-scattering precipitates quantified at fixed time points after gel removal and fixation, limiting the ability to analyze the enzyme reaction kinetics. Herein, we describe a custom reaction chamber with reaction medium recirculation and filtering and an imaging system that permits the continuous monitoring of in-gel enzymatic activity even in the presence of turbidity. Images were continuously collected using time-lapse high-resolution digital imaging, and processing routines were developed to obtain kinetic traces of the in-gel activities and analyze reaction time courses. This system also permitted the evaluation of enzymatic activity topology within the protein bands of the gel. This approach was used to analyze the reaction kinetics of two mitochondrial complexes in native gels. Complex IV kinetics showed a short initial linear phase in which catalytic rates could be calculated, whereas Complex V activity revealed a significant lag phase followed by two linear phases. The utility of monitoring the entire kinetic behavior of these reactions in native gels, as well as the general application of this approach, is discussed. Published by Elsevier Inc.

Catalytic activity of certain antibodies as a potential tool for drug synthesis and for directed prodrug therapies.

PubMed

Wójcik, T; Kieć-Kononowicz, K

2008-01-01

Catalytic activity of certain antibodies was proposed by Linus Pauling for the very first time more than six decades ago. Since then few examples of catalytic antibodies (abzymes) were found in human organism. From late 80's many synthetic abzymes were obtained after immunization by Transition State Analogs (TSA). Another approach is based on functional mimicry of antibody to an active site of an enzyme. Detection of an abzymatic activity requires special immunoassays. This unique strategy can be employed for new methods of drug synthesis, as well as for in vivo therapies. Catalytic antibodies seem to be a promising tool for therapeutic purposes, because of their specifity and stereoselectivity.

Enhanced catalytic activity without the use of an external light source using microwave-synthesized CuO nanopetals

PubMed Central

Bajaj, Sonal; Nayak, Arpan Kumar; Pradhan, Debabrata; Tekade, Pradip

2017-01-01

We report enhanced catalytic activity of CuO nanopetals synthesized by microwave-assisted wet chemical synthesis. The catalytic reaction of CuO nanopetals and H2O2 was studied with the application of external light source and also under dark conditions for the degradation of the hazardous dye methylene blue. The CuO nanopetals showed significant catalytic activity for the fast degradation of methylene blue and rhodamine B (RhB) under dark conditions, without the application of an external light source. This increased catalytic activity was attributed to the co-operative role of H2O2 and the large specific surface area (≈40 m2·g−1) of the nanopetals. We propose a detail mechanism for this fast degradation. A separate study of the effect of different H2O2 concentrations for the degradation of methylene blue under dark conditions is also illustrated. PMID:28685117

Topotactic Metal-Insulator Transition in Epitaxial SrFeO x Thin Films

DOE PAGES

Khare, Amit; Shin, Dongwon; Yoo, Tae Sup; ...

2017-07-31

Multivalent transition metal oxides provide fascinating and rich physics related to oxygen stoichiometry. In particular, the adoptability of various valence states of transition metals enables perovskite oxides to display mixed (oxygen) ionic and electronic conduction and catalytic activity useful in many practical applications, including solid-oxide fuel cells (SOFCs), rechargeable batteries, gas sensors, and memristive devices. For proper realization of the ionic conduction and catalytic activity, it is essential to understand the reversible oxidation and reduction process, which is governed by oxygen storage/release steps in oxides. Topotactic phase transformation facilitates the redox process in perovskites with specific oxygen vacancy ordering bymore » largely varying the oxygen concentration of a material without losing the lattice framework. The concentration and diffusion of oxide ions (O 2–), the valence state of the transition metal cations, and the thermodynamic structural integrity together provide fundamental understanding and ways to explicitly control the redox reaction.[6] In addition, it offers an attractive route for tuning the emergent physical properties of transition metal oxides, via strong coupling between the crystal lattice and electronic structure.« less

Catalytic Effect of Pd Clusters in the Poly( N-vinyl-2-pyrrolidone) Combustion

NASA Astrophysics Data System (ADS)

Schiavo, L.; De Nicola, S.; Carotenuto, G.

2018-01-01

Pd(0) is able to catalyze oxygen-involving reactions because of its capability to convert molecular oxygen to the very reactive atomic form. Consequently, the embedding of a little amount of Pd(0) clusters in polymeric phases can be technologically exploited to enhance the incineration kinetic of these polymers. The effect of nanostructuration on the Pd(0) catalytic activity in the polymer incineration reaction has been studied using poly( N-vinyl-2-pyrrolidone) ( \\overline{Mw} = 10,000 gmol-1) as polymeric model system. A change in the PVP incineration kinetic mechanism with significant increase in the reaction rate was experimentally found. The kinetic of the Pd(0)-catalyzed combustion has been studied by isothermal thermogravimetric analysis. After a short induction time, the combustion in presence of Pd(0) clusters shifted to a zero-order kinetic from a second-order kinetic control, which is operative in pure PVP combustion reaction. In addition, the activation energy resulted much lowered compared to the pure PVP incineration case (from 300 to 260 kJ/mol).

Noble-metal-free bimetallic alloy nanoparticle-catalytic gasification of phenol in supercritical water

DOE PAGES

Jia, Lijuan; Yu, Jiangdong; Chen, Yuan; ...

2017-08-01

The exploration of non-noble-metal catalysts for high efficiency gasification of biomass in supercritical water (SCW) is of great significance for the sustainable development. A series of Ni–M (M = Co or Zn) bimetallic nanoparticles supported on graphitized carbon black were synthesized and examined as catalysts for gasification of phenol in SCW. We found that a nearly complete gasification of phenol can be achieved even at a low temperature of 450 °C with the bimetallic nanoparticles catalysts. Kinetic study indicated the activation energy for phenol gasification were 20.4 ± 2.6 and 43.6 ± 2.6 kJ/mol for Ni20Zn15 and Ni20Co15 catalyst, respectively.more » Furthermore, XRD, XPS and TEM were performed to characterize the catalysts and the results showed the formation of NiCo and NiZn alloy phase. Catalyst recycling experiments were also conducted to evaluate the stability of the catalysts. The characterization of used catalysts suggest that the severe agglomeration of nanoparticles leads to the decrease in catalytic activity.« less

Enzyme Sorption onto Soil and Biocarbon Amendments Alters Catalytic Capacity and Depends on the Specific Protein and pH

NASA Astrophysics Data System (ADS)

Foster, E.; Fogle, E. J.; Cotrufo, M. F.

2017-12-01

Enzymes catalyze biogeochemical reactions in soils and play a key role in nutrient cycling in agricultural systems. Often, to increase soil nutrients, agricultural managers add organic amendments and have recently experimented with charcoal-like biocarbon products. These amendments can enhance soil water and nutrient holding capacity through increasing porosity. However, the large surface area of the biocarbon has the potential to sorb nutrients and other organic molecules. Does the biocarbon decrease nutrient cycling through sorption of enzymes? In a laboratory setting, we compared the interaction of two purified enzymes β-glucosidase and acid phosphatase with a sandy clay loam and two biocarbons. We quantified the sorbed enzymes at three different pHs using a Bradford protein assay and then measured the activity of the sorbed enzyme via high-throughput fluorometric analysis. Both sorption and activity depended upon the solid phase, pH, and specific enzyme. Overall the high surface area biocarbon impacted the catalytic capacity of the enzymes more than the loam soil, which may have implications for soil nutrient management with these organic amendments.

Noble-metal-free bimetallic alloy nanoparticle-catalytic gasification of phenol in supercritical water

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

Jia, Lijuan; Yu, Jiangdong; Chen, Yuan

The exploration of non-noble-metal catalysts for high efficiency gasification of biomass in supercritical water (SCW) is of great significance for the sustainable development. A series of Ni–M (M = Co or Zn) bimetallic nanoparticles supported on graphitized carbon black were synthesized and examined as catalysts for gasification of phenol in SCW. We found that a nearly complete gasification of phenol can be achieved even at a low temperature of 450 °C with the bimetallic nanoparticles catalysts. Kinetic study indicated the activation energy for phenol gasification were 20.4 ± 2.6 and 43.6 ± 2.6 kJ/mol for Ni20Zn15 and Ni20Co15 catalyst, respectively.more » Furthermore, XRD, XPS and TEM were performed to characterize the catalysts and the results showed the formation of NiCo and NiZn alloy phase. Catalyst recycling experiments were also conducted to evaluate the stability of the catalysts. The characterization of used catalysts suggest that the severe agglomeration of nanoparticles leads to the decrease in catalytic activity.« less

Tunable Bifunctional Activity of Mnx Co3-x O4 Nanocrystals Decorated on Carbon Nanotubes for Oxygen Electrocatalysis.

PubMed

Zhao, Tingting; Gadipelli, Srinivas; He, Guanjie; Ward, Matthew J; Do, David; Zhang, Peng; Guo, Zhengxiao

2018-04-25

Noble-metal-free electrocatalysts are attractive for cathodic oxygen catalysis in alkaline membrane fuel cells, metal-air batteries, and electrolyzers. However, much of the structure-activity relationship is poorly understood. Herein, the comprehensive development of manganese cobalt oxide/nitrogen-doped multiwalled carbon nanotube hybrids (Mn x Co 3-x O 4 @NCNTs) is reported for highly reversible oxygen reduction and evolution reactions (ORR and OER, respectively). The hybrid structures are rationally designed by fine control of surface chemistry and synthesis conditions, including tuning of functional groups at surfaces, congruent growth of nanocrystals with controllable phases and particle sizes, and ensuring strong coupling across catalyst-support interfaces. Electrochemical tests reveal distinctly different oxygen catalytic activities among the hybrids, Mn x Co 3-x O 4 @NCNTs. Nanocrystalline MnCo 2 O 4 @NCNTs (MCO@NCNTs) hybrids show superior ORR activity, with a favorable potential to reach 3 mA cm -2 and a high current density response, equivalent to that of the commercial Pt/C standard. Moreover, the hybrid structure exhibits tunable and durable catalytic activities for both ORR and OER, with a lowest overall potential of 0.93 V. It is clear that the long-term electrochemical activities can be ensured by rational design of hybrid structures from the nanoscale. © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Preparation of PdCu Alloy Nanocatalysts for Nitrate Hydrogenation and Carbon Monoxide Oxidation

DOE PAGES

Cai, Fan; Yang, Lefu; Shan, Shiyao; ...

2016-06-30

Alloying Pd with Cu is important for catalytic reactions such as denitrification reaction and CO oxidation reaction, but understanding of the catalyst preparation and its correlation with the catalyst’s activity and selectivity remains elusive. Herein, we report the results of investigations of the preparation of PdCu alloy nanocatalysts using different methods and the catalytic properties of the catalysts in catalytic denitrification reaction and CO oxidation reaction. PdCu alloy nanocatalysts were prepared by conventional dry impregnation method and ligand-capping based wet chemical synthesis method, and subsequent thermochemical activation as well. The alloying characteristics depend on the bimetallic composition. PdCu/Al 2O 3more » with a Pd/Cu ratio of 50:50 was shown to exhibit an optimized hydrogenation activity for the catalytic denitrification reaction. The catalytic activity of the PdCu catalysts was shown to be highly dependent on the support, as evidenced by the observation of an enhanced catalytic activity for CO oxidation reaction using TiO 2 and CeO 2 supports with high oxygen storage capacity. Lastly, we discussed the implications of the results to the refinement of the preparation of the alloy nanocatalysts.« less

Electrochemistry of metalloproteins: protein film electrochemistry for the study of E. coli [NiFe]-hydrogenase-1.

PubMed

Evans, Rhiannon M; Armstrong, Fraser A

2014-01-01

Protein film electrochemistry is a technique which allows the direct control of redox-active enzymes, providing particularly detailed information on their catalytic properties. The enzyme is deposited onto a working electrode tip, and through control of the applied potential the enzyme activity is monitored as electrical current, allowing for direct study of inherent activity as electrons are transferred to and from the enzyme redox center(s). No mediators are used. Because the only enzyme present in the experiment is bound at the electrode surface, gaseous and liquid phase inhibitors can be introduced and removed whilst the enzyme remains in situ. Potential control means that kinetics and thermodynamics are explored simultaneously; the kinetics of a reaction can be studied as a function of potential. Steady-state catalytic rates are observed directly as current (for a given potential) and non-steady-state rates (such as interconversions between different forms of the enzyme) are observed from the change in current with time. The more active the enzyme, the higher the current and the better the signal-to-noise. In this chapter we outline the practical aspects of PFE for studying electroactive enzymes, using the Escherichia coli [NiFe]-hydrogenase 1 (Hyd-1) as an example.

Aligned carbon nanotube with electro-catalytic activity for oxygen reduction reaction

DOEpatents

Liu, Di-Jia; Yang, Junbing; Wang, Xiaoping

2010-08-03

A catalyst for an electro-chemical oxygen reduction reaction (ORR) of a bundle of longitudinally aligned carbon nanotubes having a catalytically active transition metal incorporated longitudinally in said nanotubes. A method of making an electro-chemical catalyst for an oxygen reduction reaction (ORR) having a bundle of longitudinally aligned carbon nanotubes with a catalytically active transition metal incorporated throughout the nanotubes, where a substrate is in a first reaction zone, and a combination selected from one or more of a hydrocarbon and an organometallic compound containing an catalytically active transition metal and a nitrogen containing compound and an inert gas and a reducing gas is introduced into the first reaction zone which is maintained at a first reaction temperature for a time sufficient to vaporize material therein. The vaporized material is then introduced to a second reaction zone maintained at a second reaction temperature for a time sufficient to grow longitudinally aligned carbon nanotubes over the substrate with a catalytically active transition metal incorporated throughout the nanotubes.

Room-Temperature and Aqueous-Phase Synthesis of Plasmonic Molybdenum Oxide Nanoparticles for Visible-Light-Enhanced Hydrogen Generation.

PubMed

Shi, Jiayuan; Kuwahara, Yasutaka; Wen, Meicheng; Navlani-García, Miriam; Mori, Kohsuke; An, Taicheng; Yamashita, Hiromi

2016-09-06

A straightforward aqueous synthesis of MoO3-x nanoparticles at room temperature was developed by using (NH4 )6 Mo7 O24 ⋅4 H2 O and MoCl5 as precursors in the absence of reductants, inert gas, and organic solvents. SEM and TEM images indicate the as-prepared products are nanoparticles with diameters of 90-180 nm. The diffuse reflectance UV-visible-near-IR spectra of the samples indicate localized surface plasmon resonance (LSPR) properties generated by the introduction of oxygen vacancies. Owing to its strong plasmonic absorption in the visible-light and near-infrared region, such nanostructures exhibit an enhancement of activity toward visible-light catalytic hydrogen generation. MoO3-x nanoparticles synthesized with a molar ratio of Mo(VI) /Mo(V) 1:1 show the highest yield of H2 evolution. The cycling catalytic performance has been investigated to indicate the structural and chemical stability of the as-prepared plasmonic MoO3-x nanoparticles, which reveals its potential application in visible-light catalytic hydrogen production. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetic cobaltic nanoparticle-anchored carbon nanocomposite derived from cobalt-dipicolinic acid coordination polymer: An enhanced catalyst for environmental oxidative and reductive reactions.

PubMed

Wu, Chang-Hsun; Lin, Jyun-Ting; Lin, Kun-Yi Andrew

2018-05-01

Direct carbonization of cobalt complexes represents as a convenient approach to prepare magnetic carbon/cobalt nanocomposites (MCCNs) as heterogeneous environmental catalysts. However, most of MCCNs derived from consist of sheet-like carbon matrices with very sparse cobaltic nanoparticles (NPs), making them exhibit relatively low catalytic activities, porosity and magnetism. In this study, dipicolinic acid (DPA) is selected to prepare a 3-dimensional cobalt coordination polymer (CoDPA). MCCN derived from CoDPA can consist of a porous carbon matrix embedded with highly-dense Co 0 and Co 3 O 4 NPs. This magnetic Co 0 /Co 3 O 4 NP-anchored carbon composite (MCNC) appears as a promising heterogeneous catalyst for oxidative and reductive environmental catalytic reactions. As peroxymonosulfate (PMS) activation is selected as a model catalytic oxidative reaction, MCNC exhibits a much higher catalytic activity than Co 3 O 4 , a benchmark catalyst for PMS activation. The reductive catalytic activity of MCNC is demonstrated through 4-nitrophenol (4-NP) reduction in the presence of NaBH 4 . MCNC could rapidly react with NaBH 4 to generate H 2 for hydrogenation of 4-NP to 4-aminophenol (4-AP). In comparison with other precious metallic catalysts, MCNC also shows a relatively high catalytic activity. These results indicate that MCNC is a conveniently prepared and highly effective and stable carbon-supported cobaltic heterogeneous catalyst for versatile environmental catalytic applications. Copyright © 2018 Elsevier Inc. All rights reserved.

Reverse micelle synthesis of nanoscale metal containing catalysts. [Nickel metal (with a nickel oxide surface layer) and iron oxyhydroxide nanoscale powders

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

Darab, J.G.; Fulton, J.L.; Linehan, J.C.

1993-03-01

The need for morphological control during the synthesis of catalyst precursor powders is generally accepted to be important. In the liquefaction of coal, for example, iron-bearing catalyst precursor particles containing individual crystallites with diameters in the 1-100 nanometer range are believed to achieve good dispersion through out the coal-solvent slurry during liquefaction 2 runs and to undergo chemical transformations to catalytically active iron sulfide phases. The production of the nanoscale powders described here employs the confining spherical microdomains comprising the aqueous phase of a modified reverse micelle (MRM) microemulsion system as nanoscale reaction vessels in which polymerization, electrochemical reduction andmore » precipitation of solvated salts can occur. The goal is to take advantage of the confining nature of micelles to kinetically hinder transformation processes which readily occur in bulk aqueous solution in order to control the morphology and phase of the resulting powder. We have prepared a variety of metal, alloy, and metal- and mixed metal-oxide nanoscale powders from appropriate MRM systems. Examples of nanoscale powders produced include Co, Mo-Co, Ni[sub 3]Fe, Ni, and various oxides and oxyhydroxides of iron. Here, we discuss the preparation and characterization of nickel metal (with a nickel oxide surface layer) and iron oxyhydroxide MRM nanoscale powders. We have used extended x-ray absorption fine structure (EXAFS) spectroscopy to study the chemical polymerization process in situ, x-ray diffraction (XRD), scanning and transmission electron microcroscopies (SEM and TEM), elemental analysis and structural modelling to characterize the nanoscale powders produced. The catalytic activity of these powders is currently being studied.« less

Studying Gastric Lipase Adsorption Onto Phospholipid Monolayers by Surface Tensiometry, Ellipsometry, and Atomic Force Microscopy.

PubMed

Bénarouche, A; Sams, L; Bourlieu, C; Vié, V; Point, V; Cavalier, J F; Carrière, F

2017-01-01

The access to kinetic parameters of lipolytic enzyme adsorption onto lipids is essential for a better understanding of the overall catalytic process carried out by these interfacial enzymes. Gastric lipase, for instance, shows an apparent optimum activity on triglycerides (TAG) at acidic pH, which is controlled by its pH-dependent adsorption at lipid-water interfaces. Since gastric lipase acts on TAG droplets covered by phospholipids, but does not hydrolyze these lipids, phospholipid monolayers spread at the air-water interfaces can be used as biomimetic interfaces to study lipase adsorption and penetration through the phospholipid layer, independently from the catalytic activity. The adsorption of recombinant dog gastric lipase (rDGL) onto 1,2-dilauroyl-sn-glycero-3-phosphocholine (DLPC) monolayers can be monitored by surface tensiometry at various enzyme concentrations, pHs, and surface pressures (Π). These experimental data and the use of Langmuir adsorption isotherm and Verger-de Haas' lipase kinetics models further allow estimating various parameters including the adsorption equilibrium constant (K Ads ), the interfacial concentration [Formula: see text] , the molar fraction [Formula: see text] (Φ E*(%) , mol%), and the molecular area [Formula: see text] of rDGL adsorbed onto the DLPC monolayer under various conditions. Additional insight into rDGL adsorption/insertion on phospholipid monolayers can be obtained by combining ellipsometry, Langmuir-Blodgett film transfer, and atomic force microscopy. When using multicomponent phospholipid monolayers with phase separation, these techniques allow to visualizing how rDGL preferentially partitions toward liquid expanded phase and at phase boundaries, gets adsorbed at various levels of insertion and impacts on the lateral organization of lipids. © 2017 Elsevier Inc. All rights reserved.

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.

Constitutive production of catalytic antibodies to a Staphylococcus aureus virulence factor and effect of infection.

PubMed

Brown, Eric L; Nishiyama, Yasuhiro; Dunkle, Jesse W; Aggarwal, Shreya; Planque, Stephanie; Watanabe, Kenji; Csencsits-Smith, Keri; Bowden, M Gabriela; Kaplan, Sheldon L; Paul, Sudhir

2012-03-23

Antibodies that recognize microbial B lymphocyte superantigenic epitopes are produced constitutively with no requirement for adaptive immune maturation. We report cleavage of the Staphylococcus aureus virulence factor extracellular fibrinogen-binding protein (Efb) by catalytic antibodies produced with no exposure to the bacterium and reduction of the catalytic antibody activity following infection. IgG catalytic antibodies that specifically hydrolyzed Efb via a nucleophilic catalytic mechanism were found in the blood of healthy humans and aseptic mice free of S. aureus infection. IgG hydrolyzed peptide bonds on the C-terminal side of basic amino acids, including a bond located within the C3b-binding domain of Efb. Efb digested with the IgG lost its ability to bind C3b and inhibit complement-dependent antibody-mediated red blood cell lysis. In addition to catalysis, the IgG expressed saturable Efb binding activity. IgG from S. aureus-infected mice displayed reduced Efb cleaving activity and increased Efb binding activity compared with uninfected controls, suggesting differing effects of the infection on the antibody subsets responsible for the two activities. IgG from children hospitalized for S. aureus infection also displayed reduced Efb cleavage compared with healthy children. These data suggest a potential defense function for constitutively produced catalytic antibodies to a putative superantigenic site of Efb, but an adaptive catalytic response appears to be proscribed.

Fe-Mn bi-metallic oxides loaded on granular activated carbon to enhance dye removal by catalytic ozonation.

PubMed

Tang, Shoufeng; Yuan, Deling; Zhang, Qi; Liu, Yameng; Zhang, Qi; Liu, Zhengquan; Huang, Haiming

2016-09-01

A Fe-Mn bi-metallic oxide supported on granular activated carbon (Fe-Mn GAC) has been fabricated by an impregnation-desiccation method and tested in the catalytic ozonation of methyl orange (MO) degradation and mineralization. X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy characterizations revealed that Fe-Mn oxides were successfully loaded and uniformly distributed on the GAC, and nitrogen adsorption isotherms showed that the supported GAC retained a large surface area and a high pore volume compared with the pristine GAC. The catalytic activity was systematically assessed by monitoring the MO removal efficiencies at different operational parameters, such as catalyst dosage, initial solution pH, and ozone flow rate. The Fe-Mn GAC exhibited better catalytic activity relative to ozone alone and GAC alone, improving the TOC removal by 24.5 and 11.5 % and COD removal by 13.6 and 7.3 %, respectively. The reusability of the hybrid was examined over five consecutive cyclic treatments. The Fe-Mn GAC catalytic activity was only a slight loss in the cycles, showing good stability. The addition of Na2CO3 as hydroxyl radicals (•OH) scavengers proved that the catalytic ozonation mechanism was the enhanced generation of •OH by the Fe-Mn GAC. The above results render the Fe-Mn GAC an industrially promising candidate for catalytic ozonation of dye contaminant removal.

Development of a Catalytic Coating for a Shuttle Flight Experiment

NASA Technical Reports Server (NTRS)

Stewart, David A.; Goekcen, Tahir; Sepka, Steven E.; Leiser, Daniel B.; Rezin, Marc D.

2010-01-01

A spray-on coating was developed for use on the shuttle wing tiles to obtain data that could be correlated with computational fluid dynamics (CFD) solutions to better understand the effect of chemical heating on a fore-body heat shield having a turbulent boundary layer during planetary entry at hypersonic speed. The selection of a spray-on coating was conducted in two Phases 1) screening tests to select the catalytic coating formulation and 2) surface property determination using both arc-jet and side-arm facilities at NASA Ames Research Center. Comparison of the predicted surface temperature profile over a flat-plate with measured values obtained during arc-jet exposure (Phase I study) was used to validate the surface properties obtained during Phase II.

Performance Testing of the Vapor Phase Catalytic Ammonia Removal Engineering Development Unit

NASA Technical Reports Server (NTRS)

Flynn, Michael; Tleimat, Maher; Nalette, Tim; Quinn, Gregory

2005-01-01

This paper describes the results of performance testing of the Vapor Phase Catalytic Ammonia Removal (VPCAR) technology. The VPCAR technology is currently being developed by NASA as a Mars transit vehicle water recycling system. NASA has recently completed-a grant-to develop a next generation VPCAR system. This grant concluded with the shipment of the final deliverable to NASA on 8/31/03. This paper presents the results of mass, power, volume, and acoustic measurements for the delivered system. Product water purity analysis for a Mars transit mission and a simulated planetary base wastewater ersatz are also provided.

Composition and methods for improved fuel production

DOEpatents

Steele, Philip H.; Tanneru, Sathishkumar; Gajjela, Sanjeev K.

2015-12-29

Certain embodiments of the present invention are configured to produce boiler and transportation fuels. A first phase of the method may include oxidation and/or hyper-acidification of bio-oil to produce an intermediate product. A second phase of the method may include catalytic deoxygenation, esterification, or olefination/esterification of the intermediate product under pressurized syngas. The composition of the resulting product--e.g., a boiler fuel--produced by these methods may be used directly or further upgraded to a transportation fuel. Certain embodiments of the present invention also include catalytic compositions configured for use in the method embodiments.

Selenium/Tellurium-Containing Hyperbranched Polymers: Effect of Molecular Weight and Degree of Branching on Glutathione Peroxidase-Like Activity.

PubMed

Thomas, Joice; Dong, Zeyuan; Dehaen, Wim; Smet, Mario

2012-12-21

A series of novel hyperbranched polyselenides and polytellurides with multiple catalytic sites at the branching units has been synthesized via the polycondensation of A2 + B3 monomers. The GPx-like activities of these polymer mimics were assessed and it was found that the polytellurides showed higher GPx-like activities than the corresponding polyselenides. Interestingly, the polymers with higher molecular weights and degree of branching (DB) showed higher GPx-like activities than the analogous lower molecular weight polymer. The enhancement in the catalytical activity of the hyperbranched polymers with increasing molecular weight affirmed the importance of the incorporation of multiple catalytic groups in the macromolecule which increases the local concentration of catalytic sites. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Perovskite-type catalytic materials for environmental applications.

PubMed

Labhasetwar, Nitin; Saravanan, Govindachetty; Kumar Megarajan, Suresh; Manwar, Nilesh; Khobragade, Rohini; Doggali, Pradeep; Grasset, Fabien

2015-06-01

Perovskites are mixed-metal oxides that are attracting much scientific and application interest owing to their low price, adaptability, and thermal stability, which often depend on bulk and surface characteristics. These materials have been extensively explored for their catalytic, electrical, magnetic, and optical properties. They are promising candidates for the photocatalytic splitting of water and have also been extensively studied for environmental catalysis applications. Oxygen and cation non-stoichiometry can be tailored in a large number of perovskite compositions to achieve the desired catalytic activity, including multifunctional catalytic properties. Despite the extensive uses, the commercial success for this class of perovskite-based catalytic materials has not been achieved for vehicle exhaust emission control or for many other environmental applications. With recent advances in synthesis techniques, including the preparation of supported perovskites, and increasing understanding of promoted substitute perovskite-type materials, there is a growing interest in applied studies of perovskite-type catalytic materials. We have studied a number of perovskites based on Co, Mn, Ru, and Fe and their substituted compositions for their catalytic activity in terms of diesel soot oxidation, three-way catalysis, N 2 O decomposition, low-temperature CO oxidation, oxidation of volatile organic compounds, etc. The enhanced catalytic activity of these materials is attributed mainly to their altered redox properties, the promotional effect of co-ions, and the increased exposure of catalytically active transition metals in certain preparations. The recent lowering of sulfur content in fuel and concerns over the cost and availability of precious metals are responsible for renewed interest in perovskite-type catalysts for environmental applications.

Perovskite-type catalytic materials for environmental applications

PubMed Central

Labhasetwar, Nitin; Saravanan, Govindachetty; Kumar Megarajan, Suresh; Manwar, Nilesh; Khobragade, Rohini; Doggali, Pradeep; Grasset, Fabien

2015-01-01

Perovskites are mixed-metal oxides that are attracting much scientific and application interest owing to their low price, adaptability, and thermal stability, which often depend on bulk and surface characteristics. These materials have been extensively explored for their catalytic, electrical, magnetic, and optical properties. They are promising candidates for the photocatalytic splitting of water and have also been extensively studied for environmental catalysis applications. Oxygen and cation non-stoichiometry can be tailored in a large number of perovskite compositions to achieve the desired catalytic activity, including multifunctional catalytic properties. Despite the extensive uses, the commercial success for this class of perovskite-based catalytic materials has not been achieved for vehicle exhaust emission control or for many other environmental applications. With recent advances in synthesis techniques, including the preparation of supported perovskites, and increasing understanding of promoted substitute perovskite-type materials, there is a growing interest in applied studies of perovskite-type catalytic materials. We have studied a number of perovskites based on Co, Mn, Ru, and Fe and their substituted compositions for their catalytic activity in terms of diesel soot oxidation, three-way catalysis, N2O decomposition, low-temperature CO oxidation, oxidation of volatile organic compounds, etc. The enhanced catalytic activity of these materials is attributed mainly to their altered redox properties, the promotional effect of co-ions, and the increased exposure of catalytically active transition metals in certain preparations. The recent lowering of sulfur content in fuel and concerns over the cost and availability of precious metals are responsible for renewed interest in perovskite-type catalysts for environmental applications. PMID:27877813

Tailoring nanoscopic confines to maximize catalytic activity of hydronium ions

NASA Astrophysics Data System (ADS)

Shi, Hui; Eckstein, Sebastian; Vjunov, Aleksei; Camaioni, Donald M.; Lercher, Johannes A.

2017-05-01

Acid catalysis by hydronium ions is ubiquitous in aqueous-phase organic reactions. Here we show that hydronium ion catalysis, exemplified by intramolecular dehydration of cyclohexanol, is markedly influenced by steric constraints, yielding turnover rates that increase by up to two orders of magnitude in tight confines relative to an aqueous solution of a Brønsted acid. The higher activities in zeolites BEA and FAU than in water are caused by more positive activation entropies that more than offset higher activation enthalpies. The higher activity in zeolite MFI with pores smaller than BEA and FAU is caused by a lower activation enthalpy in the tighter confines that more than offsets a less positive activation entropy. Molecularly sized pores significantly enhance the association between hydronium ions and alcohols in a steric environment resembling the constraints in pockets of enzymes stabilizing active sites.

Catalytic functionalities of supported sulfides. I. Effect of support and additives on the CoMo catalyst

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

Muralidhar, G.; Massoth, F.E.; Shabtai, J.

1984-01-01

C-S hydrogenolysis (HDS) of thiophene, hydrogenation (HYD) of 1-hexene, and hydrocracking (HCG) of 2,4,4-trimethyl-1-pentene, were used as separate model test reactions to differentiate and assess the catalytic functionalities of sulfided CoMo catalysts, and their dependence on the nature of the support and incorporation of additives. Rate constants and relative catalyst activities for these three reaction types were determined. HDS and HYD activities of CoMo supported on different types of Al/sub 2/O/sub 3/ were higher, while the HCG activity was lower compared with CoMo supported on SiO/sub 2/-Al/sub 2/O/sub 3/, SiO/sub 2/-MgO, or TiO/sub 2/. For SiO/sub 2/-Al/sub 2/O/sub 3/ supportsmore » both HDS and HYD activities decreased with increase in SiO/sub 2/ content from 10 to 75%, while HCG activity showed the opposite trend. Additives to a finished CoMo catalyst at 0.5% level caused variations in HDS and HCG activities, while HYD was essentially unaffected. HDS was promoted by NH/sub 4/HF/sub 2/ and NH/sub 4/Cl, but depressed by NaNO/sub 3/, Ca(NO/sub 3/)/sub 2/, and H/sub 3/BO/sub 3/. HCG was promoted by NH/sub 4/HF/sub 2/, NH/sub 4/Cl, and H/sub 3/BO/sub 3/. Additives at 5% level, prior to or after CoMo impregnation, showed a strong depressing effect on HDS and a lesser effect on HYD, while HCG was strongly promoted by NH/sub 4/HF/sub 2/, Ti isopropoxide, and H/sub 3/BO/sub 3/. The changes in catalytic functionalities are rationalized in terms of different interactions between CoMo phase, support, and additives. 3 tables, 1 figure.« less

Charge Transfer and Catalysis at the Metal Support Interface

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

Baker, Lawrence Robert

Kinetic, electronic, and spectroscopic characterization of model Pt–support systems are used to demonstrate the relationship between charge transfer and catalytic activity and selectivity. The results show that charge flow controls the activity and selectivity of supported metal catalysts. This dissertation builds on extensive existing knowledge of metal–support interactions in heterogeneous catalysis. The results show the prominent role of charge transfer at catalytic interfaces to determine catalytic activity and selectivity. Further, this research demonstrates the possibility of selectively driving catalytic chemistry by controlling charge flow and presents solid-state devices and doped supports as novel methods for obtaining electronic control over catalyticmore » reaction kinetics.« less

Enhancement of photoassimilate utilization by manipulation of starch regulatory enzymes

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

Okita, Thomas W.

ADPglucose pyrophosphorylase (AGPase) and the plastidial starch phosphorylase1 (Pho1) are two regulatory enzymes whose catalytic activities are essential for starch granule synthesis. Conversion of the pre-starch granule to the mature form is dependent on AGPase, which produces ADPglucose, the substrate used by starch synthases. The catalytic activity of AGPase is controlled by small effector molecules and a prime goal of this project was to decipher the role of the two subunit types that comprise the heterotetrameric enzyme structure. Extensive genetic and biochemical studies showed that catalysis was contributed mainly by the small subunit although the large subunit was required formore » maximum activity. Both subunits were needed for allosteric regulatory properties. We had also demonstrated that the AGPase catalyzed reaction limits the amount of starch accumulation in developing rice seeds and that carbon flux into rice seed starch can be increased by expression of a cytoplasmic-localized, up-regulated bacterial AGPase enzyme form. Results of subsequent physiological and metabolite studies showed that the AGPase reaction is no longer limiting in the AGPase transgenic rice lines and that one or more downstream processes prevent further increases in starch biosynthesis. Further studies showed that over-production of ADPglucose dramatically alters the gene program during rice seed development. Although the expression of nearly all of the genes are down-regulated, levels of a starch binding domain containing protein (SBDCP) are elevated. This SBDCP was found to bind to and inhibit the catalytic activity of starch synthase III and, thereby preventing maximum starch synthesis from occurring. Surprisingly, repression of SBDCP elevated expression of starch synthase III resulting in increasing rice grain weight. A second phase of this project examined the structure-function of Pho1, the enzyme required during the initial phase of pre-starch granule formation and its maturation to a starch granule. Although Pho1 catalyzes a reversible reaction, our DoE supported studies clearly demonstrated that the kinetic properties of this enzyme strongly favor synthesis of starch and that these catalytic properties are independent of the L80 peptide, a structural domain that is absent in phosphorylases from other organisms. Interesting expression of a Pho1 lacking the L80 peptide enhanced plant growth and seed yields, suggesting that Pho1 has a second function in controlling growth. Overall, results from these biochemical and physiological studies have increased our fundamental understanding on how these important starch regulatory enzymes operate at the molecular level and in planta, which will collectively aid in efforts to increase the utilization of higher plants as a renewable source of energy.« less

The self-healing of defects induced by the hydriding phase transformation in palladium nanoparticles

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

Ulvestad, A.; Yau, A.

Nanosizing can dramatically alter material properties by enhancing surface thermodynamic contributions, shortening diffusion lengths, and increasing the number of catalytically active sites per unit volume. These mechanisms have been used to explain the improved properties of catalysts, battery materials, plasmonic materials, etc. Here we show that Pd nanoparticles also have the ability to self-heal defects in their crystal structures. Using Bragg coherent diffractive imaging, we image dislocations nucleated deep in a Pd nanoparticle during the forward hydriding phase transformation that heal during the reverse transformation, despite the region surrounding the dislocations remaining in the hydrogen-poor phase. We show that defectivemore » Pd nanoparticles exhibit sloped isotherms, indicating that defects act as additional barriers to the phase transformation. Our results resolve the formation and healing of structural defects during phase transformations at the single nanoparticle level and offer an additional perspective as to how and why nanoparticles differ from their bulk counterparts.« less

Selective C-O Hydrogenolysis and Decarboxylation of Biomass-Derived Heterocyclic Compounds over Heterogeneous Catalysts

NASA Astrophysics Data System (ADS)

Chia, Mei

The catalytic deoxygenation of biomass-derived compounds through selective C-O hydrogenolysis, catalytic transfer hydrogenation and lactonization, and decarboxylation to value-added chemicals over heterogeneous catalysts was examined under liquid phase reaction conditions. The reactions studied involve the conversion or production of heterocyclic compounds, specifically, cyclic ethers, lactones, and 2-pyrones. A bimetallic RhRe/C catalyst was found to be selective for the hydrogenolysis of secondary C-O bonds for a broad range cyclic ethers and polyols. Results from experimentally-observed reactivity trends, NH3 temperature-programmed desorption, fructose dehydration reaction studies, and first-principles density functional theory (DFT) calculations are consistent with the hypothesis of a bifunctional catalyst which facilitates acid-catalyzed ring-opening and dehydration coupled with metal-catalyzed hydrogenation. C-O hydrogenolysis and fructose dehydration activities were observed to decrease with an increase in reduction temperature and a decrease in the number of surface metallic Re atoms measured by in situ X-ray absorption spectroscopy. No C-O hydrogenolysis activity was detected over RhRe/C under water-free conditions. The activation of water molecules by Re atoms on the surface of metallic Rh is suggested to result in the formation of Bronsted acidity over RhRe/C. The catalytic transfer hydrogenation and lactonization of levulinic acid and its esters to gamma-valerolactone was accomplished through the Meerwein-Ponndorf-Verley reaction over metal oxide catalysts using secondary alcohols as the hydrogen donor. ZrO2 was a highly active material for CTH under batch and continuous flow reaction conditions; the initial activity of the catalyst was repeatedly regenerable by calcination in air, with no observable loss in catalytic activity. Lastly, the 2-pyrone, triacetic acid lactone, is shown to be a promising biorenewable platform chemical from which a wide range of chemical intermediates and end products can be obtained using heterogeneous catalysts or by thermal decomposition. Mechanistic insights from experimentally-observed reactivity trends and results from DFT calculations indicate that 2-pyrones undergo reactions unique to their structure such as keto-enol tautomerization, retro Diels-Alder, and nucleophilic attack by water. Ring-opening and decarboxylation reactions were found to be governed by key structural features such as the degree of saturation in the ring (e.g., C4=C5 bond), nature of the solvent, and presence of an acid catalyst.

Positional effects of hydroxy groups on catalytic activity of proton-responsive half-sandwich Cp*Iridium(III) complexes

DOE PAGES

Suna, Yuki; Fujita, Etsuko; Ertem, Mehmed Z.; ...

2014-11-12

Proton-responsive half-sandwich Cp*Ir(III) complexes possessing a bipyridine ligand with two hydroxy groups at the 3,3'-, 4,4'-, 5,5'- or 6,6'-positions (3DHBP, 4DHBP, 5DHBP, or 6DHBP) were systematically investigated. UV-vis titration data provided average pK a values of the hydroxy groups on the ligands. Both hydroxy groups were found to deprotonate in the pH 4.6–5.6 range for the 4–6DHBP complexes. One of the hydroxy groups of the 3DHBP complex exhibited the low pK a value of < 0.4 because the deprotonation is facilitated by the strong intramolecular hydrogen bond formed between the generated oxyanion and the remaining hydroxy group, which in turnmore » leads to an elevated pK a value of ~13.6 for the second deprotonation step. The crystal structures of the 4– and 6DHBP complexes obtained from basic aqueous solutions revealed their deprotonated forms. The intramolecular hydrogen bond in the 3DHBP complex was also observed in the crystal structures. The catalytic activities of these complexes in aqueous phase reactions, at appropriate pH, for hydrogenation of carbon dioxide (pH 8.5), dehydrogenation of formic acid (pH 1.8), transfer hydrogenation reactions using formic acid/formate as a hydrogen source (pH 7.2 and 2.6) were investigated to compare the positional effects of the hydroxy groups. The 4– and 6DHBP complexes exhibited remarkably enhanced catalytic activities under basic conditions because of the resonance effect of the strong electrondonating oxyanions, whereas the 5DHBP complex exhibited negligible activity despite the presence of electron-donating groups. The 3DHBP complex exhibited relatively high catalytic activity at low pH owing to the one strong electron-donating oxyanion group stabilized by the intramolecular hydrogen bond. DFT calculations were employed to study the mechanism of CO₂ hydrogenation by the 4DHBP and 6DHBP complexes, and comparison of the activation free energies of the H₂ heterolysis and CO₂ insertion steps indicated that H₂ heterolysis is the rate-determining step for both complexes. The presence of a pendent base in the 6DHBP complex was found to facilitate the rate-determining step, and renders 6DHBP a more effective catalyst for formate production.« less

Catalytic properties of IgMs with amylolytic activity isolated from patients with multiple sclerosis.

PubMed

Ivanen, Dina R; Kulminskaya, Anna A; Shabalin, Konstantin A; Isaeva-Ivanova, Luydmila V; Ershova, Nadezhda A; Saveliev, Andrew N; Nevinsky, Gregory A; Neustroev, Kirill N

2004-08-01

Recently, amylolytic activity was detected in IgMs isolated from the sera of the patients with multiple sclerosis. All purified samples of IgM were electrophoretically homogenous and did not contain any co-purified a-amylase and a-glucosidase activities, in accordance with a set of criteria developed for abzymes. The amylolytic activity of abzymes was studied in the hydrolysis of p-nitrophenyl a-D-maltooligosaccharides with different degrees of polymerization from 1 to 8 by TLC and reverse-phase HPLC techniques. All IgM samples isolated from 54 patients with clinically definite multiple sclerosis demonstrated hydrolytic activity towards the above artificial substrates. The Michaelis constant values (Km) in the hydrolysis of p-nitrophenyl a-D-maltoheptaoside were in the range of 10 p-nitrophenyl or p-nitrophenyl a-D-glucosides, thus indicating the presence of an a-D-glucosidase activity. For a number of the investigated samples, specific amylolytic activity increased depending on the length of substrates (from p-nitrophenyl maltopentaoside to p-nitrophenyl maltohexaoside); for other IgMs, the opposite dependence was observed. All IgMs studied did not exhibit any other glycoside hydrolase activities toward p-nitrophenyl glycoside substrates. Abzyme fractions from different donors demonstrated catalytic heterogeneity in Michaelis-Menten parameters and different modes of action in the hydrolysis of p-nitrophenyl maltooligosaccharides. Enzymatic properties of the IgMs tested varied from human a-amylases. All investigated abzyme samples did not show transglycosylating ability.

Contaminant removal from enclosed atmospheres by regenerable adsorbents

NASA Technical Reports Server (NTRS)

Goldsmith, R. L.; Mcnulty, K. J.; Freedland, G. M.; Turk, A.; Nwankwo, J.

1974-01-01

A system for removing contaminants from spacecraft atmospheres was studied, which utilizes catalyst-impregnated activated carbon followed by in-situ regeneration by low-temperature catalytic oxidation of the adsorbed contaminants. Platinum was deposited on activated carbon by liquid phase impregnation with chloroplatinic acid, followed by drying and high-temperature reduction. Results were obtained for the seven selected spacecraft contaminants by means of three experimental test systems. The results indicate that the contaminants could be removed by oxidation with very little loss in adsorptive capacity. The advantages of a catalyst-impregnated carbon for oxidative regeneration are found to be significant enough to warrent its use.

Polypeptides having xylanase activity and polynucleotides encoding same

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

Spodsberg, Nikolaj; Shaghasi, Tarana

The present invention relates to polypeptides having xylanase activity, catalytic domains, and carbohydrate binding domains, and polynucleotides encoding the polypeptides, catalytic domains, and carbohydrate binding domains. The present invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides, catalytic domains, and carbohydrate binding domains.

Polypeptides having endoglucanase activity and polynucleotides encoding same

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

Spodsberg, Nikolaj; Shagasi, Tarana

The present invention relates to isolated polypeptides having endoglucanase activity, catalytic domains, cellulose binding domains and polynucleotides encoding the polypeptides, catalytic domains or cellulose binding domains. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides, catalytic domains or cellulose binding domains.

Polypeptides having endoglucanase activity and polynucleotides encoding same

DOEpatents

Spodsberg, Nikolaj; Shagasi, Tarana

2015-06-30

The present invention relates to isolated polypeptides having endoglucanase activity, catalytic domains, cellulose binding domains and polynucleotides encoding the polypeptides, catalytic domains or cellulose binding domains. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides, catalytic domains or cellulose binding domains.

Polypeptides having cellobiohydrolase activity and polynucleotides encoding same

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

Stringer, Mary Ann; McBrayer, Brett

2016-11-29

The present invention relates to isolated polypeptides having cellobiohydrolase activity, catalytic domains, and cellulose binding domains and polynucleotides encoding the polypeptides, catalytic domains, and cellulose binding domains. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides, catalytic domains, or cellulose binding domains.

Advanced catalytic combustors for low pollutant emissions, phase 1

NASA Technical Reports Server (NTRS)

Dodds, W. J.

1979-01-01

The feasibility of employing the known attractive and distinguishing features of catalytic combustion technology to reduce nitric oxide emissions from gas turbine engines during subsonic, stratospheric cruise operation was investigated. Six conceptual combustor designs employing catalytic combustion were defined and evaluated for their potential to meet specific emissions and performance goals. Based on these evaluations, two parallel-staged, fixed-geometry designs were identified as the most promising concepts. Additional design studies were conducted to produce detailed preliminary designs of these two combustors. Results indicate that cruise nitric oxide emissions can be reduced by an order of magnitude relative to current technology levels by the use of catalytic combustion. Also, these combustors have the potential for operating over the EPA landing-takeoff cycle and at cruise with a low pressure drop, high combustion efficiency and with a very low overall level of emission pollutants. The use of catalytic combustion, however, requires advanced technology generation in order to obtain the time-temperature catalytic reactor performance and durability required for practical aircraft engine combustors.

Evaluation of a new polymeric stationary phase with reversed-phase properties for high temperature liquid chromatography.

PubMed

Vanhoenacker, Gerd; Dos Santos Pereira, Alberto; Kotsuka, Takashi; Cabooter, Deirdre; Desmet, Gert; Sandra, Pat

2010-05-07

The performance of a polymeric stationary phase with reversed-phase properties (ET-RP1) was evaluated for LC separations at elevated temperature. The most significant observation was that the reduced plate height (h) decreased from 3.4 at 25 degrees C (optimal flow 0.5 mL/min) to 2.4 at 150 degrees C (optimal flow 2.5 mL/min) which is comparable to the efficiency obtained with silica-based reversed-phase columns of 4.6mm ID operated at 0.8 mL/min. The phase showed no deterioration after long use at 150 degrees C within the pH range 1-9. Catalytic activity originating from the stationary phase material, e.g. as experienced on zirconium columns operated at elevated temperature, was absent. The performance of ET-RP1 is illustrated with the analysis of some pharmaceutical samples by LC and LC-MS. Operation at elevated temperature also allows to reduce the amount of organic modifier or to replace acetonitrile and methanol by the biodegradable ethanol. Copyright (c) 2009 Elsevier B.V. All rights reserved.

Probing Conformational Changes of Human DNA Polymerase λ Using Mass Spectrometry-Based Protein Footprinting

PubMed Central

Fowler, Jason D.; Brown, Jessica A.; Kvaratskhelia, Mamuka; Suo, Zucai

2009-01-01

SUMMARY Crystallographic studies of the C-terminal, DNA polymerase β-like domain of human DNA polymerase lambda (fPolλ) suggested that the catalytic cycle might not involve a large protein domain rearrangement as observed with several replicative DNA polymerases and DNA polymerase β. To examine solution-phase protein conformation changes in fPolλ, which also contains a breast cancer susceptibility gene 1 C-terminal domain and a Proline-rich domain at its N-terminus, we used a mass spectrometry - based protein footprinting approach. In parallel experiments, surface accessibility maps for Arg residues were compared for the free fPolλ versus the binary complex of enzyme•gapped DNA and the ternary complex of enzyme•gapped DNA•dNTP. These experiments suggested that fPolλ does not undergo major conformational changes during the catalysis in the solution phase. Furthermore, the mass spectrometry-based protein footprinting experiments revealed that active site residue R386 was shielded from the surface only in the presence of both a gapped DNA substrate and an incoming nucleotide dNTP. Site-directed mutagenesis and pre-steady state kinetic studies confirmed the importance of R386 for the enzyme activity, and indicated the key role for its guanidino group in stabilizing the negative charges of an incoming nucleotide and the leaving pyrophosphate product. We suggest that such interactions could be shared by and important for catalytic functions of other DNA polymerases. PMID:19467241

Structure, bonding, and catalytic activity of monodisperse, transition-metal-substituted CeO2 nanoparticles.

PubMed

Elias, Joseph S; Risch, Marcel; Giordano, Livia; Mansour, Azzam N; Shao-Horn, Yang

2014-12-10

We present a simple and generalizable synthetic route toward phase-pure, monodisperse transition-metal-substituted ceria nanoparticles (M0.1Ce0.9O2-x, M = Mn, Fe, Co, Ni, Cu). The solution-based pyrolysis of a series of heterobimetallic Schiff base complexes ensures a rigorous control of the size, morphology and composition of 3 nm M0.1Ce0.9O2-x crystallites for CO oxidation catalysis and other applications. X-ray absorption spectroscopy confirms the dispersion of aliovalent (M(3+) and M(2+)) transition metal ions into the ceria matrix without the formation of any bulk transition metal oxide phases, while steady-state CO oxidation catalysis reveals an order of magnitude increase in catalytic activity with copper substitution. Density functional calculations of model slabs of these compounds confirm the stabilization of M(3+) and M(2+) in the lattice of CeO2. These results highlight the role of the host CeO2 lattice in stabilizing high oxidation states of aliovalent transition metal dopants that ordinarily would be intractable, such as Cu(3+), as well as demonstrating a rational approach to catalyst design. The current work demonstrates, for the first time, a generalizable approach for the preparation of transition-metal-substituted CeO2 for a broad range of transition metals with unparalleled synthetic control and illustrates that Cu(3+) is implicated in the mechanism for CO oxidation on CuO-CeO2 catalysts.

Exposing high-energy surfaces by rapid-anneal solid phase epitaxy

DOE PAGES

Wang, Y.; Song, Y.; Peng, R.; ...

2017-08-08

The functional design of nanoscale transition metal oxide heterostructures depends critically on the growth of atomically flat epitaxial thin films. Much of the time, improved functionality is expected for heterostructures and surfaces with orientations that do not have the lowest surface free energy. For example, crystal faces with a high surface free energy, such as rutile (001) planes, frequently exhibit higher catalytic activities but are correspondingly harder to synthesize due to energy-lowering faceting transitions. We propose a broadly applicable rapid-anneal solid phase epitaxial synthesis approach for the creation of atomically flat, high surface free energy oxide heterostructures. We also demonstratemore » its efficacy via the synthesis of atomically flat, epitaxial RuO 2(001) films with a superior oxygen evolution activity, quantified by their lower onset potential and higher current density, relative to that of more common RuO 2(110) films.« less

Cordierite-supported metal oxide for non-methane hydrocarbon oxidation in cooking oil fumes.

PubMed

Huang, Yonghai; Yi, Honghong; Tang, Xiaolong; Zhao, Shunzheng; Gao, Fengyu; Wang, Jiangen; Yang, Zhongyu

2018-05-21

Cooking emission is an important reason for the air quality deterioration in the metropolitan area in China. Transition metal oxide and different loading of manganese oxide supported on cordierite were prepared by incipient wetness impregnation method and were used for non-methane hydrocarbon (NMHC) oxidation in cooking oil fumes (COFs). The effects of different calcination temperature and different Mn content were also studied. The SEM photographs and CO 2 temperature-programmed desorption revealed 5 wt% Mn/cordierite had the best pore structure and the largest number of the weak and moderate basic sites so it showed the best performance for NMHC oxidation. XRD analysis exhibited 5 wt% Mn/cordierite had the best dispersion of active phase and the active phase was MnO 2 when the calcination temperature was 400℃ which were good for the catalytic oxidation of NMHC.

Identification of Human UDP-Glucuronosyltransferase 1A4 as the Major Isozyme Responsible for the Glucuronidation of 20(S)-Protopanaxadiol in Human Liver Microsomes

PubMed Central

Li, Jia; He, Chunyong; Fang, Lianxiang; Yang, Li; Wang, Zhengtao

2016-01-01

20(S)-protopanaxadiol (PPD), one of the representative aglycones of ginsenosides, has a broad spectrum of pharmacological activities. Although phase I metabolism has been investigated extensively, information regarding phase II metabolism of this compound remains to be elucidated. Here, a glucuronidated metabolite of PPD in human liver microsomes (HLMs) and rat liver microsomes (RLMs) was unambiguously identified as PPD-3-O-β-d-glucuronide by nuclear magnetic resonance spectroscopy and high resolution mass spectrometry. The chemical inhibition and recombinant human UDP-Glucuronosyltransferase (UGT) isoforms assay showed that the PPD glucuronidation was mainly catalyzed by UGT1A4 in HLM, whereas UGT1A3 showed weak catalytic activity. In conclusion, PPD-3-O-β-d-glucuronide was first identified as the principal glucuronidation metabolite of PPD in HLMs, which was catalyzed by UGT1A4. PMID:27005621

Synthesis of an ultradense forest of vertically aligned triple-walled carbon nanotubes of uniform diameter and length using hollow catalytic nanoparticles.

PubMed

Baliyan, Ankur; Nakajima, Yoshikata; Fukuda, Takahiro; Uchida, Takashi; Hanajiri, Tatsuro; Maekawa, Toru

2014-01-22

It still remains a crucial challenge to actively control carbon nanotube (CNT) structure such as the alignment, area density, diameter, length, chirality, and number of walls. Here, we synthesize an ultradense forest of CNTs of a uniform internal diameter by the plasma-enhanced chemical vapor deposition (PECVD) method using hollow nanoparticles (HNPs) modified with ligand as a catalyst. The diameters of the HNPs and internal cavities in the HNPs are uniform. A monolayer of densely packed HNPs is self-assembled on a silicon substrate by spin coating. HNPs shrink via the collapse of the internal cavities and phase transition from iron oxide to metallic iron in hydrogen plasma during the PECVD process. Agglomeration of catalytic NPs is avoided on account of the shrinkage of the NPs and ligand attached to the NPs. Diffusion of NPs into the substrate, which would inactivate the growth of CNTs, is also avoided on account of the ligand. As a result, an ultradense forest of triple-walled CNTs of a uniform internal diameter is successfully synthesized. The area density of the grown CNTs is as high as 0.6 × 10(12) cm(-2). Finally, the activity of the catalytic NPs and the NP/carbon interactions during the growth process of CNTs are investigated and discussed. We believe that the present approach may make a great contribution to the development of an innovative synthetic method for CNTs with selective properties.

Preparation and characterization of TiO2/HZSM-11 zeolite for photodegradation of dichlorvos in aqueous solution.

PubMed

Gomez, Silvina; Marchena, Candelaria Leal; Pizzio, Luis; Pierella, Liliana

2013-08-15

The TiO2/HZSM-11 materials were synthesized using titanium isopropoxide as a TiO2 precursor and HZSM-11 a medium pore size zeolite with high thermal and chemical resistance as support. The amount of titanium isopropoxide was varied in order to obtain TiO2 concentrations of 3, 10, 20, 30 and 50 wt% in the final material. They were characterized by a series of complementary techniques: X-ray diffraction (XRD), ultraviolet-visible diffuse reflectance spectroscopy (DRS), transmittance Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The surface area of the TiO2/HZSM-11 samples decreased with the increment of TiO2 loading. As result of the increment of the calcination temperature from 450 to 800°C an increase in the size of the anatase crystals was observed. However, the X-ray diffraction patterns of the solids only presented the characteristic peaks of the anatase phase. The catalytic activity of the materials in the photodegradation of Dichlorvos (DDVP) depended on the TiO2 amount the thermal treatment temperature. The sample containing 30% TiO2 calcined at 450°C showed the best catalytic performance and it can be reused without noticeable activity loss during at least four cycles. The catalytic performance was similar to that of the P25 Degussa used as a reference but its separation, recovery and reuse was easier. Copyright © 2013 Elsevier B.V. All rights reserved.

Adjusting the catalytic properties of cobalt ferrite nanoparticles by pulsed laser fragmentation in water with defined energy dose.

PubMed

Waag, Friedrich; Gökce, Bilal; Kalapu, Chakrapani; Bendt, Georg; Salamon, Soma; Landers, Joachim; Hagemann, Ulrich; Heidelmann, Markus; Schulz, Stephan; Wende, Heiko; Hartmann, Nils; Behrens, Malte; Barcikowski, Stephan

2017-10-13

Highly active, structurally disordered CoFe 2 O 4 /CoO electrocatalysts are synthesized by pulsed laser fragmentation in liquid (PLFL) of a commercial CoFe 2 O 4 powder dispersed in water. A partial transformation of the CoFe 2 O 4 educt to CoO is observed and proposed to be a thermal decomposition process induced by the picosecond pulsed laser irradiation. The overpotential in the OER in aqueous alkaline media at 10 mA cm -2 is reduced by 23% compared to the educt down to 0.32 V with a Tafel slope of 71 mV dec -1 . Importantly, the catalytic activity is systematically adjustable by the number of PLFL treatment cycles. The occurrence of thermal melting and decomposition during one PLFL cycle is verified by modelling the laser beam energy distribution within the irradiated colloid volume and comparing the by single particles absorbed part to threshold energies. Thermal decomposition leads to a massive reduction in particle size and crystal transformations towards crystalline CoO and amorphous CoFe 2 O 4 . Subsequently, thermal melting forms multi-phase spherical and network-like particles. Additionally, Fe-based layered double hydroxides at higher process cycle repetitions emerge as a byproduct. The results show that PLFL is a promising method that allows modification of the structural order in oxides and thus access to catalytically interesting materials.

Exchange of active site residues alters substrate specificity in extremely thermostable β-glycosidase from Thermococcus kodakarensis KOD1.

PubMed

Hwa, Kuo Yuan; Subramani, Boopathi; Shen, San-Tai; Lee, Yu-May

2015-09-01

β-Glycosidase from Thermococcus kodakarensis KOD1 is a hyperthermophilic enzyme with β-glucosidase, β-mannosidase, β-fucosidase and β-galactosidase activities. Sequence alignment with other β-glycosidases from hyperthermophilic archaea showed two unique active site residues, Gln77 and Asp206. These residues were represented by Arg and Asp in all other hyperthermophilic β-glycosidases. The two active site residues were mutated to Q77R, D206N and D206Q, to study the role of these unique active site residues in catalytic activity and to alter the substrate specificity to enhance its β-glucosidase activity. The secondary structure analysis of all the mutants showed no change in their structure and exhibited in similar conformation like wild-type as they all existed in dimer form in an SDS-PAGE under non-reducing conditions. Q77R and D206Q affected the catalytic activity of the enzyme whereas the D206N altered the catalytic turn-over rate for glucosidase and mannosidase activities with fucosidase activity remain unchanged. Gln77 is reported to interact with catalytic nucleophile and Asp206 with axial C2-hydroxyl group of substrates. Q77R might have made some changes in three dimensional structure due to its electrostatic effect and lost its catalytic activity. The extended side chains of D206Q is predicted to affect the substrate binding during catalysis. The high-catalytic turn-over rate by D206N for β-glucosidase activity makes it a useful enzyme in cellulose degradation at high temperatures. Copyright © 2015 Elsevier Inc. All rights reserved.

The isothiocyanate class of bioactive nutrients covalently inhibit the MEKK1 protein kinase

PubMed Central

Cross, Janet V; Foss, Frank W; Rady, Joshua M; Macdonald, Timothy L; Templeton, Dennis J

2007-01-01

Background Dietary isothiocyanates (ITCs) are electrophilic compounds that have diverse biological activities including induction of apoptosis and effects on cell cycle. They protect against experimental carcinogenesis in animals, an activity believed to result from the transcriptional induction of "Phase 2" enzymes. The molecular mechanism of action of ITCs is unknown. Since ITCs are electrophiles capable of reacting with sulfhydryl groups on amino acids, we hypothesized that ITCs induce their biological effects through covalent modification of proteins, leading to changes in cell regulatory events. We previously demonstrated that stress-signaling kinase pathways are inhibited by other electrophilic compounds such as menadione. We therefore tested the effects of nutritional ITCs on MEKK1, an upstream regulator of the SAPK/JNK signal transduction pathway. Methods The activity of MEKK1 expressed in cells was monitored using in vitro kinase assays to measure changes in catalytic activity. The activity of endogenous MEKK1, immunopurified from ITC treated and untreated LnCAP cells was also measured by in vitro kinase assay. A novel labeling and affinity reagent for detection of protein modification by ITCs was synthesized and used in competition assays to monitor direct modification of MEKK1 by ITC. Finally, immunoblots with phospho-specific antibodies were used to measure the activity of MAPK protein kinases. Results ITCs inhibited the MEKK1 protein kinase in a manner dependent on a specific cysteine residue in the ATP binding pocket. Inhibition of MEKK1 catalytic activity was due to direct, covalent and irreversible modification of the MEKK1 protein itself. In addition, ITCs inhibited the catalytic activity of endogenous MEKK1. This correlated with inhibition of the downstream target of MEKK1 activity, i.e. the SAPK/JNK kinase. This inhibition was specific to SAPK, as parallel MAPK pathways were unaffected. Conclusion These results demonstrate that MEKK1 is directly modified and inhibited by ITCs, and that this correlates with inhibition of downstream activation of SAPK. These results support the conclusion that ITCs may carry out many of their actions by directly targeting important cell regulatory proteins. PMID:17894894

Improvement of activity and stability of chloroperoxidase by chemical modification

PubMed Central

Liu, Jian-Zhong; Wang, Min

2007-01-01

Background Enzymes show relative instability in solvents or at elevated temperature and lower activity in organic solvent than in water. These limit the industrial applications of enzymes. Results In order to improve the activity and stability of chloroperoxidase, chloroperoxidase was modified by citraconic anhydride, maleic anhydride or phthalic anhydride. The catalytic activities, thermostabilities and organic solvent tolerances of native and modified enzymes were compared. In aqueous buffer, modified chloroperoxidases showed similar Km values and greater catalytic efficiencies kcat/Km for both sulfoxidation and oxidation of phenol compared to native chloroperoxidase. Of these modified chloroperoxidases, citraconic anhydride-modified chloroperoxidase showed the greatest catalytic efficiency in aqueous buffer. These modifications of chloroperoxidase increased their catalytic efficiencies for sulfoxidation by 12%~26% and catalytic efficiencies for phenol oxidation by 7%~53% in aqueous buffer. However, in organic solvent (DMF), modified chloroperoxidases had lower Km values and higher catalytic efficiencies kcat/Km than native chloroperoxidase. These modifications also improved their thermostabilities by 1~2-fold and solvent tolerances of DMF. CD studies show that these modifications did not change the secondary structure of chloroperoxidase. Fluorescence spectra proved that these modifications changed the environment of tryptophan. Conclusion Chemical modification of epsilon-amino groups of lysine residues of chloroperoxidase using citraconic anhydride, maleic anhydride or phthalic anhydride is a simple and powerful method to enhance catalytic properties of enzyme. The improvements of the activity and stability of chloroperoxidase are related to side chain reorientations of aromatics upon both modifications. PMID:17511866

Dimerization Interface of 3-Hydroxyacyl-CoA Dehydrogenase Tunes the Formation of Its Catalytic Intermediate

PubMed Central

Jin, Ying-Hua; Fan, Jun; Sun, Fei

2014-01-01

3-hydroxyacyl-CoA dehydrogenase (HAD, EC 1.1.1.35) is a homodimeric enzyme localized in the mitochondrial matrix, which catalyzes the third step in fatty acid β-oxidation. The crystal structures of human HAD and subsequent complexes with cofactor/substrate enabled better understanding of HAD catalytic mechanism. However, numerous human diseases were found related to mutations at HAD dimerization interface that is away from the catalytic pocket. The role of HAD dimerization in its catalytic activity needs to be elucidated. Here, we solved the crystal structure of Caenorhabditis elegans HAD (cHAD) that is highly conserved to human HAD. Even though the cHAD mutants (R204A, Y209A and R204A/Y209A) with attenuated interactions on the dimerization interface still maintain a dimerization form, their enzymatic activities significantly decrease compared to that of the wild type. Such reduced activities are in consistency with the reduced ratios of the catalytic intermediate formation. Further molecular dynamics simulations results reveal that the alteration of the dimerization interface will increase the fluctuation of a distal region (a.a. 60–80) that plays an important role in the substrate binding. The increased fluctuation decreases the stability of the catalytic intermediate formation, and therefore the enzymatic activity is attenuated. Our study reveals the molecular mechanism about the essential role of the HAD dimerization interface in its catalytic activity via allosteric effects. PMID:24763278

Highly efficient catalytic systems based on Pd-coated microbeads

NASA Astrophysics Data System (ADS)

Lim, Jin Hyun; Cho, Ahyoung; Lee, Seung Hwan; Park, Bumkyo; Kang, Dong Woo; Koo, Chong Min; Yu, Taekyung; Park, Bum Jun

2018-01-01

The efficiency of two prototype catalysis systems using palladium (Pd)-coated microparticles was investigated with regard to the recovery and recyclability of the catalytic particles. One such system was the interface-adsorption method, in which polymer particles coated with Pd nanoparticles strongly and irreversibly attach to the oil-water interface. Due to the irreversible adsorption of the catalytic particles to the interface, particle loss was completely prevented while mixing the aqueous solution and while collecting the products. The other system was based on the magnetic field-associated particle recovery method. The use of polymeric microparticles containing Pd nanoparticles and magnetite nanoparticles accelerated the sedimentation of the particles in the aqueous phase by applying a strong magnetic field, consequently suppressing drainage of the particles from the reactor along the product stream. Upon multiple runs of the catalytic reactions, it was found that conversion does not change significantly, demonstrating the excellent recyclability and performance efficiency in the catalytic processes.

Determining the Catalytic Activity of Transition Metal-Doped TiO2 Nanoparticles Using Surface Spectroscopic Analysis

NASA Astrophysics Data System (ADS)

Yang, Sena; Lee, Hangil

2017-11-01

The modified TiO2 nanoparticles (NPs) to enhance their catalytic activities by doping them with the five transition metals (Cr, Mn, Fe, Co, and Ni) have been investigated using various surface analysis techniques such as scanning electron microscopy (SEM), Raman spectroscopy, scanning transmission X-ray microscopy (STXM), and high-resolution photoemission spectroscopy (HRPES). To compare catalytic activities of these transition metal-doped TiO2 nanoparticles (TM-TiO2) with those of TiO2 NPs, we monitored their performances in the catalytic oxidation of 2-aminothiophenol (2-ATP) by using HRPES and on the oxidation of 2-ATP in aqueous solution by taking electrochemistry (EC) measurements. As a result, we clearly investigate that the increased defect structures induced by the doped transition metal are closely correlated with the enhancement of catalytic activities of TiO2 NPs and confirm that Fe- and Co-doped TiO2 NPs can act as efficient catalysts.

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.

Mutational analysis of polynucleotide phosphorylase from Escherichia coli.

PubMed

Jarrige, Anne; Bréchemier-Baey, Dominique; Mathy, Nathalie; Duché, Ophélie; Portier, Claude

2002-08-16

Polynucleotide phosphorylase (PNPase), a homotrimeric exoribonuclease present in bacteria, is involved in mRNA degradation. In Escherichia coli, expression of this enzyme is autocontrolled at the translational level. We introduced about 30 mutations in the pnp gene by site-directed mutagenesis, most of them in phylogenetically conserved residues, and determined their effects on the three catalytic activities of PNPase, phosphorolysis, polymerisation and phosphate exchange, as well as on the efficiency of translational repression. The data are presented and discussed in the light of the crystallographic structure of PNPase from Streptomyces antibioticus. The results show that both PNPase activity and the presence of the KH and S1 RNA-binding domains are required for autocontrol. Deletions of these RNA-binding domains do not abolish any of the three catalytic activities, indicating that they are contained in a domain independent of the catalytic centre. Moreover, the catalytic centre was located around the tungsten-binding site identified by crystallography. Some mutations affect the three catalytic activities differently, an observation consistent with the presence of different subsites.

Retro-binding thrombin active site inhibitors: identification of an orally active inhibitor of thrombin catalytic activity.

PubMed

Iwanowicz, Edwin J; Kimball, S David; Lin, James; Lau, Wan; Han, W-C; Wang, Tammy C; Roberts, Daniel G M; Schumacher, W A; Ogletree, Martin L; Seiler, Steven M

2002-11-04

A series of retro-binding inhibitors of human alpha-thrombin was prepared to elucidate structure-activity relationships (SAR) and optimize in vivo performance. Compounds 9 and 11, orally active inhibitors of thrombin catalytic activity, were identified to be efficacious in a thrombin-induced lethality model in mice.

A three-nucleotide helix I is sufficient for full activity of a hammerhead ribozyme: advantages of an asymmetric design.

PubMed Central

Tabler, M; Homann, M; Tzortzakaki, S; Sczakiel, G

1994-01-01

Trans-cleaving hammerhead ribozymes with long target-specific antisense sequences flanking the catalytic domain share some features with conventional antisense RNA and are therefore termed 'catalytic antisense RNAs'. Sequences 5' to the catalytic domain form helix I and sequences 3' to it form helix III when complexed with the target RNA. A catalytic antisense RNA of more than 400 nucleotides, and specific for the human immunodeficiency virus type 1 (HIV-1), was systematically truncated within the arm that constituted originally a helix I of 128 base pairs. The resulting ribozymes formed helices I of 13, 8, 5, 3, 2, 1 and 0 nucleotides, respectively, and a helix III of about 280 nucleotides. When their in vitro cleavage activity was compared with the original catalytic antisense RNA, it was found that a helix I of as little as three nucleotides was sufficient for full endonucleolytic activity. The catalytically active constructs inhibited HIV-1 replication about four-fold more effectively than the inactive ones when tested in human cells. A conventional hammerhead ribozyme having helices of just 8 nucleotides on either side failed to cleave the target RNA in vitro when tested under the conditions for catalytic antisense RNA. Cleavage activity could only be detected after heat-treatment of the ribozyme substrate mixture which indicates that hammerhead ribozymes with short arms do not associate as efficiently to the target RNA as catalytic antisense RNA. The requirement of just a three-nucleotide helix I allows simple PCR-based generation strategies for asymmetric hammerhead ribozymes. Advantages of an asymmetric design will be discussed. Images PMID:7937118

Structural and Dynamic Insights into the Mechanism of Allosteric Signal Transmission in ERK2-Mediated MKP3 Activation.

PubMed

Lu, Chang; Liu, Xin; Zhang, Chen-Song; Gong, Haipeng; Wu, Jia-Wei; Wang, Zhi-Xin

2017-11-21

The mitogen-activated protein kinases (MAPKs) are key components of cellular signal transduction pathways, which are down-regulated by the MAPK phosphatases (MKPs). Catalytic activity of the MKPs is controlled both by their ability to recognize selective MAPKs and by allosteric activation upon binding to MAPK substrates. Here, we use a combination of experimental and computational techniques to elucidate the molecular mechanism for the ERK2-induced MKP3 activation. Mutational and kinetic study shows that the 334 FNFM 337 motif in the MKP3 catalytic domain is essential for MKP3-mediated ERK2 inactivation and is responsible for ERK2-mediated MKP3 activation. The long-term molecular dynamics (MD) simulations further reveal a complete dynamic process in which the catalytic domain of MKP3 gradually changes to a conformation that resembles an active MKP catalytic domain over the time scale of the simulation, providing a direct time-dependent observation of allosteric signal transmission in ERK2-induced MKP3 activation.

Understanding Anionic "Ligandless" Palladium Species in the Mizoroki-Heck Reaction.

PubMed

Schroeter, Felix; Strassner, Thomas

2018-05-07

The anionic complex [NBu 4 ][Pd(DMSO)Cl 3 ], as a "ligandless" system, was shown to be an active catalyst in the Mizoroki-Heck coupling of aryl chlorides in the absence of strongly σ-donating ligands. To investigate the experimentally observed influence of halides and the amount of water on the catalytic activity, we employed a combination of experiments and theoretical calculations. The presence of water was shown to be critical for the formation of the active palladium(0) species by oxidation of in situ generated tributylamine. Oxidative addition to an anionic palladium(0) species was found to be the rate-determining step of the catalytic cycle. For the ensuing steps, both neutral and anionic pathways were considered. It was shown that, in the absence of strongly σ-donating neutral ligands, chloride ions stabilize the catalytic intermediates. Therefore, an anionic pathway is preferred, which explains the need for tetrabutylammonium chloride as an additive. The study of the influence of bromide ions on the catalytic activity revealed that the strongly exergonic displacement of the neutral substrates by bromide ions lowers the catalytic activity.

Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution

PubMed Central

Bergmann, Arno; Martinez-Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; de Araújo, Jorge Ferreira; Reier, Tobias; Dau, Holger; Strasser, Peter

2015-01-01

Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co3+/4+ ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions. PMID:26456525

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.

Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution.

PubMed

Bergmann, Arno; Martinez-Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; de Araújo, Jorge Ferreira; Reier, Tobias; Dau, Holger; Strasser, Peter

2015-10-12

Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co(3+/4+) ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides. We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions.

Computational Study of Pincer Iridium Catalytic Systems: C-H, N-H, and C-C Bond Activation and C-C Coupling Reactions

NASA Astrophysics Data System (ADS)

Zhou, Tian

Computational chemistry has achieved vast progress in the last decades in the field, which was considered to be only experimental before. DFT (density functional theory) calculations have been proven to be able to be applied to large systems, while maintaining high accuracy. One of the most important achievements of DFT calculations is in exploring the mechanism of bond activation reactions catalyzed by organometallic complexes. In this dissertation, we discuss DFT studies of several catalytic systems explored in the lab of Professor Alan S. Goldman. Headlines in the work are: (1) (R4PCP)Ir alkane dehydrogenation catalysts are highly selective and different from ( R4POCOP)Ir catalysts, predicting different rate-/selectivity-determining steps; (2) The study of the mechanism for double C-H addition/cyclometalation of phenanthrene or biphenyl by (tBu4PCP)Ir(I) and ( iPr4PCP)Ir illustrates that neutral Ir(III) C-H addition products can undergo a very facile second C-H addition, particularly in the case of sterically less-crowded Ir(I) complexes; (3) (iPr4PCP)Ir pure solid phase catalyst is highly effective in producing high yields of alpha-olefin products, since the activation enthalpy for dehydrogenation is higher than that for isomerization via an allyl pathway; higher temperatures favor the dehydrogenation/isomerization ratio; (4) (PCP)Ir(H)2(N2H4) complex follows a hydrogen transfer mechanism to undergo both dehydrogenation to form N 2 and H2, as well as hydrogen transfer followed by N-N bond cleavage to form NH3, N2, and H2; (5) The key for the catalytic effect of solvent molecule in CO insertion reaction for RMn(CO)5 is hydrogen bond assisted interaction. The basicity of the solvent determines the strength of the hydrogen bond interaction during the catalytic path and determines the catalytic power of the solvent; and (6) Dehydrogenative coupling of unactivated C-H bonds (intermolecular vinyl-vinyl, intramolecular vinyl-benzyl) is catalyzed by precursors of the (iPr4 PCP)Ir fragment. The key step for this mechanism is a Ir(III) vinyl hydride complex undergoing addition of a styrenyl ortho C-H bond to give an Ir(III) metalloindene plus H2.

[New iron-porphyrin/vanadium-substituted polyoxometalate catalyst: synthesis, characterization and catalytic activity].

PubMed

Dong, Xiao-li; Zhang, Zhen-cheng; An, Qing-da; Zhang, Shao-yin; Wang, Shao-jun

2007-12-01

A new kind of iron-porphyrin/vanadium-substituted polyoxometalate coordination compound was synthesized by the ion exchange reaction of FeTTMAPPI and H5PMo10V2o40 in solution. The new catalyst was characterized by IR spectrometry and UV-Vis spectrometry. As an excellent catalyst, its effects on benzene hydroxylation and catalytic capabilities were studied with H2O2 solution as the oxidant. The results indicated that the products contained the conjugated structure of porphyrin and the cage structure of polyoxometalate, the V atom in polyoxometalate is the main centre of catalytic activity, meanwhile the presence of iron-porphyrin could increase its catalytic activity greatly.

A catalytic chiral gel microfluidic reactor assembled via dynamic covalent chemistry† †Electronic supplementary information (ESI) available: Experimental details, additional characterization and catalytic data. See DOI: 10.1039/c5sc00314h Click here for additional data file.

PubMed Central

Liu, Haoliang; Feng, Juan; Chen, Liuping

2015-01-01

A novel dynamic covalent gel strategy is reported to immobilize an asymmetric catalyst within the channels of a microfluidic flow reactor. A layer of a catalytically active Mn–salen dynamic covalent imine gel matrix was coated onto a functionalized capillary. Mn–salen active moiety was incorporated into dynamic covalent imine gel matrix via the reaction of a chiral Mn–salen dialdehyde unit with a tetraamine linker. The catalytic activity of the capillary reactor has been demonstrated in enantioselective kinetic resolution of secondary alcohols. PMID:28706652

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.

Slow ligand-induced conformational switch increases the catalytic rate in Plasmodium falciparum hypoxanthine guanine xanthine phosphoribosyltransferase.

PubMed

Roy, Sourav; Karmakar, Tarak; Prahlada Rao, Vasudeva S; Nagappa, Lakshmeesha K; Balasubramanian, Sundaram; Balaram, Hemalatha

2015-05-01

P. falciparum (Pf) hypoxanthine guanine xanthine phosphoribosyltransferase (HGXPRT) exhibits a unique mechanism of activation where the enzyme switches from a low activity (unactivated) to a high activity (activated) state upon pre-incubation with substrate/products. Xanthine phosphoribosylation by unactivated PfHGXPRT exhibits a lag phase, the duration of which reduces with an increase in concentration of the enzyme or substrate, PRPP·Mg(2+). Activated PfHGXPRT does not display the lag phase and exhibits a ten-fold drop in the Km value for PRPP·Mg(2+). These observations suggest the involvement of ligand-mediated oligomerization and conformational changes in the process of activation. The dipeptide Leu-Lys in the PPi binding site of human and T. gondii HG(X)PRT that facilitates PRPP·Mg(2+) binding by isomerization from trans to cis conformation is conserved in PfHGXPRT. Free energy calculations using the well-tempered metadynamics technique show the ligand-free enzyme to be more stable when this dipeptide is in the trans conformation than in the cis conformation. The high rotational energy barrier observed for the conformational change from experimental and computational studies permits delineation of the activation mechanism.

Metal-organic frameworks: versatile heterogeneous catalysts for efficient catalytic organic transformations.

PubMed

Chughtai, Adeel H; Ahmad, Nazir; Younus, Hussein A; Laypkov, A; Verpoort, Francis

2015-10-07

Novel catalytic materials are highly demanded to perform a variety of catalytic organic reactions. MOFs combine the benefits of heterogeneous catalysis like easy post reaction separation, catalyst reusability, high stability and homogeneous catalysis such as high efficiency, selectivity, controllability and mild reaction conditions. The possible organization of active centers like metallic nodes, organic linkers, and their chemical synthetic functionalization on the nanoscale shows potential to build up MOFs particularly modified for catalytic challenges. In this review, we have summarized the recent research progress in heterogeneous catalysis by MOFs and their catalytic behavior in various organic reactions, highlighting the key features of MOFs as catalysts based on the active sites in the framework. Examples of their post functionalization, inclusion of active guest species and metal nanoparticles have been discussed. Finally, the use of MOFs as catalysts for asymmetric heterogeneous catalysis and stability of MOFs has been presented as separate sections.

A recyclable Au(I) catalyst for selective homocoupling of arylboronic acids: significant enhancement of nano-surface binding for stability and catalytic activity.

PubMed

Zhang, Xin; Zhao, Haitao; Wang, Jianhui

2010-08-01

Au nanoparticles stabilized by polystyrene-co-polymethacrylic acid microspheres (PS-co-PMAA) were prepared and characterized via X-ray diffraction (XRD), and transmission electron microscope (TEM). The Au nanoparticles supported on the microspheres showed highly selective catalytic activity for homo-coupling reactions of arylboronic acids in a system of aryl-halides and arylboronic acids. X-ray photoelectron spectroscopy (XPS) spectra of the catalyst shows large amounts of Au(I) complexes band to the surface of the Au nanoparticles, which contributes to the selective homocoupling of the arylboronic acids. More importantly, this supported Au complex is a highly recyclable catalyst. The supported Au catalyst can be recycled and reused at least 6 times for a phenylboronic acid reactant, whereas the parent complex shows very low catalytic activity for this compound. The high catalytic activity of this material is attributed to: (1) the high surface to volume ratio which leads to more active sites being exposed to reactants; (2) the strong surface binding of the Au nanoparticle to the Au(I) complexes, which enhances both the stability and the catalytic activity of these complexes.

Mössbauer study of Cu1-xZnxFe2O4 catalytic materials

NASA Astrophysics Data System (ADS)

Koleva, K.; Velinov, N.; Tsoncheva, T.; Mitov, I.

2014-04-01

Copper zinc ferrites (Cu1-xZnxFe2O4) with different composition (x = 1; 0.2; 0.5; 0.8) were prepared by conventional thermal method. Formation of well crystallized ferrite phase with cubic structure and crystallites size of about 19.08-24.39 nm was observed by Powder X-ray diffraction and Mössbauer spectroscopy. The ferrite materials were tested as catalysts in methanol decomposition to CO and H2. A strong dependence of the catalytic behaviour of Cu1-xZnxFe2O4 ferrites of their composition and the phase transformations which occurred under the reaction medium was established.

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

Elliott, Douglas C.; Neuenschwander, Gary G.; Hart, Todd R.

Fast pyrolysis of biomass can be used to produce a raw bio-oil product, which can be upgraded by catalytic hydroprocessing to hydrocarbon liquid products. In this study the upgraded products were distilled to recover light naphtha and oils and to produce a distillation resid with useful properties for coker processing and production of renewable, low-sulfur electrode carbon. For this hydroprocessing work, phase separation of the bio-oil was applied as a preparatory step to concentrate the heavier, more phenolic components thus generating a more amenable feedstock for resid production. Low residual oxygen content products were produced by continuous-flow, catalytic hydroprocessing ofmore » the phase separated bio-oil.« less

A combination of directing groups and chiral anion phase-transfer catalysis for enantioselective fluorination of alkenes

PubMed Central

Wu, Jeffrey; Wang, Yi-Ming; Drljevic, Amela; Rauniyar, Vivek; Phipps, Robert J.; Toste, F. Dean

2013-01-01

We report a catalytic enantioselective electrophilic fluorination of alkenes to form tertiary and quaternary C(sp3)-F bonds and generate β-amino- and β-aryl-allylic fluorides. The reaction takes advantage of the ability of chiral phosphate anions to serve as solid–liquid phase transfer catalysts and hydrogen bond with directing groups on the substrate. A variety of heterocyclic, carbocyclic, and acyclic alkenes react with good to excellent yields and high enantioselectivities. Further, we demonstrate a one-pot, tandem dihalogenation–cyclization reaction, using the same catalytic system twice in series, with an analogous electrophilic brominating reagent in the second step. PMID:23922394

Solid state proton and electron mediating membrane and use in catalytic membrane reactors

DOEpatents

White, J.H.; Schwartz, M.; Sammells, A.F.

1998-10-13

This invention provides catalytic proton and electron mediating membranes useful in catalytic reactors. The membranes have an oxidation and a reduction surface and comprise a single-phase mixed metal oxide material of the formula: AB{sub 1{minus}x}B{prime}{sub x}O{sub 3{minus}y} wherein A is selected from Ca, Sr or Ba ions; B is selected from Ce, Tb, Pr, or Th ions; B{prime} is selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Ga, or In ions, or combinations thereof; and x is greater than or equal to 0.02 and less than or equal to 0.5. The membranes can further comprise a catalyst on either the oxidation or reduction surface, or both. Membranes include those which are fabricated by combining powders of metal oxides or metal carbonates of metal A ion, metal B ion and metal B{prime} ion such that the stoichiometric ratio A:B:B{prime} is 1:1{minus}x:x where 0.2{<=}{times}0.5, repeatedly calcining and milling the combined powders until a single-phase material is obtained and pressing and sintering the single phase material to obtain a membrane. 6 figs.

Efficient catalytic decomposition of formic acid for the selective generation of H2 and H/D exchange with a water-soluble rhodium complex in aqueous solution.

PubMed

Fukuzumi, Shunichi; Kobayashi, Takeshi; Suenobu, Tomoyoshi

2008-01-01

Formic acid (HCOOH) decomposes efficiently to afford H2 and CO2 selectively in the presence of a catalytic amount of a water-soluble rhodium aqua complex, [Rh(III)(Cp*)(bpy)(H2O)]2+ (Cp*=pentamethylcyclopentadienyl, bpy=2,2'-bipyridine) in aqueous solution at 298 K. No CO was produced in this catalytic decomposition of HCOOH. The decomposition rate reached a maximum value at pH 3.8. No deterioration of the catalyst was observed during the catalytic decomposition of HCOOH, and the catalytic activity remained the same for the repeated addition of HCOOH. The rhodium-hydride complex was detected as the catalytic active species that undergoes efficient H/D exchange with water. When the catalytic decomposition of HCOOH was performed in D2O, D2 was produced selectively. Such an efficient H/D exchange and the observation of a deuterium kinetic isotope effect in the catalytic decomposition of DCOOH in H2O provide valuable mechanistic insight into this efficient and selective decomposition process.

Investigations into the development of catalytic activity in anti-acetylcholinesterase idiotypic and anti-idiotypic antibodies.

PubMed

Johnson, Glynis; Moore, Samuel W

2009-01-01

We have previously described anti-acetylcholinesterase antibodies that display acetylcholinesterase-like catalytic activity. No evidence of contaminating enzymes was found, and the antibodies are kinetically and apparently structurally distinct from both acetylcholinesterase (AChE) and butyrylcholinesterase. We have also mimicked the antibody catalytic sites in anti-anti-idiotypic (Ab3) antibodies. Independently from us, similar acetylcholinesterase-like antibodies have been raised as anti-idiotypic (Ab2) antibodies against a non-catalytic anti-acetylcholinesterase antibody, AE-2. In this paper, we describe an epitope analysis, using synthetic peptides in ELISA and competition ELISA, and a peptide array, of five catalytic anti-acetylcholinesterase antibodies (Ab1s), three catalytic Ab3s, as well as antibody AE-2 and a non-catalytic Ab2. The catalytic Ab1s and Ab3s recognized three Pro- and Gly-containing sequences ((40)PPMGPRRFL, (78)PGFEGTE, and (258)PPGGTGGNDTELVAC) on the AChE surface. As these sequences do not adjoin in the AChE structure, recognition would appear to be due to cross-reaction. This was confirmed by the observation that the sequences superimpose structurally. The non-catalytic antibodies, AE-2 and the Ab2, recognized AChE's peripheral anionic site (PAS), in particular, the sequence (70)YQYVD, which contains two of the site's residues. The crystal structure of the AChE tetramer (Bourne et al., 1999) shows direct interaction and high complementarity between the (257)CPPGGTGGNDTELVAC sequence and the PAS. Antibodies recognizing the sequence and the PAS may, in turn, be complementary; this may account for the apparent paradox of catalytic development in both Ab1s and Ab2s. The PAS binds, but does not hydrolyze, substrate. The catalytic Ab1s, therefore, recognize a site that may function as a substrate analog, and this, together with the presence of an Arg-Glu salt bridge in the epitope, suggests mechanisms whereby catalytic activity may have developed. In conclusion, the development of AChE-like catalytic activity in anti-AChE Ab1s and Ab2s appears to be the result of a combination of structural complementarity to a substrate-binding site, charge complementarity to a salt bridge, and specific structural peculiarities of the AChE molecule. Copyright 2008 John Wiley & Sons, Ltd.

Enhanced catalytic activity through the tuning of micropore environment and supercritical CO2 processing: Al(porphyrin)-based porous organic polymers for the degradation of a nerve agent simulant.

PubMed

Totten, Ryan K; Kim, Ye-Seong; Weston, Mitchell H; Farha, Omar K; Hupp, Joseph T; Nguyen, SonBinh T

2013-08-14

An Al(porphyrin) functionalized with a large axial ligand was incorporated into a porous organic polymer (POP) using a cobalt-catalyzed acetylene trimerization strategy. Removal of the axial ligand afforded a microporous POP that is catalytically active in the methanolysis of a nerve agent simulant. Supercritical CO2 processing of the POP dramatically increased the pore size and volume, allowing for significantly higher catalytic activities.

Molecular Evolution of Human PON to Design Enhanced Catalytic Efficiency for Hydrolysis of Nerve Agents

DTIC Science & Technology

2011-12-01

8   C.   Catalytic activity of evolved variants with GA ................................................................. 11   D...several variants of rePON1 with enhanced activity towards a racemic mixture of CMP-Coumarin by screening ‘neutral drift’ libraries of rePON1 (e.g. 1G3, 2G9...22. The most active variant was 3B3, which had ~250-fold higher catalytic efficiency (kcat/Km 20x106 M-1min-1) compared to the wild-type-like

Alcohol conversion

DOEpatents

Wachs, Israel E.; Cai, Yeping

2002-01-01

Preparing an aldehyde from an alcohol by contacting the alcohol in the presence of oxygen with a catalyst prepared by contacting an intimate mixture containing metal oxide support particles and particles of a catalytically active metal oxide from Groups VA, VIA, or VIIA, with a gaseous stream containing an alcohol to cause metal oxide from the discrete catalytically active metal oxide particles to migrate to the metal oxide support particles and to form a monolayer of catalytically active metal oxide on said metal oxide support particles.

Ethanol dehydrogenation on copper catalysts with ytterbium stabilized tetragonal ZrO2 support

NASA Astrophysics Data System (ADS)

Chuklina, S. G.; Pylinina, A. I.; Podzorova, L. I.; Mikhailina, N. A.; Mikhalenko, I. I.

2016-12-01

The physicochemical and catalytic properties of Cu-containing crystalline zirconia, obtained via sol-gel synthesis in the presence of Yb3+ ions and polyvinylpyrrolidone, are studied. DTG/DSC, TEM, XRD and BET methods are used to analyze the crystallization, texture, phase uniformity, surface and porosity of ZrO2 nanopowders. It is shown that increasing the copper content (1, 3, and 5 wt % from ZrO2) raises the dehydrogenation activity in the temperature range of 100-400°C and lowers the activation energy of acetaldehyde formation. It is found that the activity of all Cu/ t-ZrO2 catalysts grows under the effects of the reaction medium, due to the migration and redispersion of copper.

Intramolecular proton shuttle supports not only catalytic but also noncatalytic function of carbonic anhydrase II

PubMed Central

Becker, Holger M.; Klier, Michael; Schüler, Christina; McKenna, Robert; Deitmer, Joachim W.

2011-01-01

Carbonic anhydrases (CAs) catalyze the reversible hydration of CO2 to HCO3− and H+. The rate-limiting step in this reaction is the shuttle of protons between the catalytic center of the enzyme and the bulk solution. In carbonic anhydrase II (CAII), the fastest and most wide-spread isoform, this H+ shuttle is facilitated by the side chain of His64, whereas CA isoforms such as carbonic anhydrase III (CAIII), which lack such a shuttle, have only low catalytic activity in vitro. By using heterologous protein expression in Xenopus oocytes, we tested the role of this intramolecular H+ shuttle on CA activity in an intact cell. The data revealed that CAIII, shown in vitro to have ∼1,000-fold reduced activity as compared with CAII, displays significant catalytic activity in the intact cell. Furthermore, we tested the hypothesis that the H+ shuttle in CAII itself can facilitate transport activity of the monocarboxylate transporters 1 and 4 (MCT1/4) independent of catalytic activity. Our results show that His64 is essential for the enhancement of lactate transport via MCT1/4, because a mutation of this residue to alanine (CAII-H64A) abolishes the CAII-induced increase in MCT1/4 activity. However, injection of 4-methylimidazole, which acts as an exogenous H+ donor/acceptor, can restore the ability of CAII-H64A to enhance transport activity of MCT1/4. These findings support the hypothesis that the H+ shuttle in CAII not only facilitates CAII catalytic activity but also can enhance activity of acid-/base-transporting proteins such as MCT1/4 in a direct, noncatalytic manner, possibly by acting as an “H+-collecting antenna.” PMID:21282642

Effect of high-temperature on the swellable organically-modified silica (SOMS) and its application to gas-phase hydrodechlorination of trichloroethylene

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

Sohn, Hyuntae; Celik, Gokhan; Gunduz, Seval

Pd catalysts supported on swellable organically-modified silica (SOMS) and high-temperature-treated swellable organically-modified silica (H-SOMS) were characterized and tested for gas-phase hydrodechlorination (HDC) of trichloroethylene (TCE) conditions. The high-temperature treatment on SOMS resulted in an increase in surface area and pore diameter as well as significant improvement of Pd dispersion on H-SOMS with smaller Pd particle sizes compared to the Pd/SOMS catalyst. Although the high-temperature treatment led to some alteration of the SOMS polysiloxane network, the hydrophobicity and organic vapor adsorption characteristics of SOMS were preserved. The reduction and oxidation characteristics of Pd on SOMS and HSOMS were investigated in situmore » using XANES technique. It was found that the Pd sites in the pores of SOMS was accessible to small molecules such as H 2, facilitating the reduction of PdO x, whereas oxidation of metallic Pd was limited even at higher temperatures when O 2 was used. This effect was only observed over Pd/SOMS catalyst. For Pd/H-SOMS, because the pores were more widely open than Pd/SOMS, both reduction and oxidation of Pd were observed. Finally, the catalytic activity of Pd/H-SOMS for gas-phase HDC of TCE was significantly better than Pd/SOMS. When water was added to the reactant stream (TCE + H 2O), both Pd/SOMS and Pd/H-SOMS maintained its catalytic performances due to hydrophobic property of the supports.« less

Template-Mediated Ni(II) Dispersion in Mesoporous SiO2 for Preparation of Highly Dispersed Ni Catalysts: Influence of Template Type.

PubMed

Ning, Xin; Lu, Yiyuan; Fu, Heyun; Wan, Haiqin; Xu, Zhaoyi; Zheng, Shourong

2017-06-07

Supported Ni catalysts on three mesoporous SiO 2 supports (i.e., SBA-15, MCM-41, and HMS) were prepared using a solid-state reaction between Ni(NO 3 ) 2 and organic template-occluded mesoporous SiO 2 . For comparison, supported Ni catalysts on mesoporous SiO 2 synthesized by the conventional impregnation method were also included. The catalysts were characterized by scanning electron microscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, N 2 adsorption, X-ray photoelectron spectroscopy, H 2 temperature-programmed reduction, transmission electron microscopy, and transmission electron microscopy-energy-dispersive X-ray. The catalytic properties of the catalysts were evaluated using gas-phase catalytic hydrodechlorination of 1,2-dichloroethane. The results showed that upon grinding Ni(NO 3 ) 2 with template-occluded mesoporous SiO 2 , strong coordination between Ni 2+ and dodecylamine was identified in the Ni(NO 3 ) 2 -HMS system. Additionally, the results of H 2 temperature-programmed reduction revealed that NiO in calcined NiO/HMS was reduced at higher temperature than those in calcined NiO/SBA-15 and NiO/MCM-41, reflecting the presence of a strong interaction between NiO and mesoporous SiO 2 in NiO/HMS. Consistently, the average particle sizes of metallic Ni were found to be 2.7, 3.4, and 9.6 nm in H 2 -reduced Ni/HMS, Ni/SBA-15, and Ni/MCM-41, respectively, indicative of a much higher Ni dispersion in Ni/HMS. For the catalytic hydrodechlorination of 1,2-dichloroethane, Ni/MCM-41 synthesized by the solid-state reaction method exhibited a catalytic activity similar to that prepared by the impregnation method, while higher catalytic activities were observed on Ni/HMS and Ni/SBA-15 than on their counterparts prepared by the impregnation method. Furthermore, a higher conversion was identified on Ni/HMS than on Ni/SBA-15 and Ni/MCM-41, highlighting the importance of template type for the preparation of highly dispersed metal catalysts on mesoporous SiO 2 .

Investigation of the Fusarium virguliforme Transcriptomes Induced during Infection of Soybean Roots Suggests that Enzymes with Hydrolytic Activities Could Play a Major Role in Root Necrosis

PubMed Central

Sahu, Binod B.; Baumbach, Jordan L.; Singh, Prashant; Srivastava, Subodh K.; Yi, Xiaoping

2017-01-01

Sudden death syndrome (SDS) is caused by the fungal pathogen, Fusarium virguliforme, and is a major threat to soybean production in North America. There are two major components of this disease: (i) root necrosis and (ii) foliar SDS. Root symptoms consist of root necrosis with vascular discoloration. Foliar SDS is characterized by interveinal chlorosis and leaf necrosis, and in severe cases by flower and pod abscission. A major toxin involved in initiating foliar SDS has been identified. Nothing is known about how root necrosis develops. In order to unravel the mechanisms used by the pathogen to cause root necrosis, the transcriptome of the pathogen in infected soybean root tissues of a susceptible cultivar, ‘Essex’, was investigated. The transcriptomes of the germinating conidia and mycelia were also examined. Of the 14,845 predicted F. virguliforme genes, we observed that 12,017 (81%) were expressed in germinating conidia and 12,208 (82%) in mycelia and 10,626 (72%) in infected soybean roots. Of the 10,626 genes induced in infected roots, 224 were transcribed only following infection. Expression of several infection-induced genes encoding enzymes with oxidation-reduction properties suggests that degradation of antimicrobial compounds such as the phytoalexin, glyceollin, could be important in early stages of the root tissue infection. Enzymes with hydrolytic and catalytic activities could play an important role in establishing the necrotrophic phase. The expression of a large number of genes encoding enzymes with catalytic and hydrolytic activities during the late infection stages suggests that cell wall degradation could be involved in root necrosis and the establishment of the necrotrophic phase in this pathogen. PMID:28095498

Solvent effects in acid-catalyzed dehydration of the Diels-Alder cycloadduct between 2,5-dimethylfuran and maleic anhydride

NASA Astrophysics Data System (ADS)

Salavati-fard, Taha; Caratzoulas, Stavros; Doren, Douglas J.

2017-03-01

Dehydration of the cycloadduct produced from the Diels-Alder reaction between 2,5-dimethylfuran and maleic anhydride to 3,6-dimethylphthalic anhydride exemplifies an important step in producing platform chemicals from biomass. The mechanisms of dehydration and catalytic effects of Lewis and Brønsted acids are investigated with density functional theory. The uncatalyzed reaction has a very high activation barrier (68.7 kcal/mol) in the gas phase and it is not significantly affected by solvation. With a Lewis acid catalyst, modeled as an alkali ion, the activation barriers are reduced, but intermediates are also stabilized. The net effect in vacuum is that the energetic span, or apparent activation energy of the catalytic cycle, is 77.9 kcal/mol, even higher than the barrier in the uncatalyzed case. In solution, however, the energetic span is reduced by as much as 20 kcal/mol, due to differences in the solvation energy of the transition states and intermediates. In the case of a Brønsted acid catalyst, modeled as a proton, the gas phase transition state energies are reduced even more than in the Lewis acid case, and there is no strong stabilization of the intermediates. The energetic span in vacuum is only 13.8 kcal/mol and is reduced even further in solution. Brønsted acid catalysis appears to be the preferred mechanism for dehydration of this cycloadduct. Since the Diels-Alder reaction that produced the molecule has previously been shown to be catalyzed by Brønsted acids, this suggests that a single catalyst could be used to accelerate both steps.

Investigation of the Fusarium virguliforme Transcriptomes Induced during Infection of Soybean Roots Suggests that Enzymes with Hydrolytic Activities Could Play a Major Role in Root Necrosis.

PubMed

Sahu, Binod B; Baumbach, Jordan L; Singh, Prashant; Srivastava, Subodh K; Yi, Xiaoping; Bhattacharyya, Madan K

2017-01-01

Sudden death syndrome (SDS) is caused by the fungal pathogen, Fusarium virguliforme, and is a major threat to soybean production in North America. There are two major components of this disease: (i) root necrosis and (ii) foliar SDS. Root symptoms consist of root necrosis with vascular discoloration. Foliar SDS is characterized by interveinal chlorosis and leaf necrosis, and in severe cases by flower and pod abscission. A major toxin involved in initiating foliar SDS has been identified. Nothing is known about how root necrosis develops. In order to unravel the mechanisms used by the pathogen to cause root necrosis, the transcriptome of the pathogen in infected soybean root tissues of a susceptible cultivar, 'Essex', was investigated. The transcriptomes of the germinating conidia and mycelia were also examined. Of the 14,845 predicted F. virguliforme genes, we observed that 12,017 (81%) were expressed in germinating conidia and 12,208 (82%) in mycelia and 10,626 (72%) in infected soybean roots. Of the 10,626 genes induced in infected roots, 224 were transcribed only following infection. Expression of several infection-induced genes encoding enzymes with oxidation-reduction properties suggests that degradation of antimicrobial compounds such as the phytoalexin, glyceollin, could be important in early stages of the root tissue infection. Enzymes with hydrolytic and catalytic activities could play an important role in establishing the necrotrophic phase. The expression of a large number of genes encoding enzymes with catalytic and hydrolytic activities during the late infection stages suggests that cell wall degradation could be involved in root necrosis and the establishment of the necrotrophic phase in this pathogen.

Phase control synthesis of α, β and α/β Bi2O3 hetero-junction with enhanced and synergistic photocatalytic activity on degradation of toxic dye, Rhodamine-B under natural sunlight.

PubMed

Bera, Kamal Kanti; Majumdar, Rituparna; Chakraborty, Malay; Bhattacharya, Swapan Kumar

2018-06-15

Nano particles of a few α/β Bi 2 O 3 hetero-junctions of various compositions synthesized by one- pot hydrothermal method, exhibit exceptional and synergistic photo-catalytic activity for the degradation of Rhodamine-B in aqueous solution under natural sunlight. Pure α and pure β Bi 2 O 3 are also synthesized by control post heating of synthesized hetero-junction. The nano-materials were characterized by diffraction (XRD), microscopic and spectroscopic techniques. The XRD reveals α-β phase hetero-junctions of Bi 2 O 3 are made of α-Bi 2 O 3 and β-Bi 2 O 3 with average dimensions within 13-113 and 5-71 nm respectively and having band gap range of 2.4- 2.9 eV. The spectrophotometrically determined % degradation of the dye and associated rate constant on the best hetero-junction are increased by 4.5(/2.1) and 3.3(/1.2) times than these on pure α (/β). The effects of operational parameters and trapping agents have been analyzed. The maximum removal of the dye was achieved up to 99.6% in 3 h using 0.5 g/L photo-catalyst at pH 3. The reusability test shows that the photo-catalytic activity is retained excellently due to change in chemical nature of the catalyst from α -Bi 2 O 3 to β-Bi 2 O 3, Bi 2 O 2 CO 3 and BiOCl. A suitable mechanism is proposed. Copyright © 2018 Elsevier B.V. All rights reserved.

Methods of increasing secretion of polypeptides having biological activity

DOEpatents

Merino, Sandra

2014-05-27

The present invention relates to methods for producing a secreted polypeptide having biological activity, comprising: (a) transforming a fungal host cell with a fusion protein construct encoding a fusion protein, which comprises: (i) a first polynucleotide encoding a signal peptide; (ii) a second polynucleotide encoding at least a catalytic domain of an endoglucanase or a portion thereof; and (iii) a third polynucleotide encoding at least a catalytic domain of a polypeptide having biological activity; wherein the signal peptide and at least the catalytic domain of the endoglucanase increases secretion of the polypeptide having biological activity compared to the absence of at least the catalytic domain of the endoglucanase; (b) cultivating the transformed fungal host cell under conditions suitable for production of the fusion protein; and (c) recovering the fusion protein, a component thereof, or a combination thereof, having biological activity, from the cultivation medium.

Methods of increasing secretion of polypeptides having biological activity

DOEpatents

Merino, Sandra

2014-10-28

The present invention relates to methods for producing a secreted polypeptide having biological activity, comprising: (a) transforming a fungal host cell with a fusion protein construct encoding a fusion protein, which comprises: (i) a first polynucleotide encoding a signal peptide; (ii) a second polynucleotide encoding at least a catalytic domain of an endoglucanase or a portion thereof; and (iii) a third polynucleotide encoding at least a catalytic domain of a polypeptide having biological activity; wherein the signal peptide and at least the catalytic domain of the endoglucanase increases secretion of the polypeptide having biological activity compared to the absence of at least the catalytic domain of the endoglucanase; (b) cultivating the transformed fungal host cell under conditions suitable for production of the fusion protein; and (c) recovering the fusion protein, a component thereof, or a combination thereof, having biological activity, from the cultivation medium.

Methods of increasing secretion of polypeptides having biological activity

DOEpatents

Merino, Sandra

2015-04-14

The present invention relates to methods for producing a secreted polypeptide having biological activity, comprising: (a) transforming a fungal host cell with a fusion protein construct encoding a fusion protein, which comprises: (i) a first polynucleotide encoding a signal peptide; (ii) a second polynucleotide encoding at least a catalytic domain of an endoglucanase or a portion thereof; and (iii) a third polynucleotide encoding at least a catalytic domain of a polypeptide having biological activity; wherein the signal peptide and at least the catalytic domain of the endoglucanase increases secretion of the polypeptide having biological activity compared to the absence of at least the catalytic domain of the endoglucanase; (b) cultivating the transformed fungal host cell under conditions suitable for production of the fusion protein; and (c) recovering the fusion protein, a component thereof, or a combination thereof, having biological activity, from the cultivation medium.

Methods of increasing secretion of polypeptides having biological activity

DOEpatents

Merino, Sandra

2013-10-01

The present invention relates to methods for producing a secreted polypeptide having biological activity, comprising: (a) transforming a fungal host cell with a fusion protein construct encoding a fusion protein, which comprises: (i) a first polynucleotide encoding a signal peptide; (ii) a second polynucleotide encoding at least a catalytic domain of an endoglucanase or a portion thereof; and (iii) a third polynucleotide encoding at least a catalytic domain of a polypeptide having biological activity; wherein the signal peptide and at least the catalytic domain of the endoglucanase increases secretion of the polypeptide having biological activity compared to the absence of at least the catalytic domain of the endoglucanase; (b) cultivating the transformed fungal host cell under conditions suitable for production of the fusion protein; and (c) recovering the fusion protein, a component thereof, or a combination thereof, having biological activity, from the cultivation medium.

Fabrication of bismuth ferrite based hybrid nanostructures: Insight into a catalytic and sensing properties for the detection of biomolecules

NASA Astrophysics Data System (ADS)

Bharathkumar, S.; Sakar, M.; Balakumar, S.

2018-04-01

We made an attempt to construct a photocatalytic and biosensor platform by using bismuth ferrite (BiFeO3/BFO) particulates and fibers nanostructures towards the degradation of dye and electrochemical sensing of ascorbic acid. The crystal phase and morphology of the BFO nanostructures were confirmed using XRD and FESEM respectively. Further, their photocatalytic activity was tested under sunlight. The BFO fibers showed relatively an enhanced degradation property and an efficient electrochemical sensing property compared to the Particulates.

Effect of preparation procedures on catalytic activity and selectivity of copper-based mixed oxides in selective catalytic oxidation of ammonia into nitrogen and water vapour

NASA Astrophysics Data System (ADS)

Jabłońska, Magdalena; Nocuń, Marek; Gołąbek, Kinga; Palkovits, Regina

2017-11-01

The selective oxidation of ammonia into nitrogen and water vapour (NH3-SCO) was studied over Cu-Mg(Zn)-Al-(Zr) mixed metal oxides, obtained by coprecipitation and their subsequent calcination. The effect of acid-base properties of Cu-Mg-Al-Ox on catalytic activity was investigated by changing the Mg/Al molar ratio. Other Cu-containing oxides were prepared by rehydration of calcined Mg-Al hydrotalcite-like compounds or thermal decomposition of metal nitrate precursors. XRD, BET, NH3-TPD, H2-TPR, XPS, FTIR with adsorption of pyridine and CO as well as TEM techniques were used for catalysts characterization. The results of catalytic tests revealed a crucial role of easily reducible highly dispersed copper oxide species to obtain enhanced activity and N2 selectivity in NH3-SCO. The selective catalytic reduction of NO by NH3 (NH3-SCR) and in situ DRIFT of NH3 sorption indicated that NH3-SCO proceeds according to the internal selective catalytic reduction mechanism (i-SCR).

ZIF-67 incorporated with carbon derived from pomelo peels: A highly efficient bifunctional catalyst for oxygen reduction/evolution reactions

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

Wang, Hao; Yin, Feng-Xiang; Chen, Biao-Hua

Developing carbon catalyst materials using natural, abundant and renewable resources as precursors plays an increasingly important role in clean energy generation and environmental protection. In this work, N-doped pomelo-peel-derived carbon (NPC) materials were prepared using a widely available food waste-pomelo peels and melamine. The synthetic NPC exhibits well-defined porosities and a highly doped-N content (e.g. 6.38 at% for NPC-2), therefore affords excellent oxygen reduction reaction (ORR) catalytic activities in alkaline electrolytes. NPC was further integrated with ZIF-67 to form ZIF-67@NPC hybrids through solvothermal reactions. The hybrid catalysts show substantially enhanced ORR catalytic activities comparable to that of commercial 20 wamore » Pt/C. Furthermore, the catalysts also exhibit excellent oxygen evolution reaction (OER) catalytic activities. Among all prepared ZIF-67@NPC hybrids, the optimal composition with ZIF-67 to NPC ratio of 2:1 exhibits the best ORR and OER bifunctional catalytic performance and the smallest Delta E (E-OER@10 mA cm(-2)-E-ORR@-1 mA cm(-2)) value of 0.79 V. The catalyst also demonstrated desirable 4-electron transfer pathways and superior catalytic stabilities. The Co-N-4 in ZIF-67, electrochemical active surface area, and the strong interactions between ZIF-67 and NPC are attributed as the main contributors to the bifunctional catalytic activities. These factors act synergistically, resulting in substantially enhanced bifunctional catalytic activities and stabilities; consequently, this hybrid catalyst is among the best of the reported bifunctional electrocatalysts and is promising for use in metal-air batteries and fuel cells. (C) 2016 Elsevier B.V. All rights reserved.« less

Catalytic propane dehydrogenation over In₂O₃–Ga₂O₃ mixed oxides

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

Tan, Shuai; Gil, Laura Briones; Subramanian, Nachal

2015-08-26

We have investigated the catalytic performance of novel In₂O₃–Ga₂O₃ mixed oxides synthesized by the alcoholic-coprecipitation method for propane dehydrogenation (PDH). Reactivity measurements reveal that the activities of In₂O₃–Ga₂O₃ catalysts are 1–3-fold (on an active metal basis) and 12–28-fold (on a surface area basis) higher than an In₂O₃–Al₂O₃ catalyst in terms of C₃H₈ conversion. The structure, composition, and surface properties of the In₂O₃–Ga₂O₃ catalysts are thoroughly characterized. NH₃-TPD shows that the binary oxide system generates more acid sites than the corresponding single-component catalysts. Raman spectroscopy suggests that catalysts that produce coke of a more graphitic nature suppress cracking reactions, leading tomore » higher C₃H₆ selectivity. Lower reaction temperature also leads to higher C₃H₆ selectivity by slowing down the rate of side reactions. XRD, XPS, and XANES measurements, strongly suggest that metallic indium and In₂O₃ clusters are formed on the catalyst surface during the reaction. The agglomeration of In₂O₃ domains and formation of a metallic indium phase are found to be irreversible under O₂ or H₂ treatment conditions used here, and may be responsible for loss of activity with increasing time on stream.« less

Order-disorder transitions in lattice gases with annealed reactive constraints

NASA Astrophysics Data System (ADS)

Dudka, Maxym; Bénichou, Olivier; Oshanin, Gleb

2018-04-01

We study equilibrium properties of catalytically-activated reactions taking place on a lattice of adsorption sites. The particles undergo continuous exchanges with a reservoir maintained at a constant chemical potential μ and react when they appear at the neighbouring sites, provided that some reactive conditions are fulfilled. We model the latter in two different ways: in the Model I some fraction p of the bonds connecting neighbouring sites possesses special catalytic properties such that any two As appearing on the sites connected by such a bond instantaneously react and desorb. In the Model II some fraction p of the adsorption sites possesses such properties and neighbouring particles react if at least one of them resides on a catalytic site. For the case of annealed disorder in the distribution of the catalyst, which is tantamount to the situation when the reaction may take place at any point on the lattice but happens with a finite probability p, we provide an exact solution for both models for the interior of an infinitely large Cayley tree—the so-called Bethe lattice. We show that both models exhibit a rich critical behaviour: for the annealed Model I it is characterised by a transition into an ordered state and a re-entrant transition into a disordered phase, which both are continuous. For the annealed Model II, which represents a rather exotic model of statistical mechanics in which interactions of any particle with its environment have a peculiar Boolean form, the transition to an ordered state is always continuous, while the re-entrant transition into the disordered phase may be either continuous or discontinuous, depending on the value of p.

One-step microwave-assisted colloidal synthesis of hybrid silver oxide/silver nanoparticles: characterization and catalytic study

NASA Astrophysics Data System (ADS)

Prakoso, S. P.; Taufik, A.; Saleh, R.

2017-04-01

This study reports the characterization and catalytic activities of silver-oxide/silver nanoparticles (Ag2O/Ag NPs) synthesized by microwave-assisted colloidal method in the presence of anionic sodium dodecyl sulfate (SDS) surfactant. To promote different contents of silver in silver oxide, the volume ratio (VR) of ethylene glycol (EG) was varied (VR: 10% to 14%) in relation to the total volume of distilled water solvent. The plasmonic resonance of Ag2O/Ag NPs could be detected around a wavelength of 350 nm, and it is suggested that Ag2O/Ag NPs were successfully formed in the colloid solution following exposure to microwaves. Additionally, the growth rate for each crystal phase within Ag2O and Ag was influenced by an increase of EG as revealed by x-ray diffraction patterns. The morphology, average diameter, and uniformity of Ag2O/Ag NPs were studied simultaneously by transmission electron microscopy. Infrared absorption measurement of Ag2O/Ag NPs confirmed the existence of SDS surfactant as a protective agent. Based on the characterization data, Ag2O/Ag NPs synthesized using this technique exhibited good properties, with high-yield production of NPs. The photocatalytic experiments demonstrate the key role of the crystal phase of Ag2O/Ag NPs in photocatalytic efficiency.

Roles of human POLD1 and POLD3 in genome stability

PubMed Central

Tumini, Emanuela; Barroso, Sonia; -Calero, Carmen Pérez; Aguilera, Andrés

2016-01-01

DNA replication is essential for cellular proliferation. If improperly controlled it can constitute a major source of genome instability, frequently associated with cancer and aging. POLD1 is the catalytic subunit and POLD3 is an accessory subunit of the replicative Pol δ polymerase, which also functions in DNA repair, as well as the translesion synthesis polymerase Pol ζ, whose catalytic subunit is REV3L. In cells depleted of POLD1 or POLD3 we found a differential but general increase in genome instability as manifested by DNA breaks, S-phase progression impairment and chromosome abnormalities. Importantly, we showed that both proteins are needed to maintain the proper amount of active replication origins and that POLD3-depletion causes anaphase bridges accumulation. In addition, POLD3-associated DNA damage showed to be dependent on RNA-DNA hybrids pointing toward an additional and specific role of this subunit in genome stability. Interestingly, a similar increase in RNA-DNA hybrids-dependent genome instability was observed in REV3L-depleted cells. Our findings demonstrate a key role of POLD1 and POLD3 in genome stability and S-phase progression revealing RNA-DNA hybrids-dependent effects for POLD3 that might be partly due to its Pol ζ interaction. PMID:27974823

Extended vapor-liquid-solid growth of silicon carbide nanowires.

PubMed

Rajesh, John Anthuvan; Pandurangan, Arumugam

2014-04-01

We developed an alloy catalytic method to explain extended vapor-liquid-solid (VLS) growth of silicon carbide nanowires (SiC NWs) by a simple thermal evaporation of silicon and activated carbon mixture using lanthanum nickel (LaNi5) alloy as catalyst in a chemical vapor deposition process. The LaNi5 alloy binary phase diagram and the phase relationships in the La-Ni-Si ternary system were play a key role to determine the growth parameters in this VLS mechanism. Different reaction temperatures (1300, 1350 and 1400 degrees C) were applied to prove the established growth process by experimentally. Scanning electron microscopy and transmission electron microscopy studies show that the crystalline quality of the SiC NWs increases with the temperature at which they have been synthesized. La-Ni alloyed catalyst particles observed on the top of the SiC NWs confirms that the growth process follows this extended VLS mechanism. The X-ray diffraction and confocal Raman spectroscopy analyses demonstrate that the crystalline structure of the SiC NWs was zinc blende 3C-SiC. Optical property of the SiC NWs was investigated by photoluminescence technique at room temperature. Such a new alloy catalytic method may be extended to synthesis other one-dimensional nanostructures.

Structure-activity correlations in a nickel-borate oxygen evolution catalyst.

PubMed

Bediako, D Kwabena; Lassalle-Kaiser, Benedikt; Surendranath, Yogesh; Yano, Junko; Yachandra, Vittal K; Nocera, Daniel G

2012-04-18

An oxygen evolution catalyst that forms as a thin film from Ni(aq)(2+) solutions containing borate electrolyte (Ni-B(i)) has been studied by in situ X-ray absorption spectroscopy. A dramatic increase in catalytic rate, induced by anodic activation of the electrodeposited films, is accompanied by structure and oxidation state changes. Coulometric measurements correlated with X-ray absorption near-edge structure spectra of the active catalyst show that the nickel centers in activated films possess an average oxidation state of +3.6, indicating that a substantial proportion of nickel centers exist in a formal oxidation state of Ni(IV). In contrast, nickel centers in nonactivated films exist predominantly as Ni(III). Extended X-ray absorption fine structure reveals that activated catalyst films comprise bis-oxo/hydroxo-bridged nickel centers organized into sheets of edge-sharing NiO(6) octahedra. Diminished long-range ordering in catalyst films is due to their ostensibly amorphous nature. Nonactivated films display a similar oxidic nature but exhibit a distortion in the local coordination geometry about nickel centers, characteristic of Jahn-Teller distorted Ni(III) centers. Our findings indicate that the increase in catalytic activity of films is accompanied by changes in oxidation state and structure that are reminiscent of those observed for conversion of β-NiOOH to γ-NiOOH and consequently challenge the long-held notion that the β-NiOOH phase is a more efficient oxygen-evolving catalyst. © 2012 American Chemical Society

Enzymatic and antisense effects of a specific anti-Ki-ras ribozyme in vitro and in cell culture.

PubMed Central

Giannini, C D; Roth, W K; Piiper, A; Zeuzem, S

1999-01-01

Due to their mode of action, ribozymes show antisense effects in addition to their specific cleavage activity. In the present study we investigated whether a hammerhead ribozyme is capable of cleaving mutated Ki-ras mRNA in a pancreatic carcinoma cell line and whether antisense effects contribute to the activity of the ribozyme. A 2[prime]-O-allyl modified hammerhead ribozyme was designed to cleave specifically the mutated form of the Ki- ras mRNA (GUU motif in codon 12). The activity was monitored by RT-PCR on Ki- ras RNA expression by determination of the relative amount of wild type to mutant Ki-ras mRNA, by 5-bromo-2[prime]-deoxy-uridine incorporation on cell proliferation and by colony formation in soft agar on malignancy in the human pancreatic adenocarcinoma cell line CFPAC-1, which is heterozygous for the Ki-ras mutation. A catalytically inactive ribozyme was used as control to differentiate between antisense and cleavage activity and a ribozyme with random guide sequences as negative control. The catalytically active anti-Ki-ras ribozyme was at least 2-fold more potent in decreasing cellular Ki-ras mRNA levels, inhibiting cell proliferation and colony formation in soft agar than the catalytically inactive ribozyme. The catalytically active anti-Ki-ras ribozyme, but not the catalytically inactive or random ribozyme, increased the ratio of wild type to mutated Ki-ras mRNA in CFPAC-1 cells. In conclusion, both cleavage activity and antisense effects contribute to the activity of the catalytically active anti-Ki-ras hammerhead ribozyme. Specific ribozymes might be useful in the treatment of pancreatic carcinomas containing an oncogenic GTT mutation in codon 12 of the Ki-ras gene. PMID:10373591

A Facile synthesis of superparamagnetic Fe3O4 nanofibers with superior peroxidase-like catalytic activity for sensitive colorimetric detection of L-cysteine

NASA Astrophysics Data System (ADS)

Chen, Sihui; Chi, Maoqiang; Zhu, Yun; Gao, Mu; Wang, Ce; Lu, Xiaofeng

2018-05-01

Superaramagnetic Fe3O4 nanomaterials are good candidates as enzyme mimics due to their excellent catalytic activity, high stability and facile synthesis. However, the morphology of Fe3O4 nanomaterials has much influence on their enzyme-like catalytic activity. In this work, we have developed a simple polymer-assisted thermochemical reduction approach to prepare Fe3O4 nanofibers for peroxidase-like catalytic applications. The as-prepared Fe3O4 nanofibers show a higher catalytic activity than commercial Fe3O4 nanoparticles. The steady-state kinetic assay result shows that the Michaelis-Menten constant value of the as-obtained Fe3O4 nanofibers is similar to that of horseradish peroxidase (HRP), indicating their superior affinity to the 3,3‧,5,5‧-tetramethylbenzidine (TMB) and H2O2 substrate. Based on the outstanding catalytic activity, a sensing platform for the detection of L-cysteine has been performed and the limit of detection is as low as 0.028 μM. In addition, an excellent selectivity toward L-cysteine over other types of amino acids, glucose and metal ions has been achieved as well. This work offers an original means for the fabrication of superparamagnetic Fe3O4 nanofibers and demonstrates their delightful potential applications in the fields of biosensing, environmental monitoring, and medical diagnostics.

Cell Cycle Regulates Nuclear Stability of AID and Determines the Cellular Response to AID

PubMed Central

Le, Quy; Maizels, Nancy

2015-01-01

AID (Activation Induced Deaminase) deaminates cytosines in DNA to initiate immunoglobulin gene diversification and to reprogram CpG methylation in early development. AID is potentially highly mutagenic, and it causes genomic instability evident as translocations in B cell malignancies. Here we show that AID is cell cycle regulated. By high content screening microscopy, we demonstrate that AID undergoes nuclear degradation more slowly in G1 phase than in S or G2-M phase, and that mutations that affect regulatory phosphorylation or catalytic activity can alter AID stability and abundance. We directly test the role of cell cycle regulation by fusing AID to tags that destabilize nuclear protein outside of G1 or S-G2/M phases. We show that enforced nuclear localization of AID in G1 phase accelerates somatic hypermutation and class switch recombination, and is well-tolerated; while nuclear AID compromises viability in S-G2/M phase cells. We identify AID derivatives that accelerate somatic hypermutation with minimal impact on viability, which will be useful tools for engineering genes and proteins by iterative mutagenesis and selection. Our results further suggest that use of cell cycle tags to regulate nuclear stability may be generally applicable to studying DNA repair and to engineering the genome. PMID:26355458

Bimetallic Cu-Ni nanoparticles supported on activated carbon for catalytic oxidation of benzyl alcohol

NASA Astrophysics Data System (ADS)

Kimi, Melody; Jaidie, Mohd Muazmil Hadi; Pang, Suh Cem

2018-01-01

A series of bimetallic copper-nickel (CuNix, x = 0.1, 0.2, 0.5 and 1) nanoparticles supported on activated carbon (AC) were prepared by deposition-precipitation method for the oxidation of benzyl alcohol to benzaldehyde using hydrogen peroxide as oxidising agent. Analyses by means of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) confirmed that Cu and Ni was successfully added on the surface of activated carbon. CuNi1/AC showed the best catalytic activity for the oxidation of benzyl alcohols to the corresponding aldehyde within a short reaction period at 80 °C. The catalytic performance is significantly enhanced by the addition of equal amount of Ni as compared to the monometallic counterpart. This result indicates the synergistic effect between Ni and Cu particles in the catalytic oxidation reaction.

Mechanistic Studies on the Copper-Catalyzed N-Arylation of Amides

PubMed Central

Strieter, Eric R.; Bhayana, Brijesh; Buchwald, Stephen L.

2009-01-01

The copper-catalyzed N-arylation of amides, i.e., the Goldberg reaction, is an efficient method for the construction of products relevant to both industry and academic settings. Herein, we present mechanistic details concerning the catalytic and stoichiometric N-arylation of amides. In the context of the catalytic reaction, our findings reveal the importance of chelating diamine ligands in controlling the concentration of the active catalytic species. The consistency between the catalytic and stoichiometric results suggest that the activation of aryl halides occurs through a 1,2-diamine-ligated copper(I) amidate complex. Kinetic studies on the stoichiometric N-arylation of aryl iodides using 1,2-diamine ligated Cu(I) amidates also provide insights into the mechanism of aryl halide activation. PMID:19072233

Scanning mass spectrometer for quantitative reaction studies on catalytically active microstructures.

PubMed

Roos, M; Kielbassa, S; Schirling, C; Häring, T; Bansmann, J; Behm, R J

2007-08-01

We describe an apparatus for spatially resolving scanning mass spectrometry which is able to measure the gas composition above catalytically active microstructures or arrays of these microstructures with a lateral resolution of better than 100 mum under reaction conditions and which allows us to quantitatively determine reaction rates on individual microstructures. Measurements of the three-dimensional gas composition at different vertical distances and separations between active structures allow the evaluation of gas phase mass transport effects. The system is based on a piezoelectrically driven positioning substage for controlled lateral and vertical positioning of the sample under a rigidly mounted capillary probe connecting to a mass spectrometer. Measurements can be performed at pressures in the range of <10(-2)-10 mbars and temperatures between room temperature and 450 degrees C. The performance of the setup is demonstrated using the CO oxidation reaction on Pt microstructures on Si with sizes between 100 and 300 mum and distances in the same order of magnitude, evaluating CO(2) formation and CO consumption above the microstructures. The rapidly decaying lateral resolution with increasing distance between sample and probe underlines the effects of (lateral) gas transport in the room between sample and probe. The reaction rates and apparent activation energy obtained from such measurements agree with previous data on extended surfaces, demonstrating the feasibility of determining absolute reaction rates on individual microstructures.

Production, purification, and characterization of an extracellular acid protease from the marine Antarctic yeast Rhodotorula mucilaginosa L7.

PubMed

Lario, Luciana Daniela; Chaud, Luciana; Almeida, María das Graças; Converti, Attilio; Durães Sette, Lara; Pessoa, Adalberto

2015-11-01

The production, purification, and characterization of an extracellular protease released by Rhodotorula mucilaginosa L7 were evaluated in this study. This strain was isolated from an Antarctic marine alga and previously selected among others based on the capacity to produce the highest extracellular proteolytic activity in preliminary tests. R. mucilaginosa L7 was grown in Saboraud-dextrose medium at 25 °C, and the cell growth, pH of the medium, extracellular protease production and the glucose and protein consumption were determined as a function of time. The protease was then purified, and the effects of pH, temperature, and salt concentration on the catalytic activity and enzyme stability were determined. Enzyme production started at the beginning of the exponential phase of growth and reached a maximum after 48 h, which was accompanied by a decrease in the pH as well as reductions of the protein and glucose concentrations in the medium. The purified protease presented optimal catalytic activity at pH 5.0 and 50 °C. Finally, the enzyme was stable in the presence of high concentrations of NaCl. These characteristics are of interest for future studies and may lead to potential biotechnological applications that require enzyme activity and stability under acidic conditions and/or high salt concentrations. Copyright © 2015 The British Mycological Society. Published by Elsevier Ltd. All rights reserved.

Regulation of accumulation of ammonium-inducible glutamate dehydrogenase catalytic activity and antigen during the cell cycle of fully induced, synchronous Chlorella sorokiniana cells.

PubMed

Yeung, A T; Bascomb, N F; Turner, K J; Schmidt, R R

1981-05-01

By use of a rocket immunoelectrophoresis-activity stain procedure, it was shown that catalytic activity of an ammonium-inducible nicotinamide adenine dinucleotide phosphate-specific glutamate dehydrogenase (NADP-GDH) was accompanied by a coincident increase in enzyme antigen during the cell cycle of preinduced synchronous Chlorella sorokiniana cells growing in the continuous presence of ammonia. Between the fourth and fifth hours of the G-1 phase of the cell cycle, a three- to fourfold increase in linear accumulation of enzyme antigen was observed. Pulse-chase studies with [35S]sulfate, coupled with a specific indirect immunoadsorption procedure for enzyme antigen, showed that NADP-GDH antigen undergoes continuous degradation (i.e., a half-life of 88 to 110 min) during its linear pattern of accumulation during the cell cycle. The apparent half-life of the enzyme increased by approximately 23% of the 4.5-h positive rate change in antigen accumulation during the cell cycle. This increase in half-life is insufficient in itself to account for the large change in rate of NADP-GDH antigen accumulation. The data from immunoelectrophoresis, pulse-chase, and initial 35S incorporation rate experiments taken together support the inference that changes in the rate of NADP-GDH synthesis are primarily responsible for the accumulation patterns of NADP-GDH activity during the C. sorokiniana cell cycle.

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

An Assessment of the Technical Readiness of the Vapor Phase Catalytic Ammonia Removal Process (VPCAR) Technology

NASA Technical Reports Server (NTRS)

Flynn, Michael

2000-01-01

This poster provides an assessment of the technical readiness of the Vapor Phase Catalytic Ammonia Removal Process (VPCAR). The VPCAR technology is a fully regenerative water recycling technology designed specifically for applications such as a near term Mars exploration mission. The VPCAR technology is a highly integrated distillation/catalytic oxidation based water processor. It is designed to accept a combined wastewater stream (urine, condensate, and hygiene) and produces potable water in a single process step which requires -no regularly scheduled re-supply or maintenance for a 3 year mission. The technology is designed to be modular and to fit into a volume comparable to a single International Space Station Rack (when sized for a crew of 6). This poster provides a description of the VPCAR technology and a summary of the current performance of the technology. Also provided are the results of two separate NASA sponsored system trade studies which investigated the potential payback of further development of the VPCAR technology.

Vacuum distillation: vapor filtered-catalytic oxidation water reclamation system utilizing radioisotopes

NASA Technical Reports Server (NTRS)

Honegger, R. J.; Remus, G. A.; Kurg, E. K.

1971-01-01

The development of a functional model water reclamation system is discussed. The system produces potable water by distillation from the urine and respiration-perspiration condensate at the normal rate generated by four men. Basic processes employed are vacuum distillation, vapor filtration, vapor phase catalytic oxidation, and condensation. The system is designed to use four 75-watt isotope heaters for distillation thermal input, and one 45-watt isotope for the catalytic oxidation unit. The system is capable of collecting and storing urine, and provides for stabilizing the urine by chemical pretreatment. The functional model system is designed for operation in a weightless condition with liquid-vapor phase separators for the evaporator still, and centrifugal separators for urine collection and vapor condensation. The system provides for storing and dispensing reclaimed potable water. The system operates in a batch mode for 40 days, with urine residues accumulating in the evaporator. The evaporator still and residue are removed to storage and replaced with a fresh still for the next 40-day period.

Reversible Regulation of Catalytic Activity of Gold Nanoparticles with DNA Nanomachines

NASA Astrophysics Data System (ADS)

Zhou, Peipei; Jia, Sisi; Pan, Dun; Wang, Lihua; Gao, Jimin; Lu, Jianxin; Shi, Jiye; Tang, Zisheng; Liu, Huajie

2015-09-01

Reversible catalysis regulation has gained much attention and traditional strategies utilized reversible ligand coordination for switching catalyst’s conformations. However, it remains challenging to regulate the catalytic activity of metal nanoparticle-based catalysts. Herein, we report a new DNA nanomachine-driven reversible nano-shield strategy for circumventing this problem. The basic idea is based on the fact that the conformational change of surface-attached DNA nanomachines will cause the variation of the exposed surface active area on metal nanoparticles. As a proof-of-concept study, we immobilized G-rich DNA strands on gold nanoparticles (AuNPs) which have glucose oxidase (GOx) like activity. Through the reversible conformational change of the G-rich DNA between a flexible single-stranded form and a compact G-quadruplex form, the catalytic activity of AuNPs has been regulated reversibly for several cycles. This strategy is reliable and robust, which demonstrated the possibility of reversibly adjusting catalytic activity with external surface coverage switching, rather than coordination interactions.

Probing active cocaine vaccination performance through catalytic and noncatalytic hapten design.

PubMed

Cai, Xiaoqing; Whitfield, Timothy; Hixon, Mark S; Grant, Yanabel; Koob, George F; Janda, Kim D

2013-05-09

Presently, there are no FDA-approved medications to treat cocaine addiction. Active vaccination has emerged as one approach to intervene through the rapid sequestering of the circulating drug, thus terminating both psychoactive effects and drug toxicity. Herein, we report our efforts examining two complementary, but mechanistically distinct active vaccines, i.e., noncatalytic and catalytic, for cocaine treatment. A cocaine-like hapten GNE and a cocaine transition-state analogue GNT were used to generate the active vaccines, respectively. GNE-KLH (keyhole limpet hemocyannin) was found to elicit persistent high-titer, cocaine-specific antibodies and blunt cocaine-induced locomotor behaviors. Catalytic antibodies induced by GNT-KLH were also shown to produce potent titers and suppress locomotor response in mice; however, upon repeated cocaine challenges, the vaccine's protecting effects waned. In depth kinetic analysis suggested that loss of catalytic activity was due to antibody modification by cocaine. The work provides new insights for the development of active vaccines for the treatment of cocaine abuse.

Probing Active Cocaine Vaccination Performance through Catalytic and Noncatalytic Hapten Design

PubMed Central

Cai, Xiaoqing; Whitfield, Timothy; Hixon, Mark S.; Grant, Yanabel; Koob, George F.; Janda, Kim D.

2013-01-01

Presently, there are no FDA-approved medications to treat cocaine addiction. Active vaccination has emerged as one approach to intervene through the rapid sequestering of the circulating drug, thus terminating both psychoactive effects and drug toxicity. Herein, we report our efforts examining two complimentary, but mechanistically distinct active vaccines, i.e., noncatalytic and catalytic, for cocaine treatment. A cocaine-like hapten GNE and a cocaine transition-state analogue GNT were used to generate the active vaccines, respectively. GNE-KLH was found to elicit persistent high-titer, cocaine-specific antibodies, and blunt cocaine induced locomotor behaviors. Catalytic antibodies induced by GNT-KLH were also shown to produce potent titers and suppress locomotor response in mice; however, upon repeated cocaine challenges the vaccine’s protecting effects waned. In depth kinetic analysis suggested that loss of catalytic activity was due to antibody modification by cocaine. The work provides new insights for the development of active vaccines for the treatment of cocaine abuse. PMID:23627877