Investigating the performance of catalyst layer micro-structures with different platinum loadings

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

Khakaz-Baboli, Moben; Harvey, David; Pharoah, Jon

In this study a four-phase micro-structure of a PEFC catalyst layer was reconstructed by randomly placing overlapping spheres for each solid catalyst phase. The micro-structure was mirrored to make a micro-structure. A body-fit computational mesh was produced for the reconstructed micro-structure in OpenFOAM. Associated conservation equations were solved within all the phases with electrochemical reaction as the boundary condition at the interface between ionomer and platinum phases. The study is focused on the platinum loading of CL. The polarization curves of the micro-structure performance have been compared for different platinum loadings. This paper gives increased insight into the relatively greatermore » losses at decreased platinum loadings.« less

Improved process for generating ClF/sub 3/ from ClF and F/sub 2/

DOEpatents

Reiner, R.H.; Pashley, J.H.; Barber, E.J.

The invention is an improvement in the process for producing gaseous ClF/sub 3/ by reacting ClF and F/sub 2/ at elevated temperature. The improved process comprises conducting the reaction in the presence of NiF/sub 2/, which preferably is in the form of particles or in the form of a film or layer on a particulate substrate. The nickel fluoride acts as a reaction catalyst, significantly increasing the reaction rate and thus permitting valuable reductions in process temperature, pressure, and/or reactor volume.

Degradation forecast for PEMFC cathode-catalysts under cyclic loads

NASA Astrophysics Data System (ADS)

Moein-Jahromi, M.; Kermani, M. J.; Movahed, S.

2017-08-01

Degradation of Fuel Cell (FC) components under cyclic loads is one of the biggest bottlenecks in FC commercialization. In this paper, a novel experimental based algorithm is presented to predict the Catalyst Layer (CL) performance loss during cyclic load. The algorithm consists of two models namely Models 1 and 2. The Model 1 calculates the Electro-Chemical Surface Area (ECSA) and agglomerate size (e.g. agglomerate radius, rt,agg) for the catalyst layer under cyclic load. The Model 2 is the already-existing model from our earlier studies that computes catalyst performance with fixed structural parameters. Combinations of these two Models predict the CL performance under an arbitrary cyclic load. A set of parametric/sensitivity studies is performed to investigate the effects of operating parameters on the percentage of Voltage Degradation Rate (VDR%) with rank 1 for the most influential one. Amongst the considered parameters (such as: temperature, relative humidity, pressure, minimum and maximum voltage of the cyclic load), the results show that temperature and pressure have the most and the least influences on the VDR%, respectively. So that, increase of temperature from 60 °C to 80 °C leads to over 20% VDR intensification, the VDR will also reduce 1.41% by increasing pressure from 2 atm to 4 atm.

Platinum Assisted Vapor–Liquid–Solid Growth of Er–Si Nanowires and Their Optical Properties

PubMed Central

2010-01-01

We report the optical activation of erbium coated silicon nanowires (Er–SiNWs) grown with the assist of platinum (Pt) and gold (Au), respectively. The NWs were grown on Si substrates by using a chemical vapor transport process using SiCl4 and ErCl4 as precursors. Pt as well as Au worked successfully as vapor–liquid–solid (VLS) catalysts for growing SiNWs with diameters of ~100 nm and length of several micrometers, respectively. The SiNWs have core–shell structures where the Er-crystalline layer is sandwiched between silica layers. Photoluminescence spectra analyses showed the optical activity of SiNWs from both Pt and Au. A stronger Er3+ luminescence of 1,534 nm was observed from the SiNWs with Pt at room- and low-temperature (25 K) using the 488- and/or 477-nm line of an Ar laser that may be due to the uniform incorporation of more Er ions into NWs with the exclusion of the formation of catalyst-induced deep levels in the band-gap. Pt would be used as a VLS catalyst for high performance optically active Er–SiNWs. PMID:20672113

Platinum assisted vapor-liquid-solid growth of er-si nanowires and their optical properties.

PubMed

Kim, Myoung-Ha; Kim, Il-Soo; Park, Yong-Hee; Park, Tae-Eon; Shin, Jung H; Choi, Heon-Jin

2009-11-14

We report the optical activation of erbium coated silicon nanowires (Er-SiNWs) grown with the assist of platinum (Pt) and gold (Au), respectively. The NWs were grown on Si substrates by using a chemical vapor transport process using SiCl4 and ErCl4 as precursors. Pt as well as Au worked successfully as vapor-liquid-solid (VLS) catalysts for growing SiNWs with diameters of ~100 nm and length of several micrometers, respectively. The SiNWs have core-shell structures where the Er-crystalline layer is sandwiched between silica layers. Photoluminescence spectra analyses showed the optical activity of SiNWs from both Pt and Au. A stronger Er3+ luminescence of 1,534 nm was observed from the SiNWs with Pt at room- and low-temperature (25 K) using the 488- and/or 477-nm line of an Ar laser that may be due to the uniform incorporation of more Er ions into NWs with the exclusion of the formation of catalyst-induced deep levels in the band-gap. Pt would be used as a VLS catalyst for high performance optically active Er-SiNWs.

Platinum Assisted Vapor-Liquid-Solid Growth of Er-Si Nanowires and Their Optical Properties

NASA Astrophysics Data System (ADS)

Kim, Myoung-Ha; Kim, Il-Soo; Park, Yong-Hee; Park, Tae-Eon; Shin, Jung H.; Choi, Heon-Jin

2010-02-01

We report the optical activation of erbium coated silicon nanowires (Er-SiNWs) grown with the assist of platinum (Pt) and gold (Au), respectively. The NWs were grown on Si substrates by using a chemical vapor transport process using SiCl4 and ErCl4 as precursors. Pt as well as Au worked successfully as vapor-liquid-solid (VLS) catalysts for growing SiNWs with diameters of ~100 nm and length of several micrometers, respectively. The SiNWs have core-shell structures where the Er-crystalline layer is sandwiched between silica layers. Photoluminescence spectra analyses showed the optical activity of SiNWs from both Pt and Au. A stronger Er3+ luminescence of 1,534 nm was observed from the SiNWs with Pt at room- and low-temperature (25 K) using the 488- and/or 477-nm line of an Ar laser that may be due to the uniform incorporation of more Er ions into NWs with the exclusion of the formation of catalyst-induced deep levels in the band-gap. Pt would be used as a VLS catalyst for high performance optically active Er-SiNWs.

Production of furfural from xylose, water-insoluble hemicelluloses and water-soluble fraction of corncob via a tin-loaded montmorillonite solid acid catalyst.

PubMed

Li, Huiling; Ren, Junli; Zhong, Linjie; Sun, Runcang; Liang, Lei

2015-01-01

The conversion of xylose, water-insoluble hemicelluloses (WIH) and water-soluble fraction (WSF) of corncob to furfural was performed using montmorillonite with tin ions (Sn-MMT) containing double acid sites as a solid acid catalyst. The co-existence of Lewis acids and Brønsted acids in Sn-MMT was shown to improve the furfural yield and selectivity. 76.79% furfural yield and 82.45% furfural selectivity were obtained from xylose using Sn-MMT as a catalyst in a biphasic system with 2-s-butylphenol (SBP) as the organic extracting layer and dimethyl sulfoxide (DMSO) as the co-solvent in contact with an aqueous phase saturated with NaCl (SBP/NaCl-DMSO) at 180°C for 30min. Furthermore, Sn-MMT also demonstrated the excellent catalytic performance in the conversion of pentose-rich materials of corncob and 39.56% and 54.15% furfural yields can be directly obtained from WIH and WSF in the SBP/NaCl-DMSO system, respectively. Copyright © 2014 Elsevier Ltd. All rights reserved.

Unsupported Pt-Ni Aerogels with Enhanced High Current Performance and Durability in Fuel Cell Cathodes.

PubMed

Henning, Sebastian; Ishikawa, Hiroshi; Kühn, Laura; Herranz, Juan; Müller, Elisabeth; Eychmüller, Alexander; Schmidt, Thomas J

2017-08-28

Highly active and durable oxygen reduction catalysts are needed to reduce the costs and enhance the service life of polymer electrolyte fuel cells (PEFCs). This can be accomplished by alloying Pt with a transition metal (for example Ni) and by eliminating the corrodible, carbon-based catalyst support. However, materials combining both approaches have seldom been implemented in PEFC cathodes. In this work, an unsupported Pt-Ni alloy nanochain ensemble (aerogel) demonstrates high current PEFC performance commensurate with that of a carbon-supported benchmark (Pt/C) following optimization of the aerogel's catalyst layer (CL) structure. The latter is accomplished using a soluble filler to shift the CL's pore size distribution towards larger pores which improves reactant and product transport. Chiefly, the optimized PEFC aerogel cathodes display a circa 2.5-fold larger surface-specific ORR activity than Pt/C and maintain 90 % of the initial activity after an accelerated stress test (vs. 40 % for Pt/C). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

In situ investigation on ultrafast oxygen evolution reactions of water splitting in proton exchange membrane electrolyzer cells

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

Mo, Jingke; Kang, Zhenye; Yang, Gaoqiang

We present that the oxygen evolution reaction (OER) is a half reaction in electrochemical devices, including low-temperature water electrolysis, which is considered as one of the most promising methods to generate hydrogen/oxygen for the storage of energy. It is affected by many factors, and its mechanism is still not completely understood. A proton exchange membrane electrolyzer cell (PEMEC) with optical access to the surface of anode catalyst layer (CL) coupled with a distinguished high-speed and micro-scale visualization system (HMVS) was developed to in situ investigate OERs. It was revealed in real time that OERs only occur on the anode CLmore » adjacent to liquid/gas diffusion layer (LGDL). The CL electrical conductivity plays a crucial role in OERs on CLs. The large in-plane electrical resistance of CLs becomes a threshold of OERs over the entire CL, and causes a lot of catalyst waste in the middle of LGDL pores. Moreover, the oxygen bubble nucleation, growth, and detachment and the effect of current density on those processes were also characterized. Here, this study proposes a new approach for better understanding the mechanisms of OERs and optimizing the design and fabrication of membrane electrode assemblies.« less

In situ investigation on ultrafast oxygen evolution reactions of water splitting in proton exchange membrane electrolyzer cells

DOE PAGES

Mo, Jingke; Kang, Zhenye; Yang, Gaoqiang; ...

2017-08-25

We present that the oxygen evolution reaction (OER) is a half reaction in electrochemical devices, including low-temperature water electrolysis, which is considered as one of the most promising methods to generate hydrogen/oxygen for the storage of energy. It is affected by many factors, and its mechanism is still not completely understood. A proton exchange membrane electrolyzer cell (PEMEC) with optical access to the surface of anode catalyst layer (CL) coupled with a distinguished high-speed and micro-scale visualization system (HMVS) was developed to in situ investigate OERs. It was revealed in real time that OERs only occur on the anode CLmore » adjacent to liquid/gas diffusion layer (LGDL). The CL electrical conductivity plays a crucial role in OERs on CLs. The large in-plane electrical resistance of CLs becomes a threshold of OERs over the entire CL, and causes a lot of catalyst waste in the middle of LGDL pores. Moreover, the oxygen bubble nucleation, growth, and detachment and the effect of current density on those processes were also characterized. Here, this study proposes a new approach for better understanding the mechanisms of OERs and optimizing the design and fabrication of membrane electrode assemblies.« less

A Study of Ziegler–Natta Propylene Polymerization Catalysts by Spectroscopic Methods

PubMed Central

Tkachenko, Olga P.; Kucherov, Alexey V.; Kustov, Leonid M.; Virkkunen, Ville; Leinonen, Timo; Denifl, Peter

2017-01-01

Ziegler–Natta polymerization catalysts were characterized by a complex of surface- and bulk-sensitive methods (DRIFTS, XPS, ESR, and XAS = XANES + EXAFS). A diffuse-reflectance Fourier-transform IR spectroscopy (DRIFTS) study showed the presence of strong Lewis acid sites in different concentrations and absence of strong basic sites in the polymerization catalysts. X-ray photoelectron spectroscopy (XPS), electron-spin resonance (ESR), and (X-ray absorption near-edge structure (XANES) analysis revealed the presence of Ti4+, Ti3+, Ti2+, and Ti1+ species in the surface layers and in the bulk of catalysts. The samples under study differ drastically in terms of the number of ESR-visible paramagnetic sites. The EXAFS study shows the presence of a Cl atom as a nearest neighbor of the absorbing Ti atom. PMID:28772850

A New Bioinspired Perchlorate Reduction Catalyst with Significantly Enhanced Stability via Rational Tuning of Rhenium Coordination Chemistry and Heterogeneous Reaction Pathway.

PubMed

Liu, Jinyong; Han, Mengwei; Wu, Dimao; Chen, Xi; Choe, Jong Kwon; Werth, Charles J; Strathmann, Timothy J

2016-06-07

Rapid reduction of aqueous ClO4(-) to Cl(-) by H2 has been realized by a heterogeneous Re(hoz)2-Pd/C catalyst integrating Re(O)(hoz)2Cl complex (hoz = oxazolinyl-phenolato bidentate ligand) and Pd nanoparticles on carbon support, but ClOx(-) intermediates formed during reactions with concentrated ClO4(-) promote irreversible Re complex decomposition and catalyst deactivation. The original catalyst design mimics the microbial ClO4(-) reductase, which integrates Mo(MGD)2 complex (MGD = molybdopterin guanine dinucleotide) for oxygen atom transfer (OAT). Perchlorate-reducing microorganisms employ a separate enzyme, chlorite dismutase, to prevent accumulation of the destructive ClO2(-) intermediate. The structural intricacy of MGD ligand and the two-enzyme mechanism for microbial ClO4(-) reduction inspired us to improve catalyst stability by rationally tuning Re ligand structure and adding a ClOx(-) scavenger. Two new Re complexes, Re(O)(htz)2Cl and Re(O)(hoz)(htz)Cl (htz = thiazolinyl-phenolato bidentate ligand), significantly mitigate Re complex decomposition by slightly lowering the OAT activity when immobilized in Pd/C. Further stability enhancement is then obtained by switching the nanoparticles from Pd to Rh, which exhibits high reactivity with ClOx(-) intermediates and thus prevents their deactivating reaction with the Re complex. Compared to Re(hoz)2-Pd/C, the new Re(hoz)(htz)-Rh/C catalyst exhibits similar ClO4(-) reduction activity but superior stability, evidenced by a decrease of Re leaching from 37% to 0.25% and stability of surface Re speciation following the treatment of a concentrated "challenge" solution containing 1000 ppm of ClO4(-). This work demonstrates the pivotal roles of coordination chemistry control and tuning of individual catalyst components for achieving both high activity and stability in environmental catalyst applications.

Cooperative Friedel-Crafts catalysis in heterobimetallic regime: alkylation of aromatics by pi-activated alcohols.

PubMed

Choudhury, Joyanta; Podder, Susmita; Roy, Sujit

2005-05-04

The highly active Friedel-Crafts alkylation (FCA) catalyst, [Ir(COD)Cl(SnCl3)(SnCl4)(arene)]+Cl- (1-SnCl4), is easily generated in one-pot from [Ir(COD)Cl]2 or [Ir(COD)(mu-Cl)Cl(SnCl3)]2 (1) and SnCl4. The reaction of arenes, heteroarenes with benzyl, and allyl alcohols is promoted by 1-SnCl4 (1 mol %) with high turnover frequency. Kinetic evidence is presented to establish FCA pattern. From dual-catalyst combination studies varying the transition metal and main group metal partner, the efficiency of the present catalysts is attributed to the electrophilic "IrIII-SnIV" core.

Study on the decomposition of trace benzene over V2O5-WO3 ...

EPA Pesticide Factsheets

Commercial and laboratory-prepared V2O5–WO3/TiO2-based catalysts with different compositions were tested for catalytic decomposition of chlorobenzene （ClBz） in simulated flue gas. Resonance enhanced multiphoton ionization-time of flight mass spectrometry (REMPI-TOFMS) was employed to measure real-time, trace concentrations of ClBz contained in the flue gas before and after the catalyst. The effects of various parameters, including vanadium content of the catalyst, the catalyst support, as well as the reaction temperature on decomposition of ClBz were investigated. The results showed that the ClBz decomposition efficiency was significantly enhanced when nano-TiO2 instead of conventional TiO2 was used as the catalyst support. No promotion effects were found in the ClBz decomposition process when the catalysts were wet-impregnated with CuO and CeO2. Tests with different concentrations (1,000, 500, and 100 ppb) of ClBz showed that ClBz-decomposition efficiency decreased with increasing concentration, unless active sites were plentiful. A comparison between ClBz and benzene decomposition on the V2O5–WO3/TiO2-based catalyst and the relative kinetics analysis showed that two different active sites were likely involved in the decomposition mechanism and the V=O and V-O-Ti groups may only work for the degradation of the phenyl group and the benzene ring rather than the C-Cl bond. V2O5-WO3/TiO2 based catalysts, that have been used for destruction of a wide variet

Carbon Nanotube Microarrays Grown on Nanoflake Substrates

NASA Technical Reports Server (NTRS)

Schmidt, Howard K.; Hauge, Robert H.; Pint, Cary; Pheasant, Sean

2013-01-01

This innovation consists of a new composition of matter where single-walled carbon nanotubes (SWNTs) are grown in aligned arrays from nanostructured flakes that are coated in Fe catalyst. This method of growth of aligned SWNTs, which can yield well over 400 percent SWNT mass per unit substrate mass, exceeds current yields for entangled SWNT growth. In addition, processing can be performed with minimal wet etching treatments, leaving aligned SWNTs with superior properties over those that exist in entangled mats. The alignment of the nanotubes is similar to that achieved in vertically aligned nanotubes, which are called "carpets. " Because these flakes are grown in a state where they are airborne in a reactor, these flakes, after growing SWNTs, are termed "flying carpets. " These flakes are created in a roll-to-roll evaporator system, where three subsequent evaporations are performed on a 100-ft (approx. =30-m) roll of Mylar. The first layer is composed of a water-soluble "release layer, " which can be a material such as NaCl. After depositing NaCl, the second layer involves 40 nm of supporting layer material . either Al2O3 or MgO. The thickness of the layer can be tuned to synthesize flakes that are larger or smaller than those obtained with a 40-nm deposition. Finally, the third layer consists of a thin Fe catalyst layer with a thickness of 0.5 nm. The thickness of this layer ultimately determines the diameter of SWNT growth, and a layer that is too thick will result in the growth of multiwalled carbon nanotubes instead of single-wall nanotubes. However, between a thickness of 0.5 nm to 1 nm, single-walled carbon nanotubes are known to be the primary constituent. After this three-layer deposition process, the Mylar is rolled through a bath of water, which allows catalyst-coated flakes to detach from the Mylar. The flakes are then collected and dried. The method described here for making such flakes is analogous to that which is used to make birefringent ink that is coated on U.S. currency. After deposition, the growth is carried out in a hot-filament chemical vapor deposition apparatus. A tungsten hot filament placed in the flow of H2 at a temperature greater than 1,600 C creates atomic hydrogen, which serves to reduce the Fe catalyst into a metallic state. The catalyst can now precipitate SWNTs in the presence of growth gases. The gases used for the experiments reported are C2H2, H2O, and H2, at rates of 2, 2, and 400 standard cubic centimeters per minute (sccm), respectively. In order to retain the flakes, a cage is constructed by spot welding stainless steel or copper mesh to form an enclosed area, in which the flakes are placed prior to growth. This allows growth gases and atomic hydrogen to reach the flakes, but does not allow the flakes, which rapidly nucleate SWNTs, to escape from the cage.

Towards the preparation of realistic model Ziegler-Natta catalysts: XPS study of the MgCl 2/TiCl 4 interaction with flat SiO 2/Si(1 0 0)

NASA Astrophysics Data System (ADS)

Siokou, Angeliki; Ntais, Spyridon

2003-08-01

Despite of the wide use of supported Ti based Ziegler-Natta catalysts in the olefin polymerization industry, questions concerning the role of each one of the catalyst components in the polymerization process, have not found a satisfactory answer yet. This is mainly because of the high sensitivity of these systems to oxygen and atmospheric moisture that makes their study in an atomic level rather complicated. Realistic surface science models of the pre-activated SiO 2 supported MgCl 2/TiCl 4 and TiCl 4 Ziegler-Natta catalysts were prepared by spin coating on flat conductive SiO 2/Si(1 0 0) supports under inert atmosphere. This preparation technique resembles the wet chemical impregnation which is the industrial method of the catalyst preparation. XPS analysis showed that the catalyst precursor anchors on the silica surface through bonding of the Ti atoms with surface silanes or siloxanes, while Mg is attached to the Ti through chlorine bridges. Thermal treatment of the catalysts at 723 K leads to total Cl desorption when MgCl 2 is not present while a significant amount of the Ti atoms is reduced to the Ti 3+ state.

High performance supercapacitor using porous carbon nanomaterial from corn cob

NASA Astrophysics Data System (ADS)

Sharma, Nallin; Mishra, Neeraj; Sharon, Madhuri; Sharon, Maheshwar

2013-06-01

Carbon synthesized from corn-cob has been used as an electrode in Electrochemical Double Layer Capacitor (EDLC). Dried Corn Cobs, soaked in 1N KOH, 1N HCl or 5% ZnCl2 at 10 0°C for 24 hr, were pyrolyzed in presence of Ar using Co as catalyst at 700-900 °C having dwell time of 60-180 min. The morphology of thus obtained carbon was studied under SEM that showed it to be porous carbon. All the carbon samples synthesized using different parameters were used as electrode for EDLC. Cyclic Voltammetry was used to measure the capacitance. Carbon synthesized from corn cobs pre-treated with 5% ZnCl2 using Co as catalyst pyrolyzed at 700°C for a dwell time of 120 min gave higher Specific capacitance of 270 F/g at scan rate of 5 mV/s. Moreover, this carbon, as observed under SEM, exhibited larger pore size.

Study on the treatment of 2-sec-butyl-4,6-dinitrophenol (DNBP) wastewater by ClO2 in the presence of aluminum oxide as catalyst.

PubMed

Wang, Hui-Long; Dong, Jing; Jiang, Wen-Feng

2010-11-15

The chlorine dioxide (ClO(2)) oxidative degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) in aqueous solution was studied in detail using Al(2)O(3) as a heterogeneous catalyst. The operating parameters such as the ClO(2) concentration, catalyst dosage, initial DNBP concentration, reaction time and pH were evaluated. Compared with the conventional ClO(2) oxidation process without the catalyst, the ClO(2) catalytic oxidation system could significantly enhance the degradation efficiency. Under the optimal condition (DNBP concentration 39 mg L(-1), ClO(2) concentration 0.355 g L(-1), reaction time 60 min, catalyst dosage 10.7 g L(-1) and pH 4.66), degradation efficiency approached 99.1%. The catalyst was used at least 8 cycles without any appreciable loss of activity. The kinetic studies revealed that the ClO(2) catalytic oxidation degradation of DNBP followed pseudo-first-order kinetics with respect to DNBP concentration. The ClO(2) catalytic oxidation process was found to be very effective in the decolorization and COD(Cr) reduction of real wastewater from DNBP manufacturing. Thus, this study showed potential application of ClO(2) catalytic oxidation process in degradation of organic contaminants and industrial effluents. Copyright © 2010 Elsevier B.V. All rights reserved.

Eliminating micro-porous layer from gas diffusion electrode for use in high temperature polymer electrolyte membrane fuel cell

NASA Astrophysics Data System (ADS)

Su, Huaneng; Xu, Qian; Chong, Junjie; Li, Huaming; Sita, Cordellia; Pasupathi, Sivakumar

2017-02-01

In this work, we report a simple strategy to improve the performance of high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) by eliminating the micro-porous layer (MPL) from its gas diffusion electrodes (GDEs). Due to the absence of liquid water and the general use of high amount of catalyst, the MPL in a HT-PEMFC system works limitedly. Contrarily, the elimination of the MPL leads to an interlaced micropore/macropore composited structure in the catalyst layer (CL), which favors gas transport and catalyst utilization, resulting in a greatly improved single cell performance. At the normal working voltage (0.6 V), the current density of the GDE eliminated MPL reaches 0.29 A cm-2, and a maximum power density of 0.54 W cm-2 at 0.36 V is obtained, which are comparable to the best results yet reported for the HT-PEMFCs with similar Pt loading and operated using air. Furthermore, the MPL-free GDE maintains an excellent durability during a preliminary 1400 h HT-PEMFC operation, owing to its structure advantages, indicating the feasibility of this electrode for practical applications.

Application of a Re-Pd bimetallic catalyst for treatment of perchlorate in waste ion-exchange regenerant brine.

PubMed

Liu, Jinyong; Choe, Jong Kwon; Sasnow, Zachary; Werth, Charles J; Strathmann, Timothy J

2013-01-01

Concentrated sodium chloride (NaCl) brines are often used to regenerate ion-exchange (IX) resins applied to treat drinking water sources contaminated with perchlorate (ClO(4)(-)), generating large volumes of contaminated waste brine. Chemical and biological processes for ClO(4)(-) reduction are often inhibited severely by high salt levels, making it difficult to recycle waste brines. Recent work demonstrated that novel rhenium-palladium bimetallic catalysts on activated carbon support (Re-Pd/C) can efficiently reduce ClO(4)(-) to chloride (Cl(-)) under acidic conditions, and here the applicability of the process for treating waste IX brines was examined. Experiments conducted in synthetic NaCl-only brine (6-12 wt%) showed higher Re-Pd/C catalyst activity than in comparable freshwater solutions, but the rate constant for ClO(4)(-) reduction measured in a real IX waste brine was found to be 65 times lower than in the synthetic NaCl brine. Through a series of experiments, co-contamination of the IX waste brine by excess NO(3)(-) (which the catalyst reduces principally to NH(4)(+)) was found to be the primary cause for deactivation of the Re-Pd/C catalyst, most likely by altering the immobilized Re component. Pre-treatment of NO(3)(-) using a different bimetallic catalyst (In-Pd/Al(2)O(3)) improved selectivity for N(2) over NH(4)(+) and enabled facile ClO(4)(-) reduction by the Re-Pd/C catalyst. Thus, sequential catalytic treatment may be a promising strategy for enabling reuse of waste IX brine containing NO(3)(-) and ClO(4)(-). Copyright © 2012 Elsevier Ltd. All rights reserved.

Synthesis and Characterization of AlCl3 Impregnated Molybdenum Oxide as Heterogeneous Nano-Catalyst for the Friedel-Crafts Acylation Reaction in Ambient Condition.

PubMed

Jadhav, Arvind H; Chinnappan, Amutha; Hiremath, Vishwanath; Seo, Jeong Gil

2015-10-01

Aluminum trichloride (AlCl3) impregnated molybdenum oxide heterogeneous nano-catalyst was prepared by using simple impregnation method. The prepared heterogeneous catalyst was characterized by powder X-ray diffraction, FT-IR spectroscopy, solid-state NMR spectroscopy, SEM imaging, and EDX mapping. The catalytic activity of this protocol was evaluated as heterogeneous catalyst for the Friedel-Crafts acylation reaction at room temperature. The impregnated MoO4(AlCl2)2 catalyst showed tremendous catalytic activity in Friedel-Crafts acylation reaction under solvent-free and mild reaction condition. As a result, 84.0% yield of acyl product with 100% consumption of reactants in 18 h reaction time at room temperature was achieved. The effects of different solvents system with MoO4(AlCl2)2 catalyst in acylation reaction was also investigated. By using optimized reaction condition various acylated derivatives were prepared. In addition, the catalyst was separated by simple filtration process after the reaction and reused several times. Therefore, heterogeneous MoO4(AlCl2)2 catalyst was found environmentally benign catalyst, very convenient, high yielding, and clean method for the Friedel-Crafts acylation reaction under solvent-free and ambient reaction condition.

Construction of hierarchically porous graphitized carbon-supported NiFe layered double hydroxides with a core-shell structure as an enhanced electrocatalyst for the oxygen evolution reaction.

PubMed

Ni, Yuanman; Yao, Lihua; Wang, Yin; Liu, Bing; Cao, Minhua; Hu, Changwen

2017-08-17

The oxygen evolution reaction (OER) is a vital half-reaction in water splitting and metal-air batteries. Developing earth-abundant, highly efficient and durable OER catalysts has faced huge challenges until now, because OER is a strict kinetic sluggish process. Herein, we report the construction of hierarchically porous graphitized carbon (HPGC) supported NiFe layered double hydroxides (LDHs) with a core-shell structure (denoted as HPGC@NiFe) by a facile strategy. The HPGC was first obtained by pyrolysing phenolic resin nanospheres with FeCl 3 and ZnCl 2 as the catalyst and the activator, respectively. Then the NiFe LDH arrays were directly grown on the HPGC by a one-step hydrothermal method. The as-synthesized HPGC@NiFe reveals excellent OER properties with a low onset potential, a lower overpotential of 265 mV (corresponding to the current density at 10 mA cm -2 ) and a small Tafel slope (56 mV per decade). And its catalytic activity is even superior to that of the start-of-the-art noble-metal catalyst IrO 2 /C. Notably, the HPGC@NiFe electrode shows admirable stability measured by performing 2000 cycle CVs and long-term electrolysis for 50 h. The prominent performance can be attributed to the synergistic effect between the NiFe-LDHs and the hierarchically porous graphitized carbon, in which the former can increase the exposure of the active sites, while the latter can increase the charge transfer efficiency. Our research implies the possibility for the development of low-cost layered double hydroxides as a promising candidate in electrochemical energy storage and conversion equipment.

[Pd(μ-Cl)Cl(IPr*)]2: a highly hindered pre-catalyst for the synthesis of tetra-ortho-substituted biaryls via Grignard reagent cross-coupling.

PubMed

Lesieur, Mathieu; Slawin, Alexandra M Z; Cazin, Catherine S J

2014-08-14

The new well-defined catalyst [Pd(μ-Cl)Cl(IPr*)]2 enables the efficient Grignard reagent cross-coupling for the synthesis of tetra-ortho-substituted biaryls. The high reactivity of the complex is associated with the important bulkiness of the IPr* ligand. The dimer represents the most efficient catalyst reported to date for this challenging transformation.

Catalyzed Atomic Layer Deposition of Silicon Oxide at Ultralow Temperature Using Alkylamine.

PubMed

Mayangsari, Tirta R; Park, Jae-Min; Yusup, Luchana L; Gu, Jiyeon; Yoo, Jin-Hyuk; Kim, Heon-Do; Lee, Won-Jun

2018-06-12

We report the catalyzed atomic layer deposition (ALD) of silicon oxide using Si 2 Cl 6 , H 2 O, and various alkylamines. The density functional theory (DFT) calculations using the periodic slab model of the SiO 2 surface were performed for the selection of alternative Lewis base catalysts with high catalytic activities. During the first half-reaction, the catalysts with less steric hindrance such as pyridine would be more effective than bulky alkylamines despite lower nucleophilicity. On the other hand, during the second half-reaction, the catalysts with a high nucleophilicity such as triethylamine (Et 3 N) would be more efficient because the steric hindrance is less critical. The in situ process monitoring shows that the calculated atomic charge is a good indicator for expecting the catalyst activity in the ALD reaction. The use of Et 3 N in the second half-reaction was essential to improving the growth rate as well as the step coverage of the film because the Et 3 N-catalyzed process deposited a SiO 2 film with a step coverage of 98% that is better than 93% of the pyridine-catalyzed process. The adsorption of pyridine, ammonia (NH 3 ), or trimethylamine (Me 3 N) salts was more favorable than that of Et 3 N, n-Pr 3 N, or i Pr 3 N salts. Therefore, Et 3 N was expected to incorporate less amine salts in the film as compared to pyridine, and the compositional analyses confirmed that the concentrations of Cl and N by the Et 3 N-catalyzed process were significantly lower than those by the pyridine-catalyzed process.

Dramatic Improvement on Catalyst Loadings and Molar Ratios of Coupling Partners for Ni/Cr-Mediated Coupling Reactions: Heterobimetallic Catalysts

PubMed Central

Liu, Xiang; Henderson, James A.; Sasaki, Takeo; Kishi, Yoshito

2009-01-01

Two new ligands 1a,b have been reported. Upon treatment with one equivalent of NiCl2·(MeOCH2)2, 1a,b give the corresponding Ni-complexes. X-ray analysis of 1a·NiCl2 has established that the NiCl2 is selectively coordinated to the phenanthroline nitrogens. Ni/Cr-heterobimetallic catalysts 1a,b·CrCl2/NiCl2, prepared from 1a,b·NiCl2, have been shown to behave exceptionally well for the catalytic asymmetric Ni/Cr-mediated couplings, with the highlights including: (1) 1~2 mol % catalysts are sufficient to complete the coupling, (2) only a negligible amount of the dimers, by-products formed through the alkenyl Ni-species, is observed, (3) the coupling completes even with a 1:1 molar ratio of the coupling partners, and (4) the asymmetric induction is practically identical with that obtained in the coupling with the Cr-catalyst prepared from (S)-sulfonamide 2a,b. Using 4 additional aldehydes, a scope of the new Ni/Cr-heterobimetallic catalysts is briefly studied. Applicability of new catalysts to polyfunctional substrates has been demonstrated, with use of two C-C bond-formations chosen from the halichondrin/E7389 synthesis as examples. PMID:19874019

Bimolecular Coupling as a Vector for Decomposition of Fast-Initiating Olefin Metathesis Catalysts.

PubMed

Bailey, Gwendolyn A; Foscato, Marco; Higman, Carolyn S; Day, Craig S; Jensen, Vidar R; Fogg, Deryn E

2018-06-06

The correlation between rapid initiation and rapid decomposition in olefin metathesis is probed for a series of fast-initiating, phosphine-free Ru catalysts: the Hoveyda catalyst HII, RuCl 2 (L)(═CHC 6 H 4 - o-O i Pr); the Grela catalyst nG (a derivative of HII with a nitro group para to O i Pr); the Piers catalyst PII, [RuCl 2 (L)(═CHPCy 3 )]OTf; the third-generation Grubbs catalyst GIII, RuCl 2 (L)(py) 2 (═CHPh); and dianiline catalyst DA, RuCl 2 (L)( o-dianiline)(═CHPh), in all of which L = H 2 IMes = N,N'-bis(mesityl)imidazolin-2-ylidene. Prior studies of ethylene metathesis have established that various Ru metathesis catalysts can decompose by β-elimination of propene from the metallacyclobutane intermediate RuCl 2 (H 2 IMes)(κ 2 -C 3 H 6 ), Ru-2. The present work demonstrates that in metathesis of terminal olefins, β-elimination yields only ca. 25-40% propenes for HII, nG, PII, or DA, and none for GIII. The discrepancy is attributed to competing decomposition via bimolecular coupling of methylidene intermediate RuCl 2 (H 2 IMes)(═CH 2 ), Ru-1. Direct evidence for methylidene coupling is presented, via the controlled decomposition of transiently stabilized adducts of Ru-1, RuCl 2 (H 2 IMes)L n (═CH 2 ) (L n = py n' ; n' = 1, 2, or o-dianiline). These adducts were synthesized by treating in situ-generated metallacyclobutane Ru-2 with pyridine or o-dianiline, and were isolated by precipitating at low temperature (-116 or -78 °C, respectively). On warming, both undergo methylidene coupling, liberating ethylene and forming RuCl 2 (H 2 IMes)L n . A mechanism is proposed based on kinetic studies and molecular-level computational analysis. Bimolecular coupling emerges as an important contributor to the instability of Ru-1, and a potentially major pathway for decomposition of fast-initiating, phosphine-free metathesis catalysts.

The influence of coating solution and calcination condition on the durability of Ir1-xSnxO2/Ti anodes for oxygen evolution

NASA Astrophysics Data System (ADS)

Kato, Zenta; Kashima, Ryo; Tatsumi, Kohei; Fukuyama, Shinnosuke; Izumiya, Koichi; Kumagai, Naokazu; Hashimoto, Koji

2016-12-01

For oxygen formation without forming chlorine in seawater electrolysis for hydrogen production we have been using the anode consisting of three layers of MnO2-type multiple oxide catalyst, intermediate layer and titanium substrate. The intermediate layer was used for prevention of oxidation of the titanium substrate during anodic polarization for oxygen evolution and was prepared by calcination of butanol solutions of H2IrCl6 and SnCl4 coated on titanium. The protectiveness of Ir1-xSnxO2 layer formed was directly examined using Ir1-xSnxO2/Ti anodes in H2SO4 solution changing the preparation conditions of the layer. When the sum of Ir4+ and Sn4+ was 0.1 M, the highest protectiveness was observed at 0.06 M Sn4+. Although an increase in calcination temperature led to the formation of Ir1-x-ySnxTiyO2 triple oxide with a slightly lower catalytic activity for oxygen evolution, the anode calcined at 450 °C showed the highest protectiveness.

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.

Palladium-pyridyl catalytic films: a highly active and recyclable catalyst for hydrogenation of styrene under mild conditions.

PubMed

Gao, Shuiying; Li, Weijin; Cao, Rong

2015-03-01

Palladium-pyridyl catalytic films, (PdCl2/bpy)n, were created by alternating immersions of a substrate in PdCl2 and bpy (bpy=4, 4'-bipyridyl) solutions. The as-prepared (PdCl2/bpy)10 catalyst demonstrated a remarkable catalytic activity toward hydrogenation of styrene under mild conditions and the turnover frequency (TOF) is as high as 6944h(-1). Pd(II) ions of (PdCl2/bpy)n films are in situ reduced to Pd nanoparticles (NPs) during the hydrogenation of styrene process, which results in the catalytic activity of the films. The results of X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) further demonstrate that Pd(II) ions of (PdCl2/bpy)n films were gradually converted to Pd(0) states. The catalytic activity is related to bilayer numbers and the activity increases with the number of bilayers below 10 bilayers. The solid substrates coated with (PdCl2/bpy)n multilayer catalysts were easily removed from the reaction mixture without separation filtration. Moreover, (PdCl2/bpy)n catalysts were reused for 10 consecutive reactions without loss of activity. The present (PdCl2/bpy)n heterogeneous catalysts have the advantages of easy separation and good recyclability. Copyright © 2014 Elsevier Inc. All rights reserved.

Oxidation of elemental mercury vapor over gamma-Al2O3 supported CuCl2 catalyst for mercury emissions control

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

Liu, Zhouyang; Liu, Xin; Lee, Joo-Youp

2015-09-01

In our previous studies, CuCl2 demonstrated excellent Hg(0) oxidation capability and holds potential for Hg(0) oxidation in coal-fired power plants. In this study, the properties and performances of CuCl2 supported onto gamma-Al2O3 with high surface area were investigated. From various characterization techniques using XPS, XAFS, XRD, TPR, SEM and TGA, the existence of multiple copper species was identified. At low CuCl2 loadings, CuCl2 forms copper aluminate species with gamma-Al2O3 and is inactive for Hg(0) oxidation. At high loadings, amorphous CuCl2 forms onto the gamma-Al2O3 surface, working as a redox catalyst for Hg(0) oxidation by consuming Cl to be converted intomore » CuCl and then being regenerated back into CuCl2 in the presence of O-2 and HCl gases. The 10%(wt) CuCl2/gamma-Al2O3 catalyst showed excellent Hg(0) oxidation performance and SO2 resistance at 140 degrees C under simulated flue gas conditions containing 6%(v) O-2 and 10 ppmv HCl. The oxidized Hg(0) in the form of HgCl2 has a high solubility in water and can be easily captured by other air pollution control systems such as wet scrubbers in coal-fired power plants. The CuCl2/gamma-Al2O3 catalyst can be used as a low temperature Hg(0) oxidation catalyst. (C) 2015 Elsevier B.V. All rights reserved.« less

Processing of catalysts by atomic layer epitaxy: modification of supports

NASA Astrophysics Data System (ADS)

Lindblad, Marina; Haukka, Suvi; Kytökivi, Arla; Lakomaa, Eeva-Liisa; Rautiainen, Aimo; Suntola, Tuomo

1997-11-01

Different supports were modified with titania, zirconia and chromia by the atomic layer epitaxy technique (ALE). In ALE, a metal precursor is bound to the support in saturating gas-solid reactions. Surface oxides are grown by alternating reactions of the metal precursor and an oxidizing agent. Growth mechanisms differ depending on the precursor-support pair and the processing conditions. In this work, the influences of the support, precursor and reaction temperature were investigated by comparing the growth of titania from Ti(OCH(CH 3) 2) 4 on silica and alumina, titania from TiCl 4 and Ti(OCH(CH 3) 2) 4 on silica, and zirconia from ZrCl 4 on silica and alumina. The modification of porous oxides supported on metal substrates (monoliths) was demonstrated for the growth of chromia from Cr(acac) 3.

A facile approach towards increasing the nitrogen-content in nitrogen-doped carbon nanotubes via halogenated catalysts

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

Ombaka, L.M.; Ndungu, P.G.; Department of Applied Chemistry, Doornfontein Campus, University of Johannesburg, P.O. Box 17011, Johannesburg 2028

Nitrogen-doped carbon nanotubes (N-CNTs) have been synthesized at 850 °C via a CVD deposition technique by use of three ferrocenyl derivative catalysts, i.e. para-CN, -CF{sub 3} and -Cl substituted-phenyl rings. The synthesized catalysts have been characterized by NMR, IR, HR-MS and XRD. The XRD analysis of the para-CF{sub 3} catalyst indicates that steric factors influence the X-ray structure of 1,1′-ferrocenylphenyldiacrylonitriles. Acetonitrile or pyridine was used as carbon and nitrogen sources to yield mixtures of N-CNTs and carbon spheres (CS). The N-CNTs obtained from the para-CF{sub 3} catalysts, in pyridine, have the highest nitrogen-doping level, show a helical morphology and aremore » less thermally stable compared with those synthesized by use of the para-CN and -Cl as catalyst. This suggests that fluorine heteroatoms enhance nitrogen-doping in N-CNTs and formation of helical-N-CNTs (H-N-CNTs). The para-CF{sub 3} and para-Cl catalysts in acetonitrile yielded iron-filled N-CNTs, indicating that halogens promote encapsulation of iron into the cavity of N-CNT. The use of acetonitrile, as carbon and nitrogen source, with the para-CN and -Cl as catalysts also yielded a mixture of N-CNTs and carbon nanofibres (CNFs), with less abundance of CNFs in the products obtained using para-Cl catalysts. However, para-CF{sub 3} catalyst in acetonitrile gave N-CNTs as the only shaped carbon nanomaterials. - Graphical abstract: Graphical abstract showing the synthesis of N-CNTs using halogenated-ferrocenyl derivatives as catalyst with pyridine or acetonitrile as nitrogen and carbon sources via the chemical vapour deposition technique. - Highlights: • N-CNTs were synthesized from halogenated ferrocenyl catalysts. • Halogenated catalysts promote nitrogen-doping and pyridinic nitrogen in N-CNTs. • Halogenated catalysts facilitate iron filling of N-CNTs.« less

Methods of fabrication of graphene nanoribbons

DOEpatents

Zhang, Yuegang

2015-06-23

Methods of fabricating graphene nanoribbons include depositing a catalyst layer on a substrate. A masking layer is deposited on the catalyst layer. The masking layer and the catalyst layer are etched to form a structure on the substrate, the structure comprising a portion of the catalyst layer and a portion of the masking layer disposed on the catalyst layer, with sidewalls of the catalyst layer being exposed. A graphene layer is formed on a sidewall of the catalyst layer with a carbon-containing gas.

Selective methane chlorination to methyl chloride by zeolite Y-based catalysts

NASA Astrophysics Data System (ADS)

Joo, Hyeonho; Kim, Daeho; Lim, Kwang Soo; Choi, Yong Nam; Na, Kyungsu

2018-03-01

The CH4 chlorination over Y zeolites was investigated to produce CH3Cl in a high yield. Three different catalytic systems based on Y zeolite were tested for enhancement of CH4 conversion and CH3Cl selectivity: (i) HY zeolites in H+-form having various Si/Al ratios, (ii) Pt/HY zeolites supporting Pt metal nanoparticles, (iii) Pt/NaY zeolites in Na+-form supporting Pt metal nanoparticles. The reaction was carried out using the gas mixture of CH4 and Cl2 with the respective flow rates of 15 and 10 mL min-1 at 300-350 °C using a fixed-bed reactor under a continuous gas flow condition (gas hourly space velocity = 3000 mL g-1 h-1). Above the reaction temperature of 300 °C, the CH4 chlorination is spontaneous even in the absence of catalyst, achieving 23.6% of CH4 conversion with 73.4% of CH3Cl selectivity. Under sufficient supplement of thermal energy, Cl2 molecules can be dissociated to two chlorine radicals, which triggered the C-H bond activation of CH4 molecule and thereby various chlorinated methane products (i.e., CH3Cl, CH2Cl2, CHCl3, CCl4) could be produced. When the catalysts were used under the same reaction condition, enhancement in the CH4 conversion was observed. The Pt-free HY zeolite series with varied Si/Al ratios gave around 27% of CH4 conversion, but there was a slight decrease in CH3Cl selectivity with about 64%. Despite the difference in acidity of HY zeolites having different Si/Al ratios, no prominent effect of the Si/Al ratios on the catalytic performance was observed. This suggests that the catalytic contribution of HY zeolites under the present reaction condition is not strong enough to overcome the spontaneous CH4 chlorination. When the Pt/HY zeolite catalysts were used, the CH4 conversion reached further up to 30% but the CH3Cl selectivity decreased to 60%. Such an enhancement of CH4 conversion could be attributed to the strong catalytic activity of HY and Pt/HY zeolite catalysts. However, both catalysts induced the radical cleavage of Cl2 more favorably, which ultimately decreased the CH3Cl selectivity. Such trade-off relationship between CH4 conversion and CH3Cl selectivity can be slightly broken by using Pt/NaY zeolite catalyst that is known to possess Frustrated Lewis Pairs (FLP) that are very useful for ionic cleavage of H2 to H+ and H-. Similarly, in the present work, Pt/NaY(FLP) catalysts enhanced the CH4 conversion while keeping the CH3Cl selectivity as compared to the Pt/HY zeolite catalysts.

The catalytic pyrolysis of food waste by microwave heating.

PubMed

Liu, Haili; Ma, Xiaoqian; Li, Longjun; Hu, ZhiFeng; Guo, Pingsheng; Jiang, Yuhui

2014-08-01

This study describes a series of experiments that tested the use of microwave pyrolysis for treating food waste. Characteristics including rise in temperature, and the three-phase products, were analyzed at different microwave power levels, after adding 5% (mass basis) metal oxides and chloride salts to the food waste. Results indicated that, the metal oxides MgO, Fe₂O₃ and MnO₂ and the chloride salts CuCl₂ and NaCl can lower the yield of bio-oil and enhance the yield of gas. Meanwhile, the metal oxides MgO and MnO₂ can also lower the low heating value (LHV) of solid residues and increase the pH values of the lower layer bio-oils. However, the chloride salts CuCl₂ and NaCl had the opposite effects. The optimal microwave power for treating food waste was 400W; among the tested catalysts, CuCl₂ was the best catalyst and had the largest energy ratio of production to consumption (ERPC), followed by MnO₂. Copyright © 2014 Elsevier Ltd. All rights reserved.

Cu2O Photocathode for Low Bias Photoelectrochemical Water Splitting Enabled by NiFe-Layered Double Hydroxide Co-Catalyst

PubMed Central

Qi, Huan; Wolfe, Jonathan; Fichou, Denis; Chen, Zhong

2016-01-01

Layered double hydroxides (LDHs) are bimetallic hydroxides that currently attract considerable attention as co-catalysts in photoelectrochemical (PEC) systems in view of water splitting under solar light. A wide spectrum of LDHs can be easily prepared on demand by tuning their chemical composition and structural morphology. We describe here the electrochemical growth of NiFe-LDH overlayers on Cu2O electrodes and study their PEC behavior. By using the modified Cu2O/NiFe-LDH electrodes we observe a remarkable seven-fold increase of the photocurrent intensity under an applied voltage as low as −0.2 V vs Ag/AgCl. The origin of such a pronounced effect is the improved electron transfer towards the electrolyte brought by the NiFe-LDH overlayer due to an appropriate energy level alignment. Long-term photostability tests reveal that Cu2O/NiFe-LDH photocathodes show no photocurrent loss after 40 hours of operation under light at −0.2 V vs Ag/AgCl low bias condition. These improved performances make Cu2O/NiFe-LDH a suitable photocathode material for low voltage H2 production. Indeed, after 8 hours of H2 production under −0.2 V vs Ag/AgCl the PEC cell delivers a 78% faradaic efficiency. This unprecedented use of Cu2O/NiFe-LDH as an efficient photocathode opens new perspectives in view of low biasd or self-biased PEC water splitting under sunlight illumination. PMID:27487918

Transport phenomena in polymer electrolyte membrane fuel cells via voltage loss breakdown

NASA Astrophysics Data System (ADS)

Flick, Sarah; Dhanushkodi, Shankar R.; Mérida, Walter

2015-04-01

This study presents a voltage loss breakdown method based on in-situ experimental data to systematically analyze the different overpotentials of a polymer electrolyte membrane fuel cell. This study includes a systematic breakdown of the anodic overpotentials via the use of a reference electrode system. This work demonstrates the de-convolution of the individual overpotentials for both anode and cathode side, including the distinction between mass-transport overpotentials in cathode porous transport layer (PTL) and electrode, based on in-situ polarization tests under different operating conditions. This method is used to study the relationship between mass-transport losses inside the cathode catalyst layer (CL) and the PTL for both a single layer and two-layer PTL configuration. We conclude that the micro-porous layer (MPL) significantly improves the water removal within the cell, especially inside the cathode electrode, and therefore the mass transport within the cathode CL. This study supports the theory that the MPL on the cathode leads to an increase in water permeation from cathode to anode due to its function as a capillary barrier. This is reflected in increased anodic mass-transport overpotential, decreased ohmic losses and decreased cathode mass-transport losses, especially in the cathode electrode.

Noncovalent immobilization of electrocatalysts on carbon electrodes for fuel production.

PubMed

Blakemore, James D; Gupta, Ayush; Warren, Jeffrey J; Brunschwig, Bruce S; Gray, Harry B

2013-12-11

We show that molecular catalysts for fuel-forming reactions can be immobilized on graphitic carbon electrode surfaces via noncovalent interactions. A pyrene-appended bipyridine ligand (P) serves as the linker between each complex and the surface. Immobilization of a rhodium proton-reduction catalyst, [Cp*Rh(P)Cl]Cl (1), and a rhenium CO2-reduction catalyst, Re(P)(CO)3Cl (2), afford electrocatalytically active assemblies. X-ray photoelectron spectroscopy and electrochemistry confirm catalyst immobilization. Reduction of 1 in the presence of p-toluenesulfonic acid results in catalytic H2 production, while reduction of 2 in the presence of CO2 results in catalytic CO production.

Microscale measurements of oxygen concentration across the thickness of diffusion media in operating polymer electrolyte fuel cells

NASA Astrophysics Data System (ADS)

Epting, William K.; Litster, Shawn

2016-02-01

Although polymer electrolyte fuel cells (PEFCs) offer promise as efficient, low emission power sources, the large amount of platinum catalyst used for the cathode's oxygen reduction (ORR) results in high costs. One approach to using less Pt is to increase the oxygen concentration at the catalyst by reducing the oxygen transport resistances. An important resistance is that of the diffusion media (DM). The DM are highly heterogeneous porous carbon fiber substrates with a graded composition of additives across their thickness. In this work we use an oxygen microsensor with a micro-positioning system to measure the oxygen concentration and presence of liquid water in the pores at discrete points across the thickness of a commercial carbon felt DM in operating PEFCs. Under conditions with no liquid water, the DM accounts for 60% of the oxygen depletion, with 60-70% of that depletion being due to the thin microporous layer (MPL) on the catalyst layer (CL) side. Using concentration gradient data, we quantify the non-uniform local transport resistance across the DM and relate it to high resolution 3D X-ray computed tomography of the same DM.

A delafossite-based copper catalyst for sustainable Cl2 production by HCl oxidation.

PubMed

Mondelli, Cecilia; Amrute, Amol P; Schmidt, Timm; Pérez-Ramírez, Javier

2011-07-07

A copper catalyst based on a delafossite precursor (CuAlO(2)) displays high activity and extraordinary lifetime in the gas-phase oxidation of HCl to Cl(2), representing a cost-effective alternative to RuO(2)-based catalysts for chlorine recycling. This journal is © The Royal Society of Chemistry 2011

Impact of initial catalyst form on the 3D structure and performance of ball-milled Ni-catalyzed MgH 2 for hydrogen storage

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

House, Stephen D.; Vajo, John J.; Ren, Chai

Although it has been shown that the hydrogen storage kinetics of metal hydrides can be significantly improved by the addition of transition metal-based catalysts, relatively little attention has been paid to the impact that the form in which these catalysts are introduced during synthesis has on the resulting structure and how this alters performance. Two mixtures of MgH 2 doped with Ni were prepared via high-energy ball-milling under identical conditions, one using a pure Ni nanopowder catalyst and the other using anhydrous NiCl 2. The resulting Ni catalyst particles of the NiCl 2-doped material were 10-100 times smaller, as wellmore » as more uniform in size and shape. Electron tomography revealed that the additive form also altered its incorporation and 3D spatial distribution, with Ni particles limited to the outer surface in the NiCl 2-doped case. The significantly lower desorption performance measured in the NiCl 2-doped material is attributed to regions of MgCl 2 acting as barriers between the MgH 2 and Ni, hindering the ability of the latter to effectively catalyze the reactions. Finally, this work demonstrates the hazards in assuming different catalyst forms produce similar final structures and highlights the potential of catalyst form as a synthesis tool for optimizing the material structure and performance.« less

Impact of initial catalyst form on the 3D structure and performance of ball-milled Ni-catalyzed MgH 2 for hydrogen storage

DOE PAGES

House, Stephen D.; Vajo, John J.; Ren, Chai; ...

2017-02-24

Although it has been shown that the hydrogen storage kinetics of metal hydrides can be significantly improved by the addition of transition metal-based catalysts, relatively little attention has been paid to the impact that the form in which these catalysts are introduced during synthesis has on the resulting structure and how this alters performance. Two mixtures of MgH 2 doped with Ni were prepared via high-energy ball-milling under identical conditions, one using a pure Ni nanopowder catalyst and the other using anhydrous NiCl 2. The resulting Ni catalyst particles of the NiCl 2-doped material were 10-100 times smaller, as wellmore » as more uniform in size and shape. Electron tomography revealed that the additive form also altered its incorporation and 3D spatial distribution, with Ni particles limited to the outer surface in the NiCl 2-doped case. The significantly lower desorption performance measured in the NiCl 2-doped material is attributed to regions of MgCl 2 acting as barriers between the MgH 2 and Ni, hindering the ability of the latter to effectively catalyze the reactions. Finally, this work demonstrates the hazards in assuming different catalyst forms produce similar final structures and highlights the potential of catalyst form as a synthesis tool for optimizing the material structure and performance.« less

Furfural Production from d-Xylose and Xylan by Using Stable Nafion NR50 and NaCl in a Microwave-Assisted Biphasic Reaction.

PubMed

Le Guenic, Sarah; Gergela, David; Ceballos, Claire; Delbecq, Frederic; Len, Christophe

2016-08-22

Pentose dehydration and direct transformation of xylan into furfural were performed in a water-cyclopentyl methyl ether (CPME) biphasic system under microwave irradiation. Heated up between 170 and 190 °C in the presence of Nafion NR50 and NaCl, d-xylose, l-arabinose and xylan gave furfural with maximum yields of 80%, 42% and 55%, respectively. The influence of temperature and reaction time on the reaction kinetics was discussed. This study was also completed by the survey of different reactant ratios, such as organic layer-water or catalyst-inorganic salt ratios. The exchange between proton and cation induced by an excess of NaCl was monitored, and a synergetic effect between the remaining protons and the released HCl was also discovered.

Analyzing the influence of high electrode potentials on intrinsic properties of catalyst coated membranes using impedance spectroscopy

NASA Astrophysics Data System (ADS)

Alink, Robert; Schüßler, Martina; Pospischil, Maximilian; Erath, Denis; Gerteisen, Dietmar

2016-09-01

Catalyst layers (CLs) with varying ionomer contents are produced using a stencil coating and screen printing technique. The optimum ionomer content of 31-34 wt% confirms the findings of other groups and performance is found to be independent of production technique. A new CL impedance transition line model is developed and fitted to in-situ data. The results indicate that the protonic contact resistance between CL and membrane is an important factor for the used transfer-decal process, especially for CLs with low ionomer loading. When subjected to potentials higher than 1.2 V, an increased performance is observed for low ionomer loading CLs. It is found that by applying the high potential to the electrode a significantly increased proton conductivity is counteracting and superimposing the loss of electrochemical surface area (ECSA) due to carbon corrosion. After aging, the performance of the 15 wt% CL is at the same level as the 31-34 wt% ionomer content CLs at the beginning of life, even though the ECSA is reduced due to carbon corrosion or platinum dissolution. The findings indicate that for the optimization of the ionomer loading, either the changing wetting properties or the redistribution of ionomer during lifetime have to be taken into account.

Effects of Pt and ionomer ratios on the structure of catalyst layer: A theoretical model for polymer electrolyte fuel cells

NASA Astrophysics Data System (ADS)

Ishikawa, H.; Sugawara, Y.; Inoue, G.; Kawase, M.

2018-01-01

The 3D structure of the catalyst layer (CL) in the polymer electrolyte fuel cell (PEFC) is modeled with a Pt/carbon (Pt/C) ratio of 0.4-2.3 and ionomer/carbon (i/C) ratio of 0.5-1.5, and the structural properties are evaluated by numerical simulation. The models are constructed by mimicking the actual shapes of Pt particles and carbon aggregates, as well as the ionomer adhesion in real CLs. CLs with different compositions are characterized by structural properties such as Pt inter-particle distance, ionomer coating thickness, pore size distribution, tortuosity, and ionomer coverage on Pt. The results for Pt/C = 1.0, i/C = 1.0 with Pt loading of 0.3 mg cm-2 and 50% porosity are validated against measured data for CLs with the same composition. With increasing i/C ratio, the smaller pores disappear and the number of isolated pores increases; while the ionomer connection and its coverage on Pt are significantly enhanced at i/C ∼1.0. With increasing Pt/C ratio, the Pt inter-particle distance decreases as the particles connect with each other. The tortuosity of the pores and the ionomer exhibits a trade-off relation depending on the ionomer volume. Further CL design concepts to optimize both O2 diffusion and H+ conduction are discussed.

Long life hydrocarbon conversion catalyst and method of making

DOEpatents

Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Gao, Yufei [Kennewick, WA

2002-11-12

The present invention includes a catalyst that has at least four layers, (1) porous support, (2) buffer layer, (3) interfacial layer, and optionally (4) catalyst layer. The buffer layer provides a transition of thermal expansion coefficient from the porous support to the interfacial layer thereby reducing thermal expansion stress as the catalyst is heated to high operating temperatures. The method of the present invention for making the at least three layer catalyst has the steps of (1) selecting a porous support, (2) solution depositing an interfacial layer thereon, and optionally (3) depositing a catalyst material onto the interfacial layer; wherein the improvement comprises (4) depositing a buffer layer between the porous support and the interfacial layer.

Fischer-Tropsch Synthesis: XANES Investigation of Hydrogen Chloride Poisoned Iron and Cobalt-Based Catalysts at the K-Edges of Cl, Fe, and Co

DOE PAGES

Pendyala, Venkat Ramana Rao; Jacobs, Gary; Ma, Wenping; ...

2016-07-23

The effect of co-fed hydrogen chloride (HCl) in syngas on the performance of iron and cobalt-based Fischer-Tropsch (FT) catalysts was investigated in our earlier studies [ACS Catal. 5 (2015) 3124-3136 and DOE final report 2011; Catal. Lett. 144 (2014) 1127-1133]. For an iron catalyst, lower HCl concentrations (< 2.0 ppmw of HCl)) in syngas did not significantly affect the activity, whereas rapid deactivation occurred at higher concentrations (~20 ppmw). With cobalt catalysts, even low concentrations of HCl (100 ppbw) caused catalyst deactivation, and the deactivation rate increased with increasing HCl concentration in the syngas. The deactivation of the catalysts ismore » explained by the chloride being adsorbed on the catalyst surface to (1) block the active sites and/or (2) electronically modify the sites. In this study, XANES spectroscopy was employed to investigate HCl poisoning mechanism on the iron and cobalt catalysts. Cl K-edge normalized XANES results indicate that Cl is indeed present on the catalyst following HCl poisoning and exhibits a structure similar to the family of compounds MCl; two main peaks are formed, with the second peak consisting of a main peak and a higher energy shoulder. At the Co K and Fe K edges, the white line was observed to be slightly increased relative to the same catalyst under clean conditions. There is then the additional possibility that Cl adsorption may act in part to intercept electron density from the FT metallic function (e.g.,cobalt or iron carbide). If so, this would result in less back-donation and therefore hinder the scission of molecules such as CO.« less

Photo-reduction of CO2 Using a Rhenium Complex Covalently Supported on a Graphene/TiO2 Composite.

PubMed

Cui, Shi-Cong; Sun, Xue-Zhong; Liu, Jin-Gang

2016-07-07

One of the promising solutions for decreasing atmospheric CO2 is artificial photosynthesis, in which CO2 can be photoconverted into solar fuels. In this study, a rhenium complex Re(PyBn)(CO)3 Cl (PyBn=1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole) was covalently grafted onto the surface of reduced graphene oxide (rGO). This was further combined with TiO2 to fabricate a novel catalyst composite TiO2 -rGO-Re(PyBn)(CO)3 Cl for CO2 photo-reduction. This hybrid composite demonstrated high selectivity conversion of CO2 into CO under xenon-lamp irradiation. Compared with the unsupported homogeneous catalyst Re(PyBn)(CO)3 Cl, the covalent immobilized catalyst composite TiO2 -rGO-Re(PyBn)(CO)3 Cl enhanced the turnover number six times and significantly improved catalyst stability. During the process of CO2 photo-reduction, intermediate species with lifetimes longer than hundreds of microseconds were observed and the formation of CO products was revealed using timeresolved infrared spectroscopy. A plausible mechanism for CO2 photo-reduction by the TiO2 -rGO-Re(PyBn)(CO)3 Cl catalyst composite has been suggested. The obtained results have implications for the future design of efficient catalyst composites for CO2 photo-conversion. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Catalysts for oxidation of mercury in flue gas

DOEpatents

Granite, Evan J [Wexford, PA; Pennline, Henry W [Bethel Park, PA

2010-08-17

Two new classes of catalysts for the removal of heavy metal contaminants, especially mercury (Hg) from effluent gases. Both of these classes of catalysts are excellent absorbers of HCl and Cl.sub.2 present in effluent gases. This adsorption of oxidizing agents aids in the oxidation of heavy metal contaminants. The catalysts remove mercury by oxidizing the Hg into mercury (II) moieties. For one class of catalysts, the active component is selected from the group consisting of iridium (Ir) and iridum-platinum (Ir/Pt) alloys. The Ir and Ir/Pt alloy catalysts are especially corrosion resistant. For the other class of catalyst, the active component is partially combusted coal or "Thief" carbon impregnated with Cl.sub.2. Untreated Thief carbon catalyst can be self-activating in the presence of effluent gas streams. The Thief carbon catalyst is disposable by means of capture from the effluent gas stream in a particulate collection device (PCD).

The Experimental Measurement of Local and Bulk Oxygen Transport Resistances in the Catalyst Layer of Proton Exchange Membrane Fuel Cells.

PubMed

Wang, Chao; Cheng, Xiaojing; Lu, Jiabin; Shen, Shuiyun; Yan, Xiaohui; Yin, Jiewei; Wei, Guanghua; Zhang, Junliang

2017-12-07

Remarkable progress has been made in reducing the cathodic Pt loading of PEMFCs; however, a huge performance loss appears at high current densities, indicating the existence of a large oxygen transport resistance associated with the ultralow Pt loading catalyst layer. To reduce the Pt loading without sacrificing cell performance, it is essential to illuminate the oxygen transport mechanism in the catalyst layer. Toward this goal, an experimental approach to measure the oxygen transport resistance in catalyst layers is proposed and realized for the first time in this study. The measuring approach involves a dual-layer catalyst layer design, which consists of a dummy catalyst layer and a practical catalyst layer, followed by changing the thickness of dummy layer to respectively quantify the local and bulk resistances via limiting current measurements combined with linear extrapolation. The experimental results clearly reveal that the local resistance dominates the total resistance in the catalyst layer.

Recovery of Platinum Group Metals from Spent Catalysts Using Iron Chloride Vapor Treatment

NASA Astrophysics Data System (ADS)

Taninouchi, Yu-ki; Okabe, Toru H.

2018-05-01

The recovery of platinum group metals (PGMs) from spent automobile catalysts is a difficult process because of their relatively low contents in the scrap. In this study, to improve the efficiency of the existing recycling techniques, a novel physical concentration method involving treatment with FeCl2 vapor has been examined. The reactions occurring between typical catalyst components and FeCl2 vapor are discussed from the thermodynamic point of view, and the validity of the proposed technique was experimentally verified. The obtained results indicate that the vapor treatment at around 1200 K (927 °C) can effectively alloy PGMs (Pt, Pd, and Rh) with Fe, resulting in the formation of a ferromagnetic alloy. It was also confirmed that cordierite and alumina (the major catalyst components) remained unreacted after the vapor treatment, while ceria species were converted into oxychlorides. The samples simulating the automobile catalyst were also subjected to magnetic separation after the treatment with FeCl2 vapor; as a result, PGMs were successfully extracted and concentrated in the form of a magnetic powder. Thus, the FeCl2 vapor treatment followed by magnetic separation can be utilized for recovering PGMs directly from spent catalysts as an effective pretreatment for the currently used recycling methods.

Catalyst, method of making, and reactions using the catalyst

DOEpatents

Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Gao, Yufei [Kennewick, WA

2009-03-03

The present invention includes a catalyst having a layered structure with, (1) a porous support, (2) a buffer layer, (3) an interfacial layer, and optionally (4) a catalyst layer. The invention also provides a process in which a reactant is converted to a product by passing through a reaction chamber containing the catalyst.

Catalyst, method of making, and reactions using the catalyst

DOEpatents

Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Gao, Yufei [Kennewick, WA

2002-08-27

The present invention includes a catalyst having a layered structure with, (1) a porous support, (2) a buffer layer, (3) an interfacial layer, and optionally (4) a catalyst layer. The invention also provides a process in which a reactant is converted to a product by passing through a reaction chamber containing the catalyst.

Catalyst, Method Of Making, And Reactions Using The Catalyst

DOEpatents

Tonkovich, Anna Lee Y.; Wang, Yong; Gao, Yufei

2004-07-13

The present invention includes a catalyst having a layered structure with, (1) a porous support, (2) a buffer layer, (3) an interfacial layer, and optionally (4) a catalyst layer. The invention also provides a process in which a reactant is converted to a product by passing through a reaction chamber containing the catalyst.

Impact of linker engineering on the catalytic activity of metal–organic frameworks containing Pd(II)–bipyridine complexes

DOE PAGES

Li, Xinle; Van Zeeland, Ryan; Maligal-Ganesh, Raghu V.; ...

2016-08-09

A series of mixed-linker bipyridyl metal–organic framework (MOF)-supported palladium(II) catalysts were used to elucidate the electronic and steric effects of linker substitution on the activity of these catalysts in the context of Suzuki–Miyaura cross-coupling reactions. m-6,6'-Me 2bpy-MOF-PdCl 2 exhibited 110- and 496-fold enhancements in activity compared to nonfunctionalized m-bpy-MOF-PdCl 2 and m-4,4'-Me 2bpy-MOF-PdCl 2, respectively. Furthermore, this result clearly demonstrates that the stereoelectronic properties of metal-binding linker units are critical to the activity of single-site organometallic catalysts in MOFs and highlights the importance of linker engineering in the design and development of efficient MOF catalysts.

Catalytic activity of CuOn-La2O3/gamma-Al2O3 for microwave assisted ClO2 catalytic oxidation of phenol wastewater.

PubMed

Bi, Xiaoyi; Wang, Peng; Jiang, Hong

2008-06-15

In order to develop a catalyst with high activity and stability for microwave assisted ClO2 catalytic oxidation, we prepared CuOn-La2O3/gamma-Al2O3 by impregnation-deposition method, and determined its properties using BET, XRF, XPS and chemical analysis techniques. The test results show that, better thermal ability of gamma-Al2O3 and high loading of Cu in the catalyst can be achieved by adding La2O3. The microwave assisted ClO2 catalytic oxidation process with CuOn-La2O3/gamma-Al2O3 used as catalyst was also investigated, and the results show that the catalyst has an excellent catalytic activity in treating synthetic wastewater containing 100 mg/L phenol, and 91.66% of phenol and 50.35% of total organic carbon (TOC) can be removed under the optimum process conditions. Compared with no catalyst process, CuOn-La2O3/gamma-Al2O3 can effectively degrade contaminants in short reaction time and with low oxidant dosage, extensive pH range. The comparison of phenol removal efficiency in the different process indicates that microwave irradiation and catalyst work together to oxidize phenol effectively. It can therefore be concluded from results and discussion that CuOn-La2O3/gamma-Al2O3 is a suitable catalyst in microwave assisted ClO2 catalytic oxidation process.

Conductive polymer layers to limit transfer of fuel reactants to catalysts of fuel cells to reduce reactant crossover

DOEpatents

Stanis, Ronald J.; Lambert, Timothy N.

2016-12-06

An apparatus of an aspect includes a fuel cell catalyst layer. The fuel cell catalyst layer is operable to catalyze a reaction involving a fuel reactant. A fuel cell gas diffusion layer is coupled with the fuel cell catalyst layer. The fuel cell gas diffusion layer includes a porous electrically conductive material. The porous electrically conductive material is operable to allow the fuel reactant to transfer through the fuel cell gas diffusion layer to reach the fuel cell catalyst layer. The porous electrically conductive material is also operable to conduct electrons associated with the reaction through the fuel cell gas diffusion layer. An electrically conductive polymer material is coupled with the fuel cell gas diffusion layer. The electrically conductive polymer material is operable to limit transfer of the fuel reactant to the fuel cell catalyst layer.

Unexpected effect of catalyst concentration on photochemical CO2 reduction by trans(Cl)–Ru(bpy)(CO)2Cl2: new mechanistic insight into the CO/HCOO– selectivity† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc00199d Click here for additional data file.

PubMed Central

Kuramochi, Yusuke; Itabashi, Jun; Fukaya, Kyohei; Enomoto, Akito; Yoshida, Makoto

2015-01-01

Photochemical CO2 reduction catalysed by trans(Cl)–Ru(bpy)(CO)2Cl2 (bpy = 2,2′-bipyridine) efficiently produces carbon monoxide (CO) and formate (HCOO–) in N,N-dimethylacetamide (DMA)/water containing [Ru(bpy)3]2+ as a photosensitizer and 1-benzyl-1,4-dihydronicotinamide (BNAH) as an electron donor. We have unexpectedly found catalyst concentration dependence of the product ratio (CO/HCOO–) in the photochemical CO2 reduction: the ratio of CO/HCOO– decreases with increasing catalyst concentration. The result has led us to propose a new mechanism in which HCOO– is selectively produced by the formation of a Ru(i)–Ru(i) dimer as the catalyst intermediate. This reaction mechanism predicts that the Ru–Ru bond dissociates in the reaction of the dimer with CO2, and that the insufficient electron supply to the catalyst results in the dominant formation of HCOO–. The proposed mechanism is supported by the result that the time-course profiles of CO and HCOO– in the photochemical CO2 reduction catalysed by [Ru(bpy)(CO)2Cl]2 (0.05 mM) are very similar to those of the reduction catalysed by trans(Cl)–Ru(bpy)(CO)2Cl2 (0.10 mM), and that HCOO– formation becomes dominant under low-intensity light. The kinetic analyses based on the proposed mechanism could excellently reproduce the unusual catalyst concentration effect on the product ratio. The catalyst concentration effect observed in the photochemical CO2 reduction using [Ru(4dmbpy)3]2+ (4dmbpy = 4,4′-dimethyl-2,2′-bipyridine) instead of [Ru(bpy)3]2+ as the photosensitizer is also explained with the kinetic analyses, reflecting the smaller quenching rate constant of excited [Ru(4dmbpy)3]2+ by BNAH than that of excited [Ru(bpy)3]2+. We have further synthesized trans(Cl)–Ru(6Mes-bpy)(CO)2Cl2 (6Mes-bpy = 6,6′-dimesityl-2,2′-bipyridine), which bears bulky substituents at the 6,6′-positions in the 2,2′-bipyridyl ligand, so that the ruthenium complex cannot form the dimer due to the steric hindrance. We have found that this ruthenium complex selectively produces CO, which strongly supports the catalytic mechanism proposed in this work. PMID:28706681

PEMFC catalyst layers: the role of micropores and mesopores on water sorption and fuel cell activity.

PubMed

Soboleva, Tatyana; Malek, Kourosh; Xie, Zhong; Navessin, Titichai; Holdcroft, Steven

2011-06-01

The effects of carbon microstructure and ionomer loading on water vapor sorption and retention in catalyst layers (CLs) of PEM fuel cells are investigated using dynamic vapor sorption. Catalyst layers based on Ketjen Black and Vulcan XC-72 carbon blacks, which possess distinctly different surface areas, pore volumes, and microporosities, are studied. It is found that pores <20 nm diameter facilitate water uptake by capillary condensation in the intermediate range of relative humidities. A broad pore size distribution (PSD) is found to enhance water retention in Ketjen Black-based CLs whereas the narrower mesoporous PSD of Vulcan CLs is shown to have an enhanced water repelling action. Water vapor sorption and retention properties of CLs are correlated to electrochemical properties and fuel cell performance. Water sorption enhances electrochemical properties such as the electrochemically active surface area (ESA), double layer capacitance and proton conductivity, particularly when the ionomer content is very low. The hydrophilic properties of a CL on the anode and the cathode are adjusted by choosing the PSD of carbon and the ionomer content. It is shown that a reduction of ionomer content on either cathode or anode of an MEA does not necessarily have a significant detrimental effect on the MEA performance compared to the standard 30 wt % ionomer MEA. Under operation in air and high relative humidity, a cathode with a narrow pore size distribution and low ionomer content is shown to be beneficial due to its low water retention properties. In dry operating conditions, adequate ionomer content on the cathode is crucial, whereas it can be reduced on the anode without a significant impact on fuel cell performance. © 2011 American Chemical Society

Cathodes for lithium-air battery cells with acid electrolytes

DOEpatents

Xing, Yangchuan; Huang, Kan; Li, Yunfeng

2016-07-19

In various embodiments, the present disclosure provides a layered metal-air cathode for a metal-air battery. Generally, the layered metal-air cathode comprises an active catalyst layer, a transition layer bonded to the active catalyst layer, and a backing layer bonded to the transition layer such that the transition layer is disposed between the active catalyst layer and the backing layer.

DOE Award No. DE-FC36-03GO13108 NOVEL NON-PRECIOUS METAL CATALYSTS FOR PEMFC: CATALYST SELECTION THROUGH MOLECULAR MODELING AND DURABILITY STUDIES Final Report (September 2003 – October 2008)

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

Branko N. Popov

2009-03-03

The objective of this project is to develop novel non-precious metal electrocatalysts for oxygen reduction reaction (ORR), and demonstrate the potential of the catalysts to perform at least as good as conventional Pt catalysts currently in use in polymer electrolyte membrane fuel cell (PEMFC) with a cost at least 50 % less than a target of 0.2 g (Pt loading)/peak kW and with durability > 2,000 h operation with less than 10 % power degradation. A novel nitrogen-modified carbon-based catalyst was obtained by modifying carbon black with nitrogen-containing organic precursor in the absence of transition metal precursor. The catalyst showsmore » the onset potential of approximately 0.76 V (NHE) for ORR and the amount of H2O2 of approximately 3% at 0.5 V (NHE). Furthermore, a carbon composite catalyst was achieved through the high-temperature pyrolysis of the precursors of transition metal (Co and Fe) and nitrogen supported on the nitrogen-modified carbon-based catalyst, followed by chemical post-treatment. This catalyst showed an onset potential for ORR as high as 0.87 V (NHE), and generated less than 1 % of H2O2. The PEM fuel cell exhibited a current density of 2.3 A cm-2 at 0.2 V for a catalyst loading of 6.0 mg cm-2. No significant performance degradation was observed for 480 h continuous operation. The characterization studies indicated that the metal-nitrogen chelate complexes decompose at the temperatures above 800 oC. During the pyrolysis, the transition metals facilitate the incorporation of pyridinic and graphitic nitrogen groups into the carbon matrix, and the carbon surface modified with nitrogen is active for ORR. In order to elucidate the role of transition metal precursor played in the formation of active sites in the non-precious metal catalysts, a novel ruthenium-based chelate (RuNx) catalyst was synthesized by using RuCl3 and propylene diammine as the Ru and N precursors, respectively, followed by high-temperature pyrolysis. This catalyst exhibited comparable catalytic activity and selectivity for ORR as the Pt catalyst. A theoretical analysis is made of the four-electron reduction reaction of oxygen to water over the mixed anion and cation (202) surface of pentlandite structure Co9Se8, one of several selenide phases. Reversible potentials for forming adsorbed reaction intermediates in acid are predicted using adsorption energies calculated with the Vienna ab initio simulation program (VASP) and the known bulk solution values together in a linear Gibbs energy relationship. The effect of hydrophobic and structural properties of a single/dual-layer cathode gas diffusion layer on mass transport in PEM fuel cells was studied using an analytical expression. The simulations indicated that liquid water transport at the cathode is controlled by the fraction of hydrophilic surface and the average pore diameter in the cathode gas diffusion layer. The optimized hydrophobicity and pore geometry in a dual-layer cathode GDL leads to an effective water management, and enhances the oxygen diffusion kinetics.« less

DOE Award No. DE-FC36-03GO13108 NOVEL NON-PRECIOUS METAL CATALYSTS FOR PEMFC: CATALYST SELECTION THROUGH MOLECULAR MODELING AND DURABILITY STUDIES Final Report (September 2003 – October 2008)

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

Branko N. Popov

2009-02-20

The objective of this project is to develop novel non-precious metal electrocatalysts for oxygen reduction reaction (ORR), and demonstrate the potential of the catalysts to perform at least as good as conventional Pt catalysts currently in use in polymer electrolyte membrane fuel cell (PEMFC) with a cost at least 50 % less than a target of 0.2 g (Pt loading)/peak kW and with durability > 2,000 h operation with less than 10 % power degradation. A novel nitrogen-modified carbon-based catalyst was obtained by modifying carbon black with nitrogen-containing organic precursor in the absence of transition metal precursor. The catalyst showsmore » the onset potential of approximately 0.76 V (NHE) for ORR and the amount of H2O2 of approximately 3% at 0.5 V (NHE). Furthermore, a carbon composite catalyst was achieved through the high-temperature pyrolysis of the precursors of transition metal (Co and Fe) and nitrogen supported on the nitrogen-modified carbon-based catalyst, followed by chemical post-treatment. This catalyst showed an onset potential for ORR as high as 0.87 V (NHE), and generated less than 1 % of H2O2. The PEM fuel cell exhibited a current density of 2.3 A cm-2 at 0.2 V for a catalyst loading of 6.0 mg cm-2. No significant performance degradation was observed for 480 h continuous operation. The characterization studies indicated that the metal-nitrogen chelate complexes decompose at the temperatures above 800 oC. During the pyrolysis, the transition metals facilitate the incorporation of pyridinic and graphitic nitrogen groups into the carbon matrix, and the carbon surface modified with nitrogen is active for ORR. In order to elucidate the role of transition metal precursor played in the formation of active sites in the non-precious metal catalysts, a novel ruthenium-based chelate (RuNx) catalyst was synthesized by using RuCl3 and propylene diammine as the Ru and N precursors, respectively, followed by high-temperature pyrolysis. This catalyst exhibited comparable catalytic activity and selectivity for ORR as the Pt catalyst. A theoretical analysis is made of the four-electron reduction reaction of oxygen to water over the mixed anion and cation (202) surface of pentlandite structure Co9Se8, one of several selenide phases. Reversible potentials for forming adsorbed reaction intermediates in acid are predicted using adsorption energies calculated with the Vienna ab initio simulation program (VASP) and the known bulk solution values together in a linear Gibbs energy relationship. The effect of hydrophobic and structural properties of a single/dual-layer cathode gas diffusion layer on mass transport in PEM fuel cells was studied using an analytical expression. The simulations indicated that liquid water transport at the cathode is controlled by the fraction of hydrophilic surface and the average pore diameter in the cathode gas diffusion layer. The optimized hydrophobicity and pore geometry in a dual-layer cathode GDL leads to an effective water management, and enhances the oxygen diffusion kinetics.« less

Biosourced polymetallic catalysts: an efficient means to synthesize underexploited platform molecules from carbohydrates.

PubMed

Escande, Vincent; Olszewski, Tomasz K; Petit, Eddy; Grison, Claude

2014-07-01

Polymetallic hyperaccumulating plants growing on wastes from former mining activity were used as the starting material in the preparation of novel plant-based Lewis acid catalysts. The preparation of biosourced Lewis acid catalysts is a new way to make use of mining wastes. These catalysts were characterized by X-ray fluorescence, X-ray diffraction, inductively coupled plasma mass spectrometry, and direct infusion electrospray ionization mass spectrometry. These analyses revealed a complex composition of metal species, present mainly as polymetallic chlorides. The catalysts proved to be efficient and recyclable in a solid-state version of the Garcia Gonzalez reaction, which has been underexploited until now in efforts to use carbohydrates from biomass. This methodology was extended to various carbohydrates to obtain the corresponding polyhydroxyalkyl furans in 38-98% yield. These plant-based catalysts may be a better alternative to classical Lewis acid catalysts that were previously used for the Garcia Gonzalez reaction, such as ZnCl2 , FeCl3 , and CeCl3 , which are often unrecyclable, require aqueous treatments, or rely on metals, the current known reserves of which will be consumed in the coming decades. Moreover, the plant-based catalysts allowed novel control of the Garcia Gonzalez reaction, as two different products were obtained depending on the reaction conditions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The preparation of nanosized polyethylene particles via novel heterogeneous non-metallocene catalyst (m-CH3PhO)TiCl3/CNTs/AlEt3

NASA Astrophysics Data System (ADS)

Wang, J.; Guo, J. P.; Yi, J. J.; Huang, Q. G.; Li, H. M.; Li, Y. F.; Gao, K. J.; Yang, W. T.

2014-08-01

This paper reports the preparation of coral-shaped topological morphology nascent polyethylene (PE) particles promoted by the novel heterogeneous non-metallocene catalyst (m-CH3PhO)TiCl3/carbon nanotubes (CNTs), with AlEt3 used as a cocatalyst. Scanning electron microscope (SEM), high resolution transmission electron microscope (HR-TEM) and inductively coupled plasma (ICP) emission spectroscopy were used to determine the morphology of the catalyst particles and the content of (m-CH3PhO)TiCl3. The carbon nanotube surface was treated with Grignard Reagent prior to reacting with (m-CH3PhO)TiCl3. The catalyst system could effectively catalyze ethylene polymerization and ethylene with 1- hexene copolymerization, the catalytic activity could reach up to 5.8 kg/((gTi)h). Morphology of the obtained polymer particles by SEM and HR-TEM technique revealed that the nascent polyethylene particles looked like coral shape in micro-size. The multiwalled carbon nanotubes (MWCNTs) supported catalysts polymerized ethylene to form polymer nanocomposite in situ. The microscopic examination of this nanocomposite revealed that carbon nanoparticles in PE matrix had a good distribution and the cryogenically fractured surface was ductile-like when polymerization time was 2 min.

The catalyst layer and its dimensionality - A look into its ingredients and how to characterize their effects

NASA Astrophysics Data System (ADS)

Zamel, Nada

2016-03-01

Development of polymer electrolyte membrane (PEM) fuel cells throughout the years is established through its component optimization. This is especially true of its catalyst layer, where structuring of the layer has led to many breakthroughs. The catalyst layer acts as the heart of the cell, where it controls the half-cell reactions and their products. The complex nature of various transport phenomena simultaneously taking place in the layer requires the layer to be heterogeneous in structure. Hence, a delicate balance of the layer's ingredients, coupled with the understanding of the ingredients' interaction, is required. State-of-the-art catalyst layers are composed of a catalyst, its support, a solvent and a binder. Changes in the morphology, structure or material of any of these components ultimately affects the layer's activity and durability. In this review paper, we provide an overview of the various works tailored to understand how each component in the catalyst's ink affects the stability and life-time of the layer.

Kinetics of NiO and NiCl2 Hydrogen Reduction as Precursors and Properties of Produced Ni/Al2O3 and Ni-Pd/Al2O3 Catalysts

PubMed Central

Sokić, Miroslav; Kamberović, Željko; Nikolić, Vesna; Marković, Branislav; Korać, Marija; Anđić, Zoran; Gavrilovski, Milorad

2015-01-01

The objects of this investigation were the comparative kinetic analysis of the NiO and NiCl2 reduction by hydrogen during an induction period and elimination of the calcination during the synthesis of Ni/Al2O3 catalysts. The effect of temperature and time on NiO and NiCl2 reduction degrees was studied. Avrami I equation was selected as the most favorable kinetic model and used to determine activation energy of the NiO and NiCl2 reduction for the investigated temperature range (623–923 K) and time intervals (1–5 minutes). The investigation enabled reaching conclusions about the reaction ability and rate of the reduction processes. Afterward, Ni/Al2O3 catalysts were obtained by using oxide and chloride precursor for Ni. The catalysts were supported on alumina-based foam and prepared via aerosol route. Properties of the samples before and after low-temperature hydrogen reduction (633 K) were compared. Obtained results indicated that the synthesis of Ni/Al2O3 catalysts can be more efficient if chloride precursor for Ni is directly reduced by hydrogen during the synthesis process, without the calcination step. In addition, Ni-Pd/Al2O3 catalysts with different metal content were prepared by using chloride precursors. Lower reduction temperature was utilized and the chlorides were almost completely reduced at 533 K. PMID:25789335

Propargylic activation across a heterobimetallic ir-sn catalyst: nucleophilic substitution and indene formation with propargylic alcohols.

PubMed

Chatterjee, Paresh Nath; Roy, Sujit

2010-07-02

A nucleophilic substitution of propargylic alcohols with carbon (arene, heteroarene, and allyltrimethylsilane), sulfur (thiol), oxygen (alcohol), and nitrogen (sulfonamide) nucleophiles has been demonstrated using a high-valent [Ir(COD)(SnCl(3))Cl(mu-Cl)](2) catalyst in 1,2-dichloroethane to afford the corresponding propargylic products in moderate to excellent yields. Alkyl or aryl substituted tertiary propargylic alcohols produce substituted indenes with bulky arenes via allenylic intermediate. An electrophilic mechanism is proposed from Hammett correlation.

Membrane catalyst layer for fuel cells

DOEpatents

Wilson, Mahlon S.

1993-01-01

A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 .mu.m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm.sup.2. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. Alternatively, the catalyst layer is formed by applying a Na.sup.+ form of a perfluorosulfonate ionomer directly to the membrane, drying the film at a high temperature, and then converting the film back to the protonated form of the ionomer. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

Effects of composition of the micro porous layer and the substrate on performance in the electrochemical reduction of CO2 to CO

NASA Astrophysics Data System (ADS)

Kim, Byoungsu; Hillman, Febrian; Ariyoshi, Miho; Fujikawa, Shigenori; Kenis, Paul J. A.

2016-04-01

With the development of better catalysts, mass transport limitations are becoming a challenge to high throughput electrochemical reduction of CO2 to CO. In contrast to optimization of electrodes for fuel cells, optimization of gas diffusion electrodes (GDE) - consisting of a carbon fiber substrate (CFS), a micro porous layer (MPL), and a catalyst layer (CL) - for CO2 reduction has not received a lot of attention. Here, we studied the effect of the MPL and CFS composition on cathode performance in electroreduction of CO2 to CO. In a flow reactor, optimized GDEs exhibited a higher partial current density for CO production than Sigracet 35BC, a commercially available GDE. By performing electrochemical impedance spectroscopy in a CO2 flow reactor we determined that a loading of 20 wt% PTFE in the MPL resulted in the best performance. We also investigated the influence of the thickness and wet proof level of CFS with two different feeds, 100% CO2 and the mixture of 50% CO2 and N2, determining that thinner and lower wet proofing of the CFS yields better cathode performance than when using a thicker and higher wet proof level of CFS.

Enhanced Thermal Decomposition Properties of CL-20 through Space-Confining in Three-Dimensional Hierarchically Ordered Porous Carbon.

PubMed

Chen, Jin; He, Simin; Huang, Bing; Wu, Peng; Qiao, Zhiqiang; Wang, Jun; Zhang, Liyuan; Yang, Guangcheng; Huang, Hui

2017-03-29

High energy and low signature properties are the future trend of solid propellant development. As a new and promising oxidizer, hexanitrohexaazaisowurtzitane (CL-20) is expected to replace the conventional oxidizer ammonium perchlorate to reach above goals. However, the high pressure exponent of CL-20 hinders its application in solid propellants so that the development of effective catalysts to improve the thermal decomposition properties of CL-20 still remains challenging. Here, 3D hierarchically ordered porous carbon (3D HOPC) is presented as a catalyst for the thermal decomposition of CL-20 via synthesizing a series of nanostructured CL-20/HOPC composites. In these nanocomposites, CL-20 is homogeneously space-confined into the 3D HOPC scaffold as nanocrystals 9.2-26.5 nm in diameter. The effect of the pore textural parameters and surface modification of 3D HOPC as well as CL-20 loading amount on the thermal decomposition of CL-20 is discussed. A significant improvement of the thermal decomposition properties of CL-20 is achieved with remarkable decrease in decomposition peak temperature (from 247.0 to 174.8 °C) and activation energy (from 165.5 to 115.3 kJ/mol). The exceptional performance of 3D HOPC could be attributed to its well-connected 3D hierarchically ordered porous structure, high surface area, and the confined CL-20 nanocrystals. This work clearly demonstrates that 3D HOPC is a superior catalyst for CL-20 thermal decomposition and opens new potential for further applications of CL-20 in solid propellants.

Study of superhydrophobic electrosprayed catalyst layers using a localized reference electrode technique

NASA Astrophysics Data System (ADS)

Chaparro, A. M.; Ferreira-Aparicio, P.; Folgado, M. A.; Brightman, E.; Hinds, G.

2016-09-01

The performance of electrosprayed cathode catalyst layers in a polymer electrolyte membrane fuel cell (PEMFC) is studied using a localized reference electrode technique. Single cells with an electrosprayed cathode catalyst layer show an increase of >20% in maximum power density under standard testing conditions, compared with identical cells assembled with a conventional, state-of-the-art, gas diffusion cathode. When operated at high current density (1.2 A cm-2) the electrosprayed catalyst layers show more homogeneous distribution of the localized cathode potential, with a standard deviation from inlet to outlet of <50 mV, compared with 79 mV for the conventional gas diffusion cathode. Higher performance and homogeneity of cell response is attributed to the superhydrophobic nature of the macroporous electrosprayed catalyst layer structure, which enhances the rate of expulsion of liquid water from the cathode. On the other hand, at low current densities (<0.5 A cm-2), the electrosprayed layers exhibit more heterogeneous distribution of cathode potential than the conventional cathodes; this behavior is attributed to less favorable kinetics for oxygen reduction in very hydrophobic catalyst layers. The optimum performance may be obtained with electrosprayed catalyst layers employing a high Pt/C catalyst ratio.

Local Platinum Environments in a Solid Analogue of the Molecular Periana Catalyst

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

Soorholtz, Mario; Jones, Louis C.; Samuelis, Dominik

2016-02-16

Combining advantages of homogeneous and heterogeneous catalysis by incorporating active species on a solid support is often an effective strategy for improving overall catalyst performance, although the influences of the support are generally challenging to establish, especially at a molecular level. In this paper, we report the local compositions, and structures of platinum species incorporated into covalent triazine framework (Pt-CTF) materials, a solid analogue of the molecular Periana catalyst, Pt(bpym)Cl 2, both of which are active for the selective oxidation of methane in the presence of concentrated sulfuric acid. By using a combination of solid-state 195Pt nuclear magnetic resonance (NMR)more » spectroscopy, aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), important similarities and differences are observed between the Pt-CTF and Periana catalysts, which are likely related to their respective macroscopic reaction properties. In particular, wide-line solid-state 195Pt NMR spectra enable direct measurement, identification, and quantification of distinct platinum species in as-synthesized and used Pt-CTF catalysts. The results indicate that locally ordered and disordered Pt sites are present in as-synthesized Pt-CTF, with the former being similar to one of the two crystallographically distinct Pt sites in crystalline Pt(bpym)Cl 2. A distribution of relatively disordered Pt moieties is also present in the used catalyst, among which are the principal active sites. Similarly XAS shows good agreement between the measured data of Pt-CTF and a theoretical model based on Pt(bpym)Cl 2. Analyses of the absorption spectra of Pt-CTF used for methane oxidation suggests ligand exchange, as predicted for the molecular catalyst. XPS analyses of Pt(bpym)Cl 2, Pt-CTF, as well as the unmodified ligands, further corroborate platinum coordination by pyridinic N atoms. Aberration-corrected high-angle annular dark-field STEM proves that Pt atoms are distributed within Pt-CTF before and after catalysis. Finally, the overall results establish the close similarities of Pt-CTF and the molecular Periana catalyst Pt(bpym)Cl 2, along with differences that account for their respective properties.« less

Comparison of real waste (MSW and MPW) pyrolysis in batch reactor over different catalysts. Part II: contaminants, char and pyrolysis oil properties.

PubMed

Miskolczi, Norbert; Ateş, Funda; Borsodi, Nikolett

2013-09-01

Pyrolysis of real wastes (MPW and MSW) has been investigated at 500°C, 550°C and 600°C using Y-zeolite, β-zeolite, equilibrium FCC, MoO3, Ni-Mo-catalyst, HZSM-5 and Al(OH)3 as catalysts. The viscosity of pyrolysis oils could be decreased by the using of catalysts, especially by β-zeolite and MoO3. Both carbon frame and double bound isomerization was found in case of thermo-catalytic pyrolysis. Char morphology and texture analysis showed more coke deposits on the catalyst surface using MSW raw material. Pyrolysis oils had K, S, P Cl, Ca, Zn, Fe, Cr, Br and Sb as contaminants; and the concentrations of K, S, P, Cl and Br could be decreased by the using of catalysts. Copyright © 2013 Elsevier Ltd. All rights reserved.

Characterisation of a PdCl 2/SnCl 2 electroless plating catalyst system adsorbed on barium titanate-based electroactive ceramics

NASA Astrophysics Data System (ADS)

Meenan, B. J.; Brown, N. M. D.; Wilson, J. W.

1994-03-01

A PdCl 2/SnCl 2 metallisation catalyst system, of the type used to activate non-conducting surfaces for electroless metal deposition, has been characterised by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The substrate is a barium titanate (BaTiO 3)-based electroactive ceramic of the type used in the fabrication of multilayer ceramic capacitors (MLCC). The treatment of the substrate surface with the PdCl 2/SnCl 2 "sensitiser" solution leads to the adsorption of catalytically inactive compounds of palladium and tin. Subsequent treatment of this surface with an "accelerator" solution removes excess oxides, hydroxides and salts of tin thereby leaving the active catalyst species, Pd xSn y, on the surface. Such sites, on exposure to the appropriete electroless plating bath, are then responsible for the metal deposition. In this study, the chemical state and relative quantities of the various surface species present after each of the processing stages have been determined by XPS. The surface roughness of the substrate results in less of the tin compounds present thereon being removed on washing the catalysed surface in the accelerator solution than normally reported for such systems, thereby affecting the measured Pd: Sn ratio. SEM studies show that the accelerator solution treatment generates crystalline areas, which may be a result of coagulation of the Pd xSn y particles present, in the otherwise amorphous catalyst coating.

Isotope exchange in oxide-containing catalyst

NASA Technical Reports Server (NTRS)

Brown, Kenneth G. (Inventor); Upchurch, Billy T. (Inventor); Hess, Robert V. (Inventor); Miller, Irvin M. (Inventor); Schryer, David R. (Inventor); Sidney, Barry D. (Inventor); Wood, George M. (Inventor); Hoyt, Ronald F. (Inventor)

1989-01-01

A method of exchanging rare-isotope oxygen for common-isotope oxygen in the top several layers of an oxide-containing catalyst is disclosed. A sample of an oxide-containing catalyst is exposed to a flowing stream of reducing gas in an inert carrier gas at a temperature suitable for the removal of the reactive common-isotope oxygen atoms from the surface layer or layers of the catalyst without damaging the catalyst structure. The reduction temperature must be higher than any at which the catalyst will subsequently operate. Sufficient reducing gas is used to allow removal of all the reactive common-isotope oxygen atoms in the top several layers of the catalyst. The catalyst is then reoxidized with the desired rare-isotope oxygen in sufficient quantity to replace all of the common-isotope oxygen that was removed.

Hydrothermal liquefaction of de-oiled Jatropha curcas cake using Deep Eutectic Solvents (DESs) as catalysts and co-solvents.

PubMed

Alhassan, Yahaya; Kumar, Naveen; Bugaje, Idris M

2016-01-01

Biomass liquefaction using ionic liquids (ILs) as catalysts has received appreciable attention, in renewable fuels and chemicals production, recently. However, issues associated with the production cost, long reaction time and use of volatile solvents are undeniably challenging. Thus, Deep Eutectic Solvents (DESs) emerged as promising and potential ILs substitutes. The hydrothermal liquefaction of de-oiled Jatropha curcas cake was catalyzed by four synthesized DESs as catalysts and co-solvents for selective extraction. Proximate and ultimate analyses including ash, moisture and carbon contents of bio-crude produced varied slightly. The higher heating values found ranges from 21.15 ± 0.82 MJ/kg to 24.30 ± 0.98 MJ/kg. The bio-crude yields obtained using ChCl-KOH DES was 43.53 wt% and ChCl-p-TsOH DES was 38.31 wt%. Bio-crude yield using ChCl-FeCl3 DES was 30.80 wt%. It is suggested that, the selectivity of bio-crude could be improved, by using DESs as catalyst and co-solvent in HTL of biomass such as de-oiled J. curcas cake. Copyright © 2015 Elsevier Ltd. All rights reserved.

Shape Fixing via Salt Recrystallization: A Morphology-Controlled Approach To Convert Nanostructured Polymer to Carbon Nanomaterial as a Highly Active Catalyst for Oxygen Reduction Reaction.

PubMed

Ding, Wei; Li, Li; Xiong, Kun; Wang, Yao; Li, Wei; Nie, Yao; Chen, Siguo; Qi, Xueqiang; Wei, Zidong

2015-04-29

Herein, we report a "shape fixing via salt recrystallization" method to efficiently synthesize nitrogen-doped carbon material with a large number of active sites exposed to the three-phase zones, for use as an ORR catalyst. Self-assembled polyaniline with a 3D network structure was fixed and fully sealed inside NaCl via recrystallization of NaCl solution. During pyrolysis, the NaCl crystal functions as a fully sealed nanoreactor, which facilitates nitrogen incorporation and graphitization. The gasification in such a closed nanoreactor creates a large number of pores in the resultant samples. The 3D network structure, which is conducive to mass transport and high utilization of active sites, was found to have been accurately transferred to the final N-doped carbon materials, after dissolution of the NaCl. Use of the invented cathode catalyst in a proton exchange membrane fuel cell produces a peak power of 600 mW cm(-2), making this among the best nonprecious metal catalysts for the ORR reported so far. Furthermore, N-doped carbon materials with a nanotube or nanoshell morphology can be realized by the invented method.

Determination of NH(3) gas by combination of nanosized LaCoO(3) converter with chemiluminescence detector.

PubMed

Shi, Jinjun; Yan, Ruoxue; Zhu, Yongfa; Zhang, Xinrong

2003-10-17

Combination of a novel NH(3) converter based on nanosized materials with chemiluminescence (CL) detector for the determination of NH(3) gas was demonstrated in this paper. NH(3) gas is oxidized on different nanosized catalysts to produce NO(x), which can react with luminol to generate CL emission. Eight nanosized materials were investigated as catalyst, and CL was detected from seven of them. The nanosized LaCoO(3) was chosen as the catalyst for preparing the converter because of its higher activity than others. Under the optimized conditions, the linear range of CL intensity versus concentration of NH(3) gas is 0.04-10 ppm (r=0.9951, n=14) with the detection limit of 0.014 ppm. The method offers advantages of long lifetime of the converter, fast response and high selectivity to NH(3). There was no response while the foreign substances, such as hydrogen, oxygen, nitrogen, formaldehyde, acetone and gasoline passing through the CL detection system, and the interference of CCl(4), ethanol, ethylene and toluene was insignificant.

Sodium citrate assisted facile synthesis of AuPd alloy networks for ethanol electrooxidation with high activity and durability

NASA Astrophysics Data System (ADS)

Zhai, Yanling; Zhu, Zhijun; Lu, Xiaolin; Zhou, H. Susan

2016-10-01

The direct ethanol fuel cell is an emerging energy conversion device for which palladium is considered as the one of the most effective components for anode catalyst, however, its widespread application has been still limited by the activity and durability of the anode catalyst. In this work, AuPd alloy networks (NWs) are synthesized using H2PdCl4 and HAuCl4 as precursors reduced by NaBH4 in the presence of sodium citrate (SC). The results reveal that SC plays significant role in network structure, resulting in the enhanced electrocatalytic activity of the catalyst. This self-supported AuPd NWs catalyst exhibits much higher electrochemical catalytic activity than commercial Pd/C catalyst toward ethanol electrooxidation in alkaline solution. Significantly, AuPd NWs catalyst shows extremely high durability at the beginning of the chronoamperometry test, and as high as 49% of the mass current density (1.41 A/mgPd) remains after 4000 s current-time test at -0.3 V (vs. Ag/AgCl) in N2-saturated KOH-ethanol solution. This strategy provides a facile method for the preparation of alloy networks with high electrochemical activity, and can be potentially expanded to a variety of electrochemical applications.

Nitrogen-doped graphene/CoNi alloy encased within bamboo-like carbon nanotube hybrids as cathode catalysts in microbial fuel cells

NASA Astrophysics Data System (ADS)

Hou, Yang; Yuan, Heyang; Wen, Zhenhai; Cui, Shumao; Guo, Xiaoru; He, Zhen; Chen, Junhong

2016-03-01

Cost-effective catalysts are of key importance to the successful deployment of microbial fuel cells (MFCs) for electricity generation from organic wastes. Herein, a novel catalyst prepared by one-step synthesis strategy is reported. The catalyst features N-doped bamboo-like carbon nanotube (BCNT) in which CoNi-alloy is encapsulated at the end and/or the middle section of the tube with many graphene layers inside inner cavities of BCNT (N-G@CoNi/BCNT). The prepared N-G@CoNi/BCNT exhibits a high oxygen reduction reaction (ORR) activity with an early onset potential of 0.06 V vs. Ag/AgCl and a comparable exchange current density to that of commercial Pt/C. The excellent catalytic activity is further evidenced by a high electron transfer number of 3.63. When being applied in MFCs, the N-G@CoNi/BCNT yields an average current density of 6.7 A m-2, slightly lower than that of Pt/C but with a less mass transfer potential loss. The cost of the N-G@CoNi/BCNT for constructing a 1-m2 cathode electrode is 200 times lower than that of Pt/C. With such a competitive price and excellent electrocatalytic-activity resulting from its unique morphology, CoNi-alloy/nitrogen dopants, considerable specific surface area, and carbon-coated alloy/graphene hybridization, the present catalyst is a promising candidate for ORR catalysts in MFCs for energy recovery from wastes.

Performance of polymer nano composite membrane electrode assembly using Alginate as a dopant in polymer electrolyte membrane fuel cell

NASA Astrophysics Data System (ADS)

Mulijani, S.

2017-01-01

Polymer membrane and composite polymer for membrane electrode assembly (MEAs) are synthesized and studied for usage in direct methanol fuel cell (DMFC). In this study, we prepared 3 type of MEAs, polystyrene (PS), sulfonated polystyrene (SPS) and composite polymer SPS-alginat membrane via catalyst hot pressed method. The performance and properties of prepared MEAs were evaluated and analyzed by impedance spectrometry and scanning electron microscopy (SEM). The result showed that, water up take of MEA composite polymer SPS-alginate was obtained higher than that in SPS and PS. The proton conductivity of MEA-SPS-alginate was also higher than that PS and PSS. SEM characterization revealed that the intimate contact between the carbon catalyst layers (CL) and the membranes, and the uniformly porous structure correlate positively with the MEAs prepared by hot pressed method, exhibiting high performances for DMFC.

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

DOE PAGES

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

2016-11-10

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

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

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

Baturina, Olga; Lu, Qin; Xu, Feng

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

Apparatus and Process for Controlled Nanomanufacturing Using Catalyst Retaining Structures

NASA Technical Reports Server (NTRS)

Nguyen, Cattien (Inventor)

2013-01-01

An apparatus and method for the controlled fabrication of nanostructures using catalyst retaining structures is disclosed. The apparatus includes one or more modified force microscopes having a nanotube attached to the tip portion of the microscopes. An electric current is passed from the nanotube to a catalyst layer of a substrate, thereby causing a localized chemical reaction to occur in a resist layer adjacent the catalyst layer. The region of the resist layer where the chemical reaction occurred is etched, thereby exposing a catalyst particle or particles in the catalyst layer surrounded by a wall of unetched resist material. Subsequent chemical vapor deposition causes growth of a nanostructure to occur upward through the wall of unetched resist material having controlled characteristics of height and diameter and, for parallel systems, number density.

Oxygen-reducing catalyst layer

DOEpatents

O'Brien, Dennis P [Maplewood, MN; Schmoeckel, Alison K [Stillwater, MN; Vernstrom, George D [Cottage Grove, MN; Atanasoski, Radoslav [Edina, MN; Wood, Thomas E [Stillwater, MN; Yang, Ruizhi [Halifax, CA; Easton, E Bradley [Halifax, CA; Dahn, Jeffrey R [Hubley, CA; O'Neill, David G [Lake Elmo, MN

2011-03-22

An oxygen-reducing catalyst layer, and a method of making the oxygen-reducing catalyst layer, where the oxygen-reducing catalyst layer includes a catalytic material film disposed on a substrate with the use of physical vapor deposition and thermal treatment. The catalytic material film includes a transition metal that is substantially free of platinum. At least one of the physical vapor deposition and the thermal treatment is performed in a processing environment comprising a nitrogen-containing gas.

Pt/Al{sub 2}O{sub 3} catalysts and Pt-Sn/Al{sub 2}O{sub 3} catalysts prepared by two different methods: Hydrogen pressure effects in the reactions of n-hexane

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

Paal, Z.; Gyory, A.; Uszkurat, I.

Pt-Sn/Al{sub 2}O{sub 3} catalysts were prepared using two different methods, namely, by {open_quotes}traditional{close_quotes} coimpregnation with H{sub 2}PtCl{sub 6} and SnCl{sub 4} and by a {open_quotes}new{close_quotes} method in which the bimetallic complex precursor [Pt(NH{sub 3}){sub 4}] [SnCl{sub 6}] is prepared on the support. Their catalytic activity and selectivity in n-hexane reactions were studied as a function of the hydrogen pressure (60-480 Torr) and compared with those of monometallic Pt/Al{sub 2}O{sub 3} catalysts using H{sub 2}PtCl{sub 6} or [Pt(NH{sub 3}){sub 4}]Cl{sub 2} as Pt precursors. Pt/Al{sub 2}O{sub 3} ex [Pt(NH{sub 3}){sub 4}]Cl{sub 2} showed very low dispersion and exhibited high selectivity inmore » reactions attributed to multiatomic ensembles. The results with bimetallic catalysts can be rationalized in terms of two phases being present, a PtSn alloy phase plus Pt in fine distribution. The {open_quotes}new{close_quotes} Pt-Sn/Al{sub 2}O{sub 3} from the bimetallic precursor contains the two metals in a better dispersion, resulting in a larger number of atomically dispersed surface Pt active sites. This catalyst gave more isomers (and methylcyclopentane) and fewer fragments and less benzene than the {open_quotes}traditional{close_quotes} sample. The {open_quotes}new{close_quotes} Pt-Sn/Al{sub 2}O{sub 3} sample possessed good long-term stability. The {open_quotes}traditional{close_quotes} sample lost some of its activity and its high hydrogenolysis selectivity during long use; i.e., it approached the catalytic properties of the {open_quotes}new{close_quotes} sample. Both samples are potential candidates as catalysts with high isomerizing and low aromatic selectivities (up to 75% isohexanes plus methylcyclopentane as opposed to a maximum of 20%, benzene). The results could be explained sufficiently with a geometric model, electronic interactions playing a less important role in the catalytic phenomena observed. 59 refs., 9 figs., 5 tabs.« less

Catalyst containing oxygen transport membrane

DOEpatents

Christie, Gervase Maxwell; Wilson, Jamie Robyn; van Hassel, Bart Antonie

2012-12-04

A composite oxygen transport membrane having a dense layer, a porous support layer and an intermediate porous layer located between the dense layer and the porous support layer. Both the dense layer and the intermediate porous layer are formed from an ionic conductive material to conduct oxygen ions and an electrically conductive material to conduct electrons. The porous support layer has a high permeability, high porosity, and a high average pore diameter and the intermediate porous layer has a lower permeability and lower pore diameter than the porous support layer. Catalyst particles selected to promote oxidation of a combustible substance are located in the intermediate porous layer and in the porous support adjacent to the intermediate porous layer. The catalyst particles can be formed by wicking a solution of catalyst precursors through the porous support toward the intermediate porous layer.

The use of functionalized zirconocenes as precursors to silica-supported zirconocene olefin polymerization catalysts

NASA Astrophysics Data System (ADS)

Cheng, Xu

2001-07-01

Me3Si substituents adjacent to Cp2MCl2 (M = Ti, Zr, Hf) are converted to BrMe2Si groups using BBr 3. The high reactivity of the Si-Br bonds toward nucleophiles such as water suggested that these substituents could react with hydroxylated silica surfaces, immobilizing the metallocenes. This dissertation concerns the syntheses of electrophile-functionalized zirconocene dihalide complexes and their use as precursors to silica-supported metallocene olefin polymerization catalysts. First we extended the metallocene "functionalization" chemistry to obtain substituents bearing more than one electrophilic bond. (Me3Sn) 2C5H4 combined with CpZrCl3 in toluene to afford (eta5-Me3Sn-C5H4)CpZrCl 2 (A). Reactions of A with electrophiles (E-X = Cl2B-Cl, I-Cl, and I-I) afforded (eta5-XMe 2Sn-C5H4)CpZrCl2 (and E-Me) cleanly. The reaction of A with BBr3 afforded either (eta5-BrMe2Sn-C5H4)CpZrBr2 (25 °C, 10 min) or (eta5-Br2MeSn-C5H 4)CpZrBr2 (25 °C, 15 h). Ph2MeSi-C5H 4Li combined with ZrCl4•2THF to afford (eta 5-Ph2MeSi-C5H4)2ZrCl 2 (B). The reaction of B with BCl3 led to incomplete cleavage of the Ph-Si bonds, however treatment of B with BBr3 afforded (eta5-Br2MeSi-C 5H4)2ZrBr2 (C) efficiently. X-ray crystal structures of (eta5-ClMe2Sn-C 5H4)CpZrCl2•1/2toluene, (eta 5-Br2MeSn-C5H4)CpZrBr2•THF, B, and C were obtained. Metallocene C reacts with water to afford an oligosiloxane-supported zirconocene dibromide. Spectroscopic characterization suggested a stereoregular structure in which the metallocene units have meso symmetry. The oligomeric substance showed high activity for homogeneous ethylene polymerization. Supported metallocene olefin polymerization catalysts were prepared by combining a functionalized metallocene precursor (Cp2ZrBr 2 bearing either BrMe2Si or Br2MeSi groups) and partially dehydroxylated silica. The activities of the immobilized zirconocene catalysts decreased and the stabilities increased with increasing number of tethers. The immobilized catalyst prepared from (eta5-Br 2MeSi-C5H4)2ZrBr2, which is assumed to form two "double-tethers" to silica, was significantly more active than the catalyst prepared from [eta5-1,3-(BrMe 2Si)2C5H3]2ZrBr2, which is assumed to form four "single-tethers" to silica. Catalyst leaching was observed in all the immobilized zirconocene catalysts. Finally we report model studies on the stability of the Si-O-Si bonds toward methylaluminoxane (MAO). The reaction of (eta5-BrMe 2Si-C5H4)CpZrBr2 with tBuMe 2SiOH results in the formation of Si-O-Si bonds; addition of NEt 3 results in further reaction to afford Si-O-Zr bonds. The reaction of Me3Si-O-SiMe3 with MAO showed that Si-O-Si bonds can be cleaved under the conditions of our polymerization reactions.

Theoretical examination of effective oxygen diffusion coefficient and electrical conductivity of polymer electrolyte fuel cell porous components

NASA Astrophysics Data System (ADS)

Inoue, Gen; Yokoyama, Kouji; Ooyama, Junpei; Terao, Takeshi; Tokunaga, Tomomi; Kubo, Norio; Kawase, Motoaki

2016-09-01

The reduction of oxygen transfer resistance through porous components consisting of a gas diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL) is very important to reduce the cost and improve the performance of a PEFC system. This study involves a systematic examination of the relationship between the oxygen transfer resistance of the actual porous components and their three-dimensional structure by direct measurement with FIB-SEM and X-ray CT. Numerical simulations were carried out to model the properties of oxygen transport. Moreover, based on the model structure and theoretical equations, an approach to the design of new structures is proposed. In the case of the GDL, the binder was found to obstruct gas diffusion with a negative effect on performance. The relative diffusion coefficient of the MPL is almost equal to that of the model structure of particle packing. However, that of CL is an order of magnitude less than those of the other two components. Furthermore, an equation expressing the relative diffusion coefficient of each component can be obtained with the function of porosity. The electrical conductivity of MPL, which is lower than that of the carbon black packing, is considered to depend on the contact resistance.

Application of a mixed metal oxide catalyst to a metallic substrate

NASA Technical Reports Server (NTRS)

Sevener, Kathleen M. (Inventor); Lohner, Kevin A. (Inventor); Mays, Jeffrey A. (Inventor); Wisner, Daniel L. (Inventor)

2009-01-01

A method for applying a mixed metal oxide catalyst to a metallic substrate for the creation of a robust, high temperature catalyst system for use in decomposing propellants, particularly hydrogen peroxide propellants, for use in propulsion systems. The method begins by forming a prepared substrate material consisting of a metallic inner substrate and a bound layer of a noble metal intermediate. Alternatively, a bound ceramic coating, or frit, may be introduced between the metallic inner substrate and noble metal intermediate when the metallic substrate is oxidation resistant. A high-activity catalyst slurry is applied to the surface of the prepared substrate and dried to remove the organic solvent. The catalyst layer is then heat treated to bind the catalyst layer to the surface. The bound catalyst layer is then activated using an activation treatment and calcinations to form the high-activity catalyst system.

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

Homogeneous and heterogenized iridium water oxidation catalysts

NASA Astrophysics Data System (ADS)

Macchioni, Alceo

2014-10-01

The development of an efficient catalyst for the oxidative splitting of water into molecular oxygen, protons and electrons is of key importance for producing solar fuels through artificial photosynthesis. We are facing the problem by means of a rational approach aimed at understanding how catalytic performance may be optimized by the knowledge of the reaction mechanism of water oxidation and the fate of the catalytic site under the inevitably harsh oxidative conditions. For the purposes of our study we selected iridium water oxidation catalysts, exhibiting remarkable performance (TOF > 5 s-1 and TON > 20000). In particular, we recently focused our attention on [Cp*Ir(N,O)X] (N,O = 2-pyridincarboxylate; X = Cl or NO3) and [IrCl(Hedta)]Na water oxidation catalysts. The former exhibited a remarkable TOF whereas the latter showed a very high TON. Furthermore, [IrCl(Hedta)]Na was heterogenized onto TiO2 taking advantage of the presence of a dandling -COOH functionality. The heterogenized catalyst maintained approximately the same catalytic activity of the homogeneous analogous with the advantage that could be reused many times. Mechanistic studies were performed in order to shed some light on the rate-determining step and the transformation of catalysts when exposed to "oxidative stress". It was found that the last oxidative step, preceding oxygen liberation, is the rate-determining step when a small excess of sacrificial oxidant is used. In addition, several intermediates of the oxidative transformation of the catalyst were intercepted and characterized by NMR, X-Ray diffractometry and ESI-MS.

Dual properties of a hydrogen oxidation Ni-catalyst entrapped within a polymer promote self-defense against oxygen.

PubMed

Oughli, Alaa A; Ruff, Adrian; Boralugodage, Nilusha Priyadarshani; Rodríguez-Maciá, Patricia; Plumeré, Nicolas; Lubitz, Wolfgang; Shaw, Wendy J; Schuhmann, Wolfgang; Rüdiger, Olaf

2018-02-28

The Ni(P 2 N 2 ) 2 catalysts are among the most efficient non-noble-metal based molecular catalysts for H 2 cycling. However, these catalysts are O 2 sensitive and lack long term stability under operating conditions. Here, we show that in a redox silent polymer matrix the catalyst is dispersed into two functionally different reaction layers. Close to the electrode surface is the "active" layer where the catalyst oxidizes H 2 and exchanges electrons with the electrode generating a current. At the outer film boundary, insulation of the catalyst from the electrode forms a "protection" layer in which H 2 is used by the catalyst to convert O 2 to H 2 O, thereby providing the "active" layer with a barrier against O 2 . This simple but efficient polymer-based electrode design solves one of the biggest limitations of these otherwise very efficient catalysts enhancing its stability for catalytic H 2 oxidation as well as O 2 tolerance.

A feasible process for furfural production from the pre-hydrolysis liquor of corncob via biochar catalysts in a new biphasic system.

PubMed

Deng, Aojie; Lin, Qixuan; Yan, Yuhuan; Li, Huiling; Ren, Junli; Liu, Chuanfu; Sun, Runcang

2016-09-01

A feasible approach was developed to produce furfural from the pre-hydrolysis liquor of corncob via biochar catalysts as the solid acid catalyst in a new biphasic system with dichloromethane (DCM) as the organic phase and the concentrated pre-hydrolysis liquor (CPHL) containing NaCl as the aqueous phase. The biochar catalyst possessing many acidity groups (SO3H, COOH and phenolic OH groups) was prepared by the carbonization and sulfonation process of the corncob hydrolyzed residue. The influence of the catalytic condition on furfural yield and selectivity was comparatively studied. It was found that 81.14% furfural yield and 83.0% furfural selectivity were obtained from CPHL containing 5wt% xylose using this biochar catalyst in the CPHL-NaCl/DCM biphasic system at 170°C for 60min. In addition, with the regeneration process, this catalyst displayed the high performance and excellent recyclability. Copyright © 2016 Elsevier Ltd. All rights reserved.

Hydrodechlorination of Tetrachloromethane over Palladium Catalysts Supported on Mixed MgF₂-MgO Carriers.

PubMed

Bonarowska, Magdalena; Wojciechowska, Maria; Zieliński, Maciej; Kiderys, Angelika; Zieliński, Michał; Winiarek, Piotr; Karpiński, Zbigniew

2016-11-25

Pd/MgO, Pd/MgF₂ and Pd/MgO-MgF₂ catalysts were investigated in the reaction of CCl₄ hydrodechlorination. All the catalysts deactivated in time on stream, but the degree of deactivation varied from catalyst to catalyst. The MgF₂-supported palladium with relatively large metal particles appeared the best catalyst, characterized by good activity and selectivity to C₂-C₅ hydrocarbons. Investigation of post-reaction catalyst samples allowed to find several details associated with the working state of hydrodechlorination catalysts. The role of support acidity was quite complex. On the one hand, a definite, although not very high Lewis acidity of MgF₂ is beneficial for shaping high activity of palladium catalysts. The MgO-MgF₂ support characterized by stronger Lewis acidity than MgF₂ contributes to very good catalytic activity for a relatively long reaction period (~5 h) but subsequent neutralization of stronger acid centers (by coking) eliminates them from the catalyst. On the other hand, the role of acidity evolution, which takes place when basic supports (like MgO) are chlorided during HdCl reactions, is difficult to assess because different events associated with distribution of chlorided support species, leading to partial or even full blocking of the surface of palladium, which plays the role of active component in HdCl reactions.

Catalyst containing oxygen transport membrane

DOEpatents

Lane, Jonathan A.; Wilson, Jamie R.; Christie, Gervase Maxwell; Petigny, Nathalie; Sarantopoulos, Christos

2017-02-07

A composite oxygen transport membrane having a dense layer, a porous support layer and an intermediate porous layer located between the dense layer and the porous support layer. Both the dense layer and the intermediate porous layer are formed from an ionic conductive material to conduct oxygen ions and an electrically conductive material to conduct electrons. The porous support layer has a high permeability, high porosity, and a microstructure exhibiting substantially uniform pore size distribution as a result of using PMMA pore forming materials or a bi-modal particle size distribution of the porous support layer materials. Catalyst particles selected to promote oxidation of a combustible substance are located in the intermediate porous layer and in the porous support adjacent to the intermediate porous layer. The catalyst particles can be formed by wicking a solution of catalyst precursors through the porous support toward the intermediate porous layer.

Effect of porous structure of catalyst layer on effective oxygen diffusion coefficient in polymer electrolyte fuel cell

NASA Astrophysics Data System (ADS)

Inoue, Gen; Kawase, Motoaki

2016-09-01

It is important to reduce the oxygen diffusion resistance through PEFC porous electrode, because it is the key to reduce the PEFC cost. However, the gas diffusion coefficient of CL is lower than MPL in spite of framework consisted of same carbon blacks. In this study, in order to understand the reasons of the lower gas diffusion performance of CL, the relationship between a carbon black agglomerate structure and ionomer adhesion condition is evaluated by a numerical analysis with an actual reconstructed structure and a simulated structure. As a result, the gas diffusion property of CL strongly depends on the ionomer adhesion shape. In the case of adhesion shape with the same curvature of ionomer interface, each pore can not be connected enough. So the pore tortuosity increases. Moreover, in the case of existence of inefficient large pores formed by carbon black agglomerate and ununiformly coated ionomer, the gas diffusion performance decrease rapidly. As the measurement values in actual CL are almost equal to that with model structure with inefficient large pores. These characteristics can be confirmed by actual cross-section image obtained by FIB-SEM.

Thin Film Catalyst Layers for Direct Methanol Fuel Cells

NASA Technical Reports Server (NTRS)

Witham, C. K.; Chun, W.; Ruiz, R.; Valdez, T. I.; Narayanan, S. R.

2000-01-01

One of the primary obstacles to the widespread use of the direct methanol fuel cell (DMFC) is the high cost of the catalyst. Therefore, reducing the catalyst loading well below the current level of 8-12 mg/cm 2 would be important to commercialization. The current methods for preparation of catalyst layers consisting of catalyst, ionomer and sometimes a hydrophobic additive are applied by either painting, spraying, decal transfer or screen printing processes. Sputter deposition is a coating technique widely used in manufacturing and therefore particularly attractive. In this study we have begun to explore sputtering as a method for catalyst deposition. Present experiments focus on Pt-Ru catalyst layers for the anode.

HSPES membrane electrode assembly

NASA Technical Reports Server (NTRS)

Kindler, Andrew (Inventor); Yen, Shiao-Ping (Inventor)

2000-01-01

An improved fuel cell electrode, as well as fuel cells and membrane electrode assemblies that include such an electrode, in which the electrode includes a backing layer having a sintered layer thereon, and a non-sintered free-catalyst layer. The invention also features a method of forming the electrode by sintering a backing material with a catalyst material and then applying a free-catalyst layer.

Catalytic membrane reactor for water and wastewater treatment

NASA Astrophysics Data System (ADS)

Heng, Samuel

A double membrane reactor was fabricated and assessed for continuous treatment of water containing organic contaminants by ozonation. This innovative reactor consisted of a zeolite membrane prepared on the inner surface of a porous a-alumina support, which served as water selective extractor and active contactor, and a porous stainless membrane which was the ozone gas diffuser. The coupling of membrane separation and chemical oxidation was found to be highly beneficial to both processes. The total organic carbon (TOC) removal rate at the retentate was enhanced by up to 2.2 times, as compared to membrane ozonation. Simultaneously, clean water (< 2 mg C.L-1 ) was consistently produced on the permeate side, using a feed solution containing up to 1000 mg C.L-1, while the retentate was concentrated and treated. Most significantly, the addition of an adsorbing material, as a bed or a coated layer, onto the pores of the membrane support, was shown to further enhance TOC degradation, permeated TOC concentration, permeate flux, and moreover, ozone yield. The achievements of this project included: (1) The development of a novel low-temperature zeolite membrane activation method that generates consistently high quality membranes (i.e. high reproducibility and fewer defects). (2) The demonstration that gamma-alumina and gamma-alumina supported catalysts do not have significant activity and that the TOC removal enhancement usually observed during catalytic ozonation was due primarily to the contribution of adsorption and metal leaching. Thermogravimetric analysis (TGA) and elemental analysis (EA) of the spent catalyst showed that, during catalytic ozonation, oxygenated by-products of increased adsorbability were concentrated onto the gamma-alumina contactor, and were subsequently degraded. (3) The development of a method for coating high surface area gamma-alumina layers onto the grains of zeolite membrane support used as the active membrane contactor.

Highly Durable Supportless Pt Hollow Spheres Designed for Enhanced Oxygen Transport in Cathode Catalyst Layers of Proton Exchange Membrane Fuel Cells.

PubMed

Dogan, Didem C; Cho, Seonghun; Hwang, Sun-Mi; Kim, Young-Min; Guim, Hwanuk; Yang, Tae-Hyun; Park, Seok-Hee; Park, Gu-Gon; Yim, Sung-Dae

2016-10-10

Supportless Pt catalysts have several advantages over conventional carbon-supported Pt catalysts in that they are not susceptible to carbon corrosion. However, the need for high Pt loadings in membrane electrode assemblies (MEAs) to achieve state-of-the-art fuel cell performance has limited their application in proton exchange membrane fuel cells. Herein, we report a new approach to the design of a supportless Pt catalyst in terms of catalyst layer architecture, which is crucial for fuel cell performance as it affects water management and oxygen transport in the catalyst layers. Large Pt hollow spheres (PtHSs) 100 nm in size were designed and prepared using a carbon template method. Despite their large size, the unique structure of the PtHSs, which are composed of a thin-layered shell of Pt nanoparticles (ca. 7 nm thick), exhibited a high surface area comparable to that of commercial Pt black (PtB). The PtHS structure also exhibited twice the durability of PtB after 2000 potential cycles (0-1.3 V, 50 mV/s). A MEA fabricated with PtHSs showed significant improvement in fuel cell performance compared to PtB-based MEAs at high current densities (>800 mA/cm 2 ). This was mainly due to the 2.7 times lower mass transport resistance in the PtHS-based catalyst layers compared to that in PtB, owing to the formation of macropores between the PtHSs and high porosity (90%) in the PtHS catalyst layers. The present study demonstrates a successful example of catalyst design in terms of catalyst layer architecture, which may be applied to a real fuel cell system.

Porous Nanocrystalline Silicon Supported Bimetallic Pd-Au Catalysts: Preparation, Characterization, and Direct Hydrogen Peroxide Synthesis

PubMed Central

Potemkin, Dmitriy I.; Maslov, Dmitry K.; Loponov, Konstantin; Snytnikov, Pavel V.; Shubin, Yuri V.; Plyusnin, Pavel E.; Svintsitskiy, Dmitry A.; Sobyanin, Vladimir A.; Lapkin, Alexei A.

2018-01-01

Bimetallic Pd-Au catalysts were prepared on the porous nanocrystalline silicon (PSi) for the first time. The catalysts were tested in the reaction of direct hydrogen peroxide synthesis and characterized by standard structural and chemical techniques. It was shown that the Pd-Au/PSi catalyst prepared from conventional H2[PdCl4] and H[AuCl4] precursors contains monometallic Pd and a range of different Pd-Au alloy nanoparticles over the oxidized PSi surface. The PdAu2/PSi catalyst prepared from the [Pd(NH3)4][AuCl4]2 double complex salt (DCS) single-source precursor predominantly contains bimetallic Pd-Au alloy nanoparticles. For both catalysts the surface of bimetallic nanoparticles is Pd-enriched and contains palladium in Pd0 and Pd2+ states. Among the catalysts studied, the PdAu2/PSi catalyst was the most active and selective in the direct H2O2 synthesis with H2O2 productivity of 0.5 mol gPd-1 h-1 at selectivity of 50% and H2O2 concentration of 0.023 M in 0.03 M H2SO4-methanol solution after 5 h on stream at −10°C and atmospheric pressure. This performance is due to high activity in the H2O2 synthesis reaction and low activities in the undesirable H2O2 decomposition and hydrogenation reactions. Good performance of the PdAu2/PSi catalyst was associated with the major part of Pd in the catalyst being in the form of the bimetallic Pd-Au nanoparticles. Porous silicon was concluded to be a promising catalytic support for direct hydrogen peroxide synthesis due to its inertness with respect to undesirable side reactions, high thermal stability, and conductivity, possibility of safe operation at high temperatures and pressures and a well-established manufacturing process. PMID:29637068

Porous nanocrystalline silicon supported bimetallic Pd-Au catalysts: preparation, characterization and direct hydrogen peroxide synthesis

NASA Astrophysics Data System (ADS)

Potemkin, Dmitriy I.; Maslov, Dmitry K.; Loponov, Konstantin; Snytnikov, Pavel V.; Shubin, Yuri V.; Plyusnin, Pavel E.; Svintsitskiy, Dmitry A.; Sobyanin, Vladimir A.; Lapkin, Alexei A.

2018-03-01

Bimetallic Pd-Au catalysts were prepared on the porous nanocrystalline silicon (PSi) for the first time. The catalysts were tested in the reaction of direct hydrogen peroxide synthesis and characterised by standard structural and chemical techniques. It was shown that the Pd-Au/PSi catalyst prepared from conventional H2[PdCl4] and H[AuCl4] precursors contains monometallic Pd and a range of different Pd-Au alloy nanoparticles over the oxidized PSi surface. The PdAu2/PSi catalyst prepared from the [Pd(NH3)4][AuCl4]2 double complex salt single-source precursor predominantly contains bimetallic Pd-Au alloy nanoparticles. For both catalysts the surface of bimetallic nanoparticles is Pd-enriched and contains palladium in Pd0 and Pd2+ states. Among the catalysts studied, the PdAu2/PSi catalyst was the most active and selective in the direct H2O2 synthesis with H2O2 productivity of 0.5 at selectivity of 50 % and H2O2 concentration of 0.023 M in 0.03 M H2SO4-methanol solution after 5 h on stream at -10 °C and atmospheric pressure. This performance is due to high activity in the H2O2 synthesis reaction and low activities in the undesirable H2O2 decomposition and hydrogenation reactions. Good performance of the PdAu2/PSi catalyst was associated with the major part of Pd in the catalyst being in the form of the bimetallic Pd-Au nanoparticles. Porous silicon was concluded to be a promising catalytic support for direct hydrogen peroxide synthesis due to its inertness with respect to undesirable side reactions, high thermal stability and conductivity, possibility of safe operation at high temperatures and pressures and a well-established manufacturing process.

Fabrication of fuel cell electrodes and other catalytic structures

DOEpatents

Smith, J.L.

1987-02-11

A porous layer of catalyst material suitable for use as an electrode in a molten carbonate fuel cell includes elongated pores substantially extending across the layer thickness. The catalyst layer is prepared by depositing particulate catalyst material into polymeric flocking on a substrate surface by a procedure such as tape casting. The loaded substrate is heated in a series of steps with rising temperatures to set the tape, thermally decompose the substrate with flocking and sinter bond the catalyst particles into a porous catalytic layer with elongated pores across its thickness. Employed as an electrode, the elongated pores provide distribution of reactant gas into contact with catalyst particles wetted by molten electrolyte. 1 fig.

Fabrication of catalytic electrodes for molten carbonate fuel cells

DOEpatents

Smith, James L.

1988-01-01

A porous layer of catalyst material suitable for use as an electrode in a molten carbonate fuel cell includes elongated pores substantially extending across the layer thickness. The catalyst layer is prepared by depositing particulate catalyst material into polymeric flocking on a substrate surface by a procedure such as tape casting. The loaded substrate is heated in a series of steps with rising temperatures to set the tape, thermally decompose the substrate with flocking and sinter bond the catalyst particles into a porous catalytic layer with elongated pores across its thickness. Employed as an electrode, the elongated pores provide distribution of reactant gas into contact with catalyst particles wetted by molten electrolyte.

Catalytic valorization of starch-rich food waste into hydroxymethylfurfural (HMF): Controlling relative kinetics for high productivity.

PubMed

Yu, Iris K M; Tsang, Daniel C W; Yip, Alex C K; Chen, Season S; Wang, Lei; Ok, Yong Sik; Poon, Chi Sun

2017-08-01

This study aimed to maximize the valorization of bread waste, a typical food waste stream, into hydroxymethylfurfural (HMF) by improving our kinetic understanding. The highest HMF yield (30mol%) was achieved using SnCl 4 as catalyst, which offered strong derived Brønsted acidity and moderate Lewis acidity. We evaluated the kinetic balance between these acidities to facilitate faster desirable reactions (i.e., hydrolysis, isomerization, and dehydration) relative to undesirable reactions (i.e., rehydration and polymerization). Such catalyst selectivity of SnCl 4 , AlCl 3 , and FeCl 3 was critical in maximizing HMF yield. Higher temperature made marginal advancement by accelerating the undesirable reactions to a similar extent as the desirable pathways. The polymerization-induced metal-impregnated high-porosity carbon was a possible precursor of biochar-based catalyst, further driving up the economic potential. Preliminary economic analysis indicated a net gain of USD 43-236 per kilogram bread waste considering the thermochemical-conversion cost and chemical-trading revenue. Copyright © 2017 Elsevier Ltd. All rights reserved.

Investigating fuel-cell transport limitations using hydrogen limiting current

DOE PAGES

Spingler, Franz B.; Phillips, Adam; Schuler, Tobias; ...

2017-03-09

Reducing mass-transport losses in polymer-electrolyte fuel cells (PEFCs) is essential to increase their power density and reduce overall stack cost. At the same time, cost also motivates the reduction in expensive precious-metal catalysts, which results in higher local transport losses in the catalyst layers. Here, we use a hydrogen-pump limiting-current setup to explore the gas-phase transport losses through PEFC catalyst layers and various gas-diffusion and microporous layers. It is shown that the effective diffusivity in the gas-diffusion layers is a strong function of liquid saturation. Additionally, it is shown how the catalyst layer unexpectedly contributes significantly to the overall measuredmore » transport resistance. This is especially true for low catalyst loadings. It is also shown how the various losses can be separated into different mechanisms including diffusional processes and mass-dependent and independent ones, where the data suggests that a large part of the transport resistance in catalyst layers cannot be attributed to a gas-phase diffusional process. The technique is promising for deconvoluting transport losses in PEFCs.« less

Hollow spheres of iron carbide nanoparticles encased in graphitic layers as oxygen reduction catalysts.

PubMed

Hu, Yang; Jensen, Jens Oluf; Zhang, Wei; Cleemann, Lars N; Xing, Wei; Bjerrum, Niels J; Li, Qingfeng

2014-04-01

Nonprecious metal catalysts for the oxygen reduction reaction are the ultimate materials and the foremost subject for low-temperature fuel cells. A novel type of catalysts prepared by high-pressure pyrolysis is reported. The catalyst is featured by hollow spherical morphologies consisting of uniform iron carbide (Fe3 C) nanoparticles encased by graphitic layers, with little surface nitrogen or metallic functionalities. In acidic media the outer graphitic layers stabilize the carbide nanoparticles without depriving them of their catalytic activity towards the oxygen reduction reaction (ORR). As a result the catalyst is highly active and stable in both acid and alkaline electrolytes. The synthetic approach, the carbide-based catalyst, the structure of the catalysts, and the proposed mechanism open new avenues for the development of ORR catalysts. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

NASA Astrophysics Data System (ADS)

Jana, Rajkumar; Peter, Sebastian C.

2016-10-01

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

Carbon corrosion in PEM fuel cells during drive cycle operation

DOE PAGES

Borup, Rodney L.; Papadias, D. D.; Mukundan, Rangachary; ...

2015-09-14

One of the major contributors to degradation involves the electrocatalyst, including the corrosion of the carbons used as catalyst supports, which leads to changes in the catalyst layer structure. We have measured and quantified carbon corrosion during drive cycle operation and as a variation of the upper and lower potential limits used during drive cycle operation. The amount of carbon corrosion is exacerbated by the voltage cycling inherent in the drive cycle compared with constant potential operation. The potential gap between upper and lower potentials appears to be more important than the absolute operating potentials in the normal operating potentialmore » regime (0.40V to 0.95V) as changes in the measured carbon corrosion are similar when the upper potential was lower compared to raising the lower potential. Catalyst layer thinning was observed during the simulated drive cycle operation which had an associated decrease in catalyst layer porosity. This catalyst layer thinning is not due solely to carbon corrosion, although carbon corrosion likely plays a role; much of this thinning must be from compaction of the material in the catalyst layer. As a result, the decrease in catalyst layer porosity leads to additional performance losses due to mass transport losses.« less

A combined ToF-SIMS and XPS study for the elucidation of the role of water in the performances of a Post-Plasma Process using LaMnO3+δ as catalyst in the total oxidation of trichloroethylene

NASA Astrophysics Data System (ADS)

Nuns, N.; Beaurain, A.; Dinh, M. T. Nguyen; Vandenbroucke, A.; De Geyter, N.; Morent, R.; Leys, C.; Giraudon, J.-M.; Lamonier, J.-F.

2014-11-01

LaMnO3+δ which is an environment-friendly and inexpensive material has been previously used as catalyst in Post-Plasma Catalysis (PPC) in the total oxidation of trichloroethylene (TCE) which is a solvent widely used in dry cleaning and degreasing processes. It has been shown that the process efficiency increases in moist air (RH = 18%).The issue we want to address herein is the effect of water on the location of chlorine at the surface of the catalyst as chlorine is able to alter the catalyst structure, activity and stability. Therefore, a combined Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS) study has been carried out on the fresh LaMnO3+δ catalyst (LM) and used catalysts after performing PPC with TCE diluted in dry synthetic air (LM0) or with industrial air containing water (LM18; 18 stands for the Relative Humidity) and CO2 (about 560 ppmv) at a temperature of 150 °C. XPS and ToF-SIMS results both show the presence of chlorine on the tested catalysts whose amount increases by exposure of the catalyst to the reactive mixture in dry synthetic air. XPS results reveal that chlorine is present as both chloride ion and covalent chlorine on LM0 while organic chlorinated residues are absent on LM18 catalyst. ToF-SIMS study indicates that lanthanum excess as oxide(hydroxide) partially covering the perovskite mainly transforms into LaOCl and to a minor extent into LaCl3. Extent of Mn chlorination seems to be favored over LM0 having a higher MnClx±/MnOCl± ionic ratio compared to LM18. Furthermore ToF-SIMS clearly identifies C1 chlorinated organic ions, mainly CH2Cl+ and CHCl2-, on LM0 which may contribute to the XPS Cl organic component. From the combined ToF-SIMS and XPS results it is found that water delays the surface degradation extent of the perovskite into related (oxy)(hydroxy)chlorinated inorganic phases by less molecular chlorine and related chlorine species on the catalyst surface. A reaction scheme of Cl removal over LaMnO3+δ emphasing the role of water is given taking into account the detection of ToF-SIMS ions representative of the successive Mn intermediate states. As a consequence water allows tuning the degradation pathways of the main intermediate of the reaction, dichloroacetyl chloride (DCAC), which decomposes to give phosgene, HCCl3 and CCl4 by a successive Cl incorporation over (oxy)(hydroxy)chorinated perovskite or/and Mn species while COx species are likely formed over the perovskite.

Integrated current collector and catalyst support

DOEpatents

Bregoli, Lawrence J.

1985-10-22

An integrated current collecting electrode for a molten carbonate fuel cell includes a corrugated metal conductive strip positioned in contact with a catalyst layer. The corrugations of the metal strip form a plurality of gas channels immediately adjacent the surface of the catalyst through which a reactant gas flows. Each channel is filled with a particulate material to maintain separation between the metal strip and the catalyst in ensuring gas channel integrity. The catalyst may be in the form of a compacted, particulate material provided the particle size of the material within the gas channels is larger than that of the catalyst particles to prevent catalyst migration to the metal conductor and provide reactant gas access to the catalyst layer. The gas channels formed by the corrugations of the metal strip are arranged in an offset pattern along the direction of gas flow for improved reactant gas distribution to the catalyst layer. The particulate material positioned within the gas flow channels may be a ceramic conductor such as a perovskite or a spinel for enhanced current collection.

Integrated current collector and catalyst support

DOEpatents

Bregoli, L.J.

1984-10-17

An integrated current collecting electrode for a molten carbonate fuel cell includes a corrugated metal conductive strip positioned in contact with a catalyst layer. The corrugations of the metal strip form a plurality of gas channels immediately adjacent the surface of the catalyst through which a reactant gas flows. Each channel is filled with a particulate material to maintain separation between the metal strip and the catalyst in ensuring gas channel integrity. The catalyst may be in the form of a compacted, particulate material provided the particle size of the material within the gas channels is larger than that of the catalyst particles to prevent catalyst migration to the metal conductor and provide reactant gas access to the catalyst layer. The gas channels formed by the corrugations of the metal strip are arranged in an offset pattern along the direction of gas flow for improved reactant gas distribution to the catalyst layer. The particulate material positioned within the gas flow channels may be a ceramic conductor such as a perovskite or a spinel for enhanced current collection.

Effect of polymer binders in anode catalyst layer on performance of alkaline direct ethanol fuel cells

NASA Astrophysics Data System (ADS)

Li, Y. S.; Zhao, T. S.; Liang, Z. X.

In preparing low-temperature fuel cell electrodes, a polymer binder is essential to bind discrete catalyst particles to form a porous catalyst layer that simultaneously facilitates the transfer of ions, electrons, and reactants/products. For two types of polymer binder, namely, an A3-an anion conducting ionomer and a PTFE-a neutral polymer, an investigation is made of the effect of the content of each binder in the anode catalyst layer on the performance of an alkaline direct ethanol fuel cell (DEFC) with an anion-exchange membrane and non-platinum (non-Pt) catalysts. Experiments are performed by feeding either ethanol (C 2H 5OH) solution or ethanol-potassium hydroxide (C 2H 5OH-KOH) solution. The experimental results for the case of feeding C 2H 5OH solution without added KOH indicate that the cell performance varies with the A3 ionomer content in the anode catalyst layer, and a content of 10 wt.% exhibits the best performance. When feeding C 2H 5OH-KOH solution, the results show that: (i) in the region of low current density, the best performance is achieved for a membrane electrode assembly without any binder in the anode catalyst layer; (ii) in the region of high current density, the performance is improved with incorporation of PTFE binder in the anode catalyst layer; (iii) the PTFE binder yields better performance than does the A3 binder.

Photocatalytic acceptorless alkane dehydrogenation: scope, mechanism, and conquering deactivation with carbon dioxide.

PubMed

Chowdhury, Abhishek Dutta; Julis, Jennifer; Grabow, Kathleen; Hannebauer, Bernd; Bentrup, Ursula; Adam, Martin; Franke, Robert; Jackstell, Ralf; Beller, Matthias

2015-01-01

Alkane dehydrogenation is of special interest for basic science but also offers interesting opportunities for industry. The existing dehydrogenation methodologies make use of heterogeneous catalysts, which suffer from harsh reaction conditions and a lack of selectivity, whereas homogeneous methodologies rely mostly on unsolicited waste generation from hydrogen acceptors. Conversely, acceptorless photochemical alkane dehydrogenation in the presence of trans-Rh(PMe3 )2 (CO)Cl can be regarded as a more benign and atom efficient alternative. However, this methodology suffers from catalyst deactivation over time. Herein, we provide a detailed investigation of the trans-Rh(PMe3 )2 (CO)Cl-photocatalyzed alkane dehydrogenation using spectroscopic and theoretical investigations. These studies inspired us to utilize CO2 to prevent catalyst deactivation, which leads eventually to improved catalyst turnover numbers in the dehydrogenation of alkanes that include liquid organic hydrogen carriers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A hydrophilic-hydrophobic dual-layer microporous layer enabling the improved water management of direct methanol fuel cells operating with neat methanol

NASA Astrophysics Data System (ADS)

Yan, X. H.; Zhao, T. S.; Zhao, G.; An, L.; Zhou, X. L.

2015-10-01

Passive direct methanol fuel cells (DMFCs) operating with neat methanol can achieve the maximum system energy density. However, the anodic methanol oxidation reaction requires reactant water, which is completely supplied by water generated at the cathode, causing the system to experience a critical issue known as water starvation. A solution to this problem involves increasing the water recovery flux to meet the rate of water consumption of the anodic reaction, and increase the local water concentration as high as possible at the anode catalyst layer (CL) to improve the anodic kinetics. In the present work, a new microporous layer (MPL) consisting of a hydrophilic layer and a hydrophobic layer is proposed. The purposes of these two layers are to, respectively, trap and retain water and to create capillary pressure to prevent water loss. Our experiments have shown that the use of this novel MPL at the anode and cathode can increase the rate of water recovery and water retention, resulting in an increase in the local water concentration. As a result, the use of this dual-layer MPL to either electrode of a passive DMFC operating with neat methanol leads to a significant performance boost.

Tethered catalysts for the hydration of carbon dioxide

DOEpatents

Valdez, Carlos A; Satcher, Jr., Joe H; Aines, Roger D; Wong, Sergio E; Baker, Sarah E; Lightstone, Felice C; Stolaroff, Joshuah K

2014-11-04

A system is provided that substantially increases the efficiency of CO.sub.2 capture and removal by positioning a catalyst within an optimal distance from the air-liquid interface. The catalyst is positioned within the layer determined to be the highest concentration of carbon dioxide. A hydrophobic tether is attached to the catalyst and the hydrophobic tether modulates the position of the catalyst within the liquid layer containing the highest concentration of carbon dioxide.

Self-Catalyzing Chemiluminescence of Luminol-Diazonium Ion and Its Application for Catalyst-Free Hydrogen Peroxide Detection and Rat Arthritis Imaging.

PubMed

Zhao, Chunxin; Cui, Hongbo; Duan, Jing; Zhang, Shenghai; Lv, Jiagen

2018-02-06

We report the unique self-catalyzing chemiluminescence (CL) of luminol-diazonium ion (N 2 + -luminol) and its analytical potential. Visual CL emission was initially observed when N 2 + -luminol was subjected to alkaline aqueous H 2 O 2 without the aid of any catalysts. Further experimental investigations found peroxidase-like activity of N 2 + -luminol on the cleavage of H 2 O 2 into OH • radical. Together with other experimental evidence, the CL mechanism is suggested as the activation of N 2 + -luminol and its dediazotization product 3-hydroxyl luminol by OH • radical into corresponding intermediate radicals, and then further oxidation to excited-state 3-N 2 + -phthalic acid and 3-hydroxyphthalic acid, which finally produce 415 nm CL. The self-catalyzing CL of N 2 + -luminol provides us an opportunity to achieve the attractive catalyst-free CL detection of H 2 O 2 . Experiments demonstrated the 10 -8 M level detection sensitivity to H 2 O 2 as well as to glucose or uric acid if presubjected to glucose oxidase or uricase. With the exampled determination of serum glucose and uric acid, N 2 + -luminol shows its analytical potential for other analytes linking the production or consumption of H 2 O 2 . Under physiological condition, N 2 + -luminol exhibits highly selective and sensitive CL toward 1 O 2 among the common reactive oxygen species. This capacity supports the significant application of N 2 + -luminol for detecting 1 O 2 in live animals. By imaging the arthritis in LEW rats, N 2 + -luminol CL is demonstrated as a potential tool for mapping the inflammation-relevant biological events in a live body.

A temperature-programmed X-ray photoelectron spectroscopy (TPXPS) study of chlorine adsorption and diffusion on Ag(1 1 1)

NASA Astrophysics Data System (ADS)

Piao, H.; Adib, K.; Barteau, Mark A.

2004-05-01

Synchrotron-based temperature programmed X-ray photoelectron spectroscopy (TPXPS) has been used to investigate the surface chloridation of Ag(1 1 1) to monolayer coverages. At 100 K both atomic and molecular chlorine species are present on the surface; adsorption at 300 K or annealing the adlayer at 100 K to this temperature generates adsorbed Cl atoms. As the surface is heated from 300 to 600 K, chlorine atoms diffuse below the surface, as demonstrated by attenuation of the Cl2p signals in TPXPS experiments. Quantitative analysis of the extent of attenuation is consistent with chlorine diffusion below the topmost silver layer. For coverages in the monolayer and sub-monolayer regime, chlorine diffusion to and from the bulk appears not to be significant, in contrast to previous results obtained at higher chlorine loadings. Chlorine is removed from the surface at 650-780 K by desorption as AgCl. These results demonstrate that chlorine diffusion beneath the surface does occur at coverages and temperatures relevant to olefin epoxidation processes carried out on silver catalysts with chlorine promoters. The surface sensitivity advantages of synchrotron-based XPS experiments were critical to observing Cl diffusion to the sub-surface at low coverages.

In situ NMR spectroscopy: inulin biomass conversion in ZnCl₂ molten salt hydrate medium-SnCl₄ addition controls product distribution.

PubMed

Wang, Yingxiong; Pedersen, Christian Marcus; Qiao, Yan; Deng, Tiansheng; Shi, Jing; Hou, Xianglin

2015-01-22

The dehydration of inulin biomass to the platform chemicals, 5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA), in ZnCl2 molten salt hydrate medium was investigated. The influence of the Lewis acid catalyst, SnCl4, on the product distribution was examined. An in situ(1)H NMR technique was employed to follow the reaction at the molecular level. The experimental results revealed that only 5-HMF was obtained from degradation of inulin biomass in ZnCl2 molten salt hydrate medium, while the LA was gradually becoming the main product when the reaction temperature was increased in the presence of the Lewis acid catalyst SnCl4. In situ NMR spectroscopy could monitor the reaction and give valuable insight. Copyright © 2014 Elsevier Ltd. All rights reserved.

Metallic Nanowire Interconnections for Integrated Circuit Fabrication

NASA Technical Reports Server (NTRS)

Ng, Hou Tee (Inventor); Li, Jun (Inventor); Meyyappan, Meyya (Inventor)

2007-01-01

A method for fabricating an electrical interconnect between two or more electrical components. A conductive layer is provided on a substarte and a thin, patterned catalyst array is deposited on an exposed surface of the conductive layer. A gas or vapor of a metallic precursor of a metal nanowire (MeNW) is provided around the catalyst array, and MeNWs grow between the conductive layer and the catalyst array. The catalyst array and a portion of each of the MeNWs are removed to provide exposed ends of the MeNWs.

The Mechanism of Low-Temperature Oxidation of Carbon Monoxide by Oxygen over the PdCl2–CuCl2/γ-Al2O3 Nanocatalyst

PubMed Central

Bruk, Lev; Titov, Denis; Ustyugov, Alexander; Chernikova, Valeriya; Tkachenko, Olga; Kustov, Leonid; Murzin, Vadim; Oshanina, Irina; Temkin, Oleg

2018-01-01

The state of palladium and copper on the surface of the PdCl2–CuCl2/γ-Al2O3 nanocatalyst for the low-temperature oxidation of CO by molecular oxygen was studied by various spectroscopic techniques. Using X-ray absorption spectroscopy (XAS), powder X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), freshly prepared samples of the catalyst were studied. The same samples were also evaluated after interaction with CO, O2, and H2O vapor in various combinations. It was shown that copper exists in the form of Cu2Cl(OH)3 (paratacamite) nanophase on the surface of the catalyst. No palladium-containing crystalline phases were identified. Palladium coordination initially is comprised of four chlorine atoms. It was shown by XAS that this catalyst is not capable of oxidizing CO at room temperature in the absence of H2O and O2 over 12 h. Copper(II) and palladium(II) are reduced to Cu(I) and Pd(I,0) species, respectively, in the presence of CO and H2O vapor (without O2). It was found by DRIFTS that both linear (2114 cm−1, 1990 cm−1) and bridging (1928 cm−1) forms of coordinated CO were formed upon adsorption onto the catalyst surface. Moreover, the formation of CO2 was detected upon the interaction of the coordinated CO with oxygen. The kinetics of CO oxidation was studied at 18–38 °C at an atmospheric pressure for CO, O2, N2, and H2O (gas) mixtures in a flow reactor (steady state conditions). PMID:29614029

Facile synthesis of hollow Co3O4 microspheres and its use as a rapid responsive CL sensor of combustible gases.

PubMed

Teng, Fei; Yao, Wenqing; Zheng, Youfei; Ma, Yutao; Xu, Tongguang; Gao, Guizhi; Liang, Shuhui; Teng, Yang; Zhu, Yongfa

2008-09-15

The hollow Co(3)O(4) microspheres (HCMs) were prepared by the carbonaceous templates, which did not need the surface pretreatment. The chemiluminescence (CL) and catalytic properties for CO oxidation over these hollow samples were evaluated. The samples were characterized by scanning electron microscopy (SEM), energy disperse spectra (EDS), transmission electron microscopy (TEM), selected area electron diffraction (ED), X-ray diffraction (XRD), temperature-programmed desorption (TPD) and N(2) adsorption. The influences of filter' band length, flow rate of gas, test temperature, and particle structure on CL intensities were mainly investigated. It was found that compared with the solid Co(3)O(4) particles (SCPs), HCMs had a stronger CL intensity, which was ascribed to its hollow structure; and that CL properties of the catalysts were well correlated with their reaction activities. Moreover, HCMs were used to fabricate a highly sensitive gas detector, which is a rapid and effective method for the selection of catalysts or the detection of environmental deleterious gases.

Triphenylphosphine as Ligand for Room Temperature Ni(0)-Catalyzed Cross-Coupling Reactions of Aryl Chlorides with Arylboronic Acids

PubMed Central

Tang, Zhen-Yu; Hu, Qiao-Sheng

2008-01-01

Room temperature Ni(0)-catalyzed cross-coupling reactions of deactivated aryl chlorides with arylboronic acids with inexpensive triphenylphosphine (PPh3) as a supporting ligand have been accomplished in good to excellent yields. Air-stable Ni(PPh3)2Cl2 has also been established as catalyst precursor and highly active nickel catalysts were obtained when the reduction of Ni(PPh3)2Cl2 with n-BuLi was carried out in presence of an aryl chloride. PMID:16497011

A Highly Reactive Dicationic Iridium(III) Catalyst for Polarized Nazarov Cyclization

PubMed Central

Vaidya, Tulaza; Atesin, Abdurrahman C.; Herrick, Ildiko R.; Frontier, Alison J.; Eisenberg, Richard

2010-01-01

Pushing the Nazarov Envelope A new electrophilic complex [IrBr(CO)(diethylisopropylidene malonate)((R)-(+)-BINAP)](SbF6)2 (2) exhibits unusual activity in the catalysis of polarized Nazarov cyclization. Aryl vinyl ketones that show poor reactivity with well-known catalysts such as [Ir(CH3)(CO)(1,2-diiodobenzene)(dppe)](B(Arf)4−)2 (1), Sc(OTf)3 + LiClO4 and Cu(ClO4)2, can be cyclized with 2 + AgSbF6 (1:1) under mild conditions with concurrent AgBr precipitation. PMID:20358570

Degradation Study by Start-Up/Shut-Down Cycling of Superhydrophobic Electrosprayed Catalyst Layers Using a Localized Reference Electrode Technique.

PubMed

Ferreira-Aparicio, Paloma; Chaparro, Antonio M; Folgado, M Antonia; Conde, Julio J; Brightman, Edward; Hinds, Gareth

2017-03-29

Degradation of a polymer electrolyte membrane fuel cell (PEMFC) with electrosprayed cathode catalyst layers is investigated during cyclic start-up and shut-down events. The study is carried out within a single cell incorporating an array of reference electrodes that enables measurement of cell current as a function of local cathode potential (localized polarization curves). Accelerated degradation of the cell by start-up/shut-down cycling gives rise to inhomogeneous performance loss, which is more severe close to the gas outlet and occurs predominantly during start-up. The degradation consists primarily of loss of cathode catalyst activity and increase in cell internal resistance, which is attributed to carbon corrosion and Pt aggregation in both anode and cathode. Cells with an electrosprayed cathode catalyst layer show lower degradation rates during the first 100 cycles, compared with those of a conventional gas diffusion electrode. This difference in behavior is attributed to the high hydrophobicity of the electrosprayed catalyst layer microstructure, which retards the kinetics of corrosion of the carbon support. In the long term, however, the degradation rate is dominated by the Pt/C ratio in the cathode catalyst layer.

Simple fabrication of pineapple root-like palladium-gold catalysts as the high-efficiency cathode in direct peroxide-peroxide fuel cells.

PubMed

Wang, Xin; Ye, Ke; Sun, Ce; Zhang, Hongyu; Zhu, Kai; Cheng, Kui; Wang, Guiling; Cao, Dianxue

2017-07-15

Pd-Au/TiC electrodes with various three-dimensional structures are obtained by the pulsed potential electro-deposition in PdCl 2 /HAuCl 4 electrolytes. The morphologies of Pd-Au/TiC composite catalysts are significantly dependent on the component of deposited solutions. The surface appearance of Pd-Au catalysts changes from rime-shaped structure, to feather-like construction, then to pineapple root-like structure and finally to flower-like configuration with the increase of PdCl 2 content in electrolytes. These particular three-dimensional structures may be very suitable for H 2 O 2 electro-reduction, which assures a high utilization of Pd-Au catalysts and provides a large specific surface area. The electro-catalytic activities of H 2 O 2 reduction on the Pd-Au/TiC electrodes improve as increasing the Pd content in Pd-Au alloy catalysts. The pineapple root-like Pd 5 Au 1 /TiC electrode reveals remarkably excellent electrochemical property and desirable stability for catalyzing H 2 O 2 reduction in acid media. The direct peroxide-peroxide fuel cells with a 10 cm 3 min -1 flow rate display the open circuit voltage (OCV) of 0.85V and the peak power density of 56.5mWcm -2 at 155mAcm -2 with desirable cell stability, which is much higher than those previously reported. Copyright © 2017 Elsevier Inc. All rights reserved.

Unique Features of the Photocatalytic Reduction of H2O and CO2 by New Catalysts Based on the Analogues of CdS, Cd4P2X3 (X = Cl, Br, I).

PubMed

Roy, Anand; Chhetri, Manjeet; Prasad, Suchitra; Waghmare, Umesh V; Rao, C N R

2018-01-24

Photochemical reduction of H 2 O and CO 2 has been investigated with a new family of catalysts of the formula Cd 4 P 2 X 3 (X= Cl, Br, I), obtained by the complete aliovalent substitution of the sulfide ions in CdS by P and X (Cl, Br, I). Unlike CdS, the Cd 4 P 2 X 3 compounds exhibit hydrogen evolution and CO 2 reduction from water even in the absence of a sacrificial agent or a cocatalyst. Use of Ni x P y as the cocatalyst, enhances hydrogen evolution, reaching 3870 (apparent quantum yield (AQY) = 4.11) and 9258 (AQY = 9.83) μmol h -1 g -1 , respectively, under artificial and natural (sunlight) irradiation, in the case of Cd 4 P 2 Br 3 /Ni x P y . Electrochemical and spectroscopic studies have been employed to understand the photocatalytic activity of this family of compounds. Unlike most of the semiconductor-based photocatalysts, Cd 4 P 2 X 3 catalysts reduce CO 2 to CO and CH 4 in the absence of sacrificial-agent or cocatalyst using water as the electron source. CO, CH 4 , and H 2 have been obtained with these catalysts under artificial as well as sun-light irradiation. First-principles, calculations have been carried out to understand the electronic structure and catalytic features of these new catalysts.

Depolymerization of cellulose into high-value chemicals by using synergy of zinc chloride hydrate and sulfate ion promoted titania catalyst.

PubMed

Wei, Weiqi; Wu, Shubin

2017-10-01

Experiments for cellulose depolymerization by synergy of zinc chloride hydrate (ZnCl 2 ·RH 2 O) and sulfated titania catalyst (SO 4 2- /TiO 2 ) were investigated in this study. The results showed the introduction of sulfate into the TiO 2 significantly enhanced the catalyst acid amount, especially for Brønsted acid site, which is beneficial for subsequent cellulose depolymerization. ZnCl 2 ·RH 2 O hydrate, only a narrow composition range of water, specifically 3.0≤R≤4.0, can dissolve cellulose, which finally resulted the cellulose with low crystallinity and weak intrachain and interchain hydrogen bond network. Coupling of ZnCl 2 ·RH 2 O hydrate and SO 4 2- /TiO 2 catalyst as a mixed reaction system promoted cellulose depolymerization, and the products can be adjusted by the control of reaction conditions, the low temperature (80-100°C) seemed beneficial for glucose formation (maximal yield 50.5%), and the high temperature (120-140°C) favored to produce levulinic acid (maximal yield 43.1%). Besides, the addition of organic co-solvent making HMF as the main product (maximal yield 38.3%). Copyright © 2017 Elsevier Ltd. All rights reserved.

Kinetic control of intralayer cobalt coordination in layered hydroxides: Co(1-0.5x)(oct) Co(x)(tet) (OH)2 (Cl)x (H2O)n.

PubMed

Neilson, James R; Schwenzer, Birgit; Seshadri, Ram; Morse, Daniel E

2009-12-07

We report the synthesis and characterization of new structural variants of the isotypic compound with the generic chemical formula, Co(1-0.5x)(oct) Co(x)(tet) (OH)2 (Cl)x (H2O)n, all modifications of an alpha-Co(OH)2 lattice. We show that the occupancy of tetrahedrally coordinated cobalt sites and associated chloride ligands, x, is modulated by the rate of formation of the respective layered hydroxide salts from kinetically controlled aqueous hydrolysis at an air-water interface. This new level of structural control is uniquely enabled by the slow diffusion of a hydrolytic catalyst, a simple technique. Independent structural characterizations of the compounds separately describe various attributes of the materials on different length scales, revealing details hidden by the disordered average structures. The precise control over the population of distinct octahedrally and tetrahedrally coordinated cobalt ions in the lattice provides a gentle, generic method for modulating the coordination geometry of cobalt in the material without disturbing the lattice or using additional reagents. A mechanism is proposed to reconcile the observation of the kinetic control of the structure with competing interactions during the initial stages of hydrolysis and condensation.

Adsorption properties of regenerative materials for removal of low concentration of toluene.

PubMed

Xie, Zhen-Zhen; Wang, Lin; Cheng, Ge; Shi, Lei; Zhang, Yi-Bo

2016-12-01

A specific type of material, activated carbon fiber (ACF), was modified by SiO 2 , and the final products ACF-x were obtained as ACF-12.5, ACF-20, ACF-40, and ACF-80 according to different dosages of tetraethoxysilane (TEOS). The modified material on the ACF surface had a significant and smooth cover layer with low content of silica from scanning electron microscope (SEM) image. The modified ACF-x showed the stronger hydrophobicity, thermal stability, and adsorption capacity, which had almost no effect in the presence of water vapor and no destruction in multiple cycles. ACF-20 was proven as the most efficient adsorbent in humid conditions. The dual-function system composed of the regenerative adsorbents and the combustion catalyst would be efficient in consecutive toluene adsorption/oxidation cycles, in which the combustion catalyst was prepared by the displacement reaction of H 2 PtCl 6 with foam Ni. Therefore, the adsorption/catalytic oxidation could be a promising technique in the indoor air purification, especially in the case of very low volatile organic compound (VOC; toluene) concentration levels. Exploring highly effective adsorptive materials with less expensive costs becomes an urgent issue in the indoor air protection. ACF-20 modified by SiO 2 with Pt/Ni catalysts shows stronger hydrophobicity, thermal stability, and adsorption capacity. This dual-function system composed of the regenerative materials and the combustion catalyst would be a promising technique in the indoor air purification, especially in the case of removal of very low concentration of toluene.

Final Project Report: Development of Micro-Structural Mitigation Strategies for PEM Fuel Cells: Morphological Simulations and Experimental Approaches

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

Wessel, Silvia; Harvey, David

2013-06-28

The durability of PEM fuel cells is a primary requirement for large scale commercialization of these power systems in transportation and stationary market applications that target operational lifetimes of 5,000 hours and 40,000 hours by 2015, respectively. Key degradation modes contributing to fuel cell lifetime limitations have been largely associated with the platinum-based cathode catalyst layer. Furthermore, as fuel cells are driven to low cost materials and lower catalyst loadings in order to meet the cost targets for commercialization, the catalyst durability has become even more important. While over the past few years significant progress has been made in identifyingmore » the underlying causes of fuel cell degradation and key parameters that greatly influence the degradation rates, many gaps with respect to knowledge of the driving mechanisms still exist; in particular, the acceleration of the mechanisms due to different structural compositions and under different fuel cell conditions remains an area not well understood. The focus of this project was to address catalyst durability by using a dual path approach that coupled an extensive range of experimental analysis and testing with a multi-scale modeling approach. With this, the major technical areas/issues of catalyst and catalyst layer performance and durability that were addressed are: 1. Catalyst and catalyst layer degradation mechanisms (Pt dissolution, agglomeration, Pt loss, e.g. Pt in the membrane, carbon oxidation and/or corrosion). a. Driving force for the different degradation mechanisms. b. Relationships between MEA performance, catalyst and catalyst layer degradation and operational conditions, catalyst layer composition, and structure. 2. Materials properties a. Changes in catalyst, catalyst layer, and MEA materials properties due to degradation. 3. Catalyst performance a. Relationships between catalyst structural changes and performance. b. Stability of the three-phase boundary and its effect on performance/catalyst degradation. The key accomplishments of this project are: • The development of a molecular-dynamics based description of the carbon supported-Pt and ionomer system • The development of a composition-based, 1D-statistical Unit Cell Performance model • A modified and improved multi-pathway ORR model • An extension of the existing micro-structural catalyst model to transient operation • The coupling of a Pt Dissolution model to the modified ORR pathway model • The Development A Semi-empirical carbon corrosion model • The integration and release of an open-source forward predictive MEA performance and degradation model • Completion of correlations of BOT (beginning of test) and EOT (end of test) performance loss breakdown with cathode catalyst layer composition, morphology, material properties, and operational conditions • Catalyst layer durability windows and design curves • A design flow path of interactions from materials properties and catalyst layer effective properties to performance loss breakdown for virgin and degraded catalyst layers In order to ensure the best possible user experience we will perform a staged release of the software leading up to the webinar scheduled in October 2013. The release schedule will be as follows (please note that the manual will be released with the beta release as direct support is provided in Stage 1): • Stage 0 - Internal Ballard Release o Cross check of compilation and installation to ensure machine independence o Implement code on portable virtual machine to allow for non-UNIX use (pending) • Stage 1 - Alpha Release o The model code will be made available via a GIT, sourceforge, or other repository (under discussion at Ballard) for download and installation by a small pre-selected group of users o Users will be given three weeks to install, apply, and evaluate features of the code, providing feedback on issues or software bugs that require correction prior to beta release • Stage 2 - Beta Release o The model code repository is opened to the general public on a beta release concept, with a mechanism for bug tracking and feedback from a large user group o Code will be tracked and patched for any discovered bugs or relevant feedback from the user community, upon the completion of three months without a major bug submission the code will be moved to a full version release • Stage 3 - Full Version Release o Code is version to revision 1.0 and that version is frozen in development/patching« less

Dual properties of a hydrogen oxidation Ni-catalyst entrapped within a polymer promote self-defense against oxygen

DOE PAGES

Oughli, Alaa A.; Ruff, Adrian; Boralugodage, Nilusha Priyadarshani; ...

2018-02-28

A bio-inspired O 2 sensitive nickel catalyst dispersed in a hydrophobic and redox-silent polymer matrix shows enhanced stability for catalytic H 2 oxidation as well as O 2 tolerance. A simple but efficient electrode design separates the catalyst into two different reaction layers to promote different reactivity on the catalyst. (1) close to the electrode surface, the catalyst can directly exchange electrons with the electrode and generate current from H 2 oxidation; and (2) at the outer film boundary, the electrolyte exposed layer is electrically isolated from the electrode, which enables the H 2 reduced Ni-complex to convert O 2more » to H 2O and thus provides protection to the O 2-sensitive inner reaction layer. This strategy solves one of the biggest limitations of these otherwise outstanding catalysts and could be used to protect other similar catalysts whose wider application is currently limited by sensitivity towards oxygen.« less

Dual properties of a hydrogen oxidation Ni-catalyst entrapped within a polymer promote self-defense against oxygen

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

Oughli, Alaa A.; Ruff, Adrian; Boralugodage, Nilusha Priyadarshani

A bio-inspired O 2 sensitive nickel catalyst dispersed in a hydrophobic and redox-silent polymer matrix shows enhanced stability for catalytic H 2 oxidation as well as O 2 tolerance. A simple but efficient electrode design separates the catalyst into two different reaction layers to promote different reactivity on the catalyst. (1) close to the electrode surface, the catalyst can directly exchange electrons with the electrode and generate current from H 2 oxidation; and (2) at the outer film boundary, the electrolyte exposed layer is electrically isolated from the electrode, which enables the H 2 reduced Ni-complex to convert O 2more » to H 2O and thus provides protection to the O 2-sensitive inner reaction layer. This strategy solves one of the biggest limitations of these otherwise outstanding catalysts and could be used to protect other similar catalysts whose wider application is currently limited by sensitivity towards oxygen.« less

Exhaust gas purification system for lean burn engine

DOEpatents

Haines, Leland Milburn

2002-02-19

An exhaust gas purification system for a lean burn engine includes a thermal mass unit and a NO.sub.x conversion catalyst unit downstream of the thermal mass unit. The NO.sub.x conversion catalyst unit includes at least one catalyst section. Each catalyst section includes a catalytic layer for converting NO.sub.x coupled to a heat exchanger. The heat exchanger portion of the catalyst section acts to maintain the catalytic layer substantially at a desired temperature and cools the exhaust gas flowing from the catalytic layer into the next catalytic section in the series. In a further aspect of the invention, the exhaust gas purification system includes a dual length exhaust pipe upstream of the NO.sub.x conversion catalyst unit. The dual length exhaust pipe includes a second heat exchanger which functions to maintain the temperature of the exhaust gas flowing into the thermal mass downstream near a desired average temperature.

Facile and Green Synthesis of Palladium Nanoparticles-Graphene-Carbon Nanotube Material with High Catalytic Activity

NASA Astrophysics Data System (ADS)

Sun, Tai; Zhang, Zheye; Xiao, Junwu; Chen, Chen; Xiao, Fei; Wang, Shuai; Liu, Yunqi

2013-08-01

We report a facile and green method to synthesize a new type of catalyst by coating Pd nanoparticles (NPs) on reduced graphene oxide (rGO)-carbon nanotube (CNT) nanocomposite. An rGO-CNT nanocomposite with three-dimensional microstructures was obtained by hydrothermal treatment of an aqueous dispersion of graphene oxide (GO) and CNTs. After the rGO-CNT composites have been dipped in K2PdCl4 solution, the spontaneous redox reaction between the GO-CNT and PdCl42- led to the formation of nanohybrid materials consisting rGO-CNT decorated with 4 nm Pd NPs, which exhibited excellent and stable catalytic activity: the reduction of 4-nitrophenol to 4-aminophenol using NaBH4 as a catalyst was completed in only 20 s at room temperature, even when the Pd content of the catalyst was 1.12 wt%. This method does not require rigorous conditions or toxic agents and thus is a rapid, efficient, and green approach to the fabrication of highly active catalysts.

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

NASA Astrophysics Data System (ADS)

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

2017-10-01

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

Three dimensional metal/N-doped nanoplate carbon catalysts for oxygen reduction, the reason for using a layered nanoreactor.

PubMed

Yeganeh Ghotbi, Mohammad; Javanmard, Arash; Soleimani, Hassan

2018-02-21

A layered nanoreactor (zinc hydroxide gallate/nitrate nanohybrid) has been designed as a nano-vessel to confine the gallate/nitrate reaction inside zinc hydroxide layers for production of metal/nitrogen-doped carbon catalysts. Metals (Fe 2+ , Co 2+ and Ni 2+ ) doped and bare zinc hydroxide nitrates (ZHN) were synthesized as the α-phase hydroxide hosts. By an incomplete ion-exchange process, nitrate anions between the layers of the hosts were then partially replaced by the gallate anions to produce the layered nanoreactors. Under heat-treatment, the reaction between the remaining un-exchanged nitrate anions and the organic moiety inside the basal spacing of each nanohybrid plate resulted in obtaining highly porous 3D metal/nitrogen-doped carbon nanosheets. These catalysts were then used as extremely efficient electrocatalysts for catalyzing oxygen reduction reaction (ORR). This study is intended to show the way to get maximum electrocatalytic activity of the metal/N-doped carbon catalysts toward the ORR. This exceptionally high ORR performance originates from the increased available surface, the best pore size range and the uniform distribution of the active sites in the produced catalysts, all provided by the use of new idea of the layered nanoreactor.

CeO2-CuO/Cu2O/Cu monolithic catalysts with three-kind morphologies Cu2O layers for preferential CO oxidation

NASA Astrophysics Data System (ADS)

Jing, Guojuan; Zhang, Xuejiao; Zhang, Aiai; Li, Meng; Zeng, Shanghong; Xu, Changjin; Su, Haiquan

2018-03-01

The supports of copper slices with three-kind morphologies Cu2O layers were prepared by the hydrothermal method. The Cu2O layers are rod-like structure, three-dimensional reticular and porous morphology as well as flower-like morphology, respectively. The CeO2-CuO/Cu2O/Cu monolithic catalysts present porous and network structure or foam morphology after loading CeO2 and CuO. Cu and Ce elements are uniformly dispersed onto the support surface. It is found that the monolithic catalyst with flower-like Cu2O layer displays better low-temperature activity because of highly-dispersed CuO and high Olatt concentration. The monolithic catalysts with rod-like or reticular-morphology Cu2O layers present high-temperature activity due to larger CuO crystallite sizes and good synergistic effect at copper-ceria interfacial sites. The as-prepared CeO2-CuO/Cu2O/Cu monolithic catalysts show good performance in the CO-PROX reaction. The generation of Cu2O layers with three-kind morphologies is beneficial to the loading and dispersion of copper oxides and ceria.

Subnanometer to nanometer transition metal CO oxidation catalysts

DOEpatents

Vajda, Stefan; Fortunelli, Alessandro; Yasumatsu, Hisato

2017-12-26

The present invention provides a catalyst defined in part by a conductive substrate; a film overlaying a surface of the substrate; and a plurality of metal clusters supported by the layer, wherein each cluster comprises between 8 and 11 atoms. Further provided is a catalyst defined in part by a conductive substrate; a layer overlaying a surface of the substrate; and a plurality of metal clusters supported by the layer, wherein each cluster comprises at least two metals.

Platinum-tin catalysts supported on silica highly selective for n-hexane dehydrogenation

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

Llorca, J.; Homs, N.; Sales, J.

Silica-supported Pt-Sn catalysts were prepared by two-step impregnation from [PtCl{sub 2}(PPh{sub 3}){sub 2}] and SnCl{sub 2} solutions of appropriate concentrations to yield Pt/Sn atomic ratios ranging from 0.2 to 5.0. In these systems, the presence of true Pt-Sn alloys was confirmed by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray analysis and electron nanodiffraction. Pt and PtSn alloy phases were found on catalysts with Pt/Sn > 1, PtSn alloy alone on the catalyst with Pt/Sn = 1 and PtSn and PtSn{sub 2} alloys, together with Sn in the catalysts with Pt/Sn < 1. All these catalysts were tested in themore » skeletal reactions of n-hexane at 753 K and atmospheric pressure. The selectivity of Pt changed significantly when alloyed with tin. For Sn-rich compositions a segregation of tin toward the catalyst surface was shown by photoelectron spectroscopy, and high hydrogenolysis selectivity and fast deactivation were observed. In contrast, Pt-rich catalysts, in which a well defined PtSn alloy was observed, were much more stable and exhibited high selectivity to dehydrogenation reaction while maintaining low conversions to benzene and hydrogenolysis products. This selectivity pattern can be interpreted in terms of a change in adsorption properties due to differences in the number of adjacent Pt atoms required for the various reaction pathways. 24 refs., 11 figs., 3 tabs.« less

Reduced Graphene Oxide-Immobilized Tris(bipyridine)ruthenium(II) Complex for Efficient Visible-Light-Driven Reductive Dehalogenation Reaction.

PubMed

Li, Xiaoyan; Hao, Zhongkai; Zhang, Fang; Li, Hexing

2016-05-18

A sodium benzenesulfonate (PhSO3Na)-functionalized reduced graphene oxide was synthesized via a two-step aryl diazonium coupling and subsequent NaCl ion-exchange procedure, which was used as a support to immobilize tris(bipyridine)ruthenium(II) complex (Ru(bpy)3Cl2) by coordination reaction. This elaborated Ru(bpy)3-rGO catalyst exhibited excellent catalytic efficiency in visible-light-driven reductive dehalogenation reactions under mild conditions, even for ary chloride. Meanwhile, it showed the comparable reactivity with the corresponding homogeneous Ru(bpy)3Cl2 catalyst. This high catalytic performance could be attributed to the unique two-dimensional sheet-like structure of Ru(bpy)3-rGO, which efficiently diminished diffusion resistance of the reactants. Meanwhile, the nonconjugated PhSO3Na-linkage between Ru(II) complex and the support and the very low electrical conductivity of the catalyst inhibited energy/electron transfer from Ru(II) complex to rGO support, resulting in the decreased support-induced quenching effect. Furthermore, it could be easily recycled at least five times without significant loss of catalytic reactivity.

Synthesis and characterization of mangenese(III) porphyrin supported on imidazole modified chloromethylated MIL-101(Cr): A heterogeneous and reusable catalyst for oxidation of hydrocarbons with sodium periodate

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

Zadehahmadi, Farnaz; Tangestaninejad, Shahram, E-mail: stanges@sci.ui.ac.ir; Moghadam, Majid, E-mail: moghadamm@sci.ui.ac.ir

2014-10-15

In the present work, chloromethylated MIL-101(Cr) modified with imidazole, Im-MIL-101, was applied as a support for immobilizing of tetraphenylporphyrinatomangenese(III) chloride. The imidazole-bound MIL-101, Im-MIL-101, not only used as support for immobilization of manganese porphyrin but also applied as a heterogeneous axial base. The Mn(TPP)Cl@Im-MIL-101 catalyst was characterized by UV–vis, FT-IR, X-ray diffraction (XRD), N{sub 2} adsorption, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), elemental analysis and inductively coupled plasma (ICP) methods. The catalytic activity of this new catalytic system was investigated in the alkene epoxidation and alkane hydroxylation using NaIO{sub 4} as an oxidant in CH{sub 3}CN/H{submore » 2}O at room temperature. This heterogeneous catalyst is highly efficient, stable and reusable in the oxidation of hydrocarbons. - Highlights: • MIL-101 was modified by covalent post synthetic modification. • Mn(TPP)Cl was anchored to imidazole modified MIL-101 by covalent attachment. • A heterogeneous catalyst was prepared. • The catalyst was used for epoxidation of alkenes and hydroxylation of alkanes. • The catalyst was reusable.« less

A novel (ex situ) method to quantify oxygen diffusion coefficient of polymer fuel cells backing and catalyst layers

NASA Astrophysics Data System (ADS)

Baricci, Andrea; Casalegno, Andrea

2016-09-01

Limiting current density of oxygen reduction reaction in polymer electrolyte fuel cells is determined by several mass transport resistances that lower the concentration of oxygen on the catalyst active site. Among them, diffusion across porous media plays a significant role. Despite the extensive experimental activity documented in PEMFC literature, only few efforts have been dedicated to the measurement of the effective transport properties in porous layers. In the present work, a methodology for ex situ measurement of the effective diffusion coefficient and Knudsen radius of porous layers for polymer electrolyte fuel cells (gas diffusion layer, micro porous layer and catalyst layer) is described and applied to high temperature polymer fuel cells State of Art materials. Regression of the measured quantities by means of a quasi 2D physical model is performed to quantify the Knudsen effect, which is reported to account, respectively, for 30% and 50% of the mass transport resistance in micro porous layer and catalyst layer. On the other side, the model reveals that pressure gradient consequent to permeation in porous layers of high temperature polymer fuel cells has a negligible effect on oxygen concentration in relevant operating conditions.

A comparative parametric study of a catalytic plate methane reformer coated with segmented and continuous layers of combustion catalyst for hydrogen production

NASA Astrophysics Data System (ADS)

Mundhwa, Mayur; Parmar, Rajesh D.; Thurgood, Christopher P.

2017-03-01

A parametric comparison study is carried out between segmented and conventional continuous layer configurations of the coated combustion-catalyst to investigate their influence on the performance of methane steam reforming (MSR) for hydrogen production in a catalytic plate reactor (CPR). MSR is simulated on one side of a thin plate over a continuous layer of nickel-alumina catalyst by implementing an experimentally validated surface microkinetic model. Required thermal energy for the MSR reaction is supplied by simulating catalytic methane combustion (CMC) on the opposite side of the plate over segmented and continuous layer of a platinum-alumina catalyst by implementing power law rate model. The simulation results of both coating configurations of the combustion-catalyst are compared using the following parameters: (1) co-flow and counter-flow modes between CMC and MSR, (2) gas hourly space velocity and (3) reforming-catalyst thickness. The study explains why CPR designed with the segmented combustion-catalyst and co-flow mode shows superior performance not only in terms of high hydrogen production but also in terms of minimizing the maximum reactor plate temperature and thermal hot-spots. The study shows that the segmented coating requires 7% to 8% less combustion-side feed flow and 70% less combustion-catalyst to produce the required flow of hydrogen (29.80 mol/h) on the reforming-side to feed a 1 kW fuel-cell compared to the conventional continuous coating of the combustion-catalyst.

Friedel-Crafts Alkylation Using Elemental Aluminum Catalyst: An Undergraduate Laboratory Experiment.

ERIC Educational Resources Information Center

Meeks, B. Spencer; Lucas, Anita R.

1989-01-01

Provides methodology for carrying out the synthesis of sec-butyltoluene by the Friedel-Crafts alkylation of toluene. Suggests using simple elemental aluminum as the catalyst in place of AlCl3 or amalgamated aluminum. Notes satisfactory results for both macro- and microscale operations. (MVL)

Chlorine effect on the formation of carbon nanofibers.

PubMed

Lin, Wang-Hua; Takahashi, Yusuke; Li, Yuan-Yao; Sakoda, Akiyoshi

2012-12-01

Platelet graphite nanofibers (GNFs) and turbostratic carbon nanofibers (CNFs) are synthesized by the thermal evaporation and decomposition of a polymer-based mixture at 700 degrees C using Ni as a catalyst. The mixture consists of poly(ethylene glycol) (PEG), serving as the carbon source, and hydrochloric acid solution (HCl(aq)), serving as the promoter/additive for the growth of CNFs. High-purity zigzag-shaped platelet GNFs form with 10 wt% HCl(aq) as an additive in the PEG. The diameters of the platelet GNFs are in the range of 40-60 nm, with lengths of a few micrometers. High-resolution transmission electron microscopy images indicate a high degree of graphitization and well ordered graphene layers along the fiber axis. In contrast, high-purity turbostratic CNFs form with 20 wt% HCl(aq) in the PEG. The diameter and length of the turbostratic CNFs are 20-40 nm and a few micrometers, respectively. The participation of HCl in the thermal process leads to the formation of Ni-Cl compounds. The amount of chlorine affects the shape of the Ni catalyst, which determines the type of CNF formed.

Nucleation kinetics of MgCl2-ethanol adduct for the supported Ziegler-Natta catalysts with a thermodynamic approach

NASA Astrophysics Data System (ADS)

Ansari, Ziaul Haque; Zeng, Yan; Demopoulos, George P.; Li, Zhibao

2018-07-01

MgCl2-ethanol adducts play a key role in the synthesis of supported Ziegler-Natta catalysts. The morphology of the MgCl2-ethanol adducts, which is controlled by their crystallization process, can determine the structure and thus the property of the polyolefin products. Here we study the nucleation kinetics of MgCl2-ethanol adducts by measuring the metastable zone width (MSZW) and induction time at different temperatures. Supersaturation ratios used in induction time measurements were predicted by the Mixed Solvent Electrolyte (MSE) model embedded in OLI System. Nývlt‧s approach was applied to determine MSZW. By the induction time measurement, the effect of temperature, and supersaturation were studied. It was found that induction time decreases as either temperature or supersaturation increases. The measured MSZW and induction time are used to estimate the nucleation kinetics of the system, and thereby distinguishing between the homogeneous and heterogeneous mechanisms. The interfacial tension and other related nucleation parameters were calculated from the induction time data. XRD and TGA indicate that the MgCl2-ethanol adduct has the stoichiometry of MgCl2·6C2H5OH.

Comparison of the catalytic activity for the Suzuki-Miyaura reaction of (η(5)-Cp)Pd(IPr)Cl with (η(3)-cinnamyl)Pd(IPr)(Cl) and (η(3)-1-t-Bu-indenyl)Pd(IPr)(Cl).

PubMed

Melvin, Patrick R; Hazari, Nilay; Lant, Hannah M C; Peczak, Ian L; Shah, Hemali P

2015-01-01

Complexes of the type (η(3)-allyl)Pd(L)(Cl) and (η(3)-indenyl)Pd(L)(Cl) are highly active precatalysts for the Suzuki-Miyaura reaction. Even though allyl and indenyl ligands are similar to cyclopentadienyl (Cp) ligands, there have been no detailed comparative studies exploring the activity of precatalysts of the type (η(5)-Cp)Pd(L)(Cl) for Suzuki-Miyaura reactions. Here, we compare the catalytic activity of (η(5)-Cp)Pd(IPr)(Cl) (IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene, Cp) with two commercially available catalysts (η(3)-cinnamyl)Pd(IPr)(Cl) (Cin) and (η(3)-1-t-Bu-indenyl)Pd(IPr)(Cl) ( (tBu) Ind). We show that Cp gives slightly better catalytic activity than Cin, but significantly inferior activity than (tBu) Ind. This order of activity is rationalized by comparing the rates at which the precatalysts are activated to the monoligated Pd(0) active species along with the tendency of the starting precatalysts to comproportionate with monoligated Pd(0) to form inactive Pd(I) dimers. As part of this work the Cp supported Pd(I) dimer (μ-Cp)(μ-Cl)Pd2(IPr)2 (Cp (Dim) ) was synthesized and crystallographically characterized. It does not readily disproportionate to form monoligated Pd(0) and consequently Cp (Dim) is a poor catalyst for the Suzuki-Miyaura reaction.

In-plane and through-plane non-uniform carbon corrosion of polymer electrolyte fuel cell cathode catalyst layer during extended potential cycles

NASA Astrophysics Data System (ADS)

Ghosh, Sourov; Ohashi, Hidenori; Tabata, Hiroshi; Hashimasa, Yoshiyuki; Yamaguchi, Takeo

2017-09-01

The impact of electrochemical carbon corrosion via potential cycling durability tests mimicking start-stop operation events on the microstructure of the cathode catalyst layer in polymer electrolyte fuel cells (PEFCs) is investigated using focused ion beam (FIB) fabrication without/with the pore-filling technique and subsequent scanning electron microscope (SEM) observations. FIB/SEM investigations without pore-filling reveals that the durability test induces non-uniform cathode shrinking across the in-plane direction; the thickness of the catalyst layer decreases more under the gas flow channel compared to the area under the rim of the flow field. Furthermore, FIB/SEM investigations with the pore-filling technique reveal that the durability test also induces non-uniform cathode shrinking in the through-plane direction; the pores in the area close to the membrane are more shrunken compared with those close to the microporous layer. In particular, a thin area (1-1.5 μm) close to the membrane is found to be severely damaged; it includes closed pores that hinder mass transport through the catalyst layer. It is suggested that uneven carbon corrosion and catalyst layer compaction are responsible for the performance loss during potential cycling operation of PEFCs.

Effect of the thickness of the anode electrode catalyst layers on the performance in direct methanol fuel cells

NASA Astrophysics Data System (ADS)

Glass, Dean E.; Olah, George A.; Prakash, G. K. Surya

2017-06-01

For the large scale fuel cell manufacture, the catalyst loading and layer thickness are critical factors affecting the performance and cost of membrane electrode assemblies (MEAs). The influence of catalyst layer thicknesses at the anode of a PEM based direct methanol fuel cell (DMFC) has been investigated. Catalysts were applied with the drawdown method with varied thicknesses ranging from 1 mil to 8 mils (1 mil = 25.4 μm) with a Pt/Ru anode loading of 0.25 mg cm-2 to 2.0 mg cm-2. The MEAs with the thicker individual layers (8 mils and 4 mils) performed better overall compared to the those with the thinner layers (1 mil and painted). The peak power densities for the different loading levels followed an exponential decrease of Pt/Ru utilization at the higher loading levels. The highest power density achieved was 49 mW cm-2 with the 4 mil layers at 2.0 mg cm-2 catalyst loading whereas the highest normalized power density was 116 mW mg-1 with the 8 mil layers at 0.25 mg cm-2 loading. The 8 mil drawdowns displayed a 50% and 23% increase in normalized power density compared to the 1 mil drawdowns at 0.25 mg cm-2 and 0.5 mg cm-2 loadings, respectively.

Exceptionally high lactide polymerization activity of zirconium complexes with bridged diketiminate ligands.

PubMed

El-Zoghbi, Ibrahim; Whitehorne, Todd J J; Schaper, Frank

2013-07-07

A cyclohexanediyl-bridged, bis(N-xylyl) diketiminate ligand, (±)-C6H10(nacnac(Xyl)H)2, LH2 (Xyl = 2,6-dimethylphenyl), was obtained from the reaction of [(2,6-dimethylphenyl)amino]-pent-3-en-2-one first with Meerwein's salt, then with (±)-cyclohexanediamine. The reaction of the ligand with Zr(NMe2)4 yielded LZr(NMe2)2. Protonation of the remaining diamide ligands with EtOH or [H2NMe2]Cl yielded LZr(OEt)2 and LZrCl2, respectively. The latter complex was also obtained by the reaction of LH2 first with nBuLi and then with ZrCl4(THF)2. The dichloride complex yielded LZr(OEt)2 and LZrMe2 upon reaction with NaOEt or MeLi/AlMe3, respectively. X-ray diffraction studies showed a trans-configuration of the ancillary ligands in LZrCl2 and LZrMe2, and a cis-configuration in LZr(NMe2)2 and LZr(OEt)2. LZr(OEt)2 was tested as a catalyst for the polymerization of rac-lactide. Kinetic investigations yielded a rate law first order in catalyst and monomer and a rate constant k = 14(1) L mol(-1) s(-1), the latter being orders of magnitude higher than typical activities for group 4 complexes in lactide polymerization. Analyses of the obtained polymer revealed an atactic polymer and broad polymer molecular weight distributions with sizeable fractions of cyclic oligomers. The influence of contaminants on the polymerization activity was examined: while lactic acid deactivates the catalyst, addition of up to 1 equiv. of water or para-toluenesulfonic acid revitalized catalysts not showing maximum activity.

Preparation and characterization of [H2-DABCO][ClO4]2 as a new member of DABCO-based ionic liquids for the synthesis of pyrimido[4,5-b]-quinoline and pyrimido[4,5-d]pyrimidine derivatives

NASA Astrophysics Data System (ADS)

Shirini, Farhad; Langarudi, Mohaddeseh Safarpoor Nikoo; Daneshvar, Nader; Jamasbi, Negar; Irankhah-Khanghah, Mahsa

2018-06-01

[H2-DABCO][ClO4]2, as a novel DABCO-based ionic liquid, has been synthesized, characterized, and used as an affordable and recyclable catalyst in the synthesis of pyrimido [4,5-b]-quinoline and pyrimido [4,5-d]pyrimidine derivatives. The procedure shows several advantages over the previous methods such as simplicity, high yields, short reaction times, easy work-up, and use of a non-metal catalyst. Moreover, this paper virtually debates the impact of anions and cations on moisture-resistant property and catalytic activity in DABCO-based ionic liquids through the comparison of [DABCO](SO3H)2(Cl)2, [DABCO](SO3H)2(HSO4)2, [H2-DABCO][H2PO4]2, [H2-DABCO][HSO4]2, and [H2-DABCO][ClO4]2.

Chlorination Revisited: Does Cl- Serve as a Catalyst in the Chlorination of Phenols?

PubMed

Lau, Stephanie S; Abraham, Sonali M; Roberts, A Lynn

2016-12-20

The aqueous chlorination of (chloro)phenols is one of the best-studied reactions in the environmental literature. Previous researchers have attributed these reactions to two chlorine species: HOCl (at circum-neutral and high pH) and H 2 OCl + (at low pH). In this study, we seek to examine the roles that two largely overlooked chlorine species, Cl 2 and Cl 2 O, may play in the chlorination of (chloro)phenols. Solution pH, chloride concentration, and chlorine dose were systematically varied in order to assess the importance of different chlorine species as chlorinating agents. Our findings indicate that chlorination rates at pH < 6 increase substantially when chloride is present, attributed to the formation of Cl 2 . At pH 6.0 and a chlorine dose representative of drinking water treatment, Cl 2 O is predicted to have at best a minor impact on chlorination reactions, whereas Cl 2 may contribute more than 80% to the overall chlorination rate depending on the (chloro)phenol identity and chloride concentration. While it is not possible to preclude H 2 OCl + as a chlorinating agent, we were able to model our low-pH data by considering Cl 2 only. Even traces of chloride can generate sufficient Cl 2 to influence chlorination kinetics, highlighting the role of chloride as a catalyst in chlorination reactions.

Hydroxide catalysts for lignin depolymerization

DOEpatents

Beckham, Gregg T; Biddy, Mary J.; Kruger, Jacob S.; Chmely, Stephen C.; Sturgeon, Matthew

2017-10-17

Solid base catalysts and their use for the base-catalyzed depolymerization (BCD) of lignin to compounds such as aromatics are presented herein. Exemplary catalysts include layered double hydroxides (LDHs) as recyclable, heterogeneous catalysts for BCD of lignin.

Hydroxide catalysts for lignin depolymerization

DOEpatents

Beckham, Gregg T.; Biddy, Mary J.; Chmely, Stephen C.; Sturgeon, Matthew

2017-04-25

Solid base catalysts and their use for the base-catalyzed depolymerization (BCD) of lignin to compounds such as aromatics are presented herein. Exemplary catalysts include layered double hydroxides (LDHs) as recyclable, heterogeneous catalysts for BCD of lignin.

Rambutan-like CNT-Al2O3 scaffolds for high-performance cathode catalyst layers of polymer electrolyte fuel cells

NASA Astrophysics Data System (ADS)

Chang, KwangHyun; Cho, Seonghun; Lim, Eun Ja; Park, Seok-Hee; Yim, Sung-Dae

2018-03-01

Rambutan-like CNT-Al2O3 scaffolds are introduced as a potential candidate for CNT-based catalyst supports to overcome the CNT issues, such as the easy bundling in catalyst ink and the poor pore structure of the CNT-based catalyst layers, and to achieve high MEA performance in PEFCs. Non-porous α-phase Al2O3 balls are introduced to enable the growth of multiwalled CNTs, and Pt nanoparticles are loaded onto the CNT surfaces. In a half-cell, the Pt/CNT-Al2O3 catalyst shows much higher durability than those of a commercial Pt/C catalyst even though it shows lower oxygen reduction reaction (ORR) activity than Pt/C. After using the decal process for MEA formation, the Pt/CNT-Al2O3 shows comparable initial performance characteristics to Pt/C, overcoming the lower ORR activity, mainly due to the facile oxygen transport in the cathode catalyst layers fabricated with the CNT-Al2O3 scaffolds. The Pt/CNT-Al2O3 also exhibits much higher durability against carbon corrosion than Pt/C owing to the durable characteristics of CNTs. Systematic analysis of single cell performance for both initial and after degradation is provided to understand the origin of the high initial performance and durable behavior of Pt/CNT-Al2O3-based catalyst layers. This will provide insights into the design of electrocatalysts for high-performance MEAs in PEFCs.

Effect of catalyst on deposition of vanadium oxide in plasma ambient

NASA Astrophysics Data System (ADS)

Singh, Megha; Kumar, Prabhat; Saini, Sujit K.; Reddy, G. B.

2018-05-01

In this paper, we have studied effect of catalyst (buffer layer) on structure, morphology, crystallinity, uniformity of nanostructured thin films deposited in nitrogen plasma ambient keeping all other process parameters constant. The process used for deposition is novel known as Plasma Assisted Sublimation Process (PASP). Samples were then studied using SEM, TEM, HRTEM, Raman spectroscopy. By structural analysis it was found out that samples deposited on Ni layer composed chiefly of α-V2O5 but minor amount of other phases were present in the sample. Samples deposited on Al catalyst layer revealed different phase of V2O5, where sample deposited on Ag was composed chiefly of VO2±x phase. Further analysis revealed that morphology of samples is also affected by catalyst. While samples deposited in Al and Ag layer tend to have reasonably defined geometry, sample deposited on Ni layer were irregular in shape and size. All the results well corroborate with each other.

Percolation in a Proton Exchange Membrane Fuel Cell Catalyst Layer

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

Stacy, Stephen; Allen, Jeffrey

Water management in the catalyst layers of proton exchange membrane fuel cells (PEMFC) is confronted by two issues, flooding and dry out, both of which result in improper functioning of the fuel cell and lead to poor performance and degradation. At the present time, the data that has been reported about water percolation and wettability within a fuel cell catalyst layer is limited. A method and apparatus for measuring the percolation pressure in the catalyst layer has been developed based upon an experimental apparatus used to test water percolation in porous transport layers (PTL). The experimental setup uses a pseudomore » Hele-Shaw type testing where samples are compressed and a fluid is injected into the sample. Testing the samples gives percolation pressure plots which show trends in increasing percolation pressure with an increase in flow rate. A decrease in pressure was seen as percolation occurred in one sample, however the pressure only had a rising effect in the other sample.« less

Photocatalytic oxidation of organic compounds in a hybrid system composed of a molecular catalyst and visible light-absorbing semiconductor.

PubMed

Zhou, Xu; Li, Fei; Li, Xiaona; Li, Hua; Wang, Yong; Sun, Licheng

2015-01-14

Photocatalytic oxidation of organic compounds proceeded efficiently in a hybrid system with ruthenium aqua complexes as catalysts, BiVO4 as a light absorber, [Co(NH3)5Cl](2+) as a sacrificial electron acceptor and water as an oxygen source. The photogenerated holes in the semiconductor are used to oxidize molecular catalysts into the high-valent Ru(IV)=O intermediates for 2e(-) oxidation.

Solvent free oxidation of primary alcohols and diols using thymine iron(III) catalyst.

PubMed

Al-Hunaiti, Afnan; Niemi, Teemu; Sibaouih, Ahlam; Pihko, Petri; Leskelä, Markku; Repo, Timo

2010-12-28

In this study, we developed an efficient and selective iron-based catalyst system for the synthesis of ketones from secondary alcohols and carboxylic acids from primary alcohol. In situ generated iron catalyst of thymine-1-acetate (THA) and FeCl(3) under solvent-free condition exhibits high activity. As an example, 1-octanol and 2-octanol were oxidized to 1-octanoic acid and 2-octanone with 89% and 98% yields respectively.

A readily prepared neutral heterobimetallic titanium(IV)-rhodium(I) catalyst for intramolecular hydroacylation.

PubMed

Morgan, John P; Kundu, Kousik; Doyle, Michael P

2005-07-14

The combination of HOCMe2CH2PPh2, Ti(OiPr)4, and [Rh(cod)Cl]2 (3:1:1) in either benzene or dichloromethane produces a discrete species (tentatively formulated as complex) that is an active catalyst for intramolecular hydroacylation reactions of 3-substituted pentenals.

Facile synthesis of highly active PdAu nanowire networks as self-supported electrocatalyst for ethanol electrooxidation.

PubMed

Hong, Wei; Wang, Jin; Wang, Erkang

2014-06-25

In recent years, direct ethanol fuel cells (DEFCs) are attracting increasing attention owing to their wide applications. However, a significant challenge in the development of DEFC technology is the urgent need for highly active anode catalysts for the ethanol oxidation reaction. In this work, a facile and reproducible method for the high-yield synthesis of PdAu nanowire networks is demonstrated. The whole synthetic process is very simple, just mixing Na2PdCl4, HAuCl4, and KBr in an aqueous solution and using polyvinylpyrrolidone as a protective reagent while sodium borohydride as a reductant. The whole synthetic process can be simply performed at room temperature and completed in 30 min, which can greatly simplify the synthetic process and lower the preparation cost. Electrochemical catalytic measurement results prove that the as-prepared catalysts exhibit dramatically enhanced electrocatalytic activity for ethanol electrooxidation in alkaline solution. The facile synthetic process and excellent catalytic performance of the as-prepared catalysts demonstrate that they can be used as a promising catalyst for DEFCs.

Heterogeneous photodegradation of methylene blue with iron and tea or coffee polyphenols in aqueous solutions.

PubMed

Morikawa, Claudio Kendi; Shinohara, Makoto

2016-01-01

Recently, we developed two new Fenton catalysts using iron (Fe) and spent tea leaves or coffee grounds as raw material. In this study, Fe-to-tea or Fe-to-coffee polyphenol complexes were successfully tested as heterogeneous photo-Fenton catalysts. The photodegradation efficiency of methylene blue solutions with Fe-to-polyphenol complexes was higher than that of homogeneous iron salts in the photo-Fenton process. Furthermore, the tested Fe-to-polyphenol complexes could be reused by simply adding H2O2 to the solutions. After three sequential additions of H2O2, the conventional catalysts FeCl2·4H2O and FeCl3 removed only 16.6% and 53.6% of the dye, while the catalysts made using spent coffee grounds and tea leaves removed 94.4% and 96.0% of the dye, respectively. These results showed that the complexes formed between Fe and chlorogenic acid, caffeic acid, gallic acid and catechin, which are the main polyphenols in tea and coffee, can be used to improve the photo-Fenton process.

Use of the Wilkinson catalyst for the ortho-C-H heteroarylation of aromatic amines: facile access to highly extended π-conjugated heteroacenes for organic semiconductors.

PubMed

Huang, Yumin; Wu, Di; Huang, Jingsheng; Guo, Qiang; Li, Juan; You, Jingsong

2014-11-03

An unprecedented catalytic system composed of the Wilkinson catalyst [Rh(PPh3)3Cl] and CF3COOH enabled the highly regioselective cross-coupling of aromatic amines with a variety of heteroarenes through dual C-H bond cleavage. This protocol provided a facile and rapid route from readily available substrates to (2-aminophenyl)heteroaryl compounds, which may be conveniently transformed into highly extended π-conjugated heteroacenes. The experimental studies and calculations showed that thianaphtheno[3,2-b]indoles have large HOMO-LUMO energy gaps and low-lying HOMO levels, and could therefore potentially be high-performance organic semiconductors. Herein we report the first use of a rhodium(I) catalyst for oxidative C-H/C-H coupling reactions. The current innovative catalyst system is much less expensive than [RhCp*Cl2]2/AgSbF6 and could open the door for the application of this approach to other types of C-H activation processes. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

PubMed

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

2009-07-07

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

Synthesis, crystal structure and optical properties of two new layered cadmium iodates: Cd(IO{sub 3})X (X=Cl, OH)

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

Yang, Bing-Ping, E-mail: ybp@fjirsm.ac.cn; Mao, Jiang-Gao

Systematic explorations of new compounds in the cadmium iodate system by hydrothermal reactions led to two layered iodates, namely, Cd(IO{sub 3})X (X=Cl, OH). Cd(IO{sub 3})Cl crystallizes in the orthorhombic space group Cmca (No. 64) whereas Cd(IO{sub 3})(OH) crystallizes in the orthorhombic space group Pnma (No. 62). Cd(IO{sub 3})Cl displays a unique double layered structure composed of {sup 1}{sub ∞}[Cd−O{sub 3}Cl]{sub n} chains. Cadmium octahedrons form a 1D chain along the a-axis through edge sharing, and such chains are further interconnected via IO{sub 3} groups to form a special double layer on (020) plane. Cd(IO{sub 3})(OH) also exhibits a layered structuremore » that is composed of cadmium cations, IO{sub 3} groups and hydroxyl ions. Within a layer, chains of CdO{sub 6} edge-shared octahedra are observed along the b-axis. And these chains are connected by IO{sub 3} groups into a layer parallel to the bc plane. Spectroscopic characterizations, elemental analysis, and thermogravimetric analysis for the reported two compounds are also presented. - Graphical abstract: Two new layered cadmium iodates Cd(IO{sub 3})X (X=Cl, OH) are reported. Cd(IO{sub 3})Cl features a unique double layered structure whereas Cd(IO{sub 3})(OH) displays an ordinary layered structure. - Highlights: • Two new layered cadmium iodates Cd(IO{sub 3})X (X=Cl, OH) are reported. • Cd(IO{sub 3})Cl features a unique double layered structure. • Cd(IO{sub 3})(OH) displays an ordinary layered structure. • The spectroscopic and thermal properties have been studied in detail.« less

Synthesis of Enantioenriched Indolines by a Conjugate Addition/Asymmetric Protonation/Aza-Prins Cascade Reaction

PubMed Central

Daniels, Blake E.; Ni, Jane; Reisman, Sarah E.

2016-01-01

A conjugate addition/asymmetric protonation/aza-Prins cascade reaction has been developed for the enantioselective synthesis of fused polycyclic indolines. A catalyst system generated from ZrCl4 and 3,3’-dibromo-BINOL enables the synthesis of a range of polycyclic indolines in good yields and high enantioselectivity. A key finding is the use of TMSCl and 2,6-dibromophenol as a stoichiometric source of HCl to facilitate catalyst turnover. This transformation is the first in which a ZrCl4•BINOL complex serves as a chiral Lewis acid-assisted Brønsted acid. PMID:26844668

Preparation, characterization, and catalytic activity of zirconocene bridged on surface of silica gel

NASA Astrophysics Data System (ADS)

El Majdoub, Lotfia; Shi, Yasai; Yuan, Yuan; Zhou, Annan; Abutartour, Abubaker; Xu, Qinghong

2015-10-01

Zirconocene catalyst supported on silica gel was prepared for olefin polymerization by surface modification of calcined silica with SiCl4, and the reaction between the modified silica and cyclopentadienyl sodium and ZrCl4. The catalyst was characterized by using Fourier-transform infrared (FT-IR) spectrometer, thermogravimetric (TG), and differential scanning calorimetric (DSC) analytic spectrometer. It was found that the metallocene structure could be formed and connected on silica surface by chemical bond. Initial catalytic tests showed that the supported metallocene was catalytically active (methylaluminoxane as a cocatalyst), producing polymer with higher molecular weight than the metallocene just immobilized on the surface of silica gel.

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.

Synthesis, characterization and application of two-dimensional layered metal hydroxides for environmental remediation purposes

NASA Astrophysics Data System (ADS)

Machingauta, Cleopas

Two-dimensional layered nano composites, which include layered double hydroxides (LDHs), hydroxy double salts (HDSs) and layered hydroxide salts (LHSs) are able to intercalate different molecular species within their gallery space. These materials have a tunable structural composition which has made them applicable as fire retardants, adsorbents, catalysts, catalyst support materials, and ion exchangers. Thermal treatment of these materials results in destruction of the layers and formation of mixed metal oxides (MMOs) and spinels. MMOs have the ability to adsorb anions from solution and may also regenerate layered structures through a phenomenon known as memory effect. Zinc-nickel hydroxy nitrate was used for the uptake of a series of halogenated acetates (HAs). HAs are pollutants introduced into water systems as by-products of water chlorination and pesticide degradation; their sequestration from water is thus crucial. Optimization of layered materials for controlled uptake requires an understanding of their ion-exchange kinetics and thermodynamics. Exchange kinetics of these anions was monitored using ex-situ PXRD, UV-vis, HPLC and FTIR. It was revealed that exchange rates and uptake efficiencies are related to electronic spatial extents and the charge on carboxyl-oxygen atoms. In addition, acetate and nitrate-based HDSs were used to explore how altering the hydroxide layer affects uptake of acetate/nitrate ions. Changing the metal identities affects the interaction of the anions with the layers. From FTIR, we observed that nitrates coordinate in a D3h and Cs/C 2v symmetry; the nitrates in D3h symmetry were easily exchangeable. Interlayer hydrogen bonding was also revealed to be dependent on metal identity. Substituting divalent cations with trivalent cations produces materials with a higher charge density than HDSs and LHSs. A comparison of the uptake efficiency of zinc-aluminum, zinc-gallium and zinc-nickel hydroxy nitrates was performed using trichloroacetic acid as target anion. Uptake efficiency was better for LDHs than HDS, and between the LDHs, zinc-aluminum hydroxy nitrate was the best material for the uptake of tClAc. Calcined LDHs were applied for the uptake of methyl-orange, model azo-dye. The ability to regenerate the layered structures was helpful for improving adsorption efficiency. It has been reveal that calcined LDHs are also better adsorbents than calcined HDSs.

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

DOE PAGES

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

2016-03-09

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

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

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

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

2016-05-01

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

Controlled growth of vertically aligned carbon nanotubes on metal substrates

NASA Astrophysics Data System (ADS)

Gao, Zhaoli

Carbon nanotube (CNT) is a fascinating material with extraordinary electrical thermal and mechanical properties. Growing vertically aligned CNT (VACNT) arrays on metal substrates is an important step in bringing CNT into practical applications such as thermal interface materials (TIMs) and microelectrodes. However, the growth process is challenging due to the difficulties in preventing catalyst diffusion and controlling catalyst dewetting on metal substrates with physical surface heterogeneity. In this work, the catalyst diffusion mechanism and catalyst dewetting theory were studied for the controlled growth of VACNTs on metal substrates. The diffusion time of the catalyst, the diffusion coefficients for the catalyst in the substrate materials and the number density of catalyst nanoparticles after dewetting are identified as the key parameters, based on which three strategies are developed. Firstly, a fast-heating catalyst pretreatment strategy was used, aiming at preserving the amount of catalyst prior to CNT growth by reducing the catalyst diffusion time. The catalyst lifetime is extended from half an hour to one hour on a patterned Al thin film and a VACNT height of 106 mum, about twenty fold of that reported in the literature, was attained. Secondly, a diffusion barrier layer strategy is employed for a reduction of catalyst diffusion into the substrate materials. Enhancement of VACNT growth on Cu substrates was achieved by adopting a conformal Al2O 3 diffusion barrier layer fabricated by a specially designed atomic layer deposition (ALD) system. Lastly, a novel catalyst glancing angle deposition (GLAD) strategy is performed to manipulate the morphology of a relatively thick catalyst on metal substrates with physical surface heterogeneity, aiming to obtain uniform and dense catalyst nanoparticles after dewetting in the pretreatment process for enhanced VACNT growth. We are able to control the VACNT growth conditions on metal substrates in terms of their distribution, heights and alignments. Catalyst loss is controlled by the catalyst diffusion time and catalyst diffusion coefficients. A shorter catalyst diffusion time and smaller diffusion coefficient enhance VACNT growth on metals due to reduced catalyst loss during the pretreatment process. The dewetting behaviors of the thin film catalysts are influenced by the physical surface heterogeneity of the substrates which leads to non-uniform growth of VACNTs. The GLAD process facilitates the deposition of a relatively thick catalyst layer for the creation of dense and uniform catalyst nanoparticles. Applications of VACNT-metal structures in TIMs and microelectrodes are demonstrated. The VACNT-TIMs fabricated on Al alloy substrates have a typical thermal contact resistivity of 17.1 mm2˙K/W and their effective application in high-brightness LED thermal management was demonstrated. Electrochemical characterization was carried out on VACNT microelectrodes for the development of high resolution retinal prostheses and a satisfactory electrochemical property was again demonstrated.

Salt melt synthesis of curved nitrogen-doped carbon nanostructures: ORR kinetics boost

NASA Astrophysics Data System (ADS)

Rybarczyk, Maria K.; Gontarek, Emilia; Lieder, Marek; Titirici, Maria-Magdalena

2018-03-01

Implementing metal-free electrocatalysts for the oxygen reduction reaction (ORR) and revealing crucial chemical or topographical parameters driving their activity are vital for the development of power cells. The carbon-based catalysts are very often synthesized through carbonization of biopolymers, in particular, those one containing nitrogen groups such as chitosan. Unfortunately, the resulting carbonaceous materials usually lack specific porosity and exhibit low catalytic activity. Here, we demonstrate that pyrolysis of chitosan in a ZnCl2 melt assisted by the presence of LiCl results not only in a highly porous activated carbon material with a specific surface area of 1317.97 m2/g and the total nitrogen content of 6.5%, but also induces unexpected curvature in the grown graphitic layers. This is the first work that shows curved graphene layers obtained from a biopolymer precursor by its pyrolytic decomposition in the melted salt media. On the other hand, a carbonaceous material obtained from chitosan but without the salts has very low specific surface area of 7.8 m2/g, possesses no specific structural features, and contains 4.7% of nitrogen. The electrochemical studies show, that the former material is highly active towards four-electron pathway of the ORR in terms of an onset potential (0.89 V vs RHE) and the turnover frequency (TOFmax = 0.095 e site-1 s-1). We attribute this high catalytic performance to the presence of the pyridinic and pyrrolic sites in the structure. The ORR kinetics is probably further promoted by curvature in the graphitic layers.

Sodium chloride-catalyzed oxidation of multiwalled carbon nanotubes for environmental benefit.

PubMed

Endo, Morinobu; Takeuchi, Kenji; Tajiri, Takeyuki; Park, Ki Chul; Wang, Feng; Kim, Yoong-Ahm; Hayashi, Takuya; Terrones, Mauricio; Dresselhaus, Mildred S

2006-06-22

A sodium chloride (NaCl) catalyst (0.1 w/w %) lowers the oxidation temperature of graphitized multiwalled carbon nanotubes: MWCNT-20 (diameter: 20-70 nm) and MWCNT-80 (diameter: 80-150 nm). The analysis of the reaction kinetics indicates that the oxidation of MWCNT-20 and MWCNT-80 mixed with no NaCl exhibits single reaction processes with activation energies of E(a) = 159 and 152 kJ mol(-1), respectively. The oxidation reaction in the presence of NaCl is shown to consist of two different reaction processes, that is, a first reaction and a second reaction process. The first reaction process is dominant at a low temperature of around 600 degrees C, while the second reaction process becomes more dominant than the first one in a higher temperature region. The activation energies of the first reaction processes (MWCNT-20: E(a1) = 35.7 kJ mol(-1); MWCNT-80: E(a1) = 43.5 kJ mol(-1)) are much smaller than those of the second reaction processes (MWCNT-20: E(a2) = 170 kJ mol(-1); MWCNT-80: E(a2) = 171 kJ mol(-1)). The comparison of the kinetic parameters and the results of the spectroscopic and microscopic analyses imply that the lowering of the oxidation temperature in the presence of NaCl results from the introduction of disorder into the graphitized MWCNTs (during the first reaction process), thus increasing the facility of the oxidation reaction of the disorder-induced nanotubes (in the second reaction process). It is found that the larger nanopits and cracks on the outer graphitic layers are caused by the catalytic effect of NaCl. Therefore, the NaCl-mixed samples showed more rapid and stronger oxidation compared with that of the nonmixed samples at the same residual quantity.

Comparison of the catalytic activity for the Suzuki–Miyaura reaction of (η5-Cp)Pd(IPr)Cl with (η3-cinnamyl)Pd(IPr)(Cl) and (η3-1-t-Bu-indenyl)Pd(IPr)(Cl)

PubMed Central

Melvin, Patrick R; Lant, Hannah M C; Peczak, Ian L; Shah, Hemali P

2015-01-01

Summary Complexes of the type (η3-allyl)Pd(L)(Cl) and (η3-indenyl)Pd(L)(Cl) are highly active precatalysts for the Suzuki–Miyaura reaction. Even though allyl and indenyl ligands are similar to cyclopentadienyl (Cp) ligands, there have been no detailed comparative studies exploring the activity of precatalysts of the type (η5-Cp)Pd(L)(Cl) for Suzuki–Miyaura reactions. Here, we compare the catalytic activity of (η5-Cp)Pd(IPr)(Cl) (IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene, Cp) with two commercially available catalysts (η3-cinnamyl)Pd(IPr)(Cl) (Cin) and (η3-1-t-Bu-indenyl)Pd(IPr)(Cl) (tBu Ind). We show that Cp gives slightly better catalytic activity than Cin, but significantly inferior activity than tBu Ind. This order of activity is rationalized by comparing the rates at which the precatalysts are activated to the monoligated Pd(0) active species along with the tendency of the starting precatalysts to comproportionate with monoligated Pd(0) to form inactive Pd(I) dimers. As part of this work the Cp supported Pd(I) dimer (μ-Cp)(μ-Cl)Pd2(IPr)2 (Cp Dim) was synthesized and crystallographically characterized. It does not readily disproportionate to form monoligated Pd(0) and consequently Cp Dim is a poor catalyst for the Suzuki–Miyaura reaction. PMID:26732227

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

NASA Astrophysics Data System (ADS)

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

2013-11-01

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

Low cost fuel cell diffusion layer configured for optimized anode water management

DOEpatents

Owejan, Jon P; Nicotera, Paul D; Mench, Matthew M; Evans, Robert E

2013-08-27

A fuel cell comprises a cathode gas diffusion layer, a cathode catalyst layer, an anode gas diffusion layer, an anode catalyst layer and an electrolyte. The diffusion resistance of the anode gas diffusion layer when operated with anode fuel is higher than the diffusion resistance of the cathode gas diffusion layer. The anode gas diffusion layer may comprise filler particles having in-plane platelet geometries and be made of lower cost materials and manufacturing processes than currently available commercial carbon fiber substrates. The diffusion resistance difference between the anode gas diffusion layer and the cathode gas diffusion layer may allow for passive water balance control.

Enhancing of catalytic properties of vanadia via surface doping with phosphorus using atomic layer deposition

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

Strempel, Verena E.; Naumann d'Alnoncourt, Raoul, E-mail: r.naumann@bascat.tu-berlin.de; Löffler, Daniel

2016-01-15

Atomic layer deposition is mainly used to deposit thin films on flat substrates. Here, the authors deposit a submonolayer of phosphorus on V{sub 2}O{sub 5} in the form of catalyst powder. The goal is to prepare a model catalyst related to the vanadyl pyrophosphate catalyst (VO){sub 2}P{sub 2}O{sub 7} industrially used for the oxidation of n-butane to maleic anhydride. The oxidation state of vanadium in vanadyl pyrophosphate is 4+. In literature, it was shown that the surface of vanadyl pyrophosphate contains V{sup 5+} and is enriched in phosphorus under reaction conditions. On account of this, V{sub 2}O{sub 5} with themore » oxidation state of 5+ for vanadium partially covered with phosphorus can be regarded as a suitable model catalyst. The catalytic performance of the model catalyst prepared via atomic layer deposition was measured and compared to the performance of catalysts prepared via incipient wetness impregnation and the original V{sub 2}O{sub 5} substrate. It could be clearly shown that the dedicated deposition of phosphorus by atomic layer deposition enhances the catalytic performance of V{sub 2}O{sub 5} by suppression of total oxidation reactions, thereby increasing the selectivity to maleic anhydride.« less

Novel nano-semiconductor film layer supported nano-Pd Complex Nanostructured Catalyst Pd/Ⓕ-MeOx/AC for High Efficient Selective Hydrogenation of Phenol to Cyclohexanone.

PubMed

Si, Jiaqi; Ouyang, Wenbing; Zhang, Yanji; Xu, Wentao; Zhou, Jicheng

2017-04-28

Supported metal as a type of heterogeneous catalysts are the most widely used in industrial processes. High dispersion of the metal particles of supported catalyst is a key factor in determining the performance of such catalysts. Here we report a novel catalyst Pd/Ⓕ-MeO x /AC with complex nanostructured, Pd nanoparticles supported on the platelike nano-semiconductor film/activated carbon, prepared by the photocatalytic reduction method, which exhibited high efficient catalytic performance for selective hydrogenation of phenol to cyclohexanone. Conversion of phenol achieved up to more than 99% with a lower mole ratio (0.5%) of active components Pd and phenol within 2 h at 70 °C. The synergistic effect of metal nanoparticles and nano-semiconductors support layer and the greatly increasing of contact interface of nano-metal-semiconductors may be responsible for the high efficiency. This work provides a clear demonstration that complex nanostructured catalysts with nano-metal and nano-semiconductor film layer supported on high specific surface AC can yield enhanced catalytic activity and can afford promising approach for developing new supported catalyst.

Effect of different promoter precursors in a model Ru-Cs/graphite system on the catalytic selectivity for Fischer-Tropsch reaction

NASA Astrophysics Data System (ADS)

Eslava, José L.; Iglesias-Juez, Ana; Fernández-García, Marcos; Guerrero-Ruiz, Antonio; Rodríguez-Ramos, Inmaculada

2018-07-01

The effect of using two different promoter precursors on the Fischer-Tropsch synthesis was studied over cesium promoted ruthenium catalysts supported on a high surface area graphite support. In this work we reveal significant modifications in the selectivity values for Fischer-Tropsch reaction depending on the Cs promoter precursor (CsCl vs CsNO3). Specifically the bimetallic catalyst (4Ru-4Cs), prepared from nitrates both for metal and promoter precursors, showed a high selectivity to CO2 during reaction. By modifying the cesium precursor, it was possible to inhibit the water gas shift reaction, decreasing significantly the selectivity to CO2. In order to understand the chemical origin of these modifications a careful characterization of the materials was performed including: X-ray absorption near edge spectroscopy, transmission electron microscopy measurements, temperature programmed reduction studies, determination of the CO uptakes on the catalysts and the evolution of the CO adsorption heats as a function of surface coverages. It was found that upon reduction and under reaction atmosphere the promoter in the ex-nitrate catalyst appears as Cs2O which is considered responsible of the CO2 production, while in the catalysts prepared with Cs chloride the promoter remains as CsCl suffering a slight partial reduction.

Microenvironment effects in electrocatalysis: ionic-liquid-like coating on carbon nanotubes enhances the Pd-electrocatalytic alcohol oxidation.

PubMed

Li, Shuwen; Dong, Zhengping; Yang, Honglei; Guo, Shujing; Gou, Galian; Ren, Ren; Zhu, Zhejun; Jin, Jun; Ma, Jiantai

2013-02-11

A new catalyst consisting of ionic liquid (IL)-functionalized carbon nanotubes (CNTs) obtained through 1,3-dipolar cycloaddition support-enhanced electrocatalytic Pd nanoparticles (Pd@IL(Cl(-))-CNTs) was successfully fabricated and applied in direct ethanol alkaline fuel cells. The morphology, structure, component and stability of Pd@IL(Cl(-))-CNTs were systematic characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Raman spectra, thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The new catalyst exhibited higher electrocatalytic activity, better tolerance and electrochemical stability than the Pd nanoparticles (NPs) immobilized on CNTs (Pd@CNTs), which was ascribed to the effects of the IL, larger electrochemically active surface area (ECSA), and greater processing performance. Cyclic voltammograms (CVs) at various scan rates illustrated that the oxidation behaviors of ethanol at all electrodes were controlled by diffusion processes. The investigation of the different counteranions demonstrated that the performance of the IL-CNTs hybrid material was profoundly influenced by the subtly varied structures of the IL moiety. All the results indicated that the Pd@IL(Cl(-))-CNTs catalyst is an efficient anode catalyst, which has potential applications in direct ethanol fuel cells and the strategy of IL functionalization of CNTs could be available to prepare other carbonaceous carrier supports to enhance the dispersivity, stability, and catalytic performance of metal NPs as well. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Direct synthesis of few-layer graphene supported platinum nanocatalyst for methanol oxidation

NASA Astrophysics Data System (ADS)

Tan, Hong; Ma, Xiaohui; Sheng, Leimei; An, Kang; Yu, Liming; Zhao, Hongbin; Xu, Jiaqiang; Ren, Wei; Zhao, Xinluo

2014-11-01

High-crystalline few-layer graphene supported Pt nanoparticles have been synthesized by arc discharge evaporation of carbon electrodes containing Pt element. A high-temperature treatment under hydrogen atmosphere has been carried out to obtain a new type of Pt/graphene catalyst for methanol oxidation in direct methanol fuel cell. The morphology and structure characterizations of as-grown few-layer graphene supported Pt nanoparticles and Pt/graphene catalysts have been studied by Raman spectroscopy, scanning electron microscopy with energy-dispersive spectroscopy, and high-resolution transmission electron microscopy. Cyclic voltammograms and chronoamperometric curves show that our present Pt/graphene catalysts have larger current density for methanol oxidation, higher tolerance to carbon monoxide poisoning, and better stability during the operating procedure, compared to commercial Pt/C catalysts.

Direct deposit of catalyst on the membrane of direct feed fuel cells

NASA Technical Reports Server (NTRS)

Chun, William (Inventor); Narayanan, Sekharipuram R. (Inventor); Jeffries-Nakamura, Barbara (Inventor); Valdez, Thomas I. (Inventor); Linke, Juergen (Inventor)

2001-01-01

An improved direct liquid-feed fuel cell having a solid membrane electrolyte for electrochemical reactions of an organic fuel. Catalyst utilization and catalyst/membrane interface improvements are disclosed. Specifically, the catalyst layer is applied directly onto the membrane electrolyte.

Highly efficient and stable catalyst for peroxynitrite decomposition

Treesearch

Yurii V. Geletii; Alan J. Bailey; Jennifer J. Cowan; Ira A. Weinstock; Craig L. Hill

2001-01-01

The new cobalt substituted-polyoxometalate K7[CoAlW11O39]•15H2O and the simple CoCl2•6H2O salt are efficient catalysts for peroxynitrite decomposition. These compounds also catalyze the oxidation of ascorbic acid and the nitration of phenol by peroxynitrite.

Nickel nanoparticles-chitosan composite coated cellulose filter paper: An efficient and easily recoverable dip-catalyst for pollutants degradation.

PubMed

Kamal, Tahseen; Khan, Sher Bahadar; Asiri, Abdullah M

2016-11-01

In this report, we used cellulose filter paper (FP) as high surface area catalyst supporting green substrate for the synthesis of nickel (Ni) nanoparticles in thin chitosan (CS) coating layer and their easy separation was demonstrated for next use. In this work, FP was coated with a 1 wt% CS solution onto cellulose FP to prepare CS-FP as an economical and environment friendly host material. CS-FP was put into 0.2 M NiCl 2 aqueous solution for the adsorption of Ni 2+ ions by CS coating layer. The Ni 2+ adsorbed CS-FP was treated with 0.1 M NaBH 4 aqueous solution to convert the ions into nanoparticles. Thus, we achieved Ni nanoparticles-CS composite through water based in-situ preparation process. Successful Ni nanoparticles formations was assessed by FESEM and EDX analyses. FTIR used to track the interactions between nanoparticles and host material. Furthermore, we demonstrated that the nanocomposite displays an excellent catalytic activity and reusability in three reduction reactions of toxic compounds i.e. conversion of 4-nitrophenol to 4-aminophenol, 2-nitrophenol to 2-aminophenol, and methyl orange dye reduction by NaBH 4 . Such a fabrication process of Ni/CS-FP may be applicable for the immobilization of other metal nanoparticles onto FP for various applications in catalysis, sensing, and environmental sciences. Copyright © 2016 Elsevier Ltd. All rights reserved.

Performance evaluation of platinum-molybdenum carbide nanocatalysts with ultralow platinum loading on anode and cathode catalyst layers of proton exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Saha, Shibely; Cabrera Rodas, José Andrés; Tan, Shuai; Li, Dongmei

2018-02-01

An alternative catalyst platform, consisting of a phase-pure transition carbide (TMC) support and Pt nanoparticles (NPs) in the range of subnanometer to < 2.7 nm, is established that can be used in both anode and cathode catalyst layers. While some TMCs with low Pt loadings have demonstrated similar activity as commercial Pt catalyst in idealized disk electrode screening tests, few to none have been applied in a realistic fuel cell membrane electrode assembly (MEA). We recently reported that β-Mo2C hollow nanotubes modified with Pt NPs via atomic layer deposition (ALD) possess better activity and durability than 20% Pt/C. This paper presents systematic evaluation of the Pt/Mo2C catalysts in a MEA, investigating effects of different MEA preparation techniques, gas diffusion layers (GDL) and various Pt loadings in the ultralow range (<0.04 mg/cm2) on MEA performance. Most importantly, we demonstrate, for the first time, that Pt/Mo2C catalyst on both anode and cathode, with a loading of 0.02 mg (Pt) cm-2, generated peak power density of 414 mW cm-2 that corresponds to 10.35 kWgPt-1 using hydrogen (H2) and oxygen (O2). Accelerated degradation tests (ADT) on Pt/Mo2C catalysts show 111% higher power density than commercial 20% Pt/C after the vigorous ADT.

Catalyst patterning for nanowire devices

NASA Technical Reports Server (NTRS)

Li, Jun (Inventor); Cassell, Alan M. (Inventor); Han, Jie (Inventor)

2004-01-01

Nanowire devices may be provided that are based on carbon nanotubes or single-crystal semiconductor nanowires. The nanowire devices may be formed on a substrate. Catalyst sites may be formed on the substrate. The catalyst sites may be formed using lithography, thin metal layers that form individual catalyst sites when heated, collapsible porous catalyst-filled microscopic spheres, microscopic spheres that serve as masks for catalyst deposition, electrochemical deposition techniques, and catalyst inks. Nanowires may be grown from the catalyst sites.

Synthesis and Stabilization of Supported Metal Catalysts by Atomic Layer Deposition

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

Lu, Junling; Elam, Jeffrey W.; Stair, Peter C.

2013-03-12

Supported metal nanoparticles are among the most important cata-lysts for many practical reactions, including petroleum refining, automobile exhaust treatment, and Fischer–Tropsch synthesis. The catalytic performance strongly depends on the size, composition, and structure of the metal nanoparticles, as well as the underlying support. Scientists have used conventional synthesis methods including impregnation, ion exchange, and deposition–precipitation to control and tune these factors, to establish structure–performance relationships, and to develop better catalysts. Meanwhile, chemists have improved the stability of metal nanoparticles against sintering by the application of protective layers, such as polymers and oxides that encapsulate the metal particle. This often leadsmore » to decreased catalytic activity due to a lack of precise control over the thickness of the protective layer. A promising method of catalyst synthesis is atomic layer deposition (ALD). ALD is a variation on chemical vapor deposition in which metals, oxides, and other materials are deposited on surfaces by a sequence of self-limiting reactions. The self-limiting character of these reactions makes it possible to achieve uniform deposits on high-surface-area porous solids. Therefore, design and synthesis of advanced catalysts on the nanoscale becomes possible through precise control over the structure and composition of the underlying support, the catalytic active sites, and the protective layer. In this Account, we describe our advances in the synthesis and stabilization of supported metal catalysts by ALD. After a short introduction to the technique of ALD, we show several strategies for metal catalyst synthesis by ALD that take advantage of its self-limiting feature. Monometallic and bimetallic catalysts with precise control over the metal particle size, composition, and structure were achieved by combining ALD sequences, surface treatments, and deposition temperature control. Next, we describe ALD oxide overcoats applied with atomically precise thickness control that stabilize metal catalysts while preserving their catalytic function. We also discuss strategies for generation and control over the porosity of the overcoats that allow the embedded metal particles to remain accessible by reactants, and the details for ALD alumina overcoats on metal catalysts. Moreover, using methanol decomposition and oxidative dehydrogenation of ethane as probe reactions, we demonstrate that selectively blocking low coordination metal sites by oxide overcoats can provide another strategy to enhance both the durability and selectivity of metal catalysts.« less

Carbon nanotube synthesis via the catalytic chemical vapor deposition of methane in the presence of iron, molybdenum, and iron-molybdenum alloy thin layer catalysts

NASA Astrophysics Data System (ADS)

Yahyazadeh, Arash; Khoshandam, Behnam

In this study, we documented the catalytic chemical vapor deposition synthesis of carbon nanotubes (CNTs) using ferrocene and molybdenum hexacarbonyl as catalyst nanoparticle precursors and methane as a nontoxic and economical carbon source for the first time. Field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, wavelength dispersive X-ray spectrometry and transmission electron microscopy of the thin layer catalyst as a simple and cost effective catalyst preparation after methane decomposition reaction, along with Fourier transform infrared spectroscopy and Raman spectroscopy confirmed the growth of CNTs, from bimetallic nanoparticles, which are converted into iron-molybdenum alloy nanoparticles at 700 °C for pretreatment by hydrogen after chemical vapor deposition of thin layers. An investigation of the weight percentages of the chemical elements present in the CNTs synthesized from iron-molybdenum catalyst using quartz sheet substrate at 750 °C, confirmed a significant carbon yield of 75.4% which represents high catalyst activity. Additionally, multi-walled carbon nanotubes (∼16-55 nm in diameter and 1.2 μm in length) were observed in the iron-molybdenum alloy sample after methane decomposition reaction at 750 °C for 35 min. To show the role of iron and molybdenum coated on silicon substrate as two thin layer catalysts, samples were considered for CNTs growth (diameter ∼47-69 nm) at 800 °C and 830 °C, respectively. Moreover, the effect of hydrogen pretreatment was evaluated in terms of active metal coating properly. The best graphitic structure due to Raman spectroscopy outcomes (ID/IG ratio) was obtained for iron coated on a quartz sheet, which was estimated at 0.8505. Thermogravimetric analysis proved the thermal stability of the synthesized CNTs using iron thin-layer catalyst up to 350 °C.

X-ray spectroscopy for chemistry in the 2-4 keV energy regime at the XMaS beamline: ionic liquids, Rh and Pd catalysts in gas and liquid environments, and Cl contamination in γ-Al2O3.

PubMed

Thompson, Paul B J; Nguyen, Bao N; Nicholls, Rachel; Bourne, Richard A; Brazier, John B; Lovelock, Kevin R J; Brown, Simon D; Wermeille, Didier; Bikondoa, Oier; Lucas, Christopher A; Hase, Thomas P A; Newton, Mark A

2015-11-01

The 2-4 keV energy range provides a rich window into many facets of materials science and chemistry. Within this window, P, S, Cl, K and Ca K-edges may be found along with the L-edges of industrially important elements from Y through to Sn. Yet, compared with those that cater for energies above ca. 4-5 keV, there are relatively few resources available for X-ray spectroscopy below these energies. In addition, in situ or operando studies become to varying degrees more challenging than at higher X-ray energies due to restrictions imposed by the lower energies of the X-rays upon the design and construction of appropriate sample environments. The XMaS beamline at the ESRF has recently made efforts to extend its operational energy range to include this softer end of the X-ray spectrum. In this report the resulting performance of this resource for X-ray spectroscopy is detailed with specific attention drawn to: understanding electrostatic and charge transfer effects at the S K-edge in ionic liquids; quantification of dilution limits at the Cl K- and Rh L3-edges and structural equilibria in solution; in vacuum deposition and reduction of [Rh(I)(CO)2Cl]2 to γ-Al2O3; contamination of γ-Al2O3 by Cl and its potential role in determining the chemical character of supported Rh catalysts; and the development of chlorinated Pd catalysts in `green' solvent systems. Sample environments thus far developed are also presented, characterized and their overall performance evaluated.

Catalyst support structure, catalyst including the structure, reactor including a catalyst, and methods of forming same

DOEpatents

Van Norman, Staci A.; Aston, Victoria J.; Weimer, Alan W.

2017-05-09

Structures, catalysts, and reactors suitable for use for a variety of applications, including gas-to-liquid and coal-to-liquid processes and methods of forming the structures, catalysts, and reactors are disclosed. The catalyst material can be deposited onto an inner wall of a microtubular reactor and/or onto porous tungsten support structures using atomic layer deposition techniques.

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.

Catalytic activity during copolymerization of ethylene and 1-hexene via mixed TiO2/SiO2-supported MAO with rac-Et[Ind]2ZrCl2 metallocene catalyst.

PubMed

Jongsomjit, Bunjerd; Ngamposri, Sutti; Praserthdam, Piyasan

2005-07-14

Activities during ethylene/1-hexene copolymerization were found to increase using the mixed titania/silica-supported MAO with rac-Et[Ind]2ZrCl2 metallocene catalyst. Energy Dispersive X-ray spectorcopy (EDX) indicated that the titania was apparently located on the outer surface of silica and acted as a spacer to anchor MAO to the silica surface. IR spectra revealed the Si-O-Ti stretching at 980 cm(-1) with low content of titania. The presence of anchored titania resulted in less steric hindrance and less interaction due to supporting effect.

Biodiesel synthesis using calcined layered double hydroxide catalysts

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

Schumaker, J. Link; Crofcheck, Czarena; TAckett, S. Adam

2008-01-01

The catalytic properties of calcined Li-Al, Mg-Al and Mg-Fe layered double hydroxides (LDHs) were examined in two transesterification reactions, namely, the reaction of glyceryl tributyrate with methanol, and the reaction of soybean oil with methanol. While the Li-Al catalysts showed high activity in these reactions at the reflux temperature of methanol, the Mg-Fe and Mg-Al catalysts exhibited much lower methyl ester yields. CO2 TPD measurements revealed the presence of sites of weak, medium and strong basicity on both Mg-Al and Li-Al catalysts, the latter showing higher concentrations of medium and strong base sites; by implication, these are the main sitesmore » active in transesterification catalyzed by calcined Li-Al LDHs. Maximum activity was observed for the Li-Al catalysts when a calcination temperature of 450-500 aC was applied, corresponding to decomposition of the layered double hydroxide to the mixed oxide without formation of crystalline lithium aluminate phases.« less

Study on the water flooding in the cathode of direct methanol fuel cells.

PubMed

Im, Hun Suk; Kim, Sang-Kyung; Lim, Seongyop; Peck, Dong-Hyun; Jung, Doohwan; Hong, Won Hi

2011-07-01

Water flooding phenomena in the cathode of direct methanol fuel cells were analyzed by using electrochemical impedance spectroscopy. Two kinds of commercial gas diffusion layers with different PTFE contents of 5 wt% (GDL A5) and 20 wt% (GDL B20) were used to investigate the water flooding under various operating conditions. Water flooding was divided into two types: catalyst flooding and backing flooding. The cathode impedance spectra of each gas diffusion layer was obtained and compared under the same conditions. The diameter of the capacitive semicircle became larger with increasing current density for both, and this increase was greater for GDL B20 than GDL A5. Catalyst flooding is dominant and backing flooding is negligible when the air flow rate is high and current density is low. An equivalent model was suggested and fitted to the experimental data. Parameters for catalyst flooding and backing flooding were individually obtained. The capacitance of the catalyst layer decreases as the air flow rate decreases when the catalyst flooding is dominant.

Photocatalytic degradation of lignin on synthesized Ag-AgCl/ZnO nanorods under solar light and preliminary trials for methane fermentation.

PubMed

Li, Huifang; Lei, Zhongfang; Liu, Chunguang; Zhang, Zhenya; Lu, Baowang

2015-01-01

New photocatalysts, Ag-AgCl/ZnO nanorods, were successfully synthesized in this study by using microwave assisted chemical precipitation and deposition-precipitation-photoreduction methods. The optimal preparation condition was determined as pH 9 in distilled water and 40min for UV light photoreduction of Ag (i.e. Ag40-AgCl/ZnO) by degradation of methyl orange. This work investigated the feasibility of using Ag40-AgCl/ZnO to degrade lignin under natural solar light and then subsequent methane production with influencing factors like solution pH, dosage of catalyst and initial lignin concentration being considered. OH radicals were found to play the most important role in the photocatalytic process, and the new prepared catalyst possessed stable photocatalytic activity after 7 cycles' utilization. During the subsequent biogasification, the degraded lignin obtained from 120min photocatalysis yielded 184ml methane and 325ml biogas for per gram of removed total organic carbon, increased by 10.9% and 23.1%, respectively compared to the control. Copyright © 2014 Elsevier Ltd. All rights reserved.

Layer-by-Layer Molecular Assemblies for Dye-Sensitized Photoelectrosynthesis Cells Prepared by Atomic Layer Deposition

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

Wang, Degao; Sheridan, Matthew V.; Shan, Bing

2017-08-30

In a Dye Sensitized Photoelectrosynthesis Cell (DSPEC) the relative orientation of catalyst and chromophore play important roles. Here we introduce a new, robust, Atomic Layer Deposition (ALD) procedure for the preparation of assemblies on wide bandgap semiconductors. In the procedure, phosphonated metal complex precursors react with metal ion bridging to an external chromophore or catalyst to give assemblies bridged by Al(III), Sn(IV), Ti(IV), or Zr(IV) metal oxide units as bridges. The procedure has been extended to chromophore-catalyst assemblies for water oxidation catalysis. A SnO2 bridged assembly on SnO2/TiO2 core/shell electrodes undergoes water splitting with an incident photon conversion efficiency (IPCE)more » of 17.1% at 440 nm. Reduction of water at a Ni(II)-based catalyst on NiO films has been shown to give H2. Compared to conventional solution-based procedures, the ALD approach offers significant advantages in scope and flexibility for the preparation of stable surface structures.« less

Same-View Nano-XAFS/STEM-EDS Imagings of Pt Chemical Species in Pt/C Cathode Catalyst Layers of a Polymer Electrolyte Fuel Cell.

PubMed

Takao, Shinobu; Sekizawa, Oki; Samjeské, Gabor; Nagamatsu, Shin-ichi; Kaneko, Takuma; Yamamoto, Takashi; Higashi, Kotaro; Nagasawa, Kensaku; Uruga, Tomoya; Iwasawa, Yasuhiro

2015-06-04

We have made the first success in the same-view imagings of 2D nano-XAFS and TEM/STEM-EDS under a humid N2 atmosphere for Pt/C cathode catalyst layers in membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells (PEFCs) with Nafion membrane to examine the degradation of Pt/C cathodes by anode gas exchange cycles (start-up/shut-down simulations of PEFC vehicles). The same-view imaging under the humid N2 atmosphere provided unprecedented spatial information on the distribution of Pt nanoparticles and oxidation states in the Pt/C cathode catalyst layer as well as Nafion ionomer-filled nanoholes of carbon support in the wet MEA, which evidence the origin of the formation of Pt oxidation species and isolated Pt nanoparticles in the nanohole areas of the cathode layer with different Pt/ionomer ratios, relevant to the degradation of PEFC catalysts.

PCDD/F adsorption and destruction in the flue gas streams of MWI and MSP via Cu and Fe catalysts supported on carbon.

PubMed

Chang, Shu Hao; Yeh, Jhy Wei; Chein, Hung Min; Hsu, Li Yeh; Chi, Kai Hsien; Chang, Moo Been

2008-08-01

Catalytic destruction has been applied to control polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) emissions from different facilities. The cost of carbon-based catalysts is considerably lower than that of the metal oxide or zeolite-based catalysts used in the selective catalytic reduction (SCR) system. In this study, destruction and adsorption efficiencies of PCDD/Fs achieved with Cu/C and Fe/C catalysts from flue gas streams of a metal smelting plant (MSP) and a large-scale municipal waste incinerator (MWI), respectively, are evaluated via the pilot-scale catalytic reactor system (PCRS). The results indicate that Cu and Fe catalysts supported on carbon surface are capable of decomposing and adsorbing PCDD/ Fs from gas streams. In the testing sources of MSP and MWI, the PCDD/F removal efficiencies achieved with Cu/C catalyst at 250 degrees C reach 96%, however, the destruction efficiencies are negative (-1,390% and -112%, respectively) due to significant PCDD/F formation on catalyst promoted by copper. In addition, Fe/C catalyst is of higher removal and destruction efficiencies compared with Cu/C catalyst in both testing sources. The removal efficiencies of PCDD/Fs achieved with Fe/C catalyst are 97 and 94% for MSP and MWI, respectively, whereas the destruction efficiencies are both higher than 70%. Decrease of PCDD/F destruction efficiency and increase of adsorption efficiency with increasing chlorination of dioxin congeners is also observed in the test via three-layer Fe/C catalyst. Furthermore, the mass of 2,3,7,8-PCDD/Fs retained on catalyst decreases on the order of first to third layer of catalyst. Each gram Fe/C catalyst in first layer adsorbs 10.9, 6.91, and 3.04 ng 2,3,7,8-PCDD/Fs in 100 min testing duration as the operating temperature is controlled at 150, 200, and 250 degrees C, respectively.

Pd-catalysts for DFAFC prepared by magnetron sputtering

NASA Astrophysics Data System (ADS)

Bieloshapka, I.; Jiricek, P.; Vorokhta, M.; Tomsik, E.; Rednyk, A.; Perekrestov, R.; Jurek, K.; Ukraintsev, E.; Hruska, K.; Romanyuk, O.; Lesiak, B.

2017-10-01

Samples of a palladium catalyst for direct formic acid fuel cell (DFAFC) applications were prepared on the Elat® carbon cloth by magnetron sputtering. The quantity of Pd was equal to 3.6, 120 and 720 μg/cm2. The samples were tested in a fuel cell for electro-oxidation of formic acid, and were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The XPS measurements revealed a high contribution of PdCx phase formed at the Pd/Elat® surface interface, with carbon concentration in PdCx from x = 9.9-14.6 at.%, resulting from the C substrate and CO residual gases. Oxygen groups, e.g. hydroxyl (-OH), carbonyl (Cdbnd O) and carboxyl (COOH), resulted from the synthesis conditions due to the presence of residual gases, electro-oxidation during the reaction and oxidation in the atmosphere. Because of the formation of CO and CO2 on the catalysts during the reaction, or because of poisoning by impurities containing the -CH3 group, together with the risk of Pd losses due to dissolution in formic acid, there was a negative effect of catalyst degradation on the active area surface. The effect of different loadings of Pd layers led to increasing catalyst efficiency. Current-voltage curves showed that different amounts of catalyst did not increase the DFAFC power to a great extent. One reason for this was the catalyst structure formed on the carbon cloth. AFM and SEM measurements showed a layer-by-layer growth with no significant variations in morphology. The results for electric power recalculated for the Pd loading per 1 mg of catalyst layers in comparison to carbon substrates decorated by Pd nanoparticles showed that there is potential for applying anodes for formic acid fuel cells prepared by magnetron sputtering.

Study on corrosion migrations within catalyst-coated membranes of proton exchange membrane electrolyzer cells

DOE PAGES

Mo, Jingke; Steen, Stuart; Kang, Zhenye; ...

2017-10-09

The corrosion of low-cost, easily manufactured metallic components inside the electrochemical environment of proton exchange membrane electrolyzer cells (PEMECs) has a significant effect on their performance and durability. Here, 316 stainless steel (SS) mesh was used as a model liquid/gas diffusion layer material to investigate the migration of corrosion products in the catalyst-coated membrane of a PEMEC. Iron and nickel cation particles were found distributed throughout the anode catalyst layer, proton exchange membrane, and cathode catalyst layer, as revealed by scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. Our results indicate the corrosion products of 316 SS are transportedmore » from anode to cathode through the nanochannels of the Nafion membrane, resulting in impeded proton transport and overall PEMEC performance loss.« less

Study on corrosion migrations within catalyst-coated membranes of proton exchange membrane electrolyzer cells

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

Mo, Jingke; Steen, Stuart; Kang, Zhenye

The corrosion of low-cost, easily manufactured metallic components inside the electrochemical environment of proton exchange membrane electrolyzer cells (PEMECs) has a significant effect on their performance and durability. Here, 316 stainless steel (SS) mesh was used as a model liquid/gas diffusion layer material to investigate the migration of corrosion products in the catalyst-coated membrane of a PEMEC. Iron and nickel cation particles were found distributed throughout the anode catalyst layer, proton exchange membrane, and cathode catalyst layer, as revealed by scanning transmission electron microscopy and energy dispersive X-ray spectroscopy. Our results indicate the corrosion products of 316 SS are transportedmore » from anode to cathode through the nanochannels of the Nafion membrane, resulting in impeded proton transport and overall PEMEC performance loss.« less

Pt and PtRu catalyst bilayers increase efficiencies for ethanol oxidation in proton exchange membrane electrolysis and fuel cells

NASA Astrophysics Data System (ADS)

Altarawneh, Rakan M.; Pickup, Peter G.

2017-10-01

Polarization curves, product distributions, and reaction stoichiometries have been measured for the oxidation of ethanol at anodes consisting of Pt and PtRu bilayers and a homogeneous mixture of the two catalysts. These anode structures all show synergies between the two catalysts that can be attributed to the oxidation of acetaldehyde produced at the PtRu catalyst by the Pt catalyst. The use of a PtRu layer over a Pt layer produces the strongest effect, with higher currents than a Pt on PtRu bilayer, mixed layer, or either catalyst alone, except for Pt at high potentials. Reaction stoichiometries (average number of electrons transferred per ethanol molecule) were closer to the values for Pt alone for both of the bilayer configurations but much lower for PtRu and mixed anodes. Although Pt alone would provide the highest overall fuel cell efficiency at low power densities, the PtRu on Pt bilayer would provide higher power densities without a significant loss of efficiency. The origin of the synergy between the Pt and PtRu catalysts was elucidated by separation of the total current into the individual components for generation of carbon dioxide and the acetaldehyde and acetic acid byproducts.

High performance and durability of order-structured cathode catalyst layer based on TiO2@PANI core-shell nanowire arrays

NASA Astrophysics Data System (ADS)

Chen, Ming; Wang, Meng; Yang, Zhaoyi; Wang, Xindong

2017-06-01

In this paper, an order-structured cathode catalyst layer consisting of Pt-TiO2@PANI core-shell nanowire arrays that in situ grown on commercial gas diffusion layer (GDL) are prepared and applied to membrane electrode assembly (MEA) of proton exchange membrane fuel cell (PEMFC). In order to prepare the TiO2@PANI core-shell nanowire arrays with suitable porosity and prominent conductivity, the morphologies of the TiO2 nanoarray and electrochemical polymerization process of aniline are schematically investigated. The MEA with order-structured cathode catalyst layer is assembled in the single cell to evaluate the electrochemical performance and durability of PEMFC. As a result, the PEMFC with order-structured cathode catalyst layer shows higher peak power density (773.54 mW cm-2) than conventional PEMFC (699.30 mW cm-2). Electrochemically active surface area (ECSA) and charge transfer impedance (Rct) are measured before and after accelerated degradation test (ADT), and the corresponding experimental results indicate the novel cathode structure exhibits a better stability with respect to conventional cathode. The enhanced electrochemical performance and durability toward PEMFC can be ascribed to the order-structured cathode nanoarray structure with high specific surface area increases the utilization of catalyst and reduces the tortuosity of transport pathways, and the synergistic effect between TiO2@PANI support and Pt nanoparticles promotes the high efficiency of electrochemical reaction and improves the stability of catalyst. This research provides a facile and controllable method to prepare order-structured membrane electrode with lower Pt loading for PEMFC in the future.

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

Lei, Yu; Liu, Bin; Lu, Junling

The effect of residue chlorine on the synthesis of well-dispersed Pd nanoparticles on TiO2 supports using Pd atomic layer deposition (ALD) was investigated. The dispersion of Pd nanoparticles was compared over chlorine-containing and chlorine-free TiO2 supports prepared by selecting proper precursors. The detailed X-ray photoelectron spectroscopy and scanning transmission electron microscopy characterizations showed that higher dispersion of Pd nanoparticles was achieved on the chlorine-containing TiO2 surface than the chlorine-free TiO2. The preparation of TiO2 thin films and Pd nanoparticles was characterized by in situ FT-IR. The temperature required for complete deligation of palladium hexafluoroacetylacetonate decreased from 175 to 100 degreesmore » C with the presence of chlorine on the TiO2 surface. Density functional theory calculations confirm that Pdligand bond strength could be weakened as Pd binds to the Cl sites. The water-gas-shift reaction was chosen as the model reaction, and the catalytic performance of the ALD Pd catalysts was discussed. Compared to reported catalysts, the Pd nanocatalysts supported by TiO2/SiO2 mixed oxides showed promising performance in the low-temperature water-gas-shift reaction.« less

Cobalt/copper-decorated carbon nanofibers as novel non-precious electrocatalyst for methanol electrooxidation

PubMed Central

2014-01-01

In this study, Co/Cu-decorated carbon nanofibers are introduced as novel electrocatalyst for methanol oxidation. The introduced nanofibers have been prepared based on graphitization of poly(vinyl alcohol) which has high carbon content compared to many polymer precursors for carbon nanofiber synthesis. Typically, calcination in argon atmosphere of electrospun nanofibers composed of cobalt acetate tetrahydrate, copper acetate monohydrate, and poly(vinyl alcohol) leads to form carbon nanofibers decorated by CoCu nanoparticles. The graphitization of the poly(vinyl alcohol) has been enhanced due to presence of cobalt which acts as effective catalyst. The physicochemical characterization affirmed that the metallic nanoparticles are sheathed by thin crystalline graphite layer. Investigation of the electrocatalytic activity of the introduced nanofibers toward methanol oxidation indicates good performance, as the corresponding onset potential was small compared to many reported materials; 310 mV (vs. Ag/AgCl electrode) and a current density of 12 mA/cm2 was obtained. Moreover, due to the graphite shield, good stability was observed. Overall, the introduced study opens new avenue for cheap and stable transition metals-based nanostructures as non-precious catalysts for fuel cell applications. PMID:24387682

Study on the decomposition of trace benzene over V2O5-WO3/TiO2-based catalysts in simulated flue gas

EPA Science Inventory

Commercial and laboratory-prepared V2O5–WO3/TiO2-based catalysts with different compositions were tested for catalytic decomposition of chlorobenzene （ClBz） in simulated flue gas. Resonance enhanced multiphoton ionization-time of flight mass spectrometry (REMPI-TOFMS) was employe...

Thermally Stable TiO2 - and SiO2 -Shell-Isolated Au Nanoparticles for In Situ Plasmon-Enhanced Raman Spectroscopy of Hydrogenation Catalysts.

PubMed

Hartman, Thomas; Weckhuysen, Bert M

2018-03-12

Raman spectroscopy is known as a powerful technique for solid catalyst characterization as it provides vibrational fingerprints of (metal) oxides, reactants, and products. It can even become a strong surface-sensitive technique by implementing shell-isolated surface-enhanced Raman spectroscopy (SHINERS). Au@TiO 2 and Au@SiO 2 shell-isolated nanoparticles (SHINs) of various sizes were therefore prepared for the purpose of studying heterogeneous catalysis and the effect of metal oxide coating. Both SiO 2 - and TiO 2 -SHINs are effective SHINERS substrates and thermally stable up to 400 °C. Nano-sized Ru and Rh hydrogenation catalysts were assembled over the SHINs by wet impregnation of aqueous RuCl 3 and RhCl 3 . The substrates were implemented to study CO adsorption and hydrogenation under in situ conditions at various temperatures to illustrate the differences between catalysts and shell materials with SHINERS. This work demonstrates the potential of SHINS for in situ characterization studies in a wide range of catalytic reactions. © 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Cobalt(IV) corroles as catalysts for the electroreduction of O2: reactions of heterobimetallic dyads containing a face-to-face linked Fe(III) or Mn(III) porphyrin.

PubMed

Kadish, Karl M; Frémond, Laurent; Burdet, Fabien; Barbe, Jean-Michel; Gros, Claude P; Guilard, Roger

2006-04-01

A series of heterobinuclear cofacial porphyrin-corrole dyads containing a Co(IV) corrole linked by one of four different spacers in a face-to-face arrangement with an Fe(III) or Mn(III) porphyrin have been examined as catalysts for the electroreduction of O(2) to H(2)O and/or H(2)O(2) when adsorbed on the surface of a graphite electrode in air-saturated aqueous solutions containing 1M HClO(4). The examined compounds are represented as (PCY)M(III)ClCo(IV)Cl where P is a porphyrin dianion, C is a corrole trianion and Y is a biphenylene (B), 9,9-dimethylxanthene (X), dibenzofuran (O) or anthracene (A) spacer. The catalytic behavior of the seven investigated dyads in the two heterobimetallic (PCY)MClCoCl series of catalysts is compared on one hand to what was previously reported for related dyads with a single Co(III) corrole macrocycle linked to a free-base porphyrin with the same set of linking bridges, (PCY)H(2)Co, and on the other hand to dicobalt porphyrin-corrole dyads of the form (PCY)Co(2) which were shown to efficiently electrocatalyze the four electron reduction of O(2) at a graphite electrode in acid media. Comparisons between the four series of porphyrin-corrole dyads, (PCY)Co(2), (PCY)H(2)Co, (PCY)FeClCoCl and (PCY)MnClCoCl, show that in all cases the biscobalt dyads catalyze O(2) electroreduction at potentials more positive by an average 110mV as compared to the related series of compounds containing a Co(III) or Co(IV) corrole macrocycle linked to a free-base metalloporphyrin or a metalloporphyrin with an Fe(III) or Mn(III) central metal ion. The data indicates that the E(1/2) values where electrocatalysis is initiated is related to the initial site of electron transfer, which is the Co(III)/Co(II) porphyrin reduction process in the case of (PCY)Co(2) and the Co(IV)/Co(III) corrole reduction in the case of (PCY)MnClCoCl, (PCY)FeClCoCl and (PCY)H(2)Co. The overall data also suggests that the catalytically active form of the biscobalt dyad in (PCY)Co(2) contains a Co(II) porphyrin and a Co(IV) corrole.

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

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

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

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

Hierarchical nano-on-micro copper with enhanced catalytic activity towards electro-oxidation of hydrazine

NASA Astrophysics Data System (ADS)

Yan, Xiaodong; Liu, Yuan; Scheel, Kyle R.; Li, Yong; Yu, Yunhua; Yang, Xiaoping; Peng, Zhonghua

2018-03-01

The electrochemical properties of catalyst materials are highly dependent on the materials structure and architecture. Herein, nano-on-micro Cu electrodes are fabricated by growing Cu microcrystals on Ni foam substrate, followed by introducing Cu nanocrystals onto the surface of the Cu microcrystals. The introduction of Cu nanocrystals onto the surface of Cu microcrystals is shown to dramatically increase the electrochemically active surface area and thus significantly enhances the catalytic activity of the catalyst electrode towards electro-oxidation of hydrazine. The onset potential (-1.04 V vs. Ag/AgCl) of the nano-on-micro Cu electrode is lower than those of the reported Cu-based catalysts under similar testing conditions, and a current density of 16 mA·cm-2, which is 2 times that of the microsized Cu electrode, is achieved at a potential of -0.95 V vs. Ag/AgCl. Moreover, the nano-on-micro Cu electrode demonstrates good long-term stability.

Investigations of direct methanol fuel cell (DMFC) fading mechanisms

NASA Astrophysics Data System (ADS)

Sarma, Loka Subramanyam; Chen, Ching-Hsiang; Wang, Guo-Rung; Hsueh, Kan-Lin; Huang, Chiou-Ping; Sheu, Hwo-Shuenn; Liu, Ding-Goa; Lee, Jyh-Fu; Hwang, Bing-Joe

In this report, we present the microscopic investigations on various fading mechanisms of a direct methanol fuel cell (DMFC). High energy X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), energy dispersive X-ray spectroscopy (EDX), and Raman spectroscopic analysis were applied to a membrane-electrode-assembly (MEA) before and after fuel cell operation to figure out the various factors causing its fading. High energy XRD analysis of the fresh and faded MEA revealed that the agglomeration of the catalyst particles in the cathode layer of the faded MEA was more significant than in the anode layer of the faded MEA. The XAS analysis demonstrated that the alloying extent of Pt (J Pt) and Ru (J Ru) in the anode catalyst was increased and decreased, respectively, from the fresh to the faded MEA, indicating that the Ru environment in the anode catalyst was significantly changed after the fuel cell operation. Based on the X-ray absorption edge jump measurements at the Ru K-edge on the anode catalyst of the fresh and the faded MEA it was found that Ru was dissolved from the Pt-Ru catalyst after the fuel cell operation. Both the Ru K-edge XAS and EDX analysis on the cathode catalyst layer of the faded MEA confirms the presence of Ru environment in the cathode catalyst due to the Ru crossover from the anode to the cathode side. The changes in the membrane and the gas diffusion layer (GDL) after the fuel cell operation were observed from the Raman spectroscopy analysis.

Hydrocracking with molten zinc chloride catalyst containing 2-12% ferrous chloride

DOEpatents

Zielke, Clyde W.; Bagshaw, Gary H.

1981-01-01

In a process for hydrocracking heavy aromatic polynuclear carbonaceous feedstocks to produce hydrocarbon fuels boiling below about 475.degree. C. by contacting the feedstocks with hydrogen in the presence of a molten zinc chloride catalyst and thereafter separating at least a major portion of the hydrocarbon fuels from the spent molten zinc chloride catalyst, an improvement comprising: adjusting the FeCl.sub.2 content of the molten zinc chloride to from about 2 to about 12 mol percent based on the mixture of ferrous chloride and molten zinc chloride.

Highly efficient transition metal and nitrogen co-doped carbide-derived carbon electrocatalysts for anion exchange membrane fuel cells

NASA Astrophysics Data System (ADS)

Ratso, Sander; Kruusenberg, Ivar; Käärik, Maike; Kook, Mati; Puust, Laurits; Saar, Rando; Leis, Jaan; Tammeveski, Kaido

2018-01-01

The search for an efficient electrocatalyst for oxygen reduction reaction (ORR) to replace platinum in fuel cell cathode materials is one of the hottest topics in electrocatalysis. Among the many non-noble metal catalysts, metal/nitrogen/carbon composites made by pyrolysis of cheap materials are the most promising with control over the porosity and final structure of the catalyst a crucial point. In this work we show a method of producing a highly active ORR catalyst in alkaline media with a controllable porous structure using titanium carbide derived carbon as a base structure and dicyandiamide along with FeCl3 or CoCl2 as the dopants. The resulting transition metal-nitrogen co-doped carbide derived carbon (M/N/CDC) catalyst is highly efficient for ORR electrocatalysis with the activity in 0.1 M KOH approaching that of commercial 46.1 wt.% Pt/C. The catalyst materials are also investigated by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy to characterise the changes in morphology and composition causing the raise in electrochemical activity. MEA performance of M/N/CDC cathode materials in H2/O2 alkaline membrane fuel cell is tested with the highest power density reached being 80 mW cm-2 compared to 90 mW cm-2 for Pt/C.

Preparation and Characterization of TiO2-Based Photocatalysts by Chemical Vapour Deposition

NASA Astrophysics Data System (ADS)

Nacevski, Goran; Marinkovski, Mirko; Tomovska, Radmila; Fajgar, Radek

In the present work, a novel technique for the preparation of TiO2-based photocatalysts modified with SiO2 is presented, using a pulsed ArF laser to induce a chemical vapor deposition process. The irradiated gas mixture was composed of TiCl4/SiCl4 precursors in excess of oxygen. Laser irradiation at 193 nm with a repetition frequency of 10 Hz induced the deposition of thin nano-sized mixed oxide films. In order to improve the photocatalytic activity of the catalysts and to expand the activity from the UV to the visible part of the spectrum, doping of the catalysts with chromium oxides was performed. For that aim, the same technique of catalyst preparation was used, irradiating the same gas mixture with the addition of chromyl chloride as Cr precursor. The thin films prepared were annealed up to 500°C in order to remove crystal defects, which could be responsible for poor photocatalytic activity. The dependence of structure and properties on reaction process and irradiation conditions (laser energy and fluence, precursors pressure) were examined. The main aim was to find the best conditions for the production of highly photoactive catalysts and to decrease deactivation processes during the photo-oxidation. The composition, structure and morphology of the oxide catalysts prepared were studied by various spectroscopies, electron microscopy and diffraction techniques.

Ziegler-Natta Catalyst Based on MgCl₂/Clay/ID/TiCl₄ for the Synthesis of Spherical Particles of Polypropylene Nanocomposites.

PubMed

Cardoso, Renata da Silva; Oliveira, Jaqueline da Silva; Ramis, Luciana Bortolin; Marques, Maria de Fátima V

2018-07-01

In the present work, we have designed MgCl2/clay/internal donor (ID)/TiCl4 based bisupported Ziegler-Natta catalysts containing varying amounts of organoclay (montmorillonite) in order to synthesize spherical particles of polypropylene/clay nanocomposites (PCN). The organoclay was introduced into the catalyst support formulation and PCN was obtained using the in situ polymerization technique. Decreasing the reaction time, it was possible to obtain nanocomposites with high concentrations of clay (masterbatches). Micrographs of SEM confirmed the spherical morphology of the catalysts. In addition, XRD patterns show that the active sites for polymerization were inserted in the clay galleries. The catalytic performance was evaluated in slurry propylene polymerization using triethylaluminium as cocatalyst and silane as external electron donor at 70 °C, 4 bar, and different reaction times. The PCNs obtained containing different clay amounts were characterized by X-ray diffraction, thermal analyses, transmission electronic microscopy, and extractables in heptane. The results revealed that the synthesized PP/clay particles were also spherical showing that the morphological control is possible even using catalysts containing high amounts of clay. The PCN presented high degradation temperature (459 °C). The XRD peak related to the clay interlamellar distance has shifted to lower angles, and TEM images confirmed the formation of exfoliated/intercalated clay on the PP matrix and absence of microparticles of clay.

Morphologies, Preparations and Applications of Layered Double Hydroxide Micro-/Nanostructures

PubMed Central

Kuang, Ye; Zhao, Lina; Zhang, Shuai; Zhang, Fazhi; Dong, Mingdong; Xu, Sailong

2010-01-01

Layered double hydroxides (LDHs), also well-known as hydrotalcite-like layered clays, have been widely investigated in the fields of catalysts and catalyst support, anion exchanger, electrical and optical functional materials, flame retardants and nanoadditives. This feature article focuses on the progress in micro-/nanostructured LDHs in terms of morphology, and also on the preparations, applications, and perspectives of the LDHs with different morphologies. PMID:28883378

Preparation of Ag@AgCl-doped TiO2/sepiolite and its photocatalytic mechanism under visible light.

PubMed

Liu, Shaomin; Zhu, Dinglong; Zhu, Jinglin; Yang, Qing; Wu, Huijun

2017-10-01

A cube-like Ag@AgCl-doped TiO 2 /sepiolite (denoted Ag@AgCl-TiO 2 /sepiolite) was successfully synthesized via a novel method. X-ray diffraction, scanning electron microscopy, energy dispersion X-ray fluorescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and diffuse reflectance ultraviolet-visible spectroscopy were performed to determine the structure and physicochemical properties of Ag@AgCl-TiO 2 /sepiolite. SEM micrographs revealed that Ag@AgCl nanoparticles and TiO 2 film are well deposited on the surface of tube-like sepiolite. As a result, Ag@AgCl-TiO 2 /sepiolite exhibits a red shift relative to TiO 2 /sepiolite. Photocatalytic experiments demonstrated that the dosage of catalysts plays an important role during photocatalysis. The photoelectrochemical activities of Ag@AgCl-TiO 2 /sepiolite and TiO 2 /sepiolite were also investigated. Photocurrent responses confirmed that the ability of Ag@AgCl-TiO 2 /sepiolite to separate photo-generated electron-hole pairs is stronger than that of TiO 2 /sepiolite. Methylene Blue degradation is also improved under alkaline conditions and visible light irradiation because more OH is produced by visible light excitation. This excellent catalytic ability is mainly attributed to the formed Ag nanoparticles and the Schottky barrier at the Ag/TiO 2 interface. Active species analysis indicated that O 2 - and h + are implicated as active species in photocatalysis. Therefore, catalysts are excited to produce abundant electron-hole pairs after they absorb photons in photocatalysis. Copyright © 2017. Published by Elsevier B.V.

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

NASA Astrophysics Data System (ADS)

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

2013-05-01

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

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

PubMed Central

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

2013-01-01

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

Molecular heterogeneous catalysts derived from bipyridine-based organosilica nanotubes for C–H bond activation† †Electronic supplementary information (ESI) available: Experimental details, material characterization data, catalytic measurement details. See DOI: 10.1039/c7sc00713b Click here for additional data file.

PubMed Central

Zhang, Shengbo; Wang, Hua; Li, Mei; Han, Jinyu

2017-01-01

Heterogeneous metal complex catalysts for direct C–H activation with high activity and durability have always been desired for transforming raw materials into feedstock chemicals. This study described the design and synthesis of one-dimensional organosilica nanotubes containing 2,2′-bipyridine (bpy) ligands in the framework (BPy-NT) and their post-synthetic metalation to provide highly active and robust molecular heterogeneous catalysts. By adjusting the ratios of organosilane precursors, very short BPy-NT with ∼50 nm length could be controllably obtained. The post-synthetic metalation of bipyridine-functionalized nanotubes with [IrCp*Cl(μ-Cl)]2 (Cp* = η5-pentamethylcyclopentadienyl) and [Ir(cod)(OMe)]2 (cod = 1,5-cyclooctadiene) afforded solid catalysts, IrCp*-BPy-NT and Ir(cod)-BPy-NT, which were utilized for C–H oxidation of heterocycles and cycloalkanes as well as C–H borylation of arenes. The cut-short nanotube catalysts displayed enhanced activities and durability as compared to the analogous homogeneous catalysts and other conventional heterogeneous catalysts, benefiting from the isolated active sites as well as the fast transport of substrates and products. After the reactions, a detailed characterization of Ir-immobilized BPy-NT via TEM, SEM, nitrogen adsorption, UV/vis, XPS, and 13C CP MAS NMR indicated the molecular nature of the active species as well as stable structures of nanotube scaffolds. This study demonstrates the potential of BPy-NT with a short length as an integration platform for the construction of efficient heterogeneous catalytic systems for organic transformations. PMID:28970878

Bentonite modification with pillarization method using metal stannum

NASA Astrophysics Data System (ADS)

Widjaya, Robert R.; Juwono, Ariadne L.; Rinaldi, Nino

2017-11-01

Clay minerals have received considerable attention in the last years because of their environmental compatibility, low cost, high selectivity, and operational simplicity. Although clays are very useful for many application in the field of catalysis, they have main disadvantage: their lack of pore volume and spesific surface area. Porosity and stability of these materials are improved by pillaring the clay layers with SnCl4, which leads to materials known as pillared clays (PILC). This research aims were to characterize the Bentonite and Sn-Bentonite as catalysts for cracking and oligomerization. The Sn-Bentonite was prepared by pillarization method with a variation in metal ratio of 5 mmol dan 10 mmol.gr-1 of bentonit. The catalyst characterized by X-ray Diffraction, X-ray Fluorescence, Fourier Transform Infra Red, Brunauer Emmett Teller, Thermogravimetric Analysis. The results showed that the Sn-Bentonite catalyst had large basal spacing and good porous structure, and the specific surface areas increased. XRF detected the Sn in the Bentonite and TGA results showed the ability Sn-Bentonite in receiving heat. FTIR test showed two type of acidity, broansted and lewis acid. The characterized results indicated that Sn-Bentonite with metal ratio 5 mmol.gr-1 better than Sn-Bentonite with metal ratio 10 mmol.gr-1, in which there was a significant increase the basal spacings, specific surface area, and pore volume. The TGA results for Sn-Bentonite appeared to be more thermally stable than Bentonite.

Improvement of performance in low temperature solid oxide fuel cells operated on ethanol and air mixtures using Cu-ZnO-Al2O3 catalyst layer

NASA Astrophysics Data System (ADS)

Morales, M.; Espiell, F.; Segarra, M.

2015-10-01

Anode-supported single-chamber solid oxide fuel cells with and without Cu-ZnO-Al2O3 catalyst layers deposited on the anode support have been operated on ethanol and air mixtures. The cells consist of gadolinia-doped ceria electrolyte, Ni-doped ceria anode, and La0.6Sr0.4CoO3-δ-doped ceria cathode. Catalyst layers with different Cu-ZnO-Al2O3 ratios are deposited and sintered at several temperatures. Since the performance of single-chamber fuel cells strongly depends on catalytic properties of electrodes for partial oxidation of ethanol, the cells are electrochemically characterized as a function of the temperature, ethanol-air molar ratio and gas flow rate. In addition, catalytic activities of supported anode, catalytic layer-supported anode and cathode for partial oxidation of ethanol are analysed. Afterwards, the effect of composition and sintering temperature of catalyst layer on the cell performance are determined. The results indicate that the cell performance can be significantly enhanced using catalyst layers of 30:35:35 and 40:30:30 wt.% Cu-ZnO-Al2O3 sintered at 1100 °C, achieving power densities above 50 mW cm-2 under 0.45 ethanol-air ratio at temperatures as low as 450 °C. After testing for 15 h, all cells present a gradual loss of power density, without carbon deposition, which is mainly attributed to the partial re-oxidation of Ni at the anode.

The Effect of Silver Chloride Formation on the Kinetics of Silver Dissolution in Chloride Solution

PubMed Central

Ha, Hung; Payer, Joe

2011-01-01

The precipitation and growth of AgCl on silver in physiological NaCl solution were investigated. AgCl was found to form at bottom of scratches on the surface which may be the less effective sites for diffusion or the favorable sites for heterogeneous nucleation. Patches of silver chloride expanded laterally on the substrate until a continuous film formed. The ionic transport path through this newly formed continuous film was via spaces between AgCl patches. As the film grew, the spaces between AgCl patches closed and ion transport was primarily via micro-channels running through AgCl patches. The decrease of AgCl layer conductivity during film growth were attributed to the clogging of micro-channels or decrease in charge carrier concentration inside the micro-channels. Under thin AgCl layer, i.e. on the order of a micrometer, the dissolution of silver substrate was under mixed activation-Ohmic control. Under thick AgCl layer, i.e. on the order of tens of micrometers, the dissolution of silver substrate was mediated by the Ohmic resistance of AgCl layer. PMID:21516171

Pyrolysis of polyolefins for increasing the yield of monomers' recovery

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

Donaj, Pawel J., E-mail: pawel@mse.kth.se; Kaminsky, W.; Buzeto, F.

2012-05-15

Highlights: Black-Right-Pointing-Pointer Thermal and catalytic pyrolysis of mixed polyolefins in fluidized bed has been studied. Black-Right-Pointing-Pointer We tested applicability of a commercial Ziegler-Natta catalyst (Z-N: TiCl{sub 4}/MgCl{sub 2}). Black-Right-Pointing-Pointer The catalyst has a strong influence on product distribution, increasing gas fraction. Black-Right-Pointing-Pointer At 650 Degree-Sign C the monomer generation increased by 55% when the catalyst was used. Black-Right-Pointing-Pointer We showed the concept of treatment of mixed polyolefins without a need of separation. - Abstract: Pyrolysis of plastic waste is an alternative way of plastic recovery and could be a potential solution for the increasing stream of solid waste. The objectivemore » of this work was to increase the yield the gaseous olefins (monomers) as feedstock for polymerization process and to test the applicability of a commercial Ziegler-Natta (Z-N): TiCl{sub 4}/MgCl{sub 2} for cracking a mixture of polyolefins consisted of 46% wt. of low density polyethylene (LDPE), 30% wt. of high density polyethylene (HDPE) and 24% wt. of polypropylene (PP). Two sets of experiments have been carried out at 500 and 650 Degree-Sign C via catalytic pyrolysis (1% of Z-N catalyst) and at 650 and 730 Degree-Sign C via only-thermal pyrolysis. These experiments have been conducted in a lab-scale, fluidized quartz-bed reactor of a capacity of 1-3 kg/h at Hamburg University. The results revealed a strong influence of temperature and presence of catalyst on the product distribution. The ratios of gas/liquid/solid mass fractions via thermal pyrolysis were: 36.9/48.4/15.7% wt. and 42.4/44.7/13.9% wt. at 650 and 730 Degree-Sign C while via catalytic pyrolysis were: 6.5/89.0/4.5% wt. and 54.3/41.9/3.8% wt. at 500 and 650 Degree-Sign C, respectively. At 650 Degree-Sign C the monomer generation increased by 55% up to 23.6% wt. of total pyrolysis products distribution while the catalyst was added. Obtained yields of olefins were compared with the naphtha steam cracking process and other potentially attractive processes for feedstock generation. The concept of closed cycle material flow for polyolefins has been discussed, showing the potential benefits of feedstock recycling in a plastic waste management.« less

Efficient FeCl3/SiO2 as heterogeneous nanocatalysis for the synthesis of benzimidazoles under mild conditions

NASA Astrophysics Data System (ADS)

Taher, Mohammad Ali; Karami, Changiz; Arabi, Mehdi Sheikh; Ahmadian, Hossein; Karami, Yasaman

2016-11-01

Iron(III) supported on nano silica as a new catalyst has been synthesized. Structural properties of this complex have been studied by TEM, SEM and EDX. The average crystalline size of Iron(III) supported on nano silica is 30-50 nm. Catalytic activity of this catalyst has been investigated by synthesis of benzimidazoles from 1, 2-diaminobenzene and aromatic aldehydes, and also the other variables investigated such as the amount of catalyst, reaction temperature and the effect of various solvents are also studied. The present procedure offers several advantages such as short reaction time, simple workup, recovery and reusability of the catalyst.

Silicon nanowire synthesis by a vapor-liquid-solid approach.

PubMed

Mao, Aaron; Ng, H T; Nguyen, Pho; McNeil, Melanie; Meyyappan, M

2005-05-01

Synthesis of silicon nanowires is studied by using a vapor-liquid-solid growth technique. Silicon tetrachloride reduction with hydrogen in the gas phase is used with gold serving as catalyst to facilitate growth. Only a narrow set of conditions of SiCl4 concentration and temperature yield straight nanowires. High concentrations and temperatures generally result in particulates, catalyst coverage and deactivation, and coatinglike materials.

Silicon nanowire synthesis by a vapor-liquid-solid approach

NASA Technical Reports Server (NTRS)

Mao, Aaron; Ng, H. T.; Nguyen, Pho; McNeil, Melanie; Meyyappan, M.

2005-01-01

Synthesis of silicon nanowires is studied by using a vapor-liquid-solid growth technique. Silicon tetrachloride reduction with hydrogen in the gas phase is used with gold serving as catalyst to facilitate growth. Only a narrow set of conditions of SiCl4 concentration and temperature yield straight nanowires. High concentrations and temperatures generally result in particulates, catalyst coverage and deactivation, and coatinglike materials.

Direct synthesis of carbon nanotubes using Cu-Sn catalyst on Cu substrates and their corrosion behavior in 0.6 M NaCl solution

NASA Astrophysics Data System (ADS)

Jeong, Namjo; Jwa, Eunjin; Kim, Chansoo; Choi, Ji Yeon; Nam, Joo-youn; Park, Soon-chul; Jang, Moon-seok

2017-11-01

We report the high-yield and large-area synthesis of a spaghetti-like carbon nanotubes (CNTs) on macroscopic Cu substrates (foil and foam) using a Cu-Sn alloy catalyst. In addition, we investigate the corrosion properties of the as-synthesized CNT/Cu foil system in 0.6 M NaCl solution. Electrochemical analysis showed that the corrosion resistance of the CNT/Cu foil system improved by a factor of ∼100 compared to the as-received Cu foil. Thus, it is concluded that a dense network of CNT was uniformly coated on the Cu foil and this coating functioned as an efficient barrier to corrosion under simulated seawater conditions.

Subeutectic Synthesis of Epitaxial Si-NWs with Diverse Catalysts Using a Novel Si Precursor

PubMed Central

2010-01-01

The applicability of a novel silicon precursor with respect to reasonable nanowire (NW) growth rates, feasibility of epitaxial NW growth and versatility with respect to diverse catalysts was investigated. Epitaxial growth of Si-NWs was achieved using octochlorotrisilane (OCTS) as Si precursor and Au as catalyst. In contrast to the synthesis approach with SiCl4 as precursor, OCTS provides Si without the addition of H2. By optimizing the growth conditions, effective NW synthesis is shown for alternative catalysts, in particular, Cu, Ag, Ni, and Pt with the latter two being compatible to complementary metal-oxide-semiconductor technology. As for these catalysts, the growth temperatures are lower than the lowest liquid eutectic; we suggest that the catalyst particle is in the solid state during NW growth and that a solid-phase diffusion process, either in the bulk, on the surface, or both, must be responsible for NW nucleation. PMID:20843058

Coating of porous carbon for use in lithium air batteries

DOEpatents

Amine, Khalil; Lu, Jun; Du, Peng; Lei, Yu; Elam, Jeffrey W

2015-04-14

A cathode includes a carbon material having a surface, the surface having a first thin layer of an inert material and a first catalyst overlaying the first thin layer, the first catalyst including metal or metal oxide nanoparticles, wherein the cathode is configured for use as the cathode of a lithium-air battery.

Catalytical Photocyclization of Arylamines with a-Olefins in the Synthesis of 2-Alkylquinoline

ERIC Educational Resources Information Center

Makhmutov, Aynur; Usmanov, Salavat; Mustafin, Ahat

2016-01-01

The article deals with the results of investigation of the process of catalytical photocyclization of aniline and aniline hydrochloride with a-olefins (hexene-1, heptene-1 and octene-1). The following compounds of d- and f-metals are tested as probable catalysts: CuSO4•5H2O, EuCl3•6H2O, PrCl3•6H2O, TbCl3•6H2O, La2O3, MnO2, NiSO4•6H2O, NiCl2•6H2O,…

SBA-15/hydrotalcite nanocomposite as an efficient support for the immobilization of heteropolyacid: A triply-hybrid catalyst for the synthesis of 2-amino-4H-pyrans in water

NASA Astrophysics Data System (ADS)

Sadjadi, Samahe; Heravi, Majid M.; Zadsirjan, Vahideh; Farzaneh, Vahid

2017-12-01

To circumvent the high solubility and low surface area of heteropolyacid and in attempt to develop a bi-functional heterogeneous catalyst for promoting organic transformations, heteropolyacid was embedded in functionalized SBA-15 and subsequently hybridized with layered double hydroxide. The catalyst could be considered as a bi-functional catalyst with both acidic and basic properties. The acidic properties emerged from the SBA-15 and heteropolyacid component while layered double hydroxide render the catalyst basic. The catalyst was characterized by using SEM/EDX, FT-IR, XRD, ICP-AES, BET and elemental mapping analysis. The catalytic activity of the catalyst was studied for promoting one-pot three-component condensation of aromatic aldehydes, malononitrile or ethyl cyanoacetate and C-H activated acidic molecules in aqueous media for the synthesis of 2-amino-4H-pyran derivatives. The catalyst exhibited high catalytic activity, which was superior to the previously reported ones. Moreover, the reusability of the catalyst was excellent and the leaching of heteropolyacid was dramatically suppressed. High yields, short reaction times, eco-friendly conditions, simplicity of the procedure, reusability of the catalyst and broad substrate scope are the merits of this protocol.

Pd@Pt Core–Shell Nanoparticles with Branched Dandelion-like Morphology as Highly Efficient Catalysts for Olefin Reduction

EPA Science Inventory

A facile synthesis based on the addition of ascorbic acid to a mixture of Na2PdCl4, K2PtCl6, and Pluronic P123 results in highly branched core–shell nanoparticles (NPs) with a micro–mesoporous dandelion-like morphology comprising Pd core and Pt shell. The slow reduction kinetics ...

Effects of metal salt catalysts on yeast cell growth in ethanol conversion

Treesearch

Chung-Yun Hse; Yin Lin

2009-01-01

The effects of the addition of metal salts and metal salt-catalyzed hydrolyzates on yeast cell growth in ethanol fermentation were investigated. Four yeast strains (Saccharomyces cerevisiae WT1, Saccharomyces cerevisiae MT81, Candida sp. 1779, and Klumaromyces fragilis), four metal salts (CuCl2, FeCl3, AgNO3, and I2), two metal salt-catalyzed hydrolyzates (...

Hydrothermal assisted decoration of NiS2 and CoS nanoparticles on the reduced graphene oxide nanosheets for sunlight driven photocatalytic degradation of azo dye: Effect of background electrolyte and surface charge.

PubMed

Borthakur, Priyakshree; Das, Manash R

2018-04-15

The semiconductor NiS 2 nanoparticles with an average size of 10 ± 0.317 nm were successfully deposited on the reduced graphene oxide (rGO) sheets by simple hydrothermal method. The synthesized nanocomposite was characterized by various instrumental techniques like XRD, FTIR, FESEM, EDX, HRTEM, fluorescence spectrophotometer analysis. In this study we mainly focus on the determination of the surface potential values of NiS 2 -rGO and CoS-rGO nanocomposite under different experimental conditions and evaluated the photodegradation efficiency towards azo dye Congo Red (CR) molecule under natural sunlight irradiation. We found that the surface charge (zeta potential) of the both nanocomposite materials in presence of different inorganic ions salt solutions like NaCl, NaNO 3 , Na 2 SO 4 , MgCl 2 , CaCl 2 etc. is varied based on the polarizability of the ions as well as pH of the suspension. Different inorganic ions present in the catalyst suspension can alter the surface charge of the catalyst by forming a double layer around the molecule and thus change the electrostatic interaction between the dye molecule and the catalyst surface which change the degradation efficiency of the photocatalyst towards CR molecule. The photocatalytic efficiency of NiS 2 -rGO and CoS-rGO nanocomposite towards CR degradation was found to be 97.03% and 88.03% in 40 min, respectively under same experimental condition whereas NiS 2 and CoS nanoparticles without support exhibited photodegradation efficiency 57.89% and 50.52%, respectively. The observed improved photocatalytic activity of the metal sulfide-rGO nanocomposite results the presence of synergistic effect between the metal sulfide nanoparticles and the rGO sheets of the photocatalysts which inhibits the recombination rate of photogenerated electrons and holes. The mechanism of the degradation process was investigated by photoluminescence study in presence of terephthalic acid and also quenching experiment in presence of isopropanol and benzoquinone. The photocatalyst was characterized after degradation process and found that the crystallinity and the morphology of the nanocomposite remained unchanged. The ion-chromatography experiment confirms the formation of non-toxic products after degradation. The present study focuses on the importance of the use of metal sulphide-rGO nanocomposite towards environment remediation process and study of the influence of inorganic salts on the surface charge of the photocatalyst as well as on the degradation process. Copyright © 2018 Elsevier Inc. All rights reserved.

Sandwich-type electrode

DOEpatents

Lu, Wen-Tong P.; Garcia, Earl R.

1983-01-01

Disclosed is an improvement on a method of making an electrode wherein a suspension in a liquid is prepared of a powdered catalyst containing a noble metal, carbon powder and a binder, and the suspension is poured over a carbon substrate dried, compressed and sintered to form a solid catalyst layer bonded to the carbon substrate. The improvement is placing a carbon paper on the catalyst layer prior to compressing. The improved electrode can be used as either a cathode or an anode in a sulfur dioxide depolarized electrolyzer in a process for producing hydrogen from water.

Partial oxidation of dimethyl ether using the structured catalyst Rh/Al2O3/Al prepared through the anodic oxidation of aluminum.

PubMed

Yu, B Y; Lee, K H; Kim, K; Byun, D J; Ha, H P; Byun, J Y

2011-07-01

The partial oxidation of dimethyl ether (DME) was investigated using the structured catalyst Rh/Al2O3/Al. The porous Al2O3 layer was synthesized on the aluminum plate through anodic oxidation in an oxalic-acid solution. It was observed that about 20 nm nanopores were well developed in the Al2O3 layer. The thickness of Al2O3 layer can be adjusted by controlling the anodizing time and current density. After pore-widening and hot-water treatment, the Al2O3/Al plate was calcined at 500 degrees C for 3 h. The obtained delta-Al2O3 had a specific surface area of 160 m2/g, making it fit to be used as a catalyst support. A microchannel reactor was designed and fabricated to evaluate the catalytic activity of Rh/Al2O3/Al in the partial oxidation of DME. The structured catalyst showed an 86% maximum hydrogen yield at 450 degrees C. On the other hand, the maximum syngas yield by a pack-bed-type catalyst could be attained by using a more than fivefold Rh amount compared to that used in the structured Rh/Al2O3/Al catalyst.

Prominent roles of impurities in ionic liquid for catalytic conversion of carbohydrates

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

Zhao, Haibo; Brown, Heather M.; Holladay, Johnathan E.

2012-02-07

In the last two decades, ionic liquids have emerged as new and versatile solvents, and many of them are also catalysts for a broad range of catalytic reactions. Certain ionic liquids have been found to possess the unique capability of dissolving cellulosic biomass. The potential of such ionic liquids as solvent to enable catalytic conversion of cellulosic polymers was first explored and demonstrated by Zhao et al. This field of research has since experienced a rapid growth. Most ionic liquids have negligible vapor pressure and excellent thermal stability over a wide temperature range. For example, ionic liquids composed of 1-ethyl-3-methylimidazoliummore » (EMIM+) cation and Cl- anion was reported to be stable up to 285 C, while salts of the same cation with other anions such as BF4- and PF6- are thermally stable above 380 C under inert atmosphere. It is well known that presence of impurities in ionic liquids typically causes changes in physical properties, e.g. decreasing in melting point and viscosity. Addition of Lewis acidic metal chlorides, e.g. AlCl3 to 1-alkyl-3-methylimidazolium chloride, [AMIM]Cl, is an exothermic reaction and considerably reduces the melting point by forming [AMIM]AlCl4 or [AMIM]Al2Cl7 that are also ionic liquids but have much lower melting point than the parent [AMIM]Cl. While most early research on catalysis of ionic liquids involving metallohalide anions were typically conducted from stoichiometric ratio of such anions to organic cations, e.g. [AMIM]+, the use of pure ionic liquids only as a solvent to carry out catalysis by a catalytic amount of a metal halide as catalyst truly displayed the solvent property of such ionic liquids.4 In such reaction systems, catalytic amounts of metal halides were used to catalyze the conversion of glucose and cellulose.4,11,12 The metal chloride catalyst concentration was in the order of 10-3 M. The presence of another metal chloride in the ionic liquids, even in the order of 10-5 M concentration was found to bring a dramatic synergistic effect. Therefore, the catalytic performance of the metal halide catalyst for the conversion of carbohydrates in the ionic liquid systems is highly sensitive to the presence of impurities. This work presents findings on the role of impurities that were present in some commercially available ionic liquids used for the conversion of the cellulose.« less

General and mild Ni(0)-catalyzed α-arylation of ketones using aryl chlorides.

PubMed

Fernández-Salas, José A; Marelli, Enrico; Cordes, David B; Slawin, Alexandra M Z; Nolan, Steven P

2015-03-02

A general methodology for the α-arylation of ketones using a nickel catalyst has been developed. The new well-defined [Ni(IPr*)(cin)Cl] (1 c) pre-catalyst showed great efficiency for this transformation, allowing the coupling of a wide range of ketones, including acetophenone derivatives, with various functionalised aryl chlorides. This cinnamyl-based Ni-N-heterocyclic carbene (NHC) complex has demonstrated a different behaviour to previously reported NHC-Ni catalysts. Preliminary mechanistic studies suggest a Ni(0)/Ni(II) catalytic cycle to be at play. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Iridium clusters in KLTL zeolite: Structure and catalytic selectivity for n-hexane aromatization

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

Triantafillou, N.D.; Miller, J.T.; Gates, B.C.

Catalysts consisting of Ir clusters in zeolite KLTL were prepared by reduction of [Ir(NH{sub 3}){sub 5}Cl]Cl{sub 2} in the zeolite with H{sub 2} at temperatures 300 or 500{degrees}C. The catalysts were tested for reactions of n-hexane and H{sub 2} at 400, 440 and 480{degrees}C and were characterized by temperature-programmed reduction, hydrogen chemisorption, transmission electron microscopy, infrared spectroscopy of adsorbed CO, and extended X-ray absorption fine structure spectroscopy. The clusters consist of 4 to 6 Ir atoms on average and are sufficiently small to reside within the pores of the zeolite. The infrared spectra characteristic of terminal CO suggest that themore » support environment is slightly basic and that the Ir clusters are electron rich relative to the bulk metal. Notwithstanding the small cluster size, the support basicity, and the confining geometry of the LTL zeolite pore structure, the catalytic performance is similar to those of other Ir catalysts, with a poor selectivity for aromatization and a high selectivity for hydrogenolysis. These results are consistent with the inference that the principal requirements for selective naphtha aromatization catalysts are both a nonacidic support and a metal with a low hydrogenolsis activity, i.e., Pt. 47 refs., 6 figs., 3 tabs.« less

Porous nitrogen-enriched carbonaceous material from marine waste: chitosan-derived layered CNX catalyst for aerial oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid

EPA Science Inventory

Chitosan derived porous layered nitrogen-enriched carbonaceous CNx catalyst (PLCNx) has been synthesized from marine waste and its use demonstrated in a metal-free heterogeneous selective oxidation of 5-hydroxymethyl-furfural (HMF) to 2,5-furandicarboxylic acid (FDCA) using aeria...

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

Tesfaye, Meron; MacDonald, Andrew N.; Dudenas, Peter J.

Local gas transport limitation attributed to the ionomer thin-film in the catalyst layer is a major deterrent to widespread commercialization of polymer-electrolyte fuel cells. So far functionality and limitations of these thin-films have been assumed identical in the anode and cathode. In this study, Nafion ionomer thin-films on platinum(Pt) support were exposed to H 2 and air as model schemes, mimicking anode and cathode catalyst layers. Findings indicate decreased swelling, increased densification of ionomer matrix, and increased humidity-induced aging rates in reducing environment, compared to oxidizing and inert environments. Observed phenomenon could be related to underlying Pt-gas interaction dictating Pt-ionomermore » behavior. Presented results could have significant implications about the disparate behavior of ionomer thin-film in anode and cathode catalyst layers.« less

Layered transition metal carboxylates: efficient reusable heterogeneous catalyst for epoxidation of olefins.

PubMed

Sen, Rupam; Bhunia, Susmita; Mal, Dasarath; Koner, Subratanath; Miyashita, Yoshitaro; Okamoto, Ken-Ichi

2009-12-01

Layered metal carboxylates [M(malonato)(H(2)O)(2)](n) (M = Ni(II) and Mn(II)) that have a claylike structure have been synthesized hydrothermally and characterized. The interlayer separation in these layered carboxylates is comparable to that of the intercalation distance of the naturally occurring clay materials or layered double hydroxides (LDHs). In this study, we have demonstrated that, instead of intercalating the metal complex into layers of the clay or LDH, layered transition metal carboxylates, [M(malonato)(H(2)O)(2)](n), as such can be used as a recyclable heterogeneous catalyst in olefin epoxidation reaction. Metal carboxylates [M(malonato)(H(2)O)(2)](n) exhibit excellent catalytic performance in olefin epoxidation reaction.

A highly active and stable IrO x/SrIrO 3 catalyst for the oxygen evolution reaction

DOE PAGES

Seitz, Linsey C.; Dickens, Colin F.; Nishio, Kazunori; ...

2016-09-02

Oxygen electrochemistry plays a key role in renewable energy technologies such as fuel cells and electrolyzers, but the slow kinetics of the oxygen evolution reaction (OER) limit the performance and commercialization of such devices. Here we report an iridium oxide/strontium iridium oxide (IrO x/SrIrO 3) catalyst formed during electrochemical testing by strontium leaching from surface layers of thin films of SrIrO 3. This catalyst has demonstrated specific activity at 10 milliamps per square centimeter of oxide catalyst (OER current normalized to catalyst surface area), with only 270 to 290 millivolts of overpotential for 30 hours of continuous testing in acidicmore » electrolyte. Here, density functional theory calculations suggest the formation of highly active surface layers during strontium leaching with IrO 3 or anatase IrO 2 motifs. The IrO x/SrIrO 3 catalyst outperforms known IrO x and ruthenium oxide (RuO x) systems, the only other OER catalysts that have reasonable activity in acidic electrolyte.« less

A highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction.

PubMed

Seitz, Linsey C; Dickens, Colin F; Nishio, Kazunori; Hikita, Yasuyuki; Montoya, Joseph; Doyle, Andrew; Kirk, Charlotte; Vojvodic, Aleksandra; Hwang, Harold Y; Norskov, Jens K; Jaramillo, Thomas F

2016-09-02

Oxygen electrochemistry plays a key role in renewable energy technologies such as fuel cells and electrolyzers, but the slow kinetics of the oxygen evolution reaction (OER) limit the performance and commercialization of such devices. Here we report an iridium oxide/strontium iridium oxide (IrO x /SrIrO 3 ) catalyst formed during electrochemical testing by strontium leaching from surface layers of thin films of SrIrO 3 This catalyst has demonstrated specific activity at 10 milliamps per square centimeter of oxide catalyst (OER current normalized to catalyst surface area), with only 270 to 290 millivolts of overpotential for 30 hours of continuous testing in acidic electrolyte. Density functional theory calculations suggest the formation of highly active surface layers during strontium leaching with IrO 3 or anatase IrO 2 motifs. The IrO x /SrIrO 3 catalyst outperforms known IrO x and ruthenium oxide (RuO x ) systems, the only other OER catalysts that have reasonable activity in acidic electrolyte. Copyright © 2016, American Association for the Advancement of Science.

Morphology control of layer-structured gallium selenide nanowires.

PubMed

Peng, Hailin; Meister, Stefan; Chan, Candace K; Zhang, Xiao Feng; Cui, Yi

2007-01-01

Layer-structured group III chalcogenides have highly anisotropic properties and are attractive materials for stable photocathodes and battery electrodes. We report the controlled synthesis and characterization of layer-structured GaSe nanowires via a catalyst-assisted vapor-liquid-solid (VLS) growth mechanism during GaSe powder evaporation. GaSe nanowires consist of Se-Ga-Ga-Se layers stacked together via van der Waals interactions to form belt-shaped nanowires with a growth direction along the [11-20], width along the [1-100], and height along the [0001] direction. Nanobelts exhibit a variety of morphologies including straight, zigzag, and saw-tooth shapes. These morphologies are realized by controlling the growth temperature and time so that the actual catalysts have a chemical composition of Au, Au-Ga alloy, or Ga. The participation of Ga in the VLS catalyst is important for achieving different morphologies of GaSe. In addition, GaSe nanotubes are also prepared by a slow growth process.

Microstructural observation of fuel cell catalyst inks by Cryo-SEM and Cryo-TEM.

PubMed

Shimanuki, Junichi; Takahashi, Shinichi; Tohma, Hajime; Ohma, Atsushi; Ishihara, Ayumi; Ito, Yoshiko; Nishino, Yuri; Miyazawa, Atsuo

2017-06-01

In order to improve the electricity generation performance of fuel cell electric vehicles, it is necessary to optimize the microstructure of the catalyst layer of a polymer electrolyte fuel cell. The catalyst layer is formed by a wet coating process using catalyst inks. Therefore, it is very important to observe the microstructure of the catalyst ink. In this study, the morphology of carbon-supported platinum (Pt/C) particles in catalyst inks with a different solvent composition was investigated by cryogenic scanning electron microscopy (cryo-SEM). In addition, the morphology of the ionomer, which presumably influences the formation of agglomerated Pt/C particles in a catalyst ink, was investigated by cryogenic transmission electron microscopy (cryo-TEM). The results of a cryo-SEM observation revealed that the agglomerated Pt/C particles tended to become coarser with a higher 1-propanol (NPA) weight fraction. The results of a cryo-TEM observation indicated that the actual ionomer dispersion in a catalyst ink formed a network structure different from that of the ionomer in the solvent. © The Author 2017. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Electrochemical oxidation of methanol using dppm-bridged Ru/Pd, Ru/Pt and Ru/Au catalysts.

PubMed

Yang, Ying; McElwee-White, Lisa

2004-08-07

The electrochemical oxidation of methanol was carried out using a series of dppm-bridged Ru/Pd, Ru/Pt and Ru/Au heterobimetallic complexes as catalysts. The major oxidation products were formaldehyde dimethyl acetal (dimethoxymethane, DMM) and methyl formate (MF). The Ru/Pd and Ru/Pt bimetallic catalysts generally afforded lower product ratios of DMM/MF and higher current efficiencies than the Ru/Au catalysts. The Ru/Au bimetallics exhibited product ratios and current efficiencies similar to those obtained from the Ru mononuclear compound CpRu(PPh(3))(2)Cl. Increasing the methanol concentration afforded higher current efficiencies, while the addition of water to the samples shifted the product distribution toward the more highly oxidized product, MF.

Synthesis, spectral, thermal, X-ray single crystal of new RuCl₂(dppb)diamine complexes and their application in hydrogenation of Cinnamic aldehyde.

PubMed

Warad, Ismail; Al-Hussain, Hanan; Al-Far, Rawhi; Mahfouz, Refaat; Hammouti, Belkheir; Hadda, Taibi Ben

2012-09-01

The preparation of new three trans-[RuCl(2)(dppb)(N-N)] with mixed diamine (N-N) and 1,4-bis-(diphenylphosphino)butane (dppb) ligands, starting from RuCl(2)(PPh(3))(3) as precursor is presented. The complexes are characterized on the basis of elemental analysis, IR, (1)H, (13)C and (31)P{(1)H}NMR, FAB-MS, TG/DTA and single crystal X-ray diffraction studies. Complex (2L(1)) crystallizes in the monoclinic unit cells with the space group P2(1). The catalysts are evaluated for their Cinnamic aldehyde hydrogenation. The catalysts show excellent activity and selectivity for the unsaturated carbonyl compound under mild conditions. Copyright © 2012 Elsevier B.V. All rights reserved.

Study of catalysis for solid oxide fuel cells and direct methanol fuel cells

NASA Astrophysics Data System (ADS)

Jiang, Xirong

Fuel cells offer the enticing promise of cleaner electricity with lower environmental impact than traditional energy conversion technologies. Driven by the interest in power sources for portable electronics, and distributed generation and automotive propulsion markets, active development efforts in the technologies of both solid oxide fuel cell (SOFC) and direct methanol fuel cell (DMFC) devices have achieved significant progress. However, current catalysts for fuel cells are either of low catalytic activity or extremely expensive, presenting a key barrier toward the widespread commercialization of fuel cell devices. In this thesis work, atomic layer deposition (ALD), a novel thin film deposition technique, was employed to apply catalytic Pt to SOFC, and investigate both Pt skin catalysts and Pt-Ru catalysts for methanol oxidation, a very important reaction for DMFC, to increase the activity and utilization levels of the catalysts while simultaneously reducing the catalyst loading. For SOFCs, we explored the use of ALD for the fabrication of electrode components, including an ultra-thin Pt film for use as the electrocatalyst, and a Pt mesh structure for a current collector for SOFCs, aiming for precise control over the catalyst loading and catalyst geometry, and enhancement in the current collect efficiency. We choose Pt since it has high chemical stability and excellent catalytic activity for the O2 reduction reaction and the H2 oxidation reaction even at low operating temperatures. Working SOFC fuel cells were fabricated with ALD-deposited Pt thin films as an electrode/catalyst layer. The measured fuel cell performance reveals that comparable peak power densities were achieved for ALD-deposited Pt anodes with only one-fifth of the Pt loading relative to a DC-sputtered counterpart. In addition to the continuous electrocatalyst layer, a micro-patterned Pt structure was developed via the technique of area selective ALD. By coating yttria-stabilized zirconia, a typical solid oxide electrolyte, with patterned (octadecyltrichlorosilane) ODTS self-assembled monolayers (SAMs), Pt thin films were grown selectively on the SAM-free surface regions. Features with sizes as small as 2 mum were deposited by this combined ALD-muCP method. The micro-patterned Pt structure deposited by area selective ALD was applied to SOFCs as a current collector grid/patterned catalyst. An improvement in the fuel cell performance by a factor of 10 was observed using the Pt current collector grids/patterned catalyst integrated onto cathodic La0.6Sr 0.4Co0.2Fe0.8O3-delta. For possible catalytic anodes in DMFCs employing a 1:1 stoichiometric methanol-water reforming mixture, two strategies were employed in this thesis. One approach is to fabricate skin catalysts, where ALD Pt films of various thicknesses were used to coat sputtered Ru films forming Pt skin catalysts for study of methanol oxidation. Another strategy is to replace or alloy Pt with Ru; for this effort, both dc-sputtering and atomic layer deposition were employed to fabricate Pt-Ru catalysts of various Ru contents. The electrochemical behavior of all of the Pt skin catalysts, the DC co-sputtered Pt-Ru catalysts and the ALD co-deposited Pt-Ru catalysts were evaluated at room temperature for methanol oxidation using cyclic voltammetry and chronoamperometry in highly concentrated 16.6 M MeOH, which corresponds to the stoichiometric fuel that will be employed in next generation DMFCs that are designed to minimize or eliminate methanol crossover. The catalytic activity of sputtered Ru catalysts toward methanol oxidation is strongly enhanced by the ALD Pt overlayer, with such skin layer catalysts displaying superior catalytic activity over pure Pt. For both the DC co-sputtered catalysts and ALD co-deposited catalysts, the electrochemical studies illustrate that the optimal stoichiometry ratio for Pt to Ru is approximately 1:1, which is in good agreement with most literature.

Manipulating the dipole layer of polar organic molecules on metal surfaces via different charge-transfer channels

NASA Astrophysics Data System (ADS)

Lin, Meng-Kai; Nakayama, Yasuo; Zhuang, Ying-Jie; Wang, Chin-Yung; Pi, Tun-Wen; Ishii, Hisao; Tang, S.-J.

The key properties of organic films such as energy level alignment (ELA), work functions, and injection barriers are closely linked to this dipole layer. Using angle resolved photoemission spectroscopy (ARPES), we systemically investigate the coverage-dependent work functions and spectra line shapes of occupied molecular orbital states of a polar molecule, chloroaluminium phthalocyanine (ClAlPc), grown on Ag(111) to show that the orientations of the first ClAlPc layer can be manipulated via the molecule deposition rate and post annealing, causing ELA at organic-metal interface to differ for about 0.3 eV between Cl-up and Cl-down configuration. Moreover, by comparing the experimental results with the calculations based on both gas-phase model and realistic model of ClAlPc on Ag(111) , we evidence that the different orientations of ClAlPc dipole layers lead to different charge-transfer channels between ClAlPc and Ag, a key factor that controls the ELA at organic-metal interface.

Direct Simulations of Coupled Transport and Reaction on Nano-Scale X-Ray Computed Tomography Images of Platinum Group Metal-Free Catalyst Cathodes

DOE PAGES

Ogawa, S.; Komini Babu, S.; Chung, H. T.; ...

2016-08-22

The nano/micro-scale geometry of polymer electrolyte fuel cell (PEFC) catalyst layers critically affects cell performance. The small length scales and complex structure of these composite layers make it challenging to analyze cell performance and physics at the particle scale by experiment. We present a computational method to simulate transport and chemical reaction phenomena at the pore/particle-scale and apply it to a PEFC cathode with platinum group metal free (PGM-free) catalyst. Here, we numerically solve the governing equations for the physics with heterogeneous oxygen diffusion coefficient and proton conductivity evaluated using the actual electrode structure and ionomer distribution obtained using nano-scalemore » resolution X-ray computed tomography (nano-CT). Using this approach, the oxygen concentration and electrolyte potential distributions imposed by the oxygen reduction reaction are solved and the impact of the catalyst layer structure on performance is evaluated.« less

Direct Simulations of Coupled Transport and Reaction on Nano-Scale X-Ray Computed Tomography Images of Platinum Group Metal-Free Catalyst Cathodes

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

Ogawa, S.; Komini Babu, S.; Chung, H. T.

The nano/micro-scale geometry of polymer electrolyte fuel cell (PEFC) catalyst layers critically affects cell performance. The small length scales and complex structure of these composite layers make it challenging to analyze cell performance and physics at the particle scale by experiment. We present a computational method to simulate transport and chemical reaction phenomena at the pore/particle-scale and apply it to a PEFC cathode with platinum group metal free (PGM-free) catalyst. Here, we numerically solve the governing equations for the physics with heterogeneous oxygen diffusion coefficient and proton conductivity evaluated using the actual electrode structure and ionomer distribution obtained using nano-scalemore » resolution X-ray computed tomography (nano-CT). Using this approach, the oxygen concentration and electrolyte potential distributions imposed by the oxygen reduction reaction are solved and the impact of the catalyst layer structure on performance is evaluated.« less

Impact of Contaminants Present in Coal-Biomass Derived Synthesis Gas on Water-gas Shift and Fischer-Tropsch Synthesis Catalysts

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

Alptekin, Gokhan

2013-02-15

Co-gasification of biomass and coal in large-scale, Integrated Gasification Combined Cycle (IGCC) plants increases the efficiency and reduces the environmental impact of making synthesis gas ("syngas") that can be used in Coal-Biomass-to-Liquids (CBTL) processes for producing transportation fuels. However, the water-gas shift (WGS) and Fischer-Tropsch synthesis (FTS) catalysts used in these processes may be poisoned by multiple contaminants found in coal-biomass derived syngas; sulfur species, trace toxic metals, halides, nitrogen species, the vapors of alkali metals and their salts (e.g., KCl and NaCl), ammonia, and phosphorous. Thus, it is essential to develop a fundamental understanding of poisoning/inhibition mechanisms before investingmore » in the development of any costly mitigation technologies. We therefore investigated the impact of potential contaminants (H 2S, NH 3, HCN, AsH 3, PH 3, HCl, NaCl, KCl, AS 3, NH 4NO 3, NH 4OH, KNO 3, HBr, HF, and HNO 3) on the performance and lifetime of commercially available and generic (prepared in-house) WGS and FT catalysts.« less

XANES study of elemental mercury oxidation over RuO 2/TiO 2 and selective catalytic reduction catalysts for mercury emissions control

DOE PAGES

Liu, Zhouyang; Li, Can; Sriram, Vishnu; ...

2016-07-25

Linear combination fitting of the X-ray Absorption Near Edge Spectroscopy (XANES) was used to quantify oxidized mercury species over RuO 2/TiO 2 and Selective Catalytic Reduction (SCR) catalysts under different simulated flue gas conditions. Halogen gases play a major role in mercury oxidation. In the absence of halogen gas, elemental mercury can react with sulfur that is contained in both the RuO2/TiO2 and SCR catalysts to form HgS and HgSO 4. In the presence of HCl or HBr gas, HgCl 2 or HgBr 2 is the main oxidized mercury species. When both HCl and HBr gases are present, HgBr2 ismore » the preferred oxidation product and no HgCl 2 can be found. The formation of HgO and HgS cannot be neglected with or without halogen gas. Other simulated flue gas components such as NO, NH 3, SO 2 and CO 2 do not have significant effect on oxidized mercury speciation when halogen gas is present.« less

Direct transformation of xylan-type hemicelluloses to furfural via SnCl₄ catalysts in aqueous and biphasic systems.

PubMed

Wang, Wenju; Ren, Junli; Li, Huiling; Deng, Aojie; Sun, Runcang

2015-05-01

Direct catalytic transformation of xylan-type hemicelluloses to furfural in the aqueous system and the biphasic system were comparatively investigated under mild conditions. Screening of several promising chlorides for conversion of beech xylan in the aqueous system revealed the Lewis acid SnCl4 was the most effective catalyst. Comparing to the single aqueous system, the bio-based 2-methyltetrahydrofuran (2-MTHF)/H2O biphasic system was more conducive to the synthesis of furfural, in which the highest furfural yield of 78.1% was achieved by using SnCl4 as catalysts under the optimized reaction conditions (150°C, 120 min). Additionally, the influences of xylan-type hemicelluloses with different chemical and structural features from beech, corncob and bagasse on the furfural production were studied. It was found that furfural yield to some extent was determined by the xylose content in hemicelluloses and also had relationships with the molecular weight of hemicelluloses and the degree of crystallization. Copyright © 2015 Elsevier Ltd. All rights reserved.

Graphite-Conjugated Rhenium Catalysts for Carbon Dioxide Reduction

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

Oh, Seokjoon; Gallagher, James R.; Miller, Jeffrey T.

2016-02-17

Condensation of fac-Re(5,6-diamino-1,10-phenanthroline)(CO)(3)Cl to o-quinone edge defects on graphitic carbon surfaces generates graphite-conjugated rhenium (GCC-Re) catalysts that are highly active for CO2 reduction to CO in acetonitrile electrolyte. X-ray photo-electron and X-ray absorption spectroscopies establish the formation of surface-bound Re centers with well-defined coordination environments. GCC-Re species on glassy carbon surfaces display catalytic currents greater than 50 mA cm(-2) with 96 +/- 3% Faradaic efficiency for CO production. Normalized for the number of Re active sites, GCC-Re catalysts exhibit higher turnover frequencies than that of a soluble molecular analogue, fac-Re(1,10-phenanthroline)(CO)(3)Cl, and turnover numbers greater than 12,000. In contrast to themore » molecular analogue, GCC-Re surfaces display a Tafel slope of 150 mV/decade, indicative of a catalytic mechanism involving rate-limiting one-electron transfer. This work establishes graphite conjugation as a powerful strategy for generating well-defined, tunable, heterogeneous electrocatalysts on ubiquitous graphitic carbon surfaces.« less

Enhanced hydrothermal stability of Cu-ZSM-5 catalyst via surface modification in the selective catalytic reduction of NO with NH3

NASA Astrophysics Data System (ADS)

Zhang, Tao; Shi, Juan; Liu, Jian; Wang, Daxi; Zhao, Zhen; Cheng, Kai; Li, Jianmei

2016-07-01

The surface of Cu-ZSM-5 catalyst was modified by chemical liquid deposition (CLD) of tetraethoxysilane (TEOS) for enhancing its hydrothermal stability in the selective catalytic reduction of NO with NH3. After hydrothermal aging at 750 °C for 13 h, the catalytic performance of Cu-ZSM-5-Aged catalyst was significantly reduced for NO reduction in the entire temperature range, while that of Cu-ZSM-5-CLD-Aged catalyst was affected very little. The characterization results indicated that an inert silica layer was deposited on the surface of Cu-ZSM-5 and formed a protective layer, which prevents the detachment of Cu2+ from ZSM-5 ion-exchange positions and the dealumination of zeolite during the hydrothermal aging process. Based on the data it is hypothesized to be the primary reason for the high hydrothermal stability of Cu-ZSM-5-CLD catalyst.

Two component-three dimensional catalysis

DOEpatents

Schwartz, Michael; White, James H.; Sammells, Anthony F.

2002-01-01

This invention relates to catalytic reactor membranes having a gas-impermeable membrane for transport of oxygen anions. The membrane has an oxidation surface and a reduction surface. The membrane is coated on its oxidation surface with an adherent catalyst layer and is optionally coated on its reduction surface with a catalyst that promotes reduction of an oxygen-containing species (e.g., O.sub.2, NO.sub.2, SO.sub.2, etc.) to generate oxygen anions on the membrane. The reactor has an oxidation zone and a reduction zone separated by the membrane. A component of an oxygen containing gas in the reduction zone is reduced at the membrane and a reduced species in a reactant gas in the oxidation zone of the reactor is oxidized. The reactor optionally contains a three-dimensional catalyst in the oxidation zone. The adherent catalyst layer and the three-dimensional catalyst are selected to promote a desired oxidation reaction, particularly a partial oxidation of a hydrocarbon.

Isomerization of 7-oxabenzonorbornadienes into naphthols catalyzed by [RuCl(2)(CO)(3)](2).

PubMed

Ballantine, Melissa; Menard, Michelle L; Tam, William

2009-10-02

Ruthenium-catalyzed isomerization of 7-oxanorbornadienes into naphthols was investigated. Among the various ruthenium catalysts tested, [RuCl(2)(CO)(3)](2) gave the highest yields in the isomerization, and various substituted naphthols were synthesized in moderate to excellent yields. Both symmetrical and unsymmetrical 7-oxanorbornadienes were employed in the study, and moderate to excellent regioselectivities were observed.

Carbon Corrosion in PEM Fuel Cells and the Development of Accelerated Stress Tests

DOE PAGES

Macauley, Natalia; Papadias, Dennis D.; Fairweather, Joseph; ...

2018-03-15

Here, carbon corrosion is an important degradation mechanism that can impair PEMFC performance through the destruction of catalyst connectivity, collapse of the electrode pore structure, loss of hydrophobic character, and an increase of the catalyst particle size. In this study, carbon corrosion was quantified in situ by measurement of carbon dioxide in the fuel cell exhaust gases through non-dispersive infrared spectroscopy during simulated drive cycle operations consisting of potential cycling with varying upper and lower potential limits. These studies were conducted for three different types of carbon supports. A reduction in the catalyst layer thickness was observed during a simulatedmore » drive cycle operation with a concomitant decrease in catalyst layer porosity, which led to performance losses due to increased mass transport limitations. The observed thickness reduction was primarily due to compaction of the catalyst layer, with the actual mass of carbon oxidation (loss) contributing only a small fraction (< 20%). The dynamics of carbon corrosion are presented along with a model that simulates the transient and dynamic corrosion rates observed in our experiments. Accelerated carbon corrosion stress tests are presented and their effects are compared to those observed for the drive cycle test.« less

Carbon Corrosion in PEM Fuel Cells and the Development of Accelerated Stress Tests

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

Macauley, Natalia; Papadias, Dennis D.; Fairweather, Joseph

Here, carbon corrosion is an important degradation mechanism that can impair PEMFC performance through the destruction of catalyst connectivity, collapse of the electrode pore structure, loss of hydrophobic character, and an increase of the catalyst particle size. In this study, carbon corrosion was quantified in situ by measurement of carbon dioxide in the fuel cell exhaust gases through non-dispersive infrared spectroscopy during simulated drive cycle operations consisting of potential cycling with varying upper and lower potential limits. These studies were conducted for three different types of carbon supports. A reduction in the catalyst layer thickness was observed during a simulatedmore » drive cycle operation with a concomitant decrease in catalyst layer porosity, which led to performance losses due to increased mass transport limitations. The observed thickness reduction was primarily due to compaction of the catalyst layer, with the actual mass of carbon oxidation (loss) contributing only a small fraction (< 20%). The dynamics of carbon corrosion are presented along with a model that simulates the transient and dynamic corrosion rates observed in our experiments. Accelerated carbon corrosion stress tests are presented and their effects are compared to those observed for the drive cycle test.« less

Development of a Stochastically-driven, Forward Predictive Performance Model for PEMFCs

NASA Astrophysics Data System (ADS)

Harvey, David Benjamin Paul

A one-dimensional multi-scale coupled, transient, and mechanistic performance model for a PEMFC membrane electrode assembly has been developed. The model explicitly includes each of the 5 layers within a membrane electrode assembly and solves for the transport of charge, heat, mass, species, dissolved water, and liquid water. Key features of the model include the use of a multi-step implementation of the HOR reaction on the anode, agglomerate catalyst sub-models for both the anode and cathode catalyst layers, a unique approach that links the composition of the catalyst layer to key properties within the agglomerate model and the implementation of a stochastic input-based approach for component material properties. The model employs a new methodology for validation using statistically varying input parameters and statistically-based experimental performance data; this model represents the first stochastic input driven unit cell performance model. The stochastic input driven performance model was used to identify optimal ionomer content within the cathode catalyst layer, demonstrate the role of material variation in potential low performing MEA materials, provide explanation for the performance of low-Pt loaded MEAs, and investigate the validity of transient-sweep experimental diagnostic methods.

Heteropolyacids: An Efficient Catalyst for Synthesis of CL-20

NASA Astrophysics Data System (ADS)

Bayat, Yadollah; Mokhtari, Javad; Farhadian, Nafiseh; Bayat, Mohammad

2012-04-01

CL-20, a high-energy material with a cage-like structure, is considered the most powerful explosive today. It is usually prepared via nitration with concentrated nitric and sulfuric acid, but this technique pollutes the environment. In this article, CL-20 was synthesized by nitration of 2,6,8,12-tetraacetyl 2,4,6,8,10,12-hexaazatetracyclo[5,5,0,03,11,05,9]dodecane (TAIW) using a clean nitrating agent, heteropolyacids. Using the new nitrating agent caused the elimination of concentrated sulfuric acid during the reaction. This is an environmentally friendly technique.

Secondary amine formation from reductive amination of carbonyl compounds promoted by Lewis acid using the InCl3/Et3SiH system.

PubMed

Lee, On-Yi; Law, Ka-Lun; Yang, Dan

2009-08-06

A robust and reliable method has been developed for reductive amination of primary amines with various aldehydes and ketones using Zn(ClO(4))(2) x 6 H(2)O as a catalyst. [In-H] generated in situ via a combination of InCl(3) and Et(3)SiH is employed as an effective reducing system. A variety of secondary amines can be synthesized in a one-pot procedure in excellent yields.

Formation of multi-stereogenic centers using a catalytic diastereoselective Henry reaction.

PubMed

Arai, Takayoshi; Taneda, Yoshinori; Endo, Yoko

2010-11-14

A diastereoselective Henry reaction of chiral aldehydes with nitroalkanes was developed using a chiral sulfonyldiamine (L1)-CuCl complex. The reaction of (R)-2-phenylpropanal and nitromethane was smoothly catalyzed by the (S,S,S)-L1-CuCl complex to give the adduct with 99/1 syn/anti selectivity in 99% ee. In the reaction of (S)-2-phenylpropanal and nitroethane, the (R,R,R)-L1-CuCl catalyst yielded the expected three contiguous stereogenic centers in a highly syn-selective Henry reaction.

N,B-Bidentate Boryl Ligand-Supported Iridium Catalyst for Efficient Functional-Group-Directed C-H Borylation.

PubMed

Wang, Guanghui; Liu, Li; Wang, Hong; Ding, You-Song; Zhou, Jing; Mao, Shuai; Li, Pengfei

2017-01-11

Convenient silylborane precursors for introducing N,B-bidentate boryl ligands onto transition metals were designed, prepared, and employed in ready formation of irdium(III) complexes via Si-B oxidative addition. A practical, efficient catalytic ortho-borylation reaction of arenes with a broad range of directing groups was developed using an in situ generated catalyst from the silylborane preligand 3c and [IrCl(COD)] 2 .

Electrochemical and Spectroscopic Investigation of Molten Chloroaluminates and Related Solvents

DTIC Science & Technology

1988-11-07

chemistry of iridium carbonyl complexes known to be active Fischer-Tropsch catalysts (described below). These studies represent the first successful in...electrochemical studies, e. g., doole potential step chronocoulometry, of this system are in progress. 3: hemistry of iridium carbonyls in sodium...chloroaluminates’/The iridium carbonyl species 1r4(CO)12 and IrCl(CO)3 have previously been shown to serve as Fischer-Tropsch catalysts in acidic sodium

Copper-containing zeolite catalysts

DOEpatents

Price, G.L.; Kanazirev, V.

1996-12-10

A catalyst useful in the conversion of nitrogen oxides or in the synthesis of nitriles or imines from amines, is formed by preparing an intimate mechanical mixture of a copper (II)-containing species, such as CuO or CuCl{sub 2}, or elemental copper, with a zeolite having a pore mouth comprising 10 oxygen atoms, such as ZSM-5, converting the elemental copper or copper (II) to copper (I), and driving the copper (I) into the zeolite.

Copper-containing zeolite catalysts

DOEpatents

Price, Geoffrey L.; Kanazirev, Vladislav

1996-01-01

A catalyst useful in the conversion of nitrogen oxides or in the synthesis of nitriles or imines from amines, formed by preparing an intimate mechanical mixture of a copper (II)-containing species, such as CuO or CuCl.sub.2, or elemental copper, with a zeolite having a pore mouth comprising 10 oxygen atoms, such as ZSM-5, converting the elemental copper or copper (II) to copper (I), and driving the copper (I) into the zeolite.

Towards a practical setup for hydrogen production from formic acid.

PubMed

Sponholz, Peter; Mellmann, Dörthe; Junge, Henrik; Beller, Matthias

2013-07-01

Formic acid cracker: A mini plant that allows for continuous formic acid decomposition to hydrogen and carbon dioxide under ambient conditions is presented. By using an in situ-formed ruthenium catalyst, unprecedented turnover numbers over 1,000,000 are achieved. The active catalyst is formed in situ from commercially available [RuCl2 (benzene)]2 and 1,2-bisdiphenylphosphinoethane. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Novel low-cost Fenton-like layered Fe-titanate catalyst: preparation, characterization and application for degradation of organic colorants.

PubMed

Chen, Yongzhou; Li, Nian; Zhang, Ye; Zhang, Lide

2014-05-15

Novel low-cost layered Fe-titanate catalyst for photo-Fenton degradation of organic contaminants was successfully developed by ion exchange of Fe(3+) with Na(+) layered nano Na-titanates which was prepared by alkali hydrothermal method. The as prepared materials were characterized by powder X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectrometer (EDX). The catalytic activity of the Fe-titanate catalyst was evaluated by the decolorization of three different dyes (rhodamine 6G (R6G), methyl blue (MB), and methyl orange (MO)) under UV irradiation at room temperature. Effect of several important factors such as Fe loading in the catalyst, initial solution pH, catalyst dosage, H2O2 amount, and reaction time was systematically studied. It was found that the decolorization was very efficient for all three dyes. The efficiency reached 98% for R6G, 98.5% for MB, and 97% for MO, respectively, under optimal conditions. The oxidation process was quick, and only 15 min is needed for all three dyes. Moreover, the Fe-titanate catalyst could be used in a wider and near neutral pH range compared with classic Fenton systems which need to be operated at around pH 3.0. Kinetic analysis results showed that the oxidation kinetics was accurately represented by pseudo-first-order model. More importantly, the catalyst was very stable and could be reused for at least four cycles when operated under near neutral pH. The Fe leaching from the catalyst measured was almost negligible, which not only demonstrated the stability of the catalyst, but also avoided the formation of secondary Fe pollution. Therefore, the reported Fe-titanates are promising nanomaterials which can be used as Fenton like catalyst for the degradation of organic contaminant in wastewater. Crown Copyright © 2014. Published by Elsevier Inc. All rights reserved.

Exploring substrate/ionomer interaction under oxidizing and reducing environments

DOE PAGES

Tesfaye, Meron; MacDonald, Andrew N.; Dudenas, Peter J.; ...

2018-02-09

Local gas transport limitation attributed to the ionomer thin-film in the catalyst layer is a major deterrent to widespread commercialization of polymer-electrolyte fuel cells. So far functionality and limitations of these thin-films have been assumed identical in the anode and cathode. In this study, Nafion ionomer thin-films on platinum(Pt) support were exposed to H 2 and air as model schemes, mimicking anode and cathode catalyst layers. Findings indicate decreased swelling, increased densification of ionomer matrix, and increased humidity-induced aging rates in reducing environment, compared to oxidizing and inert environments. Observed phenomenon could be related to underlying Pt-gas interaction dictating Pt-ionomermore » behavior. Presented results could have significant implications about the disparate behavior of ionomer thin-film in anode and cathode catalyst layers.« less

Surface-Initiated Polymerization with Poly(n-hexylisocyanate) to Covalently Functionalize Silica Nanoparticles.

PubMed

Vatansever, Fatma; Hamblin, Michael R

2017-02-01

New methods are needed for covalent functionalization of nanoparticles-surface with organic polymer coronas to generate polymeric nanocomposite in a controlled manner. Here we report the use of a surface-initiated polymerization approach, mediated by titanium (IV) catalysis, to grow poly( n -hexylisocyanate) chains from silica surface. Two pathways were used to generate the interfacing in these nano-hybrids. In the first one, the nanoparticles was "seeded" with SiCl4, followed by reaction with 1,6-hexanediol to form hydroxyl groups attached directly to the surface via O-Si-O bonding. In the second pathway, the nanoparticles were initially exposed to a 9:1 mixture of trimethyl silyl chloride and chlorodimethyl octenyl silane which was then followed by hydroboration of the double bonds, to afford hydroxyl groups with a spatially controlled density and surface-attachment via O-Si-C bonding. These functionalized surfaces were then activated with the titanium tetrachloride catalyst. In our approach, thus surface tethered catalyst provided the sites for n -hexyl isocyanate monomer insertion, to "build up" the surface-grown polymer layers from the "bottom-up". A final end-capping, to seal off the chain ends, was done via acetyl chloride. Compounds were characterized by FT-IR, 1H-NMR, GC-MS, GPC, and thermogravimetric analyses.

Surface-Initiated Polymerization with Poly(n-hexylisocyanate) to Covalently Functionalize Silica Nanoparticles

PubMed Central

Vatansever, Fatma; Hamblin, Michael R.

2017-01-01

New methods are needed for covalent functionalization of nanoparticles-surface with organic polymer coronas to generate polymeric nanocomposite in a controlled manner. Here we report the use of a surface-initiated polymerization approach, mediated by titanium (IV) catalysis, to grow poly(n-hexylisocyanate) chains from silica surface. Two pathways were used to generate the interfacing in these nano-hybrids. In the first one, the nanoparticles was “seeded” with SiCl4, followed by reaction with 1,6-hexanediol to form hydroxyl groups attached directly to the surface via O-Si-O bonding. In the second pathway, the nanoparticles were initially exposed to a 9:1 mixture of trimethyl silyl chloride and chlorodimethyl octenyl silane which was then followed by hydroboration of the double bonds, to afford hydroxyl groups with a spatially controlled density and surface-attachment via O-Si-C bonding. These functionalized surfaces were then activated with the titanium tetrachloride catalyst. In our approach, thus surface tethered catalyst provided the sites for n-hexyl isocyanate monomer insertion, to “build up” the surface-grown polymer layers from the “bottom-up”. A final end-capping, to seal off the chain ends, was done via acetyl chloride. Compounds were characterized by FT-IR, 1H-NMR, GC-MS, GPC, and thermogravimetric analyses. PMID:28989336

The first chiral diene-based metal-organic frameworks for highly enantioselective carbon-carbon bond formation reactions

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

Sawano, Takahiro; Ji, Pengfei; McIsaac, Alexandra R.

2016-02-01

We have designed the first chiral diene-based metal–organic framework (MOF), E₂-MOF, and postsynthetically metalated E₂-MOF with Rh(I) complexes to afford highly active and enantioselective single-site solid catalysts for C–C bond formation reactions. Treatment of E₂-MOF with [RhCl(C₂H₄)₂]₂ led to a highly enantioselective catalyst for 1,4-additions of arylboronic acids to α,β-unsaturated ketones, whereas treatment of E₂-MOF with Rh(acac)(C₂H₄)₂ afforded a highly efficient catalyst for the asymmetric 1,2-additions of arylboronic acids to aldimines. Interestingly, E₂-MOF·Rh(acac) showed higher activity and enantioselectivity than the homogeneous control catalyst, likely due to the formation of a true single-site catalyst in the MOF. E₂-MOF·Rh(acac) was also successfullymore » recycled and reused at least seven times without loss of yield and enantioselectivity.« less

New electrocatalysts for unitized regenerative fuel cell: Pt-Ir alloy deposited on the proton exchange membrane surface by impregnation-reduction method.

PubMed

Wan, Chieh-Hao; Wu, Chun-Lin; Lin, Meng-Tsun; Shih, Chihhsiong

2010-07-01

In this paper, a modified technique to prepare Pt-Ir catalyst layer on the proton exchange membrane (PEM) surface using the impregnation-reduction (IR) method is proposed to improve the electrocatalytic activity as well as the life cycle of the bifunctional oxygen electrode (BOE). The resulted electrocatalysts were characterized by the Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Electron Probe Micro-Analysis (EPMA), and Transmission Electron Microscope (TEM). The electrocatalytic properties of the Pt-Ir layer on PEM surface for the oxygen reduction and water oxidation reactions as well as the life cycle of MEA were investigated. Experimental results showed that the Ir particles were dispersed densely in the platinum layer through the modified IR technique. The atomic ratio of Pt over Ir elements was 9:1, and the resulted thickness of the obtained Pt-Ir catalyst layer was about 1.0 microm. The Pt-Ir catalyst layer was composed of Pt layer doped with Ir nano-particles comprising nano Pt-Ir alloy phase. The large surface area of Ir core with Pt shell particles and the presence of nano Pt-Ir alloy phase led to a higher electrocatalytic activity of BOE. Due to the good binding between the Nafion membrane and the Pt-Ir alloy catalyst, as well as the composite structure of the resulted Pt-Ir, the life cycle of Unitized Regenerative Fuel Cell (URFC) is improved through this novel BOE.

Aqueous NMR Signal Enhancement by Reversible Exchange in a Single Step Using Water-Soluble Catalysts

PubMed Central

2016-01-01

Two synthetic strategies are investigated for the preparation of water-soluble iridium-based catalysts for NMR signal amplification by reversible exchange (SABRE). In one approach, PEGylation of a variant N-heterocyclic carbene provided a novel catalyst with excellent water solubility. However, while SABRE-active in ethanol solutions, the catalyst lost activity in >50% water. In a second approach, synthesis of a novel di-iridium complex precursor where the cyclooctadiene (COD) rings have been replaced by CODDA (1,2-dihydroxy-3,7-cyclooctadiene) leads to the creation of a catalyst [IrCl(CODDA)IMes] that can be dissolved and activated in water—enabling aqueous SABRE in a single step, without need for either an organic cosolvent or solvent removal followed by aqueous reconstitution. The potential utility of the CODDA catalyst for aqueous SABRE is demonstrated with the ∼(−)32-fold enhancement of 1H signals of pyridine in water with only 1 atm of parahydrogen. PMID:27350846

Pt-Pd bimetallic nanoparticles on MWCNTs: catalyst for hydrogen peroxide electrosynthesis

NASA Astrophysics Data System (ADS)

Félix-Navarro, R. M.; Beltrán-Gastélum, M.; Salazar-Gastélum, M. I.; Silva-Carrillo, C.; Reynoso-Soto, E. A.; Pérez-Sicairos, S.; Lin, S. W.; Paraguay-Delgado, F.; Alonso-Núñez, G.

2013-08-01

Bimetallic nanoparticles of Pt-Pd were deposited by the microemulsion method on a multiwall carbon nanotube (MWCNTs) to obtain a Pt-Pd/MWCNTs for electrocatalytic reduction of O2 to H2O2. The activity and selectivity of the catalyst was determined qualitatively by the rotating disk electrode method in acidic medium. The catalyst was spray-coated onto a reticulated vitreous carbon substrate and quantitatively was tested in bulk electrolysis for 20 min under potentiostatic conditions (0.5 V vs Ag/AgCl) in a 0.5 M H2SO4 electrolyte using dissolved O2. The bulk electrolysis experiments show that the Pt-Pd/MWCNTs catalyst is more efficient for H2O2 electrogeneration than a MWCNTs catalyst. Nitrobenzene degradation by electrogenerated H2O2 alone and Electro-Fenton process were also tested. Our results show that both processes decompose nitrobenzene, but the Electro-Fenton process does it more efficiently. The prepared nanoparticulated catalyst shows a great potential in environmental applications.

An all-solid-state reference electrode based on the layer-by-layer polymer coating.

PubMed

Kwon, Nak-Hyun; Lee, Kyung-Sun; Won, Mi-Sook; Shim, Yoon-Bo

2007-09-01

A solid-state reference electrode (SSRE) was fabricated by layering a silicone rubber (SR) film containing KCl on an AgCl surface, then a perfluorinated ionomer film, and finally a polyurethane-based membrane containing an ionophore, a lipophilic ionic additive, and a plasticizer, respectively. The addition of SiCl4 to the polyurethane-based membrane layer enhanced the strength of the membrane in an aqueous solution. The morphologies of the membranes were studied separately by SEM. The fabrication of the Ag/AgCl electrode through this layer-by-layer polymer coating improved the electrode stability enormously. In addition, the potential drift of the SSRE according to the pH of the medium was minimized by introducing a H+-ion-selective ionophore (tridodecylamine; TDDA) into the outmost polymer membrane. The cyclic voltammetric and potentiometric responses using the SSRE and a conventional reference electrode, respectively, were consistent. The SSRE exhibited little potential variation even in the case of the addition of very high concentrations of various salts, such as Na salicylate, LiCl, KCl, CaCl2, MgCl2, KNO3, NaCl, and NaHCO3. The practicability of the proposed SSRE was tested for the determination of blood pH and pCO2 in a flow cell system. The SSRE fabricated in the present study was stable over two years.

Spontaneous nano-gap formation in Ag film using NaCl sacrificial layer for Raman enhancement

NASA Astrophysics Data System (ADS)

Min, Kyungchan; Jeon, Wook Jin; Kim, Youngho; Choi, Jae-Young; Yu, Hak Ki

2018-03-01

We report the method of fabrication of nano-gaps (known as hot spots) in Ag thin film using a sodium chloride (NaCl) sacrificial layer for Raman enhancement. The Ag thin film (20-50 nm) on the NaCl sacrificial layer undergoes an interfacial reaction due to the AgCl formed at the interface during water molecule intercalation. The intercalated water molecules can dissolve the NaCl molecules at interfaces and form the ionic state of Na+ and Cl-, promoting the AgCl formation. The Ag atoms can migrate by the driving force of this interfacial reaction, resulting in the formation of nano-size gaps in the film. The surface-enhanced Raman scattering activity of Ag films with nano-size gaps has been investigated using Raman reporter molecules, Rhodamine 6G (R6G).

Layered electrode for electrochemical cells

DOEpatents

Swathirajan, Swathy; Mikhail, Youssef M.

2001-01-01

There is provided an electrode structure comprising a current collector sheet and first and second layers of electrode material. Together, the layers improve catalyst utilization and water management.

193Ir Mössbauer spectroscopy of Pt-IrO 2 nanoparticle catalysts developed for detection and removal of carbon monoxide from air

NASA Astrophysics Data System (ADS)

Sawicki, J. A.; Marcinkowska, K.; Wagner, F. E.

2010-08-01

Mössbauer spectroscopy of 73.0 keV gamma-ray transition in 193Ir and supplementary analytical techniques were used to study the microstructure and chemical form of polymer-supported hydrophobic bimetallic Pt-Ir catalysts for detection and removal of CO from humid air at ambient conditions. The catalysts, typically with a composition of 9 wt.% Pt and 1 wt.% Ir, were prepared by incipient wetness impregnation of polystyrene-divinylbenzene (SDB) granules with ethanol solutions of hexachloroplatinic and hexachloroiridic acids. This procedure, followed by reduction in H 2 or CO at only 200 °C or 250 °C, resulted in formation of highly-dispersed Pt-Ir particles usually smaller than 20 nm and having high catalytic activity and selectivity. Mössbauer spectra of 73.0 keV gamma-ray transition in 193Ir were taken after consecutive steps of preparation and exposure of catalysts to better understand and further improve the fabrication processes. In the as-impregnated state, iridium was found mostly as Ir(III) in [IrCl 6] 3- ions, with only a small fraction of Ir(IV) in [IrCl 6] 2- ions. The iridium in bimetallic clusters formed by reduction in hydrogen showed a strong tendency towards oxidation on exposure to air at room temperature, while Pt remained mostly metallic. In the most active and stable catalysts, the Ir and Pt in metallic regions of the clusters did not tend to segregate, unlike in Pt-Ir/silica-supported catalysts studied by us earlier. Further, this study shows that the IrO 2-like regions in the clusters exhibit stronger deviations from local symmetry and stoichiometry of crystalline IrO 2 than observed previously in Pt-Ir/silica catalysts. Our study also indicates that in the examined Pt-IrO 2 nanoparticles iridium largely provides the dissociative O 2 adsorption sites, while the CO adsorption occurs primarily at metallic Pt sites.

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

Ben Yahia, Hamdi, E-mail: benyahia.hamdi@voila.fr; Rodewald, Ute Ch.; Boulahya, Khalid

Graphical abstract: The new compounds RE{sub 4}O{sub 4}[AsO{sub 4}]Cl (RE = La, Pr, Nd, Sm, Eu, Gd) were synthesised by solid state reaction via a salt flux route and investigated by HRTEM, SAED, and single crystal X-ray diffraction. - Highlights: • We discovered the series of RE{sub 4}O{sub 4}[AsO{sub 4}]Cl (RE = La, Pr, Nd, Sm, Eu, Gd) compounds. • The RE{sub 4}O{sub 4}[AsO{sub 4}]Cl single crystals were grown using NaCl/KCl flux. • The RE{sub 4}O{sub 4}[AsO{sub 4}]Cl structures were solved using single crystal X-ray diffraction data. • The layered RE{sub 4}O{sub 4}[AsO{sub 4}]Cl compounds were further characterized using HRTEMmore » and SAED. • We observed an alternation of ordered-[RE{sub 4}O{sub 4}]{sup 4+} and disordered-[ClAsO{sub 4}]{sup 4–} layers. - Abstract: The new compounds RE{sub 4}O{sub 4}[AsO{sub 4}]Cl (RE = La, Pr, Nd, Sm, Eu, Gd) were synthesised by solid state reaction via a salt flux route and investigated by HRTEM, SAED, and single crystal X-ray diffraction. The samples crystallise with a tetragonal cell, space group P4{sub 2}/mnm and Z = 2. Their crystal structure consists of an alternation of [RE{sub 4}O{sub 4}]{sup 4+} and [ClAsO{sub 4}]{sup 4–} layers. The [RE{sub 4}O{sub 4}]{sup 4+} layer contains ORE{sub 4/4} tetrahedra which share common edges. The anions AsO{sub 4}{sup 3–} and Cl{sup –} are located between these layers in disordered manner. SAED and HRTEM experiments confirmed this structural model and enabled us to propose an ordered model for the [ClAsO{sub 4}]{sup 4–} layers.« less

Ultrahigh PEMFC performance of a thin-film, dual-electrode assembly with tailored electrode morphology.

PubMed

Jung, Chi-Young; Kim, Tae-Hyun; Yi, Sung-Chul

2014-02-01

A dual-electrode membrane electrode assembly (MEA) for proton exchange membrane fuel cells with enhanced polarization under zero relative humidity (RH) is fabricated by introducing a phase-separated morphology in an agglomerated catalyst layer of Pt/C (platinum on carbon black) and Nafion. In the catalyst layer, a sufficient level of phase separation is achieved by dispersing the Pt catalyst and the Nafion dispersion in a mixed-solvent system (propane-1,2,3-triol/1-methyl-2-pyrrolidinone).The high polymer chain mobility results in improved water uptake and regular pore-size distribution with small pore diameters. The electrochemical performance of the dual-film electrode assembly with different levels of phase separation is compared to conventional electrode assemblies. As a result, good performance at 0 % RH is obtained because self-humidification is dramatically improved by attaching this dense and phase-separated catalytic overlayer onto the conventional catalyst layer. A MEA prepared using the thin-film, dual-layered electrode exhibits 39-fold increased RH stability and 28-fold improved start-up recovery time during the on-off operation relative to the conventional device. We demonstrate the successful operation of the dual-layered electrode comprised of discriminatively phase-separated agglomerates with an ultrahigh zero RH fuel-cell performance reaching over 95 % performance of a fully humidified MEA. Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

International Assessment of Carbon Nanotube Manufacturing and Applications

DTIC Science & Technology

2007-06-01

oriented and long SWNT arrays obtained by the “fast-heating” growth process (Huang et al . 2004); the Fe/Mo catalyst nanoparticles are deposited ...and Cu layers for top-layer electrical contact. More recent work has been with gas-phase- deposited Ni and Co nanoparticles as catalysts (Sato et al ...22 3.6 Microstructure of MWCNT materials produced by a continuous process at Nano Carbon technologies

Vertical Carbon Nanotube Device in Nanoporous Templates

NASA Technical Reports Server (NTRS)

Sands, Timothy (Inventor); Fisher, Timothy Scott (Inventor); Bashir, Rashid (Inventor); Maschmann, Matthew Ralph (Inventor)

2014-01-01

A modified porous anodic alumina template (PAA) containing a thin CNT catalyst layer directly embedded into the pore walls. CNT synthesis using the template selectively catalyzes SWNTs and DWNTs from the embedded catalyst layer to the top PAA surface, creating a vertical CNT channel within the pores. Subsequent processing allows for easy contact metallization and adaptable functionalization of the CNTs and template for a myriad of applications.

Iron oxide/cassava starch-supported Ziegler-Natta catalysts for in situ ethylene polymerization.

PubMed

Chancharoenrith, Sittikorn; Kamonsatikul, Choavarit; Namkajorn, Montree; Kiatisevi, Supavadee; Somsook, Ekasith

2015-03-06

Iron oxide nanoparticles were used as supporters for in situ polymerization to produce polymer nanocomposites with well-dispersed fillers in polymer matrix. Iron oxide could be sustained as colloidal solutions by cassava starch to produce a good dispersion of iron oxide in the matrix. New supports based on iron oxide/cassava starch or cassava starch for Ziegler-Natta catalysts were utilized as heterogeneous supporters for partially hydrolyzed triethylaluminum. Then, TiCl4 was immobilized on the supports as catalysts for polymerization of ethylene. High-density polyethylene (HDPE) composites were obtained by the synthesized catalysts. A good dispersion of iron oxide/cassava starch particles was observed in the synthesized polymer matrix promoting to good mechanical properties of HDPE. Copyright © 2014 Elsevier Ltd. All rights reserved.

Tracking Co(I) Intermediate in operando in Photocatalytic Hydrogen Evolution by X-ray transient Absorption Spectroscopy and DFT Calculation

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

Li, Zhi-Jun; Zhan, Fei; Xiao, Hongyan

X-ray transient absorption spectroscopy (XTA) and optical transient spectroscopy (OTA) were used to probe the Co(I) intermediate generated in situ from an aqueous photocatalytic hydrogen evolution system, with [RuII(bpy)3]Cl2·6H2O as the photosensitizer, ascorbic acid/ascorbate as the electron donor, and the Co-polypyridyl complex ([CoII(DPABpy) Cl]Cl) as the pre-catalyst. Upon exposure to light, the XTA measured at Co K-edge visualizes the grow and decay of the Co(I) intermediate, and reveals its Co-N bond contraction of 0.09 ± 0.03 Å. Density functional theory (DFT) calculations support the bond contraction and illustrate that the metal-to-ligand π back-bonding greatly stabilizes the penta-coordinated Co(I) intermediate, whichmore » provides easy photon access. To the best of our knowledge, this is the first example of capturing the penta-coordinated Co(I) intermediate in operando with bond contraction by XTA, thereby providing new insights for fundamental understanding of structure– function relationship of cobalt-based molecular catalysts.« less

Identification of optimal solar fuel electrocatalysts via high throughput in situ optical measurements

DOE PAGES

Shinde, Aniketa; Guevarra, Dan; Haber, Joel A.; ...

2014-10-21

For many solar fuel generator designs involve illumination of a photoabsorber stack coated with a catalyst for the oxygen evolution reaction (OER). In this design, impinging light must pass through the catalyst layer before reaching the photoabsorber(s), and thus optical transmission is an important function of the OER catalyst layer. Many oxide catalysts, such as those containing elements Ni and Co, form oxide or oxyhydroxide phases in alkaline solution at operational potentials that differ from the phases observed in ambient conditions. To characterize the transparency of such catalysts during OER operation, 1031 unique compositions containing the elements Ni, Co, Ce,more » La, and Fe were prepared by a high throughput inkjet printing technique. Moreover, the catalytic current of each composition was recorded at an OER overpotential of 0.33 V with simultaneous measurement of the spectral transmission. By combining the optical and catalytic properties, the combined catalyst efficiency was calculated to identify the optimal catalysts for solar fuel applications within the material library. Our measurements required development of a new high throughput instrument with integrated electrochemistry and spectroscopy measurements, which enables various spectroelectrochemistry experiments.« less

Synthesis of platinum nanoparticle electrocatalysts by atomic layer deposition

NASA Astrophysics Data System (ADS)

Lubers, Alia Marie

Demand for energy continues to increase, and without alternatives to fossil fuel combustion the effects on our environment will become increasingly severe. Fuel cells offer a promising improvement on current methods of energy generation; they are able to convert hydrogen fuel into electricity with a theoretical efficiency of up to 83% and interface smoothly with renewable hydrogen production. Fuel cells can replace internal combustion engines in vehicles and are used in stationary applications to power homes and businesses. The efficiency of a fuel cell is maximized by its catalyst, which is often composed of platinum nanoparticles supported on carbon. Economical production of fuel cell catalysts will promote adoption of this technology. Atomic layer deposition (ALD) is a possible method for producing catalysts at a large scale when employed in a fluidized bed. ALD relies on sequential dosing of gas-phase precursors to grow a material layer by layer. We have synthesized platinum nanoparticles on a carbon particle support (Pt/C) by ALD for use in proton exchange membrane fuel cells (PEMFCs) and electrochemical hydrogen pumps. Platinum nanoparticles with different characteristics were deposited by changing two chemistries: the carbon substrate through functionalization; and the deposition process by use of either oxygen or hydrogen as ligand removing reactants. The metal depositing reactant was trimethyl(methylcyclopentadienyl)platinum(IV). Functionalizing the carbon substrate increased nucleation during deposition resulting in smaller and more dispersed nanoparticles. Use of hydrogen produced smaller nanoparticles than oxygen, due to a gentler hydrogenation reaction compared to using oxygen's destructive combustion reaction. Synthesized Pt/C materials were used as catalysts in an electrochemical hydrogen pump, a device used to separate hydrogen fuel from contaminants. Catalysts deposited by ALD on functionalized carbon using a hydrogen chemistry were the most successful hydrogen pumping catalysts, comparable to a commercial Pt/C catalyst. Synthesized Pt/C materials were also used as PEMFC catalysts. We found the ALD catalysts with lower platinum loading to be competitive with a commercial fuel cell catalyst, especially when exhibiting similar platinum particle characteristics. The functionalized carbon helped produce smaller and more dispersed platinum particles; however, it encouraged carbon corrosion within an electrode, severing electrical connections and lowering energy production. The most suitable chemistry for competitive Pt/C catalysts was produced by platinum ALD on unmodified carbon using hydrogen as a reactant. ALD is a promising method for fabricating electrocatalysts, which could help fuel cells become an economically viable alternative to fossil fuels.

High-pressure X-ray diffraction, Raman, and computational studies of MgCl2 up to 1 Mbar: Extensive pressure stability of the β-MgCl2 layered structure.

PubMed

Stavrou, Elissaios; Yao, Yansun; Zaug, Joseph M; Bastea, Sorin; Kalkan, Bora; Konôpková, Zuzana; Kunz, Martin

2016-08-12

Magnesium chloride (MgCl2) with the rhombohedral layered CdCl2-type structure (α-MgCl2) has been studied experimentally using synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy using a diamond-anvil cell up to 100 GPa at room temperature and theoretically using first-principles density functional calculations. The results reveal a pressure-induced second-order structural phase transition to a hexagonal layered CdI2-type structure (β-MgCl2) at 0.7 GPa: the stacking sequence of the Cl anions are altered resulting in a reduction of the c-axis length. Theoretical calculations confirm this phase transition sequence and the calculated transition pressure is in excellent agreement with the experiment. Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phase. According to our experimental results MgCl2 remains in a 2D layered phase up to 100 GPa and further, the 6-fold coordination of Mg cations is retained. Theoretical calculations of relative enthalpy suggest that this extensive pressure stability is due to a low enthalpy of the layered structure ruling out kinetic barrier effects. This observation is unusual, as it contradicts with the general structural behavior of highly compressed AB2 compounds.

High-pressure X-ray diffraction, Raman, and computational studies of MgCl 2 up to 1 Mbar: Extensive pressure stability of the β-MgCl 2 layered structure

DOE PAGES

Stavrou, Elissaios; Yao, Yansun; Zaug, Joseph M.; ...

2016-08-12

We studied magnesium chloride (MgCl 2) with the rhombohedral layered CdCl 2-type structure (α-MgCl 2), experimentally, using synchrotron angle-dispersive powder x-ray diffraction and Raman spectroscopy using a diamond-anvil cell up to 100 GPa at room temperature and theoretically using first-principles density functional calculations. Our results reveal a pressure-induced second-order structural phase transition to a hexagonal layered CdI 2-type structure (β-MgCl 2) at 0.7 GPa: the stacking sequence of the Cl anions are altered resulting in a reduction of the c-axis length. Theoretical calculations confirm this phase transition sequence and the calculated transition pressure is in excellent agreement with the experiment.more » Lattice dynamics calculations also reproduce the experimental Raman spectra measured for the ambient and high-pressure phase. According to our experimental results MgCl 2 remains in a 2D layered phase up to 100 GPa and further, the 6-fold coordination of Mg cations is retained. Theoretical calculations of relative enthalpy suggest that this extensive pressure stability is due to a low enthalpy of the layered structure ruling out kinetic barrier effects. Our observation is unusual, as it contradicts with the general structural behavior of highly compressed AB 2 compounds.« less

A Layered Solution Crystal Growth Technique and the Crystal Structure of (C 6H 5C 2H 4NH 3) 2PbCl 4

NASA Astrophysics Data System (ADS)

Mitzi, D. B.

1999-07-01

Single crystals of the organic-inorganic perovskite (C6H5C2H4NH3)2PbCl4 have been grown at room temperature using a layered solution approach. The bottom solution layer, contained within a long straight tube, consists of PbCl2 dissolved in concentrated aqueous HCl. A less dense layer of methanol is carefully placed on top of the HCl/PbCl2 solution using a syringe. Finally, a stoichiometric quantity of C6H5C2H4NH2 (relative to the PbCl2) is added to the top of the column. As the layers slowly diffuse together, well-formed crystals of (C6H5C2H4NH3)2PbCl4 appear near the interface between the HCl/PbCl2 and C6H5C2H4NH2 solutions. The thick, plate-like crystals are well suited for X-ray crystallography studies. Room temperature intensity data were refined using a triclinic (Poverline1) cell (a=11.1463(3) Å, b=11.2181(3) Å, c=17.6966(5) Å, α= 99.173(1)°, β=104.634(1)°, γ=89.999(1)°, V=2111.8(1) Å3, Z=4, Rf/Rw=0.031/0.044). The organic-inorganic layered perovskite structure features well-ordered sheets of corner-sharing distorted PbCl6 octahedra separated by bilayers of phenethylammonium cations. Tilting and rotation of the PbCl6 octahedra within the perovskite sheets, coupled with organic cation ordering, leads to the unusual in-sheet 2ap×2ap superstructure, where ap is the lattice constant for the ideal cubic perovskite.

Combustion of chlorinated volatile organic compounds (VOCs) using bimetallic chromium-copper supported on modified H-ZSM-5 catalyst.

PubMed

Abdullah, Ahmad Zuhairi; Bakar, Mohamad Zailani Abu; Bhatia, Subhash

2006-02-28

The paper reports on the performance of chromium or/and copper supported on H-ZSM-5(Si/Al = 240) modified with silicon tetrachloride (Cr1.5/SiCl4-Z, Cu1.5/SiCl4-Z and Cr1.0Cu0.5/SiCl4-Z) as catalysts in the combustion of chlorinated VOCs (Cl-VOCs). A reactor operated at a gas hourly space velocity (GHSV) of 32,000 h(-1), a temperature between 100 and 500 degrees C with 2500 ppm of dichloromethane (DCM), trichloromethane (TCM) and trichloroethylene (TCE) is used for activity studies. The deactivation study is conducted at a GHSV of 3800 h(-1), at 400 degrees C for up to 12 h with a feed concentration of 35,000 ppm. Treatment with silicon tetrachloride improves the chemical resistance of H-ZSM-5 against hydrogen chloride. TCM is more reactive compared to DCM but it produces more by-products due to its high chlorine content. The stabilization of TCE is attributed to resonance effects. Water vapor increases the carbon dioxide yield through its role as hydrolysis agent forming reactive carbocations and acting as hydrogen-supplying agent to suppress chlorine-transfer reactions. The deactivation of Cr1.0Cu0.5/SiCl4-Z is mainly due to the chlorination of its metal species, especially with higher Cl/H feed. Coking is limited, particularly with DCM and TCM. In accordance with the Mars-van Krevelen model, the weakening of overall metal reducibility due to chlorination leads to a loss of catalytic activity.

Immobilization of molecular catalysts in supported ionic liquid phases.

PubMed

Van Doorslaer, Charlie; Wahlen, Joos; Mertens, Pascal; Binnemans, Koen; De Vos, Dirk

2010-09-28

In a supported ionic liquid phase (SILP) catalyst system, an ionic liquid (IL) film is immobilized on a high-surface area porous solid and a homogeneous catalyst is dissolved in this supported IL layer, thereby combining the attractive features of homogeneous catalysts with the benefits of heterogeneous catalysts. In this review reliable strategies for the immobilization of molecular catalysts in SILPs are surveyed. In the first part, general aspects concerning the application of SILP catalysts are presented, focusing on the type of catalyst, support, ionic liquid and reaction conditions. Secondly, organic reactions in which SILP technology is applied to improve the performance of homogeneous transition-metal catalysts are presented: hydroformylation, metathesis reactions, carbonylation, hydrogenation, hydroamination, coupling reactions and asymmetric reactions.

Role of Surface Chemistry on Catalyst/Ionomer Interactions for Transition Metal–Nitrogen–Carbon Electrocatalysts

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

Artyushkova, Kateryna; Workman, Michael J.; Matanovic, Ivana

The role of the interaction between doped carbon-based materials and ionic conductors is essential in multiple technologies, from fuel cells and energy storage devices to conductive polymer composites. In this paper, we report how the surface chemistry of transition metal–nitrogen–carbon (MNC) electrocatalysts affects catalyst–ionomer interaction and the resulting structure of cathodes. The cathode structure resulting from these interactions is directly related to the performance in membrane electrode assembly (MEA) fuel cells. To advance the development of platinum group metal (PGM)-free electrodes for the oxygen reduction reaction it is necessary to understand the structure of the catalyst layers with focus onmore » chemistry and distribution of active sites and ionomer morphology. To assess catalyst interaction with an ionomer, X-ray photoelectron spectroscopy is applied to study the chemistry of catalyst layers while density functional theory (DFT) is used to calculate adsorption energies of the ionomer side chain on different nitrogen species. We report that a high surface concentration of hydrogenated nitrogen at the surface of MNC catalysts causes inefficient ionomer morphology, while an abundance of surface oxides promotes both an efficient distribution of active sites and an optimal ionomer–catalyst interface. The critical role of protonation of nitrogen within catalytic layers in inhibiting proton transport during fuel cell operation is also suggested. As a result, this is the first report of the effect the surface chemistry of MNC catalysts, in the presence of the ionomer, has on the structure and performance of MEA electrodes.« less

Role of Surface Chemistry on Catalyst/Ionomer Interactions for Transition Metal–Nitrogen–Carbon Electrocatalysts

DOE PAGES

Artyushkova, Kateryna; Workman, Michael J.; Matanovic, Ivana; ...

2017-12-18

The role of the interaction between doped carbon-based materials and ionic conductors is essential in multiple technologies, from fuel cells and energy storage devices to conductive polymer composites. In this paper, we report how the surface chemistry of transition metal–nitrogen–carbon (MNC) electrocatalysts affects catalyst–ionomer interaction and the resulting structure of cathodes. The cathode structure resulting from these interactions is directly related to the performance in membrane electrode assembly (MEA) fuel cells. To advance the development of platinum group metal (PGM)-free electrodes for the oxygen reduction reaction it is necessary to understand the structure of the catalyst layers with focus onmore » chemistry and distribution of active sites and ionomer morphology. To assess catalyst interaction with an ionomer, X-ray photoelectron spectroscopy is applied to study the chemistry of catalyst layers while density functional theory (DFT) is used to calculate adsorption energies of the ionomer side chain on different nitrogen species. We report that a high surface concentration of hydrogenated nitrogen at the surface of MNC catalysts causes inefficient ionomer morphology, while an abundance of surface oxides promotes both an efficient distribution of active sites and an optimal ionomer–catalyst interface. The critical role of protonation of nitrogen within catalytic layers in inhibiting proton transport during fuel cell operation is also suggested. As a result, this is the first report of the effect the surface chemistry of MNC catalysts, in the presence of the ionomer, has on the structure and performance of MEA electrodes.« less

Ir/KLTL zeolites: Structural characterization and catalysis on n-hexane reforming

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

Triantafillou, N.D.; Gates, B.C.

Ir/KLTL zeolite catalysts were prepared by incipient wetness impregnation of LTL zeolites with [Ir(NH{sub 3}){sub 5}Cl]Cl{sub 2}. The catalysts were characterized by extended X-ray absorption fine structure (EX-AFS) spectroscopy, infrared spectroscopy, and H{sub 2} chemisorption. EXAFS data show that the average Ir cluster size (after treatment at 300{degrees}C in H{sub 2}) increased from about 7 to 20 {Angstrom} as the zeolite K:Al atomic ratio increased from 0.34 to 1.56. Infrared spectra of adsorbed CO show that the electron donation to the Ir increased as the K:Al ratio increased. In contrast to the performance reported for Pt/KLTL zeolites with metal clustersmore » as small as those observed in the present experiments, the Ir/KLTL catalyst has a low selectivity for dehydrocyclization of n-hexane at 440-480{degrees}C and 1 atm with a H{sub 2}: n-hexane feed molar ratio of 6. Instead, the catalysts are selective for hydrogenolysis. The selectivity is insensitive to the K:Al ratio, but the activity for dehydrocyclization is a maximum at a K:Al atomic ratio of about 1. The results show that even the smallest Ir clusters to which electron donation is significant still behave essentially like metallic Ir in the catalytic reactions. 49 refs., 4 figs., 7 tabs.« less

Raman and electronic transport characterization of few- and single-layer-thick α-RuCl3

NASA Astrophysics Data System (ADS)

Zhou, Boyi; Henriksen, Erik

The layered magnetic semiconductor α-RuCl3, having a honeycomb lattice of spin-1/2 moments, has been identified as a potential candidate material to realize the Kitaev quantum spin liquid. In particular, bulk RuCl3 crystals have been studied and found to be on the cusp of manifesting QSL behavior. As the QSL is primarily a two-dimensional phenomenon, and since the layers of RuCl3 are weakly coupled, we propose to create and study a 2D spin-1/2 honeycomb system by isolating single sheets. Here we report the exfoliation of RuCl3 down to few- and single-layer-thick samples, which we characterize by Raman spectroscopy and atomic force microscopy at room temperature. We will also report our progress on measurements of basic electronic transport properties in the 2D RuCl3 system by controlling the chemical potential via gating in a field-effect configuration.

Method for making a uranium chloride salt product

DOEpatents

Miller, William E [Naperville, IL; Tomczuk, Zygmunt [Lockport, IL

2004-10-05

The subject apparatus provides a means to produce UCl.sub.3 in large quantities without incurring corrosion of the containment vessel or associated apparatus. Gaseous Cl is injected into a lower layer of Cd where CdCl.sub.2 is formed. Due to is lower density, the CdCl.sub.2 rises through the Cd layer into a layer of molten LiCl--KCL salt where a rotatable basket containing uranium ingots is suspended. The CdCl.sub.2 reacts with the uranium to form UCl.sub.3 and Cd. Due to density differences, the Cd sinks down to the liquid Cd layer and is reused. The UCl.sub.3 combines with the molten salt. During production the temperature is maintained at about 600.degree. C. while after the uranium has been depleted the salt temperature is lowered, the molten salt is pressure siphoned from the vessel, and the salt product LiCl--KCl-30 mol % UCl.sub.3 is solidified.

Synthesis of Different Layers of Graphene on Stainless Steel Using the CVD Method

NASA Astrophysics Data System (ADS)

Ghaemi, Ferial; Abdullah, Luqman Chuah; Tahir, Paridah Md; Yunus, Robiah

2016-11-01

In this study, different types of graphene, including single-, few-, and multi-layer graphene, were grown on a stainless steel (SS) mesh coated with Cu catalyst by using the chemical vapor deposition (CVD) method. Even though the SS mesh consisted of different types of metals, such as Fe, Ni, and Cr, which can also be used as catalysts, the reason for coating Cu catalyst on the SS surface had been related to the nature of the Cu, which promotes the growth of graphene with high quality and quantity at low temperature and time. The reaction temperature and run time, as the most important parameters of the CVD method, were varied, and thus led to the synthesis of different layers of graphene. Moreover, the presence of single-, few-, and multi-layer graphene was confirmed by employing two techniques, namely transmission electron microscopy (TEM) and Raman spectroscopy. On top of that, electron dispersive X-ray (EDX) was further applied to establish the influence of the CVD parameters on the growth of graphene.

Synthesis of Different Layers of Graphene on Stainless Steel Using the CVD Method.

PubMed

Ghaemi, Ferial; Abdullah, Luqman Chuah; Tahir, Paridah Md; Yunus, Robiah

2016-12-01

In this study, different types of graphene, including single-, few-, and multi-layer graphene, were grown on a stainless steel (SS) mesh coated with Cu catalyst by using the chemical vapor deposition (CVD) method. Even though the SS mesh consisted of different types of metals, such as Fe, Ni, and Cr, which can also be used as catalysts, the reason for coating Cu catalyst on the SS surface had been related to the nature of the Cu, which promotes the growth of graphene with high quality and quantity at low temperature and time. The reaction temperature and run time, as the most important parameters of the CVD method, were varied, and thus led to the synthesis of different layers of graphene. Moreover, the presence of single-, few-, and multi-layer graphene was confirmed by employing two techniques, namely transmission electron microscopy (TEM) and Raman spectroscopy. On top of that, electron dispersive X-ray (EDX) was further applied to establish the influence of the CVD parameters on the growth of graphene.

Preparation of arrays of long carbon nanotubes using catalyst structure

DOEpatents

Zhu, Yuntian T.; Arendt, Paul; Li, Qingwen; Zhang, Xiefie

2016-03-22

A structure for preparing an substantially aligned array of carbon nanotubes include a substrate having a first side and a second side, a buffer layer on the first side of the substrate, a catalyst on the buffer layer, and a plurality of channels through the structure for allowing a gaseous carbon source to enter the substrate at the second side and flow through the structure to the catalyst. After preparing the array, a fiber of carbon nanotubes may be spun from the array. Prior to spinning, the array can be immersed in a polymer solution. After spinning, the polymer can be cured.

Re-examination of the Pt Particle Size Effect on the Oxygen Reduction Reaction for Ultrathin Uniform Pt/C Catalyst Layers without Influence from Nafion

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

Shinozaki, Kazuma; Morimoto, Yu; Pivovar, Bryan S.

The platinum 'particle size effect' on the oxygen reduction reaction (ORR) has been re-evaluated using commercial Pt/C catalysts (2-10 nm Pt particle) and polycrystalline Pt (poly-Pt) in 0.1 M HClO4 with a rotating disk electrode method. Nafion-free catalyst layers were employed to obtain specific activities (SA) that were not perturbed (suppressed) by sulfonate anion adsorption/blocking. By using ultrathin uniform catalyst layers, O2 diffusion limitation was minimized as confirmed from the high SAs of our supported catalysts that were comparable to unsupported sputtered Pt having controlled sizes. The specific activity (SA) steeply increased for the particle sizes in the range -2-10more » nm (0.8-1.8 mA/cm2Pt at 0.9 V vs. RHE) and plateaued over -10 nm to 2.7 mA/cm2Pt for bulk poly-Pt. On the basis of the activity trend for the range of particle sizes studied, it appears that the effect of carbon support on activity is negligible. The experimental results and the concomitant profile of SA vs. particle size was found to be in an agreement to a truncated octahedral particle model that assumes active terrace sites.« less

Method for making oxygen-reducing catalyst layers

DOEpatents

O'Brien, Dennis P.; Schmoeckel, Alison K.; Vernstrom, George D.; Atanasoski, Radoslav; Wood, Thomas E.; O'Neill, David G.

2010-06-22

Methods are provided for making oxygen-reducing catalyst layers, which include simultaneous or sequential stops of physical vapor depositing an oxygen-reducing catalytic material onto a substrate, the catalytic material comprising a transition metal that is substantially free of platinum; and thermally treating the catalytic material. At least one of the physical vapor deposition and the thermal treatment is performed in a processing environment comprising a nitrogen-containing gas.

Confirming the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials by PECVD

NASA Astrophysics Data System (ADS)

Liu, Yulin; Lin, Jinghuang; Jia, Henan; Chen, Shulin; Qi, Junlei; Qu, Chaoqun; Cao, Jian; Feng, Jicai; Fei, Weidong

2017-11-01

In order to confirm the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials (NCMs), here we report a novel strategy to create different Ar+ ion states in situ in plasma enhanced chemical vapor deposition (PECVD) by separating catalyst film from the substrate. Different bombardment environments on either side of the catalyst film were created simultaneously to achieve multi-layered structural NCMs. Results showed that Ar+ ion bombardment is crucial and complex for the growth of NCMs. Firstly, Ar+ ion bombardment has both positive and negative effects on carbon nanotubes (CNTs). On one hand, Ar+ ions can break up the graphic structure of CNTs and suppress thin CNT nucleation and growth. On the other hand, Ar+ ion bombardment can remove redundant carbon layers on the surface of large catalyst particles which is essential for thick CNTs. As a result, the diameter of the CNTs depends on the Ar+ ion state. As for vertically oriented few-layer graphene (VFG), Ar+ ions are essential and can even convert the CNTs into VFG. Therefore, by combining with the catalyst separation method, specific or multi-layered structural NCMs can be obtained by PECVD only by changing the intensity of Ar+ ion bombardment, and these special NCMs are promising in many fields.

Confirming the key role of Ar+ ion bombardment in the growth feature of nanostructured carbon materials by PECVD.

PubMed

Liu, Yulin; Lin, Jinghuang; Jia, Henan; Chen, Shulin; Qi, Junlei; Qu, Chaoqun; Cao, Jian; Feng, Jicai; Fei, Weidong

2017-11-24

In order to confirm the key role of Ar + ion bombardment in the growth feature of nanostructured carbon materials (NCMs), here we report a novel strategy to create different Ar + ion states in situ in plasma enhanced chemical vapor deposition (PECVD) by separating catalyst film from the substrate. Different bombardment environments on either side of the catalyst film were created simultaneously to achieve multi-layered structural NCMs. Results showed that Ar + ion bombardment is crucial and complex for the growth of NCMs. Firstly, Ar + ion bombardment has both positive and negative effects on carbon nanotubes (CNTs). On one hand, Ar + ions can break up the graphic structure of CNTs and suppress thin CNT nucleation and growth. On the other hand, Ar + ion bombardment can remove redundant carbon layers on the surface of large catalyst particles which is essential for thick CNTs. As a result, the diameter of the CNTs depends on the Ar + ion state. As for vertically oriented few-layer graphene (VFG), Ar + ions are essential and can even convert the CNTs into VFG. Therefore, by combining with the catalyst separation method, specific or multi-layered structural NCMs can be obtained by PECVD only by changing the intensity of Ar + ion bombardment, and these special NCMs are promising in many fields.

4D in situ visualization of electrode morphology changes during accelerated degradation in fuel cells by X-ray computed tomography

NASA Astrophysics Data System (ADS)

White, Robin T.; Wu, Alex; Najm, Marina; Orfino, Francesco P.; Dutta, Monica; Kjeang, Erik

2017-05-01

A four-dimensional visualization approach, featuring three dimensions in space and one dimension in time, is proposed to study local electrode degradation effects during voltage cycling in fuel cells. Non-invasive in situ micro X-ray computed tomography (XCT) with a custom fuel cell fixture is utilized to track the same cathode catalyst layer domain throughout various degradation times from beginning-of-life (BOL) to end-of-life (EOL). With this unique approach, new information regarding damage features and trends are revealed, including crack propagation and catalyst layer thinning being quantified by means of image processing and analysis methods. Degradation heterogeneities as a result of local environmental variations under land and channel are also explored, with a higher structural degradation rate under channels being observed. Density and compositional changes resulting from carbon corrosion and catalyst layer collapse and thinning are observed by changes in relative X-ray attenuation from BOL to EOL, which also indicate possible vulnerable regions where crack initiation and propagation may occur. Electrochemical diagnostics and morphological features observed by micro-XCT are correlated by additionally collecting effective catalyst surface area, double layer capacitance, and polarization curves prior to imaging at various stages of degradation.

Enhanced catalyst stability for cyclic co methanation operations

DOEpatents

Risch, Alan P.; Rabo, Jule A.

1983-01-01

Carbon monoxide-containing gas streams are passed over a catalyst to deposit a surface layer of active surface carbon thereon essentially without the formation of inactive coke. The active carbon is thereafter reacted with steam or hydrogen to form methane. Enhanced catalyst stability for long term, cyclic operation is obtained by the incorporation of an alkali or alkaline earth dopant in a silica binding agent added to the catalyst-support additive composition.

Deconstruction of Lignin Model Compounds and Biomass-Derived Lignin using Layered Double Hydroxide Catalysts

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

Chmely, S. C.; McKinney, K. A.; Lawrence, K. R.

2013-01-01

Lignin is an underutilized value stream in current biomass conversion technologies because there exist no economic and technically feasible routes for lignin depolymerization and upgrading. Base-catalyzed deconstruction (BCD) has been applied for lignin depolymerization (e.g., the Kraft process) in the pulp and paper industry for more than a century using aqueous-phase media. However, these efforts require treatment to neutralize the resulting streams, which adds significantly to the cost of lignin deconstruction. To circumvent the need for downstream treatment, here we report recent advances in the synthesis of layered double hydroxide and metal oxide catalysts to be applied to the BCDmore » of lignin. These catalysts may prove more cost-effective than liquid-phase, non-recyclable base, and their use obviates downstream processing steps such as neutralization. Synthetic procedures for various transition-metal containing catalysts, detailed kinetics measurements using lignin model compounds, and results of the application of these catalysts to biomass-derived lignin will be presented.« less

Transesterification of edible, non-edible and used cooking oils for biodiesel production using calcined layered double hydroxides as reusable base catalysts.

PubMed

Sankaranarayanan, Sivashunmugam; Antonyraj, Churchil A; Kannan, S

2012-04-01

Fatty acid methyl esters (FAME) were produced from edible, non-edible and used cooking oils with different fatty acid contents by transesterification with methanol using calcined layered double hydroxides (LDHs) as solid base catalysts. Among the catalysts, calcined CaAl2-LDH (hydrocalumite) showed the highest activity with >90% yield of FAME using low methanol:oil molar ratio (<6:1) at 65 °C in 5 h. The activity of the catalyst was attributed to its high basicity as supported by Hammett studies and CO(2)-TPD measurements. The catalyst was successfully reused in up to four cycles. Some of the properties such as density, viscosity, neutralization number and glycerol content of the obtained biodiesel matched well with the standard DIN values. It is concluded that a scalable heterogeneously catalyzed process for production of biodiesel in high yields from a wide variety of triglyceride oils including used oils is possible using optimized conditions. Copyright © 2012 Elsevier Ltd. All rights reserved.

Solid-State Water Electrolysis with an Alkaline Membrane

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

Leng, YJ; Chen, G; Mendoza, AJ

2012-06-06

We report high-performance, durable alkaline membrane water electrolysis in a solid-state cell. An anion exchange membrane (AEM) and catalyst layer ionomer for hydroxide ion conduction were used without the addition of liquid electrolyte. At 50 degrees C, an AEM electrolysis cell using iridium oxide as the anode catalyst and Pt black as the cathode catalyst exhibited a current density of 399 mA/cm(2) at 1.80 V. We found that the durability of the AEM-based electrolysis cell could be improved by incorporating a highly durable ionomer in the catalyst layer and optimizing the water feed configuration. We demonstrated an AEM-based electrolysis cellmore » with a lifetime of > 535 h. These first-time results of water electrolysis in a solid-state membrane cell are promising for low-cost, scalable hydrogen production.« less

Secondary benzylation with benzyl alcohols catalyzed by a high-valent heterobimetallic Ir-Sn complex.

PubMed

Podder, Susmita; Choudhury, Joyanta; Roy, Sujit

2007-04-13

A highly efficient secondary benzylation procedure has been demonstrated using a high-valent heterobimetallic complex [Ir2(COD)2(SnCl3)2(Cl)2(mu-Cl)2] 1 as the catalyst in 1,2-dichloroethane to afford the corresponding benzylated products in moderate to excellent yields. The reaction was performed not only with carbon nucleophiles (arenes and heteroarenes) but also with oxygen (alcohol), nitrogen (amide and sulfonamide), and sulfur (thiol) nucleophiles. Mechanistic investigation showed the intermediacy of the ether in this reaction. An electrophilic mechanism is proposed from Hammett correlation.

NiMn layered double hydroxide nanosheets/NiCo2O4 nanowires with surface rich high valence state metal oxide as an efficient electrocatalyst for oxygen evolution reaction

NASA Astrophysics Data System (ADS)

Yang, Liting; Chen, Lin; Yang, Dawen; Yu, Xu; Xue, Huaiguo; Feng, Ligang

2018-07-01

High valence transition metal oxide is significant for anode catalyst of proton membrane water electrolysis technique. Herein, we demonstrate NiMn layered double hydroxide nanosheets/NiCo2O4 nanowires hierarchical nanocomposite catalyst with surface rich high valence metal oxide as an efficient catalyst for oxygen evolution reaction. A low overpotential of 310 mV is needed to drive a 10 mA cm-2 with a Tafel slope of 99 mV dec-1, and a remarkable stability during 8 h is demonstrated in a chronoamperometry test. Theoretical calculation displays the change in the rate-determining step on the nanocomposite electrode in comparison to NiCo2O4 nanowires alone. It is found high valence Ni and Mn oxide in the catalyst system can efficiently facilitate the charge transport across the electrode/electrolyte interface. The enhanced electrical conductivity, more accessible active sites and synergistic effects between NiMn layered double hydroxide nanosheets and NiCo2O4 nanowires can account for the excellent oxygen evolution reaction. The catalytic performance is comparable to most of the best non-noble catalysts and IrO2 noble catalyst, indicating the promising applications in water-splitting technology. It is an important step in the development of hierarchical nanocomposites by surface valence state tuning as an alternative to noble metals for oxygen evolution reaction.

Chemical Reactions and Properties of Organosilicon Compounds Related to New Materials.

DTIC Science & Technology

1985-10-31

out. The compound behaves like an olefin in some reactions, for in- stance addition of hydrogen halides or chlorine: C1 2 HCI Mes 2 SiCl-SiClMes2...polymers have been synthesized which contain some silicon atoms bonded to hydrogen . These become crosslinked when mixed with substances containing several...and highly efficient catalysts, very small amounts are required in this process. Moreover, photocatalysis using polysilanes produces polymers with

Platinum and palladium incorporation into phosphate/viologen-phosphonates of zirconium and hafnium: synthesis and characterization

NASA Astrophysics Data System (ADS)

Dokoutchaev, Alexandre; Krishnan, Venkatesan V.; Thompson, Mark E.; Balasubramanian, Mahalingam

1998-10-01

We have continued previous efforts to synthesize and characterize a microporous metal phosphate/viologen-phosphonate compound, [(ZrF) 2(PO 4)(O 3PCH 2CH 2-4,4'-bipyridinium-CH 2CH 2PO 3)] ṡF·2H 2O, ZrPO PV. A derivative of this material has been shown to be an efficient catalyst for the production of hydrogen peroxide from hydrogen and oxygen. This paper has two objectives—one is to optimize the synthetic routes leading to the preparation of MPO PV (M=zirconium or hafnium) and the second is to characterize MPO PV and the derivatives formed by Pt or Pd incorporation by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), inductively coupled plasma-mass spectrometry (ICP-MS) and X-ray absorption fine structure analysis (XAFS). Powder XRD data have shown much higher crystallinity in MPO PV samples prepared by hydrothermal methods than those prepared by reflux methods. In the hydrothermal synthesis, the amount of mineralizer (HF) present controlled the crystallite size (as determined from TEM micrographs). The larger the quantity of HF in the bomb, the larger the size of the crystals but the lower the yield of the MPO PV material. Crystal sizes of about 2.5 μm in length and 0.15 μm in diameter have been made with very large quantities of HF as mineralizer (10 times the required stoichiometric amount). Ion exchange of the material by PdCl 42- has resulted in the incorporation of the PdCl 42- ions in place of X - in the material. This has been confirmed by XAFS studies that demonstrate the oxidation state of Pd is 2+ and show four Cl atoms bound to Pd. Upon reduction it has been confirmed (by XAFS) that the palladium exists as metal with oxidation state of zero. Ion exchange by PdCl 42- and PtCl 42- and subsequent reduction of the material suspension by hydrogen result in the formation of separate Pt and Pd colloids in the close vicinity of the crystallites. TEM micrographs show clearly that the Pt metal obtained after reduction forms much smaller particles in comparison to Pd. These exchanged and reduced materials have also been investigated as catalysts for production of hydrogen peroxide in mixed acetone/water medium. The production of hydrogen peroxide is enhanced by increasing amounts of Pd in the catalyst. Hydrogen peroxide yields are the highest for catalysts containing only Pd as opposed to a mixture of Pt and Pd.

Recent Advances in Catalyst Accelerated Stress Tests for Polymer Electrolyte Membrane Fuel Cells

DOE PAGES

Stariha, Sarah; Macauley, Natalia; Sneed, Brian T.; ...

2018-03-15

The U.S. Department of Energy (DOE) set the 2020 durability target for polymer electrolyte membrane fuel cell transportation applications at 5000 hours. Since it is impractical to test every fuel cell for this length of time, there is ever increasing interest in developing accelerated stress tests (ASTs) that can accurately simulate the material component degradation in the membrane electrode assembly (MEA) observed under automotive operating conditions, but over a much shorter time frame. In this study, a square-wave catalyst AST was examined that shows a 5X time acceleration factor over the triangle-wave catalyst AST and a 25X time acceleration factormore » over the modified wet drive-cycle catalyst durability protocol, significantly decreasing the testing time. These acceleration factors were correlated to the platinum (Pt) particle size increase and associated decrease in electrochemical surface area (ECSA). This square-wave AST has been adopted by the DOE as a standard protocol to evaluate catalyst durability. We also compare three catalyst-durability protocols using state-of-the-art platinum-cobalt catalysts supported on high surface area carbon (SOA Pt-Co/HSAC) in the cathode catalyst layer. The results for each of the three tests showed both catalyst particle size increase and transition metal leaching. Moreover the acceleration factors for the alloy catalysts were smaller due to Co leaching being the predominant mechanism of voltage decay in ~5 nm PtCo/C catalysts. Finally, an extremely harsh carbon corrosion AST was run using the same SOA Pt-Co/HSAC catalyst. This showed minimal change in particle size and a low percentage Co loss from the cathode catalyst particles, despite a significant loss in catalyst layer thickness and cell performance. The carbon corrosion rates during these various ASTs were directly measured by monitoring the CO 2 emission from the cathode, further confirming the ability of the square-wave AST to evaluate the electro-catalyst independently of the support.« less

Recent Advances in Catalyst Accelerated Stress Tests for Polymer Electrolyte Membrane Fuel Cells

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

Stariha, Sarah; Macauley, Natalia; Sneed, Brian T.

The U.S. Department of Energy (DOE) set the 2020 durability target for polymer electrolyte membrane fuel cell transportation applications at 5000 hours. Since it is impractical to test every fuel cell for this length of time, there is ever increasing interest in developing accelerated stress tests (ASTs) that can accurately simulate the material component degradation in the membrane electrode assembly (MEA) observed under automotive operating conditions, but over a much shorter time frame. In this study, a square-wave catalyst AST was examined that shows a 5X time acceleration factor over the triangle-wave catalyst AST and a 25X time acceleration factormore » over the modified wet drive-cycle catalyst durability protocol, significantly decreasing the testing time. These acceleration factors were correlated to the platinum (Pt) particle size increase and associated decrease in electrochemical surface area (ECSA). This square-wave AST has been adopted by the DOE as a standard protocol to evaluate catalyst durability. We also compare three catalyst-durability protocols using state-of-the-art platinum-cobalt catalysts supported on high surface area carbon (SOA Pt-Co/HSAC) in the cathode catalyst layer. The results for each of the three tests showed both catalyst particle size increase and transition metal leaching. Moreover the acceleration factors for the alloy catalysts were smaller due to Co leaching being the predominant mechanism of voltage decay in ~5 nm PtCo/C catalysts. Finally, an extremely harsh carbon corrosion AST was run using the same SOA Pt-Co/HSAC catalyst. This showed minimal change in particle size and a low percentage Co loss from the cathode catalyst particles, despite a significant loss in catalyst layer thickness and cell performance. The carbon corrosion rates during these various ASTs were directly measured by monitoring the CO 2 emission from the cathode, further confirming the ability of the square-wave AST to evaluate the electro-catalyst independently of the support.« less

Palladium-catalyzed asymmetric quaternary stereocenter formation.

PubMed

Gottumukkala, Aditya L; Matcha, Kiran; Lutz, Martin; de Vries, Johannes G; Minnaard, Adriaan J

2012-05-29

An efficient palladium catalyst is presented for the formation of benzylic quaternary stereocenters by conjugate addition of arylboronic acids to a variety of β,β-disubstituted carbocyclic, heterocyclic, and acyclic enones. The catalyst is readily prepared from PdCl(2), PhBOX, and AgSbF(6), and provides products in up to 99% enantiomeric excess, with good yields. Based on this strategy, (-)-α-cuparenone has been prepared in only two steps. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrode-Modified Zeolites - Electrode Microstructures Contained in and on a Heterogeneous Catalyst

DTIC Science & Technology

1988-07-15

zeolite Type Y and Pt supported on gamma-alumina. The electrolytic response of zeolite-supported Pt in the absence of added electrolyte salt for water or...character of metals at sizes where’ bulk metallic properties may not be exhibited. Furthermore, electrolyses are now allowed using loadings of catalysts which...in water until the filtrate tested negatively for Cl with AgNO 3; PtY was then dried a- 135 C. Equilibrium exchnge occurs at these low weight

An intermolecular heterobimetallic system for photocatalytic water reduction.

PubMed

Hansen, Sven; Klahn, Marcus; Beweries, Torsten; Rosenthal, Uwe

2012-04-01

Teamwork: A new intermolecular heterobimetallic system for photocatalytic water reduction, consisting of a photosensitizer of the type [Ru(bpy)(2)(L)](PF(6))(2) (L=bidentate ligand), a dichloro palladium complex PdCl(2)(L) serving as the water reduction catalyst, and triethyl amine as electron donor, is presented. Variations of the ligand as well as of the palladium source results in a significant improvement of the performance of the catalyst system. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Light-Driven Water Splitting by a Covalently Linked Ruthenium-Based Chromophore–Catalyst Assembly

DOE PAGES

Sherman, Benjamin D.; Xie, Yan; Sheridan, Matthew V.; ...

2016-12-09

The preparation and characterization of new Ru(II) polypyridyl-based chromophore–catalyst assemblies, [(4,4'-PO 3H 2-bpy) 2Ru(4-Mebpy-4'-epic)Ru(bda)(pic)] 2+ (1, bpy = 2,2'-bipyridine; 4-Mebpy-4'-epic = 4-(4-methylbipyridin-4'-yl-ethyl)-pyridine; bda = 2,2'-bipyridine-6,6'-dicarboxylate; pic = 4-picoline), and [(bpy) 2Ru(4-Mebpy-4'-epic)Ru(bda)(pic)] 2+ (1') are described, as is the application of 1 in a dye-sensitized photoelectrosynthesis cell (DSPEC) for solar water splitting. Furthermore, on SnO 2/TiO 2 core–shell electrodes in a DSPEC configuration with a Pt cathode, the chromophore–catalyst assembly undergoes light-driven water oxidation at pH 5.7 in a 0.1 M acetate buffer, 0.5 M in NaClO 4. We observed photocurrents of ~0.85 mA cm –2, with illumination by a 100more » mW cm –2 white light source, after 30 s under a 0.1 V vs Ag/AgCl applied bias with a faradaic efficiency for O 2 production of 74% measured over a 5 min illumination period.« less

Light-Driven Water Splitting by a Covalently Linked Ruthenium-Based Chromophore–Catalyst Assembly

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

Sherman, Benjamin D.; Xie, Yan; Sheridan, Matthew V.

The preparation and characterization of new Ru(II) polypyridyl-based chromophore–catalyst assemblies, [(4,4'-PO 3H 2-bpy) 2Ru(4-Mebpy-4'-epic)Ru(bda)(pic)] 2+ (1, bpy = 2,2'-bipyridine; 4-Mebpy-4'-epic = 4-(4-methylbipyridin-4'-yl-ethyl)-pyridine; bda = 2,2'-bipyridine-6,6'-dicarboxylate; pic = 4-picoline), and [(bpy) 2Ru(4-Mebpy-4'-epic)Ru(bda)(pic)] 2+ (1') are described, as is the application of 1 in a dye-sensitized photoelectrosynthesis cell (DSPEC) for solar water splitting. Furthermore, on SnO 2/TiO 2 core–shell electrodes in a DSPEC configuration with a Pt cathode, the chromophore–catalyst assembly undergoes light-driven water oxidation at pH 5.7 in a 0.1 M acetate buffer, 0.5 M in NaClO 4. We observed photocurrents of ~0.85 mA cm –2, with illumination by a 100more » mW cm –2 white light source, after 30 s under a 0.1 V vs Ag/AgCl applied bias with a faradaic efficiency for O 2 production of 74% measured over a 5 min illumination period.« less

Methanol electro-oxidation on platinum modified tungsten carbides in direct methanol fuel cells: a DFT study.

PubMed

Sheng, Tian; Lin, Xiao; Chen, Zhao-Yang; Hu, P; Sun, Shi-Gang; Chu, You-Qun; Ma, Chun-An; Lin, Wen-Feng

2015-10-14

In exploration of low-cost electrocatalysts for direct methanol fuel cells (DMFCs), Pt modified tungsten carbide (WC) materials are found to be great potential candidates for decreasing Pt usage whilst exhibiting satisfactory reactivity. In this work, the mechanisms, onset potentials and activity for electrooxidation of methanol were studied on a series of Pt-modified WC catalysts where the bare W-terminated WC(0001) substrate was employed. In the surface energy calculations of a series of Pt-modified WC models, we found that the feasible structures are mono- and bi-layer Pt-modified WCs. The tri-layer Pt-modified WC model is not thermodynamically stable where the top layer Pt atoms tend to accumulate and form particles or clusters rather than being dispersed as a layer. We further calculated the mechanisms of methanol oxidation on the feasible models via methanol dehydrogenation to CO involving C-H and O-H bonds dissociating subsequently, and further CO oxidation with the C-O bond association. The onset potentials for the oxidation reactions over the Pt-modified WC catalysts were determined thermodynamically by water dissociation to surface OH* species. The activities of these Pt-modified WC catalysts were estimated from the calculated kinetic data. It has been found that the bi-layer Pt-modified WC catalysts may provide a good reactivity and an onset oxidation potential comparable to pure Pt and serve as promising electrocatalysts for DMFCs with a significant decrease in Pt usage.

A Semi-Empirical Two Step Carbon Corrosion Reaction Model in PEM Fuel Cells

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

Young, Alan; Colbow, Vesna; Harvey, David

2013-01-01

The cathode CL of a polymer electrolyte membrane fuel cell (PEMFC) was exposed to high potentials, 1.0 to 1.4 V versus a reversible hydrogen electrode (RHE), that are typically encountered during start up/shut down operation. While both platinum dissolution and carbon corrosion occurred, the carbon corrosion effects were isolated and modeled. The presented model separates the carbon corrosion process into two reaction steps; (1) oxidation of the carbon surface to carbon-oxygen groups, and (2) further corrosion of the oxidized surface to carbon dioxide/monoxide. To oxidize and corrode the cathode catalyst carbon support, the CL was subjected to an accelerated stressmore » test cycled the potential from 0.6 VRHE to an upper potential limit (UPL) ranging from 0.9 to 1.4 VRHE at varying dwell times. The reaction rate constants and specific capacitances of carbon and platinum were fitted by evaluating the double layer capacitance (Cdl) trends. Carbon surface oxidation increased the Cdl due to increased specific capacitance for carbon surfaces with carbon-oxygen groups, while the second corrosion reaction decreased the Cdl due to loss of the overall carbon surface area. The first oxidation step differed between carbon types, while both reaction rate constants were found to have a dependency on UPL, temperature, and gas relative humidity.« less

Multi-phase models for water and thermal management of proton exchange membrane fuel cell: A review

NASA Astrophysics Data System (ADS)

Zhang, Guobin; Jiao, Kui

2018-07-01

The 3D (three-dimensional) multi-phase CFD (computational fluid dynamics) model is widely utilized in optimizing water and thermal management of PEM (proton exchange membrane) fuel cell. However, a satisfactory 3D multi-phase CFD model which is able to simulate the detailed gas and liquid two-phase flow in channels and reflect its effect on performance precisely is still not developed due to the coupling difficulties and computation amount. Meanwhile, the agglomerate model of CL (catalyst layer) should also be added in 3D CFD model so as to better reflect the concentration loss and optimize CL structure in macroscopic scale. Besides, the effect of thermal management is perhaps underestimated in current 3D multi-phase CFD simulations due to the lack of coolant channel in computation domain and constant temperature boundary condition. Therefore, the 3D CFD simulations in cell and stack levels with convection boundary condition are suggested to simulate the water and thermal management more accurately. Nevertheless, with the rapid development of PEM fuel cell, current 3D CFD simulations are far from practical demand, especially at high current density and low to zero humidity and for the novel designs developed recently, such as: metal foam flow field, 3D fine mesh flow field, anode circulation etc.

Defect-rich Ni-Ti layered double hydroxide as a highly efficient support for Au nanoparticles in base-free and solvent-free selective oxidation of benzyl alcohol.

PubMed

Liu, Mengran; Fan, Guoli; Yu, Jiaying; Yang, Lan; Li, Feng

2018-04-17

Tuning the surface properties of supported metal catalysts is of vital importance for governing their catalytic performances in nanocatalysis. Here, we report highly dispersed nanometric gold nanoparticles (NPs) supported on Ni-Ti layered double hydroxides (NiTi-LDHs), which were employed in solvent-free and base-free selective oxidation of benzyl alcohol. A series of characterization techniques demonstrated that defect-rich NiTi-LDHs could efficiently stabilize Au NPs and decrease surface electron density of Au NPs. The as-formed Au/NiTi-LDH catalyst with a Ni/Ti molar ratio of 3 : 1 and an Au loading of 0.71 wt% yielded the highest turnover frequency value of ∼4981 h-1 at 120 °C among tested Au/NiTi-LDH catalysts with different Ni/Ti molar ratios, along with a high benzaldehyde selectivity of 98%. High catalytic efficiency of the catalyst was mainly correlated with surface cooperation between unique defects (i.e. defective Ti3+ species and oxygen vacancies) and abundant hydroxyl groups on the brucite-like layers of the NiTi-LDH support, which could lead to the preferential adsorption and activation of an alcohol hydroxyl moiety in benzyl alcohol and oxygen molecule, as well as the formation of more electron-deficient Ni3+ and Au0 species on the catalyst surface. Furthermore, the present Au/NiTi-LDH catalyst tolerated the oxidation of a wide variety of substrate structures into the corresponding aldehydes, acids or ketones. Our primary results illustrate that defect-rich NiTi-LDHs are promising supports which can efficiently modify surface structure and electronic properties of supported metal catalysts and consequently improve their catalytic performances.

Effect of the relationship between particle size, inter-particle distance, and metal loading of carbon supported fuel cell catalysts on their catalytic activity

NASA Astrophysics Data System (ADS)

Corradini, Patricia Gon; Pires, Felipe I.; Paganin, Valdecir A.; Perez, Joelma; Antolini, Ermete

2012-09-01

The effect of the relationship between particle size ( d), inter-particle distance ( x i ), and metal loading ( y) of carbon supported fuel cell Pt or PtRu catalysts on their catalytic activity, based on the optimum d (2.5-3 nm) and x i / d (>5) values, was evaluated. It was found that for y < 30 wt%, the optimum values of both d and x i / d can be always obtained. For y ≥ 30 wt%, instead, the positive effect of a thinner catalyst layer of the fuel cell electrode than that using catalysts with y < 30 wt% is concomitant to a decrease of the effective catalyst surface area due to an increase of d and/or a decrease of x i / d compared to their optimum values, with in turns gives rise to a decrease in the catalytic activity. The effect of the x i / d ratio has been successfully verified by experimental results on ethanol oxidation on PtRu/C catalysts with same particle size and same degree of alloying but different metal loading. Tests in direct ethanol fuel cells showed that, compared to 20 wt% PtRu/C, the negative effect of the lower x i / d on the catalytic activity of 30 and 40 wt% PtRu/C catalysts was superior to the positive effect of the thinner catalyst layer.

Constructing Sheet-On-Sheet Structured Graphitic Carbon Nitride/Reduced Graphene Oxide/Layered MnO₂ Ternary Nanocomposite with Outstanding Catalytic Properties on Thermal Decomposition of Ammonium Perchlorate.

PubMed

Xu, Jianhua; Li, Dongnan; Chen, Yu; Tan, Linghua; Kou, Bo; Wan, Fushun; Jiang, Wei; Li, Fengsheng

2017-12-15

We unprecedentedly report that layered MnO₂ nanosheets were in situ formed onto the surface of covalently bonded graphitic carbon nitride/reduced graphene oxide nanocomposite (g-C₃N₄/rGO), forming sheet-on-sheet structured two dimension (2D) graphitic carbon nitride/reduced graphene oxide/layered MnO₂ ternary nanocomposite (g-C₃N₄/rGO/MnO₂) with outstanding catalytic properties on thermal decomposition of ammonium perchlorate (AP). The covalently bonded g-C₃N₄/rGO was firstly prepared by the calcination of graphene oxide-guanidine hydrochloride precursor (GO-GndCl), following by its dispersion into the KMnO₄ aqueous solution to construct the g-C₃N₄/rGO/MnO₂ ternary nanocomposite. FT-IR, XRD, Raman as well as the XPS results clearly demonstrated the chemical interaction between g-C₃N₄, rGO and MnO₂. TEM and element mapping indicated that layered g-C₃N₄/rGO was covered with thin MnO₂ nanosheets. Furthermore, the obtained g-C₃N₄/rGO/MnO₂ nanocomposite exhibited promising catalytic capacity on thermal decomposition of AP. Upon addition of 2 wt % g-C₃N₄/rGO/MnO₂ ternary nanocomposite as catalyst, the thermal decomposition temperature of AP was largely decreased up by 142.5 °C, which was higher than that of pure g-C₃N₄, g-C₃N₄/rGO and MnO₂, respectively, demonstrating the synergistic catalysis of the as-prepared nanocomposite.

I. Hole-transporting dendrimers and their use in organic light-emitting devices (OLEDs) and II. Novel layered catalysts containing bipyridinium and zero-valent metal species

NASA Astrophysics Data System (ADS)

Koene, Shannon Carol

A series of polyaromatic ether/ester dendrimers containing a hole transporting naphthylphenylbenzyl amine at the periphery and a variety of fluorescent dyes at the core has been studied in an effort to observe energy transfer in these species. The dyes incorporated in these dendrimers include 1,4-dihydroxyanthraquinone (quinizarin), Coumarin 343, and a benzopentathiophene. These dendrimers have been incorporated into both single layer and heterostructure organic light emitting devices (OLEDs). In the case of first generation dendrimer OLEDs, excimer/exciplex formation was predominant. In third generation dendrimers, complete energy transfer from the periphery to the dye at the core was observed both in photoluminescence spectra and electroluminescence in OLEDs. Dendrimers containing different dye cores can be combined to achieve color mixing/tuning. In addition, layered catalysts were prepared via both covalent and electrostatic means to achieve the catalytic production of hydrogen peroxide from hydrogen and oxygen. Covalent catalysts were prepared by first growing layers of zirconium and a bipyridinium containing bisphosphonate onto silica particles. Palladium and/or platinum was ion-exchanged into the structure and reduced to the zero valent metal by hydrogen gas. A second set of catalysts was prepared by electrostatically depositing polycations/polyanions onto carboxylate or amine functionalized polystyrene microspheres. Anionic colloidal particles were adsorbed to the polycationic surface. An octacationic viologen oligomer was used in an attempt to increase the affinity of adsorption of the Pd particles to the surface of the microspheres. Catalytic studies of both types of catalysts are herein reported.

Enhanced MEA Performance for PEMFCs under Low Relative Humidity and Low Oxygen Content Conditions via Catalyst Functionalization

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

Xin, Le; Yang, Fan; Xie, Jian

2017-01-01

This work demonstrates that functionalizing annealed-Pt/Ketjen black EC300j (a-Pt/KB) and dealloyed-PtNi/Ketjen black EC300j (d-PtNi/KB) catalysts using p-phenyl sulfonic acid can effectively enhance performance in the membrane electrode assemblies (MEAs) of proton exchange membrane fuel cells (PEMFCs). The functionalization increased the size of both Pt and PtNi catalyst particles and resulted in the further leaching of Ni from the PtNi catalyst while promoting the formation of nanoporous PtNi nanoparticles. The size of the SO3H-Pt/KB and SO3H-PtNi/KB carbon-based aggregates decreased dramatically, leading to the formation of catalyst layers with narrower pore size distributions.MEA tests highlighted the benefits of the surface functionalization, inmore » which the cells with SO3H-Pt/KB and SO3H-PtNi/KB cathode catalysts showed superior high current density performance under reduced RH conditions, in comparison with cells containing annealed Pt/KB (a-Pt/KB) and de-alloyed PtNi/KB (d-PtNi/KB) catalysts. The performance improvement was particularly evident when using reactant gases with low relative humidity, indicating that the hydrophilic functional groups on the carbon improved the water retention in the cathode catalyst layer. These results show a new avenue for enhancing catalyst performance for the next generation of catalytic materials for PEMFCs.« less

Stabilized CdSe-CoPi composite photoanode for light-assisted water oxidation by transformation of a CdSe/cobalt metal thin film.

PubMed

Costi, Ronny; Young, Elizabeth R; Bulović, Vladimir; Nocera, Daniel G

2013-04-10

Integration of water splitting catalysts with visible-light-absorbing semiconductors would enable direct solar-energy-to-fuel conversion schemes such as those based on water splitting. A disadvantage of some common semiconductors that possess desirable optical bandgaps is their chemical instability under the conditions needed for oxygen evolution reaction (OER). In this study, we demonstrate the dual benefits gained from using a cobalt metal thin-film as the precursor for the preparation of cobalt-phosphate (CoPi) OER catalyst on cadmium chalcogenide photoanodes. The cobalt layer protects the underlying semiconductor from oxidation and degradation while forming the catalyst and simultaneously facilitates the advantageous incorporation of the cadmium chalcogenide layer into the CoPi layer during continued processing of the electrode. The resulting hybrid material forms a stable photoactive anode for light-assisted water splitting.

Transfer-free synthesis of multilayer graphene using a single-step process in an evaporator and formation confirmation by laser mode-locking.

PubMed

Kim, Won-Jun; Debnath, Pulak C; Lee, Junsu; Lee, Ju Han; Lim, Dae-Soon; Song, Yong-Won

2013-09-13

Multilayer graphene is synthesized by a simplified process employing an evaporator in which a target substrate is deposited with a Ni catalyst layer before being heated to grow graphene directly. Carbon atoms adsorbed onto the surface of the Ni source as impurities from the atmosphere are incorporated into the catalyst layer during the deposition, and diffuse toward the catalyst/substrate interface, where they crystallize as graphene with a thickness of less than 2 nm. The need for a transfer process and external carbon supply is eliminated. The graphene is characterized by conventional analysis approaches, including nano-scale visualization and Raman spectroscopy, and utilizing photonics, graphene-functionalized passive laser mode-locking is demonstrated to confirm the successful synthesis of the graphene layer, resulting in an operating center wavelength of 1569.4 nm, a pulse duration of 1.35 ps, and a repetition rate of 31.6 MHz.

Patterned carbon nanotubes fabricated by the combination of microcontact printing and diblock copolymer micelles.

PubMed

Xu, Peng; Ji, Xin; Qi, Junlei; Yang, Hongmin; Zheng, Weitao; Abetz, Volker; Jiang, Shimei; Shen, Jiacong

2010-01-01

A convenient approach to synthesize patterned carbon nanotubes (CNTs) of three morphologies on printed substrates by combination of microcontact printing (microCP) and a plasma-enhanced chemical vapor deposition (PECVD) process is presented. Micelles of polystyrene-block-poly-(2-vinylpyridine) (PS-b-P2VP) in toluene were used as nanoreactors to fabricate FeCl3 in the core domains, and the complex solution was used as an ink to print films with polydimethylsiloxane (PDMS) stamps, different morphologies (porous, dots and stripes patterns) of the FeCl3-loaded micellar films were left onto silicon substrates after printed. After removing the polymer by thermal decomposition, the left iron oxide cluster arrays on the substrate were used as catalysts for the growth of CNTs by the process of PECVD, where the CNTs uniformly distributed on the substrates according to the morphologies of patterned catalysts arrays.

An Iron(II)(1,3-bis(2'-pyridylimino)isoindoline) Complex as a Catalyst for Substrate Oxidation with H2O2. Evidence for a Transient Peroxodiiron(III) Species.

PubMed

Pap, József S; Cranswick, Matthew A; Balogh-Hergovich, E; Baráth, Gábor; Giorgi, Michel; Rohde, Gregory T; Kaizer, József; Speier, Gábor; Que, Lawrence

2013-08-01

The complex [Fe(indH)(solvent) 3 ](ClO 4 ) 2 ( 1 ) has been isolated from the reaction of equimolar amounts of 1,3-bis(2'-pyridylimino)isoindoline (indH) and Fe(ClO 4 ) 2 in acetonitrile and characterized by X-ray crystallography and several spectroscopic techniques. It is a suitable catalyst for the oxidation of thioanisoles and benzyl alcohols with H 2 O 2 as the oxidant. Hammett correlations and kinetic isotope effect experiments support the involvement of an electrophilic metal-based oxidant. A metastable green species ( 2 ) is observed when 1 is reacted with H 2 O 2 at -40 °C, which has been characterized to have a Fe III ( μ -O)( μ -O 2 )Fe III core on the basis of UV-Vis, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopic data.

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

DOE PAGES

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

2017-04-25

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

Towards ALD thin film stabilized single-atom Pd 1 catalysts

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

Piernavieja-Hermida, Mar; Lu, Zheng; White, Anderson

Supported precious metal single-atom catalysts have shown interesting activity and selectivity in recent studies. However, agglomeration of these highly mobile mononuclear surface species can eliminate their unique catalytic properties. In this paper, we study a strategy for synthesizing thin film stabilized single-atom Pd 1 catalysts using atomic layer deposition (ALD). The thermal stability of the Pd 1 catalysts is significantly enhanced by creating a nanocavity thin film structure. In situ infrared spectroscopy and Pd K-edge X-ray absorption spectroscopy (XAS) revealed that the Pd 1 was anchored on the surface through chlorine sites. The thin film stabilized Pd 1 catalysts weremore » thermally stable under both oxidation and reduction conditions. The catalytic performance in the methanol decomposition reaction is found to depend on the thickness of protecting layers. While Pd 1 catalysts showed promising activity at low temperature in a methanol decomposition reaction, 14 cycle TiO 2 protected Pd 1 was less active at high temperature. Pd L 3 edge XAS indicated that the low reactivity compared with Pd nanoparticles is due to the strong adsorption of carbon monoxide even at 250 °C. Lastly, these results clearly show that the ALD nanocavities provide a basis for future design of single-atom catalysts that are highly efficient and stable.« less

Towards ALD thin film stabilized single-atom Pd 1 catalysts

DOE PAGES

Piernavieja-Hermida, Mar; Lu, Zheng; White, Anderson; ...

2016-07-27

Supported precious metal single-atom catalysts have shown interesting activity and selectivity in recent studies. However, agglomeration of these highly mobile mononuclear surface species can eliminate their unique catalytic properties. In this paper, we study a strategy for synthesizing thin film stabilized single-atom Pd 1 catalysts using atomic layer deposition (ALD). The thermal stability of the Pd 1 catalysts is significantly enhanced by creating a nanocavity thin film structure. In situ infrared spectroscopy and Pd K-edge X-ray absorption spectroscopy (XAS) revealed that the Pd 1 was anchored on the surface through chlorine sites. The thin film stabilized Pd 1 catalysts weremore » thermally stable under both oxidation and reduction conditions. The catalytic performance in the methanol decomposition reaction is found to depend on the thickness of protecting layers. While Pd 1 catalysts showed promising activity at low temperature in a methanol decomposition reaction, 14 cycle TiO 2 protected Pd 1 was less active at high temperature. Pd L 3 edge XAS indicated that the low reactivity compared with Pd nanoparticles is due to the strong adsorption of carbon monoxide even at 250 °C. Lastly, these results clearly show that the ALD nanocavities provide a basis for future design of single-atom catalysts that are highly efficient and stable.« less

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

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

Tian, Xinlong; Tang, Haibo; Luo, Junming

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

Optimum concentration gradient of the electrocatalyst, Nafion® and poly(tetrafluoroethylene) in a membrane-electrode-assembly for enhanced performance of direct methanol fuel cells.

PubMed

Liu, Jing Hua; Jeon, Min Ku; Lee, Ki Rak; Woo, Seong Ihl

2010-12-14

A combinatorial library of membrane-electrode-assemblies (MEAs) which consisted of 27 different compositions was fabricated to optimize the multilayer structure of direct methanol fuel cells. Each spot consisted of three layers of ink and a gradient was generated by employing different concentrations of the three components (Pt catalyst, Nafion® and polytetrafluoroethylene (PTFE)) of each layer. For quick evaluation of the library, a high-throughput optical screening technique was employed for methanol electro-oxidation reaction (MOR) activity. The screening results revealed that gradient layers could lead to higher MOR activity than uniform layers. It was found that the MOR activity was higher when the concentrations of Pt catalyst and Nafion ionomer decreased downward from the top layer to the bottom layer. On the other hand, higher MOR activity was observed when PTFE concentration increased downward from the top to the bottom layer.

Enhancing the stability of copper chromite catalysts for the selective hydrogenation of furfural using ALD overcoating

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

Zhang, Hongbo; Lei, Yu; Kropf, A. Jeremy

2014-08-01

The stability of a gas-phase furfural hydrogenation catalyst (CuCr2O4 center dot CuO) was enhanced by depositing a thin Al2O3 layer using atomic layer deposition (ALD). Based on temperature-programed reduction (TPR) measurements, the reduction temperature of Cu was raised significantly, and the activation energy for furfural reduction was decreased following the ALD treatment. Thinner ALD layers yielded higher furfural hydrogenation activities. X-ray absorption fine structure (XAFS) spectroscopy studies indicated that Cu1+/Cu-0 are the active species for furfural reduction.

Catalytic Formylation of Primary and Secondary Amines with CO2 and H2 Using Abundant-Metal Catalysts.

PubMed

Affan, Mohammad A; Jessop, Philip G

2017-06-19

Catalytic hydrogenation of CO 2 is an efficient and selective way to prepare formic acid derivatives, but most of the highly active catalysts used for this purpose require precious metals. In this study, in situ abundant-metal complexes have been evaluated as potential catalysts for CO 2 hydrogenation to prepare formamides, including N-formylmorpholine, 2-ethylhexylformamide, and dimethylformamide, from the corresponding amines. From these initial screening results, the most active catalysts for these reactions were found to be MX 2 /dmpe in situ catalysts (M = Fe(II), Ni(II); X = Cl - , CH 3 CO 2 - , acac - ; dmpe = 1,2-bis(dimethylphosphino)ethane) in DMSO. The optimal reaction conditions were found to be 100-135 °C and a total pressure of 100 bar. Morpholine was formylated with a TON value of up to 18000, which is the highest TON for the hydrogenation of CO 2 to formamides using any abundant-metal-phosphine complex. With an appropriate selection of catalyst and reaction conditions, >90-98% conversion of amine to formamide could be achieved.

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

Stariha, Sarah; Macauley, Natalia; Sneed, Brian T.

The U.S. Department of Energy (DOE) set the 2020 durability target for polymer electrolyte membrane fuel cell transportation applications at 5000 hours. Since it is impractical to test every fuel cell for this length of time, there is ever increasing interest in developing accelerated stress tests (ASTs) that can accurately simulate the material component degradation in the membrane electrode assembly (MEA) observed under automotive operating conditions, but over a much shorter time frame. In this study, a square-wave catalyst AST was examined that shows a 5X time acceleration factor over the triangle-wave catalyst AST and a 25X time acceleration factormore » over the modified wet drive-cycle catalyst durability protocol, significantly decreasing the testing time. These acceleration factors were correlated to the platinum (Pt) particle size increase and associated decrease in electrochemical surface area (ECSA). This square-wave AST has been adopted by the DOE as a standard protocol to evaluate catalyst durability. We also compare three catalyst-durability protocols using state-of-the-art platinum-cobalt catalysts supported on high surface area carbon (SOA Pt-Co/HSAC) in the cathode catalyst layer. The results for each of the three tests showed both catalyst particle size increase and transition metal leaching. Moreover the acceleration factors for the alloy catalysts were smaller due to Co leaching being the predominant mechanism of voltage decay in ~5 nm PtCo/C catalysts. Finally, an extremely harsh carbon corrosion AST was run using the same SOA Pt-Co/HSAC catalyst. This showed minimal change in particle size and a low percentage Co loss from the cathode catalyst particles, despite a significant loss in catalyst layer thickness and cell performance. The carbon corrosion rates during these various ASTs were directly measured by monitoring the CO 2 emission from the cathode, further confirming the ability of the square-wave AST to evaluate the electro-catalyst independently of the support.« less

Redox inactive metal ion triggered N-dealkylation by an iron catalyst with dioxygen activation: a lesson from lipoxygenases.

PubMed

Zhang, Jisheng; Wang, Yujuan; Luo, Nengchao; Chen, Zhuqi; Wu, Kangbing; Yin, Guochuan

2015-06-07

Utilization of dioxygen as the terminal oxidant at ambient temperature is always a challenge in redox chemistry, because it is hard to oxidize a stable redox metal ion like iron(III) to its high oxidation state to initialize the catalytic cycle. Inspired by the dioxygenation and co-oxidase activity of lipoxygenases, herein, we introduce an alternative protocol to activate the sluggish iron(III) species with non-redox metal ions, which can promote its oxidizing power to facilitate substrate oxidation with dioxygen, thus initializing the catalytic cycle. In oxidations of N,N-dimethylaniline and its analogues, adding Zn(OTf)2 to the [Fe(TPA)Cl2]Cl catalyst can trigger the amine oxidation with dioxygen, whereas [Fe(TPA)Cl2]Cl alone is very sluggish. In stoichiometric oxidations, it has also been confirmed that the presence of Zn(OTf)2 can apparently improve the electron transfer capability of the [Fe(TPA)Cl2]Cl complex. Experiments using different types of substrates as trapping reagents disclosed that the iron(IV) species does not occur in the catalytic cycle, suggesting that oxidation of amines is initialized by electron transfer rather than hydrogen abstraction. Combined experiments from UV-Vis, high resolution mass spectrometry, electrochemistry, EPR and oxidation kinetics support that the improved electron transfer ability of iron(III) species originates from its interaction with added Lewis acids like Zn(2+) through a plausible chloride or OTf(-) bridge, which has promoted the redox potential of iron(III) species. The amine oxidation mechanism was also discussed based on the available data, which resembles the co-oxidase activity of lipoxygenases in oxidative dealkylation of xenobiotic metabolisms where an external electron donor is not essential for dioxygen activation.

Syntheses and molecular structures of novel Ru(II) complexes with bidentate benzimidazole based ligands and their catalytic efficiency for oxidation of benzyl alcohol

NASA Astrophysics Data System (ADS)

Dayan, Osman; Tercan, Melek; Özdemir, Namık

2016-11-01

Five bidentate ligands derived from quinoline-2-carboxylic acid, i.e. 2-(1H-benzimidazol-2-yl)quinoline (L1), 2-(1-benzyl-1H-benzimidazol-2-yl)quinoline (L2), 2-[1-(2,3,5,6-tetramethylbenzyl)-1H-benzimidazol-2-yl]quinoline (L3), 2-[1-(4-chlorobenzyl)-1H-benzimidazol-2-yl]quinoline (L4), and 2-[1-(4-methylbenzyl)-1H-benzimidazol-2-yl]quinoline (L5) were synthesized. Treatment of L1-5 with [RuCl2(p-cymene)]2 and KPF6 afforded six-coordinate piano-stool Ru(II) complexes, namely, [RuCl(L1)(p-cymene)]PF6 (C1), [RuCl(L2)(p-cymene)]PF6 (C2), [RuCl(L3)(p-cymene)]PF6 (C3), [RuCl(L4)(p-cymene)]PF6 (C4), and [RuCl(L5)(p-cymene)]PF6 (C5). Synthesized compounds were characterized with different techniques such as 1H and 13C NMR, FT-IR, and UV-vis spectroscopy. The solid state structure of L1 and C3 was confirmed by single-crystal X-ray diffraction analysis. The single crystal structure of C3 verified coordination of L3 to the Ru(II) center. The Ru(II) center has a pseudo-octahedral three legged piano stool geometry. The complexes C1-5 were tested as catalysts for the catalytic oxidation of benzyl alcohol to benzaldehyde in the presence of periodic acid (H5IO6) (Substrate/Catalyst/Oxidant = 1/0.01/0.5). The best result was obtained with C2 (3 h→90%).

Dual-component system dimethyl sulfoxide/LiCl as a solvent and catalyst for homogeneous ring-opening grafted polymerization of ε-caprolactone onto xylan.

PubMed

Zhang, Xue-Qin; Chen, Ming-Jie; Liu, Chuan-Fu; Sun, Run-Cang

2014-01-22

The preparation of xylan-graft-poly(ε-caprolactone) (xylan-g-PCL) copolymers was investigated by homogeneous ring-opening polymerization (ROP) in a dual-component system containing Lewis base LiCl and strong polar aprotic solvent dimethyl sulfoxide (DMSO). DMSO/LiCl acted as solvent, base, and catalyst for the ROP reaction. The effects of the parameters, including the reaction temperature, molar ratio of ε-caprolactone (ε-CL) to anhydroxylose units (AXU) in xylan, and reaction time, on the degree of substitution (DS) and weight percent of PCL side chain (WPCL) were investigated. The results showed that xylan-g-PCL copolymers with low DS in the range of 0.03-0.39 were obtained under the given conditions. The Fourier transform infrared spectroscopy (FTIR), (1)H nuclear magnetic resonance (NMR), (13)C NMR, (1)H-(1)H correlation spectroscopy (COSY), and (1)H-(13)C correlation two-dimensional (2D) NMR [heteronuclear single-quantum coherence (HSQC)] characterization provided more evidence of the attachment of side chains onto xylan. Only one ε-CL was confirmed to be attached onto xylan with each side chain. Integration of resonances assigned to the substituted C2 and C3 in the HSQC spectrum also indicated 69.23 and 30.77% of PCL side chains attached to AXU at C3 and C2 positions, respectively. Although the attachment of PCL onto xylan led to the decreased thermal stability of xylan, the loss of unrecovered xylan fractions with low molecular weight because of the high solubility of xylan in DMSO/LiCl resulted in the increased thermal stability of the samples. This kind of xylan derivative has potential application in environmentally friendly and biodegradable materials considering the good biodegradability of xylan and PCL.

Catalytic oxidation of low-concentration CO at ambient temperature over supported Pd-Cu catalysts.

PubMed

Wang, Fagen; Zhang, Haojie; He, Dannong

2014-01-01

The CO catalytic oxidation at ambient temperature and high space velocity was studied over the Pd-Cu/MOx (MOx = TiO2 and AI203) catalysts. The higher Brunauer-Emmett-Teller area surface of the A1203 support facilitates the dispersion of Pd2+ species, and the presence of Cu2Cl(OH)3 accelerates the re-oxidation of Pd0 to Pd2+ over the Pd-Cu/Al203 catalyst, which contributed to better performance of CO catalytic oxidation. The poorer activity of the Pd-Cu/TiO2 catalyst was attributed to the lower dispersion of Pd2+ species because of the less surface area and the non-formation of Cu2CI(OH)3 species. The presence of saturated moisture showed a negative effect on CO conversion over the two catalysts. This might be because of the competitive adsorption, the formation of carbonate species and the transformation of Cu2CI(OH)3 to inactive CuCI over the Pd-Cu/AI2O3 catalyst, which facilitates the aggregation of PdO species over the Pd-Cu/TiO2 catalyst under the moisture condition.

Catalytic microwave pyrolysis of oil palm fiber (OPF) for the biochar production.

PubMed

Hossain, Md Arafat; Ganesan, Poo Balan; Sandaran, Shanti Chandran; Rozali, Shaifulazuar Bin; Krishnasamy, Sivakumar

2017-12-01

Microwave pyrolysis of oil palm fiber (OPF) with three types of Na-based catalysts was experimentally investigated to produce biochar. Sodium hydroxide (NaOH), sodium chloride (NaCl), and sodium carbonate (Na 2 CO 3 ) with purity 99.9% were selected for this investigation. Microwave muffle reactor (Model: HAMiab-C1500) with a microwave power controller including a microwave generator was used to perform the microwave pyrolysis. OPF particles were used after removing foreign materials, impurities, and dust. Microwave power ranges from 400 to 900 W, temperature ranges from 450 to 700 °C, and N 2 flow rates ranges from 200 to -1200 cm 3 /min were used along with all three Na-based catalysts for this investigation. Lower microwave power, temperature, and N 2 flow rate have been found favorable for higher yield of biochar. NaOH is to be found as the more suitable catalyst than NaCl and Na 2 CO 3 to produce biochar. A maximum biochar yield (51.42 wt%) has been found by using the catalysts NaOH at N 2 flow rate of 200 cm 3 /min. One sample of the biochar (maximum yield without catalysts) was selected for further characterization via thermo gravimetric analysis (TGA), scanning electron microscopy (SEM), BET surface area, Fourier transform infrared spectroscopy (FTIR), and ultimate and proximate analysis. SEM and BET surface area analysis showed the presence of some pores in the biochar. High percentage of carbon (60.24 wt%) was also recorded in the sample biochar. The pores and high percentage of carbon of biochar have significant impact on soil fertilization by increasing the carbon sequestration in the soil. It assists to slow down the decomposition rate of nutrients from soil and therefore enhances the soil quality.

Synthesis and characterization of intercalated few-layer graphenes

NASA Astrophysics Data System (ADS)

Sato, Shogo; Ichikawa, Hiroaki; Iwata, Nobuyuki; Yamamoto, Hiroshi

2014-02-01

Toward achieving room-temperature superconductivity, FeCl3-intercalated few-layer graphenes (FeCl3-FLGs) and Ca-intercalated few-layer graphenes (Ca-FLGs) were synthesized. FeCl3-FLGs were synthesized by the two-zone method and Ca-FLGs were synthesized using Ca-Li alloy. The Raman spectra of the FeCl3-FLGs showed a lower-intensity peak at 1607 cm-1 than that of the corresponding bare G. The peak at 1607 cm-1 suggested that the sample was stage 4-5 FeCl3-FLGs. The room-temperature electrical resistivity of FeCl3-FLGs was 2.65 × 10-5 Ω·m, which linearly decreased with decreasing temperature with a marked change occurring at approximately 200 K. From a XRD pattern of Ca-FLGs, we concluded that Ca is intercalated in FLGs. The room-temperature resistivity of Ca-FLGs was 3.45 × 10-5 Ω·m, which increased with decreasing temperature.

Cathodoluminescence study of one-dimensional free-standing widegap-semiconductor nanostructures: GaN nanotubes, Si3N4 nanobelts and ZnS/Si nanowires.

PubMed

Sekiguchi, Takashi; Hu, Junqing; Bando, Yoshio

2004-01-01

Luminescence properties of one-dimensional free-standing widegap-semiconductor nanostructures were characterized by means of cathodoluminescence (CL). GaN nanopipes, alpha-Si3N4 nanobelts and ZnS/Si nanowires were fabricated by a catalyst-free method, namely grown in an induction furnace from powders. After the observation of morphology by scanning electron microscopy as well as the confirmation of their crystal structures by transmission electron microscopy, their CL spectra and images were observed. The CL spectra mapping as well as the monochromatic CL imaging revealed the variation of the luminescence spectra of different nanowires as well as that along a single wire. These results revealed the optical features of nanostructures.

FeCl3-Catalyzed aminohalogenation of arylmethylenecyclopropanes and arylvinylidenecyclopropanes and corresponding mechanistic studies.

PubMed

Li, Qingjiang; Shi, Min; Timmons, Cody; Li, Guigen

2006-02-16

[reaction: see text] The aminochlorination of methylenecyclopropanes (MCPs) 1 and vinylidenecyclopropanes (VCPs) has been explored with use of FeCl(3) (20 mol %) as a Lewis acid catalyst in acetonitrile under convenient mild conditions. The stereochemistry has been unambiguously confirmed by X-ray structural analysis. The aziridinium-based mechanism, accounting for both regio- and stereoselectivity, has been carefully studied. A linear free-energy relationship study of this reaction confirms consistency with the Hammet equation.

A new approach of probe sonication assisted ionic liquid conversion of glucose, cellulose and biomass into 5-hydroxymethylfurfural.

PubMed

Sarwono, Ariyanti; Man, Zakaria; Muhammad, Nawshad; Khan, Amir Sada; Hamzah, Wan Suzaini Wan; Rahim, Asyraf Hanim Abdul; Ullah, Zahoor; Wilfred, Cecilia Devi

2017-07-01

5-Hydroxymethylfurfural (HMF) has been identified as a promising biomass-derived platform chemical. In this study, one pot production of HMF was studied in ionic liquid (IL) under probe sonication technique. Compared with the conventional heating technique, the use of probe ultrasonic irradiation reduced the reaction time from hours to minutes. Glucose, cellulose and local bamboo, treated with ultrasonic, produced HMF in the yields of 43%, 31% and 13% respectively, within less than 10min. The influence of various parameters such as acoustic power, reaction time, catalysts and glucose loading were studied. About 40% HMF yield at glucose conversion above 90% could be obtained with 2% of catalyst in 3min. Negligible amount of soluble by-product was detected, and humin formation could be controlled by adjusting the different process parameters. Upon extraction of HMF, the mixture of ionic liquid and catalyst could be reused and exhibited no significant reduction of HMF yield over five successive runs. The purity of regenerated [C 4 C 1 im]Cl and HMF was confirmed by NMR spectroscopy, indicating neither changes in the chemical structure nor presence of any major contaminants during the conversion under ultrasonic treatment. 13 C NMR suggests that [C 4 C 1 im]Cl/CrCl 3 catalyses mutarotation of α-glucopyranose to β-glucopyranose leading to isomerization and finally conversion to HMF. The experimental results demonstrate that the use of probe sonication technique for conversion to HMF provides a positive process benefit. Copyright © 2017 Elsevier B.V. All rights reserved.

On the mechanism of the palladium catalyzed intramolecular Pauson-Khand-type reaction.

PubMed

Lan, Yu; Deng, Lujiang; Liu, Jing; Wang, Can; Wiest, Olaf; Yang, Zhen; Wu, Yun-Dong

2009-07-17

Density functional theory calculations and experimental studies have been carried out on the intramolecular Pauson-Khand-Type reaction mediated by a PdCl(2)-thiourea catalyst, which proceeds under mild reaction conditions and provides a useful alternative to traditional Pauson-Khand reactions. The classical mechanism of the Pauson-Khand reaction involving the alkyne/alkene C-C bond formation as the key step has been found to be energetically unfavorable and is not in line with the experimental observations. A novel reaction mechanism has been proposed for the reaction. The first step involves the cis-halometalation of the alkyne, followed by sequential alkene and carbonyl insertion. The rate-determining fourth step is an intramolecular C-Cl oxidative addition, leading to a Pd(IV) intermediate. A C-C bond formation by reductive elimination completes the reaction. The mechanism is in agreement with the key experimental observations including (1) the need of a chloride for catalytic activity and the absence of catalysis with Pd(OAc)(2) alone; (2) the rate acceleration by the addition of LiCl; both with PdCl(2) and Pd(OAc)(2) catalysts; and (3) the preferred formation of the trans diastereomer in substituted cases. The cis halometalation and the formation and stability of the Pd(IV) intermediate is studied in detail and provides general insights into these novel steps.

Irreversible Catalyst Activation Enables Hyperpolarization and Water Solubility for NMR Signal Amplification by Reversible Exchange

PubMed Central

2015-01-01

Activation of a catalyst [IrCl(COD)(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene; COD = cyclooctadiene)] for signal amplification by reversible exchange (SABRE) was monitored by in situ hyperpolarized proton NMR at 9.4 T. During the catalyst-activation process, the COD moiety undergoes hydrogenation that leads to its complete removal from the Ir complex. A transient hydride intermediate of the catalyst is observed via its hyperpolarized signatures, which could not be detected using conventional nonhyperpolarized solution NMR. SABRE enhancement of the pyridine substrate can be fully rendered only after removal of the COD moiety; failure to properly activate the catalyst in the presence of sufficient substrate can lead to irreversible deactivation consistent with oligomerization of the catalyst molecules. Following catalyst activation, results from selective RF-saturation studies support the hypothesis that substrate polarization at high field arises from nuclear cross-relaxation with hyperpolarized 1H spins of the hydride/orthohydrogen spin bath. Importantly, the chemical changes that accompanied the catalyst’s full activation were also found to endow the catalyst with water solubility, here used to demonstrate SABRE hyperpolarization of nicotinamide in water without the need for any organic cosolvent—paving the way to various biomedical applications of SABRE hyperpolarization methods. PMID:25372972

Inclusion behavior of Cs, Sr, and Ba impurities in LiCl crystal formed by layer-melt crystallization: Combined first-principles calculation and experimental study

NASA Astrophysics Data System (ADS)

Choi, Jung-Hoon; Cho, Yung-Zun; Lee, Tae-Kyo; Eun, Hee-Chul; Kim, Jun-Hong; Kim, In-Tae; Park, Geun-Il; Kang, Jeung-Ku

2013-05-01

The pyroprocessing which uses a dry method to recycle spent oxide fuel generates a waste LiCl salt containing radioactive elements. To reuse LiCl salt, the radioactive impurities has to be separated by the purification process such as layer-melt crystallization. To enhance impurity separation efficiency, it is important to understand the inclusion mechanism of impurities within the LiCl crystal. Herein, we report the inclusion properties of impurities in LiCl crystals. First of all, the substitution enthalpies of Cs+, Sr2+, and Ba2+ impurities with 0-6 at% in LiCl crystal were evaluated via first-principles calculations. Also, the molten LiCl containing 1 mol of Cs+, Sr2+, and Ba2+ impurities was crystallized through the experimental layer-melt crystallization method. These substitution enthalpy and experiment clarify that a high substitution enthalpy should result in the high separation efficiency for an impurity. Furthermore, we find that the electron density map gives a clue to the mechanism for inclusion of impurities into LiCl crystal.

Facile solvothermal synthesis of highly active and robust Pd1.87Cu0.11Sn electrocatalyst towards direct ethanol fuel cell applications

NASA Astrophysics Data System (ADS)

Jana, Rajkumar; Dhiman, Shikha; Peter, Sebastian C.

2016-08-01

Ordered intermetallic Pd1.87Cu0.11Sn ternary electrocatalyst has been synthesized by sodium borohydride reduction of precursor salts Pd(acac)2, CuCl2.2H2O and SnCl2 using one-pot solvothermal synthesis method at 220 °C with a reaction time of 24 h. To the best of our knowledge, here for the first time we report surfactant free synthesis of a novel ordered intermetallic ternary Pd1.87Cu0.11Sn nanoparticles. The ordered structure of the catalyst has been confirmed by powder x-ray diffraction, transmission electron microscopy (TEM). Composition and morphology of the nanoparticles have been confirmed through field emission scanning electron microscopy, energy-dispersive spectrometry and TEM. The electrocatalytic activity and stability of the ternary electrocatalyst towards ethanol oxidation in alkaline medium was investigated by cyclic voltammetry and chronoamperometry techniques. The catalyst is proved to be highly efficient and stable upto 500th cycle and even better than commercially available Pd/C (20 wt%) electrocatalysts. The specific and mass activity of the as synthesized ternary catalyst are found to be ∼4.76 and ∼2.9 times better than that of commercial Pd/C. The enhanced activity and stability of the ordered ternary Pd1.87Cu0.11Sn catalyst can make it as a promising candidate for the alkaline direct ethanol fuel cell application.

Magnetic porous Fe3O4/carbon octahedra derived from iron-based metal-organic framework as heterogeneous Fenton-like catalyst

NASA Astrophysics Data System (ADS)

Li, Wenhui; Wu, Xiaofeng; Li, Shuangde; Tang, Wenxiang; Chen, Yunfa

2018-04-01

The synthesis of effective and recyclable Fenton-like catalyst is still a key factor for advanced oxidation processes. Herein, magnetic porous Fe3O4/carbon octahedra were constructed by a two-step controlled calcination of iron-based metal organic framework. The porous octahedra were assembled by interpenetrated Fe3O4 nanoparticles coated with graphitic carbon layer, offering abundant mesoporous channels for the solid-liquid contact. Moreover, the oxygen-containing functional groups on the surface of graphitic carbon endow the catalysts with hydrophilic nature and well-dispersion into water. The porous Fe3O4/carbon octahedra show efficiently heterogeneous Fenton-like reactions for decomposing the organic dye methylene blue (MB) with the help of H2O2, and nearly 100% removal efficiency within 60 min. Furthermore, the magnetic catalyst retains the activity after ten cycles and can be easily separated by external magnetic field, indicating the long-term catalytic durability and recyclability. The good Fenton-like catalytic performance of the as-synthesized Fe3O4/carbon octahedra is ascribed to the unique mesoporous structure derived from MOF-framework, as well as the sacrificial role and stabilizing effect of graphitic carbon layer. This work provides a facile strategy for the controllable synthesis of integrated porous octahedral structure with graphitic carbon layer, and thereby the catalyst holds significant potential for wastewater treatment.

The effects of gas diffusion layers structure on water transportation using X-ray computed tomography based Lattice Boltzmann method

NASA Astrophysics Data System (ADS)

Jinuntuya, Fontip; Whiteley, Michael; Chen, Rui; Fly, Ashley

2018-02-01

The Gas Diffusion Layer (GDL) of a Polymer Electrolyte Membrane Fuel Cell (PEMFC) plays a crucial role in overall cell performance. It is responsible for the dissemination of reactant gasses from the gas supply channels to the reactant sites at the Catalyst Layer (CL), and the adequate removal of product water from reactant sites back to the gas channels. Existing research into water transport in GDLs has been simplified to 2D estimations of GDL structures or use virtual stochastic models. This work uses X-ray computed tomography (XCT) to reconstruct three types of GDL in a model. These models are then analysed via Lattice Boltzmann methods to understand the water transport behaviours under differing contact angles and pressure differences. In this study, the three GDL samples were tested over the contact angles of 60°, 80°, 90°, 100°, 120° and 140° under applied pressure differences of 5 kPa, 10 kPa and 15 kPa. By varying the contact angle and pressure difference, it was found that the transition between stable displacement and capillary fingering is not a gradual process. Hydrophilic contact angles in the region of 60°<θ < 90° showed stable displacement properties, whereas contact angles in the region of 100°<θ < 140° displayed capillary fingering characteristics.

Surface chemical properties of eutectic and frozen NaCl solutions probed by XPS and NEXAFS.

PubMed

Křepelová, Adéla; Huthwelker, Thomas; Bluhm, Hendrik; Ammann, Markus

2010-12-17

We study the surface of sodium chloride-water mixtures above, at, and below the eutectic temperature using X-ray photoelectron spectroscopy (XPS) and electron-yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The NaCl frozen solutions are mimicking sea-salt deposits in ice or snow. Sea-salt particles emitted from the oceans are a major contributor to the global aerosol burden and can act as a catalyst for heterogeneous chemistry or as cloud condensation nuclei. The nature of halogen ions at ice surfaces and their influence on surface melting of ice are of significant current interest. We found that the surface of the frozen solution, depending on the temperature, consists of ice and different NaCl phases, that is, NaCl, NaCl·2H(2)O, and surface-adsorbed water.

Transition metal nitride coated with atomic layers of Pt as a low-cost, highly stable electrocatalyst for the oxygen reduction reaction

DOE PAGES

Tian, Xinlong; Adzic, Radoslav R.; Luo, Junming; ...

2016-02-10

Here, the main challenges to the commercial viability of polymer electrolyte membrane fuel cells are (i) the high cost associated with using large amounts of Pt in fuel cell cathodes to compensate for the sluggish kinetics of the oxygen reduction reaction, (ii) catalyst degradation, and (iii) carbon-support corrosion. To address these obstacles, our group has focused on robust, carbon-free transition metal nitride materials with low Pt content that exhibit tunable physical and catalytic properties. Here, we report on the high performance of a novel catalyst with low Pt content, prepared by placing several layers of Pt atoms on nanoparticles ofmore » titanium nickel binary nitride. For the ORR, the catalyst exhibited a more than 400% and 200% increase in mass activity and specific activity, respectively, compared with the commercial Pt/C catalyst. It also showed excellent stability/durability, experiencing only a slight performance loss after 10,000 potential cycles, while TEM results showed its structure had remained intact. The catalyst’s outstanding performance may have resulted from the ultrahigh dispersion of Pt (several atomic layers coated on the nitride nanoparticles), and the excellent stability/durability may have been due to the good stability of nitride and synergetic effects between ultrathin Pt layer and the robust TiNiN support.« less

Ultrathin Coating of Confined Pt Nanocatalysts by Atomic Layer Deposition for Enhanced Catalytic Performance in Hydrogenation Reactions.

PubMed

Wang, Meihua; Gao, Zhe; Zhang, Bin; Yang, Huimin; Qiao, Yan; Chen, Shuai; Ge, Huibin; Zhang, Jiankang; Qin, Yong

2016-06-13

Metal-support interfaces play a prominent role in heterogeneous catalysis. However, tailoring the metal-support interfaces to realize full utilization remains a major challenge. In this work, we propose a graceful strategy to maximize the metal-oxide interfaces by coating confined nanoparticles with an ultrathin oxide layer. This is achieved by sequential deposition of ultrathin Al2 O3 coats, Pt, and a thick Al2 O3 layer on carbon nanocoils templates by atomic layer deposition (ALD), followed by removal of the templates. Compared with the Pt catalysts confined in Al2 O3 nanotubes without the ultrathin coats, the ultrathin coated samples have larger Pt-Al2 O3 interfaces. The maximized interfaces significantly improve the activity and the protecting Al2 O3 nanotubes retain the stability for hydrogenation reactions of 4-nitrophenol. We believe that applying ALD ultrathin coats on confined catalysts is a promising way to achieve enhanced performance for other catalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hierarchical assembly of AgCl@Sn-TiO2 microspheres with enhanced visible light photocatalytic performance

NASA Astrophysics Data System (ADS)

Ganeshraja, Ayyakannu Sundaram; Zhu, Kaixin; Nomura, Kiyoshi; Wang, Junhu

2018-05-01

The hierarchical silver chloride loaded tin-doped titania (AgCl@Sn-TiO2) microspheres were first time prepared by a hydrothermal method and annealing at different temperatures. The catalyst showed the enhanced visible light photocatalytic activity as compared to the plasmonic photocatalysts of AgCl and Ag/AgCl, and commercial Degussa P25 (TiO2). The improved efficiency is considered to local surface plasmonic resonance (AgCl could reduce to Ag0 during photocatalytic reaction) in enhanced broad band visible light absorption in addition to the characteristics of heterojunction between Sn-TiO2 and AgCl NPs. Moreover, the surface and bulk properties of as-synthesized samples were analyzed by 119Sn Mössbauer spectroscopy. The magnetic property of the bulk was studied as a function of magnetic field with different temperatures. These results signify the clear details of the magnetic and visible light photocatalytic activities of hierarchical AgCl@Sn-TiO2 microspheres.

Atomic layer deposited cobalt oxide: An efficient catalyst for NaBH{sub 4} hydrolysis

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

Nandi, Dip K.; Manna, Joydev; Dhara, Arpan

2016-01-15

Thin films of cobalt oxide are deposited by atomic layer deposition using dicobalt octacarbonyl [Co{sub 2}(CO){sub 8}] and ozone (O{sub 3}) at 50 °C on microscope glass substrates and polished Si(111) wafers. Self-saturated growth mechanism is verified by x-ray reflectivity measurements. As-deposited films consist of both the crystalline phases; CoO and Co{sub 3}O{sub 4} that gets converted to pure cubic-Co{sub 3}O{sub 4} phase upon annealing at 500 °C under ambient condition. Elemental composition and uniformity of the films is examined by x-ray photoelectron spectroscopy and secondary ion-mass spectroscopy. Both as-deposited and the annealed films have been successfully tested as a catalyst formore » hydrogen evolution from sodium borohydride hydrolysis. The activation energy of the hydrolysis reaction in the presence of the as-grown catalyst is found to be ca. 38 kJ mol{sup −1}. Further implementation of multiwalled carbon nanotube, as a scaffold layer, improves the hydrogen generation rate by providing higher surface area of the deposited catalyst.« less

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

NASA Technical Reports Server (NTRS)

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

1999-01-01

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

The effect of chloride ions on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation.

PubMed

Wan, Tong; Xiao, Ning; Shen, Hanjie; Yong, Xingyue

2016-11-01

The effects of Cl(-) on the corroded surface layer of 00Cr22Ni5Mo3N duplex stainless steel under cavitation in chloride solutions were investigated using nanoindentation in conjunction with XRD and XPS. The results demonstrate that Cl(-) had a strong effect on the nano-mechanical properties of the corroded surface layer under cavitation, and there was a threshold Cl(-) concentration. Furthermore, a close relationship between the nano-mechanical properties and the cavitation corrosion resistance of 00Cr22Ni5Mo3N duplex stainless steel was observed. The degradation of the nano-mechanical properties of the corroded surface layer was accelerated by the synergistic effect between cavitation erosion and corrosion. A key factor was the adsorption of Cl(-), which caused a preferential dissolution of the ferrous oxides in the passive film layer on the corroded surface layer. Cavitation further promoted the preferential dissolution of the ferrous oxides in the passive film layer. Simultaneously, cavitation accelerated the erosion of the ferrite in the corroded surface layer, resulting in the degradation of the nano-mechanical properties of the corroded surface layer on 00Cr22Ni5Mo3N duplex stainless steel under cavitation. Copyright © 2016. Published by Elsevier B.V.

Recent Advances in Solid Catalysts Obtained by Metalloporphyrins Immobilization on Layered Anionic Exchangers: A Short Review and Some New Catalytic Results.

PubMed

Nakagaki, Shirley; Mantovani, Karen Mary; Machado, Guilherme Sippel; Castro, Kelly Aparecida Dias de Freitas; Wypych, Fernando

2016-02-29

Layered materials are a very interesting class of compounds obtained by stacking of two-dimensional layers along the basal axis. A remarkable property of these materials is their capacity to interact with a variety of chemical species, irrespective of their charge (neutral, cationic or anionic). These species can be grafted onto the surface of the layered materials or intercalated between the layers, to expand or contract the interlayer distance. Metalloporphyrins, which are typically soluble oxidation catalysts, are examples of molecules that can interact with layered materials. This work presents a short review of the studies involving metalloporphyrin immobilization on two different anionic exchangers, Layered Double Hydroxides (LDHs) and Layered Hydroxide Salts (LHSs), published over the past year. After immobilization of anionic porphyrins, the resulting solids behave as reusable catalysts for heterogeneous oxidation processes. Although a large number of publications involving metalloporphyrin immobilization on LDHs exist, only a few papers have dealt with LHSs as supports, so metalloporphyrins immobilized on LHSs represent a new and promising research field. This work also describes new results on an anionic manganese porphyrin (MnP) immobilized on Mg/Al-LDH solids with different nominal Mg/Al molar ratios (2:1, 3:1 and 4:1) and intercalated with different anions (CO₃(2-) or NO₃(-)). The influence of the support composition on the MnP immobilization rates and the catalytic performance of the resulting solid in cyclooctene oxidation reactions will be reported.

A simple way to prepare Au@polypyrrole/Fe3O4 hollow capsules with high stability and their application in catalytic reduction of methylene blue dye

NASA Astrophysics Data System (ADS)

Yao, Tongjie; Cui, Tieyu; Wang, Hao; Xu, Linxu; Cui, Fang; Wu, Jie

2014-06-01

Metal nanoparticles are promising catalysts for dye degradation in treating wastewater despite the challenges of recycling and stability. In this study, we have introduced a simple way to prepare Au@polypyrrole (PPy)/Fe3O4 catalysts with Au nanoparticles embedded in a PPy/Fe3O4 capsule shell. The PPy/Fe3O4 capsule shell used as a support was constructed in one-step, which not only dramatically simplified the preparation process, but also easily controlled the magnetic properties of the catalysts through adjusting the dosage of FeCl2.4H2O. The component Au nanoparticles could catalyze the reduction of methylene blue dye with NaBH4 as a reducing agent and the reaction rate constant was calculated through the pseudo-first-order reaction equation. The Fe3O4 nanoparticles permitted quick recycling of the catalysts with a magnet due to their room-temperature superparamagnetic properties; therefore, the catalysts exhibited good reusability. In addition to catalytic activity and reusability, stability is also an important property for catalysts. Because both Au and Fe3O4 nanoparticles were wrapped in the PPy shell, compared with precursor polystyrene/Au composites and bare Fe3O4 nanoparticles, the stability of Au@PPy/Fe3O4 hollow capsules was greatly enhanced. Since the current method is simple and flexible to create recyclable catalysts with high stability, it would promote the practicability of metal nanoparticle catalysts in industrial polluted water treatment.Metal nanoparticles are promising catalysts for dye degradation in treating wastewater despite the challenges of recycling and stability. In this study, we have introduced a simple way to prepare Au@polypyrrole (PPy)/Fe3O4 catalysts with Au nanoparticles embedded in a PPy/Fe3O4 capsule shell. The PPy/Fe3O4 capsule shell used as a support was constructed in one-step, which not only dramatically simplified the preparation process, but also easily controlled the magnetic properties of the catalysts through adjusting the dosage of FeCl2.4H2O. The component Au nanoparticles could catalyze the reduction of methylene blue dye with NaBH4 as a reducing agent and the reaction rate constant was calculated through the pseudo-first-order reaction equation. The Fe3O4 nanoparticles permitted quick recycling of the catalysts with a magnet due to their room-temperature superparamagnetic properties; therefore, the catalysts exhibited good reusability. In addition to catalytic activity and reusability, stability is also an important property for catalysts. Because both Au and Fe3O4 nanoparticles were wrapped in the PPy shell, compared with precursor polystyrene/Au composites and bare Fe3O4 nanoparticles, the stability of Au@PPy/Fe3O4 hollow capsules was greatly enhanced. Since the current method is simple and flexible to create recyclable catalysts with high stability, it would promote the practicability of metal nanoparticle catalysts in industrial polluted water treatment. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00023d

A recyclable ionic liquid-oxomolybdenum(vi) catalytic system for the oxidative desulfurization of model and real diesel fuel.

PubMed

Julião, Diana; Gomes, Ana C; Pillinger, Martyn; Valença, Rita; Ribeiro, Jorge C; Gonçalves, Isabel S; Balula, Salete S

2016-10-14

The oxidative desulfurization of model and real diesel has been studied using the complex [MoO2Cl2(4,4'-di-tert-butyl-2,2'-bipyridine)] as (pre)catalyst, aq. H2O2 as oxidant, and an ionic liquid as extraction solvent. Under moderate conditions (50 °C) and short reaction times (<3 h), dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene could be completely removed from the model diesel. The (pre)catalyst 1 was transformed in situ to the active catalyst [MoO(O2)2(di-tBu-bipy)]. By sequentially performing extractive desulfurization and ECODS steps, 76% sulfur removal was achieved for a real diesel (Sinitial = 2300 ppm). For both the model and real diesels, the catalyst/IL phase could be easily recycled and reused with no loss of desulfurization efficiency.

Heterogeneous Microtesla SABRE Enhancement of 15 N NMR Signals.

PubMed

Kovtunov, Kirill V; Kovtunova, Larisa M; Gemeinhardt, Max E; Bukhtiyarov, Andrey V; Gesiorski, Jonathan; Bukhtiyarov, Valerii I; Chekmenev, Eduard Y; Koptyug, Igor V; Goodson, Boyd M

2017-08-21

The hyperpolarization of heteronuclei via signal amplification by reversible exchange (SABRE) was investigated under conditions of heterogeneous catalysis and microtesla magnetic fields. Immobilization of [IrCl(COD)(IMes)], [IMes=1,3-bis(2,4,6-trimethylphenyl), imidazole-2-ylidene; COD=cyclooctadiene] catalyst onto silica particles modified with amine linkers engenders an effective heterogeneous SABRE (HET-SABRE) catalyst that was used to demonstrate a circa 100-fold enhancement of 15 N NMR signals in 15 N-pyridine at 9.4 T following parahydrogen bubbling within a magnetic shield. No 15 N NMR enhancement was observed from the supernatant liquid following catalyst separation, which along with XPS characterization supports the fact that the effects result from SABRE under heterogeneous catalytic conditions. The technique can be developed further for producing catalyst-free agents via SABRE with hyperpolarized heteronuclear spins, and thus is promising for biomedical NMR and MRI applications. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Oxyhydrochlorination catalyst

DOEpatents

Taylor, Charles E.; Noceti, Richard P.

1992-01-01

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

Control of the dipole layer of polar organic molecules adsorbed on metal surfaces via different charge-transfer channels

NASA Astrophysics Data System (ADS)

Lin, Meng-Kai; Nakayama, Yasuo; Zhuang, Ying-Jie; Su, Kai-Jun; Wang, Chin-Yung; Pi, Tun-Wen; Metz, Sebastian; Papadopoulos, Theodoros A.; Chiang, T.-C.; Ishii, Hisao; Tang, S.-J.

2017-02-01

Organic molecules with a permanent electric dipole moment have been widely used as a template for further growth of molecular layers in device structures. Key properties of the resulting organic films such as energy level alignment (ELA), work function, and injection/collection barrier are linked to the magnitude and direction of the dipole moment at the interface. Using angle-resolved photoemission spectroscopy (ARPES), we have systematically investigated the coverage-dependent work function and spectral line shapes of occupied molecular energy states (MESs) of chloroaluminium-phthalocyanine (ClAlPc) grown on Ag(111). We demonstrate that the dipole orientation of the first ClAlPc layer can be controlled by adjusting the deposition rate and postannealing conditions, and we find that the ELA at the interface differs by ˜0.4 eV between the Cl up and down configurations of the adsorbed ClAlPc molecules. These observations are rationalized by density functional theory (DFT) calculations based on a realistic model of the ClAlPc/Ag(111) interface, which reveal that the different orientations of the ClAlPc dipole layer lead to different charge-transfer channels between the adsorbed ClAlPc and Ag(111) substrate. Our findings provide a useful framework toward method development for ELA tuning.

A Tandem Catalyst with Multiple Metal Oxide Interfaces Produced by Atomic Layer Deposition.

PubMed

Ge, Huibin; Zhang, Bin; Gu, Xiaomin; Liang, Haojie; Yang, Huimin; Gao, Zhe; Wang, Jianguo; Qin, Yong

2016-06-13

Ideal heterogeneous tandem catalysts necessitate the rational design and integration of collaborative active sites. Herein, we report on the synthesis of a new tandem catalyst with multiple metal-oxide interfaces based on a tube-in-tube nanostructure using template-assisted atomic layer deposition, in which Ni nanoparticles are supported on the outer surface of the inner Al2 O3 nanotube (Ni/Al2 O3 interface) and Pt nanoparticles are attached to the inner surface of the outer TiO2 nanotube (Pt/TiO2 interface). The tandem catalyst shows remarkably high catalytic efficiency in nitrobenzene hydrogenation over Pt/TiO2 interface with hydrogen formed in situ by the decomposition of hydrazine hydrate over Ni/Al2 O3 interface. This can be ascribed to the synergy effect of the two interfaces and the confined nanospace favoring the instant transfer of intermediates. The tube-in-tube tandem catalyst with multiple metal-oxide interfaces represents a new concept for the design of highly efficient and multifunctional nanocatalysts. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Engineering the Activity and Lifetime of Heterogeneous Catalysts for Carbon Nanotube Growth via Substrate Ion Beam Bombardment (Postprint)

DTIC Science & Technology

2014-07-31

growth. Annealing of the catalyst film in an H2 ambient induces dewetting and leads to the formation of iron nanoparticles on top of the engineered...flow) at 585 °C for 10 min to dewet the catalyst layer into discrete nanoparticles. The samples were then rapidly cooled down to room temperature in a

Atomic Layer-by-Layer Deposition of Pt on Pd Nanocubes for Catalysts with Enhanced Activity and Durability toward Oxygen Reduction

DOE PAGES

Xie, Shuifen; Choi, Sang -Il; Lu, Ning; ...

2014-05-05

Here, an effective strategy for reducing the Pt content while retaining the activity of a Pt-based catalyst is to deposit the Pt atoms as ultrathin skins of only a few atomic layers thick on nanoscale substrates made of another metal. During deposition, however, the Pt atoms often take an island growth mode because of a strong bonding between Pt atoms. Here we report a versatile route to the conformal deposition of Pt as uniform, ultrathin shells on Pd nanocubes in a solution phase. The introduction of the Pt precursor at a relatively slow rate and high temperature allowed the depositedmore » Pt atoms to spread across the entire surface of a Pd nanocube to generate a uniform shell. The thickness of the Pt shell could be controlled from one to six atomic layers by varying the amount of Pt precursor added into the system. Compared to a commercial Pt/C catalyst, the Pd@Pt nL (n = 1–6) core–shell nanocubes showed enhancements in specific activity and durability toward the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations on model (100) surfaces suggest that the enhancement in specific activity can be attributed to the weakening of OH binding through ligand and strain effects, which, in turn, increases the rate of OH hydrogenation. A volcano-type relationship between the ORR specific activity and the number of Pt atomic layers was derived, in good agreement with the experimental results. Both theoretical and experimental studies indicate that the ORR specific activity was maximized for the catalysts based on Pd@Pt 2–3L nanocubes. Because of the reduction in Pt content used and the enhancement in specific activity, the Pd@Pt 1L nanocubes showed a Pt mass activity with almost three-fold enhancement relative to the Pt/C catalyst.« less

Compositional-Spread Discovery of Catalysts for the Growth of Long-Length Dense Forests of Vertically Aligned Carbon Nanotubes

NASA Astrophysics Data System (ADS)

Christen, Hans M.; Puretzky, Alex A.; Cui, Hongtao; Lowndes, Douglas H.; Belay, Kalayu; Geohegan, David B.

2004-03-01

The growth of dense forests of vertically aligned arrays of multi-walled carbon nanotubes (VAA-MWNTs) by chemical vapor deposition [CVD] from a single metallic catalyst layer typically self-terminates after only a few hundred microns of tube length. In order to obtain maximal growth to long lengths, a systematic simultaneous study of catalyst composition and thickness is needed performed here by a compositional-spread approach. Using Pulsed-Laser Deposition (PLD), metallic layers with a wedge-shaped thickness profile are deposited onto Al-coated silicon substrates. High temperature annealing of the metal catalyst films in flowing Ar/H2 gas followed by the one-hour growth of VA-MWNTs by CVD using acetylene gas yields VAA-MWNTs. Tube height (and thus the catalytic activity) is determined as function of position and can be analyzed as a function of catalyst thickness and composition. A dependence of tube height as function of catalyst composition (Mo/Fe ratio) demonstrates that a specific catalyst composition exhibits a local maximum in catalytic activity, permitting the extension of nanotube array growth up to 4 millimeters in height. Other combinations of catalysts and the growth of single-walled tubes will be discussed. This research was sponsored by the U.S. Department of Energy under contract DE-AC05-00OR22725 with the Oak Ridge National Laboratory, managed by UT-Battelle, LLC, and the Laboratory-Directed Research and Development Program at ORNL.

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.

New Failure Mode of Flip-Chip Solder Joints Related to the Metallization of an Organic Substrate

NASA Astrophysics Data System (ADS)

Jang, J. W.; Yoo, S. J.; Hwang, H. I.; Yuk, S. Y.; Kim, C. K.; Kim, S. J.; Han, J. S.; An, S. H.

2015-10-01

We report a new failure phenomenon during flip-chip die attach. After reflow, flip-chip bumps were separated between the Al and Ti layers on the Si die side. This was mainly observed at the Si die corner. Transmission electron microscopy images revealed corrosion of the Al layer at the edge of the solder bump metallization. The corrosion at the metallization edge exhibited a notch shape with high stress concentration factor. The organic substrate had Cu metallization with an organic solderable preservative (OSP) coating layer, where a small amount of Cl ions were detected. A solder bump separation mechanism is suggested based on the reaction between Al and Cl, related to the flow of soldering flux. During reflow, the flux will dissolve the Cl-containing OSP layer and flow up to the Al layer on the Si die side. Then, the Cl-dissolved flux will actively react with Al, forming AlCl3. During cooling, solder bumps at the Si die corner will separate through the location of Al corrosion. This demonstrated that the chemistry of the substrate metallization can affect the thermomechanical reliability of flip-chip solder joints.

W-containing oxide layers obtained on aluminum and titanium by PEO as catalysts in thiophene oxidation

NASA Astrophysics Data System (ADS)

Rudnev, V. S.; Lukiyanchuk, I. V.; Vasilyeva, M. S.; Morozova, V. P.; Zelikman, V. M.; Tarkhanova, I. G.

2017-11-01

W-containing oxide layers fabricated on titanium and aluminum alloys by Plasma electrolytic oxidation (PEO) have been tested in the reaction of the peroxide oxidation of thiophene. Samples with two types of coatings have been investigated. Coatings I contained tungsten oxide in the matrix and on the surface of amorphous silica-titania or silica-alumina layers, while coatings II comprised crystalline WO3 and/or Al2(WO4)3. Aluminum-supported catalyst containing a smallest amount of transition metals in the form of tungsten oxides and manganese oxides in low oxidation levels showed high activity and stability.

Hierarchical concave layered triangular PtCu alloy nanostructures: rational integration of dendritic nanostructures for efficient formic acid electrooxidation.

PubMed

Wu, Fengxia; Lai, Jianping; Zhang, Ling; Niu, Wenxin; Lou, Baohua; Luque, Rafael; Xu, Guobao

2018-05-08

The rational construction of multi-dimensional layered noble metal nanostructures is a great challenge since noble metals are not layer-structured materials. Herein, we report a one-pot hydrothermal synthetic method for PtCu hierarchical concave layered triangular (HCLT) nanostructures using dl-carnitine, KI, poly(vinylpyrrolidone), CuCl2, and H2PtCl6. The PtCu HCLT nanostructure is comprised of multilayered triangular dendrites. Its layer number is tunable by changing dl-carnitine concentrations, and the concavity/convexity of the PtCu triangle nanostructures is tunable by changing the H2PtCl6/CuCl2 ratio or KI concentrations. Hierarchical trigonal bipyramid nanoframes are also obtained under certain conditions. Because of its advantageous nanostructure and bimetallic synergetic effect, the obtained PtCu HCLT nanostructure exhibits enhanced electrocatalytic activity and prolonged stability to formic acid oxidation compared to commercial Pt black, Pd/C and some other nanostructures.

A highly efficient green synthesis of 1, 8-dioxo-octahydroxanthenes

PubMed Central

2011-01-01

SmCl3 (20 mol%) has been used as an efficient catalyst for reaction between aromatic aldehydes and 5,5-dimethyl-1,3-cyclohexanedione at 120°C to give 1,8-dioxo-octahydroxanthene derivatives in high yield. The same reaction in water, at room temperature gave only the open chain analogue of 1,8-dioxo-octahydroxanthene. Use of eco-friendly green Lewis acid, readily available catalyst and easy isolation of the product makes this a convenient method for the synthesis of either of the products. PMID:22152051

Bridging the gap between homogeneous and heterogeneous catalysis: ortho/para H(2) conversion, hydrogen isotope scrambling, and hydrogenation of olefins by Ir(CO)Cl(PPh(3))(2).

PubMed

Matthes, Jochen; Pery, Tal; Gründemann, Stephan; Buntkowsky, Gerd; Sabo-Etienne, Sylviane; Chaudret, Bruno; Limbach, Hans-Heinrich

2004-07-14

Some transition metal complexes are known to catalyze ortho/para hydrogen conversion, hydrogen isotope scrambling, and hydrogenation reactions in liquid solution. Using the example of Vaska's complex, we present here evidence by NMR that the solvent is not necessary for these reactions to occur. Thus, solid frozen solutions or polycrystalline powdered samples of homogeneous catalysts may become heterogeneous catalysts. Comparative liquid- and solid-state studies provide novel insight into the reaction mechanisms.

Highly selective biaryl cross-coupling reactions between aryl halides and aryl Grignard reagents: a new catalyst combination of N-heterocyclic carbenes and iron, cobalt, and nickel fluorides.

PubMed

Hatakeyama, Takuji; Hashimoto, Sigma; Ishizuka, Kentaro; Nakamura, Masaharu

2009-08-26

Combinations of N-heterocyclic carbenes (NHCs) and fluoride salts of the iron-group metals (Fe, Co, and Ni) have been shown to be excellent catalysts for the cross-coupling reactions of aryl Grignard reagents (Ar(1)MgBr) with aryl and heteroaryl halides (Ar(2)X) to give unsymmetrical biaryls (Ar(1)-Ar(2)). Iron fluorides in combination with SIPr, a saturated NHC ligand, catalyze the biaryl cross-coupling between various aryl chlorides and aryl Grignard reagents in high yield and high selectivity. On the other hand, cobalt and nickel fluorides in combination with IPr, an unsaturated NHC ligand, exhibit interesting complementary reactivity in the coupling of aryl bromides or iodides; in contrast, with these substrates the iron catalysts show a lower selectivity. The formation of homocoupling byproducts is suppressed markedly to less than 5% in most cases by choosing the appropriate metal fluoride/NHC combination. The present catalyst combinations offer several synthetic advantages over existing methods: practical synthesis of a broad range of unsymmetrical biaryls without the use of palladium catalysts and phosphine ligands. On the basis of stoichiometric control experiments and theoretical studies, the origin of the unique catalytic effect of the fluoride counterion can be ascribed to the formation of a higher-valent heteroleptic metalate [Ar(1)MF(2)]MgBr as the key intermediate in our proposed catalytic cycle. First, stoichiometric control experiments revealed the stark differences in chemical reactivity between the metal fluorides and metal chlorides. Second, DFT calculations indicate that the initial reduction of di- or trivalent metal fluoride in the wake of transmetalation with PhMgCl is energetically unfavorable and that formation of a divalent heteroleptic metalate complex, [PhMF(2)]MgCl (M = Fe, Co, Ni), is dominant in the metal fluoride system. The heteroleptic ate-complex serves as a key reactive intermediate, which undergoes oxidative addition with PhCl and releases the biaryl cross-coupling product Ph-Ph with reasonable energy barriers. The present cross-coupling reaction catalyzed by iron-group metal fluorides and an NHC ligand provides a highly selective and practical method for the synthesis of unsymmetrical biaryls as well as the opportunity to gain new mechanistic insights into the metal-catalyzed cross-coupling reactions.

Recommendations for processing atmospheric attenuated backscatter profiles from Vaisala CL31 ceilometers

NASA Astrophysics Data System (ADS)

Kotthaus, Simone; O'Connor, Ewan; Münkel, Christoph; Charlton-Perez, Cristina; Haeffelin, Martial; Gabey, Andrew M.; Grimmond, C. Sue B.

2016-08-01

Ceilometer lidars are used for cloud base height detection, to probe aerosol layers in the atmosphere (e.g. detection of elevated layers of Saharan dust or volcanic ash), and to examine boundary layer dynamics. Sensor optics and acquisition algorithms can strongly influence the observed attenuated backscatter profiles; therefore, physical interpretation of the profiles requires careful application of corrections. This study addresses the widely deployed Vaisala CL31 ceilometer. Attenuated backscatter profiles are studied to evaluate the impact of both the hardware generation and firmware version. In response to this work and discussion within the CL31/TOPROF user community (TOPROF, European COST Action aiming to harmonise ground-based remote sensing networks across Europe), Vaisala released new firmware (versions 1.72 and 2.03) for the CL31 sensors. These firmware versions are tested against previous versions, showing that several artificial features introduced by the data processing have been removed. Hence, it is recommended to use this recent firmware for analysing attenuated backscatter profiles. To allow for consistent processing of historic data, correction procedures have been developed that account for artefacts detected in data collected with older firmware. Furthermore, a procedure is proposed to determine and account for the instrument-related background signal from electronic and optical components. This is necessary for using attenuated backscatter observations from any CL31 ceilometer. Recommendations are made for the processing of attenuated backscatter observed with Vaisala CL31 sensors, including the estimation of noise which is not provided in the standard CL31 output. After taking these aspects into account, attenuated backscatter profiles from Vaisala CL31 ceilometers are considered capable of providing valuable information for a range of applications including atmospheric boundary layer studies, detection of elevated aerosol layers, and model verification.

Effects of PCB Substrate Surface Finish, Flux, and Phosphorus Content on Ionic Contamination

NASA Astrophysics Data System (ADS)

Bacior, M.; Sobczak, N.; Siewiorek, A.; Kudyba, A.; Homa, M.; Nowak, R.; Dziula, M.; Masłoń, S.

2015-02-01

The ionic contamination on printed circuit boards (PCB) having different surface finishes was examined using ionograph. The study was performed at the RT on three types of PCBs covered with: (i) hot air solder leveling (HASL LF), (ii) electroless nickel immersion gold (ENIG), and (iii) organic surface protectant (OSP), all on Cu substrates, as well as two types of fluxes, namely EF2202 and RF800. In the group of boards without soldered components, the lowest average value of contamination was for the ENIG 18 µm surface (0.01 μg NaCl/cm2). Boards with soldered components were more contaminated (from 0.29 μg NaCl/cm2 for the HASL LF 18 µm surface). After spraying boards with fluxing agents, the values of contaminants were the highest. The influence of phosphorus content in Ni-P layer of ENIG finish on ionic contamination was examined. In the group of PCBs with Au coating, the smallest amount of surface contaminants (0.32 μg NaCl/cm2) was for Ni-2-5%P layer. PCBs with Ni-11%P layer were higher contaminated (0.47 μg NaCl/cm2), and another with Ni-8%P layer had 0.81 μg NaCl/cm2. PCBs without Au coating, had the lowest contamination (0.48 μg NaCl/cm2) at phosphorous content equal 11%P. Higher contamination (0.67 μg NaCl/cm2) was at 2-5%P, up to 1.98 μg NaCl/cm2 for 8% of P. Boards with Au finish have lower value of contamination than identical boards without Au layer thus contributing to better reliability of electronic assemblies, since its failures due to current leakage and corrosion can be caused by contaminants.

Highly productive CNN pincer ruthenium catalysts for the asymmetric reduction of alkyl aryl ketones.

PubMed

Baratta, Walter; Chelucci, Giorgio; Magnolia, Santo; Siega, Katia; Rigo, Pierluigi

2009-01-01

Chiral pincer ruthenium complexes of formula [RuCl(CNN)(Josiphos)] (2-7; Josiphos = 1-[1-(dicyclohexylphosphano)ethyl]-2-(diarylphosphano)ferrocene) have been prepared by treating [RuCl(2)(PPh(3))(3)] with (S,R)-Josiphos diphosphanes and 1-substituted-1-(6-arylpyridin-2-yl)methanamines (HCNN; substituent = H (1 a), Me (1 b), and tBu (1 c)) with NEt(3). By using 1 b and 1 c as a racemic mixture, complexes 4-7 were obtained through a diastereoselective synthesis promoted by acetic acid. These pincer complexes, which display correctly matched chiral PP and CNN ligands, are remarkably active catalysts for the asymmetric reduction of alkyl aryl ketones in basic alcohol media by both transfer hydrogenation (TH) and hydrogenation (HY), achieving enantioselectivities of up to 99 %. In 2-propanol, the enantioselective TH of ketones was accomplished by using a catalyst loading as low as 0.002 mol % and afforded a turnover frequency (TOF) of 10(5)-10(6) h(-1) (60 and 82 degrees C). In methanol/ethanol mixtures, the CNN pincer complexes catalyzed the asymmetric HY of ketones with H(2) (5 atm) at 0.01 mol % relative to the complex with a TOF of approximately 10(4) h(-1) at 40 degrees C.

One-pot deposition of palladium on hybrid TiO2 nanoparticles and catalytic applications in hydrogenation.

PubMed

Mehri, Afef; Kochkar, Hafedh; Daniele, Stéphane; Mendez, Violaine; Ghorbel, Abdelhamid; Berhault, Gilles

2012-03-01

One-pot deposition of Pd onto TiO(2) has been achieved through directly contacting palladium(II) salt with nanosized functionalized TiO(2) support initially obtained by sol-gel process using titanium isopropoxide and citric acid. Citrate groups act as functional moieties able to directly reduce the Pd salt avoiding any further reducing treatment. Various palladium salts (Na(2)PdCl(4) and Pd(NH(3))(4)Cl(2)·H(2)O) and titanium to citrate (Ti/CA) ratios (20, 50, and 100) were used in order to study the effect of the nature of the precursor and of the citrate content on the final Pd particle size and catalytic properties of the as-obtained Pd/TiO(2) systems. Characterization was performed using N(2) adsorption-desorption isotherms, ICP-AES, FTIR, XRD, XPS, and TEM. The as-obtained hybrid Pd/TiO(2) catalysts were tested in the selective hydrogenation (HYD) of an α,β-unsaturated aldehyde, i.e. cinnamaldehyde. Citrate-free Pd/TiO(2)-based catalysts present lower selectivity into saturated alcohol. However, citrate-functionalized Pd/TiO(2) catalyst seems to control the selectivity, the particle size and dispersion of Pd NPs leading to high intrinsic activity. Copyright © 2011 Elsevier Inc. All rights reserved.

A Silica-Supported Iron Oxide Catalyst Capable of Activating Hydrogen Peroxide at Neutral pH Values

PubMed Central

Pham, Anh Le-Tuan; Lee, Changha; Doyle, Fiona M.; Sedlak, David L.

2009-01-01

Iron oxides catalyze the conversion of hydrogen peroxide (H2O2) into oxidants capable of transforming recalcitrant contaminants. Unfortunately, the process is relatively inefficient at circumneutral pH values due to competing reactions that decompose H2O2 without producing oxidants. Silica- and alumina-containing iron oxides prepared by sol-gel processing of aqueous solutions containing Fe(ClO4)3, AlCl3 and tetraethyl orthosilicate efficiently catalyzed the decomposition of H2O2 into oxidants capable of transforming phenol at circumneutral pH values. Relative to hematite, goethite and amorphous FeOOH, the silica-iron oxide catalyst exhibited a stoichiometric efficiency, defined as the number of moles of phenol transformed per mole of H2O2 consumed, that was 10 to 40 times higher than that of the iron oxides. The silica-alumina-iron oxide catalyst had a stoichiometric efficiency that was 50 to 80 times higher than that of the iron oxides. The significant enhancement in oxidant production is attributable to the interaction of Fe with Al and Si in the mixed oxides, which alters the surface redox processes, favoring the production of strong oxidants during H2O2 decomposition. PMID:19943668

Pd/WO3/C nanocomposite with APTMS-functionalized tungsten oxide nanosheet for formic acid electrooxidation enhancement

NASA Astrophysics Data System (ADS)

Yang, Yang; Li, Yun-Hua; Zhao, Ya-Fei; Li, Peng-Wei; Li, Qiao-Xia

2018-01-01

A Pd/WO3/C nanocomposite with 3-aminopropyltrimethoxysilane (APTMS)-functionalized tungsten oxide nanosheets (Pd/WO3/C-APTMS) was synthesized and applied as the efficient anode catalyst for direct formic acid fuel cells (DFAFCs). The mechanism for synthesizing the nanocomposite is as follows: initially, [PdCl4]2- was assembled onto the tungsten oxide nanosheets modified with APTMS. Following this, Pd nanoparticles were reduced via traditional impregnation reduction of [PdCl4]2- with NaBH4. The transmission electron microscope (TEM) images revealed that the Pd nanoparticles were uniformly dispersed on WO3 nanosheets and were approximately 2.7 nm in size. The electrochemical test results showed that enhanced electrocatalytic activity for the formic acid oxidation reaction (FAOR) was obtained on the Pd/WO3/C catalyst compared with Pd/C. The higher electrocatalytic activity might be attributed to the uniform distribution of Pd with smaller particles. Furthermore, it is likely that the improvement in catalytic stability for the Pd/WO3/C catalyst is due to the hydrogen spillover effect of WO3 particles. These results indicate that this novel Pd/WO3/C-APTMS nanocomposite exhibits promising potential for use as an anode electrocatalyst in DFAFCs.

Open Component Portability Infrastructure (OPENCPI)

DTIC Science & Technology

2013-03-01

8 Figure 2. C Function vs . OpenCL Kernel...10 Figure 3. OpenCL vs . OpenCPI Layering...difference between a simple C function and the analogous OpenCL kernel. Figure 2. C Function vs . OpenCL Kernel These existing example OpenCL

Layered double hydroxide of Cd-Al/C for the Mineralization and De-coloration of Dyes in Solar and Visible Light Exposure

NASA Astrophysics Data System (ADS)

Khan, Shahid Ali; Khan, Sher Bahadar; Asiri, Abdullah M.

2016-11-01

Cd-Al/C layered double hydroxide (Cd-Al/C-LDH) and Cd-Sb/C nanocatalyst are reported here for the de-coloration and mineralization of organic dyes. These catalysts were largely characterized by FESEM, EDS, XRD, FTIR, XPS, PL and DRS. The diffuse reflectance data showed a band gap at 2.92 and 2.983 eV for Cd-Al/C-LDH and Cd-Sb/C respectively. The band gap suggested that both catalysts work well in visible range. The photoluminescence spectra indicated a peak at 623 nm for both the catalysts which further support the effectiveness of the respective catalyst in visible range. Both catalysts also showed good recyclability and durability till 4th cycle. Five dyes, acridine orange (AO), malachite green (MG), crystal violet (CV), congo red (CR) and methyl orange (MO) were used in this experiment. Various parameters of different light intensity such as visible, ultraviolet, sunlight and dark condition are observed for the de-coloration of these dyes. The de-coloration phenomenon was proceeded through adsorption assisted phot-degradation. The low cost, abundant nature, good recyclability and better dye removal efficiency make these catalysts suitable candidates for the de-coloration and mineralization of organic dyes.

Two-Dimensional Layered Double Hydroxides for Reactions of Methanation and Methane Reforming in C1 Chemistry

PubMed Central

Li, Panpan; Altaf, Naveed; Zhu, Mingyuan; Li, Jiangbing; Dai, Bin; Wang, Qiang

2018-01-01

CH4 as the paramount ingredient of natural gas plays an eminent role in C1 chemistry. CH4 catalytically converted to syngas is a significant route to transmute methane into high value-added chemicals. Moreover, the CO/CO2 methanation reaction is one of the potent technologies for CO2 valorization and the coal-derived natural gas production process. Due to the high thermal stability and high extent of dispersion of metallic particles, two-dimensional mixed metal oxides through calcined layered double hydroxides (LDHs) precursors are considered as the suitable supports or catalysts for both the reaction of methanation and methane reforming. The LDHs displayed compositional flexibility, small crystal sizes, high surface area and excellent basic properties. In this paper, we review previous works of LDHs applied in the reaction of both methanation and methane reforming, focus on the LDH-derived catalysts, which exhibit better catalytic performance and thermal stability than conventional catalysts prepared by impregnation method and also discuss the anti-coke ability and anti-sintering ability of LDH-derived catalysts. We believe that LDH-derived catalysts are promising materials in the heterogeneous catalytic field and provide new insight for the design of advance LDH-derived catalysts worthy of future research. PMID:29385064

Water reduction by a p-GaInP2 photoelectrode stabilized by an amorphous TiO2 coating and a molecular cobalt catalyst.

PubMed

Gu, Jing; Yan, Yong; Young, James L; Steirer, K Xerxes; Neale, Nathan R; Turner, John A

2016-04-01

Producing hydrogen through solar water splitting requires the coverage of large land areas. Abundant metal-based molecular catalysts offer scalability, but only if they match noble metal activities. We report on a highly active p-GaInP2 photocathode protected through a 35-nm TiO2 layer functionalized by a cobaloxime molecular catalyst (GaInP2-TiO2-cobaloxime). This photoelectrode mediates H2 production with a current density of ∼9 mA cm(-2) at a potential of 0 V versus RHE under 1-sun illumination at pH 13. The calculated turnover number for the catalyst during a 20-h period is 139,000, with an average turnover frequency of 1.9 s(-1). Bare GaInP2 shows a rapid current decay, whereas the GaInP2-TiO2-cobaloxime electrode shows ≤5% loss over 20 min, comparable to a GaInP2-TiO2-Pt catalyst particle-modified interface. The activity and corrosion resistance of the GaInP2-TiO2-cobaloxime photocathode in basic solution is made possible by an atomic layer-deposited TiO2 and an attached cobaloxime catalyst.

Enhancing substrate utilization and power production of a microbial fuel cell with nitrogen-doped carbon aerogel as cathode catalyst.

PubMed

Tardy, Gábor Márk; Lóránt, Bálint; Lóka, Máté; Nagy, Balázs; László, Krisztina

2017-07-01

Catalytic efficiency of a nitrogen-doped, mesoporous carbon aerogel cathode catalyst was investigated in a two-chambered microbial fuel cell (MFC) applying graphite felt as base material for cathode and anode, utilizing peptone as carbon source. This mesoporous carbon aerogel containing catalyst layer on the cathode increased the maximum power density normalized to the anode volume to 2.7 times higher compared to the maximum power density obtained applying graphite felt cathode without the catalyst layer. At high (2 and 3) cathode/anode volume ratios, maximum power density exceeded 40 W m -3 . At the same time, current density and specific substrate utilization rate increased by 58% resulting in 31.9 A m -3 and 18.8 g COD m -3  h -1 , respectively (normalized to anode volume). Besides the increase of the power and the rate of biodegradation, the investigated catalyst decreased the internal resistance from the range of 450-600 to 350-370 Ω. Although Pt/C catalyst proved to be more efficient, a considerable decrease in the material costs might be achieved by substituting it with nitrogen-doped carbon aerogel in MFCs. Such cathode still displays enhanced catalytic effect.

Performance of a passive direct ethanol fuel cell

NASA Astrophysics Data System (ADS)

Pereira, J. P.; Falcão, D. S.; Oliveira, V. B.; Pinto, A. M. F. R.

2014-06-01

Ethanol emerges as an attractive fuel since it is less toxic and has higher energy density than methanol and can be produced from biomass. Direct ethanol fuel cells (DEFCs) appear as a good choice for producing sustainable energy for portable applications. However, they are still far from attaining acceptable levels of power output, since their performance is affected by the slow electrochemical ethanol oxidation and water and ethanol crossover. In the present work, an experimental study on the performance of a passive DEFC is described. Tailored MEAs (membrane electrode assembly) with different catalyst loadings, anode diffusion layers and membranes were tested in order to select optimal working conditions at high ethanol concentrations and low ethanol crossover. The performance increased with an increase of membrane and anode diffusion layer thicknesses and anode catalyst loading. A maximum power density of 1.33 mW cm-2, was obtained using a Nafion 117 membrane, 4 mg cm-2 of Pt-Ru and 2 mg cm-2 of Pt on the anode and cathode catalyst layers, ELAT as anode diffusion layer, carbon cloth as cathode diffusion layer and an ethanol concentration of 2 M. As far as the authors are aware this is the first work reporting an experimental optimization of passive DEFCs.

Insight into the epitaxial encapsulation of Pd catalysts in an oriented metalloporphyrin network thin film for tandem catalysis.

PubMed

Vohra, M Ismail; Li, De-Jing; Gu, Zhi-Gang; Zhang, Jian

2017-06-14

A palladium catalyst (Pd-Cs) encapsulated metalloporphyrin network PIZA-1 thin film with bifunctional properties has been developed through a modified epitaxial layer-by-layer encapsulation approach. Combining the oxidation activity of Pd-Cs and the acetalization activity of the Lewis acidic sites in the PIZA-1 thin film, this bifunctional catalyst of the Pd-Cs@PIZA-1 thin film exhibits a good catalytic activity in a one-pot tandem oxidation-acetalization reaction. Furthermore, the surface components can be controlled by ending the top layer with different precursors in the thin film preparation procedures. The catalytic performances of these thin films with different surface composites were studied under the same conditions, which showed different reaction conversions. The result revealed that the surface component can influence the catalytic performance of the thin films. This epitaxial encapsulation offers a good understanding of the tandem catalysis for thin film materials and provides useful guidance to develop new thin film materials with catalytic properties.

Dynamics of ultrathin V-oxide layers on Rh(111) in catalytic oxidation of ammonia and CO.

PubMed

von Boehn, B; Preiss, A; Imbihl, R

2016-07-20

Catalytic oxidation of ammonia and CO has been studied in the 10(-4) mbar range using a catalyst prepared by depositing ultra-thin vanadium oxide layers on Rh(111) (θV ≈ 0.2 MLE). Using photoemission electron microscopy (PEEM) as a spatially resolving method, we observe that upon heating in an atmosphere of NH3 and O2 the spatial homogeneity of the VOx layer is removed at 800 K and a pattern consisting of macroscopic stripes develops; at elevated temperatures this pattern transforms into a pattern of circular VOx islands. Under reaction conditions the neighboring VOx islands become attracted by each other and coalesce. Similar processes of pattern formation and island coalescence are observed in catalytic CO oxidation. Reoxidation of the reduced VOx catalyst proceeds via surface diffusion of oxygen adsorbed onto Rh(111). A pattern consisting of macroscopic circular VOx islands can also be obtained by heating a Rh(111)/VOx catalyst in pure O2.

Kinetic Model of the Initial Stage of the Nanowire Growth

NASA Astrophysics Data System (ADS)

Filimonov, S. N.; Hervieu, Yu. Yu.

2018-03-01

A kinetic model of the formation of pyramid-like bulges (pedestals) at the bases of vertical nanowires is proposed. The formation of the pedestals at the early stage of the nanowire growth is assumed to be induced by a higher nucleation rate of two-dimensional islands under the catalyst droplet, as compared to the nucleation rate at the non-activated surface areas. Kinetics of the nucleation and propagation of the steps in the pyramid is described with a model of the multilayer growth, taking into account that the catalyst droplet at the nanowire top is a strong sink for adatoms. It is shown that the transition from the growth of the pyramid to the axial growth of the nanowire is possible if the appearance of a nucleus of the new layer under the catalyst droplet results in a partial dissolution of the underlying layer. In this case a segment of the nanowire sidewall is formed, preventing the lateral growth of the layers generated by the droplet.

MICROWAVE-ASSISTED PREPARATION OF 1-BUTYL-3-METHYLIMIDAZOLIUM TETRACHLOROGALLATE AND ITS CATALYTIC USE IN ACETAL FORMATION UNDER MILD CONDITIONS

EPA Science Inventory

1-Butyl-3-methylimidazolium tetrachlorogallate, [bmim][GaCl₄], prepared via microwave-assisted protocol, is found to be an active catalyst for the efficient acetalization of aldehydes under mild conditions.

Encapsulation of the heteroepitaxial growth of wide band gap γ-CuCl on silicon substrates

NASA Astrophysics Data System (ADS)

Lucas, F. O.; O'Reilly, L.; Natarajan, G.; McNally, P. J.; Daniels, S.; Taylor, D. M.; William, S.; Cameron, D. C.; Bradley, A. L.; Miltra, A.

2006-01-01

γ-CuCl semiconductor material has been identified as a candidate material for the fabrication of blue-UV optoelectronic devices on Si substrates due to its outstanding electronic, lattice and optical properties. However, CuCl thin films oxidise completely into oxyhalides of Cu II within a few days of exposure to air. Conventional encapsulation of thin γ-CuCl by sealed glass at a deposition/curing temperature greater than 250 °C cannot be used because CuCl interacts chemically with Si substrates when heated above that temperature. In this study we have investigated the behaviour of three candidate dielectric materials for use as protective layers for the heteroepitaxial growth of γ-CuCl on Si substrates: SiO 2 deposited by plasma-enhanced chemical vapour deposition (PECVD), organic polysilsesquioxane-based spin on glass material (PSSQ) and cyclo olefin copolymer (COC) thermoplastic-based material. The optical properties (UV/Vis and IR) of the capped luminescent CuCl films were studied as a function of time, up to 28 days and compared with bare uncapped films. The results clearly show the efficiency of the protective layers. Both COC and the PSSQ layer prevented CuCl film from oxidising while SiO 2 delayed the effect of oxidation. The dielectric constant of the three protective layers was evaluated at 1 MHz to be 2.3, 3.6 and 6.9 for C0C, SiO 2 and PSSQ, respectively.

Layered double hydroxide catalyst for the conversion of crude vegetable oils to a sustainable biofuel

NASA Astrophysics Data System (ADS)

Mollaeian, Keyvan

Over the last two decades, the U.S. has developed the production of biodiesel, a mixture of fatty acid methyl esters, using chiefly vegetable oils as feedstocks. However, there is much concern about the availability of high-quality vegetable oils for longterm biodiesel production. Problems have also risen due to the production of glycerol, an unwanted byproduct, as well as the need for process wash water. Therefore, this study was initiated to produce not only fatty acid methyl esters (FAMEs) but also fatty acid glycerol carbonates (FAGCs) by replacing methanol with dimethyl carbonate (DMC). The process would have no unnecessary byproducts and would be a simplified process compared to traditional biodiesel. In addition, this altering of the methylating agent could convert triglycerides, free fatty acids, and phospholipids to a sustainable biofuel. In this project, Mg-Al Layered Double Hydroxide (LDH) was optimized by calcination in different temperature varied from 250°C to 450°C. The gallery between layers was increased by intercalating sodium dodecylsulfate (SDS). During catalyst preparation, the pH was controlled ~10. In our experiment, triazabicyclodecene (TBD) was attached with trimethoxysilane (3GPS) as a coupling agent, and N-cetyl-N,N,N-trimethylammonium bromide (CTAB) was added to remove SDS from the catalyst. The catalyst was characterized by XRD, FTIR, and Raman spectroscopy. The effect of the heterogeneous catalyst on the conversion of canola oil, corn oil, and free fatty acids was investigated. To analyze the conversion of lipid oils to biofuel an in situ Raman spectroscopic method was developed. Catalyst synthesis methods and a proposed mechanism for converting triglycerides and free fatty acids to biofuel will be presented.

Crack layer theory

NASA Technical Reports Server (NTRS)

Chudnovsky, A.

1984-01-01

A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

Crack layer theory

NASA Technical Reports Server (NTRS)

Chudnovsky, A.

1987-01-01

A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

Synthesis and characterization of Sn/zeolite and catalytic activity test in the esterification reaction of sludge oil

NASA Astrophysics Data System (ADS)

Alimuddin, Andi Hairil; Usman, Thamrin; Wahyuni, Nelly; Rudiyansyah, Prawatya, Yopa Eka; Astar, Ismail; Yustira, Yudi

2017-03-01

Synthesis of Sn-Zeolite has been made to use for esterification reaction of free fatty acids in sludge oil. Catalyst characterization was accomplished using X-Ray Diffraction (XRD), X-Ray Flourecence (XRF), and Fourier Transform Infra Red (FTIR). Catalyst Sn/zeolite was synthesized by impregnated Sn of SnCl2 into the zeolite. The amount of Sn impregnated base on the value of cation exchange capacity (CEC) of zeolites. Esterification reaction of fatty acids from sludge oil using Sn/Zeolite catalyst was did by variated the reaction time. XRD analysis results showed that the catalyst Sn/zeolite was dominated by modernit and quartz. XRF analysis results was increasing amount of Sn metal and the Si/Al ratio on Sn/zeolite catalyst along with addition of Sn metal. FTIR analysis results showed that the catalyst synthesized had Bronsted acid side (the spectrum 1639.4; 1656.7; 1654.8 cm-1) and the Lewis acid (spectrum 1400.2 and 1402.2 cm-1). The results showed that the optimum conditions of esterification reaction in 4 hours reaction time, 5% concentration of the catalyst, and molar ratio was about 1:10 with a conversion percentage of products reached 96.00%, which can be achieved with a ratio was about 4:1 between Sn and zeolite on Sn/zeolite catalyst.

Rational Design of N- S- Fe- Doped Nanoporous Carbon Catalysts from Covalent Triazine Framework for High Efficient ORR.

PubMed

Zhu, Yuanzhi; Chen, Xifan; Liu, Jing; Zhang, Junfeng; Xu, Danyun; Peng, Wenchao; Li, Yang; Zhang, Guoliang; Zhang, Fengbao; Fan, Xiaobin

2018-05-15

Porous organic polymers (POFs) are promising precursors for developing high performance transition metal-nitrogen-carbon (M-N/C) catalysts towards ORR. But the rational design of POFs precursors remain a great challenge, because of the elusive structural association between the sacrificial POFs and the final M-N/C catalysts. Based on covalent triazine frameworks (CTFs), we developed a series of sulfur-doped Fe-N/C catalysts by selecting six different aromatic nitriles as building blocks. A new mixed solvent of molten FeCl3 and S was used for CTF polymerization, which benefit the formation of Fe-Nx site and make the subsequent pyrolysis process more convenient. Comprehensive study on these CTF-derived catalysts shows their ORR activities are not directly dependent on the theoretical N/C ratio of the building block, but closely correlated to the ratios of the nitrile group to benzene ring (Nnitrile/Nbenzene) and geometries of the building blocks. The high ratios of the Nnitrile/Nbenzene are crucial for ORR activity of the final catalysts due to the formation of more N-doped microporous and Fe-Nx sites in pyrolysis possess. The optimized catalyst shows high ORR performances in acid and superior ORR activity to the Pt/C catalysts under alkaline conditions. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bulk chlorine uptake by polyamide active layers of thin-film composite membranes upon exposure to free chlorine-kinetics, mechanisms, and modeling.

PubMed

Powell, Joshua; Luh, Jeanne; Coronell, Orlando

2014-01-01

We studied the volume-averaged chlorine (Cl) uptake into the bulk region of the aromatic polyamide active layer of a reverse osmosis membrane upon exposure to free chlorine. Volume-averaged measurements were obtained using Rutherford backscattering spectrometry with samples prepared at a range of free chlorine concentrations, exposure times, and mixing, rinsing, and pH conditions. Our volume-averaged measurements complement previous studies that have quantified Cl uptake at the active layer surface (top ≈ 7 nm) and advance the mechanistic understanding of Cl uptake by aromatic polyamide active layers. Our results show that surface Cl uptake is representative of and underestimates volume-averaged Cl uptake under acidic conditions and alkaline conditions, respectively. Our results also support that (i) under acidic conditions, N-chlorination followed by Orton rearrangement is the dominant Cl uptake mechanism with N-chlorination as the rate-limiting step; (ii) under alkaline conditions, N-chlorination and dechlorination of N-chlorinated amide links by hydroxyl ion are the two dominant processes; and (iii) under neutral pH conditions, the rates of N-chlorination and Orton rearrangement are comparable. We propose a kinetic model that satisfactorily describes Cl uptake under acidic and alkaline conditions, with the largest discrepancies between model and experiment occurring under alkaline conditions at relatively high chlorine exposures.

Synthesis and crystal structure of two new uranyl oxychloro-vanadate layered compounds: M7(UO 2) 8(VO 4) 2O 8Cl with M=Rb, Cs

NASA Astrophysics Data System (ADS)

Duribreux, I.; Saadi, M.; Obbade, S.; Dion, C.; Abraham, F.

2003-05-01

Two new alkali uranyl oxychloro vanadates M7(UO 2) 8(VO 4) 2O 8Cl with M=Rb, Cs, have been synthesized by solid-state reactions and their structures determined from single-crystal X-ray diffraction data. They crystallize in the orthorhombic system with space groups Pmcn and Pmmn, respectively. The a and b unit cell parameters are almost identical in both compounds while the c parameter in the Rb compound is doubled: Rb— a=21.427(5) Å, b=11.814(3) Å, c=14.203(3) Å, V=3595.1(1) Å 3, Z=4, ρmes=5.93(2) g/cm 3, ρcal=5.82(1) g/cm 3; Cs— a=21.458(3) Å, b=11.773(2) Å, c=7.495(1) Å, V=1893.6(5) Å 3, Z=2, ρmes=6.09(2) g/cm 3, ρcal=6.11(1) g/cm 3. A full-matrix least-squares refinement yielded R1=0.0221, w R2=0.0562 for 2675 independent reflections and R1=0.0386, w R2=0.1042 for 2446 independent reflections, for the Rb and Cs compounds, respectively. Data were collected with Mo( Kα) radiation and a charge coupled device (CCD) detector of a Bruker diffractometer. Both structures are characterized by [(UO 2) 8(VO 4) 2O 8Cl] n7 n- layers parallel to the (001) plane. The layers are built up from VO 4 tetrahedra, UO 7 and UO 6Cl pentagonal bipyramids, and UO 6 distorded octahedra. The UO 7 and UO 6Cl pentagonal bipyramids are associated by sharing opposite equatorial edges to form infinite chains (UO 5-UO 4Cl-UO 5) n parallel to the a axis. These chains are linked together by VO 4 tetrahedra, UO 6 octahedra, UO 7 corner sharing and UO 6Cl, Cl sharing. Both structures differ simply by the symmetry of the layers. The unit cell contains one centrosymmetric layer in the Cs compound, whereas in the two-layer unit cell of the Rb compound, two non-centrosymmetric consecutive layers are related by an inversion center. The layers appear to be held together by the alkali ions. The mobility of the M+ ions within the interlayer space in M7(UO 2) 8(VO 4) 2O 8Cl and carnotite analog compounds is compared.

Dual Layer Monolith ATR of Pyrolysis Oil for Distributed Synthesis Gas Production

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

Lawal, Adeniyi

We have successfully demonstrated a novel reactor technology, based on BASF dual layer monolith catalyst, for miniaturizing the autothermal reforming of pyrolysis oil to syngas, the second and most critical of the three steps for thermochemically converting biomass waste to liquid transportation fuel. The technology was applied to aged as well as fresh samples of pyrolysis oil derived from five different biomass feedstocks, namely switch-grass, sawdust, hardwood/softwood, golden rod and maple. Optimization of process conditions in conjunction with innovative reactor system design enabled the minimization of carbon deposit and control of the H2/CO ratio of the product gas. A comprehensivemore » techno-economic analysis of the integrated process using in part, experimental data from the project, indicates (1) net energy recovery of 49% accounting for all losses and external energy input, (2) weight of diesel oil produced as a percent of the biomass to be ~14%, and (3) for a demonstration size biomass to Fischer-Tropsch liquid plant of ~ 2000 daily barrels of diesel, the price of the diesel produced is ~$3.30 per gallon, ex. tax. However, the extension of catalyst life is critical to the realization of the projected economics. Catalyst deactivation was observed and the modes of deactivation, both reversible and irreversible were identified. An effective catalyst regeneration strategy was successfully demonstrated for reversible catalyst deactivation while a catalyst preservation strategy was proposed for preventing irreversible catalyst deactivation. Future work should therefore be focused on extending the catalyst life, and a successful demonstration of an extended (> 500 on-stream hours) catalyst life would affirm the commercial viability of the process.« less

Direct observation of morphological evolution of a catalyst during carbon nanotube forest growth: new insights into growth and growth termination

NASA Astrophysics Data System (ADS)

Jeong, Seojeong; Lee, Jaegeun; Kim, Hwan-Chul; Hwang, Jun Yeon; Ku, Bon-Cheol; Zakharov, Dmitri N.; Maruyama, Benji; Stach, Eric A.; Kim, Seung Min

2016-01-01

In this study, we develop a new methodology for transmission electron microscopy (TEM) analysis that enables us to directly investigate the interface between carbon nanotube (CNT) arrays and the catalyst and support layers for CNT forest growth without any damage induced by a post-growth TEM sample preparation. Using this methodology, we perform in situ and ex situ TEM investigations on the evolution of the morphology of the catalyst particles and observe the catalyst particles to climb up through CNT arrays during CNT forest growth. We speculate that the lifted catalysts significantly affect the growth and growth termination of CNT forests along with Ostwald ripening and sub-surface diffusion. Thus, we propose a modified growth termination model which better explains various phenomena related to the growth and growth termination of CNT forests.In this study, we develop a new methodology for transmission electron microscopy (TEM) analysis that enables us to directly investigate the interface between carbon nanotube (CNT) arrays and the catalyst and support layers for CNT forest growth without any damage induced by a post-growth TEM sample preparation. Using this methodology, we perform in situ and ex situ TEM investigations on the evolution of the morphology of the catalyst particles and observe the catalyst particles to climb up through CNT arrays during CNT forest growth. We speculate that the lifted catalysts significantly affect the growth and growth termination of CNT forests along with Ostwald ripening and sub-surface diffusion. Thus, we propose a modified growth termination model which better explains various phenomena related to the growth and growth termination of CNT forests. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05547d

Tuning the Composition of Electrodeposited Bimetallic Tin-Lead Catalysts for Enhanced Activity and Durability in Carbon Dioxide Electroreduction to Formate.

PubMed

Moore, Colin E; Gyenge, Előd L

2017-09-11

Bimetallic Sn-Pb catalysts with five different Sn/Pb atomic ratios were electrodeposited on Teflonated carbon paper and non-Teflonated carbon cloth using both fluoroborate- and oxide-containing deposition media to produce catalysts for the electrochemical reduction of CO 2 (ERC) to formate (HCOO - ). The interaction between catalyst composition, morphology, substrate, and deposition media was investigated by using cyclic voltammetry and constant potential electrolysis at -2.0 V versus Ag/AgCl for 2 h in 0.5 m KHCO 3 . The catalysts were analyzed before and after electrolysis by using SEM and XRD to determine the mechanisms of Faradaic efficiency loss and degradation. Catalysts that are mainly Sn with 15-35 at % Pb generated Faradaic efficiencies up to 95 % with a stable performance. However, pure Sn catalysts showed high initial stage formate production rates but experienced an extensive (up to 30 %) decrease of the Faradaic efficiency. The XRD results demonstrated the presence of polycrystalline SnO 2 after electrolysis using Sn-Pb catalysts with 35 at % Pb and its absence in the case of pure Sn. It is proposed that the presence of Pb (15-35 at %) in mainly Sn catalysts stabilized SnO 2 , which is responsible for the enhanced Faradaic efficiency and catalytic durability in the ERC. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Carbon nanotube nanoelectrode arrays

DOEpatents

Ren, Zhifeng; Lin, Yuehe; Yantasee, Wassana; Liu, Guodong; Lu, Fang; Tu, Yi

2008-11-18

The present invention relates to microelectode arrays (MEAs), and more particularly to carbon nanotube nanoelectrode arrays (CNT-NEAs) for chemical and biological sensing, and methods of use. A nanoelectrode array includes a carbon nanotube material comprising an array of substantially linear carbon nanotubes each having a proximal end and a distal end, the proximal end of the carbon nanotubes are attached to a catalyst substrate material so as to form the array with a pre-determined site density, wherein the carbon nanotubes are aligned with respect to one another within the array; an electrically insulating layer on the surface of the carbon nanotube material, whereby the distal end of the carbon nanotubes extend beyond the electrically insulating layer; a second adhesive electrically insulating layer on the surface of the electrically insulating layer, whereby the distal end of the carbon nanotubes extend beyond the second adhesive electrically insulating layer; and a metal wire attached to the catalyst substrate material.

Transport equations in an enzymatic glucose fuel cell

NASA Astrophysics Data System (ADS)

Jariwala, Soham; Krishnamurthy, Balaji

2018-01-01

A mathematical model is developed to study the effects of convective flux and operating temperature on the performance of an enzymatic glucose fuel cell with a membrane. The model assumes isothermal operating conditions and constant feed rate of glucose. The glucose fuel cell domain is divided into five sections, with governing equations describing transport characteristics in each region, namely - anode diffusion layer, anode catalyst layer (enzyme layer), membrane, cathode catalyst layer and cathode diffusion layer. The mass transport is assumed to be one-dimensional and the governing equations are solved numerically. The effects flow rate of glucose feed on the performance of the fuel cell are studied as it contributes significantly to the convective flux. The effects of operating temperature on the performance of a glucose fuel cell are also modeled. The cell performances are compared using cell polarization curves, which were found compliant with experimental observations.

ZIF-67-derived hollow nanocages with layered double oxides shell as high-Efficiency catalysts for CO oxidation

NASA Astrophysics Data System (ADS)

Kong, Wenpeng; Li, Jing; Chen, Yao; Ren, Yuqing; Guo, Yonghua; Niu, Shengli; Yang, Yanzhao

2018-04-01

Constructing non-precious hybrid metal oxides with specific morphology as cost-effective and highly efficient catalysts is a promising way for the automotive exhaust purification. In this work, we report a facile strategy for the fabrication of a unique hollow Co-Ni layered double oxides (HLDO) nanocages by using zeolitic imidazole frameworks (ZIFs) as template. The synthesis of intermediate core-shell and hollow Co-Ni layered double hydroxides (HLDH) nanoflakes as well as the corresponding Co-Ni oxides products were successfully controlled, and the formation process was also explained. Among ZIF-67-derived oxides, HLDO exhibits excellent catalytic activities (complete conversion of CO into CO2 at 118 °C) and long-term stability for CO oxidation. The remarkable catalytic activities of HLDO can be attributed to high surface area (258 m2 g-1) inherited from the HLDH, which could provide more active sites for CO oxidation. In addition, active oxygen species indicated by the O 1 s XPS spectrum and improved synergistic effect between NiO and Co3O4 reflected by H2-TPR, further explain the enhanced performance of the HLDO catalysts. The presented strategy for controlled design and synthesis of hollow multicomponent metal oxides will provide prospects in developing highly effective catalysts.

Geomaterials: their application to environmental remediation

PubMed Central

Yamada, Hirohisa; Tamura, Kenji; Watanabe, Yujiro; Iyi, Nobuo; Morimoto, Kazuya

2011-01-01

Geomaterials are materials inspired by geological systems originating from the billion years long history of the Earth. This article reviews three important classes of geomaterials. The first one is smectites—layered silicates with a cation-exchange capacity. Smectites are useful for removing pollutants and as intercalation compounds, catalysts and polymer nanocomposites. The second class is layered double hydroxides (LDHs). They have an anion-exchange capacity and are used as catalysts, catalyst precursors, sorbents and scavengers for halogens. The third class of geomaterials is zeolites—microporous materials with a cation-exchange capacity which are used for removing harmful cations. Zeolite composites with LDHs can absorb ammonium and phosphate ions in rivers and lakes, whereas zeolite/apatite composites can immobilize the radioactive iodine. These geomaterials are essential for environmental remediation. PMID:27877455

Scalable synthesis of interconnected porous silicon/carbon composites by the Rochow reaction as high-performance anodes of lithium ion batteries.

PubMed

Zhang, Zailei; Wang, Yanhong; Ren, Wenfeng; Tan, Qiangqiang; Chen, Yunfa; Li, Hong; Zhong, Ziyi; Su, Fabing

2014-05-12

Despite the promising application of porous Si-based anodes in future Li ion batteries, the large-scale synthesis of these materials is still a great challenge. A scalable synthesis of porous Si materials is presented by the Rochow reaction, which is commonly used to produce organosilane monomers for synthesizing organosilane products in chemical industry. Commercial Si microparticles reacted with gas CH3 Cl over various Cu-based catalyst particles to substantially create macropores within the unreacted Si accompanying with carbon deposition to generate porous Si/C composites. Taking advantage of the interconnected porous structure and conductive carbon-coated layer after simple post treatment, these composites as anodes exhibit high reversible capacity and long cycle life. It is expected that by integrating the organosilane synthesis process and controlling reaction conditions, the manufacture of porous Si-based anodes on an industrial scale is highly possible. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Continuous-flux MOVPE growth of position-controlled N-face GaN nanorods and embedded InGaN quantum wells

NASA Astrophysics Data System (ADS)

Bergbauer, W.; Strassburg, M.; Kölper, Ch; Linder, N.; Roder, C.; Lähnemann, J.; Trampert, A.; Fündling, S.; Li, S. F.; Wehmann, H.-H.; Waag, A.

2010-07-01

We demonstrate the fabrication of N-face GaN nanorods by metal organic vapour phase epitaxy (MOVPE), using continuous-flux conditions. This is in contrast to other approaches reported so far, which have been based on growth modes far off the conventional growth regimes. For position control of nanorods an SiO2 masking layer with a dense hole pattern on a c-plane sapphire substrate was used. Nanorods with InGaN/GaN heterostructures have been grown catalyst-free. High growth rates up to 25 µm h - 1 were observed and a well-adjusted carrier gas mixture between hydrogen and nitrogen enabled homogeneous nanorod diameters down to 220 nm with aspect ratios of approximately 8:1. The structural quality and defect progression within nanorods were determined by transmission electron microscopy (TEM). Different emission energies for InGaN quantum wells (QWs) could be assigned to different side facets by room temperature cathodoluminescence (CL) measurements.

Continuous-flux MOVPE growth of position-controlled N-face GaN nanorods and embedded InGaN quantum wells.

PubMed

Bergbauer, W; Strassburg, M; Kölper, Ch; Linder, N; Roder, C; Lähnemann, J; Trampert, A; Fündling, S; Li, S F; Wehmann, H-H; Waag, A

2010-07-30

We demonstrate the fabrication of N-face GaN nanorods by metal organic vapour phase epitaxy (MOVPE), using continuous-flux conditions. This is in contrast to other approaches reported so far, which have been based on growth modes far off the conventional growth regimes. For position control of nanorods an SiO(2) masking layer with a dense hole pattern on a c-plane sapphire substrate was used. Nanorods with InGaN/GaN heterostructures have been grown catalyst-free. High growth rates up to 25 microm h(-1) were observed and a well-adjusted carrier gas mixture between hydrogen and nitrogen enabled homogeneous nanorod diameters down to 220 nm with aspect ratios of approximately 8:1. The structural quality and defect progression within nanorods were determined by transmission electron microscopy (TEM). Different emission energies for InGaN quantum wells (QWs) could be assigned to different side facets by room temperature cathodoluminescence (CL) measurements.

Cascade catalysis for the homogeneous hydrogenation of CO2 to methanol.

PubMed

Huff, Chelsea A; Sanford, Melanie S

2011-11-16

This communication demonstrates the homogeneous hydrogenation of CO(2) to CH(3)OH via cascade catalysis. Three different homogeneous catalysts, (PMe(3))(4)Ru(Cl)(OAc), Sc(OTf)(3), and (PNN)Ru(CO)(H), operate in sequence to promote this transformation.

Assessment of density functional methods for the study of olefin metathesis catalysed by ruthenium alkylidene complexes

NASA Astrophysics Data System (ADS)

Śliwa, Paweł; Handzlik, Jarosław

2010-06-01

Performance of 31 DFT methods in thermochemistry of olefin metathesis involving the model catalyst (PH 3) 2(Cl) 2Ru dbnd CH 2 is studied using the CCSD(T) reference energies. The best methods are M06, ωB97X-D and PBE0, followed by MPW1B95, LC-ωPBE, M05-2X and B1B95. Among 20 functionals tested in reproduction of experimental PCy 3 dissociation energy for the Grubbs catalyst (H 2IMes)(PCy 3)(Cl) 2Ru dbnd CHPh, the M06-class and M05-2X methods are most accurate. ωB97X-D overestimates the dissociation energy, whereas MPW1B95, LC-ωPBE, PBE0 and B1B95 underestimate it, similarly to other methods, which give larger errors. LC-ωPBE, B1B95, MPW1B95 and PBE0 provide the best geometries.

Synthesis of Fe nanoparticles on polyaniline covered carbon nanotubes for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Hu, Tian-Hang; Yin, Zhong-Shu; Guo, Jian-Wei; Wang, Cheng

2014-12-01

Fe nanoparticles immobilized on polyaniline-covered carbon nanotube (CNT) surfaces (Fe NPs-PANI/CNT) are prepared by reducing FeCl3 in the mixing solution of aniline and CNT. Significantly, the structure of such composites can be effectively optimized by pretreating FeCl3 with sodium citrate (CA). In the absence of CNTs, we found these two routes have large differences in reduction behaviors and different PANI states with varied conductivities. Therefore, the self-assembly mechanism in the preparation is proposed and the controlled self-assembly manner in the pretreating route is disclosed. Under acid condition, both catalysts demonstrate high oxygen reduction reaction (ORR) activity with four-electron pathway, and high electrochemical durability, revealing a promising application in the proton exchange membrane fuel cells. However, the high Tafel slopes relating to the surface red-ox couple and porous conductivity are still the main obstacles to improve their ORR dynamic, and more efforts on these aspects are needed to drive non-noble catalyst application in future.

Brown algae hydrolysis in 1-n-butyl-3-methylimidazolium chloride with mineral acid catalyst system.

PubMed

Malihan, Lenny B; Nisola, Grace M; Chung, Wook-Jin

2012-08-01

The amenability of three brown algal species, Sargassum fulvellum, Laminaria japonica and Undaria pinnatifida, to hydrolysis were investigated using the ionic liquid (IL), 1-n-butyl-3-methylimidazolium chloride ([BMIM]Cl). Compositional analyses of the brown algae reveal that sufficient amounts of sugars (15.5-29.4 wt.%) can be recovered. Results from hydrolysis experiments show that careful selection of the type of mineral acid as catalyst and control of acid loading could maximize the recovery of sugars. Optimal reaction time and temperature were determined from the kinetic studies on the sequential reducing sugar (TRS) formation and degradation. Optimal reaction times were determined based on the extent of furfurals formation as TRS degradation products. X-ray diffraction and environmental scanning electron microscopy confirmed the suitability of [BMIM]Cl as solvent for the hydrolysis of the three brown algae. Overall results show the potential of brown algae as renewable energy resources for the production of valuable chemicals and biofuels. Copyright © 2012 Elsevier Ltd. All rights reserved.

An efficient one-pot two catalyst system in the construction of 2-substituted benzimidazoles: synthesis of benzimidazo[1,2-c]quinazolines.

PubMed

Cimarelli, Cristina; Di Nicola, Matteo; Diomedi, Simone; Giovannini, Riccardo; Hamprecht, Dieter; Properzi, Roberta; Sorana, Federico; Marcantoni, Enrico

2015-12-28

The benzimidazole core is a common moiety in a large number of natural products and pharmacologically active small molecules. The synthesis of novel benzimidazole derivatives remains a main focus in medicinal research. In continuation of the efforts towards Ce(III) catalysts for organic transformations, we observed for the first time the activity of the iodide ion and copper cation in activating CeCl3·7H2O in the selective formation of prototypical 2-substituted benzimidazoles. The one-pot CeCl3·7H2O-CuI catalytic system procedure includes the cyclo-dehydrogenation of aniline Schiff's bases, generated in situ from the condensation of 1,2-phenylenediamine and aldehydes, followed by the oxidation with iodine, which works as a hydrogen sponge. Mild reaction conditions, good to excellent yields, and clean reactions make the procedure a useful contribution to the synthesis of biologically active fused heterocycles containing benzimidazoquinazolines.

Hydrolysis of cellulose catalyzed by quaternary ammonium perrhenates in 1-allyl-3-methylimidazolium chloride.

PubMed

Wang, Jingyun; Zhou, Mingdong; Yuan, Yuguo; Zhang, Quan; Fang, Xiangchen; Zang, Shuliang

2015-12-01

Quaternary ammonium perrhenates were applied as catalyst to promote the hydrolysis of cellulose in 1-allyl-3-methylimidazolium chloride ([Amim]Cl). The quaternary ammonium perrhenates displayed good catalytic performance for cellulose hydrolysis. Water was also proven to be effective to promote cellulose hydrolysis. Accordingly, 97% of total reduced sugar (TRS) and 42% of glucose yields could be obtained under the condition of using 5mol% of tetramethyl ammonium perrhenate as catalyst, 70μL of water, ca. 0.6mmol of microcrystalline cellulose (MCC) and 2.0g of [Amim]Cl as solvent under microwave irradiation for 30min at 150°C (optimal conditions). The influence of quaternary ammonium cation on the efficiency of cellulose hydrolysis was examined based on different cation structures of perrhenates. The mechanism on perrhenate catalyzed cellulose hydrolysis is also discussed, whereas hydrogen bonding between ReO4 anion and hydroxyl groups of cellulose is assumed to be the key step for depolymerization of cellulose. Copyright © 2015. Published by Elsevier Ltd.

Molten salt-mediated formation of g-C3N4-MoS2 for visible-light-driven photocatalytic hydrogen evolution

NASA Astrophysics Data System (ADS)

Li, Ni; Zhou, Jing; Sheng, Ziqiong; Xiao, Wei

2018-02-01

Construction of two-dimensional/two-dimensional (2D/2D) hybrid with well-defined composition and microstructure is a general protocol to achieve high-performance catalysts. We herein report preparation of g-C3N4-MoS2 hybrid by pyrolysis of affordable melamine and (NH4)2MoS4 in molten LiCl-NaCl-KCl at 550 °C. Molten salts are confirmed as ideal reaction media for formation of homogeneous hybrid. Characterizations suggest a strong interaction between g-C3N4 and MoS2 in the hybrid, which results in an enhanced visible-light-driven photocatalytic hydrogen generation of the hybrid with an optimal g-C3N4/MoS2 ratio. The present study highlights the merits of molten salt methods on preparation of 2D photocatalysts and provides a rational design of 2D/2D hybrid catalysts for advanced environmental and energy applications.

Production of furfural from xylose, xylan and corncob in gamma-valerolactone using FeCl3·6H2O as catalyst.

PubMed

Zhang, Luxin; Yu, Hongbing; Wang, Pan; Li, Yong

2014-01-01

An efficient and simple one-pot monophasic reaction system with small carbon footprint for converting xylose, xylan and corncob into furfural was developed in gamma-valerolactone (GVL, an ideal sustainable solvent derived from lignocelluloses) by using FeCl3·6H2O as catalyst. Good yields of furfural from xylose were obtained, and the system was shown to work for xylan and corncob as well. A surprisingly high furfural yield of 79.6% from untreated corncob was achieved at 458 K for 100 min. Contrary to what was generally believed, the addition of water, reduced the rate of the reactions, but showed positive effect on preventing the furfural from degradation in GVL. Besides, the C6 sugars (glucose and cellulose) afforded 11.4-24.5% furfural yields when employing this catalytic approach. The reaction system proposed in this manuscript showed great potential for optimizing the catalytic process in furfural production. Copyright © 2013 Elsevier Ltd. All rights reserved.

An Iron(II)(1,3-bis(2′-pyridylimino)isoindoline) Complex as a Catalyst for Substrate Oxidation with H2O2. Evidence for a Transient Peroxodiiron(III) Species

PubMed Central

Pap, József S.; Cranswick, Matthew A.; Balogh-Hergovich, É.; Baráth, Gábor; Giorgi, Michel; Rohde, Gregory T.; Kaizer, József; Speier, Gábor; Que, Lawrence

2014-01-01

The complex [Fe(indH)(solvent)3](ClO4)2 (1) has been isolated from the reaction of equimolar amounts of 1,3-bis(2′-pyridylimino)isoindoline (indH) and Fe(ClO4)2 in acetonitrile and characterized by X-ray crystallography and several spectroscopic techniques. It is a suitable catalyst for the oxidation of thioanisoles and benzyl alcohols with H2O2 as the oxidant. Hammett correlations and kinetic isotope effect experiments support the involvement of an electrophilic metal-based oxidant. A metastable green species (2) is observed when 1 is reacted with H2O2 at −40 °C, which has been characterized to have a FeIII(μ-O)(μ-O2)FeIII core on the basis of UV-Vis, electron paramagnetic resonance, resonance Raman, and X-ray absorption spectroscopic data. PMID:24587695

Cyclopentadienyl-bis(oxazoline) magnesium and zirconium complexes in aminoalkene hydroaminations

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

Eedugurala, Naresh; Hovey, Megan; Ho, Hung -An

Here, a new class of cyclopentadiene-bis(oxazoline) compounds and their piano-stool-type organometallic complexes have been prepared as catalysts for hydroamination of aminoalkenes. The two compounds MeC(Ox Me2) 2C 5H 5 (Bo MCpH; Ox Me2 = 4,4-dimethyl-2-oxazoline) and MeC(Ox Me2) 2C 5Me 4H (Bo MCp tetH) are synthesized from C 5R 4HI (R = H, Me) and MeC(Ox Me2) 2Li. These cyclopentadiene-bis(oxazolines) are converted into ligands that support a variety of metal centers in piano-stool-type geometries, and here we report the preparation of Mg, Tl, Ti, and Zr compounds. Bo MCpH and Bo MCp tetH react with MgMe 2(O 2C 4H 8)more » 2 to give the magnesium methyl complexes {Bo MCp}MgMe and {Bo MCp tet}MgMe. Bo MCpH and Bo MCp tetH are converted to Bo MCpTl and Bo MCp tetTl by reaction with TlOEt. The thallium derivatives react with TiCl 3(THF) 3 to provide [{Bo MCp}TiCl(μ-Cl)] 2 and [{Bo MCptet}TiCl(μ-Cl)] 2, the former of which is crystallographically characterized as a dimeric species. Bo MCpH and Zr(NMe 2) 4 react to eliminate dimethylamine and afford {Bo MCp}Zr(NMe 2) 3, which is crystallographically characterized as a monomeric four-legged piano-stool compound. {Bo MCp}Zr(NMe 2) 3, {Bo MCp}MgMe, and {Bo MCp tet}MgMe are efficient catalysts for the hydroamination/cyclization of aminoalkenes under mild conditions.« less

Cyclopentadienyl-bis(oxazoline) magnesium and zirconium complexes in aminoalkene hydroaminations

DOE PAGES

Eedugurala, Naresh; Hovey, Megan; Ho, Hung -An; ...

2015-11-25

Here, a new class of cyclopentadiene-bis(oxazoline) compounds and their piano-stool-type organometallic complexes have been prepared as catalysts for hydroamination of aminoalkenes. The two compounds MeC(Ox Me2) 2C 5H 5 (Bo MCpH; Ox Me2 = 4,4-dimethyl-2-oxazoline) and MeC(Ox Me2) 2C 5Me 4H (Bo MCp tetH) are synthesized from C 5R 4HI (R = H, Me) and MeC(Ox Me2) 2Li. These cyclopentadiene-bis(oxazolines) are converted into ligands that support a variety of metal centers in piano-stool-type geometries, and here we report the preparation of Mg, Tl, Ti, and Zr compounds. Bo MCpH and Bo MCp tetH react with MgMe 2(O 2C 4H 8)more » 2 to give the magnesium methyl complexes {Bo MCp}MgMe and {Bo MCp tet}MgMe. Bo MCpH and Bo MCp tetH are converted to Bo MCpTl and Bo MCp tetTl by reaction with TlOEt. The thallium derivatives react with TiCl 3(THF) 3 to provide [{Bo MCp}TiCl(μ-Cl)] 2 and [{Bo MCptet}TiCl(μ-Cl)] 2, the former of which is crystallographically characterized as a dimeric species. Bo MCpH and Zr(NMe 2) 4 react to eliminate dimethylamine and afford {Bo MCp}Zr(NMe 2) 3, which is crystallographically characterized as a monomeric four-legged piano-stool compound. {Bo MCp}Zr(NMe 2) 3, {Bo MCp}MgMe, and {Bo MCp tet}MgMe are efficient catalysts for the hydroamination/cyclization of aminoalkenes under mild conditions.« less

Janus structured Pt–FeNC nanoparticles as a catalyst for the oxygen reduction reaction

DOE PAGES

Kuttiyiel, Kurian A.; Sasaki, Kotaro; Park, Gu -Gon; ...

2017-01-03

Here, we present a new Janus structured catalyst consisting of Pt nanoparticles on Fe–N–C nanoparticles encapsulated by graphene layers for the ORR. The ORR activity of the catalyst increases under potential cycling as the unique Janus nanostructure is further bonded due to a synergetic effect. The present study describes an important advanced approach for the future design of efficient, stable, and low-cost Pt-based electrocatalytic systems.

Single-layer transition metal sulfide catalysts

DOEpatents

Thoma, Steven G [Albuquerque, NM

2011-05-31

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

Investigating the Catalytic Growth of Carbon Nanotubes with In Situ Raman Monitoring

DTIC Science & Technology

2015-06-01

single-walled carbon nanotube growth using cobalt deposited on Si/SiO2 as a model system. In situ Raman studies revealed that thin catalyst layers... cobalt thickness were studied. Surface analyses showed that during the catalyst preparation, catalyst atoms at the interface with silica form small...nanostructures. However, highly-reducing conditions are required to reduce the small silicate domains into small cobalt particles able to grow single-walled

Very large cooperative effects in heterobimetallic titanium-chromium catalysts for ethylene polymerization/copolymerization.

PubMed

Liu, Shaofeng; Motta, Alessandro; Mouat, Aidan R; Delferro, Massimiliano; Marks, Tobin J

2014-07-23

The heterobimetallic complexes, (η(5)-indenyl)[1-Me2Si((t)BuN)TiCl2]-3-CnH2n-[N,N-bis(2-(ethylthio)ethyl)amine]CrCl3 (n = 0, Ti-C0-Cr(SNS); n = 2, Ti-C2-Cr(SNS); n = 6, Ti-C6-Cr(SNS)), (η(5)-indenyl)[1-Me2Si((t)BuN)TiCl2]-3-C2H4-[N,N-bis((o-OMe-C6H4)2P)amine]CrCl3 (Ti-C2-Cr(PNP)), and (η(5)-indenyl)[1-Me2Si((t)BuN)TiCl2]-3-C2H4-[N,N-bis((diethylamine)ethyl)-amine]CrCl3 (Ti-C2-Cr(NNN)), are synthesized, fully characterized, and employed as olefin polymerization catalysts. With ethylene as the feed and MAO as cocatalyst/activator, SNS-based complexes Ti-C0-Cr(SNS), Ti-C2-Cr(SNS), and Ti-C6-Cr(SNS) afford linear low-density polyethylenes (LLDPEs) with exclusive n-butyl branches (6.8-25.8 branches/1000 C), while under identical polymerization conditions Ti-C2-Cr(PNP) and Ti-C2-Cr(NNN) produce polyethylenes with heterogeneous branching (C2, C4, and C≥6) or negligible branching, respectively. Under identical ethylene polymerization conditions, Ti-C0-Cr(SNS) produces polyethylenes with higher activity (4.5× and 6.1×, respectively), Mn (1.3× and 1.8×, respectively), and branch density (1.4× and 3.8×, respectively), than Ti-C2-Cr(SNS) and Ti-C6-Cr(SNS). Versus a CGC(Et)Ti + SNSCr tandem catalyst, Ti-C0-Cr(SNS) yields polyethylene with somewhat lower activity, but with 22.6× higher Mn and 4.0× greater branching density under identical conditions. In ethylene +1-pentene competition experiments, Ti-C0-Cr(SNS) yields 5.5% n-propyl branches and 94.5% n-butyl branches at [1-pentene] = 0.1 M, and the estimated effective local concentration of 1-hexene is ∼8.6 M. In contrast, the tandem CGC(Et)Ti + SNSCr system yields 91.0% n-propyl branches under identical reaction conditions. The homopolymerization and 1-pentene competition results argue that close Ti···Cr spatial proximity together with weak C-H···Ti and C-H···S interactions significantly influence relative 1-hexene enchainment and chain transfer rates, supported by DFT computation, and that such effects are conversion insensitive but cocatalyst and solvent sensitive.

pH-dependent release of trace elements including platinum group elements (PGEs) from gasoline and diesel catalysts

NASA Astrophysics Data System (ADS)

Sucha, Veronika; Mihaljevic, Martin; Ettler, Vojtech; Strnad, Ladislav

2014-05-01

The release of trace metals and platinum group elements (PGEs) from automobile exhaust catalysts represents a remarkable source of higly dispersed environmental contamination. Especially, PGEs have shown increasing research interest due to their possible bioaccessibility. In our research, we focused on leaching behaviour of trace metals from gasoline and diesel automobile catalysts. While catalysts for gasoline engines contain a mixture of Pt-Pd-Rh or Pd-Rh, catalysts for diesel engines are composed only of Pt. We used dust from two crushed gasoline and two crushed diesel catalysts (new and aged). The dust of gasoline catalysts contains significant concentrations of Pt (700 mg.kg-1), Pd (11 000 mg.kg-1) and Rh (700 mg.kg-1). And the dust of diesel catalysts are composed of Pt (3 900 mg.kg-1) and they contains negligible amounts of Pd dan Rh (< 0.5 mg.kg-1, < 0.1 mg.kg-1, respectively). To evaluate leaching of trace metals from dust we used pH-stat leaching test according to the European standard CEN/TS 14997. The concentrations of cations: PGEs (Pt, Pd a Rh), K, Na, Ca, Mg, Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, La and Ce were determined by inductively coupled plasma mass spectrometry (ICP-MS) and atomic absorption spectrometry (AAS), and anions: F-, Cl-, SO42- and NO3- by high-performance liquid chromatography. Although the dusts from catalysts were relatively stable to acid/base influence, the leaching of trace metals from catalysts showed a dependence on pH. Generally, the highest concentrations were released under acidic conditions. The leaching of PGEs was higher for Pt in diesel catalysts and for Pd and Rh in gasoline catalysts. The highest concentrations of Zn and Pb were observed in old catalysts. The rare earth metals were released more from gasoline catalysts. Catalysts particles represent health risk especially with respect to their PGEs contents.

Cyclic process for producing methane with catalyst regeneration

DOEpatents

Frost, Albert C.; Risch, Alan P.

1980-01-01

Carbon monoxide-containing gas streams are passed over a catalyst capable of catalyzing the disproportionation of carbon monoxide so as to deposit a surface layer of active surface carbon on the catalyst essentially without formation of inactive coke thereon. The surface layer is contacted with steam and is thus converted to methane and CO.sub.2, from which a relatively pure methane product may be obtained. For practical commercial operations utilizing the two-step process of the invention of a cyclic basis, nickel, cobalt, ruthenium, thenium and alloys thereof are especially prepared for use in a metal state, with CO disproportionation being carried out at temperatures up to about 350.degree. C. and with the conversion of active surface carbon to methane being carried out by reaction with steam. The catalyst is employed in such cyclic operations without the necessity for employing a regeneration step as part of each processing cycle. Inactive carbon or coke that tends to form on the catalyst over the course of continuous operations utilizing such cyclic process is effectively and advantageously removed, on a periodic basis, in place of conventional burn off with an inert stream containing a low concentration of oxygen.

Interdependency of Subsurface Carbon Distribution and Graphene–Catalyst Interaction

PubMed Central

2014-01-01

The dynamics of the graphene–catalyst interaction during chemical vapor deposition are investigated using in situ, time- and depth-resolved X-ray photoelectron spectroscopy, and complementary grand canonical Monte Carlo simulations coupled to a tight-binding model. We thereby reveal the interdependency of the distribution of carbon close to the catalyst surface and the strength of the graphene–catalyst interaction. The strong interaction of epitaxial graphene with Ni(111) causes a depletion of dissolved carbon close to the catalyst surface, which prevents additional layer formation leading to a self-limiting graphene growth behavior for low exposure pressures (10–6–10–3 mbar). A further hydrocarbon pressure increase (to ∼10–1 mbar) leads to weakening of the graphene–Ni(111) interaction accompanied by additional graphene layer formation, mediated by an increased concentration of near-surface dissolved carbon. We show that growth of more weakly adhered, rotated graphene on Ni(111) is linked to an initially higher level of near-surface carbon compared to the case of epitaxial graphene growth. The key implications of these results for graphene growth control and their relevance to carbon nanotube growth are highlighted in the context of existing literature. PMID:25188018

Gradient Mn-La-Pt Catalysts with Three-layered Structure for Li-O2 battery

PubMed Central

Cai, Kedi; Yang, Rui; Lang, Xiaoshi; Zhang, Qingguo; Wang, Zhenhua; He, Tieshi

2016-01-01

Gradient Mn-La-Pt catalysts with three-layered structure of manganese dioxide (MnO2), lanthanum oxide (La2O3), and Platinum (Pt) for Li-O2 battery are prepared in this study. The mass ratio of the catalysts is respectively 5:2:3, 4:2:4, and 3:2:5 (MnO2: La2O3: Pt) which is start from the side of the electrolyte. The relationship between morphology structure and electrochemical performance of gradient catalyst is investigated by energy dispersive spectrometry and constant current charge/discharge test. The Li-O2 battery based on gradient Mn-La-Pt catalysts shows high discharge specific capacity (2707 mAh g−1), specific energy density (8400 Wh kg−1) and long cycle life (56 cycles). The improvement of the Li-O2 battery discharge capacity is attributed to the gradient distribution of MnO2 and Pt and the involvement of La2O3 that can improve the energy density of the battery. More important, this work will also provide new ideas and methods for the research of other metal-air battery. PMID:27731340

Hydrogenation of Carbon Dioxide Catalyzed by Ruthenium Trimethylphosphine Complexes: A Mechanistic Investigation using High-Pressure NMR Spectroscopy

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

Getty, April D.; Tai, Chih-Cheng; Linehan, John C.

2009-08-26

The previously reported complex, cis-(PMe3)4RuCl(OAc) (1) acts as a catalyst for CO2 hydrogenation into formic acid in the presence of a base and an alcohol co-catalyst. NMR spectroscopy has revealed that 1 exists in solution in equilibrium with fac-(PMe3)3RuCl(h2-OAc) (2), [(PMe3)4Ru(h2-OAc)]Cl (3a), and free PMe3. Complex 2 has been isolated and characterized by elemental analysis, NMR spectroscopy, and X-ray crystallography. 2 has been tested as a CO2 hydrogenation catalyst, however, it performed poorly under the conditions of catalysis used for 1. Complex 3a can be prepared by adding certain alcohols, such as MeOH, EtOH, or o-C6H5OH, to a solution ofmore » 1 in CDCl3. The chloride ion of 3a has been exchanged for the non-coordinating anions BPh4 or B(ArF )4 (B(ArF)4 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) to produce [(PMe3)4Ru(h2-OAc)]BPh4 (3b) and [(PMe3)4Ru(h2-OAc)]B(ArF)4 (3c). Both of these complexes have been isolated and characterized by elemental analysis, NMR spectroscopy, and in the case of 3b, X-ray crystallography. Complexes 3b and 3c perform just as well as 1 for CO2 hydrogenation to formic acid in the presence of an alcohol co-catalyst; however, 3b,c perform equally well without the added alcohol. High-pressure NMR has been used to investigate the mechanism of CO2 hydrogenation via 3a,b in the presence of base. Two of the intermediates involved have been identified as cis-(PMe3)4RuH2 (5) and cis-(PMe3)4Ru(H)O2CH (6), and the role of the base includes not only trapping of the formic acid product, but also initiation of the catalysis by aiding the conversion of 3b,c to 5.« less

Oriented Pt Nanoparticles Supported on Few-Layers Graphene as Highly Active Catalyst for Aqueous-Phase Reforming of Ethylene Glycol.

PubMed

Esteve-Adell, Iván; Bakker, Nadia; Primo, Ana; Hensen, Emiel; García, Hermenegildo

2016-12-14

Pt nanoparticles (NPs) strongly grafted on few-layers graphene (G) have been prepared by pyrolysis under inert atmosphere at 900 °C of chitosan films (70-120 nm thickness) containing adsorbed H 2 PtCl 6 . Preferential orientation of exposed Pt facets was assessed by X-ray diffraction of films having high Pt loading where the 111 and 222 diffraction lines were observed and also by SEM imaging comparing elemental Pt mapping with the image of the 111 oriented particles. Characterization techniques allow determination of the Pt content (from 45 ng to 1 μg cm -2 , depending on the preparation conditions), particle size distribution (9 ± 2 nm), and thickness of the films (12-20 nm). Oriented Pt NPs on G exhibit at least 2 orders of magnitude higher catalytic activity for aqueous-phase reforming of ethylene glycol to H 2 and CO 2 compared to analogous samples of randomly oriented Pt NPs supported on preformed graphene. Oriented [Formula: see text]/fl-G undergoes deactivation upon reuse, the most probable cause being Pt particle growth, probably due to the presence of high concentrations of carboxylic acids acting as mobilizing agents during the course of the reaction.

Pre-treatment for ultrafiltration: effect of pre-chlorination on membrane fouling

PubMed Central

Yu, Wenzheng; Xu, Lei; Graham, Nigel; Qu, Jiuhui

2014-01-01

Microbial effects are believed to be a major contributor to membrane fouling in drinking water treatment. Sodium hypochlorite (NaClO) is commonly applied in membrane cleaning, but its potential use as a pretreatment for controlling operational fouling has received little attention. In this study, the effect of adding a continuous low dose of NaClO (1 mg/l as active Cl) in combination with alum, before ultrafiltration, was compared with only alum as pretreatment. The results showed that the addition of NaClO substantially reduced membrane fouling both in terms of the rate of TMP development and the properties of the membrane cake layer. Although the size of nano-scale primary coagulant flocs changed little by the addition of NaClO, the cake layer on the membrane had a greater porosity and a substantially reduced thickness. NaClO was found to inactivate bacteria in the influent flow, which reduced both microbial proliferation and the production of proteins and polysaccharides in the cake layer and contributed significantly to improving the overall ultrafiltration performance. NaClO dosing had no adverse impact on the formation of currently regulated disinfection by-product compounds (THMs and HAAs). PMID:25269375

Pre-treatment for ultrafiltration: effect of pre-chlorination on membrane fouling

NASA Astrophysics Data System (ADS)

Yu, Wenzheng; Xu, Lei; Graham, Nigel; Qu, Jiuhui

2014-10-01

Microbial effects are believed to be a major contributor to membrane fouling in drinking water treatment. Sodium hypochlorite (NaClO) is commonly applied in membrane cleaning, but its potential use as a pretreatment for controlling operational fouling has received little attention. In this study, the effect of adding a continuous low dose of NaClO (1 mg/l as active Cl) in combination with alum, before ultrafiltration, was compared with only alum as pretreatment. The results showed that the addition of NaClO substantially reduced membrane fouling both in terms of the rate of TMP development and the properties of the membrane cake layer. Although the size of nano-scale primary coagulant flocs changed little by the addition of NaClO, the cake layer on the membrane had a greater porosity and a substantially reduced thickness. NaClO was found to inactivate bacteria in the influent flow, which reduced both microbial proliferation and the production of proteins and polysaccharides in the cake layer and contributed significantly to improving the overall ultrafiltration performance. NaClO dosing had no adverse impact on the formation of currently regulated disinfection by-product compounds (THMs and HAAs).

Nanoscale structural and electronic characterization of α-RuCl3 layered compound

NASA Astrophysics Data System (ADS)

Ziatdinov, Maxim; Maksov, Artem; Banerjee, Arnab; Zhou, Wu; Berlijn, Tom; Yan, Jiaqiang; Nagler, Stephen; Mandrus, David; Baddorf, Arthur; Kalinin, Sergei

The exceptional interplay of spin-orbit effects, Coulomb interaction, and electron-lattice coupling is expected to produce an elaborate phase space of α-RuCl3 layered compound, which to date remains largely unexplored. Here we employ a combination of scanning transmission electron microscopy (STEM) and scanning tunneling microscopy (STM) for detailed evaluation of the system's microscopic structural and electronic orders with a sub-nanometer precision. The STM and STEM measurements are further supported by neutron scattering, X-Ray diffraction, density functional theory (DFT), and multivariate statistical analysis. Our results show a trigonal distortion of Cl octahedral ligand cage along the C3 symmetry axes in each RuCl3 layer. The lattice distortion is limited mainly to the Cl subsystem leaving the Ru honeycomb lattice nearly intact. The STM topographic and spectroscopic characterization reveals an intra unit cell electronic symmetry breaking in a spin-orbit coupled Mott insulating phase on the Cl-terminated surface of α-RuCl3. The associated long-range charge order (CO) pattern is linked to a surface component of Cl cage distortion. We finally discuss a fine structure of CO and its potential relation to variations of average unit cell geometries found in multivariate analysis of STEM data. The research was sponsored by the U.S. Department of Energy.

[Computer modeling the hydrostatic pressure characteristics of the membrane potential for polymeric membrane, separated non-homogeneous electrolyte solutions].

PubMed

Slezak, Izabella H; Jasik-Slezak, Jolanta; Rogal, Mirosława; Slezak, Andrzej

2006-01-01

On the basis of model equation depending the membrane potential deltapsis, on mechanical pressure difference (deltaP), concentration polarization coefficient (zetas), concentration Rayleigh number (RC) and ratio concentration of solutions separated by membrane (Ch/Cl), the characteristics deltapsis = f(deltaP)zetas,RC,Ch/Cl for steady values of zetas, RC and Ch/Cl in single-membrane system were calculated. In this system neutral and isotropic polymeric membrane oriented in horizontal plane, the non-homogeneous binary electrolytic solutions of various concentrations were separated. Nonhomogeneity of solutions is results from creations of the concentration boundary layers on both sides of the membrane. Calculations were made for the case where on a one side of the membrane aqueous solution of NaCl at steady concentration 10(-3) mol x l(-1) (Cl) was placed and on the other aqueous solutions of NaCl at concentrations from 10(-3) mol x l(-1) to 2 x 10(-2) mol x l(-1) (Ch). Their densities were greater than NaCl solution's at 10(-3) mol x l(-1). It was shown that membrane potential depends on hydrodynamic state of a complex concentration boundary layer-membrane-concentration boundary layer, what is controlled by deltaP, Ch/Cl, RC and zetas.

Catalyst inks and method of application for direct methanol fuel cells

DOEpatents

Zelenay, Piotr; Davey, John; Ren, Xiaoming; Gottesfeld, Shimshon; Thomas, Sharon C.

2004-02-24

Inks are formulated for forming anode and cathode catalyst layers and applied to anode and cathode sides of a membrane for a direct methanol fuel cell. The inks comprise a Pt catalyst for the cathode and a Pt--Ru catalyst for the anode, purified water in an amount 4 to 20 times that of the catalyst by weight, and a perfluorosulfonic acid ionomer in an amount effective to provide an ionomer content in the anode and cathode surfaces of 20% to 80% by volume. The inks are prepared in a two-step process while cooling and agitating the solutions. The final solution is placed in a cooler and continuously agitated while spraying the solution over the anode or cathode surface of the membrane as determined by the catalyst content.

Investigation of the hydrogenation of SiCl4

NASA Technical Reports Server (NTRS)

Mui, J. Y. P.; Seyferth, D.

1981-01-01

A laboratory scale pressure reactor was constructed to study the 3 SiCl + 2H2 + Si yields 4 SiHCl3 reaction at pressures up to 500 psig. Reaction kinetic measurements were carried out as a function of reactor pressure, reaction temperature and H2/SiCl4 feed ratio. Based on the reaction kinetic data, the hydroclorination of SiCl4 and m.g. silicon metal is found to be an efficient process to produce SiHCl3 in good conversions and in high yields. Copper is an effective catalyst. Results of the corrosion study show that conventional nickel chromium alloys are suitable material of construction for the hydrochlorination reactor. The hydrochlorination reaction is relatively insensitive to external process parameters such as silicon particle size distribution and the impurities in the m.g. silicon metal.

Methanol-tolerant cathode catalyst composite for direct methanol fuel cells

DOEpatents

Zhu, Yimin; Zelenay, Piotr

2006-09-05

A direct methanol fuel cell (DMFC) having a methanol fuel supply, oxidant supply, and its membrane electrode assembly (MEA) formed of an anode electrode and a cathode electrode with a membrane therebetween, a methanol oxidation catalyst adjacent the anode electrode and the membrane, an oxidant reduction catalyst adjacent the cathode electrode and the membrane, comprises an oxidant reduction catalyst layer of Pt.sub.3Cr/C so that oxidation at the cathode of methanol that crosses from the anode through the membrane to the cathode is reduced with a concomitant increase of net electrical potential at the cathode electrode.

Methanol-Tolerant Cathode Catalyst Composite For Direct Methanol Fuel Cells

DOEpatents

Zhu, Yimin; Zelenay, Piotr

2006-03-21

A direct methanol fuel cell (DMFC) having a methanol fuel supply, oxidant supply, and its membrane electrode assembly (MEA) formed of an anode electrode and a cathode electrode with a membrane therebetween, a methanol oxidation catalyst adjacent the anode electrode and the membrane, an oxidant reduction catalyst adjacent the cathode electrode and the membrane, comprises an oxidant reduction catalyst layer of a platinum-chromium alloy so that oxidation at the cathode of methanol that crosses from the anode through the membrane to the cathode is reduced with a concomitant increase of net electrical potential at the cathode electrode.

Graphene-Supported Platinum Catalyst-Based Membrane Electrode Assembly for PEM Fuel Cell

NASA Astrophysics Data System (ADS)

Devrim, Yilser; Albostan, Ayhan

2016-08-01

The aim of this study is the preparation and characterization of a graphene-supported platinum (Pt) catalyst for proton exchange membrane fuel cell (PEMFC) applications. The graphene-supported Pt catalysts were prepared by chemical reduction of graphene and chloroplatinic acid (H2PtCl6) in ethylene glycol. X-ray powder diffraction, thermogravimetric analysis (TGA) and scanning electron microscopy have been used to analyze structure and surface morphology of the graphene-supported catalyst. The TGA results showed that the Pt loading of the graphene-supported catalyst was 31%. The proof of the Pt particles on the support surfaces was also verified by energy-dispersive x-ray spectroscopy analysis. The commercial carbon-supported catalyst and prepared Pt/graphene catalysts were used as both anode and cathode electrodes for PEMFC at ambient pressure and 70°C. The maximum power density was obtained for the Pt/graphene-based membrane electrode assembly (MEA) with H2/O2 reactant gases as 0.925 W cm2. The maximum current density of the Pt/graphene-based MEA can reach 1.267 and 0.43 A/cm2 at 0.6 V with H2/O2 and H2/air, respectively. The MEA prepared by the Pt/graphene catalyst shows good stability in long-term PEMFC durability tests. The PEMFC cell voltage was maintained at 0.6 V without apparent voltage drop when operated at 0.43 A/cm2 constant current density and 70°C for 400 h. As a result, PEMFC performance was found to be superlative for the graphene-supported Pt catalyst compared with the Pt/C commercial catalyst. The results indicate the graphene-supported Pt catalyst could be utilized as the electrocatalyst for PEMFC applications.

Is It Homogeneous or Heterogeneous Catalysis Derived from [RhCp*Cl2]2? In Operando-XAFS, Kinetic and Crucial Kinetic Poisoning Evidence for Subnanometer Rh4 Cluster-Based Benzene Hydrogenation Catalysis

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

Bayram, Ercan; Linehan, John C.; Fulton, John L.

2011-11-23

Determining the true, kinetically dominant catalytically active species, in the classic benzene hydrogenation system pioneered by Maitlis and co-workers 34 years ago starting with [RhCp*Cl2]2 (Cp* = [{eta}5-C5(CH3)5]), has proven to be one of the most challenging case studies in the quest to distinguish single-metal-based 'homogeneous' from polymetallic, 'heterogeneous' catalysis. The reason, this study will show, is the previous failure to use the proper combination of (i) operando spectroscopy to determine the dominant form(s) of the precatalyst's mass under catalysis (i.e., operating) conditions, plus then and crucially also (ii) the previous lack of the necessary kinetic studies, catalysis being amore » 'wholly kinetic phenomenon' as J. Halpern long ago noted. An important contribution from this study will be to reveal the power of quantitiative kinetic poisoning experiments for distinguishing single-metal, or in this case subnanometer Rh4 cluster-based catalysis from larger, polymetallic Rh(0)n nanoparticle catalysis, at least under favorable conditions. The combined operando-XAFS (X-ray absorption fine structure) spectroscopy and kinetic evidences provide a compelling case for Rh4-based, with average stoichiometry 'Rh4Cp*2.4Cl4Hc', benzene hydrogenation catalysis in 2-propanol with added Et3N and at 100 C and 50 atm initial H2 pressure. The results also reveal, however, that if even ca. 1.4% of the total soluble Rh(0)n had formed nanoparticles, then those Rh(0)n nanoparticles would have been able to account for all the observed benzene hydrogenation catalytic rate (using commercial, ca. 2 nm, polyethyleneglycol-dodecylether hydrosol stabilized Rh(0)n nanoparticles as a model system). The results 'especially the poisoning methodology developed and employed' are of significant, broader interest since determining the nature of the true catalyst continues to be a central, often vexing issue in any and all catalytic reactions. The results are also of fundamental interest in that they add to a growing body of evidence indicating that certain, appropriately ligated, coordinatively unsaturated, subnanometer M4 transition-metal clusters can be relatively robust catalysts. Also demonstrated herein is that Rh4 clusters are poisoned by Hg(0), demonstrating for the first time that the classic Hg(0) poisoning test of 'homogeneous' vs 'heterogeneous'catalysts cannot distinguish Rh4-based subnanometer catalysts from Rh(0)n nanoparticle catalysts, at least for the present examples of these two specific, Rh-based catalysts.« less

Improved sensitivity via layered-double-hydroxide-uniformity-dependent chemiluminescence.

PubMed

Li, Zenghe; Wang, Dan; Yuan, Zhiqin; Lu, Chao

2016-12-01

In the last two decades nanoparticles have been widely applied to enhance chemiluminescence (CL). The morphology of nanoparticles has an important influence on nanoparticle-amplified CL. However, studies of nanoparticle-amplified CL focus mainly on the size and shape effects, and no attempt has been made to explore the influence of uniformity in nanoparticle-amplified CL processes. In this study we have investigated nanoparticle uniformity in the luminol-H 2 O 2 CL system using layered double hydroxides (LDHs) as a model material. The results demonstrated that the uniformity of LDHs played a key role in CL amplification. A possible mechanism is that LDHs with high uniformity possess abundant catalytic active sites, which results in high CL intensity. Meanwhile, the sensitivity for H 2 O 2 detection was increased by one order of magnitude (1.0 nM). Moreover, the uniform-LDH-amplified luminol CL could be applied to selective detection of glucose in human plasma samples. Furthermore, such a uniformity-dependent CL enhancement effect could adapted to other redox CL systems-for example, the peroxynitrous acid (ONOOH) CL system.

Hydrogen and Fuel Cells | Chemistry and Nanoscience Research | NREL

Science.gov Websites

Reduction Reaction for Ultrathin Uniform Pt/C Catalyst Layers without Influence from Nafion,"" , "Benchmarking the Oxygen Reduction Reaction Activity of Pt-Based Catalysts Using Standardized , B.S. Pivovar, S.S. Kocha. ""Suppression of Oxygen Reduction Reaction Activity on Pt-Based

Treatment of ammonia by catalytic wet oxidation process over platinum-rhodium bimetallic catalyst in a trickle-bed reactor: effect of pH.

PubMed

Hung, Chang-Mao; Lin, Wei-Bang; Ho, Ching-Lin; Shen, Yun-Hwei; Hsia, Shao-Yi

2010-08-01

This work adopted aqueous solutions of ammonia for use in catalytic liquid-phase reduction in a trickle-bed reactor with a platinum-rhodium bimetallic catalyst, prepared by the co-precipitation of chloroplatinic acid (H2PtCl6) and rhodium nitrate [Rh(NO3)3]. The experimental results demonstrated that a minimal amount of ammonia was removed from the solution by wet oxidation in the absence of any catalyst, while approximately 97.0% of the ammonia was removed by wet oxidation over the platinum-rhodium bimetallic catalyst at 230 degrees C with an oxygen partial pressure of 2.0 MPa. The oxidation of ammonia has been studied as a function of pH, and the main reaction products were determined. A synergistic effect is manifest in the platinum-rhodium bimetallic structure, in which the material has the greatest capacity to reduce ammonia. The reaction pathway linked the oxidizing ammonia to nitric oxide, nitrogen, and water.

A3-Coupling catalyzed by robust Au nanoparticles covalently bonded to HS-functionalized cellulose nanocrystalline films

PubMed Central

Huang, Jian-Lin

2013-01-01

Summary We decorated HS-functionalized cellulose nanocrystallite (CNC) films with monodisperse Au nanoparticles (AuNPs) to form a novel nanocomposite catalyst AuNPs@HS-CNC. The uniform, fine AuNPs were made by the reduction of HAuCl4 solution with thiol (HS-) group-functionalized CNC films. The AuNPs@HS-CNC nanocomposites were examined by X-ray photoelectron spectroscopy (XPS), TEM, ATR-IR and solid-state NMR. Characterizations suggested that the size of the AuNPs was about 2–3 nm and they were evenly distributed onto the surface of CNC films. Furthermore, the unique nanocomposite Au@HS-CNC catalyst displayed high catalytic efficiency in promoting three-component coupling of an aldehyde, an alkyne, and an amine (A3-coupling) either in water or without solvent. Most importantly, the catalyst could be used repetitively more than 11 times without significant deactivation. Our strategy also promotes the use of naturally renewable cellulose to prepare reusable nanocomposite catalysts for organic synthesis. PMID:23946833

Mechanistic Basis for High Reactivity of (salen)Co–OTs in the Hydrolytic Kinetic Resolution of Terminal Epoxides

PubMed Central

Nielsen, Lars P. C.; Zuend, Stephan J.; Ford, David D.; Jacobsen, Eric N.

2012-01-01

The (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides is a bimetallic process with a rate controlled by partitioning between a nucleophilic (salen)Co–OH catalyst and a Lewis acidic (salen)Co–X catalyst. The commonly used (salen)Co–OAc and (salen)Co–Cl precatalysts undergo complete and irreversible counterion addition to epoxide during the course of the epoxide hydrolysis reaction, resulting in quantitative formation of weakly Lewis acidic (salen)Co–OH, and severely diminished reaction rates in the late stages of HKR reactions. In contrast, (salen)Co–OTs maintains high reactivity over the entire course of HKR reactions. We describe here an investigation of catalyst partitioning with different (salen)Co–X precatalysts, and demonstrate that counterion addition to epoxide is reversible in the case of the (salen)Co–OTs. This reversible counterion addition results in stable partitioning between nucleophilic and Lewis acidic catalyst species, allowing highly efficient catalysis throughout the course of the HKR reaction. PMID:22292515

Mechanistic basis for high reactivity of (salen)Co-OTs in the hydrolytic kinetic resolution of terminal epoxides.

PubMed

Nielsen, Lars P C; Zuend, Stephan J; Ford, David D; Jacobsen, Eric N

2012-03-02

The (salen)Co(III)-catalyzed hydrolytic kinetic resolution (HKR) of terminal epoxides is a bimetallic process with a rate controlled by partitioning between a nucleophilic (salen)Co-OH catalyst and a Lewis acidic (salen)Co-X catalyst. The commonly used (salen)Co-OAc and (salen)Co-Cl precatalysts undergo complete and irreversible counterion addition to epoxide during the course of the epoxide hydrolysis reaction, resulting in quantitative formation of weakly Lewis acidic (salen)Co-OH and severely diminished reaction rates in the late stages of HKR reactions. In contrast, (salen)Co-OTs maintains high reactivity over the entire course of HKR reactions. We describe here an investigation of catalyst partitioning with different (salen)Co-X precatalysts and demonstrate that counterion addition to epoxide is reversible in the case of the (salen)Co-OTs. This reversible counterion addition results in stable partitioning between nucleophilic and Lewis acidic catalyst species, allowing highly efficient catalysis throughout the course of the HKR reaction.

Optimization of sodium loading on zeolite support for catalyzed transesterification of triolein with methanol.

PubMed

Wang, Yu-Yuan; Chou, Hsin-Yu; Chen, Bing-Hung; Lee, Duu-Jong

2013-10-01

Optimization of sodium loading on zeolite HY for catalyzed transesterification of triolein in excess methanol to biodiesel was studied. Zeolite HY catalyst was activated by loading sodium ions to their surface via an ion-exchange method. The effects of ion-exchange process parameters, including the temperature, the process time, the pH value, as well as concentrations and sources of Na(+) cations (NaOH, NaCl and Na2SO4), on the conversion yield of triolein to biodiesel were investigated. Most of these Na(+)-activated zeolite HY catalysts could really facilitate the catalyzed transesterification reaction of triolein to biodiesel at a lower temperature near 65°C. Consequently, a high conversion yield of triglycerides to biodiesel at 97.3% was obtained at 65°C. Moreover, the durability of zeolite catalysts was examined as well. Catalytic performance tests of these zeolite catalysts in transesterification did not show a significant decrease in catalysis at least for three batch cycles. Copyright © 2013 Elsevier Ltd. All rights reserved.

Sustainable Process for the Preparation of High-Performance Thin-Film Composite Membranes using Ionic Liquids as the Reaction Medium.

PubMed

Mariën, Hanne; Bellings, Lotte; Hermans, Sanne; Vankelecom, Ivo F J

2016-05-23

A new form of interfacial polymerization to synthesize thin-film composite membranes realizes a more sustainable membrane preparation and improved nanofiltration performance. By introducing an ionic liquid (IL) as the organic reaction phase, the extremely different physicochemical properties to those of commonly used organic solvents influenced the top-layer formation in several beneficial ways. In addition to the elimination of hazardous solvents in the preparation, the m-phenylenediamine (MPD) concentration could be reduced 20-fold, and the use of surfactants and catalysts became redundant. Together with the more complete recycling of the organic phase in the water/IL system, these factors resulted in a 50 % decrease in the mass intensity of the top-layer formation. Moreover, a much thinner top layer with a high ethanol permeance of 0.61 L m(-2)  h(-1)  bar(-1) [99 % Rose Bengal (RB, 1017 Da) retention; 1 bar=0.1 MPa] was formed without the use of any additives. This EtOH permeance is 555 and 161 % higher than that for the conventional interfacial polymerization (without and with additives, respectively). In reverse osmosis, high NaCl retentions of 97 % could be obtained. Finally, the remarkable decrease in the membrane surface roughness indicates the potential for reduced fouling with this new type of membrane. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation of thin/well-tunable liquid/gas diffusion layers exhibiting superior multifunctional performance in low-temperature electrolytic water splitting

DOE PAGES

Kang, Zhenye; Mo, Jingke; Yang, Gaoqiang; ...

2016-10-11

Liquid/gas diffusion layers (LGDLs), which are located between the catalyst layer (CL) and bipolar plate (BP), play an important role in enhancing the performance of water splitting in proton exchange membrane electrolyzer cells (PEMECs). They are expected to transport electrons, heat, and reactants/products simultaneously with minimum voltage, current, thermal, interfacial, and fluidic losses. Here in this study, the thin titanium-based LGDLs with straight-through pores and well-defined pore morphologies are comprehensively investigated for the first time. The novel LGDL with a 400 μm pore size and 0.7 porosity achieved a best-ever performance of 1.66 V at 2 A cm -2 andmore » 80 °C, as compared to the published literature. The thin/well-tunable titanium based LGDLs remarkably reduce ohmic and activation losses, and it was found that porosity has a more significant impact on performance than pore size. In addition, an appropriate equivalent electrical circuit model has been established to quantify the effects of pore morphologies. The rapid electrochemical reaction phenomena at the center of the PEMEC are observed by coupling with high-speed and micro-scale visualization systems. Lastly, the observed reactions contribute reasonable and pioneering data that elucidate the effects of porosity and pore size on the PEMEC performance. This study can be a new guide for future research and development towards high-efficiency and low-cost hydrogen energy.« less

A new oxytelluride: Perovskite and CsCl intergrowth in Ba 3Yb 2O 5Te

DOE PAGES

Whalen, J. B.; Besara, T.; Vasquez, R.; ...

2013-04-27

The new oxytelluride Ba 3Yb 2O 5Te was obtained from an alkaline earth flux. Ba3Yb2O5Te crystallizes in the tetragonal space group P4/ mmm (#123), with a=4.3615(3) Å and c=11.7596(11) angstrom, Z=1. The structure combines two distinct building blocks, a Ba 2Yb 2O 5 perovskite-like double layer with square bipyramidal coordination of the ytterbium ions, and a CsCl-type BaTe layer. Short range magnetic order is apparent at below 5 K, with the magnetic behavior above this temperature dominated by crystal field effects. The structure may be considered as an analog to the Ruddlesden-Popper phases, where the NaCl-type layer has been replacedmore » by the CsCl-type layer. Finally, the two-dimensional magnetic behavior is expected based on the highly anisotropic nature of the structure.« less

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

PubMed

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

2010-11-15

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

Patterned Growth of Carbon Nanotubes or Nanofibers

NASA Technical Reports Server (NTRS)

Delzeit, Lance D.

2004-01-01

A method and apparatus for the growth of carbon nanotubes or nanofibers in a desired pattern has been invented. The essence of the method is to grow the nanotubes or nanofibers by chemical vapor deposition (CVD) onto a patterned catalyst supported by a substrate. The figure schematically depicts salient aspects of the method and apparatus in a typical application. A substrate is placed in a chamber that contains both ion-beam sputtering and CVD equipment. The substrate can be made of any of a variety of materials that include several forms of silicon or carbon, and selected polymers, metals, ceramics, and even some natural minerals and similar materials. Optionally, the substrate is first coated with a noncatalytic metal layer (which could be a single layer or could comprise multiple different sublayers) by ion-beam sputtering. The choice of metal(s) and thickness(es) of the first layer (if any) and its sublayers (if any) depends on the chemical and electrical properties required for subsequent deposition of the catalyst and the subsequent CVD of the carbon nanotubes. A typical first-sublayer metal is Pt, Pd, Cr, Mo, Ti, W, or an alloy of two or more of these elements. A typical metal for the second sublayer or for an undivided first layer is Al at a thickness .1 nm or Ir at a thickness .5 nm. Proper choice of the metal for a second sublayer of a first layer makes it possible to use a catalyst that is chemically incompatible with the substrate. In the next step, a mask having holes in the desired pattern is placed over the coated substrate. The catalyst is then deposited on the coated substrate by ion-beam sputtering through the mask. Optionally, the catalyst could be deposited by a technique other than sputtering and/or patterned by use of photolithography, electron- beam lithography, or another suitable technique. The catalytic metal can be Fe, Co, Ni, or an alloy of two or more of these elements, deposited to a typical thickness in the range from 0.1 to 20 nm.

Influence of the membrane ion exchange capacity on the catalyst layer of proton exchange membrane fuel cell

NASA Astrophysics Data System (ADS)

Navessin, Titichai

2005-07-01

This work investigated the effect of ion exchange capacity (IEC) of polymer electrolyte membranes (PEM) on the PEM fuel cell cathode catalyst layer. A series of radiation grafted ethylene tetrafluoroethylene-g-polystyrene sulfonic acid (ETFE-g-PSSA) membranes was used to provide a systematic variation of IEC. A method to fabricate gas diffusion electrodes (GDEs) was adapted and custom-made GDEs with known compositions were prepared. Oxygen electrochemistry, mass transport properties, water absorption behaviour and proton conductivity were studied in relation to the IEC. Electrochemical characterization including cyclic voltammetry, electrochemical impedance spectroscopy and linear sweep voltammetry were employed. The agglomerate model for cathodes was adapted and used to extract mass transport parameters from experimental results. Prior to investigation in fuel cell systems, studies were performed in a half-fuel cell, which simplified complicating parameters associated with fuel cell operation. It was found that membranes with higher IEC resulted in a higher active surface area of electrode. In contrast, they exhibited lower oxygen reduction performance. The extracted effective diffusion coefficient of oxygen and O2 solubility in the catalyst layer was used to estimate the extent of flooding, which revealed that ˜67--70% of void space was filled with water. The membrane's IEC regulates the extent of flooding of the cathode, which in turn affects its electrochemical characteristics. The investigation under operating fuel cell conditions revealed an increase in fuel cell performance with increasing IEC---a contradicting trend to that found for the half-fuel cell. This is explained by the interplay of electroosmotic flux and hydraulic counterflux in the membrane which affects water management in the membrane electrode assembly (MEA). The influence was most significant in the cathode catalyst layer, where it affects mass transport and electrochemical characteristics. It was found that the higher IEC facilitated better water management in MEAs. Comparing results obtained with half fuel cell and fuel cell systems revealed insights into the state of hydration and effective use of Pt in the catalyst layer. The two types of measurements provide a convenient approach to study the interplay of different mechanisms of water flux in the membrane.

Zr-doped ceria additives for enhanced PEM fuel cell durability and radical scavenger stability

DOE PAGES

Baker, Andrew M.; Williams, Stefan Thurston DuBard; Mukundan, Rangachary; ...

2017-06-06

Doped ceria compounds demonstrate excellent radical scavenging abilities and are promising additives to improve the chemical durability of polymer electrolyte membrane (PEM) fuel cells. Here in this paper, Ce 0.85Zr 0.15O 2 (CZO) nanoparticles were incorporated into the cathode catalyst layers (CLs) of PEM fuel cells (based on Nafion XL membranes containing 6.0 μg cm -2 ion-exchanged Ce) at loadings of 10 and 55 μg cm -2. When compared to a CZO-free baseline, CZO-containing membrane electrode assemblies (MEAs) demonstrated extended lifetimes during PEM chemical stability accelerated stress tests (ASTs), exhibiting reduced electrochemical gas crossover, open circuit voltage decay, and fluoridemore » emission rates. The MEA with high CZO loading (55 μg cm -2) demonstrated performance losses, which are attributed to Ce poisoning of the PEM and CL ionomer regions, which is supported by X-ray fluorescence (XRF) analysis. In the MEA with the low CZO loading (10 μg cm -2), both the beginning of life (BOL) performance and the performance after 500 hours of ASTs were nearly identical to the BOL performance of the CZO-free baseline MEA. XRF analysis of the MEA with low CZO loading reveals that the BOL PEM Ce concentrations are preserved after 1408 hours of ASTs and that Ce contents in the cathode CL are not significant enough to reduce performance. Therefore, employing a highly effective radical scavenger such as CZO, at a loading of 10 μg cm -2 in the cathode CL, dramatically mitigates degradation effects, which improves MEA chemical durability and minimizes performance losses.« less

Zr-doped ceria additives for enhanced PEM fuel cell durability and radical scavenger stability

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

Baker, Andrew M.; Williams, Stefan Thurston DuBard; Mukundan, Rangachary

Doped ceria compounds demonstrate excellent radical scavenging abilities and are promising additives to improve the chemical durability of polymer electrolyte membrane (PEM) fuel cells. Here in this paper, Ce 0.85Zr 0.15O 2 (CZO) nanoparticles were incorporated into the cathode catalyst layers (CLs) of PEM fuel cells (based on Nafion XL membranes containing 6.0 μg cm -2 ion-exchanged Ce) at loadings of 10 and 55 μg cm -2. When compared to a CZO-free baseline, CZO-containing membrane electrode assemblies (MEAs) demonstrated extended lifetimes during PEM chemical stability accelerated stress tests (ASTs), exhibiting reduced electrochemical gas crossover, open circuit voltage decay, and fluoridemore » emission rates. The MEA with high CZO loading (55 μg cm -2) demonstrated performance losses, which are attributed to Ce poisoning of the PEM and CL ionomer regions, which is supported by X-ray fluorescence (XRF) analysis. In the MEA with the low CZO loading (10 μg cm -2), both the beginning of life (BOL) performance and the performance after 500 hours of ASTs were nearly identical to the BOL performance of the CZO-free baseline MEA. XRF analysis of the MEA with low CZO loading reveals that the BOL PEM Ce concentrations are preserved after 1408 hours of ASTs and that Ce contents in the cathode CL are not significant enough to reduce performance. Therefore, employing a highly effective radical scavenger such as CZO, at a loading of 10 μg cm -2 in the cathode CL, dramatically mitigates degradation effects, which improves MEA chemical durability and minimizes performance losses.« less

Carbon corrosion of proton exchange membrane fuel cell catalyst layers studied by scanning transmission X-ray microscopy

NASA Astrophysics Data System (ADS)

Hitchcock, Adam P.; Berejnov, Viatcheslav; Lee, Vincent; West, Marcia; Colbow, Vesna; Dutta, Monica; Wessel, Silvia

2014-11-01

Scanning Transmission X-ray Microscopy (STXM) at the C 1s, F 1s and S 2p edges has been used to investigate degradation of proton exchange membrane fuel cell (PEM-FC) membrane electrode assemblies (MEA) subjected to accelerated testing protocols. Quantitative chemical maps of the catalyst, carbon support and ionomer in the cathode layer are reported for beginning-of-test (BOT), and end-of-test (EOT) samples for two types of carbon support, low surface area carbon (LSAC) and medium surface area carbon (MSAC), that were exposed to accelerated stress testing with upper potentials (UPL) of 1.0, 1.2, and 1.3 V. The results are compared in order to characterize catalyst layer degradation in terms of the amounts and spatial distributions of these species. Pt agglomeration, Pt migration and corrosion of the carbon support are all visualized, and contribute to differing degrees in these samples. It is found that there is formation of a distinct Pt-in-membrane (PTIM) band for all EOT samples. The cathode thickness shrinks due to loss of the carbon support for all MSAC samples that were exposed to the different upper potentials, but only for the most aggressive testing protocol for the LSAC support. The amount of ionomer per unit volume significantly increases indicating it is being concentrated in the cathode as the carbon corrosion takes place. S 2p spectra and mapping of the cathode catalyst layer indicates there are still sulfonate groups present, even in the most damaged material.

Preparation and characterization Al3+-bentonite Turen Malang for esterification fatty acid (palmitic acid, oleic acid and linoleic acid)

NASA Astrophysics Data System (ADS)

Abdulloh, Abdulloh; Aminah, Nanik Siti; Triyono, Mudasir, Trisunaryanti, Wega

2016-03-01

Catalyst preparation and characterization of Al3+-bentonite for esterification of palmitic acid, oleic acid and linoleic acid has been done. Al3+-bentonite catalyst was prepared from natural bentonite of Turen Malang through cation exchange reaction using AlCl3 solution. The catalysts obtained were characterized by XRD, XRF, pyridine-FTIR and surface area analyser using the BET method. Catalyst activity test of Al3+-bentonite for esterification reaction was done at 65°C using molar ratio of metanol-fatty acid of 30:1 and 0.25 g of Al3+-bentonite catalyst for the period of ½, 1, 2, 3, 4 and 5 hours. Based on the characterization results, the Al3+-bentonite Turen Malang catalyst has a d-spacing of 15.63 Ǻ, acid sites of Brönsted and Lewis respectively of 230.79 µmol/g and 99.39 µmol/g, surface area of 507.3 m2/g and the average of radius pore of 20.09 Å. GC-MS analysis results of the oil phase after esterification reaction showed the formation of biodiesel (FAME: Fatty acid methyl ester), namely methyl palmitate, methyl oleate and methyl linoleate. The number of conversions resulted in esterification reaction using Al3+-bentonite Turen Malang catalyst was 74.61%, 37.75%, and 20, 93% for the esterification of palmitic acid, oleic acid and linoleic acid respectively.

Zinc-assisted hydrodeoxygenation of biomass-derived 5-hydroxymethylfurfural to 2,5-dimethylfuran.

PubMed

Saha, Basudeb; Bohn, Christine M; Abu-Omar, Mahdi M

2014-11-01

2,5-Dimethylfuran (DMF), a promising cellulosic biofuel candidate from biomass derived intermediates, has received significant attention because of its low oxygen content, high energy density, and high octane value. A bimetallic catalyst combination containing a Lewis-acidic Zn(II) and Pd/C components is effective for 5-hydroxymethylfurfural (HMF) hydrodeoxygenation (HDO) to DMF with high conversion (99%) and selectivity (85% DMF). Control experiments for evaluating the roles of zinc and palladium revealed that ZnCl2 alone did not catalyze the reaction, whereas Pd/C produced 60% less DMF than the combination of both metals. The presence of Lewis acidic component (Zn) was also found to be beneficial for HMF HDO with Ru/C catalyst, but the synergistic effect between the two metal components is more pronounced for the Pd/Zn system than the Ru/Zn. A comparative analysis of the Pd/Zn/C catalyst to previously reported catalytic systems show that the Pd/Zn system containing at least four times less precious metal than the reported catalysts gives comparable or better DMF yields. The catalyst shows excellent recyclability up to 4 cycles, followed by a deactivation, which could be due to coke formation on the catalyst surface. The effectiveness of this combined bimetallic catalyst has also been tested for one-pot conversion of fructose to DMF. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Investigation of heterogeneous asymmetric dihydroxylation over OsO{sub 4}-(QN){sub 2}PHAL catalysts of functionalized bimodal mesoporous silica with ionic liquid

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

Qiu, Shenjie; Sun, Jihong, E-mail: jhsun@bjut.edu.cn; Li, Yuzhen

2011-08-15

Highlights: {yields} Functionalized bimodal mesoporous silica with MTMSPIm{sup +}Cl{sup -}. {yields} Mesoporous catalyst immobilized with OsO{sub 4}-(QN){sub 2}PHAL. {yields} Catalysts for asymmetric dihydroxylation reaction with high yield and enatioselectivity. {yields} Recyclable catalysts. -- Abstract: A novel synthesis of the functionalized bimodal mesoporous silica with ionic liquid (FBMMs) was performed. After grafting 1-methyl-3-(trimethoxysilyl)propylimidazolium chloride onto the surface of bimodal mesoporous silicas, 1,4-bis(9-O-quininyl)phthalazine ((QN){sub 2}-PHAL) and K{sub 2}Os(OH){sub 4}.2H{sub 2}O were immobilized onto the modified FBMMs by adsorption or ionic exchange methods, and then, the asymmetric dihydroxylation reaction was carried out by using solid catalysts. Techniques such as X-ray diffraction, Fourier Transformmore » Infrared spectroscopy, N{sub 2} adsorption and desorption were employed to characterize their structure and properties. The results showed that the mesoporous ordering degree of bimodal mesoporous silica decreased after functionalization and immobilization of OsO{sub 4}-(QN){sub 2}PHAL. Being very effective in asymmetric dihydroxylation with high yield and enantioselectivity, the prepared heterogeneous solid catalyst could be recycled for five times with little loss of enantioselectivity, with comparison of those results obtained in homophase system. Moreover, the effect of Osmium catalyst on asymmetric dihydroxylation was investigated.« less

Fuel cell anode configuration for CO tolerance

DOEpatents

Uribe, Francisco A.; Zawodzinski, Thomas A.

2004-11-16

A polymer electrolyte fuel cell (PEFC) is designed to operate on a reformate fuel stream containing oxygen and diluted hydrogen fuel with CO impurities. A polymer electrolyte membrane has an electrocatalytic surface formed from an electrocatalyst mixed with the polymer and bonded on an anode side of the membrane. An anode backing is formed of a porous electrically conductive material and has a first surface abutting the electrocatalytic surface and a second surface facing away from the membrane. The second surface has an oxidation catalyst layer effective to catalyze the oxidation of CO by oxygen present in the fuel stream where at least the layer of oxidation catalyst is formed of a non-precious metal oxidation catalyst selected from the group consisting of Cu, Fe, Co, Tb, W, Mo, Sn, and oxides thereof, and other metals having at least two low oxidation states.

Atomic-scale observation of structural and electronic orders in the layered compound α-RuCl3

NASA Astrophysics Data System (ADS)

Ziatdinov, M.; Banerjee, A.; Maksov, A.; Berlijn, T.; Zhou, W.; Cao, H. B.; Yan, J.-Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Baddorf, A. P.; Kalinin, S. V.

2016-12-01

A pseudospin-1/2 Mott phase on a honeycomb lattice is proposed to host the celebrated two-dimensional Kitaev model which has an elusive quantum spin liquid ground state, and fascinating physics relevant to the development of future templates towards topological quantum bits. Here we report a comprehensive, atomically resolved real-space study by scanning transmission electron and scanning tunnelling microscopies on a novel layered material displaying Kitaev physics, α-RuCl3. Our local crystallography analysis reveals considerable variations in the geometry of the ligand sublattice in thin films of α-RuCl3 that opens a way to realization of a spatially inhomogeneous magnetic ground state at the nanometre length scale. Using scanning tunnelling techniques, we observe the electronic energy gap of ~0.25 eV and intra-unit cell symmetry breaking of charge distribution in individual α-RuCl3 surface layer. The corresponding charge-ordered pattern has a fine structure associated with two different types of charge disproportionation at Cl-terminated surface.

Cl-Assisted Large Scale Synthesis of Cm-Scale Buckypapers of Fe₃C-Filled Carbon Nanotubes with Pseudo-Capacitor Properties: The Key Role of SBA-16 Catalyst Support as Synthesis Promoter.

PubMed

Boi, Filippo S; He, Yi; Wen, Jiqiu; Wang, Shanling; Yan, Kai; Zhang, Jingdong; Medranda, Daniel; Borowiec, Joanna; Corrias, Anna

2017-10-23

We show a novel chemical vapour deposition (CVD) approach, in which the large-scale fabrication of ferromagnetically-filled cm-scale buckypapers is achieved through the deposition of a mesoporous supported catalyst (SBA-16) on a silicon substrate. We demonstrate that SBA-16 has the crucial role of promoting the growth of carbon nanotubes (CNTs) on a horizontal plane with random orientation rather than in a vertical direction, therefore allowing a facile fabrication of cm-scale CNTs buckypapers free from the onion-crust by-product observed on the buckypaper-surface in previous reports. The morphology and composition of the obtained CNTs-buckypapers are analyzed in detail by scanning electron microscopy (SEM), Energy Dispersive X-ray (EDX), transmission electron microscopy (TEM), high resolution TEM (HRTEM), and thermogravimetric analysis (TGA), while structural analysis is performed by Rietveld Refinement of XRD data. The room temperature magnetic properties of the produced buckypapers are also investigated and reveal the presence of a high coercivity of 650 Oe. Additionally, the electrochemical performances of these buckypapers are demonstrated and reveal a behavior that is compatible with that of a pseudo-capacitor (resistive-capacitor) with better performances than those presented in other previously studied layered-buckypapers of Fe-filled CNTs, obtained by pyrolysis of dichlorobenzene-ferrocene mixtures. These measurements indicate that these materials show promise for applications in energy storage systems as flexible electrodes.

Theoretical modeling to study the impact of different oxidizers (etchants) on the plasma-assisted catalytic carbon nanofiber growth

NASA Astrophysics Data System (ADS)

Gupta, Ravi; Sharma, Suresh C.

2017-07-01

An analytical model based on the various surface deposition processes and plasma sheath kinetics of the plasma species (electrons, positively charged ions, radicals, and neutrals) has been developed to investigate the effects of different plasmas (different etchants) on the catalyzed plasma aided growth of carbon nanofibers (CNFs). In particular, the model accounts the poisoning of the catalyst nanoparticle, i.e., the formation of the amorphous carbon layer on the catalyst active surface due to the continuous dissociation of incoming hydrocarbon species from the plasma. It is observed that oxidizers (H2O and O2) in the typical hydrocarbon/hydrogen (C2H2 + H2) plasma act as the dominant etchants and remove the amorphous carbon layer from the catalyst surface and, thus, preserve and enhance the catalyst activity. However, the growth rate of CNFs is much higher when O2 is added as an etchant in the reactive plasma as compared to H2O. This is due to the dual role played by the oxygen, i.e., (i) removal of amorphous carbon from the catalyst active surface, (ii) removal of hydrogen radicals that interact with the carbon species generated on the catalyst surface and suppress their diffusion through the catalyst nanoparticles. The CNF grows much longer in the presence of O2, therefore, etching of CNF tip and deformation of catalyst nanoparticle is the maximum, and hence, the CNF tip diameter is least. Moreover, in the present investigation, we also found that the relative concentrations of H2O or O2 species in the reactive plasma have significant effects on the CNF growth. Our theoretical results are in good agreement with the experimental observations.

The coupling of carbon dioxide and epoxides by phenanthroline derivatives containing different Cu(II) complexes as catalyst

NASA Astrophysics Data System (ADS)

Kilic, Ahmet; Palali, Ahmet Arif; Durgun, Mustafa; Tasci, Zeynep; Ulusoy, Mahmut

2013-09-01

A series of the mononuclear Cu(II) metal complexes containing the ligand Bdppz [(9a,13a-dihydro-4,5,9,14-tetraaza-benzo[b]triphenylene-11-yl)-phenyl-methanone] (L1) and Aqphen [(12,17-dihydronaphthol[2,3-h]dipyrido[3,2-a:2‧,3‧-c]-phenazine-12,17-dione)] (L2) were synthesized and used as catalyst for the coupling of carbon dioxide (CO2) and liquid epoxide which served as both reactant and solvent. Dimethylamino pyridine (DMAP) was used as co-catalyst. The yields of epoxides to corresponding cyclic carbonates were determined by comparing the ratio of product to substrate in the 1H NMR spectrum of an aliquot of the reaction mixture. The mononuclear Cu(II) complexes of these ligands were synthesized by treating an ethanol solvent of the appropriate ligand with a different molar amount of CuCl2·2H2O. The Cu(II) complexes were characterized by FT-IR, UV-Vis, elemental analysis, melting point analysis, mass spectra, molar conductivity measurements and magnetic susceptibility techniques. The reaction of the Bdppz and Aqphen ligands in a 1:1, 1:2 or 1:3 mole ratio with CuCl2·2H2O afforded ionic Cu(II) complexes in the presence of Et3N.

The Concept about the Regeneration of Spent Borohydrides and Used Catalysts from Green Electricity

PubMed Central

Liu, Cheng-Hong; Chen, Bing-Hung

2015-01-01

Currently, the Brown-Schlesinger process is still regarded as the most common and mature method for the commercial production of sodium borohydride (NaBH4). However, the metallic sodium, currently produced from the electrolysis of molten NaCl that is mass-produced by evaporation of seawater or brine, is probably the most costly raw material. Recently, several reports have demonstrated the feasibility of utilizing green electricity such as offshore wind power to produce metallic sodium through electrolysis of seawater. Based on this concept, we have made improvements and modified our previously proposed life cycle of sodium borohydride (NaBH4) and ammonia borane (NH3BH3), in order to further reduce costs in the conventional Brown-Schlesinger process. In summary, the revision in the concept combining the regeneration of the spent borohydrides and the used catalysts with the green electricity is reflected in (1) that metallic sodium could be produced from NaCl of high purity obtained from the conversion of the byproduct in the synthesis of NH3BH3 to devoid the complicated purification procedures if produced from seawater; and (2) that the recycling and the regeneration processes of the spent NaBH4 and NH3BH3 as well as the used catalysts could be simultaneously carried out and combined with the proposed life cycle of borohydrides.

Decolorization and COD reduction of dyeing wastewater from a cotton textile mill using thermolysis and coagulation.

PubMed

Kumar, Pradeep; Prasad, B; Mishra, I M; Chand, Shri

2008-05-01

The decolorization and reduction of COD of dyeing wastewater from a cotton textile mill was conducted using catalytic thermal treatment (thermolysis) accompanied with/without coagulation. Thermolysis in presence of a homogeneous copper sulphate catalyst was found to be the most effective in comparison to other catalysts (FeCl(3), FeSO(4), CuO, ZnO and PAC) used. A maximum reduction of chemical oxygen demand (COD) and color of dyeing wastewater of 66.85% and 71.4%, respectively, was observed with a catalyst concentration of 5 kg/m(3) at pH 8. Commercial alum was found most effective coagulant among various coagulants (aluminum potassium sulphate, PAC, FeCl(3) and FeSO(4)) tested during coagulation operations, resulting in 58.57% COD and 74% color reduction at pH 4 and coagulant dose of 5 kg/m(3). Coagulation of the clear fluid (supernatant) obtained after treatment by thermolysis at the conditions previously used resulted in an overall reduction of 89.91% COD and 94.4% color at pH 4 and a coagulant dose of 2 kg/m(3). The application of thermolysis followed by coagulation, thus, is the most effective treatment method in removing nearly 90% COD and 95% color at a lower dose of coagulant (2 kg/m(3)). The sludge thus produced would contain lower inorganic mass coagulant and, therefore, less amount of inorganic sludge.

Surface structure and chemistry of Pt/Cu/Pt(1 1 1) near surface alloy model catalyst in CO

NASA Astrophysics Data System (ADS)

Zeng, Shibi; Nguyen, Luan; Cheng, Fang; Liu, Lacheng; Yu, Ying; Tao, Franklin (Feng)

2014-11-01

Near surface alloy (NSA) model catalyst Pt/Cu/Pt(1 1 1) was prepared on Pt(1 1 1) through a controlled vapor deposition of Cu atoms. Different coordination environments of Pt atoms of the topmost Pt layer with the underneath Cu atoms in the subsurface result in different local electronic structures of surface Pt atoms. Surface structure and chemistry of the NAS model catalyst in Torr pressure of CO were studied with high pressure scanning tunneling microscopy (HP-STM) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS). In Torr pressure of CO, the topmost Pt layer of Pt/Cu/Pt(1 1 1) is restructured to thin nanoclusters with size of about 1 nm. Photoemission feature of O 1s of CO on Pt/Cu/Pt(1 1 1) suggests CO adsorbed on both edge and surface of these formed nanoclusters. This surface is active for CO oxidation. Atomic layers of carbon are formed on Pt/Cu/Pt(1 1 1) at 573 K in 2 Torr of CO.

Platinum nanocatalysts prepared with different surfactants for C1-C3 alcohol oxidations and their surface morphologies by AFM

NASA Astrophysics Data System (ADS)

Ertan, Salih; Şen, Fatih; Şen, Selda; Gökağaç, Gülsün

2012-06-01

In this study, platinum nanoparticle catalysts have been prepared using PtCl4 as a starting material and 1-octanethiol, 1-decanethiol, 1-dodecanethiol, and 1-hexadecanethiol as surfactants for methanol, ethanol, and 2-propanol oxidation reactions. The structure, particle sizes, and surface morphologies of the catalysts were characterized by X-ray diffraction (XRD), atomic force microscopy and transmission electron microscopy (TEM). XRD and TEM results indicate that all prepared catalysts have a face-centered cubic structure and are homogeneously dispersed on the carbon support with a narrow size distribution (2.0-1.3 nm). X-ray photoelectron spectra of the catalysts were examined and it is found that platinum has two different oxidation states, Pt (0) and Pt(IV), oxygen and sulfur compounds are H2Oads and OHads, bound and unbound thiols. The electrochemical and electrocatalytic properties of these catalysts were investigated with respect to C1-C3 alcohol oxidations by cyclic voltammetry and chronoamperometry. The highest electrocatalytic activity was obtained from catalyst I which was prepared with 1-octanethiol. This may be attributed to a decrease in the ratio of bound to unbound thiol species increase in Pt (0)/Pt(IV), H2Oads/OHads ratios, electrochemical surface area, CO tolerance and percent platinum utility.

[CNN]-pincer nickel(II) complexes of N-heterocyclic carbene (NHC): synthesis and catalysis of the Kumada reaction of unactivated C-Cl bonds.

PubMed

Sun, Yunqiang; Li, Xiaoyan; Sun, Hongjian

2014-07-07

Three novel [CNN]-pincer nickel(ii) complexes with NHC-amine arms were synthesized in three steps. Complex was proven to be an efficient catalyst for the Kumada coupling of aryl chlorides or aryl dichlorides under mild conditions.