Science.gov

Sample records for bimetallic dispersed catalysts

  1. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction

    SciTech Connect

    Song, Chunshan; Schobert, H.H.

    1993-02-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on the development of novel bimetallic dispersed catalysts for temperature-programmed liquefaction. The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular that can be used in low precursors concentrations (< 1 %) but exhibit high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. The major technical approaches are, first, to prepare the desired heteronuclear organometallic molecules as catalyst precursors that contain covalently bound, two different metal atoms and sulfur in a single molecule. Such precursors will generate finely dispersed bimetallic catalysts such as Fe-Mo, Co-Mo and Ni-Mo binary sulfides upon thermal decomposition. The second major technical approach is to perform the liquefaction of coals unpregnated with the organometallic precursors under temperature-programmed conditions, where the programmed heat-up serves as a step for both catalyst activation and coal pretreatment or preconversion. Two to three different complexes for each of the Fe-Mo, Co-Mo, and Ni-Mo combinations will be prepared. Initial catalyst screening tests will be conducted using a subbituminous coal and a bituminous coal. Effects of coal rank and solvents will be examined with the selected bimetallic catalysts which showed much higher activity than the dispersed catalysts from conventional precursors.

  2. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction

    SciTech Connect

    Chunshan, Song; Kirby, S.; Schmidt, E.

    1995-12-31

    The objective of this project is to explore bimetallic dispersed catalysts for more efficient coal liquefaction. Coal liquefaction involves cleavage of methylene, dimethylene and ether bridges connecting various aromatic units and the reactions of various oxygen functional groups. This paper describes recent results on (1) hydrodeoxygenation of O-containing polycyclic model compounds using novel organometallic catalyst precursors; and (2) activity and selectivity of dispersed Fe catalysts from organometallic and inorganic precursors for hydrocracking of 4-(1-naphthylmethyl) bibenzyl. The results showed that some iron containing catalysts have higher activity in the sulfur-free form, contrary to conventional wisdom. Adding sulfur to Fe precursors with Cp-ligands decreased the activity of the resulting catalyst. This is in distinct contrast to the cases with iron pentacarbonyl and superfine Fe{sub 2}O{sub 3}, where S addition increased their catalytic activity substantially. A positive correlation between sulfur addition and increased activity can be seen, but a reversed trend between Fe cluster size and hydrocracking conversion could be observed, for carbonyl-type Fe precursors. It is apparent that the activity and selectivity of Fe catalysts for NMBB conversion depends strongly on both the type of ligand environment, the oxidation state and the number of intermetal bonds in the molecular precursor.

  3. Bimetallic Catalysts.

    ERIC Educational Resources Information Center

    Sinfelt, John H.

    1985-01-01

    Chemical reaction rates can be controlled by varying composition of miniscule clusters of metal atoms. These bimetallic catalysts have had major impact on petroleum refining, where work has involved heterogeneous catalysis (reacting molecules in a phase separate from catalyst.) Experimentation involving hydrocarbon reactions, catalytic…

  4. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Final report

    SciTech Connect

    Chunshan Song; Schobert, H.H.; Parfitt, D.P.

    1997-11-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that dispersed catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on exploring novel bimetallic dispersed catalysts for coal liquefaction and the effectiveness of temperature-programmed liquefaction using dispersed catalysts. The primary objective of this research was to explore novel bimetallic dispersed catalysts from organometallic molecular precursors, that could be used in low concentrations but exhibit relatively high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. We have synthesized and tested various catalyst precursors in liquefaction of subbituminous and bituminous coals and in model compound studies to examine how do the composition and structure of the catalytic precursors affect their effectiveness for coal liquefaction under different reaction conditions, and how do these factors affect their catalytic functions for hydrogenation of polyaromatic hydrocarbons, for cleavage of C-C bonds in polycyclic systems such as 4-(1-naphthylmethyl)bibenzyl, for hydrogenolysis of C-O bond such as that in dinaphthylether, for hydrodeoxygenation of phenolic compounds and other oxygen-containing compounds such as xanthene, and for hydrodesulfurization of polycyclic sulfur compounds such as dibenzothiophene. The novel bimetallic and monometallic precursors synthesized and tested in this project include various Mo- and Fe-based compounds.

  5. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, October--December 1992

    SciTech Connect

    Song, Chunshan; Schobert, H.H.

    1993-02-01

    Development of new catalysts is a promising approach to more efficient coal liquefaction. It has been recognized that catalysts are superior to supported catalysts for primary liquefaction of coals, because the control of initial coal dissolution or depolymerization requires intimate contact between the catalyst and coal. This research is a fundamental and exploratory study on catalytic coal liquefaction, with the emphasis on the development of novel bimetallic dispersed catalysts for temperature-programmed liquefaction. The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular that can be used in low precursors concentrations (< 1 %) but exhibit high activity for efficient hydroliquefaction of coals under temperature-programmed conditions. The major technical approaches are, first, to prepare the desired heteronuclear organometallic molecules as catalyst precursors that contain covalently bound, two different metal atoms and sulfur in a single molecule. Such precursors will generate finely dispersed bimetallic catalysts such as Fe-Mo, Co-Mo and Ni-Mo binary sulfides upon thermal decomposition. The second major technical approach is to perform the liquefaction of coals unpregnated with the organometallic precursors under temperature-programmed conditions, where the programmed heat-up serves as a step for both catalyst activation and coal pretreatment or preconversion. Two to three different complexes for each of the Fe-Mo, Co-Mo, and Ni-Mo combinations will be prepared. Initial catalyst screening tests will be conducted using a subbituminous coal and a bituminous coal. Effects of coal rank and solvents will be examined with the selected bimetallic catalysts which showed much higher activity than the dispersed catalysts from conventional precursors.

  6. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, April--June 1993

    SciTech Connect

    Song, Chunshan; Parfitt, D.P.; Schobert, H.H.

    1993-08-01

    The ultimate goal of the present research is to develop novel catalytic hydroliquefaction process using highly active dispersed catalysts. The primary objective of this research is to develop novel bimetallic dispersed catalysts from organometallic molecular precursors, that can be used in low concentrations (bimetallic dispersed catalysts for liquefaction of a Montana subbituminous coal (DECS-9) at the loading level of 0.5 wt% Mo on dmmf coal. It was found that the structure of the precursors, in particular the ligands to the metal species, affect the activity of the resulting catalyst significantly. Among the M-M` type precursors tested, Mo-Co thiocubane, Mo{sub 2}Co{sub 2}S{sub 4}(Cp){sub 2}(CO){sub 2} [Cp = cyclopentadiene], designated as MoCo-TC2, produced in-situ the best catalyst The performance of the Mo-Co bimetallic catalyst was further enhanced by using temperature programmed (TPL) conditions consisting of a low temperature soaking at 200{degrees}C, programmed heat-up to 400 or 425{degrees}C followed by a 30 minutes hold. The pro ed heat-up serves as an in-situ activation of catalyst and coal pretreatment, which contributes to more effective hydrogenation of reactive fragments at high temperature.

  7. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, October 1994--December 1994

    SciTech Connect

    Schmidt, E.; Kirby, S.; Song, Chunshan

    1995-02-01

    Coal liquefaction involves cleavage of methylene and dimethylene and ether-type bridges connecting polycyclic aromatic units. The selected compounds for model coal liquefaction reactions are 4-(l-naphthylmethyl)bibenzyl (NMBB) and several oxygen-containing compounds. This report mainly describes the synthesis and screening of selected iron and molybdenum compounds as precursors of dispersed catalysts for hydrocracking of NMBB and oxygen-containing compounds. Experiments using NMBB were carried out at 400{degrees}C for 30 min. under 6.9 MPa H{sub 2} pressure. All catalyst precursors converted NMBB predominately into naphthalene and 4-methylbibenzyl. Generally, ferrocene demonstrated very low activity as catalyst. Even sulfur addition did not increase activity. Hydrated iron sulfate FeSO{sub 4} x 7 H{sub 2}O gave similar conversion like ferrocene. In order to clarify the effect of sulfur alone on model compound conversion, NMBB was treated with sulfur in concentrations of 1.2 to 3.4 wt %, corresponding to conditions present in catalytic runs with sulfur. It was found that increasing sulfur concentrations lead to higher NMBB conversion. Furthermore, sulfur had a permanent influence on the reactor walls. It reacted with the transition metals in the steel to form a microscopic black iron sulfide layer on the surface, which could not be removed mechanically. Non catalytic runs after experiments with added sulfur yielded higher conversion than a normal run with a new reactor. The objective of the work on oxygen-compounds is to investigate the utility of highly dispersed catalysts, from organometallic precursors, in the removal of heteroatom functionality from the products of a reaction performed under liquefaction conditions. The bimetallic catalytic precursor CoMo-T2 exhibited a sizable increase in the yield of non-O-containing products, compared to the run using a standard inorganic catalyst precursor (ATTM) or a non-catalytic reaction.

  8. Structural analysis of polymer-protected Pd/Pt bimetallic clusters as dispersed catalysts by using extended x-ray absorption fine structure spectroscopy

    SciTech Connect

    Toshima, Naoki; Harada, Masafumi; Yonezawa, Tetsu; Kushihashi, Kakuta; Asakura, Kiyotaka )

    1991-09-19

    Extended X-ray absorption fine structure (EXAFS) was applied to the determination of the structure of colloidal dispersions of the poly (N-vinyl-2-pyrrolidone)-protected palladium/platinum bimetallic clusters, which work as the catalysts for selective partial hydrogenation of 1,3-cyclooctadiene to cyclooctene. The catalytic activity was found to depend on the structure of the bimetallic clusters. The EXAFS data on the Pd/Pt (4/1) bimetallic clusters, which are the most active catalysts, indicate a Pt core structure, in which the 42 Pd atoms are on the surface of the cluster particle and 13 Pt atoms are at the center of the particle, forming a core. In contrast, the Pd/Pt (1/1) bimetallic clusters are suggested to have a modified Pt core structure, in which 28 Pt atoms connect directly with each other, being located both in the core and on the surface, and 27 Pd atoms form three islands on the surface of the cluster particle. These bimetallic clusters work as active catalysts for selective hydrogenation of olefins, selective partial hydrogenation of diene to monoene, and visible light-induced hydrogen generation from water.

  9. Dispersion enhanced metal/zeolite catalysts

    DOEpatents

    Sachtler, Wolfgang M. H.; Tzou, Ming-Shin; Jiang, Hui-Jong

    1987-01-01

    Dispersion stabilized zeolite supported metal catalysts are provided as bimetallic catalyst combinations. The catalyst metal is in a reduced zero valent form while the dispersion stabilizer metal is in an unreduced ionic form. Representative catalysts are prepared from platinum or nickel as the catalyst metal and iron or chromium dispersion stabilizer.

  10. Dispersion enhanced metal/zeolite catalysts

    DOEpatents

    Sachtler, W.M.H.; Tzou, M.S.; Jiang, H.J.

    1987-03-31

    Dispersion stabilized zeolite supported metal catalysts are provided as bimetallic catalyst combinations. The catalyst metal is in a reduced zero valent form while the dispersion stabilizer metal is in an unreduced ionic form. Representative catalysts are prepared from platinum or nickel as the catalyst metal and iron or chromium dispersion stabilizer.

  11. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, April--June 1995

    SciTech Connect

    Kirby, S.; Song, Chunshan; Schobert, H.H.

    1995-09-01

    Coal liquefaction involves cleavage of methylene, dimethylene and ether bridges connecting polycyclic aromatic units and the reactions of various oxygen functional groups. Here in this quarterly, we report on our continued effort on hydrodeoxygenation of O-containing polycyclic model compounds using novel organometallic catalyst precursors. Compounds containing oxygen functional groups, especially phenols, are undesirable components of coal-derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial alternative would be the removal of these compounds, or the prevention of their formation, during the liquefaction reaction itself, rather than as a separate processing step. A novel organometallic catalyst precursor containing Co and Mo has been studied as a potential hydrogenation catalyst for coal liquefaction. To ascertain the hydrodeoxygenation activity of this catalyst under liquefaction conditions, model compounds were investigated. Anthrone, 2,6-di-t-butyl-4-methyl-phenol, dinaphthyl ether, and xanthene were reacted in the presence of the Co-Mo catalyst precursor and a precursor containing only Mo over a range of temperatures, providing a comparison of conversions to deoxygenated products. These conversions give an indication of the hydrodeoxygenating abilities of organometallic catalyst precursors within a coal liquefaction system. For example, at 400{degrees}C dinaphthylether was converted 100% (4.5% O-containing products) in the presence of the Co-Mo organometallic precursor, compared to 76.5% conversion (7.4% O-products) in the presence of the Mo catalyst.

  12. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, April--June 1996

    SciTech Connect

    Kirby, S.R.; Martin, S.C.; Song, Chunshan; Schobert, H.H.

    1996-08-01

    This quarterly report describes our recent work on two related subjects: effect of using organometallic catalyst precursor on hydrodeoxygenation under coal liquefaction conditions, and the effect of mineral matters in liquefaction reactions of coals. Oxygen functionalities, especially phenols, are undesirable components of coal derived liquids. Removal of these compounds from the products of coal liquefaction is required. A beneficial alternative would be the removal of these functionalities, or the prevention of their formation, during the liquefaction process. Organometallic precursors of Co, Ni and Mo have been studied as catalysts. To ascertain the hydrodeoxygenation properties of these catalysts under liquefaction conditions, model compounds were investigated. Anthrone, Dibutylmethyl phenol, dinaphthyl ether and xanthene were studied to provide a comparison of conversions to deoxygenated products. Studies of the deoxygenating abilities of these catalyst precursors in coal liquefaction systems have also been performed. Improvements in conversion and product quality are observed. Both these factors are dependent on the coal used. It is also considered that some mineral matters in coal may have catalytic actions. Demineralization by successive HCl/HF treatments of a low rank coal has demonstrated that removal of the inherent mineral matter imparts no serious detrimental effect upon low temperature liquefaction. It appears that elimination of such species allows for better access for gaseous H{sub 2}, as suggested by previous studies.

  13. Novel bimetallic dispersed catalysts for temperature-programmed coal liquefaction. Technical progress report, October 1995--December 1995

    SciTech Connect

    Song, C.; Cooke, W.S.; Schmidt, E.; Schobert, H.H.

    1996-02-01

    Coal liquefaction involves cleavage of methylene, dimethylene and ether bridges connecting polycyclic aromatic units and the reactions of various oxygen functional groups. Here in this quarterly, we report on the catalytic effects of several molybdenum-, cobalt-, and iron-containing compounds in the reactions of dibenzothiophene (DBT) with hydrogen under conditions related to coal liquefaction. The catalytic effects of several molybdenum-, cobalt-, and iron-containing compounds have been examined in the hydrogenation and hydrodesulfurization reactions of dibenzothiophene (DBT) under conditions related to coal liquefaction. The metal compounds are candidate catalyst precursors for direct coal liquefaction. The reactions were carried out in batch microautoclave reactors at 400{degrees}C for 30 minutes with 6.9 MPa (cold) hydrogen pressure, and tridecane solvent. A metal loading of 0.5 mol% resulted in low conversion and only hydrogenation. Addition of sulfur in 4:1 molar ratio led only to a minor increase in conversion and hydrodesulfurization. The use of a higher boiling solvent (octadecane vs. tridecane) was beneficial in providing increased conversion, hydrodesulfurization, and hydrogenation. An increase in metal compound loading to 36.2 mol% led to a dramatic increase in conversion, hydrodesulfurization, and hydrocracking. Molybdenum hexacarbonyl at 36 mol% loading, with added sulfur at 6:1 ratio and octadecane solvent, gave 100% conversion of dibenzothiophene to other products with 100% hydrodesulfurization. Ammonium tetrathiomolybdate and molybdenum(III) chloride are less active under similar conditions. A cobalt-molybdenum thiocubane complex gave unexpectedly low conversions. Iron and cobalt carbonyls also provided very low conversions, even with added sulfur.

  14. Cleaner water using bimetallic nanoparticle catalysts

    SciTech Connect

    Wong, Michael S.; Alvarez, Pedro J.J.; Fang, Yu-Iun; Akçin, Nurgül; Nutt, Michael O.; Miller, Jeffrey T.; Heck, Kimberly N.

    2010-10-22

    Groundwater contaminated by hazardous chlorinated compounds, especially chlorinated ethenes, continues to be a significant environmental problem in industrialized nations. The conventional treatment methods of activated carbon adsorption and air-stripping successfully remove these compounds by way of transferring them from the water phase into the solid or gas phase. Catalysis is a promising approach to remove chlorinated compounds completely from the environment, by converting them into safer, non-chlorinated compounds. Palladium-based materials have been shown to be very effective as hydrodechlorination catalysts for the removal of chlorinated ethenes and other related compounds. However, relatively low catalytic activity and a propensity for deactivation are significant issues that prevent their widespread use in groundwater remediation. Palladium-on-gold bimetallic nanoparticles, in contrast, were recently discovered to exhibit superior catalyst activity and improved deactivation resistance. This new type of material is a significant next-step in the development of a viable hydrodechlorination catalysis technology.

  15. Neutral bimetallic transition metal phenoxyiminato catalysts and related polymerization methods

    DOEpatents

    Marks, Tobin J.; Rodriguez, Brandon A.; Delferro, Massimiliano

    2012-08-07

    A catalyst composition comprising a neutral bimetallic diphenoxydiiminate complex of group 10 metals or Ni, Pd or Pt is disclosed. The compositions can be used for the preparation of homo- and co-polymers of olefinic monomer compounds.

  16. The catalytic behavior of precisely synthesized Pt–Pd bimetallic catalysts for use as diesel oxidation catalysts

    DOE PAGES

    Wong, Andrew P.; Kyriakidou, Eleni A.; Toops, Todd J.; Regalbuto, John R.

    2016-04-17

    The demands of stricter diesel engine emission regulations have created challenges for current exhaust systems. With advances in low-temperature internal combustion engines and their operations, advances must also be made in vehicle exhaust catalysts. Most current diesel oxidation catalysts use heavy amounts of precious group metals (PGMs) for hydrocarbon (HC), CO, and NO oxidation. These catalysts are expensive and are most often synthesized with poor bimetallic interaction and dispersion. In this paper, the goal was to study the effect of aging on diesel emission abatement of Pt–Pd bimetallic nanoparticles precisely prepared with different morphologies: well dispersed core–shell vs. well dispersedmore » homogeneously alloyed vs. poorly dispersed, poorly alloyed particles. Alumina and silica supports were studied. Particle morphology and dispersion were analyzed before and after hydrothermal treatments by XRD, EDX, and STEM. Reactivity as a function of aging was measured in simulated diesel engine exhaust. While carefully controlled bimetallic catalyst nanoparticle structure has a profound influence on initial or low temperature catalytic activity, the differences in behavior disappear with higher temperature aging as thermodynamic equilibrium is achieved. The metallic character of Pt-rich alumina-supported catalysts is such that behavior rather closely follows the Pt–Pd metal phase diagram. Nanoparticles disparately composed as well-dispersed core–shell (via seq-SEA), well-dispersed homogeneously alloyed (via co-SEA), and poorly dispersed, poorly alloyed (via co-DI) end up as well alloyed, large particles of almost the same size and activity. With Pd-rich systems, the oxidation of Pd also figures into the equilibrium, such that Pd-rich oxide phases appear in the high temperature forms along with alloyed metal cores. Finally, the small differences in activity after high temperature aging can be attributed to the synthesis methods, sequential SEA and co

  17. Controlled Surface Segregation Leads to Efficient Coke-Resistant Nickel/Platinum Bimetallic Catalysts for the Dry Reforming of Methane

    SciTech Connect

    Li, Lidong; Zhou, Lu; Ould-Chikh, Samy; Anjum, Dalaver H.; Kanoun, Mohammed B.; Scaranto, Jessica; Hedhili, Mohamed N.; Khalid, Syed; Laveille, Paco V.; Lawrence D'Souza; Clo, Alain; Basset, Jean-Marie

    2015-02-03

    The surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. Moreover, the evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO-probe IR spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near-edge structure analysis, XRD, and X-ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island-modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni-rich core and a Ni/Pt alloy shell upon thermal treatment. The catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.

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

    SciTech Connect

    Hardeman, D.; Esconjauregui, S. Cartwright, R.; D'Arsié, L.; Robertson, J.; Bhardwaj, S.; Cepek, C.; Oakes, D.; Clark, J.; Ducati, C.

    2015-01-28

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

  19. Efficient solvent-free hydrogenation of ketones over flame-prepared bimetallic Pt-Pd/ZrO(2) catalysts.

    PubMed

    Jiang, Yijiao; Büchel, Robert; Huang, Jun; Krumeich, Frank; Pratsinis, Sotiris E; Baiker, Alfons

    2012-07-01

    Named and flamed: Bimetallic Pt-Pd/ZrO(2) catalysts with different Pt/Pd atomic ratios and high dispersion of the metal nanoparticles are prepared by a single-step flame-spray pyrolysis. The catalysts show excellent activity and tunable product selectivity for the solvent-free hydrogenation of the ketone model compounds cyclopentanone and acetophenone. PMID:22674738

  20. Characterization of bimetallic Pt-Sn/Al{sub 2}O{sub 3} catalysts: Relationship between particle size and structure

    SciTech Connect

    Merlen, E.; Zanier, N.

    1996-03-01

    Pt-Sn/Al{sub 2}O{sub 3} bimetallic catalysts have been prepared using organometallic precursors and characterized. Two models depending on average platinum particle size are proposed in order to describe these solids. The catalyst obtained from a highly dispersed monometallic precursor may be described as Pt/SnO{sub x}/Al{sub 2}O{sub 3} with platinum probably in interaction with tin oxide. When the monometallic precursor has low dispersion, the bimetallic system may be described as PtSn{sup 0} + SnO{sub x}/Al{sub 2}O{sub 3}. 35 refs., 8 figs., 9 tabs.

  1. Chemisorption and FTIR study of bimetallic Pt-Au/SiO sub 2 catalysts

    SciTech Connect

    Balakrishnan, K.; Sachdev, A.; Schwank, J. )

    1990-02-01

    Pt/SiO{sub 2}, Au/SiO{sub 2}, and bimetallic Pt-Au/SiO{sub 2} catalysts were prepared by incipient wetness impregnation of nonporous SiO{sub 2}. The catalysts were characterized after reduction in H{sub 2} by static volumetric chemisorption and infrared spectroscopy. For the monometallic and the bimetallic catalysts, H{sub 2}, O{sub 2} and CO were used as adsorbates at room temperature. Additionally, for the monometallic Au/SiO{sub 2} catalyst, O{sub 2} adsorption at 473 K was also used. Infrared spectra of adsorbed CO were obtained on all catalysts. Addition of gold decreased the uptake of all three adsorbates at room temperature, without significantly influencing the relative amounts of weakly held adsorbed species which could be removed upon pumping for 30 min. Agreeing with CO chemisorption data, the total integrated intensity of the linear CO band decreased with increasing Au content. The IR results indicated a predominantly geometric effect of Au causing a shift of the linear CO band to lower wavenumbers. The shift could be rationalized in terms of decreased dipole-dipole coupling of adsorbed CO species. The results are discussed within the context of a previous investigation using electron microscopy, TPR, and reactivity data. Portions of the bimetallic catalysts were subjected to three high-temperature oxidation/reduction cycles and characterized by static chemisorption of H{sub 2} to investigate the effect of this thermal treatment on Pt dispersion.

  2. Fundamental studies of hydrogen chemisorption on supported monometallic and bimetallic catalysts using microcalorimetry

    SciTech Connect

    Narayan, R.L.

    1997-06-24

    Highly dispersed transition metal catalysts are used in numerous commercial processes such as hydrocarbon conversions. For example, the use of Pt supported on acidic alumina or silica-alumina for reforming of naphtha in the production of gasoline is well known. Another use of supported catalysts is in automobile emission control where supported Pt-Rh bimetallic catalysts are used. Supported Ru can be used in Fischer-Tropsch synthesis for the production of higher hydrocarbons from synthesis gas. While many of these catalyst systems have been in commercial operation for several decades there is still a lack of consensus regarding the exact role of the catalyst on a molecular level. In particular, little is known about the mechanisms operating on the catalyst surface at the high pressure and high temperature conditions typically used in commercial operations. This report contains the general introduction and conclusions and an appendix containing the operating instructions for a microcalorimeter. Three chapters have been processed separately. They are: the effect of K on the kinetics and thermodynamics of hydrogen adsorption on Ru/SiO{sub 2}; hydrogen adsorption states on silica supported Ru-Ag and Ru-Cu bimetallic catalysts investigated via microcalorimetry; a comparative study of hydrogen chemisorption on silica supported Ru, Rh, and Pt.

  3. Microstructural characterization of bimetallic Ni-Pt catalysts supported on SiO 2

    NASA Astrophysics Data System (ADS)

    Arenas-Alatorre, J.; Avalos-Borja, M.; Díaz, G.

    2002-04-01

    A set of Pt, Ni and a bimetallic Ni50Pt50 catalysts supported on SiO2 of low and high surface area (S=50 and 200 m2/g) with a total metal loading of 2 wt.% was characterized by high-resolution electron microscopy (HREM), conventional transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and computational techniques such as digital processing and image simulation. Special attention was placed to the identification of intermetallic phases in the Ni50Pt50/SiO2 sample. Catalysts were prepared by impregnation and submitted to calcination-reduction activation treatments. For all the set, the increase in support's surface area led to an improvement of the metal dispersion. TEM and HREM images showed significant differences in the shape and crystalline lattice of the Pt and Ni particles in the monometallic samples taken as reference. While in Pt/SiO2 catalyst we identified only reduced Pt particles, in Ni/SiO2 some NiO particles were detected. HREM characterization of the Ni50Pt50 catalysts showed that many particles have defects such as twinning and dislocations. Cubo-octahedral shapes were predominant in the bimetallic catalyst. Crystal lattice and angles measurements were consistent with the identification of NiPt and/or Ni3Pt intermetallic phases. Superlattice structures were also identified and confirmed by image simulation. EDS analysis on a particle by particle basis confirmed that in bimetallic catalysts supported in SiO2 of low and high surface area, particles were present consisting of Ni-rich, nominal and Pt-rich metal compositions. Pt-only particles were found but no Ni-only particles were detected. Among the possibilities, NiPt and Ni3Pt compositions were identified.

  4. Bimetallic catalysts for upgrading of biomass to fuels and chemicals.

    PubMed

    Alonso, David Martin; Wettstein, Stephanie G; Dumesic, James A

    2012-12-21

    Research interest in biomass conversion to fuels and chemicals has increased significantly in the last decade as the necessity for a renewable source of carbon has become more evident. Accordingly, many different reactions and processes to convert biomass into high-value products and fuels have been proposed in the literature. Special attention has been given to the conversion of lignocellulosic biomass, which does not compete with food sources and is widely available as a low cost feedstock. In this review, we start with a brief introduction on lignocellulose and the different chemical structures of its components: cellulose, hemicellulose, and lignin. These three components allow for the production of different chemicals after fractionation. After a brief overview of the main reactions involved in biomass conversion, we focus on those where bimetallic catalysts are playing an important role. Although the reactions are similar for cellulose and hemicellulose, which contain C(6) and C(5) sugars, respectively, different products are obtained, and therefore, they have been reviewed separately. The third major fraction of lignocellulose that we address is lignin, which has significant challenges to overcome, as its structure makes catalytic processing more challenging. Bimetallic catalysts offer the possibility of enabling lignocellulosic processing to become a larger part of the biofuels and renewable chemical industry. This review summarizes recent results published in the literature for biomass upgrading reactions using bimetallic catalysts. PMID:22872312

  5. Selective Hydrogenation of Phenylacetylene on Bimetallic Cu-Pd and Cu-Pt Catalysts

    NASA Astrophysics Data System (ADS)

    Cladaras, George

    /Pd species are alloyed and well-dispersed on the surface of the nanoparticles. The bimetallic catalysts were tested for the liquid phase hydrogenation of phenylacetylene and were compared to their monometallic analogs for reactivity and selectivity. Both the Pt-Cu and Pd-Cu bimetallic catalysts display a significant improvement of the selectivity to styrene, especially at high conversions. Based on the rate data, activation energy measurements and the model study done in UHV, it is concluded that the reaction mechanism has been altered in the bimetallic samples. Pt and Pd serve as sites for molecular hydrogen dissociation to hydrogen atoms, which in turn spillover onto the Cu surface where the hydrogenation reaction occurs. In summary, this work has demonstrated how Pd-Cu and Pt-Cu bimetallic catalysts can serve as both active and highly selective hydrogenation catalysts, where the Pd and Pt entities promote the hydrogenation activity of a Cu surface which maintains high selectivity for phenylacetylene hydrogenation to styrene.

  6. Bimetallic complexes and polymerization catalysts therefrom

    DOEpatents

    Patton, Jasson T.; Marks, Tobin J.; Li, Liting

    2000-11-28

    Group 3-6 or Lanthanide metal complexes possessing two metal centers, catalysts derived therefrom by combining the same with strong Lewis acids, Bronsted acid salts, salts containing a cationic oxidizing agent or subjected to bulk electrolysis in the presence of compatible, inert non-coordinating anions and the use of such catalysts for polymerizing olefins, diolefins and/or acetylenically unsaturated monomers are disclosed.

  7. The selective hydrogenation of crotonaldehyde over bimetallic catalysts

    SciTech Connect

    Schoeb, A.M.

    1997-02-01

    The selective hydrogenation of crotonaldehyde has been investigated over a monometallic Pt/SiO{sub 2} catalyst and platinum bimetallic catalysts where the second metal was either silver, copper, or tin. The effects of addition of a second metal to the Pt/SiO{sub 2} system on the selectivity to crotyl alcohol were investigated. The Pt-Sn bimetallic catalysts were characterized by hydrogen chemisorption, {sup 1}H NMR and microcalorimetry. The Pt-Ag/SiO{sub 2} and Pt-Cu/SiO{sub 2} catalysts were characterized by hydrogen chemisorption. Pt-Sn/SiO{sub 2} catalysts selectively hydrogenated crotonaldehyde to crotyl alcohol and the method of preparation of these catalysts affected the selectivity. The most selective Pt-Sn/SiO{sub 2} catalysts for the hydrogenation of crotonaldehyde to crotyl alcohol were those in which the Sn precursor was dissolved in a HCl solution. Sn increased both the rate of formation of butyraldehyde and the rate of formation of crotyl alcohol. The Pt/SiO{sub 2}, Pt-Ag/SiO{sub 2} and Pt-Cu/SiO{sub 2} catalysts produced only butyraldehyde. Initial heats of adsorption ({approximately}90 kJ/mol) measured using microcalorimetry were not affected by the presence of Sn on Pt. We can conclude that there is no through metal electronic interaction between Pt and Sn at least with respect to hydrogen surface bonds since the Pt and Pt-Sn at least with respect to hydrogen surface bonds since the Pt and Pt-Sn had similar initial heats of adsorption coupled with the invariance of the {sup 1}H NMR Knight shift.

  8. Fundamental studies of supported bimetallic catalysts by NMR spectroscopy

    SciTech Connect

    Savargaonkar, N.

    1996-10-17

    Various hydrogenation reactions on transition metals are important commercially whereas certain hydrogenolysis reactions are useful from fundamental point of view. Understanding the hydrogen mobility and kinetics of adsorption-desorption of hydrogen is important in understanding the mechanisms of such reactions involving hydrogen. The kinetics of hydrogen chemisorption was studied by means of selective excitation NMR on silica supported Pt, Rh and Pt-Rh catalysts. The activation energy of hydrogen desorption was found to be lower on silica supported Pt catalysts as compared to Rh and Pt-Rh catalysts. It was found that the rates of hydrogen adsorption and desorption on Pt-Rh catalyst were similar to those on Rh catalyst and much higher as compared to Pt catalyst. The Ru-Ag bimetallic system is much simpler to study than the Pt-Rh system and serves as a model system to characterize more complicated systems such as the K/Ru system. Ag was found to decrease the amounts of adsorbed hydrogen and the hydrogen-to-ruthenium stoichiometry. Ag reduced the populations of states with low and intermediate binding energies of hydrogen on silica supported Ru catalyst. The rates of hydrogen adsorption and desorption were also lower on silica supported Ru-Ag catalyst as compared to Ru catalyst. This report contains introductory information, the literature review, general conclusions, and four appendices. An additional four chapters and one appendix have been processed separately for inclusion on the data base.

  9. Exploration of Nanotube Structure Selectivity Using Bimetallic Catalysts

    NASA Astrophysics Data System (ADS)

    Pfefferle, Lisa

    2007-10-01

    Achieving selectivity for nanotube chirality is one of the holy grails for single-walled carbon nanotube research. One approach we are following is based on the ability to engineer the size and state of the initiating metal particle to constrain the type of cap formed. The chirality/structure of a nanotube is controlled by carbon cap formation on the metal particle during the nucleation step. It has been proposed that varying the carbon-metal catalyst binding energy could help lead to structure selectivity. One reason theoretically proposed for the favoring of armchair nanotubes, for example, is the proximity of low energy binding locations for two carbon atoms. Thus blocking sites or perturbing the binding energy on adjacent sites could in theory affect the structure of the carbon cap formed in the nucleation step. Our goal is to demonstrate structure selectivity in the growth of single wall carbon nanotubes (SWNT) using a bimetallic catalyst. The catalyst used was a bimetallic CoCr-MCM 41 and the effect of different molecular ratios between the two metals on the SWNT diameter distribution was studied. We have found that by adding Cr to the Co-MCM 41 monometallic catalyst the diameter distribution shifted in a systematic manner correlated to the development of a bimetallic phase as characterized by X-Ray absorption spectroscopy (XAS). We have also found that the shift is accompanied by suppression of metallic SWNT, particularly those with diameter over 0.9 nm. We are also currently exploring the possibility of a further narrowing of the distribution by lowering the reaction temperatures.

  10. Solvent-free Hydrodeoxygenation of Bio-oil Model Compounds Cyclopentanone and Acetophenone over Flame-made Bimetallic Pt-Pd/ZrO2 Catalysts

    PubMed Central

    Jiang, Yijiao; Büchel, Robert; Huang, Jun; Krumeich, Frank; Pratsinis, Sotiris E.; Baiker, Alfons

    2013-01-01

    Bimetallic Pt-Pd/ZrO2 catalysts with different Pt/Pd atomic ratio and homogeneous dispersion of the metal nanoparticles were prepared in a single step by flame-spray pyrolysis. The catalysts show high activity and tuneable product selectivity for the solvent-free hydrodeoxygenation of the bio-oil model compounds cyclopentanone and acetophenone. PMID:22674738

  11. Bimetallic dendrimer-encapsulated nanoparticles as catalysts: a review of the research advances

    PubMed Central

    Rempel, Garry L.

    2008-01-01

    Bimetallic dendrimer-encapsulated nanoparticles (DENs) are important materials, because they have demonstrated improvement in performance compared to the monometallic DENs in many systems when they are used as catalysts. This tutorial review focuses on the recent research advances in bimetallic DENs with respect to their synthesis, characterization, and applications as catalysts. Bimetallic DENs can be made mainly via three routes: co-complexation, sequential loading, and partial displacement. The research in bimetallic DENs has been significantly promoted by the advancement of characterization instruments. The performances of bimetallic DENs as homogeneous and heterogeneous catalysts in organic synthesis have been compared with both monometallic DENs and their physical mixtures. It is concluded that the synergistic electronic effect in bimetallic nanoparticles enhances their catalytic activities. PMID:18648686

  12. Bimetallic ruthenium-copper nanoparticles embedded in mesoporous carbon as an effective hydrogenation catalyst.

    PubMed

    Liu, Jiajia; Zhang, Li Li; Zhang, Jiatao; Liu, Tao; Zhao, X S

    2013-11-21

    Bimetallic ruthenium-copper nanoparticles embedded in the pore walls of mesoporous carbon were prepared via a template route and evaluated in terms of catalytic properties in D-glucose hydrogenation. The existence of bimetallic entities was supported by Ru L3-edge and Cu K-edge X-ray absorption results. The hydrogen spillover effect of the bimetallic catalyst on the hydrogenation reaction was evidenced by the results of both hydrogen and carbon monoxide chemisorptions. The bimetallic catalyst displayed a higher catalytic activity than the single-metal catalysts prepared using the same approach, namely ruthenium or copper nanoparticles embedded in the pore walls of mesoporous carbon. This improvement was due to the changes in the geometric and electronic structures of the bimetallic catalyst because of the presence of the second metal. PMID:24072134

  13. XAFS characterization of Pt-Mo bimetallic catalysts for CO hydrogeneration

    SciTech Connect

    Choi, Sun Hee; Lee, Jae Sung

    1997-04-15

    Molybdenum-platinum bimetallic catalysts supported on alumina exhibited high activities in CO hydrogenation than supported monometallic catalysts of Mo or Pt. The structure of Mo-Pt bimetallic catalysts, which were prepared by incipient wetness impregnation of {gamma}-alumina with the variation of the order of Mo and Pt addition, was studied by XAFS and CO chemisorption. Since molybdenum contains overlapping contribution of the first and the second shells, EXAFS of these two shells and the first shell of platinum was analyzed for the bimetallic catalysts. EXAFS showed equivocally the formation of bimetallic bonds between Mo and Pt for all bimetallic catalysts. For all bimetallic catalysts, molybdenum seemed to segregate to the surface irrespective of the sequence of the impregnation. Strong interaction of Mo atoms with the support was also identified with EXAFS and XANES for both monometallic Mo catalysts and bimetallic catalysts. Regarding the activities of CO hydrogenation, it was concluded that reduced Mo sites were responsible for the high activity and that Pt helped Mo sites become more reduced. 28 refs., 6 figs., 5 tabs.

  14. Bimetallic ruthenium-copper nanoparticles embedded in mesoporous carbon as an effective hydrogenation catalyst

    NASA Astrophysics Data System (ADS)

    Liu, Jiajia; Zhang, Li Li; Zhang, Jiatao; Liu, Tao; Zhao, X. S.

    2013-10-01

    Bimetallic ruthenium-copper nanoparticles embedded in the pore walls of mesoporous carbon were prepared via a template route and evaluated in terms of catalytic properties in d-glucose hydrogenation. The existence of bimetallic entities was supported by Ru L3-edge and Cu K-edge X-ray absorption results. The hydrogen spillover effect of the bimetallic catalyst on the hydrogenation reaction was evidenced by the results of both hydrogen and carbon monoxide chemisorptions. The bimetallic catalyst displayed a higher catalytic activity than the single-metal catalysts prepared using the same approach, namely ruthenium or copper nanoparticles embedded in the pore walls of mesoporous carbon. This improvement was due to the changes in the geometric and electronic structures of the bimetallic catalyst because of the presence of the second metal.Bimetallic ruthenium-copper nanoparticles embedded in the pore walls of mesoporous carbon were prepared via a template route and evaluated in terms of catalytic properties in d-glucose hydrogenation. The existence of bimetallic entities was supported by Ru L3-edge and Cu K-edge X-ray absorption results. The hydrogen spillover effect of the bimetallic catalyst on the hydrogenation reaction was evidenced by the results of both hydrogen and carbon monoxide chemisorptions. The bimetallic catalyst displayed a higher catalytic activity than the single-metal catalysts prepared using the same approach, namely ruthenium or copper nanoparticles embedded in the pore walls of mesoporous carbon. This improvement was due to the changes in the geometric and electronic structures of the bimetallic catalyst because of the presence of the second metal. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03813k

  15. High-performance PdRu bimetallic catalyst supported on mesoporous silica nanoparticles for phenol hydrogenation

    NASA Astrophysics Data System (ADS)

    Huang, Chao; Yang, Xu; Yang, Hui; Huang, Peiyan; Song, Huiyu; Liao, Shijun

    2014-10-01

    A high-performance PdRu bimetallic catalyst supported on mesoporous silica nanoparticles (MSN), PdRu/MSN, was prepared by a facile impregnation-hydrogen reduction method. It was found that PdRu/MSN showed 5 times higher activity than that of Pd/MSN towards the liquid-phase hydrogenation of phenol. The catalysts were characterized comprehensively by multiple techniques, X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and hydrogen temperature program reduction (TPR). It was revealed that adding Ru could effectively improve the Pd dispersion and promote the electronic interaction between the Pd and Ru, both of which contribute to enhancing the catalytic activity.

  16. Patched bimetallic surfaces are active catalysts for ammonia decomposition

    PubMed Central

    Guo, Wei; Vlachos, Dionisios G.

    2015-01-01

    Ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material's structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N−H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design. PMID:26443525

  17. Patched bimetallic surfaces are active catalysts for ammonia decomposition

    SciTech Connect

    Guo, Wei; Vlachos, Dionisios G.

    2015-10-07

    In this study, ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material’s structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.

  18. Patched bimetallic surfaces are active catalysts for ammonia decomposition.

    PubMed

    Guo, Wei; Vlachos, Dionisios G

    2015-10-07

    Ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material's structure. Core-shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core-shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-H bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.

  19. Pt-Co Bimetallic Catalyst Supported on Single Walled Carbon Nanotube: XAS and Aqueous Phase Reforming Activity Studies

    SciTech Connect

    Wang, X.; Li, N; Pfefferle, L; Haller, G

    2009-01-01

    We have developed a simple method to create a catalyst with atomically dispersed Pt on top of Co nanoparticles on single walled carbon nanotubes (SWNT) supports by sequential impregnation of Pt(II) and Co(II) solutions following by hydrogen reduction. The aqueous phase reforming activity is much higher than for Pt monometallic catalysts on SWNT supports prepared by several methods, either pre-reduced in hydrogen or in the liquid phase. The high selectivity of the monometallic catalysts is maintained for the bimetallic systems. The Extended X-ray Absorption Fine Structure (EXAFS) results at the Pt LIII edge show no observable Pt-Pt bond. Only Pt-Co bonds were observed, indicating high dispersion of Pt. The enhanced activity comes from two sources: the high dispersion of Pt and the effect of the Co as co-catalyst or modifier. This contribution demonstrates the possibility to further engineer bimetallic catalysts to improve the aqueous phase reforming activity, especially to retain good selectivity at high conversion.

  20. Fundamental studies of hydrogen interaction with supported meta and bimetallic catalysts

    SciTech Connect

    Bhatia, S.

    1993-12-07

    The thesis is divided into 3 parts: interaction of H with silica supported Ru catalysts (high pressure in situ NMR), in situ NMR study of H interaction with supported Ru-group IB bimetallic catalysts, and in-situ NMR study of H effects on silica-supported Pt, Rh and Ru catalysts.

  1. Bimetallic Au-decorated Pd catalyst for the liquid phase hydrodechlorination of 2,4-dichlorophenol

    NASA Astrophysics Data System (ADS)

    Zhou, Juan; Chen, Huan; Chen, Quanyuan; Huang, Zhaolu

    2016-11-01

    Monometallic and bimetallic Pd-Au catalysts supported on multi-walled carbon nanotubes (CNTs) with varied Au cooperation amounts were prepared using the complexing-reduction method in the presence of tetrahydrofuran (THF). The liquid phase catalytic hydrodechlorination (HDC) of 2,4-dichlorophenol (2,4-DCP) was investigated over these bimetallic catalysts. The catalysts were characterized by N2 adsorption-desorption isotherms, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and H2 chemisorption. Characterization results showed that the co-reduction of Pd and Au mainly formed alloy-like structure. The bimetallic catalysts had smaller metal particles and larger numbers of exposed active site than that of monometallic catalysts. In addition, compared with Pd(1.7)/CNTs and Au(0.4)/CNTs, the binding energies of Pd 3d5/2 shifted to higher positions while that of Au 4f7/2 had negative shifts in the Pd-Au bimetallic catalysts, which can be ascribed to the electrons transferred from metal Pd to Au and the cationization of Pd particles was enhanced. Accordingly, the bimetallic Pd-Au particles with different Au contents in the catalysts exhibited varied synergistic effects for the catalytic HDC of 2,4-DCP, with Pd(1.8)Au(0.4)/CNTs having the highest catalytic activity. For the bimetallic catalysts, a disproportional increase of turnover frequency (TOF) was observed with increasing Au content due to the enhanced cationization of Pd particles. Moreover, the dechlorination of 2,4-DCP over the supported monometallic and bimetallic catalysts proceeded via both the stepwise and concerted pathway, and the concerted pathway became predominant with Au decoration amount in the catalyst.

  2. An in-depth understanding of the bimetallic effects and coked carbon species on an active bimetallic Ni(Co)/Al2O3 dry reforming catalyst.

    PubMed

    Liao, Xin; Gerdts, Rihards; Parker, Stewart F; Chi, Lina; Zhao, Yongxiang; Hill, Martyn; Guo, Junqiu; Jones, Martin O; Jiang, Zheng

    2016-06-29

    Ni/Al2O3, Co/Al2O3 and bimetallic Ni(Co)/Al2O3 catalysts were prepared using an impregnation method and employed in CO2 dry reforming of methane under coking-favored conditions. The spent catalysts were carefully characterized using typical characterization technologies and inelastic neutron scattering spectroscopy. The bimetallic catalyst exhibited a superior activity and anti-coking performance compared to Ni/Al2O3, while the most resistant to coking behavior was Co/Al2O3. The enhanced activity of the Ni(Co)/Al2O3 bimetallic catalyst is attributed to the reduced particle size of metallic species and resistance to forming stable filamentous carbon. The overall carbon deposition on the spent bimetallic catalyst is comparable to that of the spent Ni/Al2O3 catalyst, whereas the carbon deposited on the bimetallic catalyst is mainly less-stable carbonaceous species as confirmed by SEM, TPO, Raman and INS characterization. This study provides an in depth understanding of alloy effects in catalysts, the chemical nature of coked carbon on spent Ni-based catalysts and, hopefully, inspires the creative design of a new bimetallic catalyst for dry reforming reactions. PMID:27326792

  3. An in-depth understanding of the bimetallic effects and coked carbon species on an active bimetallic Ni(Co)/Al2O3 dry reforming catalyst.

    PubMed

    Liao, Xin; Gerdts, Rihards; Parker, Stewart F; Chi, Lina; Zhao, Yongxiang; Hill, Martyn; Guo, Junqiu; Jones, Martin O; Jiang, Zheng

    2016-06-29

    Ni/Al2O3, Co/Al2O3 and bimetallic Ni(Co)/Al2O3 catalysts were prepared using an impregnation method and employed in CO2 dry reforming of methane under coking-favored conditions. The spent catalysts were carefully characterized using typical characterization technologies and inelastic neutron scattering spectroscopy. The bimetallic catalyst exhibited a superior activity and anti-coking performance compared to Ni/Al2O3, while the most resistant to coking behavior was Co/Al2O3. The enhanced activity of the Ni(Co)/Al2O3 bimetallic catalyst is attributed to the reduced particle size of metallic species and resistance to forming stable filamentous carbon. The overall carbon deposition on the spent bimetallic catalyst is comparable to that of the spent Ni/Al2O3 catalyst, whereas the carbon deposited on the bimetallic catalyst is mainly less-stable carbonaceous species as confirmed by SEM, TPO, Raman and INS characterization. This study provides an in depth understanding of alloy effects in catalysts, the chemical nature of coked carbon on spent Ni-based catalysts and, hopefully, inspires the creative design of a new bimetallic catalyst for dry reforming reactions.

  4. The effect of the surface composition of Ru-Pt bimetallic catalysts for methanol oxidation

    DOE PAGES

    Garrick, Taylor R.; Diao, Weijian; Tengco, John M.; Stach, Eric A.; Senanayake, Sanjaya D.; Chen, Donna A.; Monnier, John R.; Weidner, John W.

    2016-02-23

    Here, a series of Ru-Pt bimetallic catalysts prepared by the electroless deposition of controlled and variable amounts of Ru on the Pt surface of a commercially-available 20 wt% Pt/C catalyst has been characterized and evaluated for the oxidation of methanol. The activity of each Ru-Pt catalyst was determined as a function of surface composition via cyclic voltammetry. For the Ru-Pt bimetallic catalysts, activity passed through a maximum at approximately 50% monodisperse Ru surface coverage. However, due to the monolayer coverage of Ru on Pt, the amount of metal in the catalyst is minimized compared to a bulk 1:1 atomic ratiomore » of Ru:Pt seen in commercial bimetallic catalysts. Chemisorption and temperature programmed reduction experiments confirmed that the surface had characteristics of a true bimetallic catalyst. On a mass of Pt basis, the activity of this composition for methanol oxidation was 7 times higher than pure Pt and 3.5 times higher than a commercial catalyst with a 1:1 Pt:Ru bulk atomic ratio.« less

  5. NOVEL SUPPORTED BIMETALLIC CARBIDE CATALYSTS FOR COPROCESSING OF COAL WITH WASTE METERIALS

    SciTech Connect

    S. Ted Oyama; David F. Cox; Chunshan Song; Fred Allen; Weilin Wang; Viviane Schwartz; Xinqin Wang; Jianli Yang

    2001-01-01

    The overall objectives of this project are to explore the potential of novel monometallic and bimetallic Mo-based carbide catalysts for heavy hydrocarbon coprocessing, and to understand the fundamental chemistry related to the reaction pathways of coprocessing and the role of the catalysts in the conversion of heavy hydrocarbon resources into liquid fuels based on the model compound reactions.

  6. Non-precious bimetallic catalysts for selective dehydrogenation of an organic chemical hydride system.

    PubMed

    Al-ShaikhAli, Anaam H; Jedidi, Abdesslem; Cavallo, Luigi; Takanabe, Kazuhiro

    2015-08-21

    Methylcyclohexane (MCH)-toluene (TOL) chemical hydride cycles as hydrogen carrier systems are successful with the selective dehydrogenation of MCH to TOL, which has been achieved only using precious Pt-based catalysts. Herein, we report improved selectivity using non-precious metal nickel-based bimetallic catalysts, where the second metal occupies the unselective step sites.

  7. Patched bimetallic surfaces are active catalysts for ammonia decomposition

    DOE PAGES

    Guo, Wei; Vlachos, Dionisios G.

    2015-10-07

    In this study, ammonia decomposition is often used as an archetypical reaction for predicting new catalytic materials and understanding the very reason of why some reactions are sensitive on material’s structure. Core–shell or surface-segregated bimetallic nanoparticles expose outstanding activity for many heterogeneously catalysed reactions but the reasons remain elusive owing to the difficulties in experimentally characterizing active sites. Here by performing multiscale simulations in ammonia decomposition on various nickel loadings on platinum (111), we show that the very high activity of core–shell structures requires patches of the guest metal to create and sustain dual active sites: nickel terraces catalyse N-Hmore » bond breaking and nickel edge sites drive atomic nitrogen association. The structure sensitivity on these active catalysts depends profoundly on reaction conditions due to kinetically competing relevant elementary reaction steps. We expose a remarkable difference in active sites between transient and steady-state studies and provide insights into optimal material design.« less

  8. Effect of pretreatment conditions on particle size of bimetallic pt-au catalysts supported on ZnO/Al2O3 and its activity for toluene oxidation.

    PubMed

    Kim, Ki-Joong; Kang, Sang-Jun; Chung, Min-Chul; Jung, Sang-Chul; Jeong, Woon-Jo; Park, Gye-Choon; Kim, Sang-Chai; Boo, Su-Il; Jeong, Seung-Won; Ahn, Ho-Geun

    2010-09-01

    Bimetallic Pt-Au catalysts supported on ZnO/Al2O3 were prepared by incipient wetness impregnation (IW-IMP) method with different pretreatment conditions such as flow velocity, calcination temperature, and heating rate under H2 during the calcination procedure, and characterized by X-ray diffraction (XRD), CO chemisorption, and scanning transmission electron microscopy (STEM) equipped energy dispersive spectroscopy (EDS). Furthermore, catalytic activity for complete oxidation of toluene was measured using a flow reactor under atmospheric pressure. Finally, relationship between the particle sizes with pretreatment conditions and catalytic activity for toluene on the bimetallic Pt-Au catalysts was discussed. In these results, nanosized bimetallic Pt-Au particles on ZnO/Al2O3 could be prepared by IW-IMP method. Relationship between the Pt and Au particle size and activity for toluene oxidation was clearly observed. PMID:21133118

  9. Synergistic Effects in Bimetallic Palladium-Copper Catalysts Improve Selectivity in Oxygenate Coupling Reactions.

    PubMed

    Goulas, Konstantinos A; Sreekumar, Sanil; Song, Yuying; Kharidehal, Purnima; Gunbas, Gorkem; Dietrich, Paul J; Johnson, Gregory R; Wang, Y C; Grippo, Adam M; Grabow, Lars C; Gokhale, Amit A; Toste, F Dean

    2016-06-01

    Condensation reactions such as Guerbet and aldol are important since they allow for C-C bond formation and give higher molecular weight oxygenates. An initial study identified Pd-supported on hydrotalcite as an active catalyst for the transformation, although this catalyst showed extensive undesirable decarbonylation. A catalyst containing Pd and Cu in a 3:1 ratio dramatically decreased decarbonylation, while preserving the high catalytic rates seen with Pd-based catalysts. A combination of XRD, EXAFS, TEM, and CO chemisorption and TPD revealed the formation of CuPd bimetallic nanoparticles with a Cu-enriched surface. Finally, density functional theory studies suggest that the surface segregation of Cu atoms in the bimetallic alloy catalyst produces Cu sites with increased reactivity, while the Pd sites responsible for unselective decarbonylation pathways are selectively poisoned by CO. PMID:27195582

  10. A-site-deficiency facilitated in situ growth of bimetallic Ni-Fe nano-alloys: a novel coking-tolerant fuel cell anode catalyst

    NASA Astrophysics Data System (ADS)

    Sun, Yi-Fei; Li, Jian-Hui; Cui, Lin; Hua, Bin; Cui, Shao-Hua; Li, Jian; Luo, Jing-Li

    2015-06-01

    To date, most investigations of Ni-Fe bimetallic catalysts for solid oxide fuel cells (SOFCs) have focused on materials with micro-scale particle sizes, which severely restrict their catalytic activity. In this study, we fabricated a Ni- and/or Fe-doped A-site-deficient LaSrCrO3 perovskite (A-LSC) bimetallic anode material on which the in situ exsolution of uniformly dispersed nano Ni, Fe and Ni-Fe alloy with an average particle size of 25 to 30 nm was facilitated by the introduction of A-site deficiency under a reducing atmosphere. The dopants were shown to significantly enhance the electrical conductivity of the material by many orders of magnitude. Further characterization of the bimetallic material showed that the addition of Fe changed the reduction behavior and increased the amount of oxygen vacancies in the material. Fuel cell performance tests demonstrated that the prepared bimetallic anode catalyst with a highly catalytically active nano Ni-Fe alloy promoted the electrochemical performance in 5000 ppm H2S-syngas and improved the carbon deposition resistance compared to a monometallic anode catalyst.

  11. Catalytic oxidation of 2-Propanol over (Cr,Mn,Fe)-Pt/gamma-Al2O3 bimetallic catalysts and modeling of experimental results by artificial neural networks.

    PubMed

    Niaei, A; Salari, D; Aghazadeh, F; Caylak, N; Sepehrianazar, A

    2010-01-01

    The catalytic activity of transition metals (Cr,Mn,Fe) supported on the Pt/gamma -Al(2)O(3) industrial catalyst was investigated to bring about the complete oxidation of 2-Propanol. Catalytic studies were carried out under atmospheric pressure in a fixed bed reactor. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and ICP-AES techniques were used to characterize a series of catalysts. Results showed that the Pt-Mn/gamma -Al(2)O(3) (3.88 wt.%Mn) at calcination temperature of 300 degrees C was the most promising catalyst based on activity, which might be contributed to the quantity of manganese loading, the favorable synergetic effects between Pt and Mn and the well-dispersed bimetallic phase. An artificial neural networks (ANN) model was developed to predict the performance of catalytic oxidation process over Pt-Mn/gamma -Al(2)O(3) bimetallic catalyst based on experimental data. For this purpose the Levenberg-Marquardt (LM) learning algorithm was employed to train the model by using laboratory experimental data. A comparison between the predicted results of the designed ANN model and experimental data was also conducted. The developed model can describe the catalytic oxidation over bimetallic catalysts under different conditions. PMID:20390890

  12. XPS/STM study of model bimetallic Pd-Au/HOPG catalysts

    NASA Astrophysics Data System (ADS)

    Bukhtiyarov, Andrey V.; Prosvirin, Igor P.; Bukhtiyarov, Valerii I.

    2016-03-01

    The preparation of model bimetallic Pd-Au/HOPG catalysts has been investigated using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) techniques. Initially, model "core-shell" type Pd-Au/HOPG catalysts with similar particle size distribution (5-8 nm), but with different densities of particle locations on the HOPG surface and Pd/Au atomic ratios are prepared. Further, their thermal stability is studied within a temperature range of 50-500 °C at UHV conditions. It has been shown that annealing the model catalysts at a temperature range of 300-400 °C leads to formation of Pd-Au alloyed particles. Enhancement of heating temperature up to 500 °C results in sintering of bimetallic nanoparticles. Contribution of different parameters controlling the properties of Pd-Au alloyed particles has been discussed.

  13. Efficient method for the conversion of agricultural waste into sugar alcohols over supported bimetallic catalysts.

    PubMed

    Tathod, Anup P; Dhepe, Paresh L

    2015-02-01

    Promoter effect of Sn in the PtSn/γ-Al2O3 (AL) and PtSn/C bimetallic catalysts is studied for the conversion of variety of substrates such as, C5 sugars (xylose, arabinose), C6 sugars (glucose, fructose, galactose), hemicelluloses (xylan, arabinogalactan), inulin and agricultural wastes (bagasse, rice husk, wheat straw) into sugar alcohols (sorbitol, mannitol, xylitol, arabitol, galactitol). In all the reactions, PtSn/AL showed enhanced yields of sugar alcohols by 1.5-3 times than Pt/AL. Compared to C, AL supported bimetallic catalysts showed prominent enhancement in the yields of sugar alcohols. Bimetallic catalysts characterized by X-ray diffraction study revealed the stability of catalyst and absence of alloy formation thereby indicating that Pt and Sn are present as individual particles in PtSn/AL. The TEM analysis also confirmed stability of the catalysts and XPS study disclosed formation of electron deficient Sn species which helps in polarizing carbonyl bond to achieve enhanced hydrogenation activity. PMID:25453932

  14. Characterization of CeO2-Supported Cu-Pd Bimetallic Catalyst for the Oxygen-Assisted Water-Gas Shift Reaction

    SciTech Connect

    Fox, Elise; Velu, Subramani; Engelhard, Mark H.; Chin, Ya-Huei; Miller, Jeffrey T.; Kropf, Jeremy; Song, Chunshan

    2008-12-10

    This study was focused to investigate the roles of Cu and Pd in CuPd/CeO2 bimetallic catalysts containing 20-30 wt% Cu and 0.5-1 wt% Pd used in the oxygen-assisted water-gas shift (OWGS) reaction employing a combined bulk and surface characterization techniques such as XRD, TPR, CO chemisorption, and in-situ XPS. The catalytic activity for CO conversion and the stability of catalyst during on-stream operation increased by the addition of Cu to Pd/CeO2 or Pd to Cu/CeO2 monometallic catalysts, especially when the OWGS reaction was performed under low temperatures, below 200oC. The bimetallic catalyst after leaching with nitric acid retained about 60% of its original activity. The TPR of monometallic Cu/CeO2 showed reduction of CuO supported on CeO2 in two distinct regions, around 150 and 250oC. The high temperature peak disappeared and reduction occurred in a single step around 150oC upon Pd addition. The Pd dispersion decreased from 38.5% for Pd/CeO2 to below 1% for CuPd/CeO2 bimetallic catalyst. In-situ XPS studies showed a shift in Cu 2p peaks toward lower binding energy (BE) with concommitant shift in the Pd 3d peaks toward higher BE. Addition of Pd decreased the surface Cu concentration while the concentration of Pd remained unaltered. All these observations indicated the formation of Cu-Pd surface alloy. The valence band XP spectra collected below 10 eV corroborated the core level XP spectra and indicated that Cu is mainly involved in the catalytic reaction. The improved catalytic activity and stability of CuPd/CeO2 bimetallic catalyst was attributed to the alloy formation.

  15. Nanosegregated bimetallic oxide anode catalyst for proton exchange membrane electrolyzer

    DOEpatents

    Danilovic, Nemanja; Kang, Yijin; Markovic, Nenad; Stamenkovic, Vojislav; Myers, Deborah J.; Subbaraman, Ram

    2016-08-23

    A surface segregated bimetallic composition of the formula Ru.sub.1-xIr.sub.x wherein 0.1.ltoreq.x.ltoreq.0.75, wherein a surface of the material has an Ir concentration that is greater than an Ir concentration of the material as a whole is provided. The surface segregated material may be produced by a method including heating a bimetallic composition of the formula Ru.sub.1-xIr.sub.x, wherein 0.1.ltoreq.x.ltoreq.0.75, at a first temperature in a reducing environment, and heating the composition at a second temperature in an oxidizing environment. The surface segregated material may be utilized in electrochemical devices.

  16. Kinetics of oxygen-enhanced water gas shift on bimetallic catalysts and the roles of metals and support

    NASA Astrophysics Data System (ADS)

    Kugai, Junichiro

    dissociation and/or the subsequent reaction with chemisorbed CO as well as Pd keeps Cu in reduced state. Cu was found to keep Pd dispersed, suppress H2 activation on Pd, and facilitate CO 2 desorption from catalyst surface. While composition and structure of metal have large impacts on OWGS performance, CeO2 was shown to create new sites for H2O activation at metal-ceria interfacial region in concert with metal. These new sites strongly activate H2O to drive OWGS and WGS compared to the pure metallic sites which are present in majority on Al2O3-supported catalyst. The observed two regimes of turnover rate, the one dependent on catalyst surface area and the other independent of surface area, strongly suggested bifunctional reaction pathway where the reaction rate is determined by activation of H2O and by association of chemisorbed CO and H 2O. The associative route was also evidenced by pulse response study where the reaction occurs only when CO and H2O pulses are supplied together, and thus pre-adsorbed species such as formate and carbonate identified by FT-IR are proven to be spectators. No correlation between WGS rate and isotopic exchange rate of molecularly adsorbed D2O with H 2 showed H2O dissociation is necessary for WGS to occur. Long duration tests revealed CeO2-supported Pd-Cu, Pt-Cu and Cu catalysts are stable in OWGS condition compared to Pt, Pd, and Al 2O3-supported Pd-Cu catalysts which exhibited continuous deactivation during about 70 hours of test. The addition of Cu prevents agglomeration of monometallic Pd and carbonate formation on monometallic Pt during the reaction. The better activity and stability of Pd-Cu and Pt-Cu bimetallic catalysts in the realistic OWGS condition were ascribed to the unique active sites consisting of highly dispersed Pd in Cu or Pt in Cu on CeO2, which are good for H2O activation with low reaction inhibition by the product gases. Pt monometallic catalyst showed and highest activity in OWGS in the absence of product gases, but this

  17. Kinetics and mechanism of the liquid-phase oxidation of cyclohexene. V. Oxidation of cyclohexene in the presence of bimetallic catalysts

    SciTech Connect

    Baevskii, M.Yu.; Litvintsev, I.Yu.; Sapunov, V.N.

    1988-11-01

    The kinetics of the liquid-phase oxidation of cyclohexene in the presence of homogeneous bimetallic catalysts Co-V, Pb-V, Pb-Mo was investigated. It was shown that the activity of the bimetallic catalyst found is determined to a large degree by the nature of the epoxiding metal. A general model is proposed for the oxidation of cyclohexene in the presence of bimetallic catalysts.

  18. Structural characterization of bimetallic Pd-Cu vapor derived catalysts

    NASA Astrophysics Data System (ADS)

    Balerna, Antonella; Evangelisti, Claudio; Psaro, Rinaldo; Fusini, Graziano; Carpita, Adriano

    2016-05-01

    Pd-Cu bimetallic Solvated Metal Atoms (SMA) were synthesized by metal vapor synthesis technique and supported on PVPy resin. Since the catalytic activity, of the Pd-Cu system turned out to be quite high also compared to the corresponding monometallic system, a structural characterization, using electron microscopy techniques and X-ray Absorption Fine Structure spectroscopy, was performed. HRTEM analysis showed the presence of Pd particles distributed in a narrow range with a mean diameter of about 2.5 nm while the XAFS analysis, confirmed the presence of the Pd nanoparticles but revealed also some alloying with Cu atoms.

  19. Experimental and computational investigations of sulfur-resistant bimetallic catalysts for reforming of biomass gasification products

    SciTech Connect

    Rangan, Meghana; Yung, Matthew M.; Medlin, J. William

    2011-11-17

    A combination of density functional theory (DFT) calculations and experimental studies of supported catalysts was used to identify H{sub 2}S-resistant biomass gasification product reforming catalysts. DFT calculations were used to search for bimetallic, nickel-based (1 1 1) surfaces with lower sulfur adsorption energies and enhanced ethylene adsorption energies. These metrics were used as predictors for H{sub 2}S resistance and activity toward steam reforming of ethylene, respectively. Relative to Ni, DFT studies found that the Ni/Sn surface alloy exhibited enhanced sulfur resistance and the Ni/Ru system exhibited an improved ethylene binding energy with a small increase in sulfur binding energy. A series of supported bimetallic nickel catalysts was prepared and screened under model ethylene reforming conditions and simulated biomass tar reforming conditions. The observed experimental trends in activity were consistent with theoretical predictions, with observed reforming activities in the order Ni/Ru > Ni > Ni/Sn. Interestingly, Ni/Ru showed a high level of resistance to sulfur poisoning compared with Ni. This sulfur resistance can be partly explained by trends in sulfur versus ethylene binding energy at different types of sites across the bimetallic surface.

  20. Mono- and bimetallic Rh and Pt NSR-catalysts prepared by controlled deposition of noble metals on support or storage component.

    PubMed

    Büchel, Robert; Pratsinis, Sotiris E; Baiker, Alfons

    2012-02-22

    Mono- and bimetallic Rh and Pt based NOx storage-reduction (NSR) catalysts, where the noble metals were deposited on the Al2O3 support or BaCO3 storage component, have been prepared using a twin flame spray pyrolysis setup. The catalysts were characterized by nitrogen adsorption, CO chemisorption combined with diffuse reflectance infrared Fourier transform spectroscopy, X-ray diffraction, and scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy. The NSR performance of the catalysts was investigated by fuel lean/rich cycling in the absence and presence of SO2 (25 ppm) as well as after H2 desulfation at 750 °C. The performance increased when Rh was located on BaCO3 enabling good catalyst regeneration during the fuel rich phase. Best performance was observed for bimetallic catalysts where the noble metals were separated, with Pt on Al2O3 and Rh on BaCO3. The Rh-containing catalysts generally showed much higher tolerance to SO2 during fuel rich conditions and lost only little activity during thermal aging at 750 °C. PMID:23741085

  1. Exceptional methanol electro-oxidation activity by bimetallic concave and dendritic Pt-Cu nanocrystals catalysts

    NASA Astrophysics Data System (ADS)

    Wang, Ying-Xia; Zhou, Hui-Jing; Sun, Ping-Chuan; Chen, Tie-Hong

    2014-01-01

    PtCux (x = 1, 2 and 3) bimetallic nanocrystals with concave surface and dendritic morphology were prepared and used as electrocatalysts in methanol oxidation reaction (MOR) for polymer electrolyte membrane fuel cells. The bimetallic nanocrystals were synthesized via one-pot co-reduction of H2PtCl6 and Cu(acac)2 by oleylamine and polyvinyl pyrrolidone (PVP) in an autoclave at 180 °C. The concave dendritic bimetallic nanostructure consisted of a core rich in Cu and nanodendrites rich in Pt, which was formed via galvanic replacement of Cu by Pt. It was found that PVP played an important role in initiating, facilitating, and directing the replacement reaction. The electrochemical properties of the PtCux were characterized by cyclic voltammetry (CV) and chronoamperometry (CA). The concave dendritic PtCu2/C nanocrystals exhibited exceptionally high activity and strong poisoning resistance in MOR. At 0.75 V (vs. reversible hydrogen electrode, RHE) the mass activity and specific activity of PtCu2/C were 3.3 and 4.1 times higher than those of the commercial Pt/C catalysts, respectively. The enhanced catalytic activity could be attributed to the unique concave dendritic morphology of the bimetallic nanocrystals.

  2. Bioacid hydroconversion over Co, Ni, Cu Mono- and indium-doped bimetallic catalysts.

    PubMed

    Onyestyák, György; Harnos, Szabolcs; Kalló, Dénes

    2015-01-01

    Caprylic acid (CA) as model reactant was selectively reduced in a flow-through reactor in hydrogen stream at 21 bar total pressure and 240-360 °C over alumina loaded with the adjacent Co, Ni, Cu host and In guest metals. The main target of this research is the recognition of efficient cobalt catalysts for carboxylic group hydroconversion compared to more familiar nickel and copper composites. The catalysts were activated in H(2) flow at 21 bar and 450 °C. By variation of main metal or modification with indium, mono- or bimetallic catalysts can be obtained with low hydrodecarbonylation activity and high alcohol selectivity. These composites have higher hydrodeoxygenation (HDO) activity and alcohol selectivity than the conventional commercial catalysts applied for fatty alcohol production. Great variety of catalytic behavior indicates complexity of the surface reactions determined by several interacting factors.

  3. Growth and characterization of CNT Forests using Bimetallic Nanoparticles as Catalyst

    NASA Astrophysics Data System (ADS)

    Lee, Kyung-Hwan; Sra, A.; Jang, H.; Choi, B.; Overzet, L.; Lee, G.; Yang, D.

    2008-10-01

    We study the growth of Multiwall carbon nanotubes (MWCNT) using bimetallic nanoparticles (NP) as catalyst rather than zerovalent metal ions such as Fe, Ni, Co. One advantage of using bimetallic NP is that both the size and shape and composition (atomic ordering) can be controlled. We will describe a simple method of producing bimetallic Fe-Pt, Fe-Co alloy nanoparticles and compare MWCNT growth using them to Fe catalyst growth. The synthesis of Fe, Fe-Pt, Fe-Co NP was carried out using a bottom-up polyol process. Subsequent growth of MWCNT forests was accomplished by PECVD using acetylene as precursor. TEM and SEM analysis of the sample cross-section grown at substrate temperature of 680 ^oC indicates that the diameters of the CNTs are ˜ 10-20 nm while height of the forest varies from 30 μm for Fe to 5 μm for Fe-Pt and 80-100 μm for Fe-Co. The number of walls in the CNTs and the graphitization content could be manipulated by varying the temperature (increasing to 760 ^oC) or by pre-treatment of the nanoparticles with oxygen plasma.

  4. Characterization of Na+- beta-Zeolite Supported Pd and Pd Ag Bimetallic Catalysts using EXAFS, TEM and Flow Reactor

    SciTech Connect

    Huang,W.; Lobo, R.; Chen, J.

    2008-01-01

    Flow reactor studies of the selective hydrogenation of acetylene in the presence of ethylene have been performed on Na+ exchanged {beta}-zeolite supported Pd, Ag and PdAg catalysts, as an extension of our previous batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40-51]. Results from flow reactor studies show that the PdAg/Na+-{beta}-zeolite bimetallic catalyst has lower activity than Pd/Na+-{beta}-zeolite monometallic catalyst, while Ag/Na+-{beta}-zeolite does not show any activity for acetylene hydrogenation. However, the selectivity for the PdAg bimetallic catalyst is much higher than that for either the Pd catalyst or Ag catalyst. The selectivity to byproduct (ethane) is greatly inhibited on the PdAg bimetallic catalyst as well. The results from the current flow reactor studies confirmed the pervious results from batch reactor studies [W. Huang, J.R. McCormick, R.F. Lobo, J.G. Chen, J. Catal. 246 (2007) 40-51]. In addition, we used transmission electron microscope (TEM), extended X-ray absorption fine structure (EXAFS), and FTIR of CO adsorption to confirm the formation of Pd-Ag bimetallic alloy in the PdAg/Na+-{beta}-zeolite catalyst.

  5. [Preparation bimetallic heterogeneous Fenton-like catalyst as sepiolite supported and its surface chemical characterization].

    PubMed

    Su, Cheng-yuan; Li, Wei-guang; Liu, Xing-zhe; Wang, Kai-yao; Wang, Yong

    2013-09-01

    The reactive brilliant blue was chosen as the probe pollutant. Fe(NO3)3 concentration, MnSO4 concentration, urea concentration, water bath temperature, calcined temperature and time were as influencing factors, the process parameters of homogeneous precipitation method was optimized for the preparation of bimetallic heterogeneous Fenton-like catalyst as modified sepiolite supported. At the same time, surface chemical characteristics of catalyst were analyzed by SEM, FTIR and XRD. Results showed that: with increasing iron ion concentrations, the active ingredient of the catalyst increased. Adding small amount of manganese ion could inhibit the growth of Fe2O3 diameter and increase the activity of the catalyst. Urea concentration was increased, so that the higher the urea concentration, the higher rate of formation of crystal gains, was conducive to generate small and uniform particles. The optimal conditions were found for preparing bimetallic heterogeneous Fenton-like catalyst by Box-Behnken experiment, which were as follows: concentration of Fe(NO3)3, MnSO4 and urea were 0.18 mol x L(-1), 0.05 mol x L(-1) and 1.0 mol x L(-1), respectively. The dosage of the modified sepiolite was 40 g x L(-1) and water bath temperature was 100 degrees C. Additionally, the catalyst was calcined at 370 degrees C for 3 h. The SEM showed that the sepiolite was an a-type sepiolite, which could be used as a well catalyst support. The infrared spectrum presented the bend vibrations of the Fe-O stretch vibration. The XRD patterns of the catalysts showed the characteristic diffraction peaks of alpha-Fe2O3, and gamma-Fe2O3.

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

    SciTech Connect

    B Cheney; J Lauterbach; J Chen

    2011-12-31

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

  7. Effects of nanocrystalline CeO2 supports on the properties and performance of Ni–Rh bimetallic catalyst for oxidative steam reforming of ethanol

    SciTech Connect

    Kugai, Junichiro; Subramani, Velu; Song, Chunshan; Engelhard, Mark H.; Chin, Ya-Huei

    2006-03-10

    This study focuses on the effects of the CeO2 support properties on the catalyst properties and performance of bimetallic Ni?Rh/CeO2 catalysts containing 5 wt% Ni and 1 wt% Rh for the oxidative steam reforming (OSR) of ethanol for hydrogen production and fuel cell applications. Three CeO2 supports with different crystal sizes and surface areas were examined. The surface areas of these supports increases in the order of CeO2-I (74 m2/g) < CeO2-II (92 m2/g) < CeO2-III (154 m2/g), but their crystallite sizes were about 10.2, 29.3, and 6.5 nm, respectively. The properties of Ni?Rh/CeO2 catalysts were investigated by XRD, TPR, H2 chemisorption, and in situ XPS techniques. The Rh metal dispersion increased while the Ni metal dispersion decreased with decreasing crystallite sizes of CeO2. TPR studies revealed the existence of a Rh?CeO2 metal?support interaction as well as Ni?Rh interaction in the Ni?Rh bimetallic catalyst supported on CeO2-III with a crystallite size of about 6.5 nm. The in situ XPS studies corroborated the TPR results. The reduced Ni and Rh species were reversibly oxidized, suggesting the existence of Ni?Rh redox species rather than NiRh surface alloy in the present catalyst system. The Rh species became highly dispersed when the crystallite size of CeO2 support was smaller. Comparing the catalytic performance in the OSR of ethanol was compared with the properties of the catalysts demonstrated that both ethanol conversion and H2 selectivity increased and the selectivity for undesirable byproducts decreased with increasing Rh metal dispersion. Best catalytic performance for OSR was achieved by supporting Ni?Rh bimetallic catalysts on the nanocrystalline CeO2-III. The Ni?Rh/CeO2-III catalyst exhibited stable activity and selectivity during on-stream operations at 450 C and as well as at 600 C.

  8. Using supported Au nanoparticles as starting material for preparing uniform Au/Pd bimetallic catalysts

    SciTech Connect

    Villa, Alberto; Prati, Laura; Su, Dangshen; Wang, Di; Veith, Gabriel M

    2010-01-01

    One of the best methods for producing bulk homogeneous (composition) supported bimetallic AuPd clusters involves the immobilization of a protected Au seed followed by the addition of Pd. This paper investigates the importance of this gold seed in controlling the resulting bimetallic AuPd clusters structures, sizes and catalytic activities by investigating three different gold seeds. Uniform Au-Pd alloy were obtained when a steric/electrostatic protecting group, poly(vinyl alcohol) (PVA), was used to form the gold clusters on activated carbon (AC). In contrast Au/AC precursors prepared using Au nanoparticles with only electrostatic stabilization (tetrakis(hydroxypropyl)phosphonium chloride (THPC)), or no stabilization (magnetron sputtering) produced inhomogeneous alloys and segregation of the gold and palladium. The uniform alloyed catalyst (Pd{at}Au{sub PVA}/AC) is the most active and selective catalyst, while the inhomogenous catalysts are less active and selective. Further study of the PVA protected Au clusters revealed that the amount of PVA used is also critical for the preparation of uniform alloyed catalyst, their stability, and their catalytic activity.

  9. Bimetallic PtSn/C catalysts obtained via SOMC/M for glycerol steam reforming.

    PubMed

    Pastor-Pérez, Laura; Merlo, Andrea; Buitrago-Sierra, Robison; Casella, Mónica; Sepúlveda-Escribano, Antonio

    2015-12-01

    A detailed study on the preparation of bimetallic PtSn/C catalysts using surface-controlled synthesis methods, and on their catalytic performance in the glycerol steam reforming reaction has been carried out. In order to obtain these well-defined bimetallic phases, techniques derived from Surface Organometallic Chemistry on Metals (SOMC/M) were used. The preparation process involved the reaction between an organometallic compound ((C4H9)4Sn) and a supported transition metal (Pt) in a H2 atmosphere. Catalysts with Sn/Pt atomic ratios of 0.2, 0.3, 0.5, and 0.7 were obtained, and characterized using several techniques: ICP, H2 chemisorption, TEM and XPS. These systems were tested in the glycerol steam reforming varying the reaction conditions (glycerol concentration and reaction temperature). The best performance was observed for the catalysts with the lowest tin contents (PtSn0.2/C and PtSn0.3/C). It was observed that the presence of tin increased the catalysts' stability when working under more severe reaction conditions.

  10. Bimetallic PtSn/C catalysts obtained via SOMC/M for glycerol steam reforming.

    PubMed

    Pastor-Pérez, Laura; Merlo, Andrea; Buitrago-Sierra, Robison; Casella, Mónica; Sepúlveda-Escribano, Antonio

    2015-12-01

    A detailed study on the preparation of bimetallic PtSn/C catalysts using surface-controlled synthesis methods, and on their catalytic performance in the glycerol steam reforming reaction has been carried out. In order to obtain these well-defined bimetallic phases, techniques derived from Surface Organometallic Chemistry on Metals (SOMC/M) were used. The preparation process involved the reaction between an organometallic compound ((C4H9)4Sn) and a supported transition metal (Pt) in a H2 atmosphere. Catalysts with Sn/Pt atomic ratios of 0.2, 0.3, 0.5, and 0.7 were obtained, and characterized using several techniques: ICP, H2 chemisorption, TEM and XPS. These systems were tested in the glycerol steam reforming varying the reaction conditions (glycerol concentration and reaction temperature). The best performance was observed for the catalysts with the lowest tin contents (PtSn0.2/C and PtSn0.3/C). It was observed that the presence of tin increased the catalysts' stability when working under more severe reaction conditions. PMID:26283100

  11. Designing Pd-on-Au bimetallic nanoparticle catalysts for trichloroethene hydrodechlorination.

    PubMed

    Nutt, Michael O; Hughes, Joseph B; Michael, S Wong

    2005-03-01

    Alumina-supported palladium (Pd) catalysts have previously been shown to hydrodechlorinate trichloroethene (TCE) and other chlorinated compounds in water, at room temperature, and in the presence of hydrogen. The feasibility of this catalytic technology to remediate groundwater of halogenated compounds can be improved by re-designing the Pd material in order to increase catalytic activity. We synthesized and characterized Pd supported on gold nanoparticles (Au NPs) of different Pd loadings. In all cases, we found that these catalysts were considerably more active than Pd NPs, alumina-supported Pd, ard Pd-black (62.0, 12.2, and 0.42 L x g(Pd)(-1) x min(-1), respectively). There is a synergistic effect of the Pd-on-Au bimetallic structure, with the material with the highest TCE hydrodechlorination activity (943 L x g(Pd)(-1) x min(-1)) comprised of Au NPs partially covered by Pd metal. The Pd-on-Au bimetallic catalyst structure provides a new synthesis approach in improving the catalytic properties of monometallic Pd materials. The resulting nanoparticle-based materials should be highly suitable as hydrodehalogenation and reduction catalysts for the remediation of various organic and inorganic groundwater contaminants.

  12. Strategies for designing supported gold-palladium bimetallic catalysts for the direct synthesis of hydrogen peroxide.

    PubMed

    Edwards, Jennifer K; Freakley, Simon J; Carley, Albert F; Kiely, Christopher J; Hutchings, Graham J

    2014-03-18

    Hydrogen peroxide is a widely used chemical but is not very efficient to make in smaller than industrial scale. It is an important commodity chemical used for bleaching, disinfection, and chemical manufacture. At present, manufacturers use an indirect process in which anthraquinones are sequentially hydrogenated and oxidized in a manner that hydrogen and oxygen are never mixed. However, this process is only economic at a very large scale producing a concentrated product. For many years, the identification of a direct process has been a research goal because it could operate at the point of need, producing hydrogen peroxide at the required concentration for its applications. Research on this topic has been ongoing for about 100 years. Until the last 10 years, catalyst design was solely directed at using supported palladium nanoparticles. These catalysts require the use of bromide and acid to arrest peroxide decomposition, since palladium is a very active catalyst for hydrogen peroxide hydrogenation. Recently, chemists have shown that supported gold nanoparticles are active when gold is alloyed with palladium because this leads to a significant synergistic enhancement in activity and importantly selectivity. Crucially, bimetallic gold-based catalysts do not require the addition of bromide and acids, but with carbon dioxide as a diluent its solubility in the reaction media acts as an in situ acid promoter, which represents a greener approach for peroxide synthesis. The gold catalysts can operate under intrinsically safe conditions using dilute hydrogen and oxygen, yet these catalysts are so active that they can generate peroxide at commercially significant rates. The major problem associated with the direct synthesis of hydrogen peroxide concerns the selectivity of hydrogen usage, since in the indirect process this factor has been finely tuned over decades of operation. In this Account, we discuss how the gold-palladium bimetallic catalysts have active sites for the

  13. Designing Bimetallic Co-Catalysts: A Party of Two.

    PubMed

    Aronovitch, Eran; Kalisman, Philip; Mangel, Shai; Houben, Lothar; Amirav, Lilac; Bar-Sadan, Maya

    2015-09-17

    The enhanced catalytic properties of bimetallic particles has made them the focus of extensive research. We compare the photocatalytic activity for hydrogen production of core-shell structures of Au@Pd and Au@(Au/Pd alloy) on seeded rods of CdSe@CdS and show that Au@alloy was superior toward hydrogen production. Our finding reveals that the promotion effects of Au in Pd originate both from the alteration of the electronic structure by the Au core as well as by the atomic rearrangement of the surface. Long-term monitoring of the activity of the photocatalysts offered insights into the dynamic processes during the illumination showing that the tip morphology influenced the stability of the hybrid structures. The Au core served as a physical barrier, protecting the CdS rod against cation exchange reactions with the Pd. The coupling of these factors to achieve synergistic effects is therefore a prime aspect in the rational design of efficient cocatalysts. PMID:26722753

  14. Isomerization and hydrocracking of heptane over bimetallic bifunctional PtPd/H-Beta and PtPd/USY zeolite catalysts

    SciTech Connect

    Blomsma, E.; Martens, J.A.; Jacobs, P.A.

    1997-01-15

    Bifunctional catalysts are prepared by loading NH{sub 4}-Beta zeolites with platinum, palladium, and platinum-palladium metal combinations via cation exchange and incipient wetness impregnation with Pt(NH{sub 3}){sub 4}Cl{sub 2} and Pd(NH{sub 3}){sub 4}Cl{sub 2} complexes, followed by calcination and reduction. In comparison to the Pt and Pd loaded acid zeolites, the bimetallic Pd-Pt zeolites are found to be more active and selective in the isomerization of heptane. The noble metal phases are characterized with temperature programmed reduction and hydrogen chemisorption. The dispersion of platinum is significantly improved in presence of as little as 20 mole% of palladium. The improved Pt dispersion leads to a better intimacy and balance of the acid and hydrogenation-dehydrogenation functions in these bi-functional catalysts and suppression of undesirable hydrogenolysis and dimerization-cracking activity. On Pt/USY zeolite, the addition of palladium has similar beneficial effects on the catalytic performances. 34 refs., 4 figs., 3 tabs.

  15. Final technical report. Bimetallic complexes as methanol oxidation catalysts

    SciTech Connect

    McElwee-White, Lisa

    2002-01-21

    Our work on the electrocatalyzed oxidation of methanol was initially motivated by the interest in methanol as an anodic reactant in fuel cells. The literature on electrochemical oxidation of alcohols can be roughly grouped into two sets: fuel cell studies and inorganic chemistry studies. Work on fuel cells primarily focuses on surface-catalyzed oxidation at bulk metal anodes, usually Pt or Pt/Ru alloys. In the surface science/electrochemistry approach to these studies, single molecule catalysts are generally not considered. In contrast, the inorganic community investigates the electrooxidation of alcohols in homogeneous systems. Ruthenium complexes have been the most common catalysts in these studies. The alcohol substrates are typically either secondary alcohols (e.g., isopropanol) such that the reaction stops after 2 e{sup -} oxidation to the aldehyde and 4 e{sup -} oxidation to the carboxylic acid can be observed. Methanol, which can also undergo 6 e{sup -} oxidation to CO{sub 2}, rarely appears in the homogeneous catalysis studies. Surface studies have shown that two types of metal centers with different functions result in more effective catalysts than a single metal; however, application of this concept to homogeneous systems has not been demonstrated. The major thrust of the work is to apply this insight from the surface studies to homogeneous catalysis. Even though homogeneous systems would not be appropriate models for active sites on Pt/Ru anodes, it is possible that heterobimetallic catalysts could also utilize two metal centers for different roles. Starting from that perspective, this work involves the preparation and investigation of heterobinuclear catalysts for the electrochemical oxidation of methanol.

  16. Synthesis and Characterization of Cluster-Derived Supported Bimetallic Catalysts

    SciTech Connect

    Adams, Richard D; Amiridis, Michael D

    2008-10-10

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

  17. Novel supported bimetallic carbide catalysts for coprocessing of coal with waste materials

    SciTech Connect

    S.T. Oyama; D.F. Cox; C. Song; F. Allen

    1999-12-15

    In this reporting period the authors have continued their investigation of bimetallic nitride and carbide compounds for use in coprocessing of coal and waste plastics or rubber. Following up on their finding of a class of bimetallic nitrides, reported in the last period, they now report on a new family of bimetallic oxycarbides M{sup I}-M{sup II}-O-C (M{sup I} = Mo, W; M{sup II} = V, Nb, Cr, Fe, Co, Ni). They have carried out a preliminary test of the compounds with a model coal liquid feed and find that, in general, these carbides are even more active than the nitrides. They have identified Nb-Mo-O-C as the most promising catalyst, and this catalyst together with Mo{sub 2}C, the most active single-metal carbide are being investigated for the coprocessing reaction. Comparison is made to standard sulfide catalysts. The latter reaction is carried out in batch autoclave systems, so that preliminary tests are first carried out with a simpler five-component feedstock. The feedstock is a multi-component model mixture that simulates the combined feed of coal and waste materials. The idea is to use different compounds that are specific for each reaction type but have no overlapping products. The proposed design involves a 5-component mixture containing: 4-(1-naphthylmethyl)bibenzyl, abbreviated as NMBB, pyrene, tetradecane, dibenzothiophene and quinoline. NMBB simulates the aromatic-aliphatic as well as aliphatic-aliphatic C-C bonds in coal and in some aromatic plastics such as polystyrene. This compound has been used as a probe molecule in previous studies. Pyrene represents polyaromatic structures in coal, while tetradecane is representative of polyethylene-type plastics in chemical reactivity. Dibenzothiophene and quinoline provide sulfur and nitrogen content.

  18. Correlating Extent of Pt–Ni Bond Formation with Low-temperature Hydrogenation of Benzene and 1,3-butadiene over Supported Pt/Ni Bimetallic Catalysts

    SciTech Connect

    Lonergan, W.; Vlachos, D; Chen, J

    2010-01-01

    Low-temperature hydrogenation of benzene and 1,3-butadiene on supported Pt/Ni catalysts have been used as probe reactions to correlate hydrogenation activity with the extent of Pt-Ni bimetallic bond formation. Pt/Ni bimetallic and Pt and Ni monometallic catalysts were supported on {gamma}-Al{sub 2}O{sub 3} using incipient wetness impregnation. Two sets of bimetallic catalysts were synthesized: one set to study the effect of metal atomic ratio and the other to study the effect of impregnation sequence. Fourier transform infrared spectroscopy (FTIR) CO adsorption studies were performed to characterize the surface composition of the bimetallic nanoparticles, and transmission electron microscopy (TEM) was utilized to characterize the particle size distribution. Batch reactor studies with FTIR demonstrated that all bimetallic catalysts outperformed monometallic catalysts for both benzene and 1,3-butadiene hydrogenation. Within the two sets of bimetallic catalysts, it was found that catalysts with a smaller Pt:Ni ratio possessed higher hydrogenation activity and that catalysts synthesized using co-impregnation had greater activity than sequentially impregnated catalysts. Extended X-ray absorption fine structure (EXAFS) measurements were performed in order to verify the extent of Pt-Ni bimetallic bond formation, which was found to correlate with the hydrogenation activity.

  19. CATALYSIS SCIENCE INITIATIVE: From First Principles Design to Realization of Bimetallic Catalysts for Enhanced Selectivity

    SciTech Connect

    MAVRIKAKIS, MANOS DUMESIC, JAMES A.

    2007-05-03

    In this project, we have integrated state-of-the-art Density Functional Theory (DFT) models of heterogeneous catalytic processes with high-throughput screening of bimetallic catalytic candidates for important industrial problems. We have studied a new class of alloys characterized by a surface composition different from the bulk composition, and investigated their stability and activity for the water-gas shift reaction and the oxygen reduction reaction. The former reaction is an essential part of hydrogen production; the latter is the rate-limiting step in low temperature H2 fuel cells. We have identified alloys that have remarkable stability and activity, while having a much lower material cost for both of these reactions. Using this knowledge of bimetallic interactions, we have also made progress in the industrially relevant areas of carbohydrate reforming and conversion of biomass to liquid alkanes. One aspect of this work is the conversion of glycerol (a byproduct of biodiesel production) to synthesis gas. We have developed a bifunctional supported Pt catalyst that can cleave the carbon-carbon bond while also performing the water-gas shift reaction, which allows us to better control the H2:CO ratio. Knowledge gained from the theoretical metal-metal interactions was used to develop bimetallic catalysts that perform this reaction at low temperature, allowing for an efficient coupling of this endothermic reaction with other reactions, such as Fischer-Tropsch or methanol synthesis. In our work on liquid alkane production from biomass, we have studied deactivation and selectivity in these areas as a function of metal-support interactions and reaction conditions, with an emphasis on the bifunctionality of the catalysts studied. We have identified a stable, active catalyst for this process, where the selectivity and yield can be controlled by the reaction conditions. While complete rational design of catalysts is still elusive, this work demonstrates the power of

  20. Low-temperature aqueous-phase reforming of ethanol on bimetallic PdZn catalysts

    SciTech Connect

    Xiong, Haifeng; DelaRiva, Andrew; Wang, Yong; Dayte, Abhaya

    2015-01-01

    Bimetallic PdZn catalysts supported on carbon black (CB) and carbon nanotubes (CNTs) were found to be selective for CO-free H-2 production from ethanol at low temperature (250 degrees C). On Pd, the H-2 yield was low (similar to 0.3 mol H-2/mol ethanol reacted) and the CH4/CO2 ratio was high (similar to 1.7). Addition of Zn to Pd formed the intermetallic PdZn beta phase (atomic ratio of Zn to Pd is 1) with increased H-2 yield (similar to 1.9 mol H-2/mol ethanol reacted) and CH4/CO2 ratio of <1. The higher H-2 yield and low CH4 formation was related to the improved dehydrogenation activity of the L1(0) PdZn beta phase. The TOF increased with particle size and the CNTs provided the most active and selective catalysts, which may be ascribed to pore-confinement effects. Furthermore, no significant changes in either the supports or the PdZn beta particles was found after aqueous-phase reforming (APR) indicating that the metal nanoparticles and the carbon support are hydrothermally stable in the aqueous phase at elevated temperatures and pressures (>200 degrees C, 65 bar). No CO was detected for all the catalysts performed in aqueous-phase reaction, indicating that both monometallic Pd and bimetallic PdZn catalysts have high water-gas shift activity during APR. However, the yield of H-2 is considerably lower than the theoretical value of 6 H-2 per mole ethanol which is due to the presence of oxygenated products and methane on the PdZn catalysts.

  1. Optimization of Single and Bimetallic Noble Metal Catalysts by Strong Electrostatic Adsorption

    NASA Astrophysics Data System (ADS)

    Barnes, Sean E.

    Heterogeneous catalysts are used in over 90% of chemical processes today. These small metal particles maximize the number of active sites present, which leads to cheaper, more effective catalysts. However, the preparation of heterogeneous catalysts is still a "dark art". An alternate to dry impregnation is the method of Strong Electrostatic Adsorption (SEA). In this method the surface hydroxyl groups of the support can either protonate or deprotonate depending on the pH of the contacting solution. These surface groups then can then attract oppositely charged metal precursors. Preparation of catalysts by SEA leads to the anchoring of small, well dispersed, highly active metal particles. The aim of this work is to optimize the preparation via SEA of various supported catalysts systems, particularly Pt/carbon, Au supported on a variety of materials, and Au-Pd/carbon. Carbon supported metal catalysts are becoming increasingly important not just as electro catalyst in fuel cells, but for many aqueous phase biomass conversion reactions.

  2. Facile synthesis of ultrathin bimetallic PtSn wavy nanowires by nanoparticle attachment as enhanced hydrogenation catalysts.

    PubMed

    Ding, Jiabao; Bu, Lingzheng; Zhang, Nan; Yao, Jianlin; Huang, Yu; Huang, Xiaoqing

    2015-03-01

    Ultrathin wavy nanowires represent an emerging class of nanostructures that exhibit unique catalytic, magnetic, and electronic properties, but the controlled production of bimetallic wavy nanowires remains a significant challenge. Ultrathin bimetallic PtSn nanowires have been prepared with high yield and featuring a highly wavy structure. Owing to the ultrathin nature and unique electronic properties of these PtSn wavy nanowires, they exhibit improved catalytic performance for the hydrogenation of nitrobenzene, as well as for the hydrogenation of styrene. These results suggest a new strategy to prepare highly active catalysts through defect engineering and can significantly impact broad practical applications. PMID:25603959

  3. Nickel-cobalt bimetallic anode catalysts for direct urea fuel cell

    PubMed Central

    Xu, Wei; Zhang, Huimin; Li, Gang; Wu, Zucheng

    2014-01-01

    Nickel is an ideal non-noble metal anode catalyst for direct urea fuel cell (DUFC) due to its high activity. However, there exists a large overpotential toward urea electrooxidation. Herein, NiCo/C bimetallic nanoparticles were prepared with various Co contents (0, 10, 20, 30 and 40 wt%) to improve the activity. The best Co ratio was 10% in the aspect of cell performance, with a maximum power density of 1.57 mW cm−2 when 0.33 M urea was used as fuel, O2 as oxidant at 60°C. The effects of temperature and urea concentration on DUFC performance were investigated. Besides, direct urine fuel cell reaches a maximum power density of 0.19 mW cm−2 with an open circuit voltage of 0.38 V at 60°C. PMID:25168632

  4. Nickel-cobalt bimetallic anode catalysts for direct urea fuel cell

    NASA Astrophysics Data System (ADS)

    Xu, Wei; Zhang, Huimin; Li, Gang; Wu, Zucheng

    2014-08-01

    Nickel is an ideal non-noble metal anode catalyst for direct urea fuel cell (DUFC) due to its high activity. However, there exists a large overpotential toward urea electrooxidation. Herein, NiCo/C bimetallic nanoparticles were prepared with various Co contents (0, 10, 20, 30 and 40 wt%) to improve the activity. The best Co ratio was 10% in the aspect of cell performance, with a maximum power density of 1.57 mW cm-2 when 0.33 M urea was used as fuel, O2 as oxidant at 60°C. The effects of temperature and urea concentration on DUFC performance were investigated. Besides, direct urine fuel cell reaches a maximum power density of 0.19 mW cm-2 with an open circuit voltage of 0.38 V at 60°C.

  5. Bimetallic complexes of spiro-azacrown ligands as catalysts of phosphoester and phosphoric anhydride cleavage.

    PubMed

    Wang, Qi; Mikkola, Satu; Lönnberg, Harri

    2004-09-01

    The ability of bimetallic homo- and heteronuclear complexes of two spiro-linked ligands, viz. a biazacrown (i.e., 2,6,10,14,18,22-hexaazaspiro[11.11]tricosane (1)) and an azacrown-crown ether (i.e., 14,17,20,23,26-pentaoxa-2,6,10-triaza-spiro[11.15]heptacosane (2)), to promote the cleavage of the phosphoester linkage of dinucleoside 3',5'-phosphates and the phosphoric anhydride bridge of dinucleoside 5',5'-triphosphates was studied. In both reactions, the bimetallic homonuclear Cu2+ and Zn2+ complexes were better catalysts than their monometallic counterparts. The acceleration was two- to five-fold with the phosphoester cleavage and 3- to 20-fold with the phosphoric anhydride cleavage. Interestingly, the most-efficient catalyst of the phosphoester cleavage was the heterodinuclear Ni2+,Zn2+ complex of 1, the catalytic activity of which was up to 5- and 100-fold that of the homodinuclear Zn2+ and Ni2+ complexes, respectively. Moreover, this cooperative acceleration was observed to depend on the identity of the 5'-linked nucleoside: 3',5'-UpU and 3',5'-ApU were cleaved much faster than 3',5'-UpA, and no cooperative acceleration was observed with 3',5'-ApA. The reaction was second-order in hydroxide ion concentration, suggesting that a double deprotonation took place on going from the initial to the transition state. Evidently, in addition to deprotonation of the attacking 2'-OH group, N(3)H of the 5'-linked uridine was displaced by one of the metal ions of the cleaving agent. With the phosphoric anhydride cleavage, no similar cooperativity of two different metal ions was observed, but the greatest rate-acceleration was achieved with the homodinuclear Cu2+ complexes.

  6. Bimetallic complexes of spiro-azacrown ligands as catalysts of phosphoester and phosphoric anhydride cleavage.

    PubMed

    Wang, Qi; Mikkola, Satu; Lönnberg, Harri

    2004-09-01

    The ability of bimetallic homo- and heteronuclear complexes of two spiro-linked ligands, viz. a biazacrown (i.e., 2,6,10,14,18,22-hexaazaspiro[11.11]tricosane (1)) and an azacrown-crown ether (i.e., 14,17,20,23,26-pentaoxa-2,6,10-triaza-spiro[11.15]heptacosane (2)), to promote the cleavage of the phosphoester linkage of dinucleoside 3',5'-phosphates and the phosphoric anhydride bridge of dinucleoside 5',5'-triphosphates was studied. In both reactions, the bimetallic homonuclear Cu2+ and Zn2+ complexes were better catalysts than their monometallic counterparts. The acceleration was two- to five-fold with the phosphoester cleavage and 3- to 20-fold with the phosphoric anhydride cleavage. Interestingly, the most-efficient catalyst of the phosphoester cleavage was the heterodinuclear Ni2+,Zn2+ complex of 1, the catalytic activity of which was up to 5- and 100-fold that of the homodinuclear Zn2+ and Ni2+ complexes, respectively. Moreover, this cooperative acceleration was observed to depend on the identity of the 5'-linked nucleoside: 3',5'-UpU and 3',5'-ApU were cleaved much faster than 3',5'-UpA, and no cooperative acceleration was observed with 3',5'-ApA. The reaction was second-order in hydroxide ion concentration, suggesting that a double deprotonation took place on going from the initial to the transition state. Evidently, in addition to deprotonation of the attacking 2'-OH group, N(3)H of the 5'-linked uridine was displaced by one of the metal ions of the cleaving agent. With the phosphoric anhydride cleavage, no similar cooperativity of two different metal ions was observed, but the greatest rate-acceleration was achieved with the homodinuclear Cu2+ complexes. PMID:17191909

  7. Titania-supported bimetallic catalysts combined with HZSM-5 for Fischer-Tropsch synthesis

    SciTech Connect

    Jothimurugesan, K.; Gangwal, S.K.

    1998-04-01

    The Fischer-Tropsch synthesis (FTS) can convert coal or natural gas derived synthesis gas (CO + H{sub 2}) to liquid fuels and high-value chemicals. Fischer-Tropsch synthesis was studied in a fixed-bed reactor over single-metal and bimetallic alloy catalysts, selected from Co, Ni, and Fe, supported on TiO{sub 2} at a total metal loading of 10 wt%. The catalysts, prepared by incipient wetness impregnation using nitrate precursors, were tested as is and in combination with a HZSM-5 zeolite. The test conditions were 1 MPa, 250 C, H{sub 2}/CO = 1, and weight hourly space velocity (WHSV) = 0.77 h{sup {minus}1}. Alloying of metals resulted in a significant enhancement in CO conversion without an increase in methane selectivity. A 50:50 weight ratio Co-Ni catalyst physically mixed with HZSM-5 (5% Co-5% Ni/TiO{sub 2} + HZSM-5) gave the highest CO conversion (45.2%) at the conditions tested. This compares to conversion of 8.9% and 10.5% with Co-only and Ni-only catalysts, respectively. Mixing the Co-Ni catalyst with HZSM-5 resulted in a significant reduction in methane selectivity and a significant increase in C{sub 4}{sup +} selectivity. The aromatic fraction increased from 1.5 to 8.1 wt%, the C{sub 2}{sup +} olefins were nearly eliminated, and i-C{sub 4}H{sub 10} increased from 2.3 to 58.5 wt % in the C{sub 4} fraction.

  8. NiW and NiRu Bimetallic Catalysts for Ethylene Steam Reforming: Alternative Mechanisms for Sulfur Resistance

    SciTech Connect

    Rangan, M.; Yung, M. M.; Medlin, J. W.

    2012-06-01

    Previous investigations of Ni-based catalysts for the steam reforming of hydrocarbons have indicated that the addition of a second metal can reduce the effects of sulfur poisoning. Two systems that have previously shown promise for such applications, NiW and NiRu, are considered here for the steam reforming of ethylene, a key component of biomass derived tars. Monometallic and bimetallic Al{sub 2}O{sub 3}-supported Ni and W catalysts were employed for ethylene steam reforming in the presence and absence of sulfur. The NiW catalysts were less active than Ni in the absence of sulfur, but were more active in the presence of 50 ppm H{sub 2}S. The mechanism for the W-induced improvements in sulfur resistance appears to be different from that for Ru in NiRu. To probe reasons for the sulfur resistance of NiRu, the adsorption of S and C{sub 2}H{sub 4} on several bimetallic NiRu alloy surfaces ranging from 11 to 33 % Ru was studied using density functional theory (DFT). The DFT studies reveal that sulfur adsorption is generally favored on hollow sites containing Ru. Ethylene preferentially adsorbs atop the Ru atom in all the NiRu (111) alloys investigated. By comparing trends across the various bimetallic models considered, sulfur adsorption was observed to be correlated with the density of occupied states near the Fermi level while C{sub 2}H{sub 4} adsorption was correlated with the number of unoccupied states in the d-band. The diverging mechanisms for S and C{sub 2}H{sub 4} adsorption allow for bimetallic surfaces such as NiRu that enhance ethylene binding without accompanying increases in sulfur binding energy. In contrast, bimetallics such as NiSn and NiW appear to decrease the affinity of the surface for both the reagent and the poison.

  9. Preparation and characterization of bi-metallic nanoparticle catalyst having better anti-coking properties using reverse micelle technique

    NASA Astrophysics Data System (ADS)

    Zacharia, Thomas

    Energy needs are rising on an exponential basis. The mammoth energy sources like coal, natural gas and petroleum are the cause of pollution. The large outcry for an alternate energy source which is environmentally friendly and energy efficient is heard during the past few years. This is where “Clean-Fuel” like hydrogen gained its ground. Hydrogen is mainly produced by steam methane reforming (SMR). An alternate sustainable process which can reduce the cost as well as eliminate the waste products is Tri-reforming. In both these reforming processes nickel is used as catalyst. However as the process goes on the catalyst gets deactivated due to coking on the catalytic surface. This goal of this thesis work was to develop a bi-metallic catalyst which has better anti-coking properties compared to the conventional nickel catalyst. Tin was used to dope nickel. It was found that Ni3Sn complex around a core of Ni is coking resistant compared to pure nickel catalyst. Reverse micelle synthesis of catalyst preparation was used to control the size and shape of catalytic particles. These studies will benefit researches on hydrogen production and catalyst manufactures who work on different bi-metallic combinations.

  10. Low Temperature Hydrogenation of Benzene and Cyclohexene: A Comparative Study Between gamma-Al2O3 Supported PtCo and PtNi Bimetallic Catalysts

    SciTech Connect

    Lu, S.; Lonergan, W; Bosco, J; Wang, S; Zhu, Y; Xie, Y; Chen, J

    2008-01-01

    Supported PtCo and PtNi bimetallic and Co, Ni, Pt monometallic catalysts were prepared by impregnation method on ?-Al2O3 and evaluated for the hydrogenation of benzene and cyclohexene at low temperatures (273-343 K) and atmospheric pressure. Results from batch reactor studies with Fourier transform infrared spectroscopy (FTIR) and flow reactor studies both showed that PtCo bimetallic catalysts exhibited significantly higher activity than PtNi and monometallic Co, Ni, and Pt catalysts for benzene hydrogenation, while PtNi catalysts showed higher activity for cyclohexene hydrogenation. Results from H2 chemisorption and H2-temperature-programmed reduction (H2-TPR) studies showed that a small amount of Pt addition could increase the chemisorption capacity and make the reduction of Co or Ni much easier, especially for Co-based catalysts. Extended X-ray absorption fine structure (EXAFS) results confirmed the formation of Pt-Co and Pt-Ni bimetallic bonds in the PtCo and PtNi bimetallic catalysts, supporting the argument from previous surface science and theoretical predictions that these two bimetallic catalysts would have higher hydrogenation activity than the corresponding monometallic catalysts.

  11. Method for dispersing catalyst onto particulate material

    DOEpatents

    Utz, Bruce R.; Cugini, Anthony V.

    1992-01-01

    A method for dispersing finely divided catalyst precursors onto the surface of coal or other particulate material includes the steps of forming a wet paste mixture of the particulate material and a liquid solution containing a dissolved transition metal salt, for instance a solution of ferric nitrate. The wet paste mixture is in a state of incipient wetness with all of this solution adsorbed onto the surfaces of the particulate material without the presence of free moisture. On adding a precipitating agent such as ammonia, a catalyst precursor such as hydrated iron oxide is deposited on the surfaces of the coal. The catalyst is activated by converting it to the sulfide form for the hydrogenation or direct liquefaction of the coal.

  12. Pd-Au bimetallic catalysts: understanding alloy effects from planar models and (supported) nanoparticles.

    SciTech Connect

    Gao, Feng; Goodman, Wayne D.

    2012-12-21

    Pd-Au bimetallic catalysts often display enhanced catalytic activities and selectivities compared with Pd-alone catalysts. This enhancement is often caused by two alloy effects, i.e., ensemble and ligand effects. The ensemble effect is dilution of surface Pd by Au. With increasing surface Au coverages, contiguous Pd ensembles disappear and isolated Pd ensembles form. For certain reactions, for example vinyl acetate synthesis, this effect is responsible for reaction rate enhancement via the formation of highly active surface sites, e.g., isolated Pd pairs. The disappearance of contiguous Pd ensembles also switches off side reactions catalyzed by these sites. This explains selectivity increase of certain reactions, for example direct H2O2 synthesis. The ligand effect is electronic perturbation of Au to Pd. By direct charge transfer or affecting bond length, the ligand effect causes the Pd d band to be more filled and the d-band center away from the Fermi level. Both changes make Pd more "atomic like" therefore binding reactants and products weaker. For certain reactions, this eliminates the so-called "self poisoning" and enhances activity/selectivity.

  13. Structural analysis of palladium-decorated gold nanoparticles as colloidal bimetallic catalysts.

    SciTech Connect

    Fang, Y. L.; Miller, J. T.; Guo, N.; Heck, K. N.; Alvarez, P. J. J.; Wong, M. S.

    2011-02-02

    Bimetallic palladium-decorated gold nanoparticle (Pd/Au NP) catalysts are significantly more active than palladium-only catalysts, but the mechanism for enhancement is not completely clear for most reactions, like the aqueous-phase hydrodechlorination of trichloroethene. In this study, we conducted X-ray absorption spectroscopy on carbon-supported Pd/Au NPs to obtain information about the local atomic environment (i.e., oxidation states, coordination numbers, and bond distances) of the two metals under different treatment conditions. The as-synthesized NPs were confirmed to have a Pd-shell/Au-core nanostructure, in which the Pd was found as surface ensembles. Upon exposure to room temperature in air, a portion of the Pd, but not the Au, was oxidized. In comparison, nearly the entire surface of monometallic Pd NPs was oxidized, suggesting that Au in Pd/Au NPs imparts oxidation resistance to Pd atoms. The surface Pd was found randomly distributed, presumably as a PdAu surface alloy, after reduction at 300 C. X-ray absorption spectroscopy provides direct evidence for the Pd-shell/Au-core structure of Pd/Au NPs, and suggests that metallic Pd in the Pd/Au NPs is a source for higher catalytic activity for aqueous-phase trichloroethene hydrodechlorination.

  14. Catalytic activity of bimetallic catalysts highly sensitive to the atomic composition and phase structure at the nanoscale

    NASA Astrophysics Data System (ADS)

    Shan, Shiyao; Petkov, Valeri; Prasai, Binay; Wu, Jinfang; Joseph, Pharrah; Skeete, Zakiya; Kim, Eunjoo; Mott, Derrick; Malis, Oana; Luo, Jin; Zhong, Chuan-Jian

    2015-11-01

    The ability to determine the atomic arrangement in nanoalloy catalysts and reveal the detailed structural features responsible for the catalytically active sites is essential for understanding the correlation between the atomic structure and catalytic properties, enabling the preparation of efficient nanoalloy catalysts by design. Herein we describe a study of CO oxidation over PdCu nanoalloy catalysts focusing on gaining insights into the correlation between the atomic structures and catalytic activity of nanoalloys. PdCu nanoalloys of different bimetallic compositions are synthesized as a model system and are activated by a controlled thermochemical treatment for assessing their catalytic activity. The results show that the catalytic synergy of Pd and Cu species evolves with both the bimetallic nanoalloy composition and temperature of the thermochemical treatment reaching a maximum at a Pd : Cu ratio close to 50 : 50. The nanoalloys are characterized structurally by ex situ and in situ synchrotron X-ray diffraction, including atomic pair distribution function analysis. The structural data show that, depending on the bimetallic composition and treatment temperature, PdCu nanoalloys adopt two different structure types. One features a chemically ordered, body centered cubic (B2) type alloy consisting of two interpenetrating simple cubic lattices, each occupied with Pd or Cu species alone, and the other structure type features a chemically disordered, face-centered cubic (fcc) type of alloy wherein Pd and Cu species are intermixed at random. The catalytic activity for CO oxidation is strongly influenced by the structural features. In particular, it is revealed that the prevalence of chemical disorder in nanoalloys with a Pd : Cu ratio close to 50 : 50 makes them superior catalysts for CO oxidation in comparison with the same nanoalloys of other bimetallic compositions. However, the catalytic synergy can be diminished if the Pd50Cu50 nanoalloys undergo phase

  15. Facile Synthesis of Porous Dendritic Bimetallic Platinum-Nickel Nanocrystals as Efficient Catalysts for the Oxygen Reduction Reaction.

    PubMed

    Eid, Kamel; Wang, Hongjing; Malgras, Victor; Alothman, Zeid Abdullah; Yamauchi, Yusuke; Wang, Liang

    2016-05-01

    Certain bimetallic nanocrystals (NCs) possess promising catalytic properties for electrochemical energy conversion. Herein, we report a facile method for the one-step synthesis of porous dendritic PtNi NCs in aqueous solution at room temperature that contrasts with the traditional multistep thermal decomposition approach. The dendritic PtNi NCs assembled by interconnected arms are efficient catalysts for the oxygen reduction reaction. This direct and efficient method is favorable for the up-scaled synthesis of active catalysts used in electrochemical applications. PMID:26879517

  16. Designing supported palladium-on-gold bimetallic nano-catalysts for controlled hydrogenation of acetylene in large excess of ethylene

    NASA Astrophysics Data System (ADS)

    Malla, Pavani

    Ethylene is used as a starting point for many chemical intermediates in the petrochemical industry. It is predominantly produced through steam cracking of higher hydrocarbons (ethane, propane, butane, naphtha, and gas oil). During the cracking process, a small amount of acetylene is produced as a side product. However, acetylene must be removed since it acts as a poison for ethylene polymerization catalysts at even ppm concentrations (>5 ppm). Thus, the selective hydrogenation of acetylene to ethylene is an important process for the purification of ethylene. Conventional, low weight loading Pd catalysts are used for this selective reaction in high concentration ethylene streams. Gold was initially considered to be catalytically inactive for a long time. This changed when gold was seen in the context of the nanometric scale, which has indeed shown it to have excellent catalytic activity as a homogeneous or a heterogeneous catalyst. Gold is proved to have high selectivity to ethylene but poor at conversion. Bimetallic Au and Pd catalysts have exhibited superior activity as compared to Pd particles in semi-hydrogenation. Hydrogenation of acetylene was tested using this bimetallic combination. The Pd-on-Au bimetallic catalyst structure provides a new synthesis approach in improving the catalytic properties of monometallic Pd materials. TiO 2 as a support material and 0.05%Pd loading on 1%Au on titania support and used different treatment methods like washing plasma and reduction between the two metal loadings and was observed under 2:1 ratio. In my study there were two set of catalysts which were prepared by a modified incipient wetness impregnation technique. Out of all the reaction condition the catalyst which was reduced after impregnating gold and then impregnating palladium which was further treated in non-thermal hydrogen plasma and then pretreated in hydrogen till 250°C for 1 hour produced the best activity of 76% yield at 225°C. Stability tests were conducted

  17. Synthesis of a bimetallic catalyst with a modified-peat support

    SciTech Connect

    Bel'kevich, P.I.; Gaiduk, K.A.; Trubilko, E.V.; Bel'skaya, R.I.; Berezovik, G.K.

    1983-11-01

    Granules of oxidized cotton-grass peat with decomposition factors of 40% and 60% were impregnated with cobalt acetate solution and subjected to pyrolysis at 400-800/sup 0/C for 6 hours. These samples were impregnated with copper acetate solution and subjected to further pyrolysis at 300-400/sup 0/C. The influence of the degree of decomposition of the peat and of the temperature of the second pyrolysis stage where formation of the bimetallic carbon catalysts occurs, were investigated using the dehydrogenation of cyclohexanol. At a reaction temperature of 280/sup 0/C, the max cyclohexanone yield corresponds to 60% decomposition of the peat and a high temperature of heat treatment, while high selectivity is characteristic of samples made with the lower decomposition factor. Upon increase of the reaction temperature to 350/sup 0/C and that of the pyrolysis stage II, the degree of decomposition of the peat has little influence on the cyclohexanone yield. 8 references, 1 figure, 2 tables.

  18. General Method for Determination of the Surface Composition in Bimetallic Nanoparticle Catalysts from the L Edge X-ray Absorption Near-Edge Spectra

    SciTech Connect

    Wu, Tiapin; Childers, David; Gomez, Carolina; Karim, Ayman M.; Schweitzer, Neil; Kropf, Arthur; Wang, Hui; Bolin, Trudy B.; Hu, Yongfeng; Kovarik, Libor; Meyer, Randall; Miller, Jeffrey T.

    2012-10-08

    Bimetallic PtPd on silica nano-particle catalysts have been synthesized and their average structure determined by Pt L3 and Pd K-edge extended X-ray absorption finestructure (EXAFS) spectroscopy. The bimetallic structure is confirmed from elemental line scans by STEM for the individual 1-2 nm sized particles. A general method is described to determine the surface composition in bimetallic nanoparticles even when both metals adsorb, for example, CO. By measuring the change in the L3 X-ray absorption near-edge structure (XANES) spectra with and without CO in bimetallic particles and comparing these changes to those in monometallic particles of known size the fraction of surface atoms can be determined. The turnover rates (TOR) and neopentane hydrogenolysis and isomerization selectivities based on the surface composition suggest that the catalytic and spectroscopic properties are different from those in monometallic nano-particle catalysts. At the same neo-pentane conversion, the isomerization selectivity is higher for the PtPd catalyst while the TOR is lower than that of both Pt and Pd. As with the catalytic performance, the infrared spectra of adsorbed CO are not a linear combination of the spectra on monometallic catalysts. Density functional theory calculations indicate that the Pt-CO adsorption enthalpy increases while the Pd-CO bond energy decreases. The ability to determine the surface composition allows for a better understanding of the spectroscopic and catalytic properties of bimetallic nanoparticle catalysts.

  19. Highly Dispersed Metal Catalyst for Fuel Cell Electrodes

    SciTech Connect

    2009-03-01

    This factsheet describes a study that will bring industrial catalyst experience to fuel cell research. Specifically, industrial catalysts, such as those used in platforming, utilize precious metal platinum as an active component in a finely dispersed form.

  20. Facile synthesis of Pd-based bimetallic nanocrystals and their application as catalysts for methanol oxidation reaction

    NASA Astrophysics Data System (ADS)

    Xi, Pinxian; Cao, Yang; Yang, Fengchun; Ma, Cai; Chen, Fengjuan; Yu, Sha; Wang, Shuai; Zeng, Zhengzhi; Zhang, Xin

    2013-06-01

    We employed an efficient and facile route to synthesise monodisperse Pd-based bimetallic nanocrystals (MPd: M = Cu, Co and Ni) via a controlled co-reduction of Pd(ii) chloride and M(ii) nitrate at 200-230 °C in the presence of oleylamine (OAm). These monodisperse Pd-based nanocrystals have small dimensions, unique structures and homogeneous morphology, thus exhibit efficient catalytic activities for methanol oxidation in alkaline solution, which is much better than commercial Pd/C with same amount of palladium. The catalytic activities of these nanocrystals followed the order of NiPd/C > CoPd/C > CuPd/C > commercial Pd/C, due to the different synergistic effects. Our results show that these Pd-based bimetallic nanocrystals can be promising as practical catalysts for methanol oxidation reactions and other catalytic reactions in further investigations.We employed an efficient and facile route to synthesise monodisperse Pd-based bimetallic nanocrystals (MPd: M = Cu, Co and Ni) via a controlled co-reduction of Pd(ii) chloride and M(ii) nitrate at 200-230 °C in the presence of oleylamine (OAm). These monodisperse Pd-based nanocrystals have small dimensions, unique structures and homogeneous morphology, thus exhibit efficient catalytic activities for methanol oxidation in alkaline solution, which is much better than commercial Pd/C with same amount of palladium. The catalytic activities of these nanocrystals followed the order of NiPd/C > CoPd/C > CuPd/C > commercial Pd/C, due to the different synergistic effects. Our results show that these Pd-based bimetallic nanocrystals can be promising as practical catalysts for methanol oxidation reactions and other catalytic reactions in further investigations. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr00912b

  1. Platinum-palladium bimetallic nanoparticles on graphitic carbon nitride modified carbon black: A highly electroactive and durable catalyst for electrooxidation of alcohols

    NASA Astrophysics Data System (ADS)

    Qian, Huayu; Chen, Shouwen; Fu, Yongsheng; Wang, Xin

    2015-12-01

    A composite catalyst consisting of Pt-Pd bimetallic nanoparticles (NPs) and graphitic carbon nitride (g-C3N4) modified carbon black (CB) is designed and fabricated by a facile two-step approach. The resulting catalyst exhibits unprecedented high catalytic activity and excellent long-term stability for electrooxidation of alcohols (methanol, ethanol, ethylene glycol and glycerol) in alkaline media. The superior electrochemical performance of the composite catalyst is attributed to the specific characteristics of the unique nanostructure and the synergistic effects of individual components, including the complementary roles of Pt (dehydrogenation site) and Pd (removal of CO-like species), the template effect of the planar amino group of g-C3N4 for the dispersed decoration of Pt-Pd NPs, the high specific surface area of CB for the rapid diffusion of electrolyte and removal of the carbonaceous intermediates, as well as the structural stability of the support based on covalent interaction between g-C3N4 and CB for maintaining the durability of the catalytic system.

  2. Catalytic activity of bimetallic catalysts highly sensitive to the atomic composition and phase structure at the nanoscale.

    PubMed

    Shan, Shiyao; Petkov, Valeri; Prasai, Binay; Wu, Jinfang; Joseph, Pharrah; Skeete, Zakiya; Kim, Eunjoo; Mott, Derrick; Malis, Oana; Luo, Jin; Zhong, Chuan-Jian

    2015-12-01

    The ability to determine the atomic arrangement in nanoalloy catalysts and reveal the detailed structural features responsible for the catalytically active sites is essential for understanding the correlation between the atomic structure and catalytic properties, enabling the preparation of efficient nanoalloy catalysts by design. Herein we describe a study of CO oxidation over PdCu nanoalloy catalysts focusing on gaining insights into the correlation between the atomic structures and catalytic activity of nanoalloys. PdCu nanoalloys of different bimetallic compositions are synthesized as a model system and are activated by a controlled thermochemical treatment for assessing their catalytic activity. The results show that the catalytic synergy of Pd and Cu species evolves with both the bimetallic nanoalloy composition and temperature of the thermochemical treatment reaching a maximum at a Pd : Cu ratio close to 50 : 50. The nanoalloys are characterized structurally by ex situ and in situ synchrotron X-ray diffraction, including atomic pair distribution function analysis. The structural data show that, depending on the bimetallic composition and treatment temperature, PdCu nanoalloys adopt two different structure types. One features a chemically ordered, body centered cubic (B2) type alloy consisting of two interpenetrating simple cubic lattices, each occupied with Pd or Cu species alone, and the other structure type features a chemically disordered, face-centered cubic (fcc) type of alloy wherein Pd and Cu species are intermixed at random. The catalytic activity for CO oxidation is strongly influenced by the structural features. In particular, it is revealed that the prevalence of chemical disorder in nanoalloys with a Pd : Cu ratio close to 50 : 50 makes them superior catalysts for CO oxidation in comparison with the same nanoalloys of other bimetallic compositions. However, the catalytic synergy can be diminished if the Pd50Cu50 nanoalloys undergo

  3. 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)(-).

  4. Direct hydrogenation of biomass-derived butyric acid to n-butanol over a ruthenium-tin bimetallic catalyst.

    PubMed

    Lee, Jong-Min; Upare, Pravin P; Chang, Jong-San; Hwang, Young Kyu; Lee, Jeong Ho; Hwang, Dong Won; Hong, Do-Young; Lee, Seung Hwan; Jeong, Myung-Geun; Kim, Young Dok; Kwon, Young-Uk

    2014-11-01

    Catalytic hydrogenation of organic carboxylic acids and their esters, for example, cellulosic ethanol from fermentation of acetic acid and hydrogenation of ethyl acetate is a promising possibility for future biorefinery concepts. A hybrid conversion process based on selective hydrogenation of butyric acid combined with fermentation of glucose has been developed for producing biobutanol. ZnO-supported Ru-Sn bimetallic catalysts exhibits unprecedentedly superior performance in the vapor-phase hydrogenation of biomass-derived butyric acid to n-butanol (>98% yield) for 3500 h without deactivation. PMID:25123894

  5. Direct hydrogenation of biomass-derived butyric acid to n-butanol over a ruthenium-tin bimetallic catalyst.

    PubMed

    Lee, Jong-Min; Upare, Pravin P; Chang, Jong-San; Hwang, Young Kyu; Lee, Jeong Ho; Hwang, Dong Won; Hong, Do-Young; Lee, Seung Hwan; Jeong, Myung-Geun; Kim, Young Dok; Kwon, Young-Uk

    2014-11-01

    Catalytic hydrogenation of organic carboxylic acids and their esters, for example, cellulosic ethanol from fermentation of acetic acid and hydrogenation of ethyl acetate is a promising possibility for future biorefinery concepts. A hybrid conversion process based on selective hydrogenation of butyric acid combined with fermentation of glucose has been developed for producing biobutanol. ZnO-supported Ru-Sn bimetallic catalysts exhibits unprecedentedly superior performance in the vapor-phase hydrogenation of biomass-derived butyric acid to n-butanol (>98% yield) for 3500 h without deactivation.

  6. Mono(NCN-pincer palladium)-metalloporphyrin catalysts: evidence for supramolecular bimetallic catalysis.

    PubMed

    Suijkerbuijk, Bart M J M; Schamhart, Daniël J; Kooijman, Huub; Spek, Anthony L; van Koten, Gerard; Klein Gebbink, Robertus J M

    2010-07-21

    The synthesis and catalytic properties of ditopic mono-pincer-mono-porphyrin complexes were investigated. The statistical Adler condensation reaction of 3,5-bis(methoxymethyl)-4-bromo-benzaldehyde, p-tolylaldehyde, and pyrrole, furnished an AB(3)-type tetraphenylporphyrin, containing three meso-p-tolyl groups and one meso-3,5-bis(methoxymethyl)-4-bromophenyl group. This material was converted into the ditopic ligand [2H(Br)], which comprises one porphyrin site and an NCN-pincer type ligand moiety. In order to metalate this compound in a stepwise, site-selective manner, two distinct synthetic routes were followed. Route A relies on the introduction of a metal in the porphyrin cavity followed by pincer metalation and a reversal of this order is employed for route B. For the hetero-bimetallic pincer-porphyrin target compounds, route A invariably proved to be the highest yielding alternative, giving pincer-porphyrin hybrids of general formula [M(1)(M(2)X)] (M(1) = 2H, Mg, Co, Ni, Zn; M(2) = Pd, Br; X = Cl, Br). (195)Pt NMR spectroscopy revealed that the porphyrin metal has a modest influence on the electron density on the NCN-pincer Pt site. When the analogous cationic Pd complexes were used as Lewis acid catalysts for the double Michael addition between methyl vinyl ketone and ethyl alpha-cyanoacetate, it was noted that the catalytic activity did not depend on the central metal for M(1) = 2H, Ni, and Zn. However, when Mg occupied the porphyrin cavity, the rate of the reaction increased by a factor of six. Although a rate enhancement was observed when catalysis was conducted with a mixture of the two constituents of [Mg(PdOH(2))]BF(4) (i.e. MgTTP and [PdOH(2)(NCN)]BF(4)) this could not fully account for the rate enhancement. We believe that the rationale for this behaviour is dual, consisting of "cooperative dual catalysis" and supramolecular aggregation of two or more catalyst-substrate complexes.

  7. Synergy between Two Metal Catalysts: A Highly Active Silica-Supported Bimetallic W/Zr Catalyst for Metathesis of n-Decane.

    PubMed

    Samantaray, Manoja K; Dey, Raju; Kavitake, Santosh; Abou-Hamad, Edy; Bendjeriou-Sedjerari, Anissa; Hamieh, Ali; Basset, Jean-Marie

    2016-07-13

    A well-defined, silica-supported bimetallic precatalyst [≡Si-O-W(Me)5≡Si-O-Zr(Np)3] (4) has been synthesized for the first time by successively grafting two organometallic complexes [W(Me)6 (1) followed by ZrNp4 (2)] on a single silica support. Surprisingly, multiple-quantum NMR characterization demonstrates that W and Zr species are in close proximity to each other. Hydrogenation of this bimetallic catalyst at room temperature showed the easy formation of zirconium hydride, probably facilitated by tungsten hydride which was formed at this temperature. This bimetallic W/Zr hydride precatalyst proved to be more efficient (TON = 1436) than the monometallic W hydride (TON = 650) in the metathesis of n-decane at 150 °C. This synergy between Zr and W suggests that the slow step of alkane metathesis is the C-H bond activation that occurs on Zr. The produced olefin resulting from a β-H elimination undergoes easy metathesis on W. PMID:27248839

  8. Selective aerobic oxidation of 1,3-propanediol to 3-hydroxypropanoic acid using hydrotalcite supported bimetallic gold nanoparticle catalyst in water

    NASA Astrophysics Data System (ADS)

    Mohammad, Mujahid; Nishimura, Shun; Ebitani, Kohki

    2015-02-01

    Selective oxidation of 1,3-propanediol (1,3-PD) to 3-hydroxypropanoic acid (3-HPA), an important industrial building block, was successfully achieved using hydrotalcite-supported bimetallic Au nanoparticle catalysts in water at 343 K under aerobic and base-free conditions. The highest yield of 42% with 73% selectivity towards 3-HPA was afforded by 1wt% Au0.8Pd0.2-PVP/HT catalyst.

  9. Highly dispersed catalysts for coal liquefaction

    SciTech Connect

    Hirschon, A.S.; Wilson, R.B.

    1992-11-05

    The objectives of this project are to study the effect of pretreatment methods on the two-stage liquefaction process. In particular, the effects of dispersed catalysts and carbon monoxide atmospheres on a coal liquefaction process. The project is divided into three technical tasks. Task 1 and 2 deal with the analyses and liquefaction experiments, respectively, whereas Task 3 deals with the economic impact of utilizing the pretreatment methods. This quarter we concentrated on Tasks 1 and 2, which are summarized below. Samples of Black Thunder Subbituminous coal and the corresponding recycle solvent were received from Wilsonville. These particular samples were obtained from run [number sign]263. The samples were analyzed for a proximate and ultimate analysis, as well as heat content. We have also received samples of the iron oxide used in the Wilsonville coal liquefaction runs as well as Shell 324 and molyVanL for use in future runs. Base-line screening experiments were conducted in 300 mL autoclaves using 2.5 parts by weight of recycle solvent to 1 part Black Thunder coal at 425[degree]C for one hour. In preliminary results for the comparison of iron oxide and iron carbonyl, the iron carbonyl appears to give higher yields to soluble products.

  10. One-step synthesis of dispersed bimetallic carbides and nitrides from transition metals hexamethylenetetramine complexes

    SciTech Connect

    Chouzier, Sandra; Afanasiev, Pavel . E-mail: Pavel.Afanasiev@catalyse.cnrs.fr; Vrinat, Michel; Cseri, Tivadar; Roy-Auberger, Magalie

    2006-11-15

    Bimetallic nitrides and carbides Co(Ni)-Mo were obtained from the decomposition of transition metals complexes with hexamethylenetetramine (HMTA) under inert atmosphere. The precursor complexes were prepared by means of aqueous precipitation of ammonium molybdate with cobalt nitrate or nickel nitrate and HMTA. During the decomposition, HMTA acts at once as a reducing agent and as a source of carbon and nitrogen. The precursor's composition and the decomposition conditions are the key parameters to influence the nature of the obtained phases. The method developed provides a simple one-step way to highly divided bimetallic nitrides and carbides. -- Graphical abstract: Bimetallic nitrides and carbides Co(Ni)-Mo were obtained from the decomposition of metals complexes with hexamethylenetetramine (HMTA) under inert atmosphere. During the decomposition, HMTA acts at once as a reducing agent and as a source of carbon and nitrogen. The method provides a simple one-step way to highly divided nitrides and carbides. Display Omitted.

  11. Greatly improved electrochemical performance of lithium-oxygen batteries with a bimetallic platinum-copper alloy catalyst

    NASA Astrophysics Data System (ADS)

    Lee, Minwook; Hwang, Yubin; Yun, Kyung-Han; Chung, Yong-Chae

    2015-08-01

    Research on the cathode catalysts of lithium-oxygen (Li-O2) batteries is one of the most important branches to commercialize these batteries to overcome the sluggish kinetics during both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). In this study, a high performance catalyst based on a bimetallic Pt-Cu alloy is investigated for Li-O2 batteries using first-principles calculation. The theoretical prediction shows that the Pt-Cu alloy is much more effective than the pure Pt according to the electrochemical performance. In particular, the effectiveness of the catalytic property is maximized in the case of the PtCu (111) surface which greatly reduces the large overpotentials of the original Li-O2 batteries during the OER/ORR. It is identified for the first time that the charge overpotentials are affected mainly by the inherent surface charge character of the alloy catalyst. It is observed that the more negatively charged PtCu (111) surface can act as a weakly positively charged surface for the adsorption of Li-O intermediates and thus result in weak ionic bonding of the intermediates on the surface. As a result, the dominant factor improving the catalytic performance is clearly demonstrated, providing insight into the design of an efficient catalyst for Li-O2 battery technologies.

  12. Immobilization of ultrafine bimetallic Ni-Pt nanoparticles inside the pores of metal-organic frameworks as efficient catalysts for dehydrogenation of alkaline solution of hydrazine.

    PubMed

    Cao, Nan; Yang, Lan; Dai, Hongmei; Liu, Teng; Su, Jun; Wu, Xiaojun; Luo, Wei; Cheng, Gongzhen

    2014-10-01

    We report a facile liquid impregnation approach for immobilization of ultrafine bimetallic Ni-Pt nanoparticles (NPs) inside the pores of MIL-101. The methods of powder X-ray diffraction, N2 physisorption, X-ray photoelectron spectroscopy, transmission electron microscopy, and inductively coupled plasma-atomic emission spectroscopy were employed to characterize the NiPt@MIL-101 catalysts and further indicated the as-synthesized Ni-Pt NPs were confined in the pores of MIL-101. These as-synthesized bimetallic NiPt@MIL-101 NPs exhibit exceedingly high catalytic activity, selectivity, and durability toward hydrogen generation from alkaline solution of hydrazine. PMID:25197778

  13. Highly stable bimetallic AuIr/TiO2 catalyst: physical origin of the intrinsic stability against sintering

    NASA Astrophysics Data System (ADS)

    Marinero, Ernesto; Han, Chan Wan; Majundar, Paulami; Aguilar-Tapia, Antonio; Zanella, Rodolfo; Greeley, Jeffrey; Otarlan, Volkan

    It has been a long-lived research topic in the field of heterogeneous catalysis to find a way to stabilizing supported Au catalysts against sintering. Herein, we report highly stable AuIr bimetallic nanoparticles on TiO2 synthesized by sequential deposition-precipitation. To understand the physical origin of the high stability AuIr/TiO2 system, we have used scanning transmission electron microscopy (STEM), STEM-tomography and density functional theory (DFT) calculations. 3D structures of AuIr/TiO2 obtained by STEM-tomography indicate that AuIr nanoparticles on TiO2 have intrinsically lower free energy and less driving force for sintering than Au nanoparticles. DFT calculations on segregation behavior of AuIr slabs on TiO2 showed that the presence of Ir near the TiO2 surface increases the adhesion energy of the bimetallic slabs to the TiO2 and the attractive interactions between Ir and TiO2 lead to higher stability of the AuIr nanoparticles compared to Au nanoparticles.

  14. Catalytic amination and dechlorination of para-nitrochlorobenzene (p-NCB) in water over palladium-iron bimetallic catalyst.

    PubMed

    Xu, Xinhua; Zhou, Hongyi; Zhou, Mi

    2006-02-01

    Chemical treatment of para-nitrochlorobenzene (p-NCB) by palladium/iron (Pd/Fe) bimetallic particles represents one of the latest innovative technologies for the remediation of contaminated soil and groundwater. The amination and dechlorination reaction is believed to take place predominantly on the surface site of the Pd/Fe catalysts. The p-NCB was first transformed to p-chloroaniline (p-CAN) then quickly reduced to aniline. 100% of p-NCB was removed in 30 min when bimetallic Pd/Fe particles with 0.03% Pd at the Pd/Fe mass concentration of 3g 75 ml(-1) were used. The p-NCB removal efficiency and the subsequent dechlorination rate increased with the increase of bulk loading of palladium and Pd/Fe. As expected, p-NCB removal efficiency increased with temperature as well. In particular, the removal efficiency of p-NCB was measured to be 67%, 79%, 80%, 90% and 100% for reaction temperature 20, 25, 30, 35 and 40 degrees C, respectively. Our results show that no other intermediates were generated besides Cl(-), p-CAN and aniline during the catalytic amination and dechlorination of p-NCB.

  15. Remarkable effect of bimetallic nanocluster catalysts for aerobic oxidation of alcohols: combining metals changes the activities and the reaction pathways to aldehydes/carboxylic acids or esters.

    PubMed

    Kaizuka, Kosuke; Miyamura, Hiroyuki; Kobayashi, Shū

    2010-11-01

    Selective oxidation of alcohols catalyzed by novel carbon-stabilized polymer-incarcerated bimetallic nanocluster catalysts using molecular oxygen has been developed. The reactivity and the selectivity were strongly dependent on the combination of metals and solvent systems; aldehydes and ketones were obtained by the gold/platinum catalyst in benzotrifluoride, and esters were formed by the gold/palladium catalyst in methanol. To the best of our knowledge, this is the first example that the reaction pathway has been changed dramatically in gold catalysis by combining with a second metal. The differences in the activity and the selectivity are considered to be derived from the difference in the structure of the bimetallic clusters.

  16. Pumice-supported Pd-Pt bimetallic catalysts: Synthesis, structural characterization, and liquid-phase hydrogenation of 1,3-cyclooctadiene

    SciTech Connect

    Deganello, G.; Duca, D.; Liotta, L.F.; Martorana, A.; Venezia, M.; Benedetti, A.; Fagherazz, G.

    1995-01-01

    A series of pumice-supported palladium-platinum bimetallic catalysts were prepared and investigated by X-ray scattering (WAXS and SAXS) and XPS techniques. An alloy Pd-Pt was formed. The less abundant metal was found to segregate to the surface. The catalysts were tested in the liquid-phase hydrogenation of 1,3-cyclooctadiene to cyclooctene, and compared with similarly prepared pumice-supported palladium and platinum catalysts and other supported Pd-Pt catalysts reported in the literature. The addition of platinum reduces the activity and the selectivity of the palladium catalysts. Differences between the activity of these pumice-supported catalysts and the activity of previously described Pd and Pd-Pt catalysts on other supports, are attributed to the presence, in the latter, of diffusional processes. 50 refs., 4 figs. 2 tabs.

  17. Highly dispersive PdCoB catalysts for dechlorination of chlorophenols.

    PubMed

    Liu, Xuchen; Wang, Xingyi

    2014-06-15

    Highly dispersive PdCoB nano-particles were prepared by precipitation-reduction with NaBH4 at 273 K. Characterization showed that the dispersion of amorphous alloy PdCoB nano-particles increased with decrease in both Pd/Co ratio and preparation temperature. The size of PdCoB-L(273) (Pd/Co ratio of 0.0005) nano-particles prepared at 273 K was 5 nm and BET specific surface area was estimated to be 177 m(2)/g, much higher than those of bimetallic catalysts reported in literature. During the hydrodechlorination of 4-chlorophenol, PdCoB catalysts were effective within pH range from 2.5 to 11. The activity of PdCoB can be promoted by the increase in B/Co ratio on the surface. PdCoB-L(273) sample presented the highest efficiency, and the reaction constants described in different terms for 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol were much higher than those obtained over PdFe in literature, probably ascribed to smaller particle sizes, less agglomerations and strong synergistic effect between Pd, Co and B species. PMID:24768961

  18. Bimetallic PtAu superlattice arrays: Highly electroactive and durable catalyst for oxygen reduction and methanol oxidation reactions

    NASA Astrophysics Data System (ADS)

    Feng, Jiu-Ju; He, Li-Li; Fang, Rui; Wang, Qiao-Li; Yuan, Junhua; Wang, Ai-Jun

    2016-10-01

    Superlattice arrays, an important type of nanomaterials, have wide applications in catalysis, optic/electronics and energy storage for the synergetic effects determined by both individual metals and collective interactions. Herein, a simple one-pot solvothermal coreduction approach is developed for facile preparation of bimetallic PtAu alloyed superlattice arrays (PtAu SLAs) in oleylamine, with the assistance of urea via hydrogen bonding induced self-assembly. Urea is essential in morphology-controlled process and prevents PtAu nanoparticles from the disordered aggregation. The characterization and formation mechanism of PtAu SLAs are investigated in details. The as-synthesized hybrid nanocrystals exhibit enhanced electrocatalytic performances for oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in alkaline electrolyte in comparison with commercial Pt-C (50%, wt.%) and Pt black catalysts.

  19. Convenient immobilization of Pt-Sn bimetallic catalysts on nitrogen-doped carbon nanotubes for direct alcohol electrocatalytic oxidation.

    PubMed

    Wang, Xizhang; Xue, Hua; Yang, Lijun; Wang, Huakai; Zang, Pengyuan; Qin, Xintai; Wang, Yangnian; Ma, Yanwen; Wu, Qiang; Hu, Zheng

    2011-09-30

    Pt-Sn alloy nanoparticles were conveniently immobilized on nitrogen-doped carbon nanotubes (NCNTs) through microwave-assisted ethylene glycol reduction. The nanoparticles have a narrow particle size distribution with the average particle size around 3 nm as measured by transmission electron microscopy and x-ray diffraction. The binding energy of metallic Sn passively shifts due to the charge transfer from Sn to Pt, as revealed by x-ray photoelectron spectroscopy. In comparison with the commercial Pt/C catalyst, Pt/NCNT presents a clear increase in activity for alcohol electro-oxidation due to the improved support, while the bimetallic Pt-Sn/NCNT has even higher activity owing to the alloying of Pt with Sn. Both Pt-Sn/NCNT and Pt/NCNT catalysts exhibit competitive long-term stability to Pt/C catalyst. The low cost, simple preparation and superior electrocatalytic performance indicate the great potential of Pt-Sn/NCNT in direct alcohol fuel cells.

  20. Selective hydrogenation of acetylene on SiO2 supported Ni-In bimetallic catalysts: Promotional effect of In

    NASA Astrophysics Data System (ADS)

    Chen, Yanjun; Chen, Jixiang

    2016-11-01

    Ni/SiO2 and the bimetallic NixIn/SiO2 catalysts with different Ni/In ratios were tested for the selective hydrogenation of acetylene, and their physicochemical properties before and after the reaction were characterized by means of N2-sorption, H2-TPR, XRD, TEM, XPS, H2 chemisorption, C2H4-TPD, NH3-TPD, FT-IR of adsorbed pyridine, and TG/DTA and Raman. A promotional effect of In on the performance of Ni/SiO2 was found, and NixIn/SiO2 with a suitable Ni/In ratio gave much higher acetylene conversion, ethylene selectivity and catalyst stability than Ni/SiO2. This is ascribed to the geometrical isolation of the reactive Ni atoms with the inert In ones and the charge transfer from the In atoms to Ni ones, both of which are favorable for reducing the adsorption strength of ethylene and restraining the Csbnd C hydrogenolysis and the polymerizations of acetylene and the intermediate compounds. On the whole, Ni6In/SiO2 and Ni10In/SiO2 had better performance. Nevertheless, with increasing the In content, the selectivity to the C4+ hydrocarbons tended to increase due to the enhanced catalyst acidity because of the charge transfer from the In atoms to Ni ones. As the Lewis acid ones, the In sites could promote the polymerization. The catalyst deactivation was also analyzed. We propose that the Ni/SiO2 deactivation is mainly attributed to the phase change from metallic Ni to nickel carbide. The introduction of In inhibited the formation of nickel carbide. However, as the In content increased, the carbonaceous deposit became the main reason for the NixIn/SiO2 deactivation due to the enhanced catalyst acidity.

  1. Dispersed catalysts for co-processing and coal liquefaction

    SciTech Connect

    Bockrath, B.; Parfitt, D.; Miller, R.

    1995-12-31

    The basic goal is to improve dispersed catalysts employed in the production of clean fuels from low value hydrocarbons. The immediate objective is to determine how the properties of the catalysts may be altered to match the demands placed on them by the properties of the feedstock, the qualities of the desired end products, and the economic constraints put upon the process. Several interrelated areas of the application of dispersed catalysts to co-processing and coal conversion are under investigation. The first involves control of the selectivity of MoS{sub 2} catalysts for HDN, HDS, and hydrogenation of aromatics. A second area of research is the development and use of methods to evaluate dispersed catalysts by means of activity and selectivity tests. A micro-flow reactor has been developed for determining intrinsic reactivities using model compounds, and will be used to compare catalysts prepared in different ways. Micro-autoclaves will also be used to develop data in batch experiments at higher partial pressures of hydrogen. The third area under investigation concerns hydrogen spillover reactions between MoS{sub 2} catalysts and carbonaceous supports. Preliminary results obtained by monitoring H{sub 2}/D{sub 2} exchange reactions with a pulse-flow microreactor indicate the presence of spillover between MoS{sub 2} and a graphitic carbon. A more complete study will be made at a later stage of the project. Accomplishments and conclusions are discussed.

  2. Selectivity, activity, and metal-support interactions of Rh bimetallic catalysts. Progress report, 15 November 1981-15 August 1982

    SciTech Connect

    Haller, G L

    1982-08-01

    We report on a detailed investigation of the effect of TiO/sub 2/ support on Rh-Ag interaction as exhibited in catalytic activity. The temporal evolution of activity over Rh-Ag/TiO/sub 2/ for ethane hydrogenolysis and hydrogen chemisorption as a function of temperature, Ag to Rh ratio, the Rh particle size, Rh loading, and ambient gas were studied. Preliminary extended x-ray absorption fine structure (EXAFS) analysis of Rh/TiO/sub 2/ catalysts indicate that 100% exposed (dispersed) catalyst prepared by ion exchange may be atomically dispersed after low temperature reduction. 7 figures, 1 table.

  3. Synthesis of supported bimetallic nanoparticles with controlled size and composition distributions for active site elucidation

    SciTech Connect

    Hakim, Sikander H.; Sener, Canan; Alba Rubio, Ana C.; Gostanian, Thomas M.; O'neill, Brandon J; Ribeiro, Fabio H.; Miller, Jeffrey T.; Dumesic, James A

    2015-08-01

    Elucidation of active sites in supported bimetallic catalysts is complicated by the high level of dispersity in the nanoparticle size and composition that is inherent in conventional methods of catalyst preparation. We present a synthesis strategy that leads to highly dispersed, bimetallic nanoparticles with uniform particle size and composition by means of controlled surface reactions. We demonstrate the synthesis of three systems, RhMo, PtMo, and RhRe, consisting of a highly reducible metal with an oxophilic promoter. These catalysts are characterized by FTIR, CO chemisorption, STEM/EDS, TPR, and XAS analysis. The catalytic properties of these bimetallic nanoparticles were probed for the selective CO hydrogenolysis of (hydroxymethyl)tetrahydropyran to produce 1,6 hexanediol. Based on the characterization results and reactivity trends, the active sites in the hydrogenolysis reaction are identified to be small ensembles of the more noble metal (Rh, Pt) adjacent to highly reduced moieties of the more oxophilic metal (Mo, Re).

  4. Particle and phase thicknesses from XPS analysis of supported bimetallic catalysts: Calcined Co-Rh/Nb{sub 2}O{sub 5}

    SciTech Connect

    Frydman, A. |; Castner, D.G.; Campbell, C.T.

    1995-03-01

    The surface structure and elemental composition of a series of calcined Co-Rh/Nb{sub 2}O{sub 5} bimetallic catalysts have been investigated using X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). New formulae for the quantitative analysis of XPS intensities for supported bimetallic catalysts involving up to three separate, layered phases on spherical support particles are used for the first time. These apply an average take-off angle for photoelectrons from spherical particles whose radii are large compared to the electron attenuation length. Calcined monometallic Co/Nb{sub 2}O{sub 5} and Rh/Nb{sub 2}O{sub 5}, and four calcined bimetallic Co-Rh/Nb{sub 2}O{sub 5} catalysts with similar Co loadings ({approx} 1.9 wt%) and variable Rh loadings (0.3 to 2.3 wt%) were examined. Reference spectra for pure CoNb{sub 2}O{sub 6} (columbite) are also presented here for the first time. The catalysts were prepared by incipient wetness impregnation and calcined at 673 K to generate the oxide precursors. The XPS lineshapes and the Co (2p) spin-orbit splitting indicated the presence of two Co species, Co{sub 3}O{sub 4} and CO{sup +2}, on all calcined Co-containing catalysts. The measured XPS Co/Nb and Rh/Nb atomic ratios for the catalysts were factors of 1.5-2 and 2-4.5, respectively, greater than the bulk atomic ratios, showing that both Co and Rh oxides were surface-enriched. The measured XPS peak intensities were compared to the values predicted from several different structural models of the oxide particles.

  5. Homogeneously dispersed multimetal oxygen-evolving catalysts.

    PubMed

    Zhang, Bo; Zheng, Xueli; Voznyy, Oleksandr; Comin, Riccardo; Bajdich, Michal; García-Melchor, Max; Han, Lili; Xu, Jixian; Liu, Min; Zheng, Lirong; García de Arquer, F Pelayo; Dinh, Cao Thang; Fan, Fengjia; Yuan, Mingjian; Yassitepe, Emre; Chen, Ning; Regier, Tom; Liu, Pengfei; Li, Yuhang; De Luna, Phil; Janmohamed, Alyf; Xin, Huolin L; Yang, Huagui; Vojvodic, Aleksandra; Sargent, Edward H

    2016-04-15

    Earth-abundant first-row (3d) transition metal-based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials substantially above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution. These gelled FeCoW oxyhydroxides exhibit the lowest overpotential (191 millivolts) reported at 10 milliamperes per square centimeter in alkaline electrolyte. The catalyst shows no evidence of degradation after more than 500 hours of operation. X-ray absorption and computational studies reveal a synergistic interplay between tungsten, iron, and cobalt in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER. PMID:27013427

  6. Purification of Carbon Nanotubes Synthesized by Catalytic Decomposition of Methane using Bimetallic Fe-Co Catalysts Supported on MgO

    NASA Astrophysics Data System (ADS)

    Guan, Beh Hoe; Ramli, Irmawati; Yahya, Noorhana; Kean Pah, Lim

    2011-02-01

    This work reports the synthesis of carbon nanotubes by catalytic decomposition of methane using bimetallic Fe-Co catalysts supported on MgO. Transmission electron microscopy (TEM) results show the as-prepared carbon nanotubes are multi-walled carbon nanotubes (MWCNTs) with diameter in the range of 15nm to 45nm. Purification of as-prepared MWCNTs was carried out by acid and heat treatment method. EDX results show the Fe, Co and MgO catalysts were successfully removed by refluxing the as-prepared MWCNTs in 3M H2SO4.

  7. Bimetallic catalysts for CO.sub.2 hydrogenation and H.sub.2 generation from formic acid and/or salts thereof

    DOEpatents

    Hull, Jonathan F.; Himeda, Yuichiro; Fujita, Etsuko; Muckeman, James T.

    2015-08-04

    The invention relates to a ligand that may be used to create a catalyst including a coordination complex is formed by the addition of two metals; Cp, Cp* or an unsubstituted or substituted .pi.-arene; and two coordinating solvent species or solvent molecules. The bimetallic catalyst may be used in the hydrogenation of CO.sub.2 to form formic acid and/or salts thereof, and in the dehydrogenation of formic acid and/or salts thereof to form H.sub.2 and CO.sub.2.

  8. Highly Dispersed Alloy Catalyst for Durability

    SciTech Connect

    Vivek S. Murthi; Izzo, Elise; Bi, Wu; Guerrero, Sandra; Protsailo, Lesia

    2013-01-08

    Achieving DOE's stated 5000-hr durability goal for light-duty vehicles by 2015 will require MEAs with characteristics that are beyond the current state of the art. Significant effort was placed on developing advanced durable cathode catalysts to arrive at the best possible electrode for high performance and durability, as well as developing manufacturing processes that yield significant cost benefit. Accordingly, the overall goal of this project was to develop and construct advanced MEAs that will improve performance and durability while reducing the cost of PEMFC stacks. The project, led by UTC Power, focused on developing new catalysts/supports and integrating them with existing materials (membranes and gas diffusion layers (GDLs)) using state-of-the-art fabrication methods capable of meeting the durability requirements essential for automotive applications. Specifically, the project work aimed to lower platinum group metals (PGM) loading while increasing performance and durability. Appropriate catalysts and MEA configuration were down-selected that protects the membrane, and the layers were tailored to optimize the movements of reactants and product water through the cell to maximize performance while maintaining durability.

  9. The Effects of Oxide Supports on the Low Temperature Hydrogenation Activity of Acetone over Pt/Ni Bimetallic Catalysts on SiO2 gamma-Al2O3 and TiO2

    SciTech Connect

    S Qi; B Cheney; R Zheng; W Lonergan; W Yu; J Chen

    2011-12-31

    Low temperature (308 K) hydrogenation of acetone was used as a probe reaction to investigate the support effect on the hydrogenation activity of Pt/Ni bimetallic catalysts supported on TiO{sub 2}, SiO{sub 2} and {gamma}-Al{sub 2}O{sub 3}. The oxide supports significantly affected the catalytic properties of Pt/Ni catalysts, in which Pt/Ni/SiO2 bimetallic catalysts exhibited significantly higher activity than the other two bimetallic catalysts. TEM measurements revealed that the three supported Pt/Ni bimetallic catalysts have similar particle size distribution, while CO chemisorption measurements showed very different chemisorption capacity. Extended X-Ray absorption fine structure (EXAFS) measurements of the Pt L{sub III}-edge indicated that Pt atoms were fully reduced and the Pt-Ni bimetallic bonds were formed on all three catalysts. The extent of Pt-Ni bond formation followed the trend of SiO{sub 2} > {gamma}-Al{sub 2}O{sub 3} > TiO{sub 2}, which correlated very well with the hydrogenation activity.

  10. Effect of dispersing agent in heating process for high dispersion of coal liquefaction catalyst

    SciTech Connect

    Okada, Y.; Haneda, M.; Inokuchi, K.; Aihara, Y.; Imada, K.; Kai, T.; Sakaki, T.; Shibata, M.

    1999-07-01

    This work deals with one proposal concerning the improvement of catalytic activity on coal liquefaction. It is known that pyrite (FeS{sub 2}) transform into pyrrhotite (Fe{sub 1{minus}x}S) and aggregate at the heating process on coal liquefaction. The aggregation of liquefaction catalyst decreases the specific surface area, and causes the decline in catalytic activity. The authors investigated the effects of dispersing agent on the morphological change and the dispersing state of liquefaction catalyst at the rapid heating process. For the liquefaction tests with added dispersing agent, the product yields were compared with the results of other tests.

  11. Homogeneously dispersed, multimetal oxygen-evolving catalysts

    DOE PAGES

    Zhang, Bo; Zheng, Xueli; Voznyy, Oleksandr; Comin, Riccardo; Bajdich, Michal; Garcia-Melchor, Max; Han, Lili; Xu, Jixian; Liu, Min; Zheng, Lirong; et al

    2016-03-24

    Earth-abundant first-row (3d) transition-metal-based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials significantly above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxy-hydroxide materials with an atomically homogeneous metal distribution. These gelled FeCoW oxy-hydroxide exhibits the lowest overpotential (191 mV) reported at 10 mA per square centimeter in alkaline electrolyte. Here, the catalyst shows no evidence of degradation following more than 500 hours of operation. X-ray absorption and computationalmore » studies reveal a synergistic interplay between W, Fe and Co in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER.« less

  12. Driving the Oxygen Evolution Reaction by Nonlinear Cooperativity in Bimetallic Coordination Catalysts.

    PubMed

    Wurster, Benjamin; Grumelli, Doris; Hötger, Diana; Gutzler, Rico; Kern, Klaus

    2016-03-23

    Developing efficient catalysts for electrolysis, in particular for the oxygen evolution in the anodic half cell reaction, is an important challenge in energy conversion technologies. By taking inspiration from the catalytic properties of single-atom catalysts and metallo-proteins, we exploit the potential of metal-organic networks as electrocatalysts in the oxygen evolution reaction (OER). A dramatic enhancement of the catalytic activity toward the production of oxygen by nearly 2 orders of magnitude is demonstrated for novel heterobimetallic organic catalysts compared to metallo-porphyrins. Using a supramolecular approach we deliberately place single iron and cobalt atoms in either of two different coordination environments and observe a highly nonlinear increase in the catalytic activity depending on the coordination spheres of Fe and Co. Catalysis sets in at about 300 mV overpotential with high turnover frequencies that outperform other metal-organic catalysts like the prototypical hangman porphyrins. PMID:26937997

  13. Catalyst dispersion and activity under conditions of temperature- staged liquefaction

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1992-02-01

    The general objectives of this research are (1) to investigate the use of highly dispersed catalysts for the pretreatment of coal by mild hydrogenation, (2) to identify the active forms of catalysts under reaction conditions and (3) to clarify the mechanisms of catalysis. The ultimate objective is to ascertain if mild catalytic hydrogenation resulting in very limited or no coal solubilization is an advantageous pretreatment for the transformation of coal into transportable fuels. The experimental program will focus upon the development of effective methods of impregnating coal with catalysts, evaluating the conditions under which the catalysts are most active and establishing the relative impact of improved impregnation on conversion and product distributions obtained from coal hydrogenation.

  14. Carbon-Supported bimetallic Pd-Fe catalysts for vapor-phase hydrodeoxygenation of guaiacol

    SciTech Connect

    Sun, Junming; Karim, Ayman M.; Zhang, He; Kovarik, Libor; Li, Xiaohong S.; Hensley, Alyssa; McEwen, Jean-Sabin; Wang, Yong

    2013-10-01

    Abstract Carbon supported metal catalysts (Cu/C, Fe/C, Pd/C, Pt/C, PdFe/C and Ru/C) have been prepared, characterized and tested for vapor-phase hydrodeoxygenation (HDO) of guaiacol (GUA) at atmospheric pressure. Phenol was the major intermediate on all catalysts. Over the noble metal catalysts saturation of the aromatic ring was the major pathway observed at low temperature (250 °C), forming predominantly cyclohexanone and cyclohexanol. Substantial ring opening reaction was observed on Pt/C and Ru/C at higher reaction temperatures (e.g., 350 °C). Base metal catalysts, especially Fe/C, were found to exhibit high HDO activity without ring-saturation or ring-opening with the main products being benzene, phenol along with small amounts of cresol, toluene and trimethylbenzene (TMB). A substantial enhancement in HDO activity was observed on the PdFe/C catalysts. Compared with Fe/C, the yield to oxygen-free aromatic products (i.e., benzene/toluene/TMB) on PdFe/C increased by a factor of four at 350 °C, and by approximately a factor of two (83.2% versus 43.3%) at 450 °C. The enhanced activity of PdFe/C is attributed to the formation of PdFe alloy as evidenced by STEM, EDS and TPR.

  15. Evaluation of bimetallic catalyst PtAg/C as a glucose-tolerant oxygen reduction cathode

    NASA Astrophysics Data System (ADS)

    Guerra-Balcázar, M.; Cuevas-Muñiz, F. M.; Álvarez-Contreras, L.; Arriaga, L. G.; Ledesma-García, J.

    2012-01-01

    PtAg/C nanoparticles were synthesized by chemical reduction and evaluated for the oxygen reduction reaction (ORR) in the absence and presence of glucose. PtAg/C catalyst formed onion-like layered structures, which are uniformly distributed on the support. PtAg/C showed activity comparable to that of Pt/C ETEK for ORR. Further, the catalyst exhibited high selectivity for ORR in the presence of glucose. PtAg/C was evaluated as cathode in a microfluidic fuel cell operated with high concentration of glucose (100 mM) as fuel. The results demonstrated that the use of PtAg/C as cathode electrode achieved higher selectivity and better performance compared with Pt/C catalyst.

  16. Method of making maximally dispersed heterogeneous catalysts

    DOEpatents

    Jennison, Dwight R.

    2005-11-15

    A method of making a catalyst with monolayer or sub-monolayer metal by controlling the wetting characteristics on the support surface and increasing the adhesion between the catalytic metal and an oxide layer. There are two methods that have been demonstrated by experiment and supported by theory. In the first method, which is useful for noble metals as well as others, a negatively-charged species is introduced to the surface of a support in sub-ML coverage. The layer-by-layer growth of metal deposited onto the oxide surface is promoted because the adhesion strength of the metal-oxide interface is increased. This method can also be used to achieve nanoislands of metal upon sub-ML deposition. The negatively-charged species can either be deposited onto the oxide surface or a compound can be deposited that dissociates on, or reacts with, the surface to form the negatively-charged species. The deposited metal adatoms can thereby bond laterally to the negatively-charged species as well as vertically to the oxide surface. Thus the negatively-charged species serve as anchors for the metal. In the second method, a chemical reaction that occurs when most metals are deposited on a fully hydroxylated oxide surface is used to create cationic metal species that bind strongly both to the substrate and to metallic metal atoms. These are incorporated into the top layer of the substrate and bind strongly both to the substrate and to metallic metal atoms. In this case, these oxidized metal atoms serve as the anchors. Here, as in the previous method, nanoislands of catalytic metal can be achieved to increase catalytic activity, or monolayers or bilayers of reactive metal can also be made.

  17. Mono- and Bimetallic Ruthenium—Arene Catalysts for Olefin Metathesis: A Survey

    NASA Astrophysics Data System (ADS)

    Borguet, Yannick; Sauvage, Xavier; Demonceau, Albert; Delaude, Lionel

    In this chapter, we summarize the main achievements of our group toward the development of easily accessible, highly efficient ruthenium—arene catalyst precursors for olefin metathesis. Major advances in this field are presented chronologically, with an emphasis on catalyst design and mechanistic details. The first part of this survey focuses on monometallic complexes with the general formula RuCl2(p-cymene)(L), where L is a phosphine or N-heterocyclic carbene ancillary ligand. In the second part, we disclose recent developments in the synthesis and catalytic applications of homobimetallic ruthenium—arene complexes of generic formula (p-cymene)Ru(μ-Cl)3RuCl(η2-C2H4)(L) and their derivatives resulting from the substitution of the labile ethylene moiety with vinylidene, allenylidene, or indenylidene units

  18. Formation and characterization of highly-dispersed metal colloid catalysts

    SciTech Connect

    Wilcoxon, J.; Martino, A.; Nigrey, P.; Sylwester, A.; Klavetter, E.; Baughman, R.

    1991-01-01

    The objective of this research is to explore the feasibility of using small metal colloids, in microemulsions, as catalysts. The product of this work will be a new concept for tailoring highly dispersed materials to specific catalytic reactions. The knowledge gained from the proposed research will be broadly applicable to variety of reactions, including hydrogenation, synthesis gas conversion, and hydrogen conversion. To achieve this objective, a plan has been formulated to prepare and characterize catalyst particles in organic solvents and to explore the use of catalyst particles. In this paper, we will discuss the use of inverse micelles to solubilize significant quantities of metal compounds in hydrocarbon solvents and their reduction, decomposition, and sulfidation to give colloidal catalytic materials. We will also discuss in detail the characterization of these materials, present preliminary results for the catalytic hydropyrolysis of coals, and discuss the results of our evaluation of selected metal colloids in catalytic hydrogenation of pyrene. 9 refs., 3 tabs.

  19. Method for dispersing catalyst onto particulate material and product thereof

    DOEpatents

    Utz, Bruce R.; Cugini, Anthony V.

    1992-01-01

    A method for dispersing finely divided catalyst precursors onto the surface of coal or other particulate material includes the steps of forming a wet paste mixture of the particulate material and a liquid solution containing a dissolved transition metal salt, for instance a solution of ferric nitrate. The wet paste mixture is in a state of incipient wetness with all of this solution adsorbed onto the surfaces of the particulate material without the presence of free moisture. On adding a precipitating agent such as ammonia, a catalyst precursor such as hydrated iron oxide is deposited on the surfaces of the coal. The catalyst is activated by converting it to the sulfide form for the hydrogenation or direct liquefaction of the coal.

  20. Low-Temperature 1,3-Butadiene Hydrogenation over Supported Pt/3d/gamma-Al2O3 Bimetallic Catalysts

    SciTech Connect

    Lonergan, William W; Xing, X; Zheng, Renyang; Qi, Suitao; Huang, B; Chen, Jingguang

    2011-02-02

    Low-temperature 1,3-butadiene hydrogenation is used as a probe reaction to investigate the hydrogenation activity over several γ-Al{sub 2}O{sub 3} supported Pt/3d (3d = Co, Ni, Cu) bimetallic catalysts. Batch and flow reactor studies are employed to quantify the kinetic activity and steady-state conversion, respectively, of each catalyst. Transmission electron microscopy (TEM) is utilized to characterize particle sizes and extended X-ray absorption fine structure (EXAFS) measurements are performed to verify the Pt–3d bimetallic bond formation. Pulse carbon monoxide chemisorption measurements are also performed to characterize the number of active sites. Additionally, density functional theory (DFT) calculations are included to determine the binding energies of 1,3-butadiene and atomic hydrogen on the corresponding model surfaces. The binding energies of the adsorbates are found to correlate with the hydrogenation activity, allowing for use of such correlation to potentially predict hydrogenation catalysts with enhanced activity based on the binding energies of the adsorbates of interest.

  1. Oxidation of ethyl acetate by a high performance nanostructure (Ni, Mn)-Ag/ZSM-5 bimetallic catalysts and development of an artificial neural networks predictive modeling.

    PubMed

    Jodaei, Azadeh; Salari, Darush; Niaei, Ali; Khatamian, Masumeh; Hosseini, Seyed Ali

    2011-01-01

    The catalytic oxidation of ethyl acetate in low concentration was investigated over mono-metallic Ag/ZSM5 and bimetallic (Ni, Mn)-Ag/ZSM-5 catalysts. Catalytic studies were carried out in a catalytic fixed bed reactor under atmospheric pressure. The sequence of catalytic activity was as follows: Ni-Ag-ZSM-5 > Mn-Ag-ZSM-5 > Ag-ZSM-5 > H-ZSM-5. The catalysts were characterized by ICP-AES, X-ray diffraction (XRD), low temperature nitrogen adsorption, NH(3)-TPD, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and diffuse reflectance UV-vis spectra (UV-vis). An artificial neural networks (ANN) model was developed to predict the performance of catalytic oxidation process over bimetallic Ni-Ag/ZSM-5 catalyst based on experimental data. For this purpose the standard feed forward back propagation algorithm was employed to train the model by using laboratory experimental data. A good agreement was resulted between experimental results and those obtained by ANN. Following order for variables effects on conversion yield of ethyl acetate was predicted by ANN model: reaction temperature (32.99%) > Ag loading (27.38%) > initial ethyl acetate concentration (23.58%) > Ni loading (16.05%). PMID:21104495

  2. Synthesis of triazoles from nonactivated terminal alkynes via the three-component coupling reaction using a Pd(0)-Cu(I) bimetallic catalyst.

    PubMed

    Kamijo, Shin; Jin, Tienan; Huo, Zhibao; Yamamoto, Yoshinori

    2003-07-01

    The synthesis of triazoles via the three-component coupling reaction of unactivated terminal alkynes, allyl carbonate, and trimethylsiyl azide under the Pd(0)-Cu(I) bimetallic catalyst is developed. The reaction most probably proceeds through the formation of a pi-allylpalladium azide complex and a copper-acetylide followed by a successive [3 + 2] cycloaddition. The deallylation of the resulting allyltriazoles proceeds very easily by the Ru-catalyzed isomerization followed by the ozonolysis of the resulting propenyltriazoles to give the triazoles in high yields. PMID:12822981

  3. Surface Modified Coals for Enhanced Catalyst Dispersion and Liquefaction

    SciTech Connect

    Yaw D. Yeboah

    1998-12-04

    The aim of this study is to enhance catalyst loading and dispersion in coal for improved liquefaction by preadsorption of surfactants and catalysts on to the coal. During this reporting period, liquefaction experiments were conducted with the raw coal and catalyst loaded samples. Pretreatment of the coal and catalyst-loaded samples were done using the surfactants presented in previous reports. Liquefaction samples were tested using 6.6 g of solvent, 3.3 g coal, 6.9 MPa ambient hydrogen pressure, 425 0 C and 30 minutes. The liquid and solid products were removed from the reactor using tetrahydrofuran (THF). Coal conversions were calculated based on THF and heptane solubility. The results showed that in the absence of a catalyst, 33.8% heptane solubles was obtained with the parent coal compared to 27.8% and 27.3% with the SDS and DDAB surfactants. The presence of molybdenum, as expected, resulted in enhanced heptane solubles with or without surfactants. In the absence of surfactants, 50% heptane solubles was obtained compared to 40-47% with surfactants. Thus, it appears that pretreatment, unexpectedly, had a negative effect on liquefaction activity. It is unclear if the observed differences in results are significant. Clearly, additional experiments are needed before any firm deductions and conclusions can be drawn from the results.

  4. Surface Modified Coals for Enhanced Catalyst Dispersion and Liquefaction

    SciTech Connect

    Yaw D. Yeboah

    1998-12-04

    The aim of this study is to enhance catalyst loading and dispersion in coal for improved liquefaction by preadsorption of surfactants and catalysts on to the coal. During this reporting period, the effects of dodecyl dimethyl ethyl ammonium bromide (DDAB) (a cationic surfactant), sodium dodecyl sulfate (SDS) (an anionic surfactant), Triton X-100 (a neutral surfactant), and ferrous sulfate (as a catalyst precursor) on the coal surface charge at various pH values were determined. The results of the zeta potential measurements suggest that ferrous sulfate as catalyst precursor creates a distinctly different condition on the coal surface compared to that of molybdenum as reported in the previous progress reports. The effects of the adsorption of the surfactants also varied distinctly with the type of surfactant. With the adsorption of DDAB, the cationic surfactant, the surface charge was more positive. The opposite effect was observed for the SDS, the anionic surfactant. The coals treated with Triton X-100, the neutral surfactant, also showed an overall negative surface charge density. The adsorption of the catalyst precursor (ferrous sulfate) resulted in a net negative charge on the coal surface.

  5. From First Principles Design to Realization of Bimetallic Catalysts for Enhanced Selectivity

    SciTech Connect

    Lobo, Raul F.; Crooks, Richard M.; Mavrikakis, Manos

    2014-04-08

    “Catalysis by design” has been a dream for decades. To specify the composition and structure of matter to effect a desired catalytic transformation with desired and predicted rate and selectivity remains a monumental challenge, especially in heterogeneous catalysis. Our research thrusts have been chosen not only for their practical and scientific relevance, e.g. for more efficient and sustainable chemicals and fuels production, but also because they provide a foundation for developing and exploring broadly applicable principles and strategies for catalyst design.

  6. Hydrogen adsorption and coadsorption with CO on well-defined bimetallic PtRu surfaces a model study on the CO tolerance of bimetallic PtRu anode catalysts in low temperature polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    Diemant, T.; Hager, T.; Hoster, H. E.; Rauscher, H.; Behm, R. J.

    2003-09-01

    The influence of PtRu surface alloy formation and of coadsorbed CO on the adsorption/desorption characteristics of hydrogen on bimetallic PtRu surfaces was investigated by temperature programmed desorption, using a 40% Pt containing PtRu surface alloy pseudomorphic on a Ru(0 0 0 1) surface with an almost statistical distribution of Pt surface atoms as substrate. Alloy formation leads to a significant broadening of the desorption peak compared to pure Ru, together with a considerable down-shift in the onset of desorption. This trend is even more pronounced in the presence of coadsorbed CO. The weakening of the hydrogen adsorption bond is attributed mainly to strain effects, imposed by the considerable compression of the pseudomorphic Pt as compared to bulk Pt(1 1 1). Finally we discuss the implications of these results for the mechanistic understanding of the improved performance of PtRu anode catalysts in reformate operated polymer electrolyte fuel cells.

  7. SURFACE-MODIFIED COALS FOR ENHANCED CATALYST DISPERSION AND LIQUEFACTION

    SciTech Connect

    Dr. Yaw D. Yeboah

    1999-09-01

    This is the final report of the Department of Energy Sponsored project DE-FGF22-95PC95229 entitled, surface modified coals for enhanced catalyst dispersion and liquefaction. The aims of the study were to enhance catalyst loading and dispersion in coal for improved liquefaction by preadsorption of surfactants and catalysts on the coal and to train and educate minority scientists in catalysts and separation science. Illinois No. 6 Coal (DEC-24) was selected for the study. The surfactants investigated included dodecyl dimethyl ethyl ammonium bromide (DDAB), a cationic surfactant, sodium dodecyl sulfate, an anionic surfactant, and Triton x-100, a neutral surfactant. Ammonium molybdate tetrahydrate was used as the molybdenum catalyst precursor. Zeta potential, BET, FTIR, AFM, UV-Vis and luminescence intensity measurements were undertaken to assess the surface properties and the liquefaction activities of the coal. The parent coal had a net negative surface charge over the pH range 2-12. However, in the presence of DDAB the negativity of the surface charge decreased. At higher concentrations of DDAB, a positive surface charge resulted. In contrast to the effect of DDAB, the zeta potential of the coal became more negative than the parent coal in the presence of SDS. Adsorption of Triton reduced the net negative charge density of the coal samples. The measured surface area of the coal surface was about 30 m{sup 2}/g compared to 77m{sup 2}/g after being washed with deionized water. Addition of the surfactants decreased the surface area of the samples. Adsorption of the molybdenum catalyst increased the surface area of the coal sample. The adsorption of molybdenum on the coal was significantly promoted by preadsorption of DDAB and SDS. Molybdenum adsorption showed that, over a wide range of concentrations and pH values, the DDAB treated coal adsorbed a higher amount of molybdenum than the samples treated with SDS. The infrared spectroscopy (FTIR) and the atomic force

  8. Indirect cooperative effects leading to synergism in bimetallic homogeneous catalysts containing azolates as bridging ligands

    SciTech Connect

    Esteruelas, M.A.; Garcia, M.P.; Lopez, A.M.; Oro, L.A. )

    1991-01-01

    The binuclear compounds (H(CO)(PPh{sub 3}){sub 2}Ru({mu}-bim)Ir(COD)) (1) (bim = 2,2{prime}-biimidazolate, COD = 1,5-cyclooctadiene) and (H(CO)(PPh{sub 3}){sub 2}Ru({mu}-pz){sub 2}Ir(TFB)) (2) (pz = pyrazolate, TFB = tetrafluorobenzobarrelene) are more active catalysts for the hydrogenation of cyclohexene than the mononuclear parent compounds (RuH(Hbim)(CO)(PPh{sub 3}){sub 2}), (Ir(Hbim)(COD)), (RuH(pa)(CO)(Hpz)(PPh{sub 3}){sub 2}), and (Ir(TFB)(Hpz){sub 2})BF{sub 4}. In the presence of 1, the reaction rate is first order with respect to the concentration of 1 and cyclohexene, second order with respect to hydrogen pressure, and inversely proportional to the concentration of added phosphine. For the reaction catalyzed by 2, the experimental data are in accordance with a rate expression of the form {minus}d(cyclohexene)/dt = k(2)(cyclohexene)P(H{sub 2}) (P(H{sub 2}) = hydrogen pressure). On the basis of the kinetic results and experimental evidence, the origin of the catalytic synergism is assigned to indirect cooperative effects between the metallic centers of the binuclear complexes. The kinetic investigation of the hydrogenation of cyclohexene catalyzed by (Ir({mu}-pz)(TFB)){sub 2} (3) is also reported, suggesting that the full catalytic cycle involves binuclear species.

  9. Bimetallic Ni-Rh catalysts with low amounts of Rh for the steam and autothermal reforming of n-butane for fuel-cell applications.

    SciTech Connect

    Ferrandon, M.; Kropf, A. J.; Krause, T.; Chemical Sciences and Engineering Division

    2010-05-15

    Mono-metallic nickel and rhodium catalysts and bimetallic Ni-Rh catalysts supported on La-Al{sub 2}O{sub 3}, CeZrO{sub 2} and CeMgOx were prepared and evaluated for catalyzing the steam and autothermal reforming of n-butane. The binary Ni-Rh supported on La-Al{sub 2}O{sub 3} catalysts with low weight loading of rhodium exhibited higher H{sub 2} yields than Ni or Rh alone. The Ni-Rh/CeZrO{sub 2} catalyst exhibited higher performance and no coke formation, compared to the same metals on other supports. A NiAl{sub 2}O{sub 4} spinel phase was obtained on all Ni and Ni-Rh catalysts supported on La-Al{sub 2}O{sub 3}. The presence of rhodium stabilized the spinel phase as well as NiOx species upon reforming while Ni alone was mostly reduced into metallic species. Extended X-ray absorption fine-structure analysis showed evidence of Ni-Rh alloy during preparation and even further after an accelerated aging at 900C in a H{sub 2}/H{sub 2}O atmosphere.

  10. Surface modified coals for enhanced catalyst dispersion and liquefaction

    SciTech Connect

    Dr. Yaw D. Yeboah

    1998-10-29

    The aim of the study is to enhance catalyst loading and dispersion in coal for improved liquefaction by preadsorption of surfactants and catalysts on to the coal. During this reporting period, zeta potential measurements were conducted to assess the surface charge on the raw, pretreated and catalyzed coal samples. The surface area, transmission spectroscopy and luminescence intensity of the raw coal and pretreated coal samples were also determined to assess the quality of the coal surface. Across a broad range of pH values, the raw coal had an overall negative charge. Coal treated with anionic surfactant SDS maintained an overall net negative surface negative charge. The interaction between the coal and cationic surfactant DDAB caused the opposite effect resulting in a more positive coal surface charge. Although one would have expected little or no effect of the neutral surfactant Triton X-100, there appears to be some difference in the results of the raw coal and the coal treated with Triton X-100. The authors believe that the Triton not only binds to the nonpolar sites but also has a strong affinity for the polar sites through electrostatic bonding and interaction between the hydrophobic tails. The addition of molybdenum to coal pretreated with DDAB caused a reduction in the positive charge of the coal surface probably due to possible ionic interaction between the coal surface, the surfactant and the catalyst. The adsorption isotherm of the coal was characteristic of isotherms for porous samples and the surface area of the coal increased from 30 m{sup 2}/g to 77 m{sup 2}/g when washed with deionized water. This suggests coal washing may be one method of increasing the surface area for surfactant adsorption. Although the transmission measurements provided valuable information about the coal it resulted in little information on the amount of adsorbed Triton. However, the maximum solid-liquid ratio for optimum surfactant loading of Triton X-100 was determined via

  11. Synthesis and Characterization of Bimetallic Ni50Pt50 Catalyst Supported on SiO2 for N2O Decomposition.

    PubMed

    Angeles-Pascual, A; Esparza, R; Tellez-Vazquez, O; Velumani, S; Pérez, R

    2015-12-01

    Nanometallic and bimetallic catalyst of Ni, Pt and Ni50Pt50 were studied by the decompositions of N2O. The catalyst were prepared by incipient wetness impregnation of the silica with low superficial area of 50 m2/g supported with aqueous solution of the metal precursors, for Pt H2Pt Cl6 x 6H2O was used and for Ni, Ni(NO3)2 was used to a total metal loading of 1% wt. Catalyst were oxidized for 2 hours at 400 degrees C with O2, then the samples were reduced for 30 minutes with N2 and 2 hours with H2, all at the same temperature. The catalyst was characterized by Transmission Electron Microscopy (TEM), High Angular Annular Dark Field (HAADF), High Resolution Transmission Electron Microscopy (HR-TEM) and Termoprogramed Reduction (TPR). The mean particle sizes obtained by TEM and HAADF were about 12.5 nm for Ni/SiO2, 2.8 nm for Pt/SiO2 and 3.5 nm Ni50Pt50/SiO2 catalysts respectability. HR-TEM and HAADF analysis showed differences between Ni and Pt catalysts displaying mainly cuboctahedral shapes. Stepped surface defects were found in the Ni50Pt50/SiO2 catalyst. Finally Ni50Pt50/SiO2 was more active than Pt/SiO2 and Ni/SiO2 catalysts for the decomposition of N2O. PMID:26682368

  12. Passivation of bimetallic catalysts used in water treatment: prevention and reactivation.

    PubMed

    Chen, Jianming; Gillham, Robert W; Gui, Lai

    2013-01-01

    With respect to degradation rates and the range in contaminants treated, bimetals such as Ni-Fe or Pd-Fe generally outperform unamended granular iron. However, the catalytic enhancement is generally short-lived, lasting from a few days to months. To take advantage of the significant benefits of bimetals, this study aims at developing an effective method for the rejuvenation of passivated bimetals and alternatively, the prevention of rapid reactivity loss of bimetals. Because the most likely cause of Ni-Fe and Pd-Fe passivation is the deposition of iron oxide films over the catalyst sites, it is hypothesized that removal of the iron oxide films will restore the lost reactivity or avoiding the deposition of iron oxide films will prevent passivation. Two organic ligands (ethylenediaminetetraacetic acid (EDTA), and [s,s]-ethylenediaminedisuccinate acid ([s,s]-EDDS)) and two acids (citric acid and sulphuric acid) were tested as possible chemical reagents for both passivation rejuvenation and prevention. Trichloroethene (TCE) and Ni-Fe were chosen as probes for chlorinated solvents and bimetals respectively. The test was carried out using small glass columns packed with Ni-Fe. TCE solution containing a single reagent at various concentrations was pumped through the Ni-Fe columns with a residence time in the Ni-Fe of about 6.6 min. TCE concentrations in the influent and effluent were measured to evaluate the performance of each chemical reagent. The results show that (i) for passivated Ni-Fe, flushing with a low concentration of acid or ligand solution without mechanical mixing can fully restore the lost reactivity; and (ii) for passivation prevention, adding a small amount of a ligand or an acid to the feed solution can successfully prevent or at least substantially reduce Ni-Fe passivation. All four chemicals tested are effective in both rejuvenation and prevention, but sulphuric acid and citric acid are considered to be the most practical reagents due to their

  13. Tuning selectivity of electrochemical reactions by atomically dispersed platinum catalyst

    NASA Astrophysics Data System (ADS)

    Choi, Chang Hyuck; Kim, Minho; Kwon, Han Chang; Cho, Sung June; Yun, Seongho; Kim, Hee-Tak; Mayrhofer, Karl J. J.; Kim, Hyungjun; Choi, Minkee

    2016-03-01

    Maximum atom efficiency as well as distinct chemoselectivity is expected for electrocatalysis on atomically dispersed (or single site) metal centres, but its realization remains challenging so far, because carbon, as the most widely used electrocatalyst support, cannot effectively stabilize them. Here we report that a sulfur-doped zeolite-templated carbon, simultaneously exhibiting large sulfur content (17 wt% S), as well as a unique carbon structure (that is, highly curved three-dimensional networks of graphene nanoribbons), can stabilize a relatively high loading of platinum (5 wt%) in the form of highly dispersed species including site isolated atoms. In the oxygen reduction reaction, this catalyst does not follow a conventional four-electron pathway producing H2O, but selectively produces H2O2 even over extended times without significant degradation of the activity. Thus, this approach constitutes a potentially promising route for producing important fine chemical H2O2, and also offers opportunities for tuning the selectivity of other electrochemical reactions on various metal catalysts.

  14. Tuning selectivity of electrochemical reactions by atomically dispersed platinum catalyst

    PubMed Central

    Choi, Chang Hyuck; Kim, Minho; Kwon, Han Chang; Cho, Sung June; Yun, Seongho; Kim, Hee-Tak; Mayrhofer, Karl J. J.; Kim, Hyungjun; Choi, Minkee

    2016-01-01

    Maximum atom efficiency as well as distinct chemoselectivity is expected for electrocatalysis on atomically dispersed (or single site) metal centres, but its realization remains challenging so far, because carbon, as the most widely used electrocatalyst support, cannot effectively stabilize them. Here we report that a sulfur-doped zeolite-templated carbon, simultaneously exhibiting large sulfur content (17 wt% S), as well as a unique carbon structure (that is, highly curved three-dimensional networks of graphene nanoribbons), can stabilize a relatively high loading of platinum (5 wt%) in the form of highly dispersed species including site isolated atoms. In the oxygen reduction reaction, this catalyst does not follow a conventional four-electron pathway producing H2O, but selectively produces H2O2 even over extended times without significant degradation of the activity. Thus, this approach constitutes a potentially promising route for producing important fine chemical H2O2, and also offers opportunities for tuning the selectivity of other electrochemical reactions on various metal catalysts. PMID:26952517

  15. Preferential catalytic oxidation of carbon monoxide in presence of hydrogen over bimetallic AuPt supported on zeolite catalysts

    NASA Astrophysics Data System (ADS)

    Naknam, Pattarasuda; Luengnaruemitchai, Apanee; Wongkasemjit, Sujitra; Osuwan, Somchai

    A series of AuPt/A zeolite and Pt/A zeolite catalysts prepared by incipient wetness impregnation are investigated for the preferential oxidation (PROX) of carbon monoxide in the presence of hydrogen over the temperature range of 50-310 °C under atmospheric pressure. The results indicate that when a small amount of gold is added to the Pt/A zeolite catalyst, the CO selectivity is improved at low temperatures, and 1% AuPt/A zeolite (at a weight ratio of Au:Pt = 1:2) gives the best performance, which provides a high CO conversion in combination with a high CO selectivity. In more realistic simulated reformate gases containing 10% CO 2 and 10% H 2O, there is not much difference between those in the presence and the absence of CO 2 and H 2O. Transmission electron microscopic and X-ray diffraction studies show that the two metals, Au and Pt, appear to be severely phase separated, which is confirmed by energy dispersive investigations.

  16. Sulfur poisoning of CeO[subscript 2]-Al[subscript 2]O[subscript 3]-supported mono- and bi-metallic Ni and Rh catalysts in steam reforming of liquid hydrocarbons at low and high temperatures

    SciTech Connect

    Xie, Chao; Chen, Yongsheng; Li, Yan; Wang, Xiaoxing; Song, Chunshan

    2010-12-01

    In order to develop a better understanding on sulfur poisoning of reforming catalysts in fuel processing for hydrogen production, steam reforming of liquid hydrocarbons was performed over CeO{sub 2}-Al{sub 2}O{sub 3} supported monometallic Ni and Rh and bimetallic Rh-Ni catalysts at 550 and 800 C. XANES was used to identify the sulfur species in the used catalysts and to study their impacts on the metal surface properties probed by XPS. It was found that both monometallic catalysts rapidly deactivated at 550 C, and showed poor sulfur tolerance. Although ineffective for the Ni catalyst, increasing the temperature to 800 C dramatically improved the sulfur tolerance of the Rh catalyst. XANES revealed that metal sulfide and organic sulfide are the dominant sulfur species on the used Ni catalyst, while sulfonate and sulfate predominate on the used Rh catalyst. The presence of sulfur induced severe carbon deposition on the Ni catalyst at 800 C. The superior sulfur tolerance of the Rh catalyst at 800 C may be associated with its capability in sulfur oxidation. It is likely that the formation of the oxygen-shielded sulfur structure of sulfonate and sulfate can suppress the poisoning impact of sulfur on Rh by inhibiting direct rhodium-sulfur interaction. Moreover, XPS indicated that the metal surface properties of the Rh catalysts after the reaction without and with sulfur at 800 C are similar, suggesting that sulfur poisoning on Rh was mitigated under the high-temperature condition. Although the Rh-Ni catalyst exhibited better sulfur tolerance than the monometallic catalysts at 550 C, its catalytic performance was inferior compared with the Rh catalyst in the sulfur-containing reaction at 800 C probably due to the severe carbon deposition on the bimetallic catalyst.

  17. Advanced liquefaction using coal swelling and catalyst dispersion techniques

    SciTech Connect

    Curtis, C.W. ); Gutterman, C. ); Chander, S. )

    1992-08-26

    Research in this project centers upon developing a new approach to the direct liquefaction of coal to produce an all-distillate product slate at a sizable cost reduction over current technology. The approach integrates all aspects of the coal liquefaction process including coal selection, pretreatment, coal swelling with catalyst impregnation, coal liquefaction experimentation, product recovery with characterization, alternate bottoms processing, and a technical assessment including an economic evaluation. The project is being carried out under contract to the United States Department of Energy. On May 28, 1992, the Department of Energy authorized starting the experimental aspects of this projects; therefore, experimentation at Amoco started late in this quarterly report period. Research contracts with Auburn University, Pennsylvania State University, and Foster Wheeler Development Corporation were signed during June, 1992, so their work was just getting underway. Their work will be summarized in future quarterly reports. A set of coal samples were sent to Hazen Research for beneficiation. The samples were received and have been analyzed. The literature search covering coal swelling has been up-dated, and preliminary coal swelling experiments were carried out. Further swelling experimentation is underway. An up-date of the literature on the liquefaction of coal using dispersed catalysts is nearing completion; it will be included in the next quarterly report.

  18. Heterogenized Bimetallic Pd-Pt-Fe3O4 Nanoflakes as Extremely Robust, Magnetically Recyclable Catalysts for Chemoselective Nitroarene Reduction.

    PubMed

    Byun, Sangmoon; Song, Yeami; Kim, B Moon

    2016-06-15

    A very simple synthesis of bimetallic Pd-Pt-Fe3O4 nanoflake-shaped alloy nanoparticles (NPs) for cascade catalytic reactions such as dehydrogenation of ammonia-borane (AB) followed by the reduction of nitro compounds (R-NO2) to anilines or alkylamines (R-NH2) in methanol at ambient temperature is described. The Pd-Pt-Fe3O4 NPs were easily prepared via a solution phase hydrothermal method involving the simple one-pot coreduction of potassium tetrachloroplatinate (II) and palladium chloride (II) in polyvinylpyrrolidone with subsequent deposition on commercially available Fe3O4 NPs. The bimetallic Pd-Pt alloy NPs decorated on Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. Various nitroarene derivatives were reduced to anilines with very specific chemoselectivity in the presence of other reducible functional groups. The bimetallic Pd-Pt-Fe3O4 NPs provide a unique synergistic effect for the catalysis of cascade dehydrogenation/reduction. The nitro reduction proceeded in 5 min with nearly quantitative conversions and yields. Furthermore, the magnetically recyclable nanocatalysts were readily separated using an external magnet and reused up to 250 times without any loss of catalytic activity. A larger scale (10 mmol) reaction was also successfully performed with >99% yield. This efficient, recyclable Pd-Pt-Fe3O4 NPs system can therefore be repetitively utilized for the reduction of various nitro-containing compounds. PMID:27191706

  19. Surface structure and reaction property of CuCl2-PdCl2 bimetallic catalyst in methanol oxycarbonylation: A DFT approach

    NASA Astrophysics Data System (ADS)

    Meng, Qingsen; Wang, Shengping; Shen, Yongli; Yan, Bing; Wu, Yuanxin; Ma, Xinbin

    2014-02-01

    Surface structure of CuCl2-PdCl2 bimetallic catalyst (Wacker-type catalyst) was built employing density functional theory (DFT) calculations, and the reaction mechanism of methanol oxycarbonylation over the CuCl2-PdCl2 surfaces was also investigated. On the CuCl2-PdCl2 surface, the active site for methanol oxidation was confirmed as Cu-Cl-Cu (Pd). Comparing with pure CuCl2 surface, the introduction of Pd atom causes the electron repopulation on the surface and lowers the energy barrier for methanol oxidation, but the number of the active site decreases with the increasing of Pd doping volume. Agreed with previous experimental results, the Pd site is most favorable for the CO insertion, indicated by the lowest activation barrier for the formation of COOCH3 on Pd atom. The lowest energy barrier for the formation of DMC appears when COOCH3 species adsorbed on Pd atom and methoxyl adsorbed on Cu atoms, which is 0.42 eV. Finally, the reconstruction of the unsaturated surface is a spontaneous and exothermic process. Comparing with other surfaces, the rate-limiting step, methanol oxidation, on CuCl2-PdCl2 surface with Pd/Cu = 1:17 has the lowest energy barrier, which is agreed with the experimental observation that PdCl2-CuCl2 catalyst with Pd/Cu = 1:20 has the favorable activity. The adsorbed methoxyl will further lower the activation barrier of methanol oxidation, which is agreed with experimental observation that the Wacker-type catalysts have an induction period in the methanol oxidative carbonylation system.

  20. Thermodynamic guidelines for the design of bimetallic catalysts for oxygen electroreduction and rapid screening by scanning electrochemical microscopy. M-co (M: Pd, Ag, Au).

    PubMed

    Fernández, José L; Walsh, Darren A; Bard, Allen J

    2005-01-12

    We propose guidelines for the design of improved bimetallic (and related) electrocatalysts for the oxygen reduction reaction (ORR) in acidic media. This guide is based on simple thermodynamic principles assuming a simple mechanism where one metal breaks the oxygen-oxygen bond of molecular O(2) and the other metal acts to reduce the resulting adsorbed atomic oxygen. Analysis of the Gibbs free energies of these two reactions guides the selection of combinations of metals that can produce alloy surfaces with enhanced activity for the ORR when compared to the constituent metals. Selected systems have been tested by fabricating arrays of metallic catalysts consisting of various binary and ternary combinations of Pd, Au, Ag, and Co deposited on glassy carbon (GC) substrates. The electrocatalytic activity of these materials for the ORR in acidic medium was examined using scanning electrochemical microscopy (SECM) in a new rapid-imaging mode. This was used to rapidly screen arrays covering a wide range of catalyst compositions for their activity for the ORR in 0.5 M H(2)SO(4). Using the SECM technique, we have identified combinations of metals with enhanced electrocatalytic activities when compared with the constituent, pure metals. Addition of Co to Pd, Au, and Ag clearly decreases the ORR overpotential, in agreement with the proposed model. Catalyst spots that exhibited enhanced electrocatalytic activity in the SECM screening technique were then examined using classical rotating disk electrode (RDE) experiments. The activity of carbon black supported catalyst mixtures on a GC RDE and the electrocatalytic activity determined using the SECM screening technique showed excellent agreement. C/Pd-Co electrodes (10-30% Co) exhibited remarkable activity for ORR catalysis, close to that of carbon-supported Pt.

  1. One step electrochemical synthesis of bimetallic PdAu supported on nafion–graphene ribbon film for ethanol electrooxidation

    SciTech Connect

    Shendage, Suresh S. Singh, Abilash S.; Nagarkar, Jayashree M.

    2015-10-15

    Highlights: • Electrochemical deposition of bimetallic PdAu NPs. • Highly loaded PdAu NPs are obtained. • Nafion–graphene supported PdAu NPs shows good activity for ethanol electrooxidation. - Abstract: A nafion–graphene ribbon (Nf–GR) supported bimetallic PdAu nanoparticles (PdAu/Nf–GR) catalyst was prepared by electrochemical codeposition of Pd and Au at constant potential. The prepared catalyst was characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM) and X-ray diffraction analysis (XRD). The average particle size of PdAu nanoparticles (NPs) determined from XRD was 3.5 nm. The electrocatalytic activity of the PdAu/Nf–GR catalyst was examined by cyclic voltametry. It was observed that the as prepared catalyst showed efficient activity and good stability for ethanol electrooxidation in alkaline medium.

  2. The formation of silica, alumina and zirconia supported high surface area monometallic and bimetallic catalysts. Progress report

    SciTech Connect

    Gonzalez, R.D.

    1993-12-01

    During the current granting period, 12/01/92--11/30/93, studies have progressed along four fronts: (1) Preparation of high surface area Pt/SiO{sub 2} catalysts; (2) preparation of high surface area Pt/Al{sub 2}O{sub 3} catalysts; (3) preparation of high surface area promoted zirconia superacid catalysts and, (4) stabilization and sintering of porous Pt/SiO{sub 2} catalysts. In addition to these current studies a major review article on previously funded DOE research has been completed and will appear in Catalysis Reviews. Results of these studies are briefly described.

  3. Dynamic Structural Changes of SiO₂ Supported Pt-Ni Bimetallic Catalysts over Redox Treatments Revealed by NMR and EPR

    SciTech Connect

    Xu, Suochang; Walter, Eric D.; Zhao, Zhenchao; Hu, Mary Y.; Han, Xiuwen; Hu, Jian Z.; Bao, Xinhe

    2015-08-18

    SiO2 supported Pt-Ni bimetallic catalysts with different nickel loadings were prepared and their structural changes after redox treatments were studied by XRD, NMR, and EPR. It is found that the paramagnetic Ni species are mainly located on the surface of silica lattice. The relaxation of detected 29Si nuclei in our samples is mainly governed by a spin-diffusion mechanism. The paramagnetic effects are reflected in the spin-lattice relaxation of Q4 species, with the oxidized samples presenting faster relaxation rates than the corresponding reduced ones. Meanwhile the Q3 species, which are in close contact with the paramagnetic nickel ions, are “spectrally invisible”. In reducing atmosphere Ni gradually diffuses into Pt NPs to form PtNi alloys. While under oxidization treatment, the alloyed Ni atoms migrate outward from the core of Pt NPs and are oxidized. The main EPR spectrum results from reduced nickel species, and the reduced samples show stronger EPR signal than the corresponding oxidized ones. However, in the reduced samples, the superparamagnetic or ferromagnetic metallic Ni particles were inside the PtNi NPs, making their influence on the 29Si relaxation in the SiO2 support weaker than the oxidized samples.

  4. Uninterrupted galvanic reaction for scalable and rapid synthesis of metallic and bimetallic sponges/dendrites as efficient catalysts for 4-nitrophenol reduction.

    PubMed

    Barman, Barun Kumar; Nanda, Karuna Kar

    2015-03-01

    Here, we demonstrate an uninterrupted galvanic replacement reaction (GRR) for the synthesis of metallic (Ag, Cu and Sn) and bimetallic (Cu-M, M=Ag, Au, Pt and Pd) sponges/dendrites by sacrificing the low reduction potential metals (Mg in our case) in acidic medium. The acidic medium prevents the oxide formation on Mg surface and facilitates the uninterrupted reaction. The morphology of dendritic/spongy structures is controlled by the volume of acid used for this reaction. The growth mechanism of the spongy/dendritic microstructures is explained by diffusion-limited aggregate model (DLA), which is also largely affected by the volume of acid. The significance of this method is that the yield can be easily predicted, which is a major challenge for the commercialization of the products. Furthermore, the synthesis is complete in 1-2 minutes at room temperature. We show that the sponges/dendrites efficiently act as catalysts to reduce 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH4-a widely studied conversion process. PMID:25628256

  5. Uninterrupted galvanic reaction for scalable and rapid synthesis of metallic and bimetallic sponges/dendrites as efficient catalysts for 4-nitrophenol reduction.

    PubMed

    Barman, Barun Kumar; Nanda, Karuna Kar

    2015-03-01

    Here, we demonstrate an uninterrupted galvanic replacement reaction (GRR) for the synthesis of metallic (Ag, Cu and Sn) and bimetallic (Cu-M, M=Ag, Au, Pt and Pd) sponges/dendrites by sacrificing the low reduction potential metals (Mg in our case) in acidic medium. The acidic medium prevents the oxide formation on Mg surface and facilitates the uninterrupted reaction. The morphology of dendritic/spongy structures is controlled by the volume of acid used for this reaction. The growth mechanism of the spongy/dendritic microstructures is explained by diffusion-limited aggregate model (DLA), which is also largely affected by the volume of acid. The significance of this method is that the yield can be easily predicted, which is a major challenge for the commercialization of the products. Furthermore, the synthesis is complete in 1-2 minutes at room temperature. We show that the sponges/dendrites efficiently act as catalysts to reduce 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH4-a widely studied conversion process.

  6. Fabrication of PdCo Bimetallic Nanoparticles Anchored on Three-Dimensional Ordered N-Doped Porous Carbon as an Efficient Catalyst for Oxygen Reduction Reaction.

    PubMed

    Xue, Hairong; Tang, Jing; Gong, Hao; Guo, Hu; Fan, Xiaoli; Wang, Tao; He, Jianping; Yamauchi, Yusuke

    2016-08-17

    PdCo bimetallic nanoparticles (NPs) anchored on three-dimensional (3D) ordered N-doped porous carbon (PdCo/NPC) were fabricated by an in situ synthesis. Within this composite, N-doped porous carbon (NPC) with an ordered mesoporous structure possesses a high surface area (659.6 m(2) g(-1)), which can facilitate electrolyte infiltration. NPC also acts as a perfect 3D conductive network, guaranteeing fast electron transport. In addition, homogeneously distributed PdCo alloy NPs (∼15 nm) combined with the doping of the N element can significantly improve the electrocatalytic activity for the oxygen reduction reaction (ORR). Due to the structural and material superiority, although the weight percentage of PdCo NPs (∼8 wt%) is much smaller than that of commercial Pt/C (20 wt%), the PdCo/NPC catalyst exhibits similar excellent electrocatalytic activity; however, its superior durability and methanol-tolerance ability of the ORR are as great as those of commercial Pt/C in alkaline media.

  7. Fabrication of PdCo Bimetallic Nanoparticles Anchored on Three-Dimensional Ordered N-Doped Porous Carbon as an Efficient Catalyst for Oxygen Reduction Reaction.

    PubMed

    Xue, Hairong; Tang, Jing; Gong, Hao; Guo, Hu; Fan, Xiaoli; Wang, Tao; He, Jianping; Yamauchi, Yusuke

    2016-08-17

    PdCo bimetallic nanoparticles (NPs) anchored on three-dimensional (3D) ordered N-doped porous carbon (PdCo/NPC) were fabricated by an in situ synthesis. Within this composite, N-doped porous carbon (NPC) with an ordered mesoporous structure possesses a high surface area (659.6 m(2) g(-1)), which can facilitate electrolyte infiltration. NPC also acts as a perfect 3D conductive network, guaranteeing fast electron transport. In addition, homogeneously distributed PdCo alloy NPs (∼15 nm) combined with the doping of the N element can significantly improve the electrocatalytic activity for the oxygen reduction reaction (ORR). Due to the structural and material superiority, although the weight percentage of PdCo NPs (∼8 wt%) is much smaller than that of commercial Pt/C (20 wt%), the PdCo/NPC catalyst exhibits similar excellent electrocatalytic activity; however, its superior durability and methanol-tolerance ability of the ORR are as great as those of commercial Pt/C in alkaline media. PMID:27441490

  8. Bimetallic cerium-copper nanoparticles embedded in ordered mesoporous carbons as effective catalysts for the selective catalytic reduction of NO with NH₃.

    PubMed

    Chen, Jinghuan; Cao, Feifei; Qu, Ruiyang; Gao, Xiang; Cen, Kefa

    2015-10-15

    Bimetallic cerium-copper nanoparticles embedded in ordered mesoporous carbons (OMCs) with various Ce/Cu ratios were synthesized by "one-pot" self-assembly method, and their activities for the selective catalytic reduction (SCR) of NO with ammonia were studied. The structural and textural properties, surface chemistry, acidity, and reducibility were investigated by various techniques. Results showed that NO conversion was greatly influenced by the weight ratio of Ce to Cu. An appropriate Ce/Cu ratio in OMCs could enhance catalytic performance; the optimal catalytic performance was obtained with Ce5Cu5-OMC. Ordered mesoporous structures were formed for all synthesized samples. When Ce or Cu was incorporated into the OMCs, the amount of surface acidic oxygen functional groups increased, thereby promoting the acidic properties of the OMCs, especially those of the Cu-rich OMCs. The surface Cu(2+) species may accelerate ammonia activation and may play an important role in SCR reaction. The temperature-programmed reduction results illustrated that the Cu-rich OMCs had better reducibility, and the appropriate Ce/Cu ratio could further enhance the redox ability of the CexCuy-OMC catalysts. The existing redox cycle (Ce(4+)+Cu(+)↔Cu(2+)+Ce(3+)) promoted the activation of NH3 and consequently improved NH3-SCR activity.

  9. Propane dehydrogenation over Pt-Cu bimetallic catalysts: the nature of coke deposition and the role of copper

    NASA Astrophysics Data System (ADS)

    Han, Zhiping; Li, Shuirong; Jiang, Feng; Wang, Tuo; Ma, Xinbin; Gong, Jinlong

    2014-08-01

    This paper describes an investigation of the promotional effect of Cu on the catalytic performance of Pt/Al2O3 catalysts for propane dehydrogenation. We have shown that Pt/Al2O3 catalysts possess higher propylene selectivity and lower deactivation rate as well as enhanced anti-coking ability upon Cu addition. The optimized loading content of Cu is 0.5 wt%, which increases the propylene selectivity to 90.8% with a propylene yield of 36.5%. The origin of the enhanced catalytic performance and anti-coking ability of the Pt-Cu/Al2O3 catalyst is ascribed to the intimate interaction between Pt and Cu, which is confirmed by the change of particle morphology and atomic electronic environment of the catalyst. The Pt-Cu interaction inhibits propylene adsorption and elevates the energy barrier of C-C bond rupture. The inhibited propylene adsorption diminishes the possibility of coke formation and suppresses the cracking reaction towards the formation of lighter hydrocarbons on Pt-Cu/Al2O3, while a higher energy barrier for C-C bond cleavage suppresses the methane formation.

  10. Chirality specific and spatially uniform synthesis of single-walled carbon nanotubes from a sputtered Co-W bimetallic catalyst

    NASA Astrophysics Data System (ADS)

    An, Hua; Kumamoto, Akihito; Takezaki, Hiroki; Ohyama, Shinnosuke; Qian, Yang; Inoue, Taiki; Ikuhara, Yuichi; Chiashi, Shohei; Xiang, Rong; Maruyama, Shigeo

    2016-07-01

    Synthesis of single-walled carbon nanotubes (SWNTs) with well-defined atomic arrangements has been widely recognized in the past few decades as the biggest challenge in the SWNT community, and has become a bottleneck for the application of SWNTs in nano-electronics. Here, we report a selective synthesis of (12, 6) SWNTs with an enrichment of 50%-70% by chemical vapor deposition (CVD) using sputtered Co-W as a catalyst. This is achieved under much milder reduction and growth conditions than those in the previous report using transition-metal molecule clusters as catalyst precursors (Nature, 2014, 510, 522). Meanwhile, in-plane transmission electron microscopy unambiguously identified an intermediate structure of Co6W6C, which is strongly associated with selective growth. However, most of the W atoms disappear after a 5 min CVD growth, which implies that anchoring W may be important in this puzzling Co-W system.Synthesis of single-walled carbon nanotubes (SWNTs) with well-defined atomic arrangements has been widely recognized in the past few decades as the biggest challenge in the SWNT community, and has become a bottleneck for the application of SWNTs in nano-electronics. Here, we report a selective synthesis of (12, 6) SWNTs with an enrichment of 50%-70% by chemical vapor deposition (CVD) using sputtered Co-W as a catalyst. This is achieved under much milder reduction and growth conditions than those in the previous report using transition-metal molecule clusters as catalyst precursors (Nature, 2014, 510, 522). Meanwhile, in-plane transmission electron microscopy unambiguously identified an intermediate structure of Co6W6C, which is strongly associated with selective growth. However, most of the W atoms disappear after a 5 min CVD growth, which implies that anchoring W may be important in this puzzling Co-W system. Electronic supplementary information (ESI) available: Raman spectroscopy (G-band) of SWNTs grown from Co and Co-W catalyst; Kataura plot for chirality

  11. Synthesis and reactivity of new bimetallic oxynitrides

    SciTech Connect

    Oyama, S.T.; Ramanathan, S.; Yu, C.C.

    1995-12-31

    A new series of bimetallic oxynitride catalysts, M{sub 1}M{sub 2}O{sub x}N{sub y} (M{sub 1} = V{sub 1}, Nb, Cr, Mn and Co, M{sub 2} = Mo or W), was prepared by nitriding the bimetallic oxide precursors in an ammonia gas stream at 1000 cm{sup 3}/min (6.8x10{sup 2} {mu}mol s{sup -1}) while the temperature was raised at 5 K/min (8.3x10{sup -2} K s{sup -1}). The catalysts were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, CO chemisorption and surface area measurements. The catalytic activity of these catalysts for mixture containing 3000 ppm sulfur (dibenzothiophene), 2000 ppm nitrogen (quinoline), 500 ppm oxygen (benzofuran), 20 wt% aromatics (15 wt% tetralin and 5 wt% amylbenzene) and balance aliphatics (tetradecane). The activities of the bimetallic oxynitrides were compared to a commercial sulfided Ni-Mo/Al{sub 2}O{sub 3} catalyst tested at the same conditions. The bimetallic oxynitrides were active for quinoline HDN and V-Mo-O-N exhibiting higher HDN activity than the commercial Ni-Mo/Al{sub 2}O{sub 3} catalyst. The HDS activity of the bimetallic oxynitrides ranged from 9-37% with Co-Mo-O-N showing the highest HDS activity among the oxynitrides tested.

  12. Catalytic Oxidation of Hydroquinone in Aqueous Solution over Bimetallic PdCo Catalyst Supported on Carbon: Effect of Interferents and Electrochemical Measurement.

    PubMed

    Ye, Weichun; Shi, Xuezhao; Zhang, Yane; Hong, Chenghui; Wang, Chunming; Budzianowski, Wojciech M; Xue, Desheng

    2016-02-10

    Palladium-cobalt alloy nanoparticles were synthesized and dispersed on carbon black support, aiming to have a less expensive catalyst. Catalytic behaviors of PdCo/C catalyst for the oxidation of hydroquinone (HQ) with H2O2 in aqueous solution were evaluated using high-performance liquid chromatography (HPLC). The results revealed that PdCo/C catalyst had better catalytic activity than an equal amount of commercial Pd/C and Co/C catalysts because of the d-band hybridization between Pd and Co. The effects of pH value, solvent, and various interferents including inorganic and organic compounds on the efficiency of HQ oxidation were further investigated. Furthermore, on the basis of mixed potential theory, comprehensive electrochemical measurements such as the open-circuit potential-time (OCP-t) technique and Tafel plot were efficient to assess the catalytic activity of the catalyst, and the results obtained were consistent with those of HPLC measurements. The efficient HQ oxidation was closely associated with the catalytic activity of PdCo nanoparticles because they accelerated the electron-transfer process and facilitated the generation of OH radicals. PMID:26788813

  13. Chirality specific and spatially uniform synthesis of single-walled carbon nanotubes from a sputtered Co-W bimetallic catalyst.

    PubMed

    An, Hua; Kumamoto, Akihito; Takezaki, Hiroki; Ohyama, Shinnosuke; Qian, Yang; Inoue, Taiki; Ikuhara, Yuichi; Chiashi, Shohei; Xiang, Rong; Maruyama, Shigeo

    2016-08-14

    Synthesis of single-walled carbon nanotubes (SWNTs) with well-defined atomic arrangements has been widely recognized in the past few decades as the biggest challenge in the SWNT community, and has become a bottleneck for the application of SWNTs in nano-electronics. Here, we report a selective synthesis of (12, 6) SWNTs with an enrichment of 50%-70% by chemical vapor deposition (CVD) using sputtered Co-W as a catalyst. This is achieved under much milder reduction and growth conditions than those in the previous report using transition-metal molecule clusters as catalyst precursors (Nature, 2014, 510, 522). Meanwhile, in-plane transmission electron microscopy unambiguously identified an intermediate structure of Co6W6C, which is strongly associated with selective growth. However, most of the W atoms disappear after a 5 min CVD growth, which implies that anchoring W may be important in this puzzling Co-W system. PMID:27412697

  14. Development of a PtSn bimetallic catalyst for direct fuel cells using bio-butanol fuel.

    PubMed

    Puthiyapura, V K; Brett, D J L; Russell, A E; Lin, W F; Hardacre, C

    2015-09-01

    Pt and PtSn catalysts were studied for n-butanol electro-oxidation at various temperatures. PtSn showed a higher activity towards butanol electro-oxidation compared to Pt in acidic media. The onset potential for n-butanol oxidation on PtSn is ∼520 mV lower than that found on Pt, and significantly lower activation energy was found for PtSn compared with that for Pt. PMID:26214283

  15. The effects of cerium doping concentration on the properties and photocatalytic activity of bimetallic Mo/Ce catalyst

    NASA Astrophysics Data System (ADS)

    Allaedini, Ghazaleh; Tasirin, Siti Masrinda; Aminayi, Payam

    2016-10-01

    In this study, the characterization and photocatalytic activity of MoO3 nanoparticles doped with various doping concentrations of cerium have been investigated. The Fourier transform infrared (FT-IR) spectra of the prepared catalysts confirmed that MoO3 particles have been successfully doped by cerium. Field emission scanning electron microscopy (FESEM) was performed to visualize the surface morphology of the obtained catalysts. The XRD patterns suggested that the crystallinity of the sample with the lowest doping concentration of 15 mol % was higher in comparison with samples of higher doping concentrations. The volume-averaged crystal sizes of the obtained catalysts were calculated to be 25, 28, and 32 nm for 15, 35, and 60 mol % samples, respectively. The photocatalytic activity along with the reaction kinetics of Ce-doped MoO3 nanoparticles have also been investigated through the dye degradation of methyl orange. The synthesized Ce-doped MoO3 particles with the lowest dopant concentration of 15 mol % exhibited the highest photocatalytic activity for methyl orange dye degradation. It was observed that photo-degradation activity decreased with an increase in the doping concentration of cerium. The predicted rate constants for samples with 15, 35, and 60 mol % doping concentrations were found to be 0.0432, 0.035, and 0.029 min-1, respectively.

  16. Pt-Pd bimetallic nanoparticles dispersed in an ionic liquid and peroxidase immobilized on nanoclay applied in the development of a biosensor.

    PubMed

    Pusch, Jessica M E; Brondani, Daniela; Luza, Leandro; Dupont, Jairton; Vieira, Iolanda C

    2013-09-01

    Pt-Pd bimetallic alloy nanoparticles (NPs) dispersed in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (Pt-Pd-BMI·PF6) were employed together with a peroxidase (PO) enzyme from cauliflower immobilized on nanoclay for the development of a new biosensor for polyphenol determination by square-wave voltammetry (SWV). The biosensor demonstrated good repeatability and reproducibility, low limit of detection (LOD = 3.7 × 10(-7) mol L(-1) for caffeic acid (CA)), and adequate lifetime and stability (maintaining over 80% of the response over 80 days of evaluation, and allowing over 600 measurements by SWV for each electrode). Under optimized conditions, the proposed biosensor was applied in the determination of the bioelectrochemical polyphenolic index (BPI) for samples of commercial white wine, using CA as the phenolic compound standard. The recovery of CA from wine samples ranged from 95.5 to 108.3%. The values for the polyphenolic content obtained using the proposed biosensor showed a good correlation (r = 0.990) with those obtained with the reference spectrophotometric method (Folin-Ciocalteu method). Therefore, the proposed biosensor represents a useful tool for the rapid and accurate monitoring of polyphenolic content in wine samples and may also be applicable to other beverage samples, such as juices and teas.

  17. Catalyst dispersion and activity under conditions of temperature-staged liquefaction. Final report

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1993-02-01

    This research program involves the investigation of the use of highly dispersed catalyst precursors for the pretreatment of coals by mild hydrogenation. During the course of this effort solvent preswelling of the coal was evaluated as a means of deeply impregnating catalysts into coal, active phases of catalysts under reaction conditions were studied and the impact of these techniques were evaluated during pretreatment and temperature-staged liquefaction. Two coals, a Texas subbituminous and a Utah high volatile A bituminous, were used to examine the effects of solvent swelling pretreatment and catalyst impregnation on conversion behavior at 275{degrees}C, representative of the first, low-temperature stage in a temperature-staged liquefaction reaction. Ferrous sulfate, iron pentacarbonyl, ammonium tetrathiomolybdate, and molybdenum hexacarbonyl were used as catalyst precursors. Without swelling pretreatment, impregnation of both coals increased conversion, mainly through increased yields of preasphaltenes.

  18. Catalyst dispersion and activity under conditions of temperature-staged liquefaction

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1993-02-01

    This research program involves the investigation of the use of highly dispersed catalyst precursors for the pretreatment of coals by mild hydrogenation. During the course of this effort solvent preswelling of the coal was evaluated as a means of deeply impregnating catalysts into coal, active phases of catalysts under reaction conditions were studied and the impact of these techniques were evaluated during pretreatment and temperature-staged liquefaction. Two coals, a Texas subbituminous and a Utah high volatile A bituminous, were used to examine the effects of solvent swelling pretreatment and catalyst impregnation on conversion behavior at 275[degrees]C, representative of the first, low-temperature stage in a temperature-staged liquefaction reaction. Ferrous sulfate, iron pentacarbonyl, ammonium tetrathiomolybdate, and molybdenum hexacarbonyl were used as catalyst precursors. Without swelling pretreatment, impregnation of both coals increased conversion, mainly through increased yields of preasphaltenes.

  19. Kinetics and mechanism of the liquid-phase oxidation of cyclohexene. IV. Decomposition of cyclohexenyl hydroperoxide in the presence of bimetallic catalysts

    SciTech Connect

    Baevskii, M.Yu.; Litvintsev, I.Yu.; Sapunov, V.N.

    1988-11-01

    The kinetic principles of the decomposition of cyclohexenyl hydroperoxide in cyclohexene solution in homogeneous catalysis by vanadium-containing bimetallic systems were investigated. For Co-V and Pb-V, the formation of complexes with low activity in catalysis was demonstrated by kinetic and spectral methods. A mathematical model was obtained for the process, adequately describing the conversions of cyclohexenyl hydroperoxide in the presence of bimetallic systems.

  20. Run 263 with Black Thunder Mine subbituminous coal and dispersed molybdenum catalysts

    SciTech Connect

    Not Available

    1992-12-01

    This report presents the results of Run 263 performed at the Advanced Coal Liquefaction R D Facility in Wilsonville, Alabama. The run started on October 31, 1991 and continued until February 23, 1992. Tests were conducted by operating the reactors in the Close-Coupled Integrated Two-Stage Liquefaction mode and by processing Black Thunder Mine subbituminous coal from Wyodak-Anderson seam in Wyoming Powder River Basin. Half volume reactors were used for the entire run. In the first part of Run 263, a dispersed molybdenum catalyst was evaluated for its performance without a supported catalyst in the second stage. Molyvan L and Molyvan 822 (commercially available as friction reducing lubricants) were used as precursors for the dispersed molybdenum catalyst. The effect of the dispersed catalyst on eliminating the solids buildup was also evaluated. For the second part of the run, the hybrid catalyst system was tested with supported Criterion 324 1/1611 catalyst in the second stage at catalyst replacement rates of 2 and 3 lb/ton of MF coal. The molybdenum concentration was 100--200 ppm based on MF coal. Iron oxide was used as a slurry catalyst precursor at a rate of 1--2 wt % MF coal throughout the run with dimethyl disulfide (DMDS) as the sulfiding agent. The close-coupled reactor unit was on-stream for 2482 hours for an on-stream factor of 91.2% and the ROSE-SR[sup sm] unit was on-feed for 2126 hours for an on-stream factor of 96.4% for the entire run.

  1. Run 263 with Black Thunder Mine subbituminous coal and dispersed molybdenum catalysts. Technical progress report

    SciTech Connect

    Not Available

    1992-12-01

    This report presents the results of Run 263 performed at the Advanced Coal Liquefaction R&D Facility in Wilsonville, Alabama. The run started on October 31, 1991 and continued until February 23, 1992. Tests were conducted by operating the reactors in the Close-Coupled Integrated Two-Stage Liquefaction mode and by processing Black Thunder Mine subbituminous coal from Wyodak-Anderson seam in Wyoming Powder River Basin. Half volume reactors were used for the entire run. In the first part of Run 263, a dispersed molybdenum catalyst was evaluated for its performance without a supported catalyst in the second stage. Molyvan L and Molyvan 822 (commercially available as friction reducing lubricants) were used as precursors for the dispersed molybdenum catalyst. The effect of the dispersed catalyst on eliminating the solids buildup was also evaluated. For the second part of the run, the hybrid catalyst system was tested with supported Criterion 324 1/1611 catalyst in the second stage at catalyst replacement rates of 2 and 3 lb/ton of MF coal. The molybdenum concentration was 100--200 ppm based on MF coal. Iron oxide was used as a slurry catalyst precursor at a rate of 1--2 wt % MF coal throughout the run with dimethyl disulfide (DMDS) as the sulfiding agent. The close-coupled reactor unit was on-stream for 2482 hours for an on-stream factor of 91.2% and the ROSE-SR{sup sm} unit was on-feed for 2126 hours for an on-stream factor of 96.4% for the entire run.

  2. The calculation of surface orbital energies for specific types of active sites on dispersed metal catalysts

    SciTech Connect

    Augustine, R.L.; Lahanas, K.M.; Cole, F.

    1992-11-01

    An angular overlap calculation has been used to determine the s, p, and d orbital energy levels of the different types of surface sites present on dispersed metal catalysts. These data can permit a Frontier Molecular Orbital treatment of specific site activities as long as the surface orbital availability for overlap with adsorbed substrates is considered along with its energy value and symmetry.

  3. The calculation of surface orbital energies for specific types of active sites on dispersed metal catalysts

    SciTech Connect

    Augustine, R.L.; Lahanas, K.M.; Cole, F.

    1992-01-01

    An angular overlap calculation has been used to determine the s, p, and d orbital energy levels of the different types of surface sites present on dispersed metal catalysts. These data can permit a Frontier Molecular Orbital treatment of specific site activities as long as the surface orbital availability for overlap with adsorbed substrates is considered along with its energy value and symmetry.

  4. Catalyst dispersion and activity under conditions of temperature-staged liquefaction

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1992-02-01

    The general objectives of this research are (1) to investigate the use of highly dispersed catalysts for the pretreatment of coal by mild hydrogenation, (2) to identify the active forms of the catalysts under reaction conditions and (3) to clarify the mechanisms of catalysis. The ultimate objective is to ascertain if mild catalytic hydrogenation resulting in very limited or no coal solubilization is an advantageous pretreatment for the transformation of coal into transportable fuels. The experimental program will focus upon the development of effective methods of impregnating coal with catalysts, evaluating the conditions under which the catalysts are most active and establishing the relative impact of improved impregnation on conversion and product distributions obtained from coal hydrogenation.

  5. Improvements of Pd/C Catalyst Support Characteristics by Various Physical Dispersion Methods.

    PubMed

    Baek, Jae Ho; Kim, Ji Sun; Moon, Myung-Jun; Lee, Man Sig

    2015-07-01

    Pd/C catalysts were prepared by ion exchange in aqueous solution. Physical dispersion methods including sonication, high share mixer and stirrer were used for though high dispersion of carbon. The physical properties of the prepared Pd/C particles were investigated by BET, XRD, and FE-TEM. The dispersion of Pd nanoparticles on carbon was measured on the basis of CO adsorption capacity using a pulse technique. FE-TEM micrographs showed that Pd nano particles possessed a spherical morphology with a narrow size distribution, with particles sizes ranging from 2-25 nm. The Pd particles prepared using sonication and high share mixer are well dispersed compared to the stirrer method. In addition, metal dispersions as calculated by CO uptake were 11.3, 20.4, and 25.0% for the stirrer, sonication and high share mixer methods, respectively. PMID:26373131

  6. Synthesis, characterization, and growth simulations of Cu–Pt bimetallic nanoclusters

    PubMed Central

    Khanal, Subarna; Spitale, Ana; Bhattarai, Nabraj; Bahena, Daniel; Velazquez-Salazar, J Jesus; Mejía-Rosales, Sergio

    2014-01-01

    Summary Highly monodispersed Cu–Pt bimetallic nanoclusters were synthesized by a facile synthesis approach. Analysis of transmission electron microscopy (TEM) and spherical aberration (C s)-corrected scanning transmission electron microscopy (STEM) images shows that the average diameter of the Cu–Pt nanoclusters is 3.0 ± 1.0 nm. The high angle annular dark field (HAADF-STEM) images, intensity profiles, and energy dispersive X-ray spectroscopy (EDX) line scans, allowed us to study the distribution of Cu and Pt with atomistic resolution, finding that Pt is embedded randomly in the Cu lattice. A novel simulation method is applied to study the growth mechanism, which shows the formation of alloy structures in good agreement with the experimental evidence. The findings give insight into the formation mechanism of the nanosized Cu–Pt bimetallic catalysts. PMID:25247120

  7. Preparation of highly dispersed NiMo catalysts supported on carbon black particles of hollow spheres

    SciTech Connect

    Sakanishi, K.; Hasuo, H.; Mochida, I.

    1995-12-01

    One of unique carbon blacks, Ketjen Black (KB) which has extremely high surface area and low specific gravity, was selected as a catalyst support to prepare a highly dispersed NiMo catalyst with the function for recovery and the high activity for hydrogenation. KB-supported NiMo catalysts were prepared by means of impregnation, ion exchange, and incipient wetness methods from various kinds and amounts of Ni and Mo salts, and their activities were examined in the hydrogenation of 1-methyinaphthalene(1-MN) using a magnetic-stirred autoclave of 50 ml capacity at 380{degrees}C for 40 min under 10 MPa H{sub 2} reaction pressure. The catalyst, prepared from (NH{sub 4}){sub 2}MoS{sub 4} and Ni(OAc){sub 2} in their methanol solution by successive impregnations of Mo10% and Ni(2 wt%) in this order supported on nitric acid-treated carbon black(KB JD-O), provided the highest conversion of 86% to methyl-tetralins. Combinations of metal salts soluble in organic solvent, impregnation solvents, and surface properties of carbon black are suggested to be important for the preparation of highly active catalysts with higher dispersions of Ni and Mo on the carbon black, because they are easily agglomerated in impregnation solvent. It is also noted that KB-supported NiMo catalysts showed much higher activity for the hydrogenation than a commercial NiMo/Al{sub 2}O{sub 3} with the smaller weight of catalyst.

  8. Homogeneous Pt-bimetallic Electrocatalysts

    SciTech Connect

    Wang, Chao; Chi, Miaofang; More, Karren Leslie; Markovic, Nenad; Stamenkovic, Vojislav

    2011-01-01

    Alloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. Systematic studies of alloy catalysts are, however, often compromised by inhomogeneous distribution of alloying components. Here we introduce a general approach for the synthesis of monodispersed and highly homogeneous Pt-bimetallic alloy nanocatalysts. Pt{sub 3}M (where M = Fe, Ni, or Co) nanoparticles were prepared by an organic solvothermal method and then supported on high surface area carbon. These catalysts attained a homogeneous distribution of elements, as demonstrated by atomic-scale elemental analysis using scanning transmission electron microscopy. They also exhibited high catalytic activities for the oxygen reduction reaction (ORR), with improvement factors of 2-3 versus conventional Pt/carbon catalysts. The measured ORR catalytic activities for Pt{sub 3}M nanocatalysts validated the volcano curve established on extended surfaces, with Pt{sub 3}Co being the most active alloy.

  9. Bimetallic Pt-Au nanocatalysts electrochemically deposited on graphene and their electrocatalytic characteristics towards oxygen reduction and methanol oxidation.

    PubMed

    Hu, Yaojuan; Zhang, Hua; Wu, Ping; Zhang, Hui; Zhou, Bo; Cai, Chenxin

    2011-03-01

    The burgeoning demand for clean and energy-efficient fuel cell system requires electrocatalysts to deliver greater activity and selectivity. Bimetallic catalysts have proven superior to single metal catalysts in this respect. This work reports the preparation, characterization, and electrocatalytic characteristics of a new bimetallic nanocatalyst. The catalyst, Pt-Au-graphene, was synthesized by electrodeposition of Pt-Au nanostructures on the surface of graphene sheets, and characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), and voltammetry. The morphology and composition of the nanocatalyst can be easily controlled by adjusting the molar ratio between Pt and Au precursors. The electrocatalytic characteristics of the nanocatalysts for the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) were systematically investigated by cyclic voltammetry. The Pt-Au-graphene catalysts exhibits higher catalytic activity than Au-graphene and Pt-graphene catalysts for both the ORR and the MOR, and the highest activity is obtained at a Pt/Au molar ratio of 2:1. Moreover, graphene can significantly enhance the long-term stability of the nanocatalyst toward the MOR by effectively removing the accumulated carbonaceous species formed in the oxidation of methanol from the surface of the catalyst. Therefore, this work has demonstrated that a higher performance of ORR and the MOR could be realized at the Pt-Au-graphene electrocatalyst while Pt utilization also could be greatly diminished. This method may open a general approach for the morphology-controlled synthesis of bimetallic Pt-M nanocatalysts, which can be expected to have promising applications in fuel cells. PMID:21229152

  10. Influence of the support on the activity and selectivity of high dispersion Fe catalysts in the Fischer-Tropsch reaction

    SciTech Connect

    Cagnoli, M.V.; Marchetti, S.G.; Gallegos, N.G.; Alvarez, A.M.; Mercader, R.C.; Yeramian, A.A. Facultad de Ciencias Exactas, La Plata )

    1990-05-01

    In order to study the influence of the support on high dispersion catalysts used for the CO hydrogenation reaction, two catalysts, Fe/SiO{sub 2} and Fe/Al{sub 2}O{sub 3}, were prepared by the dry impregnation method. Selective chemisorption of CO, volumetric oxidation, and Moessbauer spectroscopy were used to determine the Fe species present as well as the metallic crystal size, the degree of dispersion, and the reduction percentage. The presence of small Fe{sup 0} crystallites with high dispersion was determined in both catalysts. Reaction rates were measured in a differential reactor and significant differences, about one order of magnitude less for the Al{sub 2}O{sub 3} than for the SiO{sub 2} supported catalysts, were found in the methane turnover frequencies. They are attributed to the interaction between the metal and the supports. The selectivity differences is also discussed in connection with distinct surface properties.

  11. Highly dispersed catalysts for coal liquefaction. Phase 1 final report, August 23--November 22, 1994

    SciTech Connect

    Hirschon, A.S.; Wilson, R.B.; Ghaly, O.

    1995-03-22

    The ultimate goal of this project is to develop novel processes for making the conversion of coal into distillable liquids competitive to that of petroleum products in the range of $25/bbl. The objectives of Phase 1 were to determine the utility of new precursors to highly dispersed catalysts for use of syngas atmospheres in coal liquefaction, and to estimate the effect of such implementation on the cost of the final product. The project is divided into three technical tasks. Tasks 1 and 2 are the analyses and liquefaction experiments, respectively, and Task 3 deals with the economic effects of using these methods during coal liquefaction. Results are presented on the following: Analytical Support--screening tests and second-stage conversions; Laboratory-Scale Operations--catalysts, coal conversion in synthetic solvents, Black Thunder screening studies, and two-stage liquefaction experiments; and Technical and economic Assessment--commercial liquefaction plant description, liquefaction plant cost; and economic analysis.

  12. Synthesis, Characterization, and Catalytic Function of Novel Highly Dispersed Tungsten Oxide Catalysts on Mesoporous Silica

    SciTech Connect

    Herrera, Jose E.; Kwak, Ja Hun; Hu, Jian Zhi; Wang, Yong; Peden, Charles HF; Macht, Josef; Iglesia, Enrique

    2006-04-01

    The physical and chemical properties of tungsten oxide supported on SBA-15 mesoporous silica prepared by a controlled grafting process through atomic layer deposition (ALD) were studied using complementary characterization methods. X-ray diffraction, optical absorption and transmission electron microscopy showed that tungsten oxide species are highly dispersed on SBA-15 surfaces, even at 30 wt.% WOx contents (surface density: 1.33 WOx/nm2). ALD methods led to samples with much better thermal stability than those prepared via impregnation. Dehydration reactions of 2-butanol and methanol dehydration were used as probe reactions. Differences in reaction rates between the samples prepared by ALD and conventional impregnation reflect the sintering resistance of catalysts prepared by ALD. Notably, temperature programmed oxidation of spent catalysts showed that carbon formation was not responsible for the different dehydration rates in samples prepared by ALD and impregnation..

  13. Synthesis, Characterization, and Catalytic Performance of Highly Dispersed Vandium Grafted SBA-15 Catalyst

    SciTech Connect

    Du,G.; Lim, S.; Pinault, M.; Wang, C.; Fang, F.; Pfefferle, L.; Hall, G.

    2008-01-01

    Vanadium oxide grafted on mesoporous silica SBA-15 has been synthesized using a controlled grafting process. Its structure has been thoroughly investigated using different characterization techniques, including N2-physisorption, X-ray diffraction, transmission electron microscopy (TEM), Raman spectroscopy, H2 temperature-programmed reduction, X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS). The spectroscopic results revealed that under dehydrated conditions, the grafted vanadium domains are highly dispersed on the SBA-15 surface, composed predominately of isolated VO4 units with distorted tetrahedral coordination. The suggested ({triple_bond}SiO)3V{double_bond}O sites on the silica surface include one short bond ({approx}1.54 Angstroms) and three long bonds (1.74 Angstroms). Methanol oxidation was used as a chemical probe reaction to examine the catalytic properties of these catalysts. At low vanadium loading, the vanadium species grafted on the surface show structural properties similar to those of vanadium-incorporated MCM-41 catalyst. However, the present mesoporous V-SBA-15 catalysts in the oxidation of methanol to formaldehyde show remarkable catalytic performance compared with that of VOx/SBA-15 catalysts synthesized through a conventional wet impregnation method, which has been attributed to the homogeneous dispersion and uniformity of the catalytic vanadium species achieved on the SBA-15 support with large pore diameter and surface area. The acidic properties of V-SBA-15 was investigated by pyridine temperature-programmed desorption, which indicated the existence of both Lewis and Broensted acid sites of the surface.

  14. High dispersed catalysts for coal liquefaction. Quarterly report No. 7, February 23, 1993--May 22, 1993

    SciTech Connect

    Hirschon, A.S.; Wilson, R.B.

    1993-08-19

    The objectives of this project are to study the effect of pretreatment methods on the two-stage liquefaction process. In particular, the effects of dispersed catalysts and carbon monoxide atmospheres on a coal liquefaction process. The project is divided into three technical tasks. Task 1 involves the analyses of the liquefaction products derived from liquefaction experiments using the catalysts Fe(CO){sub 5} and the sulfated iron catalyst, Fe{sub 2}O{sub 3}{center_dot}SO{sub 4}. We also analyzed the products derived from treating the recycle vehicle under coal liquefaction conditions with no coal or catalyst present, and found that the toluene and THF fractions had low H/C ratios. No CO or CO{sub 2} gases were detected after reaction, although considerable amount of methane gas was produced, suggesting that during the liquefaction runs the carbon oxides are produced only from the coal, as expected, but that methane gas is produced both from the recycle solvent and the coal. We now have more information about the recycle solvent from Wilsonville, who report that the residue was 63%, composed of 45% resid and 18% insoluble inorganic (CI), and a distilable portion of 37% (1050{degrees}F). During this quarter we compared coal conversions using Fe(CO){sub 5} with CO and H{sub 2}/CO atmospheres and determined the effect of using sulfated iron (Fe{sub 2}O{sub 3}{center_dot}SO{sub 4}) as a conversion catalyst. Also, the coal liquefaction recycle vehicle was subjected to coal product distribution. We found that the Fe(CO){sub 5} under a pure hydrogen atmosphere gave better conversions than under a CO/H{sub 2} atmosphere in terms of oils and asphaltenes but was equal in terms of overall conversion into soluble fractions.

  15. Bimetallic Wiregauze Supported Pt-Ru Nanocatalysts for Hydrogen Mitigation.

    PubMed

    Sanap, Kiran K; Varma, S; Waghmode, S B; Sharma, P; Manoj, N; Vatsa, R K; Bharadwaj, S R

    2015-05-01

    Passive autocatalytic recombiner (PAR) is one of the most suitable devices for mitigation of hydrogen, generated in nuclear power plant under accidental conditions. For this purpose we report development of stainless steel wire gauze supported Pt-Ru nanoparticles as catalysts. Simultaneous electroless deposition has been employed for the synthesis of the catalysts. Pt-Ru based bimetallic catalysts were characterized for their rate of coating kinetics, noble metal loading, phase purity by XRD and surface morphology by SEM, TEM and elemental analysis by SIMS. Developed catalysts were found to be active for efficient recombination of hydrogen and oxygen in air as well as in presence of various prospective poisons like CO2, CH4, CO and relative humidity. Pt-Ru based bimetallic catalyst with 0.9% loading was found to be active for CO poisoning up to 400 ppm of CO. PMID:26504972

  16. Surface modified coals for enhanced catalyst dispersion and liquefaction. Semiannual progress report, September 1, 1995--February 29, 1996

    SciTech Connect

    Abotsi, G.M.K.

    1996-10-01

    The aim of this work is to enhance catalyst loading and dispersion in coal for improved liquefaction by preadsorption of surfactants onto coal. The application of surfactants to coal beneficiation and coal-water slurry preparation is well known. However, the effects of surfactants on catalyst loading and dispersion prior to coal liquefaction have not been investigated. The current work is focused on the influence of the cationic surfactant dodecyl dimethyl ethyl ammonium bromide (DDAB) and sodium dodecyl sulfate (SDS, anionic) on the surface properties of a bituminous coal and its molybdenum uptake from solution. The results show that DDAB created positively charged sites on the coal and increased molybdenum loading compared to the original coal. In contrast, SDS rendered the coal surface negative and reduced molybdenum uptake. The results show that efficient loading of molybdenum catalyst onto coal can be achieved by pretreatment of the coal with dodecyl dimethyl ethyl ammonium bromide.

  17. Catalyst dispersion and activity under conditions of temperature- staged liquefaction. Technical progress report, July--September 1991

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1992-02-01

    The general objectives of this research are (1) to investigate the use of highly dispersed catalysts for the pretreatment of coal by mild hydrogenation, (2) to identify the active forms of catalysts under reaction conditions and (3) to clarify the mechanisms of catalysis. The ultimate objective is to ascertain if mild catalytic hydrogenation resulting in very limited or no coal solubilization is an advantageous pretreatment for the transformation of coal into transportable fuels. The experimental program will focus upon the development of effective methods of impregnating coal with catalysts, evaluating the conditions under which the catalysts are most active and establishing the relative impact of improved impregnation on conversion and product distributions obtained from coal hydrogenation.

  18. Catalyst dispersion and activity under conditions of temperature-staged liquefaction. Technical progress report, October--December 1991

    SciTech Connect

    Davis, A.; Schobert, H.H.; Mitchell, G.D.; Artok, L.

    1992-02-01

    The general objectives of this research are (1) to investigate the use of highly dispersed catalysts for the pretreatment of coal by mild hydrogenation, (2) to identify the active forms of the catalysts under reaction conditions and (3) to clarify the mechanisms of catalysis. The ultimate objective is to ascertain if mild catalytic hydrogenation resulting in very limited or no coal solubilization is an advantageous pretreatment for the transformation of coal into transportable fuels. The experimental program will focus upon the development of effective methods of impregnating coal with catalysts, evaluating the conditions under which the catalysts are most active and establishing the relative impact of improved impregnation on conversion and product distributions obtained from coal hydrogenation.

  19. Structure-Property Relationship in Metal Carbides and Bimetallic Alloys

    SciTech Connect

    Chen, Jingguan

    2014-03-04

    The primary objective of our DOE/BES sponsored research is to use carbide and bimetallic catalysts as model systems to demonstrate the feasibility of tuning the catalytic activity, selectivity and stability. Our efforts involve three parallel approaches, with the aim at studying single crystal model surfaces and bridging the “materials gap” and “pressure gap” between fundamental surface science studies and real world catalysis. The utilization of the three parallel approaches has led to the discovery of many intriguing catalytic properties of carbide and bimetallic surfaces and catalysts. During the past funding period we have utilized these combined research approaches to explore the possibility of predicting and verifying bimetallic and carbide combinations with enhanced catalytic activity, selectivity and stability.

  20. Highly Dispersed Pseudo-Homogeneous and Heterogeneous Catalysts Synthesized via Inverse Micelle Solutions for the Liquefaction of Coal

    SciTech Connect

    Hampden-Smith, M.; Kawola, J.S.; Martino, A.; Sault, A.G.; Yamanaka, S.A.

    1999-01-05

    The mission of this project was to use inverse micelle solutions to synthesize nanometer sized metal particles and test the particles as catalysts in the liquefaction of coal and other related reactions. The initial focus of the project was the synthesis of iron based materials in pseudo-homogeneous form. The frost three chapters discuss the synthesis, characterization, and catalyst testing in coal liquefaction and model coal liquefaction reactions of iron based pseudo-homogeneous materials. Later, we became interested in highly dispersed catalysts for coprocessing of coal and plastic waste. Bifunctional catalysts . to hydrogenate the coal and depolymerize the plastic waste are ideal. We began studying, based on our previously devised synthesis strategies, the synthesis of heterogeneous catalysts with a bifunctional nature. In chapter 4, we discuss the fundamental principles in heterogeneous catalysis synthesis with inverse micelle solutions. In chapter 5, we extend the synthesis of chapter 4 to practical systems and use the materials in catalyst testing. Finally in chapter 6, we return to iron and coal liquefaction now studied with the heterogeneous catalysts.

  1. A facile reflux procedure to increase active surface sites form highly active and durable supported palladium@platinum bimetallic nanodendrites

    NASA Astrophysics Data System (ADS)

    Wang, Qin; Li, Yingjun; Liu, Baocang; Xu, Guangran; Zhang, Geng; Zhao, Qi; Zhang, Jun

    2015-11-01

    A series of well-dispersed bimetallic Pd@Pt nanodendrites uniformly supported on XC-72 carbon black are fabricated by using different capping agents. These capping agents are essential for the branched morphology control. However, the surfactant adsorbed on the nanodendrites surface blocks the access of reactant molecules to the active surface sites, and the catalytic activities of these bimetallic nanodendrites are significantly restricted. Herein, a facile reflux procedure to effectively remove the capping agent molecules without significantly affecting their sizes is reported for activating supported nanocatalysts. More significantly, the structure and morphology of the nanodendrites can also be retained, enhancing the numbers of active surface sites, catalytic activity and stability toward methanol and ethanol electro-oxidation reactions. The as-obtained hot water reflux-treated Pd@Pt/C catalyst manifests superior catalytic activity and stability both in terms of surface and mass specific activities, as compared to the untreated catalysts and the commercial Pt/C and Pd/C catalysts. We anticipate that this effective and facile removal method has more general applicability to highly active nanocatalysts prepared with various surfactants, and should lead to improvements in environmental protection and energy production.

  2. A photoactive bimetallic framework for direct aminoformylation of nitroarenes

    EPA Science Inventory

    A bimetallic catalyst, AgPd@g-C3N4, was synthesized by immobilizing silver and palladium nanoparticles over the surface of graphitic carbon nitride (g-C3N4) and its utility was demonstrated for the concerted aminoformylation of aromatic nitro compounds under visible light conditi...

  3. High yielding synthesis of carboranes under mild reaction conditions using a homogeneous silver(I) catalyst: direct evidence of a bimetallic intermediate.

    PubMed

    El-Zaria, Mohamed E; Keskar, Kunal; Genady, Afaf R; Ioppolo, Joseph A; McNulty, James; Valliant, John F

    2014-05-12

    Methods used to prepare functionalized carboranes generally require heating to high temperatures, and thus limits the range of derivatives which can be prepared directly from alkynes. We show here that by using a homogeneous silver(I) catalyst it is now possible to prepare carboranes in good to excellent yield at temperatures below 40 °C, including at room temperature. The process is general and provides an important new synthetic strategy for the preparation of functionalized boron clusters.

  4. Promotion of the electrocatalytic activity of a bimetallic platinum-ruthenium catalyst by repetitive redox treatments for direct methanol fuel cell

    NASA Astrophysics Data System (ADS)

    Huang, Sheng-Yang; Yeh, Chuin-Tih

    Pt-Ru/C catalyst (12 wt%) was prepared by the incipient wetness impregnation method followed by a redox heat-treatment. Transmission electron microscopy (TEM) results revealed uniformly distributed metallic crystallites of Pt-Ru alloy nanoparticles (d PtRu = 2.1 ± 1.0 nm). The effect of redox treatments of the impregnated catalysts on methanol oxidation reaction (MOR) was examined by cyclic voltammetry (CV). The MOR activity of the PtRu/C was significantly improved after each oxidation step of the redox treatment cycles. The enhanced catalytic activity was found to be quite stable in chronoamperometry (CA) measurements. CV, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) results strongly suggested that the improved catalytic activity was due to the formation of a stable c-RuO x (x = 2-3) domain during the oxidation treatments. A bifunctional based mechanism was proposed for the MOR on the oxidized PtRu/C catalysts. Formation of Ru-OH species on the surface of c-RuO x domains was suggested as stale sites for the oxidation of carbon monoxide adsorbed on the Pt catalytic sites.

  5. Applications of Neutron Scattering in the Chemical Industry: Proton Dynamics of Highly Dispersed Materials, Characterization of Fuel Cell Catalysts, and Catalysts from Large-Scale Chemical Processes

    NASA Astrophysics Data System (ADS)

    Albers, Peter W.; Parker, Stewart F.

    The attractiveness of neutron scattering techniques for the detailed characterization of materials of high degrees of dispersity and structural complexity as encountered in the chemical industry is discussed. Neutron scattering picks up where other analytical methods leave off because of the physico-chemical properties of finely divided products and materials whose absorption behavior toward electromagnetic radiation and electrical conductivity causes serious problems. This is demonstrated by presenting typical applications from large-scale production technology and industrial catalysis. These include the determination of the proton-related surface chemistry of advanced materials that are used as reinforcing fillers in the manufacture of tires, where interrelations between surface chemistry, rheological properties, improved safety, and significant reduction of fuel consumption are the focus of recent developments. Neutron scattering allows surface science studies of the dissociative adsorption of hydrogen on nanodispersed, supported precious metal particles of fuel cell catalysts under in situ loading at realistic gas pressures of about 1 bar. Insight into the occupation of catalytically relevant surface sites provides valuable information about the catalyst in the working state and supplies essential scientific input for tailoring better catalysts by technologists. The impact of deactivation phenomena on industrial catalysts by coke deposition, chemical transformation of carbonaceous deposits, and other processes in catalytic hydrogenation processes that result in significant shortening of the time of useful operation in large-scale plants can often be traced back in detail to surface or bulk properties of catalysts or materials of catalytic relevance. A better understanding of avoidable or unavoidable aspects of catalyst deactivation phenomena under certain in-process conditions and the development of effective means for reducing deactivation leads to more energy

  6. A Frontier Molecular Orbital determination of the active sites on dispersed metal catalysts

    SciTech Connect

    Augustine, R.L.; Lahanas, K.M.

    1992-11-01

    An angular overlap calculation has been used to determine the s, p and d orbital energy levels of the different types of surface sites present on a dispersed metal catalysts. The basis for these calculations is the reported finding that a large number of catalyzed reactions take place on single atom active sites on the metal surface. Thus, these sites can be considered as surface complexes made up of the central active atom surrounded by near-neighbor metal atom ``ligands`` with localized surface orbitals perturbed only by these ``ligands``. These ``complexes`` are based on a twelve coordinate species with the ``ligands`` attached to the t{sub 2g} orbitals and the coordinate axes coincident with the direction of the e{sub g} orbitals on the central atom. These data can permit a Frontier Molecular Orbital treatment of specific site activities as long as the surface orbital availability for overlap with adsorbed substrates is considered along with its energy value and symmetry.

  7. A Frontier Molecular Orbital determination of the active sites on dispersed metal catalysts

    SciTech Connect

    Augustine, R.L.; Lahanas, K.M.

    1992-01-01

    An angular overlap calculation has been used to determine the s, p and d orbital energy levels of the different types of surface sites present on a dispersed metal catalysts. The basis for these calculations is the reported finding that a large number of catalyzed reactions take place on single atom active sites on the metal surface. Thus, these sites can be considered as surface complexes made up of the central active atom surrounded by near-neighbor metal atom ligands'' with localized surface orbitals perturbed only by these ligands''. These complexes'' are based on a twelve coordinate species with the ligands'' attached to the t{sub 2g} orbitals and the coordinate axes coincident with the direction of the e{sub g} orbitals on the central atom. These data can permit a Frontier Molecular Orbital treatment of specific site activities as long as the surface orbital availability for overlap with adsorbed substrates is considered along with its energy value and symmetry.

  8. Formation of Catalyst Model Dispersed of Pd on a thin MgO(100)

    NASA Astrophysics Data System (ADS)

    Baara, F.; Chemam, A.

    2016-04-01

    The nucleation kinetics or the formation of a catalyst model dispersed for the system Pd/thin MgO (100) are calculated by developing many programs using Fortran software. This simulation is based upon parameters studied in situ by transmission electron microscopy (TEM), related to the first quantitative study on the nucleation and the growth. Palladium nanoparticles deposited on thin MgO are tested in the temperature range 573-1073 K and deposition time of 1000 s. The nucleation kinetics are interpreted according to the theory of random nucleation. The general scheme is consisting of three stages namely, nucleation, growth and coalescence. The saturation density of clusters decreases when the substrate temperature increases following Arrhenius law. This behavior is in agreement with a recent AFM study for Ag/MgO and Au/MgO. The phenomenon of coalescence is explained via island migration process. It is shown that the coalescence occurs more rapidly when the substrate temperature is high.

  9. Ultrasound enhanced heterogeneous activation of peroxymonosulfate by a bimetallic Fe-Co/SBA-15 catalyst for the degradation of Orange II in water.

    PubMed

    Cai, Chun; Zhang, Hui; Zhong, Xing; Hou, Liwei

    2015-01-01

    Mesoporous silica SBA-15 supported iron and cobalt (Fe-Co/SBA-15) was prepared and used as catalyst in the ultrasound (US) enhanced heterogeneous activation of peroxymonosulfate (PMS, HSO5(-)) process. The effects of some important reaction parameters on the removal of Orange II by US/Fe-Co/SBA-15/PMS process were investigated. The results indicated that the removal rate of Orange II was not significantly affected by the initial pH, and it increased with the higher PMS concentration, reaction temperature, Fe-Co/SBA-15 dosage and ultrasonic power. Furthermore, sulfate radicals (SO4(-)) were assumed to be the dominating reactive species for the Orange II decolorization. Moreover, the Fe-Co/SBA-15 catalyst showed high activity during the repeated experiments. The intermediate products were identified by GC-MS, thereby a plausible degradation pathway is proposed. In addition, the chemical oxygen demand (COD) removal efficiencies at 2 and 24h were 56.8% and 80.1%, respectively and the corresponding total organic carbon (TOC) removal efficiencies were 33.8 and 53.3%. Finally, toxicity tests with activated sludge showed that the toxicity of the solution increased during the first stage and then decreased significantly with the progress of the oxidation. PMID:25262480

  10. Electrocatalytic hydrodehalogenation of atrazine in aqueous solution by Cu@Pd/Ti catalyst.

    PubMed

    Chen, Ya-Li; Xiong, Lu; Song, Xiang-Ning; Wang, Wei-Kang; Huang, Yu-Xi; Yu, Han-Qing

    2015-04-01

    Electrocatalytic hydrodehalogenation is a cost-effective approach to degrade halogenated organic pollutants in groundwater, and Pd-based catalysts have been found to be an efficient cathode material for this purpose. In this work, a novel Cu@Pd bimetallic catalyst loaded on Ti plate was prepared via combined electrodeposition and galvanic replacement for electrocatalytic hydrodehalogenation of atrazine, a typical halogenated pollutant. The obtained bimetallic catalyst with uniformly dispersed Pd nanoparticles possessed a large electrochemically active surface area of 572 cm2. The Cu@Pd/Ti cathode exhibited a higher electrocatalytic efficiency towards atrazine reduction than the individual Pd/Ti or Cu/Ti cathodes, and achieved up to 91.5% within 120 min under a current density of 1 mA cm(-2). Such an electrocatalytic reduction followed pseudo-first-order kinetics with a rate constant of 0.0214 min(-1). Atrazine was selectively transformed to dechlorinated atrazine, and its degradation pathway was identified. Current density was found to have a critical influence on the atrazine reduction due to the competitive hydrogen evolution reaction at a higher current density. The fabricated bimetallic catalyst also exhibited a good stability. This work provides an efficient and stable electrocatalyst for chlorinated contaminate removal and groundwater remediation.

  11. In situ assembly of well-dispersed gold nanoparticles on hierarchical double-walled nickel silicate hollow nanofibers as an efficient and reusable hydrogenation catalyst.

    PubMed

    Jin, Renxi; Yang, Yang; Li, Yunfeng; Fang, Lin; Xing, Yan; Song, Shuyan

    2014-05-28

    Highly dispersive and ultrafine Au nanoparticles were effectively immobilized on the surface of hierarchical double-walled nickel silicate hollow nanofibers assembled by ultrathin nanosheets, which showed remarkable catalytic performances as an efficient and reusable hydrogenation catalyst.

  12. Structural Characterization of Bimetallic Nanocrystal Electrocatalysts

    SciTech Connect

    Cullen, David A

    2016-01-01

    Late transition metal nanocrystals find applications in heterogeneous catalysis such as plasmon-enhanced catalysis and as electrode materials for fuel cells, a zero-emission and sustainable energy technology. Their commercial viability for automotive transportation has steadily increased in recent years, almost exclusively due to the discovery of more efficient bimetallic nanocatalysts for the oxygen reduction reaction (ORR) at the cathode. Despite improvements to catalyst design, achieving high activity while maintaining durability is essential to further enhance their performance for this and other important applications in catalysis. Electronic effects arising from the generation of metal-metal interfaces, from plasmonic metals, and from lattice distortions, can vastly improve sorption properties at catalytic surfaces, while increasing durability.[1] Multimetallic lattice-strained nanoparticles are thus an interesting opportunity for fundamental research.[2,3] A colloidal synthesis approach is demonstrated to produce AuPd alloy and Pd@Au core-shell nanoicosahedra as catalysts for electro-oxidations. The nanoparticles are characterized using aberration-corrected scanning transmission electron microscopy (ac-STEM) and large solid angle energy dispersive X-ray spectroscopy (EDS) on an FEI Talos 4-detector STEM/EDS system. Figure 1 shows bright-field (BF) and high-angle annular dark-field (HAADF) ac-STEM images of the alloy and core-shell nanoicosahedra together with EDS line-scans and elemental maps. These structures are unique in that the presence of twin boundaries, alloying, and core-shell morphology could create highly strained surfaces and interfaces. The shell thickness of the core-shell structures observed in HAADF-STEM images is tuned by adjusting the ratio between metal precursors (Figure 2a-f) to produce shells ranging from a few to several monolayers. Specific activity was measured in ethanol electro-oxidation to examine the effect of shell thickness on

  13. Dispersion and activity of molybdena-alumina catalysts prepared by impregnation and solid/solid wetting methods

    SciTech Connect

    Reddy, B.M.; Reddy, E.P.; Srinivas, S.T. )

    1992-07-01

    Alumina-supported molybdena catalysts were prepared by both the standard incipient wetness method and by mixing MoO{sub 3} and Al{sub 2}O{sub 3} (solid/solid wetting), followed by thermal treatment of 500 C under dry or wet O{sub 2} atmospheric conditions. These catalysts were characterized by means of O{sub 2} chemisorption at {minus}78 C, CO{sub 2} uptake at ambient temperature, X-ray diffraction (XRD), and electron spin resonance (ESR) techniques. Activities of the catalysts were determined for partial oxidation of methanol and hydrodesulfurization of thiophene at atmospheric pressure. XRD results suggest high dispersion of Mo-oxide on alumina support irrespective of their method of preparation. However, O{sub 2} and CO{sub 2} uptake measurements reveal partial coverage of the Al{sub 2}O{sub 3} support surface by the Mo-oxide phase and appear to depend on the gas atmosphere (wet or dry O{sub 2}) during heat treatments in case of solid/solid wetting method. ESR, oxygen and carbon dioxide uptakes and the catalytic properties clearly demonstrate that spontaneous spreading of MoO{sub 3} on the Al{sub 2}O{sub 3} support at 500 C in the presence of wet O{sub 2} is a most effective alternative method for preparing molybdenum-alumina catalysts.

  14. Investigation of a catalyst ink dispersion using both ultra-small-angle X-ray scattering and cryogenic TEM.

    PubMed

    Xu, Fan; Zhang, HangYu; Ilavsky, Jan; Stanciu, Lia; Ho, Derek; Justice, Matthew J; Petrache, Horia I; Xie, Jian

    2010-12-21

    The dispersion of Nafion ionomer particles and Pt/C catalyst aggregates in liquid media was studied using both ultra-small-angle X-ray scattering (USAXS) and cryogenic TEM. A systematic approach was taken to study first the dispersion of each component (i.e., ionomer particles and Pt/C aggregates), then the combination of the components, and last the catalyst ink. Multiple-level curve fitting was used to extract the particle size, size distribution, and geometry of the Pt/C aggregates and the Nafion particles in liquid media from the scattering data. The results suggest that the particle size, size distribution, and geometry are not uniform throughout the systems but rather vary significantly. It was found that the interaction of each component (i.e., the Nafion ionomer particles and the Pt/C aggregates) occurs in the dispersion. Cryogenic TEM was used to observe the size and geometry of the particles in liquid directly and to validate the scattering results. The TEM results showed excellent agreement.

  15. XAFS studies on highly dispersed Ni 2P/SiO 2 catalysts for hydrodesulfurization of 4,6-dimethyldibenzothiophene

    NASA Astrophysics Data System (ADS)

    Cho, Kye-Sung; Lee, Yong-Kul

    2010-09-01

    The Ni 2P catalysts were prepared by a new synthetic method with the use of less oxidic phosphorus precursor in order to achieve high dispersion on silica support, and their structural properties and catalytic activity in HDS of 4,6-DMDBT were studied. Comparison was made with a conventionally prepared sample which was obtained by temperature programmed reduction method. Various characterizations were conducted by BET, CO uptake, TPR, XRD and X-ray absorption spectroscopy. The amounts of CO chemisorption uptake were 64 and 20 μmol g -1 for Ni 2P/SiO 2-LT and Ni 2P/SiO 2-HT, respectively, indicating that the low temperature reduction technique led to better dispersion of Ni 2P particles on SiO 2 support. The catalytic activity in the HDS of 4,6-DMDBT followed the order, Ni 2P/SiO 2-HT(54%)catalysts highly depend on the dispersion of the Ni 2P phase.

  16. Bimetallic redox synergy in oxidative palladium catalysis.

    PubMed

    Powers, David C; Ritter, Tobias

    2012-06-19

    (II/IV) catalysis has guided the successful development of many reactions. Herein we discuss differences between monometallic Pd(IV) and bimetallic Pd(III) redox catalysis. We address whether appreciation of the relevance of bimetallic Pd(III) redox catalysis is of academic interest exclusively, serving to provide a more nuanced description of catalysis, or if the new insight regarding bimetallic Pd(III) chemistry can be a platform to enable future reaction development. To this end, we describe an example in which the hypothesis of bimetallic redox chemistry guided reaction development, leading to the discovery of reactivity distinct from monometallic catalysts.

  17. Preparation, catalysis, and characterization of highly dispersed molybdenum sulfide catalysts supported on a NaY zeolite

    SciTech Connect

    Okamoto, Yasuaki; Katsuyama, Hiromoto

    1996-06-01

    The structure and dispersion of the molybdenum sulfides supported on a NaY zeolite were studied using XAFS techniques. It was found that molybdenum sulfide species prepared by sulfiding vapor deposited Mo(CO){sub 6} or by sulfiding molybdenum oxide dimer species encaged in the zeolite are highly dispersed and thermally stabilized against sintering or restructuring. These molybdenum species are formed via molybdenum sulfide dimer species as an intermediate. On the other hand, with the molybdenum sulfide catalysts prepared by an impregnation method, the sulfidation of molybdenum oxides was incomplete. The molybdenum oxide species are suggested to be mainly located in the zeolite cavities after calcination, forming isolated molybdenum oxides in tetrahedral configurations. The molybdenum sulfide species prepared from Mo(CO){sub 6} showed much higher catalytic activities for thiophene hydrodesulfurization and butadiene hydrogenation than the molybdenum sulfides prepared by the impregnation, in conformity with a higher dispersion and higher fraction of the molybdenum sulfide species. It is demonstrated that in combination with metal carbonyl techniques, zeolite supports are very suitable for the preparation of highly dispersed molybdenum sulfides at a high Mo loading.

  18. Advanced liquefaction using coal swelling and catalyst dispersion techniques. Quarterly technical progress report, July--September 1992

    SciTech Connect

    Curtis, C.W.; Gutterman, C.; Chander, S.

    1992-12-31

    The experimental study of coal swelling ratios have been determined with a wide variety of solvents. Only marginal levels of coal swelling were observed for the hydrocarbon solvents, but high levels were found with solvents having heteroatom functionality. Blends were superior to pure solvents. The activity of various catalyst precursors for pyrene hydrogenation and coal conversion was measured. Higher coal conversions were observed for the S0{sub 2}-treated coal than the raw coal, regardless of catalyst type. Coal conversions were highest for Molyvan-L, molybdenum naphthenate, and nickel octoate, respectively. Bottoms processing consists of a combination of the ASCOT process coupling solvent deasphalting with delayed coking. Initial results indicate that a blend of butane and pentane used near the critical temperature of butane is the best solvent blend for producing a yield/temperature relationship of proper sensitivity and yet retaining an asphalt phase of reasonable viscosity. The literature concerning coal swelling, both alone and in combination with coal liquefaction, and the use of dispersed or unsupported catalysts in coal liquefaction has been updated.

  19. Small-sized and highly dispersed Pt nanoparticles loading on graphite nanoplatelets as an effective catalyst for methanol oxidation.

    PubMed

    Zhang, Genlei; Yang, Zhenzhen; Huang, Chengde; Zhang, Wen; Wang, Yuxin

    2015-06-14

    A series of high loading Pt nanoparticles (NPs) with a small particle size uniformly dispersed on graphite nanoplatelets (GNPs) have been synthesized in the presence of an imidazolium-based ionic liquid (Pt/I-IL (x)/GNPs). I-IL, an amphoteric ion used as an additive agent to stabilize Pt NPs, can also prevent the aggregation of the GNPs. The results obtained from X-ray diffraction, transmission electron microscopy and electrochemical testing showed that the I-IL assisted synthesis method resulted in size reduction of Pt NPs, an improvement of Pt dispersion on GNPs, and the identification of the relationships between the mean size of Pt NPs and the volume of I-IL. Among all as-prepared Pt/GNP catalysts with or without I-IL assisted, the sample with 10 microliters of I-IL assisted (Pt/I-IL (10)/GNPs) exhibits the highest electrocatalytic activity and the best stability toward the methanol oxidation reaction. Moreover, the Pt/I-IL (10)/GNP catalyst markedly outperforms the commercial Pt/C from Johnson Matthey in terms of both methanol oxidation activity and stability, revealed by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy.

  20. Small-sized and highly dispersed Pt nanoparticles loading on graphite nanoplatelets as an effective catalyst for methanol oxidation.

    PubMed

    Zhang, Genlei; Yang, Zhenzhen; Huang, Chengde; Zhang, Wen; Wang, Yuxin

    2015-06-14

    A series of high loading Pt nanoparticles (NPs) with a small particle size uniformly dispersed on graphite nanoplatelets (GNPs) have been synthesized in the presence of an imidazolium-based ionic liquid (Pt/I-IL (x)/GNPs). I-IL, an amphoteric ion used as an additive agent to stabilize Pt NPs, can also prevent the aggregation of the GNPs. The results obtained from X-ray diffraction, transmission electron microscopy and electrochemical testing showed that the I-IL assisted synthesis method resulted in size reduction of Pt NPs, an improvement of Pt dispersion on GNPs, and the identification of the relationships between the mean size of Pt NPs and the volume of I-IL. Among all as-prepared Pt/GNP catalysts with or without I-IL assisted, the sample with 10 microliters of I-IL assisted (Pt/I-IL (10)/GNPs) exhibits the highest electrocatalytic activity and the best stability toward the methanol oxidation reaction. Moreover, the Pt/I-IL (10)/GNP catalyst markedly outperforms the commercial Pt/C from Johnson Matthey in terms of both methanol oxidation activity and stability, revealed by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. PMID:25986338

  1. Facile synthesis of Cu-Pd bimetallic multipods for application in cyclohexane oxidation

    NASA Astrophysics Data System (ADS)

    Zhang, Zhuo-Qun; Huang, Jianliu; Zhang, Lan; Sun, Mei; Wang, You-Cheng; Lin, Yue; Zeng, Jie

    2014-10-01

    The synergy between Cu and Pd makes Cu-Pd bimetallic nanocrystals interesting materials for investigation. The scarcity of shapes of Cu-Pd bimetallic nanocrystals motivated us to explore highly branched structures, which may promote a wide range of applications. In this communication, we report a facile synthesis of Cu-Pd bimetallic multipods (19.2 ± 1.2 nm), on branches of which some high-index facets were exposed. Modification of reaction parameters concerning capping agents and reductant led to the formation of other shapes, including sphere-like nanocrystals (SNCs). When loaded onto TiO2, the as-prepared Cu-Pd bimetallic multipods exhibited excellent catalytic activity for the oxidation of cyclohexane by hydrogen peroxide and higher selectivity towards cyclohexanone than monometallic catalysts and SNCs/TiO2.

  2. Facile synthesis of Cu-Pd bimetallic multipods for application in cyclohexane oxidation.

    PubMed

    Zhang, Zhuo-Qun; Huang, Jianliu; Zhang, Lan; Sun, Mei; Wang, You-Cheng; Lin, Yue; Zeng, Jie

    2014-10-31

    The synergy between Cu and Pd makes Cu-Pd bimetallic nanocrystals interesting materials for investigation. The scarcity of shapes of Cu-Pd bimetallic nanocrystals motivated us to explore highly branched structures, which may promote a wide range of applications. In this communication, we report a facile synthesis of Cu-Pd bimetallic multipods (19.2 ± 1.2 nm), on branches of which some high-index facets were exposed. Modification of reaction parameters concerning capping agents and reductant led to the formation of other shapes, including sphere-like nanocrystals (SNCs). When loaded onto TiO2, the as-prepared Cu-Pd bimetallic multipods exhibited excellent catalytic activity for the oxidation of cyclohexane by hydrogen peroxide and higher selectivity towards cyclohexanone than monometallic catalysts and SNCs/TiO2. PMID:25297725

  3. Dispersed metal cluster catalysts by design. Synthesis, characterization, structure, and performance

    SciTech Connect

    Arslan, Ilke; Dixon, David A.; Gates, Bruce C.; Katz, Alexander

    2015-09-30

    To understand the class of metal cluster catalysts better and to lay a foundation for the prediction of properties leading to improved catalysts, we have synthesized metal catalysts with well-defined structures and varied the cluster structures and compositions systematically—including the ligands bonded to the metals. These ligands include supports and bulky organics that are being tuned to control both the electron transfer to or from the metal and the accessibility of reactants to influence catalytic properties. We have developed novel syntheses to prepare these well-defined catalysts with atomic-scale control the environment by choice and placement of ligands and applied state-of-the art spectroscopic, microscopic, and computational methods to determine their structures, reactivities, and catalytic properties. The ligands range from nearly flat MgO surfaces to enveloping zeolites to bulky calixarenes to provide controlled coverages of the metal clusters, while also enforcing unprecedented degrees of coordinative unsaturation at the metal site—thereby facilitating bonding and catalysis events at exposed metal atoms. With this wide range of ligand properties and our arsenal of characterization tools, we worked to achieve a deep, fundamental understanding of how to synthesize robust supported and ligand-modified metal clusters with controlled catalytic properties, thereby bridging the gap between active site structure and function in unsupported and supported metal catalysts. We used methods of organometallic and inorganic chemistry combined with surface chemistry for the precise synthesis of metal clusters and nanoparticles, characterizing them at various stages of preparation and under various conditions (including catalytic reaction conditions) and determining their structures and reactivities and how their catalytic properties depend on their compositions and structures. Key characterization methods included IR, NMR, and EXAFS spectroscopies to identify

  4. Monolayer dispersion of NiO in NiO/Al2O3 catalysts probed by positronium atom.

    PubMed

    Zhang, H J; Chen, Z Q; Wang, S J

    2012-01-21

    NiO/Al(2)O(3) catalysts with different NiO loadings were prepared by impregnation method. The monolayer dispersion capacity of NiO is determined to be about 9 wt.% through XRD quantitative phase analysis. Positron lifetime spectra measured for NiO/Al(2)O(3) catalysts comprise two long and two short lifetime components, where the long lifetimes τ(3) and τ(4) correspond to ortho-positronium (o-Ps) annihilation in microvoids and large pores, respectively. With increasing loading of NiO from 0 to 9 wt.%, τ(4) drops drastically from 88 to 38 ns. However, when the NiO loading is higher than 9 wt.%, τ(4) shows a slower decrease. Variation of λ(4) (1/τ(4)) as a function of the NiO content can be well fitted by two straight lines with different slopes. The relative intensity of τ(4) also shows a fast decrease followed by a slow decrease for the NiO content lower and higher than 9 wt.%, respectively. The coincidence Doppler broadening measurements reveal a continuous increase of S parameter with increasing NiO loading up to 9 wt.% and then a decrease afterwards. This is due to the variation in intensity of the narrow component contributed by the annihilation of para-positronium (p-Ps). Our results show that the annihilation behavior of positronium is very sensitive to the dispersion state of NiO on the surface of γ-Al(2)O(3). When the NiO loading is lower than monolayer dispersion capacity, spin conversion of positronium induced by NiO is the dominant effect, which causes decrease of the longest lifetime and its intensity but increase of the narrow component intensity. After the NiO loading is higher than monolayer dispersion capacity, the spin conversion effect becomes weaker and inhibition of positronium formation by NiO is strengthened, which results in decrease of both the long lifetime intensity and the narrow component intensity. The reaction rate constant is determined to be (1.50 ± 0.04) × 10(10) g mol(-1) s(-1) and (3.43 ± 0.20) × 10(9) g mol(-1) s(-1

  5. Dispersal

    USGS Publications Warehouse

    Clobert, J.; Danchin, E.; Dhondt, A.A.; Nichols, J.D.

    2001-01-01

    The ability of species to migrate and disperse is a trait that has interested ecologists for many years. Now that so many species and ecosystems face major environmental threats from habitat fragmentation and global climate change, the ability of species to adapt to these changes by dispersing, migrating, or moving between patches of habitat can be crucial to ensuring their survival. This book provides a timely and wide-ranging overview of the study of dispersal and incorporates much of the latest research. The causes, mechanisms, and consequences of dispersal at the individual, population, species and community levels are considered. The potential of new techniques and models for studying dispersal, drawn from molecular biology and demography, is also explored. Perspectives and insights are offered from the fields of evolution, conservation biology and genetics. Throughout the book, theoretical approaches are combined with empirical data, and care has been taken to include examples from as wide a range of species as possible.

  6. Versatile and efficient catalysts for energy and environmental processes: Mesoporous silica containing Au, Pd and Au-Pd

    NASA Astrophysics Data System (ADS)

    da Silva, Anderson G. M.; Fajardo, Humberto V.; Balzer, Rosana; Probst, Luiz F. D.; Lovón, Adriana S. P.; Lovón-Quintana, Juan J.; Valença, Gustavo P.; Schreine, Wido H.; Robles-Dutenhefner, Patrícia A.

    2015-07-01

    We described a versatile approach for the synthesis of Au/MCM-41, Pd/MCM-41 and Au-Pd/MCM-41 by the direct incorporation of the noble metals into the MCM-41 framework. The structural, textural and chemical properties were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), N2-adsorption (BET and BJH methods), H2-chemisorption, small angle X-ray scattering (SAXS), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The nanomaterials, being comprised of Au, Pd and Au-Pd nanoparticles and possessing high surface areas were applied as versatile and efficient catalysts in benzene, toluene and o-xylene (BTX) oxidation and in the steam reforming of ethanol for hydrogen production. The results revealed that the catalytic behavior in both processes was influenced by the experimental conditions and the nature of the catalyst employed. The Au-Pd/MCM-41 catalyst was the most active in the BTX total oxidation. On the basis of characterization data, it was proposed that the close contact between Pd and Au and the higher dispersion of Pd may be responsible for the enhanced activity of the bimetallic catalyst. However, the strong interaction between the noble metals did not improve the performance of the bimetallic catalyst in ethanol steam reforming, the Pd/MCM-41 catalyst being the most active and selective for hydrogen production.

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

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

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

  8. Advanced liquefaction using coal swelling and catalyst dispersion techniques. Quarterly technical progress report, April--June 1992

    SciTech Connect

    Curtis, C.W.; Gutterman, C.; Chander, S.

    1992-08-26

    Research in this project centers upon developing a new approach to the direct liquefaction of coal to produce an all-distillate product slate at a sizable cost reduction over current technology. The approach integrates all aspects of the coal liquefaction process including coal selection, pretreatment, coal swelling with catalyst impregnation, coal liquefaction experimentation, product recovery with characterization, alternate bottoms processing, and a technical assessment including an economic evaluation. The project is being carried out under contract to the United States Department of Energy. On May 28, 1992, the Department of Energy authorized starting the experimental aspects of this projects; therefore, experimentation at Amoco started late in this quarterly report period. Research contracts with Auburn University, Pennsylvania State University, and Foster Wheeler Development Corporation were signed during June, 1992, so their work was just getting underway. Their work will be summarized in future quarterly reports. A set of coal samples were sent to Hazen Research for beneficiation. The samples were received and have been analyzed. The literature search covering coal swelling has been up-dated, and preliminary coal swelling experiments were carried out. Further swelling experimentation is underway. An up-date of the literature on the liquefaction of coal using dispersed catalysts is nearing completion; it will be included in the next quarterly report.

  9. Advanced liquefaction using coal swelling and catalyst dispersion techniques. Quarterly progress report, July--September 1993

    SciTech Connect

    Curtis, C.W.; Gutterman, C.; Chander, S.

    1993-12-31

    The overall objective of this project is to develop a new approach for the direct liquefaction of coal to produce an all-distillate product slate at a sizable cost reduction over current technology. The approach integrates coal selection, pretreatment, coal swelling with catalyst impregnation, liquefaction, product recovery with characterization, alternate bottoms processing, and carrying out a technical assessment including an economic evaluation. The primary coal of this program, Black Thunder subbituminous coal, can be effectively beneficiated to about 3.5 wt % ash using aqueous sulfurous acid pretreatment. This treated coal can be further beneficiated to about 2 wt % ash using commercially available procedures. All three coals used in this study (Black Thunder, Burning Star bituminous, and Martin Lake lignite) are effectively swelled by a number of solvents. The most effective solvents are those having hetero-functionality. laboratory- and bench-scale liquefaction experimentation is underway using swelled and catalyst impregnated coal samples. Higher coal conversions were observed for the SO{sub 2}-treated subbituminous coal than the raw coal, regardless of catalyst type. Conversions of swelled coal were highest when Molyvan L, molybdenum naphthenate, and nickel octoate, respectively, were added to the liquefaction solvent. The study of bottoms processing consists of combining the ASCOT process which consists of coupling solvent deasphalting with delayed coking to maximize the production of coal-derived liquids while rejecting solids within the coke drum. The asphalt production phase has been completed; representative product has been evaluated. The solvent system for the deasphalting process has been established. Two ASCOT tests produced overall liquid yields (63.3 wt % and 61.5 wt %) that exceeded the combined liquid yields from the vacuum tower and ROSE process.

  10. ELECTRONIC AND CHEMICAL PROPERTIES OF PD IN BIMETALLIC SYSTEMS: HOW MUCH DO WE KNOW ABOUT HETERONUCLEAR METAL-METAL BONDING?

    SciTech Connect

    RODRIGUEZ,J.A.

    2001-09-27

    The experimental and theoretical studies described above illustrate the complex nature of the heteronuclear metal-metal bond. In many cases, bimetallic bonding induces a significant redistribution of charge around the bonded metals. This redistribution of charge is usually linked to the strength of the bimetallic bond, affects the position of the core and valence levels of the metals, and can determine the chemical reactivity of the system under study. New concepts are emerging [22,23,34,36] and eventually the coupling of experiment and theory can be useful for designing more efficient bimetallic catalysts [98,106,107].

  11. Well-dispersed Pt cubes on porous Cu foam: high-performance catalysts for the electrochemical oxidation of glucose in neutral media.

    PubMed

    Niu, Xiangheng; Lan, Minbo; Zhao, Hongli; Chen, Chen

    2013-07-15

    The investigation of highly efficient catalysts for the electrochemical oxidation of glucose is the most critical challenge to commercialize nonenzymatic glucose sensors, which display a few attractive superiorities including the sufficient stability of their properties and the desired reproducibility of results over enzyme electrodes. Herein we propose a new and very promising catalyst: Pt cubes well-dispersed on the porous Cu foam, for the the electrochemical oxidation reaction of glucose in neutral media. The catalyst is fabricated in situ on a homemade screen-printed carbon electrode (SPCE) substrate through initially synthesizing the three-dimensional (3D) porous Cu foam using a hydrogen evolution assisted electrodeposition strategy, followed by electrochemically reducing the platinic precursor simply and conveniently. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) proofs demonstrate that Pt cubes, with an average size (the distance of opposite faces) of 185.1 nm, highly dispersed on the macro/nanopore integrated Cu foam support can be reproducibly obtained. The results of electrochemical tests indicate that the cubic Pt-based catalyst exhibits significant enhancement on the catalytic activity towards the electrooxidation of glucose in the presence of chloride ions, providing a specific activity 6.7 times and a mass activity 5.3 times those of commercial Pt/C catalysts at -0.4 V (vs. Ag/AgCl). In addition, the proposed catalyst shows excellent stability of performance, with only a 2.8% loss of electrocatalytic activity after 100 repetitive measurements.

  12. Enhanced electrochemical methanation of carbon dioxide with a dispersible nanoscale copper catalyst.

    PubMed

    Manthiram, Karthish; Beberwyck, Brandon J; Alivisatos, A Paul

    2014-09-24

    Although the vast majority of hydrocarbon fuels and products are presently derived from petroleum, there is much interest in the development of routes for synthesizing these same products by hydrogenating CO2. The simplest hydrocarbon target is methane, which can utilize existing infrastructure for natural gas storage, distribution, and consumption. Electrochemical methods for methanizing CO2 currently suffer from a combination of low activities and poor selectivities. We demonstrate that copper nanoparticles supported on glassy carbon (n-Cu/C) achieve up to 4 times greater methanation current densities compared to high-purity copper foil electrodes. The n-Cu/C electrocatalyst also exhibits an average Faradaic efficiency for methanation of 80% during extended electrolysis, the highest Faradaic efficiency for room-temperature methanation reported to date. We find that the level of copper catalyst loading on the glassy carbon support has an enormous impact on the morphology of the copper under catalytic conditions and the resulting Faradaic efficiency for methane. The improved activity and Faradaic efficiency for methanation involves a mechanism that is distinct from what is generally thought to occur on copper foils. Electrochemical data indicate that the early steps of methanation on n-Cu/C involve a pre-equilibrium one-electron transfer to CO2 to form an adsorbed radical, followed by a rate-limiting non-electrochemical step in which the adsorbed CO2 radical reacts with a second CO2 molecule from solution. These nanoscale copper electrocatalysts represent a first step toward the preparation of practical methanation catalysts that can be incorporated into membrane-electrode assemblies in electrolyzers.

  13. Enhanced electrochemical methanation of carbon dioxide with a dispersible nanoscale copper catalyst.

    PubMed

    Manthiram, Karthish; Beberwyck, Brandon J; Alivisatos, A Paul

    2014-09-24

    Although the vast majority of hydrocarbon fuels and products are presently derived from petroleum, there is much interest in the development of routes for synthesizing these same products by hydrogenating CO2. The simplest hydrocarbon target is methane, which can utilize existing infrastructure for natural gas storage, distribution, and consumption. Electrochemical methods for methanizing CO2 currently suffer from a combination of low activities and poor selectivities. We demonstrate that copper nanoparticles supported on glassy carbon (n-Cu/C) achieve up to 4 times greater methanation current densities compared to high-purity copper foil electrodes. The n-Cu/C electrocatalyst also exhibits an average Faradaic efficiency for methanation of 80% during extended electrolysis, the highest Faradaic efficiency for room-temperature methanation reported to date. We find that the level of copper catalyst loading on the glassy carbon support has an enormous impact on the morphology of the copper under catalytic conditions and the resulting Faradaic efficiency for methane. The improved activity and Faradaic efficiency for methanation involves a mechanism that is distinct from what is generally thought to occur on copper foils. Electrochemical data indicate that the early steps of methanation on n-Cu/C involve a pre-equilibrium one-electron transfer to CO2 to form an adsorbed radical, followed by a rate-limiting non-electrochemical step in which the adsorbed CO2 radical reacts with a second CO2 molecule from solution. These nanoscale copper electrocatalysts represent a first step toward the preparation of practical methanation catalysts that can be incorporated into membrane-electrode assemblies in electrolyzers. PMID:25137433

  14. Atomic layer deposition-Sequential self-limiting surface reactions for advanced catalyst "bottom-up" synthesis

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    Catalyst synthesis with precise control over the structure of catalytic active sites at the atomic level is of essential importance for the scientific understanding of reaction mechanisms and for rational design of advanced catalysts with high performance. Such precise control is achievable using atomic layer deposition (ALD). ALD is similar to chemical vapor deposition (CVD), except that the deposition is split into a sequence of two self-limiting surface reactions between gaseous precursor molecules and a substrate. The unique self-limiting feature of ALD allows conformal deposition of catalytic materials on a high surface area catalyst support at the atomic level. The deposited catalytic materials can be precisely constructed on the support by varying the number and type of ALD cycles. As an alternative to the wet-chemistry based conventional methods, ALD provides a cycle-by-cycle "bottom-up" approach for nanostructuring supported catalysts with near atomic precision. In this review, we summarize recent attempts to synthesize supported catalysts with ALD. Nucleation and growth of metals by ALD on oxides and carbon materials for precise synthesis of supported monometallic catalyst are reviewed. The capability of achieving precise control over the particle size of monometallic nanoparticles by ALD is emphasized. The resulting metal catalysts with high dispersions and uniformity often show comparable or remarkably higher activity than those prepared by conventional methods. For supported bimetallic catalyst synthesis, we summarize the strategies for controlling the deposition of the secondary metal selectively on the primary metal nanoparticle but not on the support to exclude monometallic formation. As a review of the surface chemistry and growth behavior of metal ALD on metal surfaces, we demonstrate the ways to precisely tune size, composition and structure of bimetallic metal nanoparticles. The cycle-by-cycle "bottom up" construction of bimetallic (or multiple

  15. Highly Stable and Active Catalyst for Sabatier Reactions

    NASA Technical Reports Server (NTRS)

    Hu, Jianli; Brooks, Kriston P.

    2012-01-01

    Highly active Ru/TiO2 catalysts for Sabatier reaction have been developed. The catalysts have shown to be stable under repeated shutting down/startup conditions. When the Ru/TiO2 catalyst is coated on the engineered substrate Fe-CrAlY felt, activity enhancement is more than doubled when compared with an identically prepared engineered catalyst made from commercial Degussa catalyst. Also, bimetallic Ru-Rh/TiO2 catalysts show high activity at high throughput.

  16. Structure and Activity of Pt-Ni Catalysts Supported on Modified Al2O3 for Ethanol Steam Reforming.

    PubMed

    Navarro, R M; Sanchez-Sanchez, M C; Fierro, J L G

    2015-09-01

    Modification of alumina with La-, Ce-, Zr- and Mg-oxides was studied with the aim to use them as supports of bimetallic Pt-Ni catalysts for the steam reforming of ethanol. Activity results showed that modifications of Al2O3 support with the incorporation of La, Ce, Zr or Mg oxides play an essential role in the catalytic behaviour of PtNi catalysts. Bimetallic PtNi catalyst supported on bare Al2O3 showed evolution of the reaction products with time on stream consisting in the increase of C2H4 production with concomitant decrease of CH4 and CO2 production. The addition of Mg or Zr to γ-A1203 did not inhibit the appearance of ethylene but delayed its production. In the case of Ce- or La-supported catalysts, the product selectivities were stable with time-on-stream, with no changes being observed in the product distribution for 24 h. Characterization results showed that La- and Ce-containing supports improves the Pt and Ni metal exposure values. The better stability achieved for Ce and La containing catalysts was inferred to be related with a participation/assistance of lanthanum and cerium entities in the gasification of coke deposits together with a modification of Pt and Ni dispersion which lower the probability of the nucleation of coke precursors on their surfaces. PMID:26716216

  17. Hydrogasification of carbon adsorbed on sulfur-poisoned dispersed metal catalysts. Final report

    SciTech Connect

    McCarty, J.G.; Wood, B.J.

    1993-12-01

    The temperature programmed reaction of 1- to 10-atom hydrogen (TPRH) with carbon deposited on alumina supported Ni, Ru, and Co and on fused Fe catalysts has been developed to examine the effect of sulfur poisoning on coking rates and the nature of the deposited carbon. A new procedure, passivation by carbon deposition on clean reduced metals and low temperature (20--50 C) exposure to recirculate dilute H{sub 2}S with moderate 0.1 atm partial pressure of CO{sub 2} was used to slow the rate of sulfur chemisorption. This method facilitated slow uniform sulfur chemisorption to fractional saturation coverages. Fractional sulfur poisoning generally blocked sites of active surface carbon (or hydrocarbon fragments) while suppressing rates of hydrogasification as shown by the increasing temperatures in the TPRH hydrogasification rate versus temperature spectra. Fractional sulfur poisoning (e.g., half saturation) appears to inhibit H{sub 2} gasification with surface carbon surprisingly without strongly affecting catalytic activity. Sulfur poisoning to saturation levels (defined here as {approximately}1 ppm H{sub 2}S in 1-atm H{sub 2} at 500 C) always results in complete loss of activity and is also marked by the growth of a very unreactive form of carbon.

  18. Infrared study of CO adsorption on magnesia-supported ruthenium, gold, and bimetallic ruthenium-gold clusters

    SciTech Connect

    Schwank, J.; Parravano, G.; Gruber, H.L.

    1980-01-01

    An infrared study of CO adsorption on magnesia-supported ruthenium, gold, and bimetallic ruthenium-gold clusters provided evidence for metal-support interaction in the single-metal catalysts and for metal-metal interaction in the bimetallic catalysts which indicated that all the metal present existed as bimetallic clusters and that gold did not form separate clusters or segregate at the surface. The IR study was made at various degrees of coverage with CO of catalysts containing 2.1-4.7% metal (0, 11, 36, 90, and 100Vertical Bar3< gold) on magnesia and pretreated in hydrogen, helium or oxygen, and a comparison sample of 5% ruthenium on silica.

  19. Effect of cobalt precursors on the dispersion, reduction, and CO oxidation of CoO(x)/γ-Al2O3 catalysts calcined in N2.

    PubMed

    Zhang, Lingling; Dong, Lihui; Yu, Wujiang; Liu, Lianjun; Deng, Yu; Liu, Bin; Wan, Haiqin; Gao, Fei; Sun, Keqin; Dong, Lin

    2011-03-15

    The present work tentatively investigated the effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the physicochemical properties of CoO(x)/γ-Al(2)O(3) catalysts calcined in N(2). XRD, Raman, XPS, FTIR, and UV-vis DRS results suggested that CoO/γ-Al(2)O(3) was obtained from cobalt acetate precursors and CoO was dispersed on γ-Al(2)O(3) below its dispersion capacity of 1.50 mmol/(100 m(2) γ-Al(2)O(3)), whereas Co(3)O(4)/γ-Al(2)O(3) was obtained from cobalt nitrate precursors and Co(3)O(4) preferred to agglomerate above the dispersion capacity of 0.15 mmol/(100m(2) γ-Al(2)O(3)). Compared with Co(3)O(4)/γ-Al(2)O(3), CoO/γ-Al(2)O(3) catalysts were difficult to be reduced and easy to desorb oxygen species at low temperatures and presented high activities for CO oxidation as proved by H(2)-TPR, O(2)-TPD, and CO oxidation model reaction results. A surface incorporation model was proposed to explain the dispersion and reduction properties of CoO/γ-Al(2)O(3) catalysts.

  20. Effect of cobalt precursors on the dispersion, reduction, and CO oxidation of CoO(x)/γ-Al2O3 catalysts calcined in N2.

    PubMed

    Zhang, Lingling; Dong, Lihui; Yu, Wujiang; Liu, Lianjun; Deng, Yu; Liu, Bin; Wan, Haiqin; Gao, Fei; Sun, Keqin; Dong, Lin

    2011-03-15

    The present work tentatively investigated the effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the physicochemical properties of CoO(x)/γ-Al(2)O(3) catalysts calcined in N(2). XRD, Raman, XPS, FTIR, and UV-vis DRS results suggested that CoO/γ-Al(2)O(3) was obtained from cobalt acetate precursors and CoO was dispersed on γ-Al(2)O(3) below its dispersion capacity of 1.50 mmol/(100 m(2) γ-Al(2)O(3)), whereas Co(3)O(4)/γ-Al(2)O(3) was obtained from cobalt nitrate precursors and Co(3)O(4) preferred to agglomerate above the dispersion capacity of 0.15 mmol/(100m(2) γ-Al(2)O(3)). Compared with Co(3)O(4)/γ-Al(2)O(3), CoO/γ-Al(2)O(3) catalysts were difficult to be reduced and easy to desorb oxygen species at low temperatures and presented high activities for CO oxidation as proved by H(2)-TPR, O(2)-TPD, and CO oxidation model reaction results. A surface incorporation model was proposed to explain the dispersion and reduction properties of CoO/γ-Al(2)O(3) catalysts. PMID:21216407

  1. Synthesis of subnanometer-diameter vertically aligned single-walled carbon nanotubes with copper-anchored cobalt catalysts

    NASA Astrophysics Data System (ADS)

    Cui, Kehang; Kumamoto, Akihito; Xiang, Rong; An, Hua; Wang, Benjamin; Inoue, Taiki; Chiashi, Shohei; Ikuhara, Yuichi; Maruyama, Shigeo

    2016-01-01

    We synthesize vertically aligned single-walled carbon nanotubes (VA-SWNTs) with subnanometer diameters on quartz (and SiO2/Si) substrates by alcohol CVD using Cu-anchored Co catalysts. The uniform VA-SWNTs with a nanotube diameter of 1 nm are synthesized at a CVD temperature of 800 °C and have a thickness of several tens of μm. The diameter of SWNTs was reduced to 0.75 nm at 650 °C with the G/D ratio maintained above 24. Scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into a larger size, which contributed to the small diameter of SWNTs. The correlation between the catalyst size and the SWNT diameter was experimentally clarified. The subnanometer-diameter and high-quality SWNTs are expected to pave the way to replace silicon for next-generation optoelectronic and photovoltaic devices.We synthesize vertically aligned single-walled carbon nanotubes (VA-SWNTs) with subnanometer diameters on quartz (and SiO2/Si) substrates by alcohol CVD using Cu-anchored Co catalysts. The uniform VA-SWNTs with a nanotube diameter of 1 nm are synthesized at a CVD temperature of 800 °C and have a thickness of several tens of μm. The diameter of SWNTs was reduced to 0.75 nm at 650 °C with the G/D ratio maintained above 24. Scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into a larger size, which contributed to the small diameter of SWNTs. The correlation between the catalyst size and the SWNT diameter was experimentally clarified. The subnanometer-diameter and high

  2. Hydrocracking of n-decane over zeolite-supported metal sulfide catalysts. 2: Zeolite Y-supported Ni and Ni-Mo sulfides

    SciTech Connect

    Welters, W.J.J.; Waerden, O.H. van der; Beer, V.H.J. de; Santen, R.A. van

    1995-04-01

    For zeolite Y-supported nickel sulfide catalysts the influence of the metal sulfide dispersion on the hydrocracking properties for n-decane is examined. In order to obtain different nickel sulfide distributions (inside or outside the zeolite structure) and dispersions, the preparation method (impregnation of CaY or ion exchange of NaY), sulfidation procedure (direct sulfidation or sulfidation after drying), and metal loading are varied. A higher nickel sulfide surface (as measured by dynamic oxygen chemisorption) results in a strong increase of the n-decane conversion, but this is not accompanied by an improvement of the catalytic properties toward ideal hydrocracking. Additionally, some zeolite Y-supported Ni-Mo sulfide catalysts (varying in preparation method and sulfidation procedure) are tested for the hydroconversion of it-decane. However, no promoter effect could be observed. The activity of the bimetallic sulfide catalysts is always almost equal to that of the most active monometallic sulfide constituent.

  3. INTERACTION OF SULPHUR WITH BIMETALLIC SURFACES: EFFECTS OF STRUCTURAL, ELECTRONIC AND CHEMICAL PROPERTIES.

    SciTech Connect

    RODRIGUEZ,J.A.; HRBEK,J.

    2001-10-04

    In recent years, several new interesting phenomena have been discovered when studying the interaction of sulphur with bimetallic surfaces using the modern techniques of surface science. Very small amounts of sulphur can induce dramatic changes in the morphology of bimetallic surfaces. The electronic perturbations associated with the formation of a heteronuclear metal-metal bond affect the reactivity of the bonded metals toward sulphur. This can be a very important issue to consider when trying to minimize the negative effects of sulphur poisoning or dealing with the design of desulfurization catalysts.

  4. Transition metal bimetallic oxycarbides: Synthesis, characterization, and activity studies

    SciTech Connect

    Oyama, S.T.; Yu, C.C.; Ramanathan, S.

    1999-06-10

    A new family of bimetallic oxycarbide compounds M{sup I}-M{sup II}-O-C (M{sup I} = Mo, W; M{sup II} = V, Nb, Cr, Fe, Co, Ni) has been synthesized by carburizing bimetallic oxide precursors using a temperature-programmed method. The oxide precursors are prepared by conventional solid-state reaction between two appropriate monometallic oxides. The synthesis involves passing a 20 mol% CH{sub 4} in H{sub 2} mixture over the oxide precursors while raising the temperature at a linear rate of 8.3 {times} 10{sup {minus}2} K/s (5 K/min) to a final temperature (T{sub max}) which is held for a period of time (t{sub hold}). The synthesis, chemisorption properties, and reactivation of the materials indicate that the compounds can be divided into two groups of different reducibility (high and low). Their surface activity and surface area are evaluated based on CO chemisorption and N{sub 2} physisorption measurements. It is found that the CO number density correlates with the reducibility of the compounds. The catalysts were evaluated for hydroprocessing in a three-phase trickle-bed reactor operated at 3.1 MPa and 643 K. The feed was a model liquid mixture containing 3000 ppm sulfur (dibenzothiophene), 2000 ppm nitrogen (quinoline), 500 ppm oxygen (benzofuran), 20 wt% aromatics (tetralin), and balance aliphatics (tetradecane). The bimetallic oxycarbides had moderate activity for HDN of quinoline, with Nb-Mo-O-C showing higher HDN than a commercial sulfided Ni-Mo/Al{sub 2}O{sub 3} catalyst tested at the same conditions. X-ray diffraction of the spent catalysts indicated that the oxycarbides of the early transition metals were tolerant of sulfur, while those involving the late transition metals showed bulk sulfide phases.

  5. Highly dispersed pd catalyst locked in knitting aryl network polymers for Suzuki-Miyaura coupling reactions of aryl chlorides in aqueous media.

    PubMed

    Li, Buyi; Guan, Zhenhong; Wang, Wei; Yang, Xinjia; Hu, Jianglin; Tan, Bien; Li, Tao

    2012-07-01

    Highly dispersed palladium chloride catalysts locked in triphenylphosphine-functionalized knitting aryl network polymers (KAPs) are developed and exhibit excellent activity under mild conditions in the Suzuki-Miyaura cross-coupling reactions of aryl chlorides in aqueous media. This work highlights that the microporous polymers not only play the role of support materials, but also protect the Pd species from aggregation and precipitation, hence, positively effect the catalysis activity.

  6. Stellated Ag-Pt bimetallic nanoparticles: An effective platform for catalytic activity tuning

    PubMed Central

    Liu, Hui; Ye, Feng; Yao, Qiaofeng; Cao, Hongbin; Xie, Jianping; Lee, Jim Yang; Yang, Jun

    2014-01-01

    The usefulness of Pt-based nanomaterials for catalysis can be greatly enhanced by coupling morphology engineering to the strategic presence of a second or even third metal. Here we demonstrate the design and preparation of stellated Ag-Pt bimetallic nanoparticles where significant activity difference between the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR) may be realized by relegating Ag to the core or by hollowing out the core. In particular the stellated Pt surface, with an abundance of steps, edges, corner atoms, and {111} facets, is highly effective for the ORR but is ineffective for MOR. MOR activity is only observed in the presence of a Ag core through electronic coupling to the stellated Pt shell. The bimetallic Ag-Pt stellates therefore demonstrate the feasibility of tuning a Pt surface for two very different structure sensitive catalytic reactions. Stellated bimetallics may therefore be an effective platform for highly tunable catalyst designs. PMID:24495979

  7. Biosynthesis of Pd-Au alloys on carbon fiber paper: Towards an eco-friendly solution for catalysts fabrication

    NASA Astrophysics Data System (ADS)

    Zhuang, Zechao; Wang, Feifeng; Naidu, Ravendra; Chen, Zuliang

    2015-09-01

    Bimetallic nanomaterials with enhanced activity and stability have been extensively studied as emerging catalysts for hydrogen evolution reaction (HER). Expensive and environmentally unfriendly chemical synthesis routes inhibit their large-scale applications. In this work, we developed a facile and green synthesis of Pd-Au alloy nanoparticles (NPs) dispersed on carbon fiber paper (CFP) by plant-mediated bioreduction coupled with self-assembly. Engineering the morphology and composition of bimetallic catalysts synthesized by plant extracts on complex substrate is achieved. The resulting NPs are uniform in shape and have a spherical morphology with an average diameter of ∼180 nm, in which the molar ratio of Au/Pd is near 75:25 and the catalysts loading is about 0.5 mg cm-2. The Pd-Au/CFP hybrid electrode exhibits an excellent HER performance with a Tafel slope of 47 mV dec-1 and an exchange current density of 0.256 mA cm-2. Electrochemical stability tests through long-term potential cycles and potentiostatic electrolysis further confirm the high durability of the electrode. This development offers an efficient and eco-friendly catalysts synthesis route for constructing water-splitting cells and other electrocatalytic devices.

  8. Probing the interaction of Rh, Co and bimetallic Rh-Co nanoparticles with the CeO2 support: catalytic materials for alternative energy generation.

    PubMed

    Varga, E; Pusztai, P; Óvári, L; Oszkó, A; Erdőhelyi, A; Papp, C; Steinrück, H-P; Kónya, Z; Kiss, J

    2015-10-28

    The interaction of CeO2-supported Rh, Co and bimetallic Rh-Co nanoparticles, which are active catalysts in hydrogen production via steam reforming of ethanol, a process related to renewable energy generation, was studied by X-ray diffraction (XRD), high resolution electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). Furthermore, diffuse reflectance infrared spectroscopy (DRIFTS) of adsorbed CO as a probe molecule was used to characterize the morphology of metal particles. At small loadings (0.1%), Rh is in a much dispersed state on ceria, while at higher contents (1-5%), Rh forms 2-8 nm particles. Between 473-673 K pronounced oxygen transfer from ceria to Rh is observed and at 773 K significant agglomeration of Rh occurs. On reduced ceria, XPS indicates a possible electron transfer from Rh to ceria. The formation of smaller ceria crystallites upon loading with Co was concluded from XRD and HRTEM; for 10% Co, the CeO2 particle size decreased from 27.6 to 10.7 nm. A strong dissolution of Co into ceria and a certain extent of encapsulation by ceria were deduced by XRD, XPS and LEIS. In the bimetallic system, the presence of Rh enhances the reduction of cobalt and ceria. During thermal treatments, reoxidation of Co occurs, and Rh agglomeration as well as oxygen migration from ceria to Rh are hindered in the presence of cobalt.

  9. Probing the interaction of Rh, Co and bimetallic Rh-Co nanoparticles with the CeO2 support: catalytic materials for alternative energy generation.

    PubMed

    Varga, E; Pusztai, P; Óvári, L; Oszkó, A; Erdőhelyi, A; Papp, C; Steinrück, H-P; Kónya, Z; Kiss, J

    2015-10-28

    The interaction of CeO2-supported Rh, Co and bimetallic Rh-Co nanoparticles, which are active catalysts in hydrogen production via steam reforming of ethanol, a process related to renewable energy generation, was studied by X-ray diffraction (XRD), high resolution electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). Furthermore, diffuse reflectance infrared spectroscopy (DRIFTS) of adsorbed CO as a probe molecule was used to characterize the morphology of metal particles. At small loadings (0.1%), Rh is in a much dispersed state on ceria, while at higher contents (1-5%), Rh forms 2-8 nm particles. Between 473-673 K pronounced oxygen transfer from ceria to Rh is observed and at 773 K significant agglomeration of Rh occurs. On reduced ceria, XPS indicates a possible electron transfer from Rh to ceria. The formation of smaller ceria crystallites upon loading with Co was concluded from XRD and HRTEM; for 10% Co, the CeO2 particle size decreased from 27.6 to 10.7 nm. A strong dissolution of Co into ceria and a certain extent of encapsulation by ceria were deduced by XRD, XPS and LEIS. In the bimetallic system, the presence of Rh enhances the reduction of cobalt and ceria. During thermal treatments, reoxidation of Co occurs, and Rh agglomeration as well as oxygen migration from ceria to Rh are hindered in the presence of cobalt. PMID:26415514

  10. Antibacterial activity of graphene supported FeAg bimetallic nanocomposites.

    PubMed

    Ahmad, Ayyaz; Qureshi, Abdul Sattar; Li, Li; Bao, Jie; Jia, Xin; Xu, Yisheng; Guo, Xuhong

    2016-07-01

    We report the simple one pot synthesis of iron-silver (FeAg) bimetallic nanoparticles with different compositions on graphene support. The nanoparticles are well dispersed on the graphene sheet as revealed by the TEM, XRD, and Raman spectra. The antibacterial activity of graphene-FeAg nanocomposite (NC) towards Bacillus subtilis, Escherichia coli, and Staphylococcus aureus was investigated by colony counting method. Graphene-FeAg NC demonstrates excellent antibacterial activity as compared to FeAg bimetallic without graphene. To understand the antibacterial mechanism of the NC, oxidative stress caused by reactive oxygen species (ROS) and the glutathione (GSH) oxidation were investigated in the system. It has been observed that ROS production and GSH oxidation are concentration dependent while the increase in silver content up to 50% generally enhances the ROS production while ROS decreases on further increase in silver content. Graphene loaded FeAg NC demonstrates higher GSH oxidation capacity than bare FeAg bimetallic nanocomposite. The mechanism study suggests that the antibacterial activity is probably due to membrane and oxidative stress produced by the nanocomposites. The possible antibacterial pathway mainly includes the non-ROS oxidative stress (GSH oxidation) while ROS play minor role. PMID:27038914

  11. Platinum indium bimetallic in silicalite: Preparation, characterization and use in the vinylcyclohexene transformation

    SciTech Connect

    Meriaudeau, P.; Thangaraj, A.; Naccache, C.

    1996-12-31

    The discovery of bimetallic catalysts such as Pt-Re, Pt-Ir, Pt-Sn has been a major improvement in the reforming process. The metal support was chlorinated alumina. Another generation of reforming catalysts consisted of Pt supported on non acid zeolite, KL zeolite being preferred. Recently a patent from Mobil (1) claimed for the reforming of C{sub 6}-C{sub 8} n-alkanes a catalyst constituted by platinum on an indium silicalite; these solids are able to reform n-octane into ethylbenzene (EBZ) and styrene (STY). PtIn/silicalite catalysts were reinvestigated and the high performances of this type of material attributed to the existence of small PtIn clusters as well to the shape selectivity of the silicalite (2a). Also, it has been shown that PtIn bimetallic clusters supported on NaY zeolite was active and selective in the dehydrogenation of light alkanes but these materials suffered from fast deactivation (2b). In this work, we have extended the studies of the dehydrogenation-dehydrocyclisation of alkanes over PtIn bimetallic supported on silicalite to the reaction of vinylcyclohexene (VCHx) over these materials.

  12. Electrocatalytical study of carbon supported Pt, Ru and bimetallic Pt-Ru nanoparticles for oxygen reduction reaction in alkaline media

    NASA Astrophysics Data System (ADS)

    Hosseini, M. G.; Zardari, P.

    2015-08-01

    Carbon supported Pt, Ru and bimetallic Pt-Ru nanoparticles (Pt/C, Ru/C and Pt.Ru/C) have been prepared by the chemical reduction method. Particle morphology, composition and structure of nanoparticles have been investigated by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. SEM results showed a uniform dispersion of nanoparticles with rough and porous structure into carbon supports with the average particle size of 30-64 nm. EDX analysis demonstrated the presence of both Pt and Ru nanoparticles in each gas diffusion electrode. The Pt/C, Ru/C and Pt.Ru/C composites were used as electrocatalyst for oxygen reduction reaction (ORR) in alkaline media. The ORR activities of cathodes were characterized using cyclic voltammetry (CV), polarization technique, AC impedance spectroscopy (EIS) and chronoamperometry. CV and polarization curves showed significantly higher activity on Pt.Ru/C electrocatalyst than observed on Pt/C and Ru/C catalysts, which can be related to synergistic effect, which is playing a critical role in ORR activity. The Tafel slope values of 120 mV/dec showed that the first electron transfer is the rate determining step. The EIS results of cathodes under different polarization potentials indicated two different behaviours which depend on the applied dc potentials and reveal different electrochemical processes occurring on the electrodes.

  13. Enhanced dechlorination of trichloroethylene using electrospun polymer nanofibrous mats immobilized with iron/palladium bimetallic nanoparticles.

    PubMed

    Ma, Hui; Huang, Yunpeng; Shen, Mingwu; Guo, Rui; Cao, Xueyan; Shi, Xiangyang

    2012-04-15

    Fe/Pd bimetallic nanoparticles (NPs) have held great promise for treating trichloroethylene (TCE)-contaminated groundwater, without the accumulation of chlorinated intermediates. However, the conventionally used colloidal Fe/Pd NPs usually aggregate rapidly, resulting in a reduced reactivity. To reduce the particle aggregation, we employed electrospun polyacrylic acid (PAA)/polyvinyl alcohol (PVA) polymer nanofibers as a nanoreactor to immobilize Fe/Pd bimetallic NPs. In the study, the water-stable PAA/PVA nanofibrous mats were complexed with Fe (III) ions via the binding with the free carboxyl groups of PAA for subsequent formation and immobilization of zero-valent iron (ZVI) NPs. Fe/Pd bimetallic NPs were then formed by the partial reduction of Pd(II) ions with ZVI NPs. The formed electrospun nanofibrous mats containing Fe/Pd bimetallic NPs with a diameter of 2.8 nm were characterized by scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, thermogravimetric analysis, and inductively coupled plasma-atomic emission spectroscopy. The Fe/Pd NP-containing electrospun PAA/PVA nanofibrous mats exhibited higher reactivity than that of the ZVI NP-containing mats or colloidal Fe/Pd NPs in the dechlorination of trichloroethylene (TCE), which was used as a model contaminant. With the high surface area to volume ratio, high porosity, and great reusability of the fibrous mats immobilized with the bimetallic NPs, the composite nanofibrous mats should be amenable for applications in remediation of various environmental contaminants. PMID:22138171

  14. Enhanced dechlorination of trichloroethylene using electrospun polymer nanofibrous mats immobilized with iron/palladium bimetallic nanoparticles.

    PubMed

    Ma, Hui; Huang, Yunpeng; Shen, Mingwu; Guo, Rui; Cao, Xueyan; Shi, Xiangyang

    2012-04-15

    Fe/Pd bimetallic nanoparticles (NPs) have held great promise for treating trichloroethylene (TCE)-contaminated groundwater, without the accumulation of chlorinated intermediates. However, the conventionally used colloidal Fe/Pd NPs usually aggregate rapidly, resulting in a reduced reactivity. To reduce the particle aggregation, we employed electrospun polyacrylic acid (PAA)/polyvinyl alcohol (PVA) polymer nanofibers as a nanoreactor to immobilize Fe/Pd bimetallic NPs. In the study, the water-stable PAA/PVA nanofibrous mats were complexed with Fe (III) ions via the binding with the free carboxyl groups of PAA for subsequent formation and immobilization of zero-valent iron (ZVI) NPs. Fe/Pd bimetallic NPs were then formed by the partial reduction of Pd(II) ions with ZVI NPs. The formed electrospun nanofibrous mats containing Fe/Pd bimetallic NPs with a diameter of 2.8 nm were characterized by scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy, thermogravimetric analysis, and inductively coupled plasma-atomic emission spectroscopy. The Fe/Pd NP-containing electrospun PAA/PVA nanofibrous mats exhibited higher reactivity than that of the ZVI NP-containing mats or colloidal Fe/Pd NPs in the dechlorination of trichloroethylene (TCE), which was used as a model contaminant. With the high surface area to volume ratio, high porosity, and great reusability of the fibrous mats immobilized with the bimetallic NPs, the composite nanofibrous mats should be amenable for applications in remediation of various environmental contaminants.

  15. Advanced liquefaction using coal swelling and catalyst dispersion techniques. Quarterly technical progress report No. 7, April 1993--June 1993

    SciTech Connect

    Curtis, C.W.; Chander, S.; Gutterman, C.

    1994-09-01

    The overall objective of this project is to develop a new approach for the direct liquefaction of coal to produce an all-distillate product slate at a sizable cost reduction over current technology. The approach integrates coal selection, pretreatment, coal swelling with catalyst impregnation, liquefaction, product recovery with characterization, alternate bottoms processing, and carrying out a technical assessment including an economic evaluation. The project is being carried out under contract to the United States Department of Energy. All three coals used in this study (Black Thunder, Burning Star bituminous, and Martin Lake lignite) are effectively swelled by a number of solvents. The most effective solvents are those having hetero-functionality. In addition, a synergistic effect has been demonstrated, in which solvent blends are more effective for coal swelling than the pure solvents alone. Therefore, it will be necessary to use only low levels of swelling agents and yet promote the impregnation of catalyst precursors. The rate of the impregnation of catalyst precursors into swollen coal increases greatly as the effectiveness of the solvent to swell the coal increases. This effect is also demonstrated by improved catalyst precursor impregnation with increased contact temperature. Laboratory- and bench-scale liquefaction experimentation is underway using swelled and catalyst impregnated coal samples. Higher coal conversions were observed for the SO{sub 2}-treated coal than the raw coal, regardless of catalyst type. Conversions of swelled coal were highest when Molyvan-L, molybdenum naphthenate, and nickel octoate, respectively, were added to the liquefaction solvent.

  16. Development of MCM-41 based catalysts for the photo-Fenton's degradation of dye pollutants

    NASA Astrophysics Data System (ADS)

    Lam, Leung Yuk Frank

    The continuous advancement in most industries has resulted in serious water pollution problems. The industrial effluents contain a variety of highly toxic organics such as dye pollutants. Numerous processes have been demonstrated for treating such pollutants. Among them, photo-Fenton's reaction is effective for organic mineralization by hydroxyl radicals generated from the Fenton's reagents (Fe2+ and H2O2). However, there is a drawback in that it requires a separation system to recover the homogeneous ferrous ion in the treated wastewater. In this research, new heterogeneous Fenton's catalysts are developed to solve such a problem and to achieve an efficient mineralization of dye pollutants. Two methods for catalyst preparation, including sol-gel hydrothermal (SG) and metal-organic chemical vapor deposition (MOCVD) techniques, were studied in this work. For SG-prepared catalysts, the iron element was successfully doped into the MCM-41 structure. These catalysts demonstrated a good catalytic efficiency but leaching of metal ions from the developed catalyst was found. In the MOCVD technique, a rotated tubular reactor system was developed to synthesize Fe/MCM-41 catalyst with uniform metal dispersion. It was found that using oxygen as a carrier gas during metal deposition was able to increase the stability of the deposited metal. In degradation of a model dye pollutant, Orange II, a total of 85% TOC mineralization was achieved at pH 3. A disadvantage of using Fe/MCM-41 was the reduced efficiency at higher pH. Cu/MCM-41 was thus developed and showed better catalytic activities than Fe/MCM-41 at neutral pH. Having the specific catalytic properties of Fe/MCM-41 and Cu/MCM-41, bimetallic (Fe+Cu) catalysts supported on MCM-41 were developed which show better activities in the Orange II mineralization than those monometallic (Fe or Cu) catalysts. The preparation conditions of the catalysts were experimentally optimized. The effects of catalyst dosage, metal loading

  17. Roles of molecular hydrogen and a hydrogen donor solvent in the cracking of moal model compounds with dispersed catalysts

    SciTech Connect

    Suzuki, Toshimitsu; Ikenaga, Na-oki; Sakota, Takahiro

    1994-12-31

    It is of great importance to evaluate quantitative hydrogen transfer process by using coal model compounds with a hydrogen-donor solvent. Cronauer el al. showed that in the cracking of benzyl phenyl ether the hydrogen required to stabilize free radicals comes from a donor solvent or intramolecular rearrangement and not from gaseous hydrogen in the absence of a catalyst. Korobkov et al. and Schlosberg et al. showed that the thermolysis of benzyl phenyl ether and dibenzyl ether were accomplished by intramolecular rearrangements. Yokokawa et al. reported that tetralin retarded the catalyzed hydrocracking of coal model compounds containing C-C and C-O bonds. However, few studies dealt with quantitative discussion in the hydrogen transfer process from a hydrogen-donor solvent or molecular hydrogen to free radicals derived from a model compound except a series of studies by Nicole and co-workers. On the other hand, it is well known that the amount of naphthalene produced from tetralin decreases after the liquefaction of coal in tetralin with catalyst as compared to the liquefaction in the absence of catalysts. To account for this, two mechanisms are proposed. One is that the catalyst hydrogenates naphthalene produced from tetralin, and the other is that the catalyst promotes the direct hydrogen transfer from molecular hydrogen to free radicals. The purpose of this work is to elucidate the role of catalyst and tetralin by means of the quantitative treatment of the hydrogen transfer reaction stabilizing thermally decomposed free radicals. Cracking of benzyl phenyl ether (BPE), dibenzyl ether (DBE), 1,2-diphenylethane, and 1,3-diphenylpropane was studied in tetralin in the presence of highly disposed catalyst.

  18. Advanced liquefaction using coal swelling and catalyst dispersion techniques. Volume 1, Final technical report, October 1, 1991--September 30, 1994

    SciTech Connect

    Curtis, C.W.; Gutterman, C.; Chander, S.

    1994-12-31

    The overall objective of this project was to develop a new approach for the direct liquefaction of coal to produce an all-distillate product slate at a sizable cost reduction over current technology. The approach integrated coal selection, pretreatment, coal swelling with catalyst impregnation, liquefaction, product recovery with characterization, alternate bottoms processing, and a technical assessment including an economic evaluation. Heterofunctional solvents were the most effective in swelling coals. Also solvent blends such as isopropanol/water were more effective than pure solvents alone. Impregnating slurry catalysts simultaneously during coal swelling showed that better uptake was achieved with nonswelling solvent and higher impregnation temperature. Some enhancement in initial coal conversion was seen liquefying SO{sub 2}-treated Black Thunder coal with slurry catalysts, and also when hydrogen donor liquefaction solvents were used. Noncatalytic reactions showed no benefit from SO{sub 2} treatment. Coupling coal swelling and SO{sub 2} treatment with slurry catalysts was also not beneficial, although high conversion was seen with continuous operation and long residence time, however, similar high conversion was observed with untreated coal. SO{sub 2} treatment is not economically attractive unless it provides about 17% increase in coal reactivity. In most cases, the best results were obtained when the coal was untreated and the slurry catalyst was added directly into the reactor. Foster Wheeler`s ASCOT process had better average liquid yields than either Wilsonville`s vacuum tower/ROSE combination or delayed coking process. This liquid product also had good quality.

  19. Quantification of copper phases, their reducibility and dispersion in doped-CuCl2/Al2O3 catalysts for ethylene oxychlorination.

    PubMed

    Muddada, N B; Olsbye, U; Leofanti, G; Gianolio, D; Bonino, F; Bordiga, S; Fuglerud, T; Vidotto, S; Marsella, A; Lamberti, C

    2010-09-28

    The comprehensive understanding of the composition, behaviour and reactivity of a catalyst used inside industrial plants is an extremely hard task that is rarely achieved. It requires the use of different spectroscopic techniques, applied under in situ or in operando conditions, and combined with the investigation of the catalyst activity. Often the operating experimental conditions are different from technique to technique and the different results must be compared with care. In the present contribution, we combined in situ XANES/EXAFS, IR spectroscopy of adsorbed CO, CO chemisorption and catalytic tests performed using a pulse reactor in depletive mode. This multitechnical approach resulted in the understanding of the role that dopants (LiCl, KCl, CsCl, MgCl(2) LaCl(3)) have in the nature, relative fraction, reducibility and dispersion of Cu-phases on CuCl(2)/gamma-Al(2)O(3) catalysts for oxychlorination reaction, a key step of the PVC chemistry. In the undoped catalyst two Cu phases coexist: Cu-aluminate and supported CuCl(2), being the latter the only active one [J. Catal., 2000, 189, 91]. EXAFS and XANES highlighted that all dopants contribute more or less efficiently in increasing the fraction of the active copper species, that reaches a value of almost 100% in the case of MgCl(2) or LaCl(3). EXAFS directly, and IR indirectly, proved that the addition of KCl or CsCl (and less efficiently of LiCl) results in the formation of mixed CuK(x)Cl(2+x) or CuCs(x)Cl(2+x) phases, so altering the chemical nature of the active phase. XANES spectroscopy indicates that addition of MgCl(2) or LaCl(3) does not affect the reducibility by ethylene (under static conditions) of the active CuCl(2) phase and that the reducibilility of the new copper-dopant mixed chloride are in the order CuCl(2) > CuLi(x)Cl(2+x) > CuK(x)Cl(2+x) > CuCs(x)Cl(2+x). However, when reduction is done inside a pulse reactor, a more informative picture comes out. The last technique is able to differentiate

  20. Nanopore and nanoparticle catalysts.

    PubMed

    Thomas, J M; Raja, R

    2001-01-01

    The design, atomic characterization, performance, and relevance to clean technology of two distinct categories of new nanocatalysts are described and interpreted. Exceptional molecular selectivity and high activity are exhibited by these catalysts. The first category consists of extended, crystallographically ordered inorganic solids possessing nanopores (apertures, cages, and channels), the diameters of which fall in the range of about 0.4 to about 1.5 nm, and the second of discrete bimetallic nanoparticles of diameter 1 to 2 nm, distributed more or less uniformly along the inner walls of mesoporous (ca. 3 to 10 nm diameter) silica supports. Using the principles and practices of solid-state and organometallic chemistry and advanced physico-chemical techniques for in situ and ex situ characterization, a variety of powerful new catalysts has been evolved. Apart from those that, inter alia, simulate the behavior of enzymes in their specificity, shape selectivity, regio-selectivity, and ability to function under ambient conditions, many of these new nanocatalysts are also viable as agents for effecting commercially significant processes in a clean, benign, solvent-free, single-step fashion. In particular, a bifunctional, molecular sieve nanopore catalyst is described that converts cyclohexanone in air and ammonia to its oxime and caprolactam, and a bimetallic nanoparticle catalyst that selectively converts cyclic polyenes into desirable intermediates. Nanocatalysts in the first category are especially effective in facilitating highly selective oxidations in air, and those in the second are well suited to effecting rapid and selective hydrogenations of a range of organic compounds.

  1. Bimetallic nanoparticles for arsenic detection.

    PubMed

    Moghimi, Nafiseh; Mohapatra, Mamata; Leung, Kam Tong

    2015-06-01

    Effective and sensitive monitoring of heavy metal ions, particularly arsenic, in drinking water is very important to risk management of public health. Arsenic is one of the most serious natural pollutants in soil and water in more than 70 countries in the world. The need for very sensitive sensors to detect ultralow amounts of arsenic has attracted great research interest. Here, bimetallic FePt, FeAu, FePd, and AuPt nanoparticles (NPs) are electrochemically deposited on the Si(100) substrate, and their electrochemical properties are studied for As(III) detection. We show that trace amounts of As(III) in neutral pH could be determined by using anodic stripping voltammetry. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, and Pd) than pristine noble metal NPs (without Fe alloying). Limit of detection and linear range are obtained for FePt, FeAu, and FePd NPs. The best performance is found for FePt NPs with a limit of detection of 0.8 ppb and a sensitivity of 0.42 μA ppb(-1). The selectivity of the sensor has also been tested in the presence of a large amount of Cu(II), as the most detrimental interferer ion for As detection. The bimetallic NPs therefore promise to be an effective, high-performance electrochemical sensor for the detection of ultratrace quantities of arsenic.

  2. Bimetallic nanoparticles for arsenic detection.

    PubMed

    Moghimi, Nafiseh; Mohapatra, Mamata; Leung, Kam Tong

    2015-06-01

    Effective and sensitive monitoring of heavy metal ions, particularly arsenic, in drinking water is very important to risk management of public health. Arsenic is one of the most serious natural pollutants in soil and water in more than 70 countries in the world. The need for very sensitive sensors to detect ultralow amounts of arsenic has attracted great research interest. Here, bimetallic FePt, FeAu, FePd, and AuPt nanoparticles (NPs) are electrochemically deposited on the Si(100) substrate, and their electrochemical properties are studied for As(III) detection. We show that trace amounts of As(III) in neutral pH could be determined by using anodic stripping voltammetry. The synergistic effect of alloying with Fe leads to better performance for Fe-noble metal NPs (Au, Pt, and Pd) than pristine noble metal NPs (without Fe alloying). Limit of detection and linear range are obtained for FePt, FeAu, and FePd NPs. The best performance is found for FePt NPs with a limit of detection of 0.8 ppb and a sensitivity of 0.42 μA ppb(-1). The selectivity of the sensor has also been tested in the presence of a large amount of Cu(II), as the most detrimental interferer ion for As detection. The bimetallic NPs therefore promise to be an effective, high-performance electrochemical sensor for the detection of ultratrace quantities of arsenic. PMID:25938763

  3. P–C-Activated Bimetallic Rhodium Xantphos Complexes: Formation and Catalytic Dehydrocoupling of Amine–Boranes**

    PubMed Central

    Johnson, Heather C; Weller, Andrew S

    2015-01-01

    {Rh(xantphos)}-based phosphido dimers form by P–C activation of xantphos (4,5-bis(diphenylphosphino)-9,9-dimethylxanthene) in the presence of amine–boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H2BNMeH]n from H3B⋅NMeH2 and dimeric [H2BNMe2]2 from H3B⋅NMe2H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine–borane dehydropolymerization. PMID:26140498

  4. A Systematic Investigation of p-Nitrophenol Reduction by Bimetallic Dendrimer Encapsulated Nanoparticles

    PubMed Central

    2013-01-01

    We demonstrate that the reduction of p-nitrophenol to p-aminophenol by NaBH4 is catalyzed by both monometallic and bimetallic nanoparticles (NPs). We also demonstrate a straightforward and precise method for the synthesis of bimetallic nanoparticles using poly(amido)amine dendrimers. The resulting dendrimer encapsulated nanoparticles (DENs) are monodisperse, and the size distribution does not vary with different elemental combinations. Random alloys of Pt/Cu, Pd/Cu, Pd/Au, Pt/Au, and Au/Cu DENs were synthesized and evaluated as catalysts for p-nitrophenol reduction. These combinations are chosen in order to selectively tune the binding energy of the p-nitrophenol adsorbate to the nanoparticle surface. Following the Brønsted–Evans–Polanyi (BEP) relation, we show that the binding energy can reasonably predict the reaction rates of p-nitrophenol reduction. We demonstrate that the measured reaction rate constants of the bimetallic DENs is not always a simple average of the properties of the constituent metals. In particular, DENs containing metals with similar lattice constants produce a binding energy close to the average of the two constituents, whereas DENs containing metals with a lattice mismatch show a bimodal distribution of binding energies. Overall, in this work we present a uniform method for synthesizing pure and bimetallic DENs and demonstrate that their catalytic properties are dependent on the adsorbate’s binding energy. PMID:23616909

  5. Synergistic geometric and electronic effects for electrochemical reduction of carbon dioxide using gold-copper bimetallic nanoparticles.

    PubMed

    Kim, Dohyung; Resasco, Joaquin; Yu, Yi; Asiri, Abdullah Mohamed; Yang, Peidong

    2014-09-11

    Highly efficient and selective electrochemical reduction of carbon dioxide represents one of the biggest scientific challenges in artificial photosynthesis, where carbon dioxide and water are converted into chemical fuels from solar energy. However, our fundamental understanding of the reaction is still limited and we do not have the capability to design an outstanding catalyst with great activity and selectivity a priori. Here we assemble uniform gold-copper bimetallic nanoparticles with different compositions into ordered monolayers, which serve as a well-defined platform to understand their fundamental catalytic activity in carbon dioxide reduction. We find that two important factors related to intermediate binding, the electronic effect and the geometric effect, dictate the activity of gold-copper bimetallic nanoparticles. These nanoparticle monolayers also show great mass activities, outperforming conventional carbon dioxide reduction catalysts. The insights gained through this study may serve as a foundation for designing better carbon dioxide electrochemical reduction catalysts.

  6. Synergistic geometric and electronic effects for electrochemical reduction of carbon dioxide using gold-copper bimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Kim, Dohyung; Resasco, Joaquin; Yu, Yi; Asiri, Abdullah Mohamed; Yang, Peidong

    2014-09-01

    Highly efficient and selective electrochemical reduction of carbon dioxide represents one of the biggest scientific challenges in artificial photosynthesis, where carbon dioxide and water are converted into chemical fuels from solar energy. However, our fundamental understanding of the reaction is still limited and we do not have the capability to design an outstanding catalyst with great activity and selectivity a priori. Here we assemble uniform gold-copper bimetallic nanoparticles with different compositions into ordered monolayers, which serve as a well-defined platform to understand their fundamental catalytic activity in carbon dioxide reduction. We find that two important factors related to intermediate binding, the electronic effect and the geometric effect, dictate the activity of gold-copper bimetallic nanoparticles. These nanoparticle monolayers also show great mass activities, outperforming conventional carbon dioxide reduction catalysts. The insights gained through this study may serve as a foundation for designing better carbon dioxide electrochemical reduction catalysts.

  7. Synergistic geometric and electronic effects for electrochemical reduction of carbon dioxide using gold-copper bimetallic nanoparticles.

    PubMed

    Kim, Dohyung; Resasco, Joaquin; Yu, Yi; Asiri, Abdullah Mohamed; Yang, Peidong

    2014-01-01

    Highly efficient and selective electrochemical reduction of carbon dioxide represents one of the biggest scientific challenges in artificial photosynthesis, where carbon dioxide and water are converted into chemical fuels from solar energy. However, our fundamental understanding of the reaction is still limited and we do not have the capability to design an outstanding catalyst with great activity and selectivity a priori. Here we assemble uniform gold-copper bimetallic nanoparticles with different compositions into ordered monolayers, which serve as a well-defined platform to understand their fundamental catalytic activity in carbon dioxide reduction. We find that two important factors related to intermediate binding, the electronic effect and the geometric effect, dictate the activity of gold-copper bimetallic nanoparticles. These nanoparticle monolayers also show great mass activities, outperforming conventional carbon dioxide reduction catalysts. The insights gained through this study may serve as a foundation for designing better carbon dioxide electrochemical reduction catalysts. PMID:25208828

  8. Bimetallic Nanocatalysts in Mesoporous Silica for Hydrogen Production from Coal-Derived Fuels

    SciTech Connect

    Kuila, Debasish; Ilias, Shamsuddin

    2013-02-13

    In steam reforming reactions (SRRs) of alkanes and alcohols to produce H2, noble metals such as platinum (Pt) and palladium (Pd) are extensively used as catalyst. These metals are expensive; so, to reduce noble-metal loading, bi-metallic nanocatalysts containing non-noble metals in MCM-41 (Mobil Composition of Material No. 41, a mesoporous material) as a support material with high-surface area were synthesized using one-pot hydrothermal procedure with a surfactant such as cetyltrimethylammonium bromide (CTAB) as a template. Bi-metallic nanocatalysts of Pd-Ni and Pd-Co with varying metal loadings in MCM-41 were characterized by x-ray diffraction (XRD), N2 adsorption, and Transmission electron microscopy (TEM) techniques. The BET surface area of MCM-41 (~1000 m2/g) containing metal nanoparticles decreases with the increase in metal loading. The FTIR studies confirm strong interaction between Si-O-M (M = Pd, Ni, Co) units and successful inclusion of metal into the mesoporous silica matrix. The catalyst activities were examined in steam reforming of methanol (SRM) reactions to produce hydrogen. Reference tests using catalysts containing individual metals (Pd, Ni and Co) were also performed to investigate the effect of the bimetallic system on the catalytic behavior in the SRM reactions. The bimetallic system remarkably improves the hydrogen selectivity, methanol conversion and stability of the catalyst. The results are consistent with a synergistic behavior for the Pd-Ni-bimetallic system. The performance, durability and thermal stability of the Pd-Ni/MCM-41 and Pd-Co/MCM-41 suggest that these materials may be promising catalysts for hydrogen production from biofuels. A part of this work for synthesis and characterization of Pd-Ni-MCM-41 and its activity for SRM reactions has been published (“Development of Mesoporous Silica Encapsulated Pd-Ni Nanocatalyst for Hydrogen Production” in “Production and Purification of Ultraclean

  9. Magnetic Compensation in the Bimetallic Oxalates

    SciTech Connect

    Reis, Peter L; Fishman, Randy Scott; Reboredo, Fernando A; Moreno, Juana

    2008-01-01

    Bimetallic oxalates are layered molecule-based magnets with either ferromagnetic or antiferromagnetic interactions between transition metals M(II) and M'(III) on an open honeycomb lattice. Some Fe(II)Fe(III) bimetallic oxalates exhibit magnetic compensation (MC) at a compensation temperature Tcomp ≈ 30 K below the ferrimagnetic transition temperature Tc ≈ 45 K. To see if MC is possible in other bimetallic oxalates, we construct a theoretical model for bimetallic oxalates that exhibit antiferromagnetic interactions. By varying the M(II) and M'(III) average orbital angular momentum, which can be controlled by the choice of interlayer cations, we have found regions of MC in the families M(II)Mn(III) with M = Fe, Co, or Ni and V(II)M'(III) with M' = Cr or V but not in the family M(II)Ru(III) with M = Fe or Cu.

  10. Mechanical alloying of a hydrogenation catalyst used for the remediation of contaminated compounds

    NASA Technical Reports Server (NTRS)

    Quinn, Jacqueline W. (Inventor); Clausen, Christian A. (Inventor); Geiger, Cherie L. (Inventor); Aitken, Brian S. (Inventor)

    2012-01-01

    A hydrogenation catalyst including a base material coated with a catalytic metal is made using mechanical milling techniques. The hydrogenation catalysts are used as an excellent catalyst for the dehalogenation of contaminated compounds and the remediation of other industrial compounds. Preferably, the hydrogenation catalyst is a bimetallic particle including zero-valent metal particles coated with a catalytic material. The mechanical milling technique is simpler and cheaper than previously used methods for producing hydrogenation catalysts.

  11. Mechanical alloying of a hydrogenation catalyst used for the remediation of contaminated compounds

    NASA Technical Reports Server (NTRS)

    Quinn, Jacqueline W. (Inventor); Clausen, Christian A. (Inventor); Geiger, Cherie L. (Inventor); Aitken, Brian S. (Inventor)

    2010-01-01

    A hydrogenation catalyst including a base material coated with a catalytic metal is made using mechanical milling techniques. The hydrogenation catalysts are used as an excellent catalyst for the dehalogenation of contaminated compounds and the remediation of other industrial compounds. Preferably, the hydrogenation catalyst is a bimetallic particle including zero-valent metal particles coated with a catalytic material. The mechanical milling technique is simpler and cheaper than previously used methods for producing hydrogenation catalysts.

  12. Advanced liquefaction using coal swelling and catalyst dispersion techniques. Quarterly technical progress report, October--December 1992

    SciTech Connect

    Curtis, C.W.; Gutterman, C.; Chander, S.

    1992-12-31

    The evaluation of various catalyst pre or pyrene coal conversion continued. Higher coal conversions were observed for the S0{sub 2}-treated coal than the raw coal, regardless of catalyst type. Coal conversions were highest for Molyvan-L, molybdenum naphthenate, and nickel octoate. A technique to measure the effect of coal swelling and catalyst impregnation upon coal liquefaction has been developed, and experimentation is under way. Reactivity tests have been performed using S0{sub 2}-treated and untreated swelled Black Thunder Coal. Thermal reactions with swelled coals yielded much less coal conversion and pyrene conversion than did the swelled coal reactions with Molyvan-L. The study of bottoms processing consists of coupling solvent deasphalting with delayed coking to maximize the production of coal-derived liquids while rejecting solids within the coke drum. The batch deasphalting screening tests have been completed. While n-butane/pentane solvent blends initially appeared best, pentane alone at 380{degree}F provided an oil yield (63.6 wt%) that was desired for subsequent tests. The production of asphalt for the transport tests is underway. The target deasphalted oil yields are 40, 50 and 60 wt% of feed. This would produce asphalt with ash levels ranging from 20 to 30 wt% with which to run the transport tests.

  13. Advanced liquefaction using coal swelling and catalyst dispersion techniques. Quarterly technical progress report, January--March 1993

    SciTech Connect

    Curtis, C.W.; Gutterman, C.; Chander, S.

    1993-09-01

    The overall objective of this project is to develop a new approach for the direct liquefaction of coal to produce an all-distillate product slate at a sizable cost reduction over current technology. The approach integrates coal selection, pretreatment, coal swelling with catalyst impregnation, liquefaction, product recovery with characterization, alternate bottoms processing, and carrying out a technical assessment including an economic evaluation. The primary coal of this program, Black Thunder subbituminous coal, can be effectively beneficiated to about 4 wt% ash using aqueous sulfurous acid pretreatment. This treated coal can be further beneficiated to about 2 wt% ash using commercially available procedures. All three coals used in this study (Black Thunder, Burning Star bituminous, and Martin Lake lignite) are effectively swelled by a number of solvents. The most effective solvents are those having hetero-functionality. In addition, a synergistic effect has been demonstrated, in which solvent blends are more effective for coal swelling than the pure solvents alone. Therefore, it will be necessary to use only low levels of swelling agents and yet promote the impregnation of catalyst precursors. The rate of the impregnation of catalyst precursors into swollen coal increases greatly as the effectiveness of the solvent to swell the coal increases.

  14. Controlling the dispersion of supported polyoxometalate heterogeneous catalysts: impact of hybridization and the role of hydrophilicity–hydrophobicity balance and supramolecularity

    PubMed Central

    Swalus, Colas; Arendt, Eglantine; Eloy, Pierre; Devillers, Michel

    2014-01-01

    Summary The hybridization of polyoxometalates (POMs) through an organic–inorganic association offers several processing advantages in the design of heterogeneous catalysts. A clear understanding of the organization of these hybrid materials on solid surfaces is necessary to optimise their properties. Herein, we report for the first time the organization of Keggin phosphotungstic [PW12O40]3− and Wells–Dawson (WD) phosphomolybdic [P2Mo18O62]6− anions deposited on mica (hydrophilic), and highly oriented pyrolytic graphite (HOPG) (hydrophobic) surfaces. Next, the supramolecular organization of the organic–inorganic hybrid materials formed from the association of POM anions and dimethyldioctadecylammonium bromide (DODA) is investigated as a function of the hydrophilic or hydrophobic nature of the surfaces. The height of the Keggin-POM anions, measured with tapping mode (TM-AFM) is always in good agreement with the molecular dimension of symmetric Keggin-POM anions (ca. 1 nm). However, the asymmetric WD-POM anions form monolayer assemblies on the surfaces with the orientation of their long molecular axis (ca. 1.6 nm) depending on the hydrophilic or hydrophobic properties of the substrate. Namely, the long axis is parallel on mica, and perpendicular on HOPG. When hybridized with DODA, the organization of the hybrid material is dictated by the interaction of the alkyl side chains of DODA with the substrate surface. On HOPG, the DODA–POM hybrid forms small domains of epitaxially arranged straight nanorod structures with their orientation parallel to each other. Conversely, randomly distributed nanospheres are formed when the hybrid material is deposited on freshly cleaved mica. Finally, a UV–ozone treatment of the hybrid material allows one to obtain highly dispersed isolated POM entities on both hydrophilic and hydrophobic surfaces. The hybridization strategy to prevent the clustering of POMs on various supports would enable to develop highly dispersed POM

  15. Controlling the dispersion of supported polyoxometalate heterogeneous catalysts: impact of hybridization and the role of hydrophilicity-hydrophobicity balance and supramolecularity.

    PubMed

    Raj, Gijo; Swalus, Colas; Arendt, Eglantine; Eloy, Pierre; Devillers, Michel; Gaigneaux, Eric M

    2014-01-01

    The hybridization of polyoxometalates (POMs) through an organic-inorganic association offers several processing advantages in the design of heterogeneous catalysts. A clear understanding of the organization of these hybrid materials on solid surfaces is necessary to optimise their properties. Herein, we report for the first time the organization of Keggin phosphotungstic [PW12O40](3-) and Wells-Dawson (WD) phosphomolybdic [P2Mo18O62](6-) anions deposited on mica (hydrophilic), and highly oriented pyrolytic graphite (HOPG) (hydrophobic) surfaces. Next, the supramolecular organization of the organic-inorganic hybrid materials formed from the association of POM anions and dimethyldioctadecylammonium bromide (DODA) is investigated as a function of the hydrophilic or hydrophobic nature of the surfaces. The height of the Keggin-POM anions, measured with tapping mode (TM-AFM) is always in good agreement with the molecular dimension of symmetric Keggin-POM anions (ca. 1 nm). However, the asymmetric WD-POM anions form monolayer assemblies on the surfaces with the orientation of their long molecular axis (ca. 1.6 nm) depending on the hydrophilic or hydrophobic properties of the substrate. Namely, the long axis is parallel on mica, and perpendicular on HOPG. When hybridized with DODA, the organization of the hybrid material is dictated by the interaction of the alkyl side chains of DODA with the substrate surface. On HOPG, the DODA-POM hybrid forms small domains of epitaxially arranged straight nanorod structures with their orientation parallel to each other. Conversely, randomly distributed nanospheres are formed when the hybrid material is deposited on freshly cleaved mica. Finally, a UV-ozone treatment of the hybrid material allows one to obtain highly dispersed isolated POM entities on both hydrophilic and hydrophobic surfaces. The hybridization strategy to prevent the clustering of POMs on various supports would enable to develop highly dispersed POM-based heterogeneous

  16. Catalysts and process for liquid hydrocarbon fuel production

    DOEpatents

    White, Mark G.; Ranaweera, Samantha A.; Henry, William P.

    2016-08-02

    The present invention provides a novel process and system in which a mixture of carbon monoxide and hydrogen synthesis gas, or syngas, is converted into hydrocarbon mixtures composed of high quality distillates, gasoline components, and lower molecular weight gaseous olefins in one reactor or step. The invention utilizes a novel supported bimetallic ion complex catalyst for conversion, and provides methods of preparing such novel catalysts and use of the novel catalysts in the process and system of the invention.

  17. Remarkable enhancement of electrocatalytic activity by tuning the interface of Pd-Au bimetallic nanoparticle tubes.

    PubMed

    Cui, Chun-Hua; Yu, Jin-Wen; Li, Hui-Hui; Gao, Min-Rui; Liang, Hai-Wei; Yu, Shu-Hong

    2011-05-24

    The interface, which formed in a bimetallic system, is a critical issue to investigate the fundamental mechanism of enhanced catalytic activity. Here, we designed unsupported Pd-Au bimetallic nanoparticle tubes with a tunable interface, which was qualitatively controlled by the proportion of Pd and Au nanoparticles (NPs), to demonstrate the remarkably enhanced effect of Pd and Au NPs in electro-oxidation of ethanol. The results demonstrated that the electrocatalytic activity is highly relative to the interface and has no direct relation with individual metal component in the Pd-Au system. This effect helps us in achieving a fundamental understanding of the relationship between their activity and the interface structure and chemical properties and, consequently, is helpful in designing new catalysts with high performances. PMID:21506570

  18. Fabrication of Isolated Metal-Organic Polyhedra in Confined Cavities: Adsorbents/Catalysts with Unusual Dispersity and Activity.

    PubMed

    Kang, Ying-Hu; Liu, Xiao-Dan; Yan, Ni; Jiang, Yao; Liu, Xiao-Qin; Sun, Lin-Bing; Li, Jian-Rong

    2016-05-18

    Metal-organic polyhedra (MOPs) have attracted great attention due to their intriguing structure. However, the applications of MOPs are severely hindered by two shortcomings, namely low dispersity and poor stability. Here we report the introduction of four MOPs (constructed from dicopper and carboxylates) to cavity-structured mesoporous silica SBA-16 via a double-solvent strategy to overcome both shortcomings simultaneously. By judicious design, the dimension of MOPs is just between the size of cavities and entrances of SBA-16, MOP molecules are thus confined in the cavities. This leads to the formation of isolated MOPs with unusual dispersion, making the active sites highly accessible. Hence, the adsorption capacity on carbon dioxide and propene as well as catalytic performance on ring opening are much superior to bulk MOPs. More importantly, the structure and catalytic activity of MOPs in confined cavities are well preserved after exposure to humid atmosphere, whereas those of bulk MOPs are degraded seriously. PMID:27049737

  19. Correlation between Fischer-Tropsch catalytic activity and composition of catalysts

    PubMed Central

    2011-01-01

    This paper presents the synthesis and characterization of monometallic and bimetallic cobalt and iron nanoparticles supported on alumina. The catalysts were prepared by a wet impregnation method. Samples were characterized using temperature-programmed reduction (TPR), temperature-programmed oxidation (TPO), CO-chemisorption, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM-EDX) and N2-adsorption analysis. Fischer-Tropsch synthesis (FTS) was carried out in a fixed-bed microreactor at 543 K and 1 atm, with H2/CO = 2 v/v and space velocity, SV = 12L/g.h. The physicochemical properties and the FTS activity of the bimetallic catalysts were analyzed and compared with those of monometallic cobalt and iron catalysts at similar operating conditions. H2-TPR analysis of cobalt catalyst indicated three temperature regions at 506°C (low), 650°C (medium) and 731°C (high). The incorporation of iron up to 30% into cobalt catalysts increased the reduction, CO chemisorption and number of cobalt active sites of the catalyst while an opposite trend was observed for the iron-riched bimetallic catalysts. The CO conversion was 6.3% and 4.6%, over the monometallic cobalt and iron catalysts, respectively. Bimetallic catalysts enhanced the CO conversion. Amongst the catalysts studied, bimetallic catalyst with the composition of 70Co30Fe showed the highest CO conversion (8.1%) while exhibiting the same product selectivity as that of monometallic Co catalyst. Monometallic iron catalyst showed the lowest selectivity for C5+ hydrocarbons (1.6%). PMID:22047220

  20. Hierarchical paramecium-like hollow and solid Au/Pt bimetallic nanostructures constructed using goethite as template

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Repo, Eveliina; Heikkilä, Mikko; Leskelä, Markku; Sillanpää, Mika

    2010-10-01

    Novel hollow and solid paramecium-like hierarchical Au/Pt bimetallic nanostructures were constructed using goethite as template via a seed-mediated growth method. Transmission electron microscopy (TEM), ξ-potential measurement, UV-vis spectroscopy, energy dispersive x-ray spectroscopy (EDS), ICP-AES measurement, x-ray powder diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) were utilized to systematically characterize the bimetallic nanostructures. It is found that the core structure of the paramecium-like bimetallic nanomaterial is closely related to reducing agent. When ascorbic acid is used as reducing agent, goethite serves as in situ sacrificed template and hollow paramecium-like bimetallic structure is obtained. When NH2OH·HCl is used, solid nanostructure with preserved goethite core is produced. Heating the reaction solution is necessary to obtain the paramecium-like morphology with rough interconnected Pt cilia shell. The thickness of Pt cilia layer can be controlled by adjusting the molar ratio of H2PtCl6 to Au nanoseeds. The overgrowth of the rough Pt cilia is proposed to be via an autocatalytic and three-dimensional heterogeneous nucleation process first through flower-like morphology. Both the hollow and solid hierarchical paramecium-like Au/Pt bimetallic nanostructures show good catalytic activities.

  1. Hierarchical paramecium-like hollow and solid Au/Pt bimetallic nanostructures constructed using goethite as template.

    PubMed

    Liu, Wei; Repo, Eveliina; Heikkilä, Mikko; Leskelä, Markku; Sillanpää, Mika

    2010-10-01

    Novel hollow and solid paramecium-like hierarchical Au/Pt bimetallic nanostructures were constructed using goethite as template via a seed-mediated growth method. Transmission electron microscopy (TEM), xi-potential measurement, UV-vis spectroscopy, energy dispersive x-ray spectroscopy (EDS), ICP-AES measurement, x-ray powder diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) were utilized to systematically characterize the bimetallic nanostructures. It is found that the core structure of the paramecium-like bimetallic nanomaterial is closely related to reducing agent. When ascorbic acid is used as reducing agent, goethite serves as in situ sacrificed template and hollow paramecium-like bimetallic structure is obtained. When NH(2)OH.HCl is used, solid nanostructure with preserved goethite core is produced. Heating the reaction solution is necessary to obtain the paramecium-like morphology with rough interconnected Pt cilia shell. The thickness of Pt cilia layer can be controlled by adjusting the molar ratio of H(2)PtCl(6) to Au nanoseeds. The overgrowth of the rough Pt cilia is proposed to be via an autocatalytic and three-dimensional heterogeneous nucleation process first through flower-like morphology. Both the hollow and solid hierarchical paramecium-like Au/Pt bimetallic nanostructures show good catalytic activities.

  2. Polymer-supported CuPd nanoalloy as a synergistic catalyst for electrocatalytic reduction of carbon dioxide to methane

    PubMed Central

    Zhang, Sheng; Kang, Peng; Bakir, Mohammed; Lapides, Alexander M.; Dares, Christopher J.; Meyer, Thomas J.

    2015-01-01

    Developing sustainable energy strategies based on CO2 reduction is an increasingly important issue given the world’s continued reliance on hydrocarbon fuels and the rise in CO2 concentrations in the atmosphere. An important option is electrochemical or photoelectrochemical CO2 reduction to carbon fuels. We describe here an electrodeposition strategy for preparing highly dispersed, ultrafine metal nanoparticle catalysts on an electroactive polymeric film including nanoalloys of Cu and Pd. Compared with nanoCu catalysts, which are state-of-the-art catalysts for CO2 reduction to hydrocarbons, the bimetallic CuPd nanoalloy catalyst exhibits a greater than twofold enhancement in Faradaic efficiency for CO2 reduction to methane. The origin of the enhancement is suggested to arise from a synergistic reactivity interplay between Pd–H sites and Cu–CO sites during electrochemical CO2 reduction. The polymer substrate also appears to provide a basis for the local concentration of CO2 resulting in the enhancement of catalytic current densities by threefold. The procedure for preparation of the nanoalloy catalyst is straightforward and appears to be generally applicable to the preparation of catalytic electrodes for incorporation into electrolysis devices. PMID:26668386

  3. Ostwald-Driven Phase Separation in Bimetallic Nanoparticle Assemblies.

    PubMed

    Prévot, Geoffroy; Nguyen, Nhat Tai; Alloyeau, Damien; Ricolleau, Christian; Nelayah, Jaysen

    2016-04-26

    The compositional stability of bimetallic nanoparticles (NPs) is crucial for many applications. We have studied the coarsening of amorphous carbon-supported Au-Pd NPs during annealing at 873 K. Using scanning transmission electron microscopy and energy-dispersive spectroscopy measurements, we show that, despite a complete miscibility of the two metals, the particle assembly undergoes a phase separation during annealing, which leads to two distinct populations: Au-rich NPs with a mean radius of 3.5 nm and large Pd-rich NPs with a mean radius of 25 nm. Thermodynamic calculations and kinetic Monte Carlo simulations explain this behavior that is driven by the competition between surface and mixing energy and by the different mobilities of the two atomic species. PMID:26989906

  4. Effect of titania on the characteristics of a Tin-Platinum catalyst

    NASA Astrophysics Data System (ADS)

    Morales-Gil, P.; Nava, N.; Baggio-Saitovitch, E.

    2015-06-01

    Pt-Sn bimetallic catalysts dispersed on alumina are commonly used for reforming and dehydrogenation reactions. In this research work, Pt and Sn were supported on titania. The resulting interactions between the components in the prepared samples, before and after treatment with hydrogen, were studied by Mössbauer spectroscopy, X-ray diffraction and Rietveld refinement. The results show the presence of Pt and SnO2 after calcinations. After the reduction process, metallic Pt, PtSn, and Pt3Sn alloys were identified. The Rietveld refinement analysis shows that some Ti4+ atoms were replaced by Sn4+ atoms in the titania structure. Finally, the Mössbauer spectroscopy and X-ray diffraction results indicate that metallic platinum and SnO2 are encapsulated by a TiOx layer.

  5. Beneficial Role of Copper in the Enhancement of Durability of Ordered Intermetallic PtFeCu Catalyst for Electrocatalytic Oxygen Reduction.

    PubMed

    Arumugam, Balamurugan; Tamaki, Takanori; Yamaguchi, Takeo

    2015-08-01

    Design of Pt alloy catalysts with enhanced activity and durability is a key challenge for polymer electrolyte membrane fuel cells. In the present work, we compare the durability of the ordered intermetallic face-centered tetragonal (fct) PtFeCu catalyst for the oxygen reduction reaction (ORR) relative to its counterpart bimetallic catalysts, i.e., the ordered intermetallic fct-PtFe catalyst and the commercial catalyst from Tanaka Kikinzoku Kogyo, TKK-PtC. Although both fct catalysts initially exhibited an ordered structure and mass activity approximately 2.5 times higher than that of TKK-Pt/C, the presence of Cu at the ordered intermetallic fct-PtFeCu catalyst led to a significant enhancement in durability compared to that of the ordered intermetallic fct-PtFe catalyst. The ordered intermetallic fct-PtFeCu catalyst retained more than 70% of its mass activity and electrochemically active surface area (ECSA) over 10 000 durability cycles carried out at 60 °C. In contrast, the ordered intermetallic fct-PtFe catalyst maintained only about 40% of its activity. The temperature of the durability experiment is also shown to be important: the catalyst was more severely degraded at 60 °C than at room temperature. To obtain insight into the observed enhancement in durability of fct-PtFeCu catalyst, a postmortem analysis of the ordered intermetallic fct-PtFeCu catalyst was carried out using scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX) line scan. The STEM-EDX line scans of the ordered intermetallic fct-PtFeCu catalyst over 10 000 durability cycles showed a smaller degree of Fe and Cu dissolution from the catalyst. Conversely, large dissolution of Fe was identified in the ordered intermetallic fct-PtFe catalyst, indicating a lesser retention of Fe that causes the destruction of ordered structure and gives rise to poor durability. The enhancement in the durability of the ordered intermetallic fct-PtFeCu catalyst is ascribed to

  6. Liquefaction with microencapsulated catalysts

    DOEpatents

    Weller, Sol W.

    1985-01-01

    A method of dispersing a liquefaction catalyst within coal or other carbonaceous solids involves providing a suspension in oil of microcapsules containing the catalyst. An aqueous solution of a catalytic metal salt is emulsified in the water-immiscible oil and the resulting minute droplets microencapsulated in polymeric shells by interfacial polycondensation. The catalyst is subsequently blended and dispersed throughout the powdered carbonaceous material to be liquefied. At liquefaction temperatures the polymeric microcapsules are destroyed and the catalyst converted to minute crystallites in intimate contact with the carbonaceous material.

  7. Synthesis of homogeneous Pt-bimetallic nanoparticles as highly efficient electrocatalysts.

    SciTech Connect

    Wang, C.; Chi, M.; Li, D.; van der Vliet, D.; Wang, G.; Lin, Q.; Mitchell, J.; More, K. L.; Markovic, N. M.; Stamenkovic, V. R.

    2011-01-01

    Alloying has shown enormous potential for tailoring the atomic and electronic structures, and improving the performance of catalytic materials. Systematic studies of alloy catalysts are, however, often compromised by inhomogeneous distribution of alloying components. Here we introduce a general approach for the synthesis of monodispersed and highly homogeneous Pt-bimetallic alloy nanocatalysts. Pt{sub 3}M (where M = Fe, Ni, or Co) nanoparticles were prepared by an organic solvothermal method and then supported on high surface area carbon. These catalysts attained a homogeneous distribution of elements, as demonstrated by atomic-scale elemental analysis using scanning transmission electron microscopy. They also exhibited high catalytic activities for the oxygen reduction reaction (ORR), with improvement factors of 2-3 versus conventional Pt/carbon catalysts. The measured ORR catalytic activities for Pt{sub 3}M nanocatalysts validated the volcano curve established on extended surfaces, with Pt{sub 3}Co being the most active alloy.

  8. Novel Pt/Mg(In)(Al)O catalysts for ethane and propane dehydrogenation

    SciTech Connect

    Sun, Pingping; Siddiqi, Georges; Vining, William C.; Chi, Miaofang; Bell, Alexis T.

    2011-10-28

    Catalysts for the dehydrogenation of light alkanes were prepared by dispersing Pt on the surface of a calcined hydrotalcite-like support containing indium, Mg(In)(Al)O. Upon reduction in H{sub 2} at temperatures above 673 K, bimetallic particles of PtIn are observed by TEM, which have an average diameter of 1 nm. Analysis of Pt LIII-edge extended X-ray absorption fine structure (EXAFS) data shows that the In content of the bimetallic particles increases with increasing bulk In/Pt ratio and reduction temperature. Pt LIII-edge X-ray absorption near edge structure (XANES) indicates that an increasing donation of electronic charge from In to Pt occurs with increasing In content in the PtIn particles. The activity and selectivity of the Pt/Mg(In)(Al)O catalysts for ethane and propane dehydrogenation reactions are strongly dependent on the bulk In/Pt ratio. For both reactants, maximum activity was achieved for a bulk In/Pt ratio of 0.48, and at this In/Pt ratio, the selectivity to alkene was nearly 100%. Coke deposition was observed after catalyst use for either ethane or propane dehydrogenation, and it was observed that the alloying of Pt with In greatly reduced the amount of coke deposited. Characterization of the deposit by Raman spectroscopy indicates that the coke is present as highly disordered graphite particles <30 nm in diameter. While the amount of coke deposited during ethane and propane dehydrogenation are comparable, the effects on activity are dependent on reactant composition. Coke deposition had no effect on ethane dehydrogenation activity, but caused a loss in propane dehydrogenation activity. This difference is attributed to the greater ease with which coke produced on the surface of PtIn nanoparticles migrates to the support during ethane dehydrogenation versus propane dehydrogenation.

  9. Facile One-Step Synthesis of Three-Dimensional Pd-Ag Bimetallic Alloy Networks and Their Electrocatalytic Activity toward Ethanol Oxidation.

    PubMed

    Fu, Shaofang; Zhu, Chengzhou; Du, Dan; Lin, Yuehe

    2015-07-01

    The three-dimensional palladium networks and palladium-silver bimetallic alloy networks were synthesized at room temperature on a large scale using a rapid and simple strategy. The results revealed that the morphology of the networks is not affected by the composition. We demonstrated that the as-prepared unsupported networks exhibited excellent electrochemical activity and stability toward ethanol oxidation reaction in alkaline media due to the formation of palladium-silver alloys as well as the porous nanostructures. The results indicate that the well-defined three-dimensional palladium-silver bimetallic alloy networks are promising catalysts for fuel cells.

  10. Simultaneous detection of electronic structure changes from two elements of a bifunctional catalyst using wavelength-dispersive X-ray emission spectroscopy and in situ electrochemistry.

    PubMed

    Gul, Sheraz; Ng, Jia Wei Desmond; Alonso-Mori, Roberto; Kern, Jan; Sokaras, Dimosthenis; Anzenberg, Eitan; Lassalle-Kaiser, Benedikt; Gorlin, Yelena; Weng, Tsu-Chien; Zwart, Petrus H; Zhang, Jin Z; Bergmann, Uwe; Yachandra, Vittal K; Jaramillo, Thomas F; Yano, Junko

    2015-04-14

    Multielectron catalytic reactions, such as water oxidation, nitrogen reduction, or hydrogen production in enzymes and inorganic catalysts often involve multimetallic clusters. In these systems, the reaction takes place between metals or metals and ligands to facilitate charge transfer, bond formation/breaking, substrate binding, and release of products. In this study, we present a method to detect X-ray emission signals from multiple elements simultaneously, which allows for the study of charge transfer and the sequential chemistry occurring between elements. Kβ X-ray emission spectroscopy (XES) probes charge and spin states of metals as well as their ligand environment. A wavelength-dispersive spectrometer based on the von Hamos geometry was used to disperse Kβ signals of multiple elements onto a position detector, enabling an XES spectrum to be measured in a single-shot mode. This overcomes the scanning needs of the scanning spectrometers, providing data free from temporal and normalization errors and therefore ideal to follow sequential chemistry at multiple sites. We have applied this method to study MnOx-based bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In particular, we investigated the effects of adding a secondary element, Ni, to form MnNiOx and its impact on the chemical states and catalytic activity, by tracking the redox characteristics of each element upon sweeping the electrode potential. The detection scheme we describe here is general and can be applied to time-resolved studies of materials consisting of multiple elements, to follow the dynamics of catalytic and electron transfer reactions.

  11. Simultaneous detection of electronic structure changes from two elements of a bifunctional catalyst using wavelength-dispersive X-ray emission spectroscopy and in situ electrochemistry

    DOE PAGES

    Gul, Sheraz; Ng, Jia Wei Desmond; Alonso-Mori, Roberto; Kern, Jan; Sokaras, Dimosthenis; Anzenberg, Eitan; Lassalle-Kaiser, Benedikt; Gorlin, Yelena; Weng, Tsu-Chien; Zwart, Petrus H.; et al

    2015-02-25

    Multielectron catalytic reactions, such as water oxidation, nitrogen reduction, or hydrogen production in enzymes and inorganic catalysts often involve multimetallic clusters. In these systems, the reaction takes place between metals or metals and ligands to facilitate charge transfer, bond formation/breaking, substrate binding, and release of products. In this study, we present a method to detect X-ray emission signals from multiple elements simultaneously, which allows for the study of charge transfer and the sequential chemistry occurring between elements. Kβ X-ray emission spectroscopy (XES) probes charge and spin states of metals as well as their ligand environment. A wavelength-dispersive spectrometer based onmore » the von Hamos geometry was used to disperse Kβ signals of multiple elements onto a position detector, enabling an XES spectrum to be measured in a single-shot mode. This overcomes the scanning needs of the scanning spectrometers, providing data free from temporal and normalization errors and therefore ideal to follow sequential chemistry at multiple sites. We have applied this method to study MnOx-based bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In particular, we investigated the effects of adding a secondary element, Ni, to form MnNiOx and its impact on the chemical states and catalytic activity, by tracking the redox characteristics of each element upon sweeping the electrode potential. In conclusion, the detection scheme we describe here is general and can be applied to time-resolved studies of materials consisting of multiple elements, to follow the dynamics of catalytic and electron transfer reactions.« less

  12. Simultaneous detection of electronic structure changes from two elements of a bifunctional catalyst using wavelength-dispersive X-ray emission spectroscopy and in situ electrochemistry

    SciTech Connect

    Gul, Sheraz; Ng, Jia Wei Desmond; Alonso-Mori, Roberto; Kern, Jan; Sokaras, Dimosthenis; Anzenberg, Eitan; Lassalle-Kaiser, Benedikt; Gorlin, Yelena; Weng, Tsu-Chien; Zwart, Petrus H.; Zhang, Jin Z.; Bergmann, Uwe; Yachandra, Vittal K.; Jaramillo, Thomas F.; Yano, Junko

    2015-02-25

    Multielectron catalytic reactions, such as water oxidation, nitrogen reduction, or hydrogen production in enzymes and inorganic catalysts often involve multimetallic clusters. In these systems, the reaction takes place between metals or metals and ligands to facilitate charge transfer, bond formation/breaking, substrate binding, and release of products. In this study, we present a method to detect X-ray emission signals from multiple elements simultaneously, which allows for the study of charge transfer and the sequential chemistry occurring between elements. Kβ X-ray emission spectroscopy (XES) probes charge and spin states of metals as well as their ligand environment. A wavelength-dispersive spectrometer based on the von Hamos geometry was used to disperse Kβ signals of multiple elements onto a position detector, enabling an XES spectrum to be measured in a single-shot mode. This overcomes the scanning needs of the scanning spectrometers, providing data free from temporal and normalization errors and therefore ideal to follow sequential chemistry at multiple sites. We have applied this method to study MnOx-based bifunctional electrocatalysts for the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). In particular, we investigated the effects of adding a secondary element, Ni, to form MnNiOx and its impact on the chemical states and catalytic activity, by tracking the redox characteristics of each element upon sweeping the electrode potential. In conclusion, the detection scheme we describe here is general and can be applied to time-resolved studies of materials consisting of multiple elements, to follow the dynamics of catalytic and electron transfer reactions.

  13. Tailoring Silica-alumina Supported Pt-Pd As Poison Tolerant Catalyst For Aromatics Hydrogenation

    SciTech Connect

    Yu, Yanzhe; Gutierrez, Oliver Y.; Haller, Gary L.; Colby, Robert J.; Kabius, Bernd C.; Rob van Veen, J. A.; Jentys, Andreas; Lercher, Johannes A.

    2013-08-01

    The tailoring of the physicochemical and catalytic properties of mono- and bimetallic Pt-Pd catalysts supported on amorphous silica-alumina is studied. Electron energy loss spectroscopy and extended X-ray absorption fine structure analyses indicated that bimetallic Pt-Pd and relatively large monometallic Pd particles were formed, whereas the X-ray absorption near edge structure provided direct evidence for the electronic deficiency of the Pt atoms. The heterogeneous distribution of metal particles was also shown by high resolution transmission electron microscopy. The average structure of the bimetallic particles (Pt-rich core and Pd-rich shell) and the presence of Pd particles led to surface Pd enrichment, which was independently shown by IR spectra of adsorbed CO. The specific metal distribution, average size, and surface composition of the Pt-Pd particles depend to a large extent on the metal precursors. In the presence of NH3 ligands, Pt-Pd particles with a fairly homogeneous bulk and surface metal distribution were formed. Also high Lewis acid site concentration of the carrier leads to more homogeneous bimetallic particles. All catalysts were active for the hydrogenation of tetralin in the absence and presence of quinoline and dibenzothiophene (DBT). Monometallic Pt catalysts had the highest hydrogenation activity in poison-free and quinoline-containing feed. When DBT was present, bimetallic Pt-Pd catalysts with the most homogenous metal distribution showed the highest activity. The higher resistance of bimetallic catalysts towards sulfur poisoning compared to their monometallic Pt counterparts results from the weakened metal-sulfur bond on the electron deficient Pt atoms. Thus, increasing the fraction of electron deficient Pt on the surface of the bimetallic particles increases the efficiency of the catalyst in the presence of sulfur.

  14. Monodispersed bimetallic PdAg nanoparticles with twinned structures: formation and enhancement for the methanol oxidation.

    PubMed

    Yin, Zhen; Zhang, Yining; Chen, Kai; Li, Jing; Li, Wenjing; Tang, Pei; Zhao, Huabo; Zhu, Qingjun; Bao, Xinhe; Ma, Ding

    2014-01-01

    Monodispersed bimetallic PdAg nanoparticles can be fabricated through the emulsion-assisted ethylene glycol (EG) ternary system. Different compositions of bimetallic PdAg nanoparticles, Pd₈₀Ag₂₀, Pd₆₅Ag₃₅ and Pd₄₆Ag₅₄ can be obtained via adjusting the reaction parameters. For the formation process of the bimetallic PdAg nanoparticles, there have two-stage growth processes: firstly, nucleation and growth of the primary nanoclusters; secondly, formation of the secondary nanoparticles with the size-selection and relax process via the coalescence or aggregation of the primary nanoclusters. The as-prepared PdAg can be supported on the carbon black without any post-treatment, which exhibited high electro-oxidation activity towards methanol oxidation under alkaline media. More importantly, carbon-supported Pd₈₀Ag₂₀ nanoparticles reveal distinctly superior activities for the methanol oxidation, even if compared with commercial Pt/C electro-catalyst. It is concluded that the enhanced activity is dependant on the unique twinning structure with heterogeneous phase due to the dominating coalescence growth in EG ternary system. PMID:24608736

  15. Monodispersed bimetallic PdAg nanoparticles with twinned structures: Formation and enhancement for the methanol oxidation

    PubMed Central

    Yin, Zhen; Zhang, Yining; Chen, Kai; Li, Jing; Li, Wenjing; Tang, Pei; Zhao, Huabo; Zhu, Qingjun; Bao, Xinhe; Ma, Ding

    2014-01-01

    Monodispersed bimetallic PdAg nanoparticles can be fabricated through the emulsion-assisted ethylene glycol (EG) ternary system. Different compositions of bimetallic PdAg nanoparticles, Pd80Ag20, Pd65Ag35 and Pd46Ag54 can be obtained via adjusting the reaction parameters. For the formation process of the bimetallic PdAg nanoparticles, there have two-stage growth processes: firstly, nucleation and growth of the primary nanoclusters; secondly, formation of the secondary nanoparticles with the size-selection and relax process via the coalescence or aggregation of the primary nanoclusters. The as-prepared PdAg can be supported on the carbon black without any post-treatment, which exhibited high electro-oxidation activity towards methanol oxidation under alkaline media. More importantly, carbon-supported Pd80Ag20 nanoparticles reveal distinctly superior activities for the methanol oxidation, even if compared with commercial Pt/C electro-catalyst. It is concluded that the enhanced activity is dependant on the unique twinning structure with heterogeneous phase due to the dominating coalescence growth in EG ternary system. PMID:24608736

  16. Reductive dechlorination of trichloroethylene by iron bimetallics

    SciTech Connect

    Orth, R.G.; Dauda, T.; McKenzie, D.E.

    1998-07-01

    Reductive dechlorination using a zero valence metal such as iron has seen an increase in interest with the extension of iron dechlorination to in-situ treatment of ground water. Studies to increase the rate of dechlorination and the long term stability have lead many to examine the use of bimetallic iron systems. Results are shown for bimetallic iron systems of Cu, Sn, Ni, Ag, Au, and Pd. All of these bimetallic couples form a galvanic couple which increase corrosion rates and the production of hydrogen. Increased rates of reaction normalized to surface area were observed for all the couples. The reaction rates were found to depended on surface area and surface coverage of the iron. The results of studies in deuterium oxide indicate that the pathways changed as the bimetallic is changed and that the pathway in all cases could be a combination of dehydrohalgenation and sequential dechlorination. Degradation of DNAPL TCE by iron was found to be zero order and the type of product observed was different from that observed for TCE dissolved in water.

  17. The remarkable activity and stability of a highly dispersive beta-brass Cu-Zn catalyst for the production of ethylene glycol

    NASA Astrophysics Data System (ADS)

    Li, Molly Meng-Jung; Zheng, Jianwei; Qu, Jin; Liao, Fenglin; Raine, Elizabeth; Kuo, Winson C. H.; Su, Shei Sia; Po, Pang; Yuan, Youzhu; Tsang, Shik Chi Edman

    2016-02-01

    Incorporation of Zn atoms into a nanosize Cu lattice is known to alter the electronic properties of Cu, improving catalytic performance in a number of industrially important reactions. However the structural influence of Zn on the Cu phase is not well studied. Here, we show that Cu nano-clusters modified with increasing concentration of Zn, derived from ZnO support doped with Ga3+, can dramatically enhance their stability against metal sintering. As a result, the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol, an important reaction well known for deactivation from copper nanoparticle sintering, can show greatly enhanced activity and stability with the CuZn alloy catalysts due to no noticeable sintering. HRTEM, nano-diffraction and EXAFS characterization reveal the presence of a small beta-brass CuZn alloy phase (body-centred cubic, bcc) which appears to greatly stabilise Cu atoms from aggregation in accelerated deactivation tests. DFT calculations also indicate that the small bcc CuZn phase is more stable against Cu adatom migration than the fcc CuZn phase with the ability to maintain a higher Cu dispersion on its surface.

  18. The remarkable activity and stability of a highly dispersive beta-brass Cu-Zn catalyst for the production of ethylene glycol.

    PubMed

    Li, Molly Meng-Jung; Zheng, Jianwei; Qu, Jin; Liao, Fenglin; Raine, Elizabeth; Kuo, Winson C H; Su, Shei Sia; Po, Pang; Yuan, Youzhu; Tsang, Shik Chi Edman

    2016-02-09

    Incorporation of Zn atoms into a nanosize Cu lattice is known to alter the electronic properties of Cu, improving catalytic performance in a number of industrially important reactions. However the structural influence of Zn on the Cu phase is not well studied. Here, we show that Cu nano-clusters modified with increasing concentration of Zn, derived from ZnO support doped with Ga(3+), can dramatically enhance their stability against metal sintering. As a result, the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol, an important reaction well known for deactivation from copper nanoparticle sintering, can show greatly enhanced activity and stability with the CuZn alloy catalysts due to no noticeable sintering. HRTEM, nano-diffraction and EXAFS characterization reveal the presence of a small beta-brass CuZn alloy phase (body-centred cubic, bcc) which appears to greatly stabilise Cu atoms from aggregation in accelerated deactivation tests. DFT calculations also indicate that the small bcc CuZn phase is more stable against Cu adatom migration than the fcc CuZn phase with the ability to maintain a higher Cu dispersion on its surface.

  19. The remarkable activity and stability of a highly dispersive beta-brass Cu-Zn catalyst for the production of ethylene glycol

    PubMed Central

    Li, Molly Meng-Jung; Zheng, Jianwei; Qu, Jin; Liao, Fenglin; Raine, Elizabeth; Kuo, Winson C. H.; Su, Shei Sia; Po, Pang; Yuan, Youzhu; Tsang, Shik Chi Edman

    2016-01-01

    Incorporation of Zn atoms into a nanosize Cu lattice is known to alter the electronic properties of Cu, improving catalytic performance in a number of industrially important reactions. However the structural influence of Zn on the Cu phase is not well studied. Here, we show that Cu nano-clusters modified with increasing concentration of Zn, derived from ZnO support doped with Ga3+, can dramatically enhance their stability against metal sintering. As a result, the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol, an important reaction well known for deactivation from copper nanoparticle sintering, can show greatly enhanced activity and stability with the CuZn alloy catalysts due to no noticeable sintering. HRTEM, nano-diffraction and EXAFS characterization reveal the presence of a small beta-brass CuZn alloy phase (body-centred cubic, bcc) which appears to greatly stabilise Cu atoms from aggregation in accelerated deactivation tests. DFT calculations also indicate that the small bcc CuZn phase is more stable against Cu adatom migration than the fcc CuZn phase with the ability to maintain a higher Cu dispersion on its surface. PMID:26856760

  20. The remarkable activity and stability of a highly dispersive beta-brass Cu-Zn catalyst for the production of ethylene glycol.

    PubMed

    Li, Molly Meng-Jung; Zheng, Jianwei; Qu, Jin; Liao, Fenglin; Raine, Elizabeth; Kuo, Winson C H; Su, Shei Sia; Po, Pang; Yuan, Youzhu; Tsang, Shik Chi Edman

    2016-01-01

    Incorporation of Zn atoms into a nanosize Cu lattice is known to alter the electronic properties of Cu, improving catalytic performance in a number of industrially important reactions. However the structural influence of Zn on the Cu phase is not well studied. Here, we show that Cu nano-clusters modified with increasing concentration of Zn, derived from ZnO support doped with Ga(3+), can dramatically enhance their stability against metal sintering. As a result, the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol, an important reaction well known for deactivation from copper nanoparticle sintering, can show greatly enhanced activity and stability with the CuZn alloy catalysts due to no noticeable sintering. HRTEM, nano-diffraction and EXAFS characterization reveal the presence of a small beta-brass CuZn alloy phase (body-centred cubic, bcc) which appears to greatly stabilise Cu atoms from aggregation in accelerated deactivation tests. DFT calculations also indicate that the small bcc CuZn phase is more stable against Cu adatom migration than the fcc CuZn phase with the ability to maintain a higher Cu dispersion on its surface. PMID:26856760

  1. Controlled synthesis and synergistic effects of graphene-supported PdAu bimetallic nanoparticles with tunable catalytic properties

    NASA Astrophysics Data System (ADS)

    Liu, Chang-Hai; Liu, Rui-Hua; Sun, Qi-Jun; Chang, Jian-Bing; Gao, Xu; Liu, Yang; Lee, Shuit-Tong; Kang, Zhen-Hui; Wang, Sui-Dong

    2015-03-01

    to the catalysis of reduction reaction. By the present method, the bimetallic combination can be tailored for distinct types of catalytic reactions. Electronic supplementary information (ESI) available: This section includes TEM images, HRTEM images, size distribution, XPS survey spectra and Raman spectra of PdAu bimetal-NP-graphene hybrids; catalytic results of the oxidation of cis-cyclooctene, and time-dependent UV-vis absorption spectra for reduction of 4-nitrophenol with PdAu bimetal-NP-graphene hybrids as catalysts. See DOI: 10.1039/c4nr06855f

  2. Core-shell Rh-Pt nanocubes: A model for studying compressive strain effects in bimetallic nanocatalysts

    NASA Astrophysics Data System (ADS)

    Harak, Ethan William

    Shape-controlled bimetallic nanocatalysts often have increased activities and stabilities over their monometallic counterparts due to surface strain effects and electron transfer between the two metals. Here, we demonstrate that the degree of surface strain can be manipulated in shape-controlled nanocrystals through a bimetallic core shell architecture. This ability is achieved in a model core shell Rh Pt nanocube system through control of shell thickness. An increase in the Pt shell thickness leads to more compressive strain, which can increase the Pt 4f7/2 binding energy by as much as 0.13 eV. This change in electronic structure is correlated with a weakening of surface-adsorbate interactions, which we exploit to reduce catalyst poisoning by CO during formic acid electrooxidation. In fact, by precisely controlling the Pt shell thickness, the maximum current density achieved with Rh Pt nanocubes was 3.5 times greater than that achieved with similarly sized Pt nanocubes, with decreased CO generation as well. This system serves as a model for how bimetallic architectures can be used to manipulate the electronic structure of nanoparticle surfaces for efficient catalysis. The strategy employed here should enable the performance of bimetallic nanomaterials comprised of more cost-effective metals to be enhanced as well.

  3. Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness.

    PubMed

    Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E; Huang, Yu

    2012-02-01

    Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50 mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications. PMID:22159178

  4. Final Technical Report: First Principles Investigations for the Ensemble Effects of PdAu and PtAu Bimetallic Nanocatalysts

    SciTech Connect

    Ruqian Wu

    2012-05-18

    Bimetallic surfaces with tunable chemical properties have attracted broad attention in recent years due to their ample potential for heterogeneous catalysis applications. The local chemical properties of constituents are strongly altered from their parent metals by 'ligand effect', a term encompassing the influences of charge transfer, orbital rehybridization and lattice strain. In comparison to the aforementioned, the 'ensemble effect' associated with particular arrangements of the active constituents have received much less attention, despite their notable importance towards the determination of reactivity and selectivity of bimetallic catalysts. We performed theoretical studies for understanding the ensemble effects on bimetallic catalysis: (i) simulations for the formation of different ensembles on PdAu and PtAu nanoclusters; (ii) studies of the size, shape, and substrate dependence of their electronic properties; and (iii) simulations for model reactions such as CO oxidation, methanol, ethylene and water dehydrogenation on PdAu and PtAu nanoclusters. In close collaboration with leading experimental groups, our theoretical research elucidated the fundamentals of Au based bimetallic nanocatalysts.

  5. Platinum-ruthenium bimetallic clusters on graphite: a comparison of vapor deposition and electroless deposition methods.

    PubMed

    Galhenage, Randima P; Xie, Kangmin; Diao, Weijian; Tengco, John Meynard M; Seuser, Grant S; Monnier, John R; Chen, Donna A

    2015-11-14

    Bimetallic Pt-Ru clusters have been grown on highly ordered pyrolytic graphite (HOPG) surfaces by vapor deposition and by electroless deposition. These studies help to bridge the material gap between well-characterized vapor deposited clusters and electrolessly deposited clusters, which are better suited for industrial catalyst preparation. In the vapor deposition experiments, bimetallic clusters were formed by the sequential deposition of Pt on Ru or Ru on Pt. Seed clusters of the first metal were grown on HOPG surfaces that were sputtered with Ar(+) to introduce defects, which act as nucleation sites for Pt or Ru. On the unmodified HOPG surface, both Pt and Ru clusters preferentially nucleated at the step edges, whereas on the sputtered surface, clusters with relatively uniform sizes and spatial distributions were formed. Low energy ion scattering experiments showed that the surface compositions of the bimetallic clusters are Pt-rich, regardless of the order of deposition, indicating that the interdiffusion of metals within the clusters is facile at room temperature. Bimetallic clusters on sputtered HOPG were prepared by the electroless deposition of Pt on Ru seed clusters from a Pt(+2) solution using dimethylamine borane as the reducing agent at pH 11 and 40 °C. After exposure to the electroless deposition bath, Pt was selectively deposited on Ru, as demonstrated by the detection of Pt on the surface by XPS, and the increase in the average cluster height without an increase in the number of clusters, indicating that Pt atoms are incorporated into the Ru seed clusters. Electroless deposition of Ru on Pt seed clusters was also achieved, but it should be noted that this deposition method is extremely sensitive to the presence of other metal ions in solution that have a higher reduction potential than the metal ion targeted for deposition.

  6. Platinum-ruthenium bimetallic clusters on graphite: a comparison of vapor deposition and electroless deposition methods.

    PubMed

    Galhenage, Randima P; Xie, Kangmin; Diao, Weijian; Tengco, John Meynard M; Seuser, Grant S; Monnier, John R; Chen, Donna A

    2015-11-14

    Bimetallic Pt-Ru clusters have been grown on highly ordered pyrolytic graphite (HOPG) surfaces by vapor deposition and by electroless deposition. These studies help to bridge the material gap between well-characterized vapor deposited clusters and electrolessly deposited clusters, which are better suited for industrial catalyst preparation. In the vapor deposition experiments, bimetallic clusters were formed by the sequential deposition of Pt on Ru or Ru on Pt. Seed clusters of the first metal were grown on HOPG surfaces that were sputtered with Ar(+) to introduce defects, which act as nucleation sites for Pt or Ru. On the unmodified HOPG surface, both Pt and Ru clusters preferentially nucleated at the step edges, whereas on the sputtered surface, clusters with relatively uniform sizes and spatial distributions were formed. Low energy ion scattering experiments showed that the surface compositions of the bimetallic clusters are Pt-rich, regardless of the order of deposition, indicating that the interdiffusion of metals within the clusters is facile at room temperature. Bimetallic clusters on sputtered HOPG were prepared by the electroless deposition of Pt on Ru seed clusters from a Pt(+2) solution using dimethylamine borane as the reducing agent at pH 11 and 40 °C. After exposure to the electroless deposition bath, Pt was selectively deposited on Ru, as demonstrated by the detection of Pt on the surface by XPS, and the increase in the average cluster height without an increase in the number of clusters, indicating that Pt atoms are incorporated into the Ru seed clusters. Electroless deposition of Ru on Pt seed clusters was also achieved, but it should be noted that this deposition method is extremely sensitive to the presence of other metal ions in solution that have a higher reduction potential than the metal ion targeted for deposition. PMID:26018140

  7. Ordered macroporous bimetallic nanostructures: design, characterization, and applications.

    PubMed

    Lu, Lehui; Eychmüller, Alexander

    2008-02-01

    Ordered porous metal nanomaterials have current and future potential applications, for example, as catalysts, as photonic crystals, as sensors, as porous electrodes, as substrates for surface-enhanced Raman scattering (SERS), in separation technology, and in other emerging nanotechnologies. Methods for creating such materials are commonly characterized as "templating", a technique that involves first the creation of a sacrificial template with a specific porous structure, followed by the filling of these pores with desired metal materials and finally the removal of the starting template, leaving behind a metal replica of the original template. From the viewpoint of practical applications, ordered metal nanostructures with hierarchical porosity, namely, macropores in combination with micropores or mesopores, are of particular interest because macropores allow large guest molecules to access and an efficient mass transport through the porous structures is enabled while the micropores or mesopores enhance the selectivity and the surface area of the metal nanostructures. For this objective, colloidal crystals (or artificial opals) consisting of three-dimensional (3D) long-range ordered arrays of silica or polymer microspheres are ideal starting templates. However, with respect to the colloidal crystal templating strategies for production of ordered porous metal nanostructures, there are two challenging questions for materials scientists: (1) how to uniformly and controllably fill the interstitial space of the colloidal crystal templates and (2) how to generate ordered composite metal nanostructures with hierarchical porosity. This Account reports on recent work in the development and applications of ordered macroporous bimetallic nanostructures in our laboratories. A series of strategies have been explored to address the challenges in colloidal crystal template techniques. By rationally tailoring experimental parameters, we could readily and selectively design

  8. Highly porous non-precious bimetallic electrocatalysts for efficient hydrogen evolution

    PubMed Central

    Lu, Qi; Hutchings, Gregory S.; Yu, Weiting; Zhou, Yang; Forest, Robert V.; Tao, Runzhe; Rosen, Jonathan; Yonemoto, Bryan T.; Cao, Zeyuan; Zheng, Haimei; Xiao, John Q.; Jiao, Feng; Chen, Jingguang G.

    2015-01-01

    A robust and efficient non-precious metal catalyst for hydrogen evolution reaction is one of the key components for carbon dioxide-free hydrogen production. Here we report that a hierarchical nanoporous copper-titanium bimetallic electrocatalyst is able to produce hydrogen from water under a mild overpotential at more than twice the rate of state-of-the-art carbon-supported platinum catalyst. Although both copper and titanium are known to be poor hydrogen evolution catalysts, the combination of these two elements creates unique copper-copper-titanium hollow sites, which have a hydrogen-binding energy very similar to that of platinum, resulting in an exceptional hydrogen evolution activity. In addition, the hierarchical porosity of the nanoporous copper-titanium catalyst also contributes to its high hydrogen evolution activity, because it provides a large-surface area for electrocatalytic hydrogen evolution, and improves the mass transport properties. Moreover, the catalyst is self-supported, eliminating the overpotential associated with the catalyst/support interface. PMID:25910892

  9. Highly porous non-precious bimetallic electrocatalysts for efficient hydrogen evolution

    SciTech Connect

    Lu, Qi; Hutchings, Gregory S.; Yu, Weiting; Zhou, Yang; Forest, Robert V.; Tao, Runzhe; Rosen, Jonathan; Yonemoto, Bryan T.; Cao, Zeyuan; Zheng, Haimei; Xiao, John Q.; Jiao, Feng; Chen, Jingguang G.

    2015-03-16

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

  10. Highly porous non-precious bimetallic electrocatalysts for efficient hydrogen evolution

    DOE PAGES

    Lu, Qi; Hutchings, Gregory S.; Yu, Weiting; Zhou, Yang; Forest, Robert V.; Tao, Runzhe; Rosen, Jonathan; Yonemoto, Bryan T.; Cao, Zeyuan; Zheng, Haimei; et al

    2015-03-16

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

  11. Highly porous non-precious bimetallic electrocatalysts for efficient hydrogen evolution

    NASA Astrophysics Data System (ADS)

    Lu, Qi; Hutchings, Gregory S.; Yu, Weiting; Zhou, Yang; Forest, Robert V.; Tao, Runzhe; Rosen, Jonathan; Yonemoto, Bryan T.; Cao, Zeyuan; Zheng, Haimei; Xiao, John Q.; Jiao, Feng; Chen, Jingguang G.

    2015-03-01

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

  12. Hydrocarbon fuel reforming catalyst and use thereof

    DOEpatents

    Ming, Qimin; Healey, Todd; Irving, Patricia Marie

    2006-06-27

    The subject invention is a catalyst consisting of an oxide or mixed oxide support and bimetallic catalytically active compounds. The supporting oxide can be a single oxide, such as Al.sub.2O.sub.3; it also can be a mixture of oxides, such as Y.sub.2O.sub.3 stabilized ZrO.sub.2 (YSZ), Al.sub.2O.sub.3 with CeO.sub.2, Al.sub.2O.sub.3 with YSZ and others. The bimetallic compounds, acting as active components, are selected from platinum, and ruthenium, prepared in an appropriate ratio. The catalyst is used in the steam reforming of hydrocarbons to produce hydrogen for applications such as polymer electrolyte membrane fuel cells.

  13. Synthesis of subnanometer-diameter vertically aligned single-walled carbon nanotubes with copper-anchored cobalt catalysts.

    PubMed

    Cui, Kehang; Kumamoto, Akihito; Xiang, Rong; An, Hua; Wang, Benjamin; Inoue, Taiki; Chiashi, Shohei; Ikuhara, Yuichi; Maruyama, Shigeo

    2016-01-21

    We synthesize vertically aligned single-walled carbon nanotubes (VA-SWNTs) with subnanometer diameters on quartz (and SiO2/Si) substrates by alcohol CVD using Cu-anchored Co catalysts. The uniform VA-SWNTs with a nanotube diameter of 1 nm are synthesized at a CVD temperature of 800 °C and have a thickness of several tens of μm. The diameter of SWNTs was reduced to 0.75 nm at 650 °C with the G/D ratio maintained above 24. Scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into a larger size, which contributed to the small diameter of SWNTs. The correlation between the catalyst size and the SWNT diameter was experimentally clarified. The subnanometer-diameter and high-quality SWNTs are expected to pave the way to replace silicon for next-generation optoelectronic and photovoltaic devices. PMID:26690843

  14. Development of Pd-Cu/hematite catalyst for selective nitrate reduction.

    PubMed

    Jung, Sungyoon; Bae, Sungjun; Lee, Woojin

    2014-08-19

    A new hematite-supported Pd-Cu bimetallic catalyst (Pd-Cu/hematite) was developed in order to actively and selectively reduce nitrate (NO3(-)) to nitrogen gas (N2). Four different iron-bearing soil minerals (hematite (H), goethite (G), maghemite (M), and lepidocrocite (L)) were transformed to hematite by calcination and used for synthesis of different Pd-Cu/hematite-H, G, M, and L catalysts. Their characteristics were identified using X-ray diffraction (XRD), specific surface area (BET), temperature programed reduction (TPR), transmission electron microscopy with energy dispersive X-ray (TEM-EDX), H2 pulse chemisorption, zeta-potential, and X-ray photoelectron spectroscopy (XPS). Pd-Cu/hematite-H exhibited the highest NO3(-) removal (96.4%) after 90 min, while a lower removal (90.9, 51.1, and 30.5%) was observed in Pd-Cu/hematite-G, M, and L, respectively. The results of TEM-EDX, and TPR analysis revealed that Pd-Cu/hematite-H possessed the closest contact distance between the Cu and Pd sites on the hematite surface among the different Pd-Cu/hematite catalysts. The high removal can be also attributed to the highly active metallic sites on its positively charged surface. The XPS analysis demonstrated that the amount of hydrogen molecules can have a pivotal function on NO3(-) removal and a ratio of nitrogen to hydrogen molecule (N:H) on the Pd sites can critically determine N2 selectivity.

  15. The use of mechanical alloying for the preparation of palladized magnesium bimetallic particles for the remediation of PCBs.

    PubMed

    Coutts, Janelle L; Devor, Robert W; Aitken, Brian; Hampton, Michael D; Quinn, Jacqueline W; Clausen, Christian A; Geiger, Cherie L

    2011-09-15

    The kinetic rate of dechlorination of a polychlorinated biphenyl (PCB-151) by mechanically alloyed Mg/Pd was studied for optimization of the bimetallic system. Bimetal production was first carried out in a small-scale environment using a SPEX 8000M high-energy ball mill with 4-μm-magnesium and palladium impregnated on graphite, with optimized parameters including milling time and Pd-loading. A 5.57-g sample of bimetal containing 0.1257% Pd and ball milled for 3 min resulted in a degradation rate of 0.00176 min(-1)g(-1) catalyst as the most reactive bimetal. The process was then scaled-up, using a Red Devil 5400 Twin-Arm Paint Shaker, fitted with custom plates to hold milling canisters. Optimization parameters tested included milling time, number of ball bearings used, Pd-loading, and total bimetal mass milled. An 85-g sample of bimetal containing 0.1059% Pd and ball-milled for 23 min with 16 ball bearings yielded the most reactive bimetal with a degradation rate of 0.00122 min(-1)g(-1) catalyst. Further testing showed adsorption did not hinder extraction efficiency and that dechlorination products were only seen when using the bimetallic system, as opposed to any of its single components. The bimetallic system was also tested for its ability to degrade a second PCB congener, PCB-45, and a PCB mixture (Arochlor 1254); both contaminants were seen to degrade successfully. PMID:21807459

  16. Alumina-supported sulfided catalysts: V. Effect of P and F on the catalytic activity of hydrodesulfurization sulfided catalysts

    SciTech Connect

    Startsev, A.N.; Klimov, O.V.; Kalinkin, A.V.; Mastikhin, V.M.

    1994-07-01

    Phosphorus and flourine additives incorporated into the Ni-Mo/Al{sub 2}O{sub 3} sulfided catalysts on various stages of their preparation considerably lower the activation energy of the thiophene hydrogenolysis reaction. The interaction of promoting additives with the active component of the hydrodesulfurization catalyst is proved by XPS and {sup 31}P NMR. The effect of additives is discussed in terms of a synchronous mechanism involving interaction of reacting molecules in the coordination sphere of a bimetallic sulfide compound.

  17. Stainless steel to titanium bimetallic transitions

    NASA Astrophysics Data System (ADS)

    Kaluzny, J. A.; Grimm, C.; Passarelli, D.

    2015-12-01

    In order to use stainless steel piping in an LCLS-II (Linac Coherent Light Source Upgrade) cryomodule, stainless steel to titanium bimetallic transitions are needed to connect the stainless steel piping to the titanium cavity helium vessel. Explosion bonded stainless steel to titanium transition pieces and bimetallic transition material samples have been tested. A sample transition tube was subjected to tests and x-ray examinations between tests. Samples of the bonded joint material were impact and tensile tested at room temperature as well as liquid helium temperature. The joint has been used successfully in horizontal tests of LCLS-II cavity helium vessels and is planned to be used in LCLS-II cryomodules. Results of material sample and transition tube tests will be presented. Operated by Fermi Research Alliance, LLC under Contract No. De-AC02-07CH11359 with the United States Department of Energy.

  18. Stainless Steel to Titanium Bimetallic Transitions

    SciTech Connect

    Kaluzny, J. A.; Grimm, C.; Passarelli, D.

    2015-01-01

    In order to use stainless steel piping in an LCLS-II (Linac Coherent Light Source Upgrade) cryomodule, stainless steel to titanium bimetallic transitions are needed to connect the stainless steel piping to the titanium cavity helium vessel. Explosion bonded stainless steel to titanium transition pieces and bimetallic transition material samples have been tested. A sample transition tube was subjected to tests and x-ray examinations between tests. Samples of the bonded joint material were impact and tensile tested at room temperature as well as liquid helium temperature. The joint has been used successfully in horizontal tests of LCLS-II cavity helium vessels and is planned to be used in LCLS-II cryomodules. Results of material sample and transition tube tests will be presented.

  19. Electrodeposition of Au/Ag bimetallic dendrites assisted by Faradaic AC-electroosmosis flow

    SciTech Connect

    Ji, Jianlong; Li, Pengwei; Sang, Shengbo Zhang, Wendong Li, Gang; Hu, Jie; Zhou, Zhaoying Yang, Xing; Dong, Hualai

    2014-03-15

    Au/Ag bimetallic dendrites were synthesized successfully from the corresponding aqueous solution via the AC electrodeposition method. Both of the morphologies and compositions could be tuned by the electrolyte concentration and AC frequency. The prepared bimetallic dendrites were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and UV–vis spectroscopy. The underlying dendrite growth mechanism was then proposed in the context of the Directed Electrochemical Nanowires Assembly (DENA) models. Owing to the unscreened voltage dropping in the electrolyte bulk, electromigration dominates the species flux process, and cations tend to accumulate in areas with strong electric field intensity, such as electrode edges. Moreover, Faradaic AC-electro-osmosis (ACEO) flow could increase the effective diffusion layer thickness in these areas during the electrochemical reaction, and leads to dendrite growth. Further Micro-Raman observations illustrated that the Au/Ag bimetallic dendrites exhibited pronounced surface-enhanced Raman scattering (SERS) activity, using 4-mercaptopyridine (4-MP) as model molecules.

  20. Characterization of Bimetallic Castings with an Austenitic Working Surface Layer and an Unalloyed Cast Steel Base

    NASA Astrophysics Data System (ADS)

    Wróbel, Tomasz

    2014-05-01

    The paper presents the technology of bimetallic castings based on the founding method of layer coating directly in the cast process of the so-called method of mold cavity preparation. The prepared castings consist of two fundamental parts, i.e., the base and the working surface layer. The base part of the bimetallic casting is typical foundry material, i.e., unalloyed cast steel, whereas the working layer is a plate of austenitic alloy steel sort X2CrNi 18-9. The quality of the joint between the base part and the working layer was evaluated on the basis of ultrasonic non-destructive testing and structure examinations containing metallographic macro- and microscopic studies with the use of a light microscope (LOM) with microhardness measurements and a scanning electron microscope (SEM) with microanalysis of the chemical composition (energy dispersive spectroscopy—EDS). On the basis of the obtained results it was confirmed that the decisive phenomena needed to create a permanent joint between the two components of the bimetallic casting are carbon and heat transport in the direction from the high-carbon and hot base material which was poured into the mold in the form of liquid metal to the low-carbon and cold material of the working layer which was placed in the mold cavity in the form of a monolithic insert.

  1. Electrodeposition of Au/Ag bimetallic dendrites assisted by Faradaic AC-electroosmosis flow

    NASA Astrophysics Data System (ADS)

    Ji, Jianlong; Li, Pengwei; Sang, Shengbo; Zhang, Wendong; Zhou, Zhaoying; Yang, Xing; Dong, Hualai; Li, Gang; Hu, Jie

    2014-03-01

    Au/Ag bimetallic dendrites were synthesized successfully from the corresponding aqueous solution via the AC electrodeposition method. Both of the morphologies and compositions could be tuned by the electrolyte concentration and AC frequency. The prepared bimetallic dendrites were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and UV-vis spectroscopy. The underlying dendrite growth mechanism was then proposed in the context of the Directed Electrochemical Nanowires Assembly (DENA) models. Owing to the unscreened voltage dropping in the electrolyte bulk, electromigration dominates the species flux process, and cations tend to accumulate in areas with strong electric field intensity, such as electrode edges. Moreover, Faradaic AC-electro-osmosis (ACEO) flow could increase the effective diffusion layer thickness in these areas during the electrochemical reaction, and leads to dendrite growth. Further Micro-Raman observations illustrated that the Au/Ag bimetallic dendrites exhibited pronounced surface-enhanced Raman scattering (SERS) activity, using 4-mercaptopyridine (4-MP) as model molecules.

  2. Laser synthesis of ligand-free bimetallic nanoparticles for plasmonic applications.

    PubMed

    Intartaglia, R; Das, G; Bagga, K; Gopalakrishnan, A; Genovese, A; Povia, M; Di Fabrizio, E; Cingolani, R; Diaspro, A; Brandi, F

    2013-03-01

    A picosecond laser ablation approach has been developed for the synthesis of ligand-free AuAg bimetallic NPs where the relative amount of Ag is controlled in situ through a laser shielding effect. Various measurements, such as optical spectroscopy, transmission electron microscopy combined with energy dispersive X-ray spectroscopy and inductively coupled plasma optical emission spectrometry, revealed the generation of homogenous 15 nm average size bimetallic NPs with different compositions and tunable localized surface plasmon resonance. Furthermore, ligand-free metallic nanoparticles with respect to chemically synthesized nanoparticles display outstanding properties, i.e. featureless Raman background spectrum, which is a basic requirement in many plasmonic applications such as Surface Enhanced Raman Spectroscopy. Various molecules were chemisorbed on the nanoparticle and SERS investigations were carried out, by varying the laser wavelength. The SERS enhancement factor for AuAg bimetallic NPs shows an enhancement factor of about 5.7 × 10(5) with respect to the flat AuAg surface. PMID:23196320

  3. Laser synthesis of ligand-free bimetallic nanoparticles for plasmonic applications.

    PubMed

    Intartaglia, R; Das, G; Bagga, K; Gopalakrishnan, A; Genovese, A; Povia, M; Di Fabrizio, E; Cingolani, R; Diaspro, A; Brandi, F

    2013-03-01

    A picosecond laser ablation approach has been developed for the synthesis of ligand-free AuAg bimetallic NPs where the relative amount of Ag is controlled in situ through a laser shielding effect. Various measurements, such as optical spectroscopy, transmission electron microscopy combined with energy dispersive X-ray spectroscopy and inductively coupled plasma optical emission spectrometry, revealed the generation of homogenous 15 nm average size bimetallic NPs with different compositions and tunable localized surface plasmon resonance. Furthermore, ligand-free metallic nanoparticles with respect to chemically synthesized nanoparticles display outstanding properties, i.e. featureless Raman background spectrum, which is a basic requirement in many plasmonic applications such as Surface Enhanced Raman Spectroscopy. Various molecules were chemisorbed on the nanoparticle and SERS investigations were carried out, by varying the laser wavelength. The SERS enhancement factor for AuAg bimetallic NPs shows an enhancement factor of about 5.7 × 10(5) with respect to the flat AuAg surface.

  4. Structural characteristics and catalytic properties of highly dispersed ZrO{sub 2}/SiO{sub 2} and V{sub 2}O{sub 5}/ZrO{sub 2}/SiO{sub 2} catalysts

    SciTech Connect

    Gao, X.; Wachs, I.E.; Fierro, J.L.G.

    1999-04-27

    Highly dispersed ZrO{sub 2}/SiO{sub 2} and V{sub 2}O{sub 5}/ZrO{sub 2}/SiO{sub 2} catalysts were successfully synthesized by the incipient wetness impregnation method. The surface structures of these catalysts in hydrated and dehydrated states were characterized by in situ Raman and UV-vis-near-infrared diffuse reflectance spectroscopies. Temperature-programmed reduction and methanol oxidation were employed as chemical probe reactions to examine the reducibility and reactivity/selectivity properties of these catalysts. These characterization techniques demonstrate that both zirconium oxide and vanadium oxide species are highly dispersed as two-dimensional metal oxide overlayers on the silica support. The spectroscopic results revealed that the surface vanadium oxide species on the highly dispersed ZrO{sub 2}/SiO{sub 2} supports are predominantly isolated VO{sub 4} units [O{double_bond}V(O-Support){sub 3}] in the dehydrated state and become polymerized vanadium oxide species upon hydration. The surface vanadium oxide species preferentially interact with the zirconium oxide species on the silica surface. The substitution of Si{sup IV}-O{sup {minus}} by Zr{sup IV}-O{sup {minus}} ligands significantly affects the chemical properties of the isolated VO{sub 4} units: the reducibility of the surface vanadium oxide species increases, and the methanol oxidation turnover frequency (TOF) increases by 1--2 orders of magnitude relative to V{sub 2}O{sub 5}/SiO{sub 2}. The present study demonstrates that the support effect, variation in the reactivity of supported metal oxide catalysts due to different oxide supports, essentially originates from the difference in oxygenated ligands around the active metal cations.

  5. Origin of synergistic effect over Ni-based bimetallic surfaces: A density functional theory study

    NASA Astrophysics Data System (ADS)

    Fan, Chen; Zhu, Yi-An; Xu, Yue; Zhou, Yan; Zhou, Xing-Gui; Chen, De

    2012-07-01

    Density functional theory calculations have been conducted to explore the physical origin of the synergistic effect over Ni-based surface alloys using methane dissociation as a probe reaction. Some late transition metal atoms (M = Cu, Ru, Rh, Pd, Ag, Pt, and Au) are substituted for surface Ni atoms to examine the variation in electronic structure and adsorption property of Ni(111). Two types of threefold hollow sites, namely, the Ni2M and Ni3 sites, are taken into account. The calculated results indicate that the variation in the CHx adsorption energy at the Ni2M and Ni3 sites is dominated by the ensemble and ligand effect, respectively, and the other factors such as surface and adsorbate distortion and electrostatic interaction affect the catalytic properties of the bimetallic surfaces to a smaller extent. Both the Brønsted-Evans-Polanyi relationship and the scaling correlation hold true on the Ni-based bimetallic surfaces. With the combination of these two linear energy relations, the corrected binding energy of atomic C is found to be a good descriptor for representing the catalytic activity of the alloyed surfaces. Considering the compromise between the catalytic activity and catalyst stability, we suggest that the Rh/Ni catalyst is a good candidate for methane dissociation.

  6. Sophisticated Design of Covalent Organic Frameworks with Controllable Bimetallic Docking for a Cascade Reaction.

    PubMed

    Leng, Wenguang; Peng, Yongsheng; Zhang, Jianqiang; Lu, Hui; Feng, Xiao; Ge, Rile; Dong, Bin; Wang, Bo; Hu, Xiangping; Gao, Yanan

    2016-06-27

    Precise control of the number and position of the catalytic metal ions in heterogeneous catalysts remains a big challenge. Here we synthesized a series of two-dimensional (2D) covalent organic frameworks (COFs) containing two different types of nitrogen ligands, namely imine and bipyridine, with controllable contents. For the first time, the selective coordination of the two nitrogen ligands of the 2D COFs to two different metal complexes, chloro(1,5-cyclooctadiene)rhodium(I) (Rh(COD)Cl) and palladium(II) acetate (Pd(OAc)2 ), has been realized using a programmed synthetic procedure. The bimetallically docked COFs showed excellent catalytic activity in a one-pot addition-oxidation cascade reaction. The high surface area, controllable metal-loading content, and predesigned active sites make them ideal candidates for their use as heterogeneous catalysts in a wide range of chemical reactions.

  7. Pd-Pt Bimetallic Nanodendrites with High Activity for Oxygen Reduction

    SciTech Connect

    Lim, B.; Tao, J.; Jiang, M.; Camargo, P.H.C.; Cho, E.C.; Lu, X.; Zhu, Y.; Xia, Y.

    2009-06-05

    Controlling the morphology of Pt nanostructures can provide a great opportunity to improve their catalytic properties and increase their activity on a mass basis. We synthesized Pd-Pt bimetallic nanodendrites consisting of a dense array of Pt branches on a Pd core by reducing K{sub 2}PtCl{sub 4} with L-ascorbic acid in the presence of uniform Pd nanocrystal seeds in an aqueous solution. The Pt branches supported on faceted Pd nanocrystals exhibited relatively large surface areas and particularly active facets toward the oxygen reduction reaction (ORR), the rate-determining step in a proton-exchange membrane fuel cell. The Pd-Pt nanodendrites were two and a half times more active on the basis of equivalent Pt mass for the ORR than the state-of-the-art Pt/C catalyst and five times more active than the first-generation supportless Pt-black catalyst.

  8. Pillared montmorillonite catalysts for coal liquefaction

    SciTech Connect

    Sharma, R.K.; Olson, E.S.

    1994-12-31

    Pillared clays contain large micropores and have considerable potential for catalytic hydrogenation and cleavage of coal macromolecules. Pillared montmorillonite-supported catalysts were prepared by the intercalation of polynuclear hydroxychromium cations and subsequent impregnation of nickel and molybdenum. Infrared and thermogravimetric studies of pyridine-adsorbed catalysts indicated the presence of both Lewis and Bronsted acid sites. Thus, the catalysts have both acidic properties that can aid in hydrocracking and cleavage of carbon-heteroatom bonds as well as hydrogen-activating bimetallic sites. These catalysts were applied to the hydrodesulfurization and liquefaction of coal-derived intermediates. The reactions of model organosulfur compounds and coal liquids were carried out at 300{degrees}-400{degrees}C for 3 hours in the presence of 1000 psi of molecular hydrogen. Reaction products were analyzed by GC/FT-IR/MS/AED. The catalysts have been found to be very effective in removing sulfur from model compounds as well as liquefaction products.

  9. Green synthesis and applications of Au-Ag bimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Meena Kumari, M.; Jacob, John; Philip, Daizy

    2015-02-01

    This paper reports for the first time the synthesis of bimetallic nanoparticles at room temperature using the fruit juice of pomegranate. Simultaneous reduction of gold and silver ions in different molar ratios leads to the formation of alloy as well as core-shell nanostructures. The nanoparticles have been characterized using UV-vis spectroscopy, transmission electron microscopy, Fourier Transform Infrared Spectroscopy and X-ray diffraction. The synthesized alloy particles are used as catalysts in the reduction of 2-, 3-, 4-nitrophenols to the corresponding amines and in the degradation of methyl orange. The reduction kinetics for all the reactions follows pseudo-first order. The rate constants follow the order k4-nitrophenol < k2-nitrophenol < k3-nitrophenol. Thermal conductivity is measured as a function of volume fraction and it is observed that the incorporation of the alloy nanoparticles enhances the thermal conductivity of the base fluid (water) showing nanofluid application. The nitric oxide and hydroxyl radical scavenging activity shown by the nanoparticles promise the potential application in biomedical field.

  10. Green synthesis and applications of Au-Ag bimetallic nanoparticles.

    PubMed

    Meena Kumari, M; Jacob, John; Philip, Daizy

    2015-02-25

    This paper reports for the first time the synthesis of bimetallic nanoparticles at room temperature using the fruit juice of pomegranate. Simultaneous reduction of gold and silver ions in different molar ratios leads to the formation of alloy as well as core-shell nanostructures. The nanoparticles have been characterized using UV-vis spectroscopy, transmission electron microscopy, Fourier Transform Infrared Spectroscopy and X-ray diffraction. The synthesized alloy particles are used as catalysts in the reduction of 2-, 3-, 4-nitrophenols to the corresponding amines and in the degradation of methyl orange. The reduction kinetics for all the reactions follows pseudo-first order. The rate constants follow the order k4-nitrophenol

  11. Tetranuclear Zn/4f coordination clusters as highly efficient catalysts for Friedel-Crafts alkylation.

    PubMed

    Griffiths, Kieran; Kumar, Prashant; Akien, Geoffrey R; Chilton, Nicholas F; Abdul-Sada, Alaa; Tizzard, Graham J; Coles, Simon J; Kostakis, George E

    2016-06-14

    A series of custom-designed, high yield, isoskeletal tetranuclear Zn/4f coordination clusters showing high efficiency as catalysts with low catalytic loadings in Friedel-Crafts alkylation are described for the first time. The possibility of altering the 4f centers in these catalysts without altering the core topology allows us to further confirm their stability via EPR and NMR, as well to gain insights into the plausible reaction mechanism, showcasing the usefulness of these bimetallic systems as catalysts. PMID:27248829

  12. Synthesis of Co-based bimetallic nanocrystals with one-dimensional structure for selective control on syngas conversion

    NASA Astrophysics Data System (ADS)

    Ba, Rongbin; Zhao, Yonghui; Yu, Lujing; Song, Jianjun; Huang, Shuangshuang; Zhong, Liangshu; Sun, Yuhan; Zhu, Yan

    2015-07-01

    Co-based bimetallic nanocrystals with one-dimensional (1D) branches were synthesized by the heterogeneous nucleation of Co atoms onto prenucleated seeds, such as Pd or Cu, through a facile wet-chemical route. The peripheral branches (rod-like) of the Co-Pd and Co-Cu nanocrystals were outspread along the (001) direction and were enclosed by (101) facets. By switching the prenucleated metals to form robust Co-Pd or Co-Cu bimetallic nanocatalysts, the selectivity of CO hydrogenation could be adjusted purposely towards heavy paraffins, light olefins or oxygenates. The Anderson-Schulz-Flory chain-lengthening probabilities for products were up to 0.9 over Co-Pd nanocrystals, showing that long-chain hydrocarbons can be formed with high selectivity using the targeted design of Co-Pd nanocrystal catalysts. These Co-based bimetallic nanocrystals with a 1D structure exhibited superior catalytic activities over the corresponding Co-based nanoparticles for synthesis gas conversion.Co-based bimetallic nanocrystals with one-dimensional (1D) branches were synthesized by the heterogeneous nucleation of Co atoms onto prenucleated seeds, such as Pd or Cu, through a facile wet-chemical route. The peripheral branches (rod-like) of the Co-Pd and Co-Cu nanocrystals were outspread along the (001) direction and were enclosed by (101) facets. By switching the prenucleated metals to form robust Co-Pd or Co-Cu bimetallic nanocatalysts, the selectivity of CO hydrogenation could be adjusted purposely towards heavy paraffins, light olefins or oxygenates. The Anderson-Schulz-Flory chain-lengthening probabilities for products were up to 0.9 over Co-Pd nanocrystals, showing that long-chain hydrocarbons can be formed with high selectivity using the targeted design of Co-Pd nanocrystal catalysts. These Co-based bimetallic nanocrystals with a 1D structure exhibited superior catalytic activities over the corresponding Co-based nanoparticles for synthesis gas conversion. Electronic supplementary

  13. Tube-to-header joint for bimetallic construction

    NASA Technical Reports Server (NTRS)

    Lessmann, G. G.; Stoner, D. R.

    1967-01-01

    Design advantages of bimetallic construction enables an all-welded bimetallic joint to be made from the accessible header side of the tube-to-header joint. In the two-piece header design the weld joints completely seal the tube-header plate crevice and prevent crevice and stringer corrosion.

  14. PD/MG BIMETALLIC CORROSION CELLS FOR DECHLORINATING PCBS

    EPA Science Inventory

    Two dissimilar metals immersed in a conducting solution develop different corrosion potentials forming a bimetallic corrosion cell. Enhanced corrosion of an active metal like Mg combined with catalytic hydrogenation properties of a noble metal like Pd in such bimetallic cells can...

  15. Ag/Au bi-metallic film based color surface plasmon resonance biosensor with enhanced sensitivity, color contrast and great linearity.

    PubMed

    Li, Chung-Tien; Lo, Kun-Chi; Chang, Hsin-Yun; Wu, Hsieh-Ting; Ho, Jennifer H; Yen, Ta-Jen

    2012-01-01

    In wavelength surface plasmon resonance (SPR) biosensor, the manipulation of SPR dispersion relation by Ag/Au bi-metallic film was first time implemented. Due to the enhanced resonant wavelength shift and the sharper SPR slope of using Ag/Au bi-metallic film, the illuminated color of reflection shows one order of magnitude greater contrast than conventional SPR biosensors. Such an Ag/Au bi-metallic film based color SPR biosensor (CSPRB) allows the detail bio-interactions, for example 100 nM streptavidin, to be distinguished by directly observing the color change of reflection through naked eyes rather than the analysis of spectrometer. In addition to the enhanced sensitivity and color contrast, this CSPRB also possesses a great linear detection range up to 0.0254 RIU, which leading to the application of point-of-care tests. PMID:22560104

  16. AuRu/AC as an effective catalyst for hydrogenation reactions

    DOE PAGES

    Villa, Alberto; Chan-Thaw, Carine E.; Campisi, Sebastiano; Bianchi, Claudia L.; Wang, Di; Kotula, Paul G.; Kübel, Christian; Prati, Laura

    2015-03-23

    AuRu bimetallic catalysts have been prepared by sequential deposition of Au on Ru or vice versa obtaining different nanostructures: when Ru has been deposited on Au, a Aucore–Rushell has been observed, whereas the deposition of Au on Ru leads to a bimetallic phase with Ru enrichment on the surface. In the latter case, the unexpected Ru enrichment could be attributed to the weak adhesion of Ru on the carbon support, thus allowing Ru particles to diffuse on Au particles. Both structures result very active in catalysing the liquid phase hydrogenolysis of glycerol and levulinic acid but the activity, the selectivitymore » and the stability depend on the structure of the bimetallic nanoparticles. Ru@Au/AC core–shell structure mostly behaved as the monometallic Ru, whereas the presence of bimetallic AuRu phase in Au@Ru/AC provides a great beneficial effect on both activity and stability.« less

  17. A N-heterocyclic tetracarbene Pd(ii) moiety containing a Pd(ii)-Pb(ii) bimetallic MOF for three-component cyclotrimerization via benzyne.

    PubMed

    Dong, Ying; Li, Yue; Wei, Yong-Liang; Wang, Jian-Cheng; Ma, Jian-Ping; Ji, Jun; Yao, Bing-Jian; Dong, Yu-Bin

    2016-08-18

    A novel Pd(ii)-Pb(ii) bimetallic metal-organic framework Pd(ii)-Pb(ii)-MOF (B) which contains an N-heterocyclic tetracarbene Pd(ii) moiety was synthesized based on a chelating N-heterocyclic dicarbene Pd(ii)-NHDC ligand (A) under solvothermal conditions. It can be a highly active heterogeneous catalyst for three-component cyclotrimerization via benzyne species.

  18. Insight into the Catalytic Mechanism of Bimetallic Platinum–Copper Core–Shell Nanostructures for Nonaqueous Oxygen Evolution Reactions

    SciTech Connect

    Ma, Lu; Luo, Xiangyi; Kropf, A. Jeremy; Wen, Jianguo; Wang, Xiaoping; Lee, Sungsik; Myers, Deborah J.; Miller, Dean; Wu, Tianpin; Lu, Jun; Amine, Khalil

    2016-01-01

    The oxygen evolution reaction (OER) plays a critical role in multiple energy conversion and storage applications. However, its sluggish kinetics usually results in large voltage polarization and unnecessary energy loss. Therefore, designing efficient catalysts that could facilitate this process has become an emerging topic. Here, we present a unique Pt–Cu core–shell nanostructure for catalyzing the nonaqueous OER. The catalysts were systematically investigated with comprehensive spectroscopic techniques, and applied in nonaqueous Li–O2 electrochemical cells, which exhibited dramatically reduced charging overpotential (<0.2 V). The superior performance is explained by the robust Cu(I) surface sites stabilized by the Pt core in the nanostructure. The insights into the catalytic mechanism of the unique Pt–Cu core–shell nanostructure gained in this work are expected to serve as a guide for future design of other nanostructured bimetallic OER catalysts.

  19. Synthesis and characterization of Fe-Co catalyst prepared via reverse microemulsion method

    NASA Astrophysics Data System (ADS)

    Mohd Zabidi, Noor Asmawati; Abdul Aziz, Muhammad Nur Azizi; Ali, Sardar; Taha, Mohd Faisal

    2012-09-01

    This paper reports the characterization of bimetallic catalyst systems comprising cobalt and iron on CNTs support prepared via reverse microemulsion method. The properties of the bimetallic catalyst were characterized using TEM, FESEM and N2 adsorption. Based on TEM analyses, the calculated average particle sizes ranged from 4.6 nm to 5.2 nm for the various catalyst compositions. The performance of the Co-based catalyst in a Fischer-Tropsch reaction was evaluated in a fixed-bed reactor at 220°C, 1 atm and H2/CO v/v ratio of 2:1 v/v and space velocity of 12 L/g.h. Amongst the catalysts tested, the 90Co10Fe/CNTs resulted in the highest CO conversion of 14.1% whereas the 100Co/CNTs resulted in the highest C5+ hydrocarbon selectivity.

  20. Bimetallic nanostructures. II. Finite temperature and applications

    NASA Astrophysics Data System (ADS)

    Montejano-Carrizales, J. M.; Morán-López, J. L.

    1990-12-01

    A systematic study of ordering and segregation at finite temperatures in bimetallic nanoclusters is presented. Icosahedral and cubo-octahedral clusters, with a total number of atoms, N = 13, 55 and 147, are studied. The equilibrium configuration is obtained by calculating the free energy within the regular solution model. The theory is applied to CuPd, NiPt and CuNi nanoclusters. We present results for the temperature dependence of the concentrations at the different shells around the central atom. In most of the cases a strong segregation is found.

  1. Field assessment of nanoscale bimetallic particles for groundwater treatment.

    PubMed

    Elliott, D W; Zhang, W X

    2001-12-15

    A field demonstration was performed in which nanoscale bimetallic (Fe/Pd) particles were gravity-fed into groundwater contaminated bytrichloroethene and other chlorinated aliphatic hydrocarbons at a manufacturing site. With diameters on the order of 100-200 nm, the nanoparticles are uniquely suited to rapidly degrade redox-amenable contaminants and for optimal subsurface delivery and dispersion. Approximately 1.7 kg of the nanoparticles was fed into the test area over a 2-day period, resulting in minimal clogging of the injection well. The test area was located within a well-characterized region of the contaminant plume and included an injection well and three piezometer couplets spaced 1.5 m apart. Despite the low nanoparticle dosage, trichloroethene reduction efficiencies of up to 96% were observed over a 4-week monitoring period with the highest values observed at the injection well and adjacent piezometers. Data from the field assessment were consistent with the results of pre-injection laboratory studies, which showed rapid dechlorination of target chlorinated compounds accompanied by a sharp decrease of standard oxidation potential and an increase in pH. PMID:11775172

  2. Nanosized Pt-Co catalysts for the preferential CO oxidation.

    PubMed

    Ko, Eun-Yong; Park, Eun Duck; Seo, Kyung Won; Lee, Hyun Chul; Lee, Doohwan; Kim, Soonho

    2006-11-01

    The preferential CO oxidation in the presence of excess hydrogen was studied over Pt-Co/gamma-Al2O3. CO chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX) and temperature programmed reduction (TPR) were conducted to characterize active catalysts. The catalytic activity for CO oxidation and methanation at low temperatures increased with the amounts of cobalt in Pt-Co/gamma-Al2O3. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Co and Pt was determined to be 10. The co-impregnated Pt-Co/gamma-Al2O3 appeared to be superior to Pt/Co/gamma-Al2O3 and Co/Pt/gamma-Al2O3. The reductive pretreatment at high temperature such as 773 K increased the CO2 selectivity over a wide reaction temperature. The bimetallic phase of Pt-Co seems to give rise to high catalytic activity in selective oxidation of CO in H2-rich stream. PMID:17252813

  3. Enhanced Dry Reforming of Methane on Ni and Ni-Pt Catalysts Synthesized by Atomic Layer Deposition

    SciTech Connect

    Gould, Troy D.; Montemore, Matthew M.; Lubers, Alia M.; Ellis, Lucas D.; Weimer, Alan; Falconer, John L.; Medlin, James W.

    2015-02-25

    Atomic layer deposition (ALD) was used to deposit Ni and Pt on alumina supports to form monometallic and bimetallic catalysts with initial particle sizes of 1–2.4 nm. The ALD catalysts were more active (per mass of metal) than catalysts prepared by incipient wetness (IW) for dry reforming of methane (DRM), and they did not form carbon whiskers during reaction due to their sufficiently small size. Catalysts modified by Pt ALD had higher rates of reaction per mass of metal and inhibited coking, whereas NiPt catalysts synthesized by IW still formed carbon whiskers. Temperature-programmed reduction of Ni catalysts modified by Pt ALD indicated the presence of bimetallic interaction. Density functional theory calculations suggested that under reaction conditions, the NiPt surfaces form Ni-terminated surfaces that are associated with higher DRM rates (due to their C and O adsorption energies, as well as the CO formation and CH4 dissociation energies).

  4. BIMETALLIC LITHIUM BOROHYDRIDES TOWARD REVERSIBLE HYDROGEN STORAGE

    SciTech Connect

    Au, M.

    2010-10-21

    Borohydrides such as LiBH{sub 4} have been studied as candidates for hydrogen storage because of their high hydrogen contents (18.4 wt% for LiBH{sub 4}). Limited success has been made in reducing the dehydrogenation temperature by adding reactants such as metals, metal oxides and metal halides. However, full rehydrogenation has not been realized because of multi-step decomposition processes and the stable intermediate species produced. It is suggested that adding second cation in LiBH{sub 4} may reduce the binding energy of B-H. The second cation may also provide the pathway for full rehydrogenation. In this work, several bimetallic borohydrides were synthesized using wet chemistry, high pressure reactive ball milling and sintering processes. The investigation found that the thermodynamic stability was reduced, but the full rehydrogenation is still a challenge. Although our experiments show the partial reversibility of the bimetallic borohydrides, it was not sustainable during dehydriding-rehydriding cycles because of the accumulation of hydrogen inert species.

  5. Atomic structure and thermal stability of Pt-Fe bimetallic nanoparticles: from alloy to core/shell architectures.

    PubMed

    Huang, Rao; Wen, Yu-Hua; Shao, Gui-Fang; Sun, Shi-Gang

    2016-06-22

    Bimetallic nanoparticles comprising noble metal and non-noble metal have attracted intense interest over the past few decades due to their low cost and significantly enhanced catalytic performances. In this article, we have explored the atomic structure and thermal stability of Pt-Fe alloy and core-shell nanoparticles by molecular dynamics simulations. In Fe-core/Pt-shell nanoparticles, Fe with three different structures, i.e., body-centered cubic (bcc), face-centered cubic (fcc), and amorphous phases, has been considered. Our results show that Pt-Fe alloy is the most stable configuration among the four types of bimetallic nanoparticles. It has been discovered that the amorphous Fe cannot stably exist in the core and preferentially transforms into the fcc phase. The phase transition from bcc to hexagonal close packed (hcp) has also been observed in bcc-Fe-core/Pt-shell nanoparticles. In contrast, Fe with the fcc structure is the most preferred as the core component. These findings are helpful for understanding the structure-property relationships of Pt-Fe bimetallic nanoparticles, and are also of significance to the synthesis and application of noble metal based nanoparticle catalysts. PMID:27297782

  6. Atomic structure and thermal stability of Pt-Fe bimetallic nanoparticles: from alloy to core/shell architectures.

    PubMed

    Huang, Rao; Wen, Yu-Hua; Shao, Gui-Fang; Sun, Shi-Gang

    2016-06-22

    Bimetallic nanoparticles comprising noble metal and non-noble metal have attracted intense interest over the past few decades due to their low cost and significantly enhanced catalytic performances. In this article, we have explored the atomic structure and thermal stability of Pt-Fe alloy and core-shell nanoparticles by molecular dynamics simulations. In Fe-core/Pt-shell nanoparticles, Fe with three different structures, i.e., body-centered cubic (bcc), face-centered cubic (fcc), and amorphous phases, has been considered. Our results show that Pt-Fe alloy is the most stable configuration among the four types of bimetallic nanoparticles. It has been discovered that the amorphous Fe cannot stably exist in the core and preferentially transforms into the fcc phase. The phase transition from bcc to hexagonal close packed (hcp) has also been observed in bcc-Fe-core/Pt-shell nanoparticles. In contrast, Fe with the fcc structure is the most preferred as the core component. These findings are helpful for understanding the structure-property relationships of Pt-Fe bimetallic nanoparticles, and are also of significance to the synthesis and application of noble metal based nanoparticle catalysts.

  7. Homogeneity and elemental distribution in self-assembled bimetallic Pd-Pt aerogels prepared by a spontaneous one-step gelation process.

    PubMed

    Oezaslan, M; Liu, W; Nachtegaal, M; Frenkel, A I; Rutkowski, B; Werheid, M; Herrmann, A-K; Laugier-Bonnaud, C; Yilmaz, H-C; Gaponik, N; Czyrska-Filemonowicz, A; Eychmüller, A; Schmidt, T J

    2016-07-27

    a commercially available unsupported Pt black catalyst. We show that the Pd-Pt aerogels possess a high utilization of catalytically active centers for electrocatalytic applications based on the nanostructured bimetallic framework. Knowledge about the homogeneity and chemical distribution of the bimetallic aerogels can help to further optimize their preparation by the spontaneous one-step gelation process and to tune their electrocatalytic reactivity. PMID:27411594

  8. Impact of Multifunctional Bimetallic Materials on Lithium Battery Electrochemistry.

    PubMed

    Durham, Jessica L; Poyraz, Altug S; Takeuchi, Esther S; Marschilok, Amy C; Takeuchi, Kenneth J

    2016-09-20

    Electric energy storage devices such as batteries are complex systems comprised of a variety of materials with each playing separate yet interactive roles, complicated by length scale interactions occurring from the molecular to the mesoscale. Thus, addressing specific battery issues such as functional capacity requires a comprehensive perspective initiating with atomic level concepts. For example, the electroactive materials which contribute to the functional capacity in a battery comprise approximately 30% or less of the total device mass. Thus, the design and implementation of multifunctional materials can conceptually reduce or eliminate the contribution of passive materials to the size and mass of the final system. Material multifunctionality can be achieved through appropriate material design on the atomic level resulting in bimetallic electroactive materials where one metal cation forms mesoscale conductive networks upon discharge while the other metal cations can contribute to atomic level structure and net functional secondary capacity, a device level issue. Specifically, this Account provides insight into the multimechanism electrochemical redox processes of bimetallic cathode materials based on transition metal oxides (MM'O) or phosphorus oxides (MM'PO) where M = Ag and M' = V or Fe. One discharge process can be described as reduction-displacement where Ag(+) is reduced to Ag(0) and displaced from the parent structure. This reduction-displacement reaction in silver-containing bimetallic electrodes allows for the in situ formation of a conductive network, enhancing the electrochemical performance of the electrode and reducing or eliminating the need for conductive additives. A second discharge process occurs through the reduction of the second transition metal, V or Fe, where the oxidation state of the metal center is reduced and lithium cations are inserted into the structure. As both metal centers contribute to the functional capacity, determining the

  9. Impact of Multifunctional Bimetallic Materials on Lithium Battery Electrochemistry.

    PubMed

    Durham, Jessica L; Poyraz, Altug S; Takeuchi, Esther S; Marschilok, Amy C; Takeuchi, Kenneth J

    2016-09-20

    Electric energy storage devices such as batteries are complex systems comprised of a variety of materials with each playing separate yet interactive roles, complicated by length scale interactions occurring from the molecular to the mesoscale. Thus, addressing specific battery issues such as functional capacity requires a comprehensive perspective initiating with atomic level concepts. For example, the electroactive materials which contribute to the functional capacity in a battery comprise approximately 30% or less of the total device mass. Thus, the design and implementation of multifunctional materials can conceptually reduce or eliminate the contribution of passive materials to the size and mass of the final system. Material multifunctionality can be achieved through appropriate material design on the atomic level resulting in bimetallic electroactive materials where one metal cation forms mesoscale conductive networks upon discharge while the other metal cations can contribute to atomic level structure and net functional secondary capacity, a device level issue. Specifically, this Account provides insight into the multimechanism electrochemical redox processes of bimetallic cathode materials based on transition metal oxides (MM'O) or phosphorus oxides (MM'PO) where M = Ag and M' = V or Fe. One discharge process can be described as reduction-displacement where Ag(+) is reduced to Ag(0) and displaced from the parent structure. This reduction-displacement reaction in silver-containing bimetallic electrodes allows for the in situ formation of a conductive network, enhancing the electrochemical performance of the electrode and reducing or eliminating the need for conductive additives. A second discharge process occurs through the reduction of the second transition metal, V or Fe, where the oxidation state of the metal center is reduced and lithium cations are inserted into the structure. As both metal centers contribute to the functional capacity, determining the

  10. Synthesis of bimetallic Pt-Pd core-shell nanocrystals and their high electrocatalytic activity modulated by Pd shell thickness

    NASA Astrophysics Data System (ADS)

    Li, Yujing; Wang, Zhi Wei; Chiu, Chin-Yi; Ruan, Lingyan; Yang, Wenbing; Yang, Yang; Palmer, Richard E.; Huang, Yu

    2012-01-01

    Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more resistant to the CO poisoning than Pt NCs and Pt black. It is also demonstrated that the bimetallic Pt-Pd core-shell NCs can enhance the current density of the methanol oxidation reaction, lowering the over-potential by 35 mV with respect to the Pt core NCs. Further investigation reveals that the Pd/Pt ratio of 1/3, which corresponds to nearly monolayer Pd deposition on Pt core NCs, gives the highest oxidation current density and lowest over-potential. This study shows for the first time the systematic investigation of effects of Pd atomic shells on Pt-Pd bimetallic nanocatalysts, providing valuable guidelines for designing high-performance catalysts for fuel cell applications.Bimetallic Pt-Pd core-shell nanocrystals (NCs) are synthesized through a two-step process with controlled Pd thickness from sub-monolayer to multiple atomic layers. The oxygen reduction reaction (ORR) catalytic activity and methanol oxidation reactivity of the core-shell NCs for fuel cell applications in alkaline solution are systematically studied and compared based on different Pd thickness. It is found that the Pd shell helps to reduce the over-potential of ORR by up to 50mV when compared to commercial Pd black, while generating up to 3-fold higher kinetic current density. The carbon monoxide poisoning test shows that the bimetallic NCs are more

  11. Catalytically Active Bimetallic Nanoparticles Supported on Porous Carbon Capsules Derived From Metal-Organic Framework Composites.

    PubMed

    Yang, Hui; Bradley, Siobhan J; Chan, Andrew; Waterhouse, Geoffrey I N; Nann, Thomas; Kruger, Paul E; Telfer, Shane G

    2016-09-14

    We report a new methodology for producing monometallic or bimetallic nanoparticles confined within hollow nitrogen-doped porous carbon capsules. The capsules are derived from metal-organic framework (MOF) crystals that are coated with a shell of a secondary material comprising either a metal-tannic acid coordination polymer or a resorcinol-formaldehyde polymer. Platinum nanoparticles are optionally sandwiched between the MOF core and the shell. Pyrolysis of the MOF-shell composites produces hollow capsules of porous nitrogen-doped carbon that bear either monometallic (Pt, Co, and Ni) or alloyed (PtCo and PtNi) metal nanoparticles. The Co and Ni components of the bimetallic nanoparticles are derived from the shell surrounding the MOF crystals. The hollow capsules prevent sintering and detachment of the nanoparticles, and their porous walls allow for efficient mass transport. Alloyed PtCo nanoparticles embedded in the capsule walls are highly active, selective, and recyclable catalysts for the hydrogenation of nitroarenes to anilines. PMID:27575666

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

    SciTech Connect

    Zhu, Jing; Zheng, Xin; Wang, Jie; Wu, Zexing; Han, Lili; Lin, Ruoqian; Xin, Huolin L.; Wang, Deli

    2015-09-15

    Controlling the size, composition, and structure of bimetallic nanoparticles is of particular interest in the field of electrocatalysts for fuel cells. In the present work, structurally ordered nanoparticles with intermetallic phases of Pt3Zn and PtZn have been successfully synthesized via an impregnation reduction method, followed by post heat-treatment. The Pt3Zn and PtZn ordered intermetallic nanoparticles are well dispersed on a carbon support with ultrasmall mean particle sizes of ~5 nm and ~3 nm in diameter, respectively, which are credited to the evaporation of the zinc element at high temperature. These catalysts are less susceptible to CO poisoning relative to Pt/C and exhibited enhanced catalytic activity and stability toward formic acid electrooxidation. The mass activities of the as-prepared catalysts were approximately 2 to 3 times that of commercial Pt at 0.5 V (vs. RHE). As a result, this facile synthetic strategy is scalable for mass production of catalytic materials.

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

    DOE PAGES

    Zhu, Jing; Zheng, Xin; Wang, Jie; Wu, Zexing; Han, Lili; Lin, Ruoqian; Xin, Huolin L.; Wang, Deli

    2015-09-15

    Controlling the size, composition, and structure of bimetallic nanoparticles is of particular interest in the field of electrocatalysts for fuel cells. In the present work, structurally ordered nanoparticles with intermetallic phases of Pt3Zn and PtZn have been successfully synthesized via an impregnation reduction method, followed by post heat-treatment. The Pt3Zn and PtZn ordered intermetallic nanoparticles are well dispersed on a carbon support with ultrasmall mean particle sizes of ~5 nm and ~3 nm in diameter, respectively, which are credited to the evaporation of the zinc element at high temperature. These catalysts are less susceptible to CO poisoning relative to Pt/Cmore » and exhibited enhanced catalytic activity and stability toward formic acid electrooxidation. The mass activities of the as-prepared catalysts were approximately 2 to 3 times that of commercial Pt at 0.5 V (vs. RHE). As a result, this facile synthetic strategy is scalable for mass production of catalytic materials.« less

  14. Enhanced antibacterial activity of bimetallic gold-silver core-shell nanoparticles at low silver concentration

    NASA Astrophysics Data System (ADS)

    Banerjee, Madhuchanda; Sharma, Shilpa; Chattopadhyay, Arun; Ghosh, Siddhartha Sankar

    2011-12-01

    Herein we report the development of bimetallic Au@Ag core-shell nanoparticles (NPs) where gold nanoparticles (Au NPs) served as the seeds for continuous deposition of silver atoms on its surface. The core-shell structure and morphology were examined by UV-Vis spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD). The core-shell NPs showed antibacterial activity against both Gram negative (Escherichia coli and Pseudomonas aeruginosa) and Gram positive (Enterococcus faecalis and Pediococcus acidilactici) bacteria at low concentration of silver present in the shell, with more efficacy against Gram negative bacteria. TEM and flow cytometric studies showed that the core-shell NPs attached to the bacterial surface and caused membrane damage leading to cell death. The enhanced antibacterial properties of Au@Ag core-shell NPs was possibly due to the more active silver atoms in the shell surrounding gold core due to high surface free energy of the surface Ag atoms owing to shell thinness in the bimetallic NP structure.Herein we report the development of bimetallic Au@Ag core-shell nanoparticles (NPs) where gold nanoparticles (Au NPs) served as the seeds for continuous deposition of silver atoms on its surface. The core-shell structure and morphology were examined by UV-Vis spectroscopy, transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD). The core-shell NPs showed antibacterial activity against both Gram negative (Escherichia coli and Pseudomonas aeruginosa) and Gram positive (Enterococcus faecalis and Pediococcus acidilactici) bacteria at low concentration of silver present in the shell, with more efficacy against Gram negative bacteria. TEM and flow cytometric studies showed that the core-shell NPs attached to the bacterial surface and caused membrane damage leading to cell death. The enhanced antibacterial properties of Au@Ag core-shell NPs was

  15. Modeling the melting temperature of nanoscaled bimetallic alloys.

    PubMed

    Li, Ming; Zhu, Tian-Shu

    2016-06-22

    The effect of size, composition and dimension on the melting temperature of nanoscaled bimetallic alloys was investigated by considering the interatomic interaction. The established thermodynamics model without any arbitrarily adjustable parameters can be used to predict the melting temperature of nanoscaled bimetallic alloys. It is found that, the melting temperature and interatomic interaction of nanoscaled bimetallic alloys decrease with the decrease in size and the increasing composition of the lower surface energy metal. Moreover, for the nanoscaled bimetallic alloys with the same size and composition, the dependence of the melting temperature on the dimension can be sequenced as follows: nanoparticles > nanowires > thin films. The accuracy of the developed model is verified by the recent experimental and computer simulation results.

  16. Bimetallic Nanoshells for Metal - Enhanced Fluorescence with Broad Band Fluorophores.

    PubMed

    Zhang, Jian; Fu, Yi; Mahdavi, Farhad

    2012-11-15

    In this article, we reported the near-field interactions between the Ru(bpy)(3) (2+) complexes and plasmon resonances from the bimetallic nanoshells. The metallic nanoshells were fabricated on 20 nm silica spheres as cores by depositing 10 nm monometallic or bimetallic shells. There were approx. 15 Ru(bpy)(3) (2+) complexes in the silica core. The metal shells were constituted of silver or/and gold. The bimetallic shells could be generated in homogeneous or heterogeneous geometries. The homogeneous bimetallic shells contained 10 nm silver-gold alloys. The heterogeneous bimetallic shells contained successive 5 nm gold and 5 nm silver shells, or alternatively, 5 nm silver and 5 nm gold shells. Optical properties of metal nanoshells were studied on both the ensemble spectra and single nanoparticle imaging measurements. The heterogeneous bimetallic shells were found to have a large scale of metal-enhanced emission relative to the monometallic or homogeneous bimetallic shells. It is because the heterogeneous bimetallic shells may display split dual plasmon resonances which can interact with the excitation and emission bands of the Ru(bpy)(3) (2+) complexes in the silica cores leading to more efficient near-field interactions. The prediction can be demonstrated by the lifetimes. Therefore, it is suggested that both the compositions and geometries of the metal shells can influence the interactions with the fluorophores in the cores. This observation also offers us an opportunity for developing plasmon-based fluorescence metal nanoparticles as novel nanoparticle imaging agents which have high performances in fluorescence cell or tissue imaging. PMID:23230456

  17. On the synergistic catalytic properties of bimetallic mesoporous materials containing aluminum and zirconium: the Prins cyclisation of citronellal.

    PubMed

    Telalović, Selvedin; Ramanathan, Anand; Ng, Jeck Fei; Maheswari, Rajamanickam; Kwakernaak, Cees; Soulimani, Fouad; Brouwer, Hans C; Chuah, Gaik Khuan; Weckhuysen, Bert M; Hanefeld, Ulf

    2011-02-11

    Bimetallic three-dimensional amorphous mesoporous materials, Al-Zr-TUD-1 materials, were synthesised by using a surfactant-free, one-pot procedure employing triethanolamine (TEA) as a complexing reagent. The amount of aluminium and zirconium was varied in order to study the effect of these metals on the Brønsted and Lewis acidity, as well as on the resulting catalytic activity of the material. The materials were characterised by various techniques, including elemental analysis, X-ray diffraction, high-resolution TEM, N(2) physisorption, temperature-programmed desorption (TPD) of NH(3), and (27) Al MAS NMR, XPS and FT-IR spectroscopy using pyridine and CO as probe molecules. Al-Zr-TUD-1 materials are mesoporous with surface areas ranging from 700-900 m(2) g(-1), an average pore size of around 4 nm and a pore volume of around 0.70 cm(3) g(-1). The synthesised Al-Zr-TUD-1 materials were tested as catalyst materials in the Lewis acid catalysed Meerwein-Ponndorf-Verley reduction of 4-tert-butylcyclohexanone, the intermolecular Prins synthesis of nopol and in the intramolecular Prins cyclisation of citronellal. Although Al-Zr-TUD-1 catalysts possess a lower amount of acid sites than their monometallic counterparts, according to TPD of NH(3), these materials outperformed those of the monometallic Al-TUD-1 as well as Zr-TUD-1 in the Prins cyclisation of citronellal. This proves the existence of synergistic properties of Al-Zr-TUD-1. Due to the intramolecular nature of the Prins cyclisation of citronellal, the hydrophilic surface of the catalyst as well as the presence of both Brønsted and Lewis acid sites synergy could be obtained with bimetallic Al-Zr-TUD-1. Besides spectroscopic investigation of the active sites of the catalyst material a thorough testing of the catalyst in different types of reactions is crucial in identifying its specific active sites.

  18. Oxidation catalyst

    DOEpatents

    Ceyer, Sylvia T.; Lahr, David L.

    2010-11-09

    The present invention generally relates to catalyst systems and methods for oxidation of carbon monoxide. The invention involves catalyst compositions which may be advantageously altered by, for example, modification of the catalyst surface to enhance catalyst performance. Catalyst systems of the present invention may be capable of performing the oxidation of carbon monoxide at relatively lower temperatures (e.g., 200 K and below) and at relatively higher reaction rates than known catalysts. Additionally, catalyst systems disclosed herein may be substantially lower in cost than current commercial catalysts. Such catalyst systems may be useful in, for example, catalytic converters, fuel cells, sensors, and the like.

  19. Reaction pathways of model compounds of biomass-derived oxygenates on Fe/Ni bimetallic surfaces

    NASA Astrophysics Data System (ADS)

    Yu, Weiting; Chen, Jingguang G.

    2015-10-01

    Controlling the activity and selectivity of converting biomass-derivatives to fuels and valuable chemicals is critical for the utilization of biomass feedstocks. There are primarily three classes of non-food competing biomass, cellulose, hemicellulose and lignin. In the current work, glycolaldehyde, furfural and acetaldehyde are studied as model compounds of the three classes of biomass-derivatives. Monometallic Ni(111) and monolayer (ML) Fe/Ni(111) bimetallic surfaces are studied for the reaction pathways of the three biomass surrogates. The ML Fe/Ni(111) surface is identified as an efficient surface for the conversion of biomass-derivatives from the combined results of density functional theory (DFT) calculations and temperature programmed desorption (TPD) experiments. A correlation is also established between the optimized adsorption geometry and experimental reaction pathways. These results should provide helpful insights in catalyst design for the upgrading and conversion of biomass.

  20. Computational study of alkynes insertion into metal-hydride bonds catalyzed by bimetallic complexes.

    PubMed

    Di Tommaso, Stefania; Tognetti, Vincent; Sicilia, Emilia; Adamo, Carlo; Russo, Nino

    2010-11-01

    Density Functional Theory investigations on the insertion mechanism of phenylacetylene into metal-hydride bonds in bimetallic (Pt,Os) catalysts have been carried out. The results obtained have been also compared with the non-reactive monometallic (Os-based) system, to elucidate the cooperative effects and to explain the observed absence of reactivity. The identified reaction path involves phenylacetylene coordination followed by the insertion into the metal-hydride bond, leading to the formation of the experimentally observed products. Both steps do not require large energies compatible with the experimental conditions. The comparison with the reaction path for the monometallic species gives some hints on the cooperative effects due to the presence of the second metal which is related to its role in the CO release for creating a coordination site for phenylacetylene and not in the insertion energetics. The calculations provide a detailed analysis of the reaction complexity and provide a rationale for the efficiency of the process. PMID:20883042

  1. Bimetallic promotion of cooperative hydrogen transfer and heteroatom removal in coal liquefaction

    SciTech Connect

    Eisch, J.J.

    1991-10-01

    The ultimate objective of this research is to uncover new catalytic processes for the liquefaction of coal and for upgrading coal-derived fuels by removing undesirable organosulfur, organonitrogen and organooxygen constituents. Basic to both the liquefaction of coal and the purification of coal liquids is the transfer of hydrogen from such sources as dihydrogen, metal hydrides or partially reduced aromatic hydrocarbons to the extensive aromatic rings in coal itself or to aromatic sulfides, amines or ethers. Accordingly, this study is exploring how such crucial hydrogen-transfer processes might be catalyzed by soluble, low-valent transition metal complexes and/or Lewis acids under moderate conditions of temperature and pressure. By learning the mechanism whereby H{sub 2}, metal hydrides or partially hydrogenated aromatics do transfer hydrogen to model aromatic compounds, with the aid of homogeneous, bimetallic catalysts, we hope to identify new methods for producing superior fuels from coal.

  2. Supported Copper, Nickel and Copper-Nickel Nanoparticle Catalysts for Low Temperature Water-Gas-Shift Reaction

    NASA Astrophysics Data System (ADS)

    Lin, Jiann-Horng

    Hydrogen is being considered worldwide as a future replacement for gasoline, diesel fuel, natural gas in both the transportation and non-transportation sectors. Hydrogen is a versatile energy carrier that can be produced from a variety of widely available primary energy sources, including coal, natural gas, biomass, solar, wind, and nuclear power. Coal, the most abundant fossil fuel on the planet, is being looked at as the possible future major source of H2, due to the development of the integrated gasification combined cycle (IGCC) and integrated gasification fuel cell technologies (IGFC). The gasification of coal produces syngas consisting of predominately carbon monoxide and hydrogen with some remaining hydrocarbons, carbon dioxide and water. Then, the water-gas shift reaction is used to convert CO to CO2 and additional hydrogen. The present work describes the synthesis of model Cu, Ni and Cu-Ni catalysts prepared from metal colloids, and compares their behavior in the WGS reaction to that of traditional impregnation catalysts. Initially, we systematically explored the performance of traditional Cu, Ni and Cu-Ni WGS catalysts made by impregnation methods. Various bimetallic Cu-Ni catalysts were prepared by supported impregnation and compared to monometallic Cu and Ni catalysts. The presence of Cu in bimetallic catalysts suppressed undesirable methanation side reaction, while the Ni component was important for high WGS activity. Colloidal Cu, Ni and Cu-Ni alloy nanoparticles obtained by chemical reduction were deposited onto alumina to prepare supported catalysts. The resulting Cu and Ni nanoparticle catalysts were found to be 2.5 times more active in the WGS reaction per unit mass of active metal as compared to catalysts prepared by the conventional impregnation technique. The powder XRD and HAADF-STEM provided evidence supporting the formation of Cu-Ni particles containing the Cu core and Cu-Ni alloy shell. The XPS data indicated surface segregation of Cu in

  3. 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.

  4. Effect of surface oxidation of the support on the thiophene hydrodesulfurization activity of Mo, Ni, and NiMo catalysts supported on activated carbon

    SciTech Connect

    Calafat, A. |; Lopez-Agudo, A.; Palacios, J.M.

    1996-08-01

    The present investigation attempts to provide a better understanding of the influence of the nature of the carbon support on the HDS activity of Mo, Ni, and NiMo catalysts. For this purpose a high purity activated carbon was subjected to oxidative treatments with HNO{sub 3} to modify its surface properties. NiMo catalysts supported on the resulting activated carbons were prepared and characterized by TPR, XRD, and SEM-EDX, and their activity for HDS of thiophene at 30 bars and 375{degrees}C was evaluated. The results obtained showed that oxidation of the carbon surface does not affect the HDS activity and other characteristics of the supported Mo phase. In contrast, the HDS activity of the Ni catalysts is enhanced by acid treatments of the carbon support. In this case, introduction of oxygen-containing functional groups (O{sub (s)}) leads to a strong interaction of O{sub (s)}-Ni during impregnation, which becomes essential to achieving and preserving high nickel dispersion. This effect on NiMo/C catalysts. The synergistic effect of the bimetallic catalysts is observed only when oxygen functional groups are present on the carbon surface, which are necessary for a good HDS activity, mainly because they enhance Ni-Mo interactions that produce the highly active Ni-Mo-S phase. A NiMoO{sub 4}-like phase formed during impregnation seems to be the precursor for the active sulfide phase over the present NiMo/C catalysts. 34 refs., 6 figs., 5 tabs.

  5. Selective hydrogen production from formic acid decomposition on Pd-Au bimetallic surfaces.

    PubMed

    Yu, Wen-Yueh; Mullen, Gregory M; Flaherty, David W; Mullins, C Buddie

    2014-08-01

    Pd-Au catalysts have shown exceptional performance for selective hydrogen production via HCOOH decomposition, a promising alternative to solve issues associated with hydrogen storage and distribution. In this study, we utilized temperature-programmed desorption (TPD) and reactive molecular beam scattering (RMBS) in an attempt to unravel the factors governing the catalytic properties of Pd-Au bimetallic surfaces for HCOOH decomposition. Our results show that Pd atoms at the Pd-Au surface are responsible for activating HCOOH molecules; however, the selectivity of the reaction is dictated by the identity of the surface metal atoms adjacent to the Pd atoms. Pd atoms that reside at Pd-Au interface sites tend to favor dehydrogenation of HCOOH, whereas Pd atoms in Pd(111)-like sites, which lack neighboring Au atoms, favor dehydration of HCOOH. These observations suggest that the reactivity and selectivity of HCOOH decomposition on Pd-Au catalysts can be tailored by controlling the arrangement of surface Pd and Au atoms. The findings in this study may prove informative for rational design of Pd-Au catalysts for associated reactions including selective HCOOH decomposition for hydrogen production and electro-oxidation of HCOOH in the direct formic acid fuel cell.

  6. Shaped Ir-Ni bimetallic nanoparticles for minimizing Ir utilization in oxygen evolution reaction.

    PubMed

    Lim, Jinkyu; Yang, Sungeun; Kim, Chanyeon; Roh, Chi-Woo; Kwon, Yongwoo; Kim, Yong-Tae; Lee, Hyunjoo

    2016-04-25

    Shaped Ir-Ni bimetallic nanoparticles were synthesized and used for electrocatalytic oxygen evolution reaction (OER). The obtained bimetallic nanoparticles showed significantly enhanced Ir mass activity and durability compared with Ir nanoparticles. PMID:27034092

  7. Silver doped catalysts for treatment of exhaust

    DOEpatents

    Park, Paul Worn; Hester, Virgil Raymond; Ragle, Christie Susan; Boyer, Carrie L.

    2009-06-02

    A method of making an exhaust treatment element includes washcoating a substrate with a slurry that includes a catalyst support material. At least some of the catalyst support material from the slurry may be transferred to the substrate, and silver metal (Ag) is dispersed within the catalyst support material.

  8. Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters

    NASA Astrophysics Data System (ADS)

    Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki

    2016-08-01

    Understanding of the “structure-activity” relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au3+ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size.

  9. Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters.

    PubMed

    Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki

    2016-01-01

    Understanding of the "structure-activity" relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au(3+) ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size. PMID:27476577

  10. Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters

    PubMed Central

    Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki

    2016-01-01

    Understanding of the “structure-activity” relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au3+ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size. PMID:27476577

  11. A New Class of Highly Dispersed VOx Catalysts on Mesoporous Silica: Synthesis, Characterization, and Catalytic Activity in the Partial Oxidation of Ethanol

    SciTech Connect

    Kwak, Ja Hun; Herrera, Jose E.; Hu, Jian Zhi; Wang, Yong; Peden, Charles HF

    2006-01-26

    The morphology of vanadium oxide supported on a titania-modified mesoporous silica (MCM-41), obtained by means of a careful grafting process through atomic layer deposition, was studied using a variety of characterization techniques. The XRD together with TEM, 51V-NMR, Raman, FTIR and DRS-UV-Vis results showed that the vanadia species are extremely well dispersed onto the surface of the mesoporous support; the dispersion being stable upon thermal treatments up to 400 °C. Studies of the catalytic activity of these materials were performed using the partial oxidation of ethanol as a probe reaction. The results indicate an intrinsic relationship between dispersion, the presence of a TiO2-VOx phase, and catalytic activity for oxidation and dehydration.

  12. Photochemical synthesis of mono and bimetallic nanoparticles and their use in catalysis

    NASA Astrophysics Data System (ADS)

    Pardoe, Andrea

    2011-07-01

    Nanomaterials have become a popular topic of research over the years because of their many important applications. It can be a challenge to stabilize the particles at a nanometer size, while having control over their surface features. Copper nanoparticles were synthesized photochemically using a photogenerated radical allowing spatial and temporal control over their formation. The synthesis was affected by the stabilizers used, which changed the size, dispersity, rate of formation, and oxidation rate. Copper nanoparticles suffer from their fast oxidation in air, so copper-silver bimetallic nanoparticles were synthesized in attempts to overcome the oxidation of copper nanoparticles. Bimetallic nanoparticles were synthesized, but preventing the oxidation of the copper nanoparticles proved difficult. One important application of nanoparticles that was explored here is in catalyzing organic reactions. Because of the fast oxidation of copper nanoparticles, silver nanoparticles were synthesized photochemically on different supports including TiO2 and hydrotalcite (HTC). Their catalytic efficiency was tested using alcohol oxidations. Different silver nanoparticle shapes (decahedra and plates) were compared with the spheres to see the different catalytic efficiencies.

  13. Thermal stability of bimetallic Au/Fe nanoparticles in silica matrix

    SciTech Connect

    Pannu, Compesh Singh, Udai B. Hooda, Sonu Kabiraj, D. Avasthi, D. K.

    2014-04-24

    Thin silica film containing Au and Fe bimetallic nanoparticles were prepared by atom beam cosputtering. The samples were annealed at different temperatures from 400 to 800° C to study the thermal stability of bimetallic nanoparticles using X ray diffraction. It is observed that at 800° C strong structural rearrangement took place leading to thermal decomposition of bimetallic nanoparticles.

  14. Well-dispersed Co3O4/Co2MnO4 nanocomposites as a synergistic bifunctional catalyst for oxygen reduction and oxygen evolution reactions.

    PubMed

    Wang, Dengdeng; Chen, Xu; Evans, David G; Yang, Wensheng

    2013-06-21

    Co3O4/Co2MnO4 nanocomposites, derived from a single-source CoMn-layered double hydroxide precursor, exhibit excellent bifunctional oxygen electrode activities for both oxygen reduction and evolution reactions, which can be attributed to the large specific surface area and well-dispersed heterogeneous structure of the nanocomposites.

  15. Intercalation of aggregation-free and well-dispersed gold nanoparticles into the walls of mesoporous silica as a robust "green" catalyst for n-alkane oxidation.

    PubMed

    Chen, Lifang; Hu, Juncheng; Richards, Ryan

    2009-01-28

    Aggregate-free and well-dispersed gold nanoparticles were intercalated into the walls of mesoporous silica forming a nanoreactor demonstrating high catalytic activity for "green" alkane oxidation. The material is robust and can be recycled. The method may be developed to intercalate other metal or alloy nanoparticles into the walls of mesoporous silica.

  16. Catalytic activity of bimetallic nickel alloys for solid-oxide fuel cell anode reactions from density-functional theory

    NASA Astrophysics Data System (ADS)

    An, Wei; Gatewood, Daniel; Dunlap, Brett; Turner, C. Heath

    2011-05-01

    We present density-functional theory calculations of the chemisorption of atomic species O, S, C, H and reaction intermediates OH, SH, and CHn (n = 1, 2, and 3) on M/Ni alloy model catalysts (M = Bi, Mo, Fe, Co, and Cu). The activity of the Ni alloy catalysts for solid-oxide fuel cell (SOFC) anode oxidation reactions is predicted, based on a simple descriptor, i.e., the binding energy of oxygen. First, we find that the binding of undesirable intermediates, such as C and S, can be inhibited and the catalytic activity of planar Ni-based anodes can be tuned towards oxidation by selectively forming a bimetallic surface alloy. In particular, Cu/Ni, Fe/Ni, and Co/Ni anode catalysts are found to be most active towards anode oxidation. On the other hand, the Mo/Ni alloy surface is predicted to be the most effective catalyst in terms of inhibiting the deposition of C and S (while still preserving relatively high catalytic activity). The formation of a surface alloy, which has the alloy element enriched on the topmost surface, was found to be critical to the activity of the Ni alloy catalysts.

  17. Degradation of chlorofluorocarbons using granular iron and bimetallic irons.

    PubMed

    Jeen, Sung-Wook; Lazar, Snezana; Gui, Lai; Gillham, Robert W

    2014-03-01

    Degradation of trichlorofluoromethane (CFC11) and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC113) by granular iron and bimetallic (nickel- or palladium-enhanced) irons was studied in flow-through column tests. Both compounds were rapidly degraded, following pseudo-first-order kinetics with respect to the parent compounds. The average pseudo-first-order rate constants for CFC11 were similar among different materials, except for palladium-enhanced iron (PdFe), in which the rate of degradation was about two times faster than for the other materials. In the case of CFC113, the rate constants for bimetallic irons were about two to three times greater than for the regular iron material. The smaller than expected differences in degradation rate constants of chlorofluorocarbons (CFCs) between regular iron and bimetallic irons suggested little, if any, catalytic effect of the bimetallic materials in the initial degradation step. Subsequent degradation steps involved catalytic hydrogenation, however, playing a significant role in further degradation of reaction intermediates. The degradation intermediates and final products of CFC11 and CFC113 suggested that degradation proceeded through hydrogenolysis and α/β-elimination in the presence of regular iron (Fe) and nickel-enhanced iron (NiFe). Even though there is only minor benefit in the use of bimetallic iron in terms of degradation kinetics of the parent CFCs, enhanced degradation rates of intermediates such as chlorotriflouroethene (CTFE) in subsequent reaction steps could be beneficial. PMID:24492233

  18. Degradation of chlorofluorocarbons using granular iron and bimetallic irons.

    PubMed

    Jeen, Sung-Wook; Lazar, Snezana; Gui, Lai; Gillham, Robert W

    2014-03-01

    Degradation of trichlorofluoromethane (CFC11) and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC113) by granular iron and bimetallic (nickel- or palladium-enhanced) irons was studied in flow-through column tests. Both compounds were rapidly degraded, following pseudo-first-order kinetics with respect to the parent compounds. The average pseudo-first-order rate constants for CFC11 were similar among different materials, except for palladium-enhanced iron (PdFe), in which the rate of degradation was about two times faster than for the other materials. In the case of CFC113, the rate constants for bimetallic irons were about two to three times greater than for the regular iron material. The smaller than expected differences in degradation rate constants of chlorofluorocarbons (CFCs) between regular iron and bimetallic irons suggested little, if any, catalytic effect of the bimetallic materials in the initial degradation step. Subsequent degradation steps involved catalytic hydrogenation, however, playing a significant role in further degradation of reaction intermediates. The degradation intermediates and final products of CFC11 and CFC113 suggested that degradation proceeded through hydrogenolysis and α/β-elimination in the presence of regular iron (Fe) and nickel-enhanced iron (NiFe). Even though there is only minor benefit in the use of bimetallic iron in terms of degradation kinetics of the parent CFCs, enhanced degradation rates of intermediates such as chlorotriflouroethene (CTFE) in subsequent reaction steps could be beneficial.

  19. Bimetallic strip for low temperature use

    DOEpatents

    Bussiere, Jean F.; Welch, David O.; Suenaga, Masaki

    1981-01-01

    There is provided a class of mechanically pre-stressed structures, suitably bi-layer strips comprising a layer of group 5 transition metals in intimate contact with a layer of an intermetallic compound of said transition metals with certain group 3A, 4A or 5A metals or metalloids suitably gallium, indium, silicon, germanium, tin, arsenic or antimony. The changes of Young's modulus of these bi-layered combinations at temperatures in the region of but somewhat above absolute zero provides a useful means of sensing temperature changes. Such bi-metallic strips may be used as control strips in thermostats, in direct dial reading instruments, or the like. The structures are made by preparing a sandwich of a group 5B transition metal strip between the substantially thicker strips of an alloy between copper and a predetermined group 3A, 4A or 5A metal or metalloid, holding the three layers of the sandwich in intimate contact heating the same, cooling the same and removing the copper alloy and then removing one of the two thus formed interlayer alloys between said transition metal and the metal previously alloyed with copper.

  20. Investigating the Dispersion Behavior in Solvents, Biocompatibility, and Use as Support for Highly Efficient Metal Catalysts of Exfoliated Graphitic Carbon Nitride.

    PubMed

    Ayán-Varela, M; Villar-Rodil, S; Paredes, J I; Munuera, J M; Pagán, A; Lozano-Pérez, A A; Cenis, J L; Martínez-Alonso, A; Tascón, J M D

    2015-11-01

    The liquid-phase exfoliation of graphitic carbon nitride (g-C3N4) to afford colloidal dispersions of two-dimensional flakes constitutes an attractive route to facilitate the processing and implementation of this novel material toward different technological applications, but quantitative knowledge about its dispersibility in solvents is lacking. Here, we investigate the dispersion behavior of exfoliated g-C3N4 in a wide range of solvents and evaluate the obtained results on the basis of solvent surface energy and Hildebrand/Hansen solubility parameters. Estimates of the three Hansen parameters for exfoliated g-C3N4 from the experimentally derived data yielded δD ≈ 17.8 MPa(1/2), δP ≈ 10.8 MPa(1/2), and δH ≈ 15.4 MPa(1/2). The relatively high δH value suggested that, contrary to the case of other two-dimensional materials (e.g., graphene or transition metal dichalcogenides), hydrogen-bonding plays a substantial role in the efficient interaction, and thus dispersibility, of exfoliated g-C3N4 with solvents. Such an outcome was attributed to a high density of primary and/or secondary amines in the material, the presence of which was associated with incomplete condensation of the structure. Furthermore, cell proliferation tests carried out on thin films of exfoliated g-C3N4 using murine fibroblasts suggested that this material is highly biocompatible and noncytotoxic. Finally, the exfoliated g-C3N4 flakes were used as supports in the synthesis of Pd nanoparticles, and the resulting hybrids exhibited an exceptional catalytic activity in the reduction of nitroarenes.

  1. Structural characteristics and reactivity/reducibility properties of dispersed and bilayered V{sub 2}O{sub 5}/TiO{sub 2}/SiO{sub 2} catalysts

    SciTech Connect

    Gao, X.; Wachs, I.E.; Bare, S.R.; Fierro, J.L.G.

    1999-01-28

    Dispersed and bilayered V{sub 2}O{sub 5}/TiO{sub 2}/SiO{sub 2} catalysts were successfully synthesized by the incipient wetness impregnation method, and their surface structures under various conditions were extensively investigated by combined in situ Raman, UV-vis-NIR diffuse reflectance and X-ray absorption near-edge spectroscopies, as well as X-ray photoelectron spectroscopy. Temperature-programmed reduction and methanol oxidation were employed as chemical probe reactions to examine the reducibility and reactivity/selectivity of these catalysts. The spectroscopic results revealed that both vanadium oxide and titanium oxide on SiO{sub 2} are dispersed as two-dimensional metal oxide overlayers. The surface vanadium oxide species on the dispersed TiO{sub 2}/SiO{sub 2} are predominantly isolated VO{sub 4} units [O{double_bond}V(O-support){sub 3}] in the dehydrated state and become polymerized VO{sub 5}/VO{sub 6} units upon hydration. The surface vanadium oxide species preferentially interact with the surface titanium oxide species on silica, and the V(V) cations possess oxygenated ligands of Si(IV){single_bond}O{sup {minus}} and Ti(IV){single_bond}O{sup {minus}} in the O{double_bond}V(O-support){sub 3} unit with varying ratios from 3:0 to 0:3, which depends on the vanadia and titania loadings. The varying ratio of the Si(IV){single_bond}O{sup {minus}} and Ti(IV){single_bond}O{sup {minus}} oxygenated ligands significantly affects the chemical properties of the isolated VO{sub 4} units. Consequently, the reducibility of the surface vanadium oxide species is altered and the reduction occurs over a wider temperature range. In addition, the methanol oxidation turn-over frequency of the surface VO{sub 4} species on TiO{sub 2}/SiO{sub 2} increases an order of magnitude relative to V{sub 2}O{sub 5}/SiO{sub 2}. Thus, the oxygenated ligands around the V cations play a critical role in determining the reactivity of the surface vanadium oxide species on the oxide supports.

  2. Development of bi-metallic Fe-Bi nanocomposites: synthesis and characterization.

    PubMed

    Mattei, J G; Pelletier, F; Ciuculescu, D; Lecante, P; Amiens, C; Casanove, M J

    2012-11-01

    We investigate the formation of bi-metallic particles in the Fe-Bi system, well known as totally immiscible in the bulk, using a large combination of structural and element-sensitive techniques, well-adapted to the nanoscale. The synthesis approach makes use of the kinetics of decomposition of the different precursors to achieve a controlled sequential growth of the different elements. Different ligands have also been used in order to limit the size and ensure dispersion of the synthesized particles. Our results give evidence for the presence of body-centered cubic ferromagnetic iron nanograins together with larger bismuth crystallites. Interestingly, while the iron particles remain very small, the resistance to oxidation of the Fe-Bi nanocomposites highly depends on the stabilizing ligand used in the synthesis. The presence of both metals, Fe and Bi, in a single cluster has been clearly revealed in the oxidation resistant composite synthesized using the HMDS ligand.

  3. Millimeter thick ionic polymer membrane-based IPMCs with bimetallic Pd-Pt electrodes

    NASA Astrophysics Data System (ADS)

    Palmre, Viljar; Kim, Sung Jun; Kim, Kwang

    2011-04-01

    Ionic polymer metal composites (IPMC) are a low-voltage driven Electroactive Polymers (EAP) that can be used as actuators or sensors. This paper presents a comparative study of millimeter thick ionic polymer membrane-based IPMCs with high-performance Pd-Pt electrodes and conventional Pt electrodes. IPMCs assembled with different electrodes are characterized in terms of electromechanical, -chemical and mechanolelectrical properties. The SEM and energy dispersive X-ray (EDS) analysis are used to investigate the distribution of deposited electrode metals in the cross-section of Pd-Pt IPMCs. The study shows that IPMCs assembled with millimeter thick ionic polymer membranes and bimetallic Pd-Pt electrodes are superior in mechanoelectrical sensing and, also, show considerably higher blocking forces compared to the conventional type of IPMCs. Blocking forces more than 30 grams are measured under 4V DC. However, the actuation response is slower than conventional IPMCs having approximately 0.2-0.3 mm thickness.

  4. Numerical Simulation of the Proton Spin-Lattice Relaxation in Bimetallic Chain Compounds

    NASA Astrophysics Data System (ADS)

    Yamamoto, S.

    In response to recent proton spin relaxation-time measurements on a bimetallic chain compound NiCu(C7H6N2O6) (H2O)3\\cdot2H2O, we simulate the Raman relaxation process in Heisenberg alternating-spin chains on the assumption of predominantly dipolar hyperfine interactions between protons and magnetic ions. The relaxation time T1 is formulated within the spin-wave theory and is estimated as a function of temperature and an applied field H by a quantum Monte Carlo method. The low-temperature behavior of the relaxation rate T1-1 qualitatively varies with (S,s), while T1-1 is almost proportional to H-1/2 due to the characteristic dispersion relations.

  5. New catalysts for coal processing: metal carbides and nitrides. Semiannual report, November 1, 1995 - July 17, 1996

    SciTech Connect

    Oyama, S. T.; Cox, D. F.

    1996-04-01

    Work involving the synthesis of monometallic transition metal carbides supported on alumina is described. The catalysts have excellent initial activity in the hydrodechlorination of CCl{sub 2}F{sub 2} (CFC 12), but deactivate with time by the deposition of carbon. Initial work on the preparation of unsupported bimetallic oxynitrides is also described.

  6. Carbon-protected bimetallic carbide nanoparticles for a highly efficient alkaline hydrogen evolution reaction.

    PubMed

    Liu, Yipu; Li, Guo-Dong; Yuan, Long; Ge, Lei; Ding, Hong; Wang, Dejun; Zou, Xiaoxin

    2015-02-21

    The hydrogen evolution reaction (HER) is one of the two important half reactions in current water-alkali and chlor-alkali electrolyzers. To make this reaction energy-efficient, development of highly active and durable catalytic materials in an alkaline environment is required. Herein we report the synthesis of carbon-coated cobalt-tungsten carbide nanoparticles that have proven to be efficient noble metal-free electrocatalysts for alkaline HER. The catalyst affords a current density of 10 mA cm(-2) at a low overpotential of 73 mV, which is close to that (33 mV) required by Pt/C to obtain the same current density. In addition, this catalyst operates stably at large current densities (>30 mA cm(-1)) for as long as 18 h, and gives nearly 100% Faradaic yield during alkaline HER. The excellent catalytic performance (activity and stability) of this nanocomposite material is attributed to the cooperative effect between nanosized bimetallic carbide and the carbon protection layer outside the metal carbide. The results presented herein offer the exciting possibility of using carbon-armoured metal carbides for an efficient alkaline HER, although pristine metal carbides are not, generally, chemically stable enough under such strong alkaline conditions.

  7. Synthesis of Pt-Pd bimetallic nanoparticles anchored on graphene for highly active methanol electro-oxidation

    NASA Astrophysics Data System (ADS)

    Zhang, Yuting; Chang, Gang; Shu, Honghui; Oyama, Munetaka; Liu, Xiong; He, Yunbin

    2014-09-01

    A simple, one-step reduction route was employed to synthesize bimetallic Pt-Pd nanoparticles (Pt-PdNPs) supported on graphene (G) sheets, in which the reduction of graphite oxide and metal precursor was carried out simultaneously using ascorbic acid as a soft reductant. The morphology and structure of Pt-PdNPs/G composites were characterized using X-ray diffraction, Transmission Electron Microscopy, Field Emission Scanning Electron Microscopy and X-ray Photoelectron Spectroscopy analysis. The results show that Pt-Pd bimetallic nanoparticles were successfully synthesized and evenly anchored on the graphene sheets. Electrochemical experiments, including cyclic voltammetry and chronoamperometric measurements, were performed to investigate the electrochemical and electrocatalytic properties of the Pt-PdNPs/G composites. It was found that Pt-PdNPs/G composites show better electrocatalytic activity and stability towards the electro-oxidation of methanol than its counterparts such as composites composed of graphene-supported monometallic nanoparticles (PtNPs/G, PdNPs/G) and free-standing (Pt-PdNPs) and Vulcan-supported bimetallic Pt-Pd nanoparticles (Pt-PdNPs/V). The results could be attributed to the synergetic effects of the Pt-Pd nanoparticles and the enhanced electron transfer of graphene. The electrocatalytic activity of Pt-PdNPs/G changed with the Pd content in the Pt-Pd alloy, and the best performance was achieved with a Pt-Pd ratio of 1/3 in an alkaline environment. Our study indicates the potential use of Pt-PdNPs/G as new anode catalyst materials for direct methanol fuel cells.

  8. Advanced liquefaction using coal swelling and catalyst dispersion techniques. Volume 2, appendices. Final technical report, October 1, 1991--September 30, 1994

    SciTech Connect

    Curtis, C.W.; Chander, S.; Gutterman, C.

    1995-04-01

    Liquefaction experiments were undertaken using subbituminous Black Thunder mine coal to observe the effects of aqueous SO{sub 2} coal beneficiation and the introduction of various coal swelling solvents and catalyst precursors. Aqueous SO{sub 2} beneficiation of Black Thunder coal removed alkali metals and alkaline earth metals, increased the sulfur content and increased the catalytic liquefaction conversion to THF solubles compared to untreated Black Thunder coal. The liquefaction solvent had varying effects on coal conversion, depending upon the type of solvent added. The hydrogen donor solvent, dihydroanthracene, was most effective, while a coal-derived Wilsonville solvent promoted more coal conversion than did relatively inert 1-methylnaphthalene. Swelling of coal with hydrogen bonding solvents tetrahydrofuran (THF), isopropanol, and methanol, prior to reaction resulted in increased noncatalytic conversion of both untreated and SO{sub 2} treated Black Thunder coals, while dimethylsulfoxide (DMSO), which was absorbed more into the coal than any other swelling solvent, was detrimental to coal conversion. Swelling of SO{sub 2} treated coal before liquefaction resulted in the highest coal conversions; however, the untreated coal showed the most improvements in catalytic reactions when swelled in either THF, isopropanol, or methanol prior to liquefaction. The aprotic solvent DMSO was detrimental to coal conversion.

  9. TOPICAL REVIEW: Nanostructured catalysts in fuel cells

    NASA Astrophysics Data System (ADS)

    Zhong, Chuan-Jian; Luo, Jin; Fang, Bin; Wanjala, Bridgid N.; Njoki, Peter N.; Loukrakpam, Rameshwori; Yin, Jun

    2010-02-01

    One of the most important challenges for the ultimate commercialization of fuel cells is the preparation of active, robust, and low-cost catalysts. This review highlights some findings of our investigations in the last few years in developing advanced approaches to nanostructured catalysts that address this challenge. Emphasis is placed on nanoengineering-based fabrication, processing, and characterization of multimetallic nanoparticles with controllable size (1-10 nm), shape, composition (e.g. MlnM2100-n, M1nM2mM3100-n-m, M1@M2, where M (1 or 2) = Pt, Co, Ni, V, Fe, Cu, Pd, W, Ag, Au etc) and morphology (e.g. alloy, core@shell etc). In addition to an overview of the fundamental issues and the recent progress in fuel cell catalysts, results from evaluations of the electrocatalytic performance of nanoengineered catalysts in fuel cell reactions are discussed. This approach differs from other traditional approaches to the preparation of supported catalysts in the ability to control the particle size, composition, phase, and surface properties. An understanding of how the nanoscale properties of the multimetallic nanoparticles differ from their bulk-scale counterparts, and how the interaction between the nanoparticles and the support materials relates to the size sintering or evolution in the thermal activation process, is also discussed. The fact that the bimetallic gold-platinum nanoparticle system displays a single-phase character different from the miscibility gap known for its bulk-scale counterpart serves as an important indication of the nanoscale manipulation of the structural properties, which is useful for refining the design and preparation of the bimetallic catalysts. The insight gained from probing how nanoparticle-nanoparticle and nanoparticle-substrate interactions relate to the size evolution in the activation process of nanoparticles on planar substrates serves as an important guiding principle in the control of nanoparticle sintering on different

  10. Lattice-matched bimetallic CuPd-graphene nanocatalysts for facile conversion of biomass-derived polyols to chemicals.

    PubMed

    Jin, Xin; Dang, Lianna; Lohrman, Jessica; Subramaniam, Bala; Ren, Shenqiang; Chaudhari, Raghunath V

    2013-02-26

    A bimetallic nanocatalyst with unique surface configuration displays extraordinary performance for converting biomass-derived polyols to chemicals, with potentially much broader applications in the design of novel catalysts for several reactions of industrial relevance. The synthesis of nanostructured metal catalysts containing a large population of active surface facets is critical to achieve high activity and selectivity in catalytic reactions. Here, we describe a new strategy for synthesizing copper-based nanocatalysts on reduced graphene oxide support in which the catalytically active {111} facet is achieved as the dominant surface by lattice-match engineering. This method yields highly active Cu-graphene catalysts (turnover frequency = 33-114 mol/g atom Cu/h) for converting biopolyols (glycerol, xylitol, and sorbitol) to value-added chemicals, such as lactic acid and other useful co-products consisting of diols and linear alcohols. Palladium incorporation in the Cu-graphene system in trace amounts results in a tandem synergistic system in which the hydrogen generated in situ from polyols is used for sequential hydrogenolysis of the feedstock itself. Furthermore, the Pd addition remarkably enhances the overall stability of the nanocatalysts. The insights gained from this synthetic methodology open new vistas for exploiting graphene-based supports to develop novel and improved metal-based catalysts for a variety of heterogeneous catalytic reactions. PMID:23297693

  11. Preparation and characterization of nickel based multicomponent catalysts

    NASA Astrophysics Data System (ADS)

    Lazar, Mihaela; Mihet, Maria; Dan, Monica; Almasan, Valer; Marginean, Petru

    2009-08-01

    Two series of modified alumina supported nickel catalysts were prepared and characterized. First series consist in bimetallic Ni-Au and Ni-Ag catalysts supported on alumina; the second series consist in Ni catalysts supported on bicomponent oxides. The catalysts were prepared by impregnation: Ni/Al2O3, Ni/CeO2-Al2O3 and Ni/La2O3-Al2O3 (10 wt% Ni and 6 wt% additional oxide) and co-impregnation: Ni-Au/Al2O3 and Ni-Ag/Al2O3 (10 wt% Ni and 1 wt% Au or Ag). The catalytic surface was characterized by N2 adsorption-desorption isotherms. The catalytic sites were characterized by hydrogen Thermo Programmed Desorption (TPD) method.

  12. Effect of temperature for synthesizing single-walled carbon nanotubes by catalytic chemical vapor deposition over Mo-Co-MgO catalyst

    SciTech Connect

    Niu Zhiqiang; Fang Yan

    2008-06-03

    The influence of temperature on synthesizing single-walled carbon nanotubes (SWCNTs) by catalytic chemical vapor deposition of methane over Mo-Co-MgO catalyst was studied by Transmission Electron Microscope (TEM) and Raman scattering. The Mo-Co-MgO bimetallic catalyst was prepared by decomposing the mixture of magnesium nitrate, ammonium molybdate, citric acid, and cobalt nitrate. The results show that Mo-Co-MgO bimetallic catalyst is effective to synthesize SWCNTs. By using Mo-Co-MgO bimetallic catalyst, generation of SWCNTs even at 940 K was demonstrated. The optimum temperature of synthesizing SWCNTs over Mo-Co-MgO bimetallic catalyst may be about 1123 K. At 1123 K, the diameters of SWCNTs are in the range of 0.75-1.65 nm. The content of SWCNTs is increased with the increase of temperature below 1123 K and the carbon yield rate is also increased with the increase of synthesis temperature. Therefore, the amount of SWCNTs increases with the increase of temperature below 1123 K. However, above 1123 K, the content of SWCNTs is decreased with the increase of temperature; therefore, it is not effective to increase the amount of SWCNTs through increasing synthesis temperature above 1123 K.

  13. Bimetallic alloy electrocatalysts with multilayered platinum-skin surfaces

    DOEpatents

    Stamenkovic, Vojislav R.; Wang, Chao; Markovic, Nenad M.

    2016-01-26

    Compositions and methods of preparing a bimetallic alloy having enhanced electrocatalytic properties are provided. The composition comprises a PtNi substrate having a surface layer, a near-surface layer, and an inner layer, where the surface layer comprises a nickel-depleted composition, such that the surface layer comprises a platinum skin having at least one atomic layer of platinum.

  14. Self-discharge in bimetallic cells containing alkali metal

    NASA Technical Reports Server (NTRS)

    Foster, M. S.; Hesson, J. C.; Shimotake, H.

    1969-01-01

    Theoretical analysis of thermally regenerative bimetallic cells with alkali metal anodes shows a relation between the current drawn and the rate of discharge under open-circuit conditions. The self-discharge rate of the cell is due to the dissolution and ionization of alkali metal atoms in the fused-salt electrolyte

  15. Spectroscopic Elucidation of First Steps of Supported Bimetallic Cluster Formation

    SciTech Connect

    Kulkarni, A.; Gates, B.C.

    2009-12-23

    Initial steps of bimetallic Ru-Os cluster formation on MgO in the presence of H{sub 2} are analyzed by EXAFS and IR spectroscopy. Ru-Os bond formation takes place after decarbonylation of Ru{sub 3} clusters and subsequently, at higher temperatures, of Os{sub 3} clusters to generate coordinative unsaturation.

  16. Lithium-tellurium bimetallic cell has increased voltage

    NASA Technical Reports Server (NTRS)

    Cairns, E. J.; Rogers, G. L.; Shimotake, H.

    1968-01-01

    Lithium-tellurium secondary cell with a fused lithium halide electrolyte, tested in the temperature range 467 degrees to 500 degrees C, showed improvement over the sodium bismuth cell. The voltage of this bimetallic cell was increased by using the more electropositive anode material, lithium, and the more electronegative cathode material, tellurium.

  17. Single Cobalt Atoms with Precise N-Coordination as Superior Oxygen Reduction Reaction Catalysts.

    PubMed

    Yin, Peiqun; Yao, Tao; Wu, Yuen; Zheng, Lirong; Lin, Yue; Liu, Wei; Ju, Huanxin; Zhu, Junfa; Hong, Xun; Deng, Zhaoxiang; Zhou, Gang; Wei, Shiqiang; Li, Yadong

    2016-08-26

    A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal-organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-Nx single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials. PMID:27491018

  18. Pillared-clay catalysts containing mixed-metal complexes I. Preparation and characterization

    SciTech Connect

    Lee, W.Y.; Tatarchuk, B.J. ); Raythatha, R.H. )

    1989-01-01

    High-surface-area pillared clays were prepared from naturally occurring montmorillonites by exchanging interlayer ions with polyoxocations containing (i) iron, (ii) aluminum, (iii) discrete mixtures of (i) and (ii), or (iv) iron and aluminum located within the same complex. The valence state, solid-state properties, and stability of these pillars were determined following reduction and oxidation using Moessbauer spectroscopy, X-ray diffraction, and BET surface area measurements. Controlled atmosphere electron microscopy and transmission electron microscopy were also used to follow the nucleation and sintering behavior of the pillars during reduction. Moessbauer data suggested interlayer formation of metallic iron domains following reduction of types (i) and (iii) pillared systems. The magnetic properties and the oxidation behavior deduced from Moessbauer analysis and the complementary insights provided by XRD strongly indicated that these crystallites were in the form of thin-film/pancake-shape islands most likely conforming to the geometry of the interlayer region. The expanded structures of types (ii) and (iii) pillared systems were found to be relatively stable following reduction up to 723 K due to the irreducible nature of discrete aluminum pillars under these conditions. Intercalation of clays with mixtures of chemically distinct pillars appears to provide a unique method for preparing highly dispersed metallic or even bimetallic catalysts possessing two-dimensional sieve-like behavior with high overall surface areas and high loadings of the active metal.

  19. Single Cobalt Atoms with Precise N-Coordination as Superior Oxygen Reduction Reaction Catalysts.

    PubMed

    Yin, Peiqun; Yao, Tao; Wu, Yuen; Zheng, Lirong; Lin, Yue; Liu, Wei; Ju, Huanxin; Zhu, Junfa; Hong, Xun; Deng, Zhaoxiang; Zhou, Gang; Wei, Shiqiang; Li, Yadong

    2016-08-26

    A new strategy for achieving stable Co single atoms (SAs) on nitrogen-doped porous carbon with high metal loading over 4 wt % is reported. The strategy is based on a pyrolysis process of predesigned bimetallic Zn/Co metal-organic frameworks, during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800 °C. The spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements both confirm the atomic dispersion of Co atoms stabilized by as-generated N-doped porous carbon. Surprisingly, the obtained Co-Nx single sites exhibit superior ORR performance with a half-wave potential (0.881 V) that is more positive than commercial Pt/C (0.811 V) and most reported non-precious metal catalysts. Durability tests revealed that the Co single atoms exhibit outstanding chemical stability during electrocatalysis and thermal stability that resists sintering at 900 °C. Our findings open up a new routine for general and practical synthesis of a variety of materials bearing single atoms, which could facilitate new discoveries at the atomic scale in condensed materials.

  20. Three-Dimensional Graphene Supported Bimetallic Nanocomposites with DNA Regulated-Flexibly Switchable Peroxidase-Like Activity.

    PubMed

    Yuan, Fang; Zhao, Huimin; Zang, Hongmei; Ye, Fei; Quan, Xie

    2016-04-20

    A synergistic bimetallic enzyme mimetic catalyst, three-dimensional (3D) graphene/Fe3O4-AuNPs, was successfully fabricated which exhibited flexibly switchable peroxidase-like activity. Compared to the traditional 2D graphene-based monometallic composite, the introduced 3D structure, which was induced by the addition of glutamic acid, and bimetallic anchoring approach dramatically improved the catalytic activity, as well as the catalysis velocity and its affinity for substrate. Herein, Fe3O4NPs acted as supporters for AuNPs, which contributed to enhance the efficiency of electron transfer. On the basis of the measurement of Mott-Schottky plots of graphene and metal anchored hybrids, the catalysis mechanism was elucidated by the decrease of Fermi level resulted from the chemical doping behavior. Notably, the catalytic activity was able to be regulated by the adsorption and desorption of single-stranded DNA molecules, which laid a basis for its utilization in the construction of single-stranded DNA-based colorimetric biosensors. This strategy not only simplified the operation process including labeling, modification, and imprinting, but also protected the intrinsic affinity between the target and biological probe. Accordingly, based on the peroxidase-like activity and its controllability, our prepared nanohybrids was successfully adopted in the visualized and label-free sensing detections of glucose, sequence-specific DNA, mismatched nucleotides, and oxytetracycline. PMID:27018504

  1. HDS catalysts performance and properties

    SciTech Connect

    Panarello, F.; Guanziroli, S.

    1995-12-31

    The European refiners are being asked to produce cleaner diesel fuel which might reduce engine emissions. To meet this requirement they have to increase the hydrotreatment capacity and to use the best catalysts in terms of activity and deactivation performances. In particular, Co-Mo on gamma-alumina catalysts are currently in use to reduce diesel sulfur content. In the past, different chemical-physical modifications have been studied in order to improve the catalysts performances, many theoretical correlations between one or more chemical-physical properties and activity have been suggested. We tested different Co-Mo catalysts in pilot plant units with various refinery streams and run length up to two thousand hours. We performed on fresh, exhausted and regenerated catalysts samples, elemental composition, surface properties, metal dispersion and metal distribution analyses. Among the various chemical-physical properties the metal distribution is the parameter that correlates in the most satisfactory way with the catalytic performances.

  2. Novel platinum-palladium bimetallic nanoparticles synthesized by Dioscorea bulbifera: anticancer and antioxidant activities.

    PubMed

    Ghosh, Sougata; Nitnavare, Rahul; Dewle, Ankush; Tomar, Geetanjali B; Chippalkatti, Rohan; More, Piyush; Kitture, Rohini; Kale, Sangeeta; Bellare, Jayesh; Chopade, Balu A

    2015-01-01

    Medicinal plants serve as rich sources of diverse bioactive phytochemicals that might even take part in bioreduction and stabilization of phytogenic nanoparticles with immense therapeutic properties. Herein, we report for the first time the rapid efficient synthesis of novel platinum-palladium bimetallic nanoparticles (Pt-PdNPs) along with individual platinum (PtNPs) and palladium (PdNPs) nanoparticles using a medicinal plant, Dioscorea bulbifera tuber extract (DBTE). High-resolution transmission electron microscopy revealed monodispersed PtNPs of size 2-5 nm, while PdNPs and Pt-PdNPs between 10 and 25 nm. Energy dispersive spectroscopy analysis confirmed 30.88% ± 1.73% elemental Pt and 68.96% ± 1.48% elemental Pd in the bimetallic nanoparticles. Fourier transform infrared spectra indicated strong peaks at 3,373 cm(-1), attributed to hydroxyl group of polyphenolic compounds in DBTE that might play a key role in bioreduction in addition to the sharp peaks at 2,937, 1,647, 1,518, and 1,024 cm(-1), associated with C-H stretching, N-H bending in primary amines, N-O stretching in nitro group, and C-C stretch, respectively. Anticancer activity against HeLa cells showed that Pt-PdNPs exhibited more pronounced cell death of 74.25% compared to individual PtNPs (12.6%) or PdNPs (33.15%). Further, Pt-PdNPs showed an enhanced scavenging activity against 2,2-diphenyl-1-picrylhydrazyl, superoxide, nitric oxide, and hydroxyl radicals.

  3. Novel platinum-palladium bimetallic nanoparticles synthesized by Dioscorea bulbifera: anticancer and antioxidant activities.

    PubMed

    Ghosh, Sougata; Nitnavare, Rahul; Dewle, Ankush; Tomar, Geetanjali B; Chippalkatti, Rohan; More, Piyush; Kitture, Rohini; Kale, Sangeeta; Bellare, Jayesh; Chopade, Balu A

    2015-01-01

    Medicinal plants serve as rich sources of diverse bioactive phytochemicals that might even take part in bioreduction and stabilization of phytogenic nanoparticles with immense therapeutic properties. Herein, we report for the first time the rapid efficient synthesis of novel platinum-palladium bimetallic nanoparticles (Pt-PdNPs) along with individual platinum (PtNPs) and palladium (PdNPs) nanoparticles using a medicinal plant, Dioscorea bulbifera tuber extract (DBTE). High-resolution transmission electron microscopy revealed monodispersed PtNPs of size 2-5 nm, while PdNPs and Pt-PdNPs between 10 and 25 nm. Energy dispersive spectroscopy analysis confirmed 30.88% ± 1.73% elemental Pt and 68.96% ± 1.48% elemental Pd in the bimetallic nanoparticles. Fourier transform infrared spectra indicated strong peaks at 3,373 cm(-1), attributed to hydroxyl group of polyphenolic compounds in DBTE that might play a key role in bioreduction in addition to the sharp peaks at 2,937, 1,647, 1,518, and 1,024 cm(-1), associated with C-H stretching, N-H bending in primary amines, N-O stretching in nitro group, and C-C stretch, respectively. Anticancer activity against HeLa cells showed that Pt-PdNPs exhibited more pronounced cell death of 74.25% compared to individual PtNPs (12.6%) or PdNPs (33.15%). Further, Pt-PdNPs showed an enhanced scavenging activity against 2,2-diphenyl-1-picrylhydrazyl, superoxide, nitric oxide, and hydroxyl radicals. PMID:26719690

  4. Novel platinum–palladium bimetallic nanoparticles synthesized by Dioscorea bulbifera: anticancer and antioxidant activities

    PubMed Central

    Ghosh, Sougata; Nitnavare, Rahul; Dewle, Ankush; Tomar, Geetanjali B; Chippalkatti, Rohan; More, Piyush; Kitture, Rohini; Kale, Sangeeta; Bellare, Jayesh; Chopade, Balu A

    2015-01-01

    Medicinal plants serve as rich sources of diverse bioactive phytochemicals that might even take part in bioreduction and stabilization of phytogenic nanoparticles with immense therapeutic properties. Herein, we report for the first time the rapid efficient synthesis of novel platinum–palladium bimetallic nanoparticles (Pt–PdNPs) along with individual platinum (PtNPs) and palladium (PdNPs) nanoparticles using a medicinal plant, Dioscorea bulbifera tuber extract (DBTE). High-resolution transmission electron microscopy revealed monodispersed PtNPs of size 2–5 nm, while PdNPs and Pt–PdNPs between 10 and 25 nm. Energy dispersive spectroscopy analysis confirmed 30.88%±1.73% elemental Pt and 68.96%±1.48% elemental Pd in the bimetallic nanoparticles. Fourier transform infrared spectra indicated strong peaks at 3,373 cm−1, attributed to hydroxyl group of polyphenolic compounds in DBTE that might play a key role in bioreduction in addition to the sharp peaks at 2,937, 1,647, 1,518, and 1,024 cm−1, associated with C–H stretching, N–H bending in primary amines, N–O stretching in nitro group, and C–C stretch, respectively. Anticancer activity against HeLa cells showed that Pt–PdNPs exhibited more pronounced cell death of 74.25% compared to individual PtNPs (12.6%) or PdNPs (33.15%). Further, Pt–PdNPs showed an enhanced scavenging activity against 2,2-diphenyl-1-picrylhydrazyl, superoxide, nitric oxide, and hydroxyl radicals. PMID:26719690

  5. Noble metal ionic catalysts.

    PubMed

    Hegde, M S; Madras, Giridhar; Patil, K C

    2009-06-16

    Because of growing environmental concerns and increasingly stringent regulations governing auto emissions, new more efficient exhaust catalysts are needed to reduce the amount of pollutants released from internal combustion engines. To accomplish this goal, the major pollutants in exhaust-CO, NO(x), and unburned hydrocarbons-need to be fully converted to CO(2), N(2), and H(2)O. Most exhaust catalysts contain nanocrystalline noble metals (Pt, Pd, Rh) dispersed on oxide supports such as Al(2)O(3) or SiO(2) promoted by CeO(2). However, in conventional catalysts, only the surface atoms of the noble metal particles serve as adsorption sites, and even in 4-6 nm metal particles, only 1/4 to 1/5 of the total noble metal atoms are utilized for catalytic conversion. The complete dispersion of noble metals can be achieved only as ions within an oxide support. In this Account, we describe a novel solution to this dispersion problem: a new solution combustion method for synthesizing dispersed noble metal ionic catalysts. We have synthesized nanocrystalline, single-phase Ce(1-x)M(x)O(2-delta) and Ce(1-x-y)Ti(y)M(x)O(2-delta) (M = Pt, Pd, Rh; x = 0.01-0.02, delta approximately x, y = 0.15-0.25) oxides in fluorite structure. In these oxide catalysts, Pt(2+), Pd(2+), or Rh(3+) ions are substituted only to the extent of 1-2% of Ce(4+) ion. Lower-valent noble metal ion substitution in CeO(2) creates oxygen vacancies. Reducing molecules (CO, H(2), NH(3)) are adsorbed onto electron-deficient noble metal ions, while oxidizing (O(2), NO) molecules are absorbed onto electron-rich oxide ion vacancy sites. The rates of CO and hydrocarbon oxidation and NO(x) reduction (with >80% N(2) selectivity) are 15-30 times higher in the presence of these ionic catalysts than when the same amount of noble metal loaded on an oxide support is used. Catalysts with palladium ion dispersed in CeO(2) or Ce(1-x)Ti(x)O(2) were far superior to Pt or Rh ionic catalysts. Therefore, we have demonstrated that the

  6. On the Synergistic Catalytic Properties of Bimetallic Mesoporous Materials Containing Aluminum and Zirconium: The Prins Cyclisation of Citronellal

    PubMed Central

    Telalović, Selvedin; Ramanathan, Anand; Ng, Jeck Fei; Maheswari, Rajamanickam; Kwakernaak, Cees; Soulimani, Fouad; Brouwer, Hans C; Chuah, Gaik Khuan; Weckhuysen, Bert M; Hanefeld, Ulf

    2011-01-01

    Bimetallic three-dimensional amorphous mesoporous materials, Al-Zr-TUD-1 materials, were synthesised by using a surfactant-free, one-pot procedure employing triethanolamine (TEA) as a complexing reagent. The amount of aluminium and zirconium was varied in order to study the effect of these metals on the Brønsted and Lewis acidity, as well as on the resulting catalytic activity of the material. The materials were characterised by various techniques, including elemental analysis, X-ray diffraction, high-resolution TEM, N2 physisorption, temperature-programmed desorption (TPD) of NH3, and 27Al MAS NMR, XPS and FT-IR spectroscopy using pyridine and CO as probe molecules. Al-Zr-TUD-1 materials are mesoporous with surface areas ranging from 700–900 m2 g−1, an average pore size of around 4 nm and a pore volume of around 0.70 cm3 g−1. The synthesised Al-Zr-TUD-1 materials were tested as catalyst materials in the Lewis acid catalysed Meerwein–Ponndorf–Verley reduction of 4-tert-butylcyclohexanone, the intermolecular Prins synthesis of nopol and in the intramolecular Prins cyclisation of citronellal. Although Al-Zr-TUD-1 catalysts possess a lower amount of acid sites than their monometallic counterparts, according to TPD of NH3, these materials outperformed those of the monometallic Al-TUD-1 as well as Zr-TUD-1 in the Prins cyclisation of citronellal. This proves the existence of synergistic properties of Al-Zr-TUD-1. Due to the intramolecular nature of the Prins cyclisation of citronellal, the hydrophilic surface of the catalyst as well as the presence of both Brønsted and Lewis acid sites synergy could be obtained with bimetallic Al-Zr-TUD-1. Besides spectroscopic investigation of the active sites of the catalyst material a thorough testing of the catalyst in different types of reactions is crucial in identifying its specific active sites. PMID:21259348

  7. Bimetallic promotion of cooperative hydrogen transfer and heteroatom removal in coal liquefaction. Quarterly summary, June 1, 1991--August 31, 1991

    SciTech Connect

    Eisch, J.J.

    1991-10-01

    The ultimate objective of this research is to uncover new catalytic processes for the liquefaction of coal and for upgrading coal-derived fuels by removing undesirable organosulfur, organonitrogen and organooxygen constituents. Basic to both the liquefaction of coal and the purification of coal liquids is the transfer of hydrogen from such sources as dihydrogen, metal hydrides or partially reduced aromatic hydrocarbons to the extensive aromatic rings in coal itself or to aromatic sulfides, amines or ethers. Accordingly, this study is exploring how such crucial hydrogen-transfer processes might be catalyzed by soluble, low-valent transition metal complexes and/or Lewis acids under moderate conditions of temperature and pressure. By learning the mechanism whereby H{sub 2}, metal hydrides or partially hydrogenated aromatics do transfer hydrogen to model aromatic compounds, with the aid of homogeneous, bimetallic catalysts, we hope to identify new methods for producing superior fuels from coal.

  8. Improvement of microbead cracking catalyst manufacture

    SciTech Connect

    Mirskii, Ya.B.; Kosolapova, A.P.; Meged, N.F.

    1986-11-01

    In order to improve the manufacturing process for KMTsR microbead catalyst for use in new cracking units, the authors consider the method of increasing the content of aluminum oxide in its amorphous part. A microbead catalyst of zeolite, containing rare-earth elements of the KMTsR type was obtained by spray-drying a slurry prepared by mechanical dispersion of hydrogel beads, with the subsequent molding and processing operations the same as in the production of bead catalyst.

  9. Catalyst and method for aqueous phase reactions

    DOEpatents

    Elliott, Douglas C.; Hart, Todd R.

    1999-01-01

    The present invention is a catalyst in the form of a plurality of porous particles wherein each particle is a support having nickel metal catalytic phase or reduced nickel deposited thereon in a first dispersed phase and an additional metal deposited onto the support in a second dispersed phase. The additional metal is effective in retarding or reducing agglomeration or sintering of the nickel metal catalytic phase without substantially affecting the catalytic activity, thereby increasing the life time of the catalyst.

  10. Centrifugally cast bimetallic pipe for offshore corrosion resistant pipelines

    SciTech Connect

    Yoshitake, A.; Torigoe, T.

    1994-12-31

    Centrifugally cast bimetallic pipes and fittings have been developed for the use of offshore oil and gas production. The metallurgical properties, mechanical properties, and corrosion properties of centrifugal a cast bimetallic pipe with outside metal of API 5L X52 to X65 internally clad with alloy 825 and 625 are discussed. First, molten steel for outer pipe is introduced into a rotating metallic mold. During the solidification of the outer pipe (carbon steel), the temperature of the pipe inside is monitored. After the solidification of the outer pipe, and when a certain temperature is reached, then a corrosion resistant alloy such as Alloy 825 or 625 for inside layer is poured. By controlling the casting conditions and selecting suitable flux, sound metallurgical bonded bimetallic pipe is produced with a minimum mixing layer at the interface also keeping a homogeneous outside wall thickness along the pipe length. The weld joints of the pipe are also evaluated from the view points of weldability, mechanical strength, fracture toughness, and corrosion resistance properties. The welding method applied was basically TIG welding (GTAW). COD tests at {minus}10 C are applied to the welds to investigate fracture toughness of the weld joints. Huey test according to ASTM A262C is carried out on the root of the welds as the corrosion test. As a result, the weld joint using filler wire of alloy625 from root to cover pass has proved a very reliable method from the point of view of mechanical and corrosion resistance properties. These centrifugally cast bimetallic pipes and fittings have been widely used for riser pipes, template process lines, top side and subsea manifolds, and flow bends for christmas trees in the North Sea.

  11. Synthesis and characterization of Ni-Au bimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Nik Roselina, N. R.; Azizan, A.; Hyie, Koay Mei; Murad, Mardziah Che; Abdullah, Abdul Hakim

    2015-04-01

    Bimetallic structure of nanoparticles is of great interest due to their extraordinary properties, especially in combining the specialty of the core and its shell. This work reports the effect of pH on the synthesis of Ni-Au (nickel-gold) bimetallic nanoparticles. The synthesis involves a two-step process where Ni nanoparticles were first synthesized using polyol method with hydrazine as the reducing agent. This was followed by the process of reducing AuCl4- to Au in the solution containing pre-prepared Ni to form Ni-Au bimetallic nanoparticles using sodium citrate as the reducing agent. The results obtained from Transmission Electron Microscopy (TEM) show that the process can possibly produce either core-shell structure, or mixture of Ni and Au nanoparticles. Magnetic property of core-shell structure investigated using Vibrating Sample Magnetometer (VSM) demonstrated typical characteristic of ferromagnetic with an increased magnetization as compared to Ni nanoparticles. The saturation magnetization (Ms) and coercivity (Hc) were obtained as 19.1 emu/g and 222.3 Oe, respectively.

  12. Enhanced dehalogenation of halogenated methanes by bimetallic Cu/Al.

    PubMed

    Lien, Hsing-Lung; Zhang, Weixian

    2002-10-01

    A low-cost and high effective copper/aluminum (Cu/Al) bimetal has been developed for treatments of halogenated methanes, including dichloromethane, in near neutral and high pH aqueous systems. Bimetallic Cu/Al was prepared by a simple two-step synthetic method where Cu was deposited onto the Al surface. The presence of Cu on Al significantly enhanced rates of degradation of halogenated methanes and reduced toxic halogenated intermediates. The stability of Cu/Al was preliminarily studied by a multi-spiking batch experiment where complete degradation of carbon tetrachloride was achieved for seven times although the Cu/Al aging was found. Roles of Cu may involve protecting Al against an undesirable oxidation with water, enhancing reaction rates through the galvanic corrosion, and increasing the selectivity to a benign compound (i.e., methane). Kinetic analyses indicated that the activity of bimetallic Cu/Al was comparable to that of iron-based bimetals (e.g., palladized iron) and zero-valent metals. Bimetallic Cu/Al could be a promising reactive reagent for remediation of halogenated solvents-contaminated groundwater associated with high pH problems.

  13. Catalytic dechlorination of Aroclor 1242 by Ni/Fe bimetallic nanoparticles.

    PubMed

    Zhang, Zhen; Hu, Sai; Baig, Shams Ali; Tang, Jie; Xu, Xinhua

    2012-11-01

    Ni/Fe bimetallic nanoparticles were synthesized for treatment of Aroclor 1242, in order to evaluate their applicability for in situ remediation of groundwater and soil contaminated by polychlorinated biphenyls (PCBs). Our experimental results indicate that the total PCB concentration changed during the reduction of 3,5-dichlorobiphenyl (PCB 14), and biphenyl was produced as the final product. Initially, the concentration of 3-chlorobiphenyl (PCB 2) was increased in the prophase reaction and then slowly decreased, suggesting that Aroclor 1242 was first adsorbed by Ni/Fe nanoparticles, and then, the higher chlorinated congeners were converted gradually to the lower chlorinated congeners, and finally to biphenyl. The dechlorination efficiency of Aroclor 1242 reached approximately 80% at 25°C in just 5h, then 95.6% and 95.8% in 10h and 24h, respectively. The study revealed that high Ni/Fe nanoparticle dosage and high Ni content in Ni/Fe nanoparticles favor the catalytic dechlorination reaction. Moreover, a comparison of different types of catalysts on the dechlorination of Aroclor 1242 indicated that Ni/Mg and Mg powders showed a greater reactivity than Ni/Fe and Fe nanoparticles, respectively.

  14. Properties of two-dimensional insulators: A DFT study of bimetallic oxide CrW2O9 clusters adsorption on MgO ultrathin films

    NASA Astrophysics Data System (ADS)

    Zhu, Jia; Zhang, Hui; Zhao, Ling; Xiong, Wei; Huang, Xin; Wang, Bin; Zhang, Yongfan

    2016-08-01

    Periodic density functional theory calculations have been performed to study the electronic properties of bimetallic oxide CrW2O9 clusters adsorbed on MgO/Ag(001) ultrathin films (<1 nm). Our results show that after deposition completely different structures, electronic properties and chemical reactivity of dispersed CrW2O9 clusters on ultrathin films are observed compared with that on the thick MgO surface. On the thick MgO(001) surface, adsorbed CrW2O9 clusters are distorted significantly and just a little electron transfer occurs from oxide surface to clusters, which originates from the formation of adsorption dative bonds at interface. Whereas on the MgO/Ag(001) ultrathin films, the resulting CrW2O9 clusters keep the cyclic structures and the geometries are similar to that of gas-phase [CrW2O9]-. Interestingly, we predicted the occurrence of a net transfer of one electron by direct electron tunneling from the MgO/Ag(001) films to CrW2O9 clusters through the thin MgO dielectric barrier. Furthermore, our work reveals a progressive Lewis acid site where spin density preferentially localizes around the Cr atom not the W atoms for CrW2O9/MgO/Ag(001) system, indicating a potentially good bimetallic oxide for better catalytic activities with respect to that of pure W3O9 clusters. As a consequence, present results reveal that the adsorption of bimetallic oxide CrW2O9 clusters on the MgO/Ag(001) ultrathin films provide a new perspective to tune and modify the properties and chemical reactivity of bimetallic oxide adsorbates as a function of the thickness of the oxide films.

  15. Core-shell composite metal catalysts incased into natural ceramic nanotubes

    NASA Astrophysics Data System (ADS)

    Vinokurov, V.; Berberov, A.; Afonin, D.; Borzaev, H.; Ivanov, E.; Gushchin, P.; Lvov, Y.

    2014-08-01

    The bimetallic halloysite nanotubes were prepared by the injection of halloysite- containing aerosols into the microwave plasma reactor. Nanotubes contain metal nanoparticles formed from the metal salt solution in the lumen of nanotubes and the iron oxide nanoparticles at the outer surface of nanotubes. Such halloysite composites may be sputtered onto the surface of the porous carrier forming the nanostructured catalyst, as was shown by the pure halloysite sputtering onto the model porous ceramic surface.

  16. 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.

  17. Surface modification processes during methane decomposition on Cu-promoted Ni–ZrO2 catalysts

    PubMed Central

    Wolfbeisser, Astrid; Klötzer, Bernhard; Mayr, Lukas; Rameshan, Raffael; Zemlyanov, Dmitry; Bernardi, Johannes; Rupprechter, Günther

    2015-01-01

    The surface chemistry of methane on Ni–ZrO2 and bimetallic CuNi–ZrO2 catalysts and the stability of the CuNi alloy under reaction conditions of methane decomposition were investigated by combining reactivity measurements and in situ synchrotron-based near-ambient pressure XPS. Cu was selected as an exemplary promoter for modifying the reactivity of Ni and enhancing the resistance against coke formation. We observed an activation process occurring in methane between 650 and 735 K with the exact temperature depending on the composition which resulted in an irreversible modification of the catalytic performance of the bimetallic catalysts towards a Ni-like behaviour. The sudden increase in catalytic activity could be explained by an increase in the concentration of reduced Ni atoms at the catalyst surface in the active state, likely as a consequence of the interaction with methane. Cu addition to Ni improved the desired resistance against carbon deposition by lowering the amount of coke formed. As a key conclusion, the CuNi alloy shows limited stability under relevant reaction conditions. This system is stable only in a limited range of temperature up to ~700 K in methane. Beyond this temperature, segregation of Ni species causes a fast increase in methane decomposition rate. In view of the applicability of this system, a detailed understanding of the stability and surface composition of the bimetallic phases present and the influence of the Cu promoter on the surface chemistry under relevant reaction conditions are essential. PMID:25815163

  18. Growth of carbon nanotubes on surfaces: the effects of catalyst and substrate.

    PubMed

    Murcia, Angel Berenguer; Geng, Junfeng

    2013-08-01

    We report a study of synthesising air-stable, nearly monodispersed bimetallic colloids of Co/Pd and Fe/Mo of varying compositions as active catalysts for the growth of carbon nanotubes. Using these catalysts we have investigated the effects of catalyst and substrate on the carbon nanostructures formed in a plasma-enhanced chemical vapour deposition (PECVD) process. We will show how it is possible to assess the influence of both the catalyst and the support on the controlled growth of carbon nanotube and nanofiber arrays. The importance of the composition of the catalytic nuclei will be put into perspective with other results from the literature. Furthermore, the influence of other synthetic parameters such as the nature of the nanoparticle catalysts will also be analysed and discussed in detail. PMID:23882847

  19. NOVEL METALLIC AND BIMETALLIC CROSS-LINKED POLY (VINYL ALCOHOL) NANOCOMPOSITES PREPARED UNDER MICROWAVE IRRADIATION

    EPA Science Inventory

    A facile microwave irradiation approach that results in a cross-linking reaction of poly (vinyl alcohol) (PVA) with metallic and bimetallic systems is described. Nanocomposites of PVA cross-linked metallic systems such as Pt, Cu, and In and bimetallic systems such as Pt-In, Ag-P...

  20. PREPARATION OF NOVEL METALLIC AND BIMETALLIC CROSS-LINKED POLY (VINYL ALCOHOL) NANOCOMPOSITES UNDER MICROWAVE IRRADIATION

    EPA Science Inventory

    A facile method utilizing microwave irradiation is described that accomplishes the cross-linking reaction of PVA with metallic and bimetallic systems. Nanocomposites of PVA-cross-linked metallic systems such as Pt, Cu, and In and bimetallic systems such as Pt-In, Ag-Pt, Pt-Fe, Cu...

  1. Catalyst increases COS conversion

    SciTech Connect

    Goodboy, K.P.

    1985-02-18

    Increasingly stringent air quality legislation is placing greater emphasis on conversion of COS and CS/sub 2/ in Claus plants for the maximum sulfur recovery. Overall sulfur recovery goals are dependent upon outstanding service from the Claus catalyst in each reactor because catalyst activity is a major factor influencing plant performance. Today's catalyst are much improved over those used 10 years ago for the Claus (H/sub 2/S/SO/sub 2/) reaction. Recent technical efforts have focused on the conversion of COS and CS/sub 2/. These carbon-sulfur compounds can account for as much as 50% of the sulfur going to the incinerator, which essentially converts all remaining sulfur species to SO/sub 2/ for atmospheric dispersion. Previously, the mechanism of Claus COS conversion, i.e., hydrolysis or oxidation by SO/sub 2/, was studied and the conclusion was that oxidation by SO/sub 2/ appears to be the predominate mode of COS conversion on sulfated alumina catalysts.

  2. Cleave and capture chemistry illustrated through bimetallic-induced fragmentation of tetrahydrofuran

    NASA Astrophysics Data System (ADS)

    Mulvey, Robert E.; Blair, Victoria L.; Clegg, William; Kennedy, Alan R.; Klett, Jan; Russo, Luca

    2010-07-01

    The cleavage of ethers is commonly encountered in organometallic chemistry, although rarely studied in the context of new, emerging bimetallic reagents. Recently, it was reported that a bimetallic sodium-zinc base can deprotonate cyclic tetrahydrofuran under mild conditions without opening its heterocyclic (OC4) ring. In marked contrast to this synergic sedation, herein we show that switching to the more reactive sodium-magnesium or sodium-manganese bases promotes cleavage of at least six bonds in tetrahydrofuran, but uniquely the ring fragments are captured in separate crystalline complexes. Oxide fragments occupy guest positions in bimetallic, inverse crown ethers and C4 fragments ultimately appear in bimetallated butadiene molecules. These results demonstrate the special synergic reactivity that can be executed by bimetallic reagents, which include the ability to capture and control, and thereby study, reactive fragments from sensitive substrates.

  3. Cleave and capture chemistry illustrated through bimetallic-induced fragmentation of tetrahydrofuran.

    PubMed

    Mulvey, Robert E; Blair, Victoria L; Clegg, William; Kennedy, Alan R; Klett, Jan; Russo, Luca

    2010-07-01

    The cleavage of ethers is commonly encountered in organometallic chemistry, although rarely studied in the context of new, emerging bimetallic reagents. Recently, it was reported that a bimetallic sodium-zinc base can deprotonate cyclic tetrahydrofuran under mild conditions without opening its heterocyclic (OC(4)) ring. In marked contrast to this synergic sedation, herein we show that switching to the more reactive sodium-magnesium or sodium-manganese bases promotes cleavage of at least six bonds in tetrahydrofuran, but uniquely the ring fragments are captured in separate crystalline complexes. Oxide fragments occupy guest positions in bimetallic, inverse crown ethers and C(4) fragments ultimately appear in bimetallated butadiene molecules. These results demonstrate the special synergic reactivity that can be executed by bimetallic reagents, which include the ability to capture and control, and thereby study, reactive fragments from sensitive substrates. PMID:20571579

  4. Synthesis of Bimetallic Platinum Nanoparticles for Biosensors

    PubMed Central

    Leteba, Gerard M.; Lang, Candace I.

    2013-01-01

    The use of magnetic nanomaterials in biosensing applications is growing as a consequence of their remarkable properties; but controlling the composition and shape of metallic nanoalloys is problematic when more than one precursor is required for wet chemistry synthesis. We have developed a successful simultaneous reduction method for preparation of near-spherical platinum-based nanoalloys containing magnetic solutes. We avoided particular difficulties in preparing platinum nanoalloys containing Ni, Co and Fe by the identification of appropriate synthesis temperatures and chemistry. We used transmission electron microscopy (TEM) to show that our particles have a narrow size distribution, uniform size and morphology, and good crystallinity in the as-synthesized condition. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) confirms the coexistence of Pt with the magnetic solute in a face-centered cubic (FCC) solid solution. PMID:23941910

  5. New microbead cracking catalysts

    SciTech Connect

    Nefedov, S.K.; Guseinov, A.M.; Il'ina, L.M.; Melik-Akhnazarov, T.K.; Stankevich, V.A.

    1984-05-01

    This article reports on the preparation and testing of an experimental batch of KMTsU catalysts using a cocurrent-flow fluid-bed reactor. The proposed manufacturing process is based on the regulation of the density and pore structure of an aluminosilicate matrix by varying the conditions of syneresis and wet treatment in the activation stage. It is recommended that the medium should be at a lower pH in obtaining the gel, that the temperature and pH of the medium should be lower in the activation stage, and that additional dispersion of the gel should be accomplished before spray-drying. The results of the tests on the KMTsU catalyst demonstrate its sufficiently high stable activity, high density (900-920 kg/m/sup 3/), and attrition resistance (92-94%).

  6. Characterization of model three-way catalysts. 3: Infrared study of the surface composition of platinum-rhodium ceria-alumina catalysts

    SciTech Connect

    Rogemond, E.; Frety, R.; Perrichon, V.; Primet, M.; Chevrier, M.; Gauthier, C.; Mathis, F.

    1999-09-10

    The surface composition of model and commercial bimetallic PtRh catalysts supported on ceria-alumina was tentatively determined by FTIR spectroscopy using the successive adsorption of NO at 473 K and CO at 298 K method which was previously applied to the case of PtRh/Al{sub 2}O{sub 3} catalysts. The study of monometallic model catalysts shows that the adsorption of NO at 473 K on rhodium gives an intense band at 1912 cm{sup {minus}1} which is not modified by the presence of ceria and therefore can be used to quantify the number of surface rhodium atoms. However, the chemisorption properties of platinum toward the subsequent adsorption of CO at 298 K are strongly modified and the quantification of the surface platinum atoms could not be directly measured. However, their number could be indirectly obtained by combining the NO adsorption for rhodium and hydrogen volumetric adsorption for the total number of surface metal atoms, assuming that NO adsorption does not induce an important segregation of rhodium for bimetallic particles. Thus, for the fresh bimetallic model catalyst, the same composition was obtained at the surface and in the bulk. After aging at 1273 K, no rhodium was detected at the surface. This absence of surface rhodium atoms was confirmed by the data obtained from the direct adsorption of CO on platinum at room temperature, which gave the same number of surface atoms as hydrogen chemisorption. Similar results have been obtained with two commercial three-way catalysts. In particular, after aging at 1273 K, rhodium was practically not detected on the surface.

  7. Fabrication a new modified electrochemical sensor based on Au-Pd bimetallic nanoparticle decorated graphene for citalopram determination.

    PubMed

    Daneshvar, Leili; Rounaghi, Gholam Hossein; Es'haghi, Zarrin; Chamsaz, Mahmoud; Tarahomi, Somayeh

    2016-12-01

    This paper proposes a simple approach for sensing of citalopram (CTL) using gold-palladium bimetallic nanoparticles (Au-PdNPs) decorated graphene modified gold electrode. Au-PdNPs were deposited at the surface of a graphene modified gold electrode with simple electrodeposition method. The morphology and the electrochemical properties of the modified electrode were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), energy dispersion spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave voltammetry (SWV). The novel sensor exhibited an excellent catalytic activity towards the oxidation of CTL. The oxidation peak current of CTL, was linear in the range of 0.5-50μM with a detection limit 0.049μM with respect to concentration of citalopram. The proposed sensor was successfully applied for determination of CTL tablet and human plasma samples with satisfactory results. PMID:27612758

  8. Photocatalytic degradation of DIPA using bimetallic Cu-Ni/TiO2 photocatalyst under visible light irradiation.

    PubMed

    Riaz, Nadia; Bustam, Mohamad Azmi; Chong, Fai Kait; Man, Zakaria B; Khan, Muhammad Saqib; Shariff, Azmi M

    2014-01-01

    Bimetallic Cu-Ni/TiO2 photocatalysts were synthesized using wet impregnation (WI) method with TiO2 (Degussa-P25) as support and calcined at different temperatures (180, 200, and 300°C) for the photodegradation of DIPA under visible light. The photocatalysts were characterized using TGA, FESEM, UV-Vis diffuse reflectance spectroscopy, fourier transform infrared spectroscopy (FTIR) and temperature programmed reduction (TPR). The results from the photodegradation experiments revealed that the Cu-Ni/TiO2 photocatalysts exhibited much higher photocatalytic activities compared to bare TiO2. It was found that photocatalyst calcined at 200°C had the highest photocatalyst activities with highest chemical oxygen demand (COD) removal (86.82%). According to the structural and surface analysis, the enhanced photocatalytic activity could be attributed to its strong absorption into the visible region and high metal dispersion.

  9. Photocatalytic Degradation of DIPA Using Bimetallic Cu-Ni/TiO2 Photocatalyst under Visible Light Irradiation

    PubMed Central

    Bustam, Mohamad Azmi; Chong, Fai Kait; Man, Zakaria B.; Khan, Muhammad Saqib; Shariff, Azmi M.

    2014-01-01

    Bimetallic Cu-Ni/TiO2 photocatalysts were synthesized using wet impregnation (WI) method with TiO2 (Degussa-P25) as support and calcined at different temperatures (180, 200, and 300°C) for the photodegradation of DIPA under visible light. The photocatalysts were characterized using TGA, FESEM, UV-Vis diffuse reflectance spectroscopy, fourier transform infrared spectroscopy (FTIR) and temperature programmed reduction (TPR). The results from the photodegradation experiments revealed that the Cu-Ni/TiO2 photocatalysts exhibited much higher photocatalytic activities compared to bare TiO2. It was found that photocatalyst calcined at 200°C had the highest photocatalyst activities with highest chemical oxygen demand (COD) removal (86.82%). According to the structural and surface analysis, the enhanced photocatalytic activity could be attributed to its strong absorption into the visible region and high metal dispersion. PMID:25105158

  10. Fabrication a new modified electrochemical sensor based on Au-Pd bimetallic nanoparticle decorated graphene for citalopram determination.

    PubMed

    Daneshvar, Leili; Rounaghi, Gholam Hossein; Es'haghi, Zarrin; Chamsaz, Mahmoud; Tarahomi, Somayeh

    2016-12-01

    This paper proposes a simple approach for sensing of citalopram (CTL) using gold-palladium bimetallic nanoparticles (Au-PdNPs) decorated graphene modified gold electrode. Au-PdNPs were deposited at the surface of a graphene modified gold electrode with simple electrodeposition method. The morphology and the electrochemical properties of the modified electrode were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), energy dispersion spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and square wave voltammetry (SWV). The novel sensor exhibited an excellent catalytic activity towards the oxidation of CTL. The oxidation peak current of CTL, was linear in the range of 0.5-50μM with a detection limit 0.049μM with respect to concentration of citalopram. The proposed sensor was successfully applied for determination of CTL tablet and human plasma samples with satisfactory results.

  11. AuRu/AC as an effective catalyst for hydrogenation reactions

    SciTech Connect

    Villa, Alberto; Chan-Thaw, Carine E.; Campisi, Sebastiano; Bianchi, Claudia L.; Wang, Di; Kotula, Paul G.; Kübel, Christian; Prati, Laura

    2015-03-23

    AuRu bimetallic catalysts have been prepared by sequential deposition of Au on Ru or vice versa obtaining different nanostructures: when Ru has been deposited on Au, a Aucore–Rushell has been observed, whereas the deposition of Au on Ru leads to a bimetallic phase with Ru enrichment on the surface. In the latter case, the unexpected Ru enrichment could be attributed to the weak adhesion of Ru on the carbon support, thus allowing Ru particles to diffuse on Au particles. Both structures result very active in catalysing the liquid phase hydrogenolysis of glycerol and levulinic acid but the activity, the selectivity and the stability depend on the structure of the bimetallic nanoparticles. Ru@Au/AC core–shell structure mostly behaved as the monometallic Ru, whereas the presence of bimetallic AuRu phase in Au@Ru/AC provides a great beneficial effect on both activity and stability.

  12. Photo-oxidation catalysts

    DOEpatents

    Pitts, J. Roland; Liu, Ping; Smith, R. Davis

    2009-07-14

    Photo-oxidation catalysts and methods for cleaning a metal-based catalyst are disclosed. An exemplary catalyst system implementing a photo-oxidation catalyst may comprise a metal-based catalyst, and a photo-oxidation catalyst for cleaning the metal-based catalyst in the presence of light. The exposure to light enables the photo-oxidation catalyst to substantially oxidize absorbed contaminants and reduce accumulation of the contaminants on the metal-based catalyst. Applications are also disclosed.

  13. Intermolecular forces: a solution to dispersion interactions.

    PubMed

    Shimizu, Ken D

    2013-12-01

    London dispersion forces have been cited as an important factor in protein folding, drug–receptor interactions, and catalyst selectivities. However, careful analysis of a model system finds that the dispersion interactions are only minor contributors to the formation of complexes in solution.

  14. Steam gasification of carbon: Catalyst properties

    SciTech Connect

    Falconer, J.L.

    1991-12-13

    This research uses several techniques to measure the concentration of catalyst sites and determine their stoichiometry for the catalyzed gasification of carbon. Both alkali and alkaline earth oxides are effective catalysts for accelerating the gasification rate of coal chars, but only a fraction of the catalyst appears to be in a form that is effective for gasification, and the composition of that catalyst is not established. Transient techniques with {sup 13}C labeling, are being used to study the surface processes, to measure the concentration of active sites, and to determine the specific reaction rates. We have used secondary ion mass spectrometry (SIMS) for both high surface area samples of carbon/alkali carbonate mixtures and for model carbon surfaces with deposited alkali atoms. SIMS provides a direct measure of surface composition. The combination of these results can provide knowledge of catalyst dispersion and composition, and thus indicate the way to optimally utilize carbon gasification catalysts.

  15. Supported Pd/Sn bimetallic nanoparticles for reductive dechlorination of aqueous trichloroethylene.

    PubMed

    Lin, Chin Jung; Liou, Ya Hsuan; Lo, Shang-Lien

    2009-01-01

    A Pd/Sn bimetallic nanoparticles resin (nano-Pd/Sn/resin) was successfully synthesized for reductive transformation of aqueous trichloroethylene (TCE). The physicochemical properties of the prepared resin were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, N(2) isothermal sorption at and X-ray photospectroscopy. The surface-area-normalized rate constants (k(SA)) of Sn particles in the nanoscale range (50-100 nm) were 4.5 times larger than the k(SA) for powdered Sn (0.04 mm). After depositing 1 wt% Pd onto nano-Sn surface, k(SA) was further enhanced by about a factor of 2. Groundwater constituents such as sulfide nitrate and dissolved oxygen had significant negative effects on the rate of TCE degradation by the nano-Pd/Sn/resin. A wet-chemical method regeneration method was observed to effectively restore the reactivity of the poisoned nano-Pd/Sn/resin after dipping in sulfide solution for 2d. In all cases, less than 0.5% of the degraded TCE appeared as chlorinated byproducts including the three dichloroethene isomers. The nano-Pd/Sn/resin technique performs well in transforming TCE into nontoxic hydrocarbons, as compared with other published methods.

  16. Activity Descriptor Identification for Oxygen Reduction on Platinum-Based Bimetallic Nanoparticles: In Situ Observation of the Linear Composition–Strain–Activity Relationship

    PubMed Central

    2016-01-01

    Despite recent progress in developing active and durable oxygen reduction catalysts with reduced Pt content, lack of elegant bottom-up synthesis procedures with knowledge over the control of atomic arrangement and morphology of the Pt–alloy catalysts still hinders fuel cell commercialization. To follow a less empirical synthesis path for improved Pt-based catalysts, it is essential to correlate catalytic performance to properties that can be easily controlled and measured experimentally. Herein, using Pt–Co alloy nanoparticles (NPs) with varying atomic composition as an example, we show that the atomic distribution of Pt-based bimetallic NPs under operating conditions is strongly dependent on the initial atomic ratio by employing microscopic and in situ spectroscopic techniques. The PtxCo/C NPs with high Co content possess a Co concentration gradient such that Co is concentrated in the core and gradually depletes in the near-surface region, whereas the PtxCo/C NPs with low Co content possess a relatively uniform distribution of Co with low Co population in the near-surface region. Despite their different atomic structure, the oxygen reduction reaction (ORR) activity of PtxCo/C and Pt/C NPs is linearly related to the bulk average Pt–Pt bond length (RPt–Pt). The RPt–Pt is further shown to contract linearly with the increase in Co/Pt composition. These linear correlations together demonstrate that (i) the improved ORR activity of PtxCo/C NPs over pure Pt NPs originates predominantly from the compressive strain and (ii) the RPt–Pt is a valid strain descriptor that bridges the activity and atomic composition of Pt-based bimetallic NPs. PMID:25559440

  17. Activity descriptor identification for oxygen reduction on platinum-based bimetallic nanoparticles: in situ observation of the linear composition-strain-activity relationship.

    PubMed

    Jia, Qingying; Liang, Wentao; Bates, Michael K; Mani, Prasanna; Lee, Wendy; Mukerjee, Sanjeev

    2015-01-27

    Despite recent progress in developing active and durable oxygen reduction catalysts with reduced Pt content, lack of elegant bottom-up synthesis procedures with knowledge over the control of atomic arrangement and morphology of the Pt-alloy catalysts still hinders fuel cell commercialization. To follow a less empirical synthesis path for improved Pt-based catalysts, it is essential to correlate catalytic performance to properties that can be easily controlled and measured experimentally. Herein, using Pt-Co alloy nanoparticles (NPs) with varying atomic composition as an example, we show that the atomic distribution of Pt-based bimetallic NPs under operating conditions is strongly dependent on the initial atomic ratio by employing microscopic and in situ spectroscopic techniques. The PtxCo/C NPs with high Co content possess a Co concentration gradient such that Co is concentrated in the core and gradually depletes in the near-surface region, whereas the PtxCo/C NPs with low Co content possess a relatively uniform distribution of Co with low Co population in the near-surface region. Despite their different atomic structure, the oxygen reduction reaction (ORR) activity of PtxCo/C and Pt/C NPs is linearly related to the bulk average Pt-Pt bond length (RPt-Pt). The RPt-Pt is further shown to contract linearly with the increase in Co/Pt composition. These linear correlations together demonstrate that (i) the improved ORR activity of PtxCo/C NPs over pure Pt NPs originates predominantly from the compressive strain and (ii) the RPt-Pt is a valid strain descriptor that bridges the activity and atomic composition of Pt-based bimetallic NPs.

  18. Computational Chemistry-Based Identification of Ultra-Low Temperature Water-Gas-Shift Catalysts

    SciTech Connect

    Manos Mavrikakis

    2008-08-31

    The current work seeks to identify novel, catalytically-active, stable, poison-resistant LWGS catalysts that retain the superior activity typical of conventional Cu catalysts but can be operated at similar or lower temperatures. A database for the Binding Energies (BEs) of the LWGS relevant species, namely CO, O and OH on the most-stable, close-packed facets of a set of 17 catalytically relevant transition metals was established. This BE data and a database of previously established segregation energies was utilized to predict the stability of bimetallic NSAs that could be synthesized by combinations of the 17 parent transition metals. NSAs that were potentially stable both in vacuo and under the influence of strong-binding WGS intermediates were then selected for adsorption studies. A set of 40 NSAs were identified that satisfied all three screener criteria and the binding energies of CO, O and OH were calculated on a set of 66, 43 and 79 NSA candidates respectively. Several NSAs were found that bound intermediates weaker than the monometallic catalysts and were thus potentially poison-resistant. Finally, kinetic studies were performed and resulted in the discovery of a specific NSA-based bimetallic catalyst Cu/Pt that is potentially a promising LWGS catalyst. This stable Cu/Pt subsurface alloy is expected to provide facile H{sub 2}O activation and remain relatively resistant from the poisoning by CO, S and formate intermediates.

  19. Structural models and atomic distribution of bimetallic nanoparticles as investigated by X-ray absorption spectroscopy.

    PubMed

    Hwang, Bing-Joe; Sarma, Loka Subramanyam; Chen, Jiun-Ming; Chen, Ching-Hsiang; Shih, Shou-Chu; Wang, Guo-Rung; Liu, Din-Goa; Lee, Jyh-Fu; Tang, Mau-Tsu

    2005-08-10

    In this report, we describe a general methodology to determine the extent of alloying or atomic distribution quantitatively in bimetallic nanoparticles (NPs) by X-ray absorption spectroscopy (XAS). The structural parameters determined in these studies serve as a quantitative index and provide a general route to determine the structural aspects of the bimetallic NPs. We have derived various types of possible structural models based on the extent of alloying and coordination number parameters of bimetallic NPs. We also discussed the nature of homo- and heterometallic interactions in bimetallic NPs based on the extent of alloying. Herein, we use carbon-supported platinum-ruthenium bimetallic nanoparticles to demonstrate the proposed methodology, and this can be extended further to get more insights into the alloying extent or atomic distribution of other bimetallic systems. The results demonstrated in this paper open up methods to determine the atomic distribution of bimetallic NPs, which is an extremely important parameter that strongly influences the physicochemical properties of NPs and their applications.

  20. Nanoporous Au: an unsupported pure gold catalyst?

    SciTech Connect

    Wittstock, A; Neumann, B; Schaefer, A; Dumbuya, K; Kuebel, C; Biener, M; Zielasek, V; Steinrueck, H; Gottfried, M; Biener, J; Hamza, A; B?umer, M

    2008-09-04

    The unique properties of gold especially in low temperature CO oxidation have been ascribed to a combination of various effects. In particular, particle sizes below a few nm and specific particle-support interactions have been shown to play important roles. On the contrary, recent reports revealed that monolithic nanoporous gold (npAu) prepared by leaching a less noble metal, such as Ag, out of the corresponding alloy can also exhibit remarkably high catalytic activity for CO oxidation, even though no support is present. Therefore, it was claimed to be a pure and unsupported gold catalyst. We investigated npAu with respect to its morphology, surface composition and catalytic properties. In particular, we studied the reaction kinetics for low temperature CO oxidation in detail taking mass transport limitation due to the porous structure of the material into account. Our results reveal that Ag, even if removed almost completely from the bulk, segregates to the surface resulting in surface concentrations of up to 10 at%. Our data suggest that this Ag plays a significant role in activation of molecular oxygen. Therefore, npAu should be considered as a bimetallic catalyst rather than a pure Au catalyst.

  1. Single-catalyst high-weight% hydrogen storage in an N-heterocycle synthesized from lignin hydrogenolysis products and ammonia

    PubMed Central

    Forberg, Daniel; Schwob, Tobias; Zaheer, Muhammad; Friedrich, Martin; Miyajima, Nobuyoshi; Kempe, Rhett

    2016-01-01

    Large-scale energy storage and the utilization of biomass as a sustainable carbon source are global challenges of this century. The reversible storage of hydrogen covalently bound in chemical compounds is a particularly promising energy storage technology. For this, compounds that can be sustainably synthesized and that permit high-weight% hydrogen storage would be highly desirable. Herein, we report that catalytically modified lignin, an indigestible, abundantly available and hitherto barely used biomass, can be harnessed to reversibly store hydrogen. A novel reusable bimetallic catalyst has been developed, which is able to hydrogenate and dehydrogenate N-heterocycles most efficiently. Furthermore, a particular N-heterocycle has been identified that can be synthesized catalytically in one step from the main lignin hydrogenolysis product and ammonia, and in which the new bimetallic catalyst allows multiple cycles of high-weight% hydrogen storage. PMID:27762267

  2. Physical and Numerical Analysis of Extrusion Process for Production of Bimetallic Tubes

    SciTech Connect

    Misiolek, W.Z.; Sikka, V.K.

    2006-08-10

    Bimetallic tubes are used for very specific applications where one of the two metals provides strength and the other provides specific properties such as aqueous corrosion and carburization, coking resistance, and special electrical and thermal properties. Bimetallic tubes have application in pulp and paper industry for heat-recovery boilers, in the chemical industry for ethylene production, and in the petrochemical industry for deep oil well explorations. Although bimetallic tubes have major applications in energy-intensive industry, they often are not used because of their cost and manufacturing sources in the United States. This project was intended to address both of these issues.

  3. Hydrodechlorination of 1,2-Dichloroethane Catalyzedby Dendrimer-Derived Pt-Cu/SiO2 Catalysts

    SciTech Connect

    Xie, Hong; Howe, Jane Y; Schwartz, Viviane; Monnier, J. R.; Williams, Christopher T.; Ploehn, Harry J.

    2008-01-01

    Dendrimer-metal-nanocomposites (DMNs) were used as precursors to prepare SiO2 supported monometallic Pt, Cu and bimetallic Pt-Cu catalysts with Pt/Cu atomic ratios of 1:1 (Pt50Cu50) and 1:3 (Pt25Cu75). After impregnation of these DMNs onto the support, the catalysts were thermally treated and activated following an optimized protocol. Scanning transmission electron microscopy (STEM) shows that the metal nanoparticles in dendrimer-derived SiO2-supported catalysts are smaller and have a more narrow size distribution than those in conventional catalysts prepared using corresponding metal salts via the wet impregnation method. Slow deactivation was observed for hydrodechlorination of 1,2-dichloroethane over monometallic Cu catalysts, which showed an activity about one to two orders of magnitude lower than that of the Pt-containing catalysts. Hydrodechlorination of 1,2-dichloroethane over Pt and Pt50Cu50 catalysts mainly produces ethane and the selectivity towards ethane increases with temperature. For Pt25Cu75 catalyst, the selectivity towards ethane decreases in favor of ethylene. The overall activity decreases with increasing Cu loading in the catalysts. Activity based on surface Pt sites suggests the formation of bi-functional surfaces in Pt25Cu75 catalyst favoring C-Cl bond scission on Cu sites and hydrogenation of intermediate .CH2CH2. on Pt sites. Furthermore, kinetic analyses suggest different reaction mechanisms for hydrodechlorination of 1,2-dichloroethane over Pt and Cu-enriched surfaces in the Pt-Cu bimetallic catalysts.

  4. Green synthesis and characterization of Au@Pt core-shell bimetallic nanoparticles using gallic acid

    NASA Astrophysics Data System (ADS)

    Zhang, Guojun; Zheng, Hongmei; Shen, Ming; Wang, Lei; Wang, Xiaosan

    2015-06-01

    In this study, we developed a facile and benign green synthesis approach for the successful fabrication of well-dispersed urchin-like Au@Pt core-shell nanoparticles (NPs) using gallic acid (GA) as both a reducing and protecting agent. The proposed one-step synthesis exploits the differences in the reduction potentials of AuCl4- and PtCl62-, where the AuCl4- ions are preferentially reduced to Au cores and the PtCl62- ions are then deposited continuously onto the Au core surface as a Pt shell. The as-prepared Au@Pt NPs were characterized by transmission electron microscope (TEM); high-resolution transmission electron microscope (HR-TEM); scanning electron microscope (SEM); UV-vis absorption spectra (UV-vis); X-ray diffraction (XRD); Fourier transmission infrared spectra (FT-IR). We systematically investigated the effects of some experimental parameters on the formation of the Au@Pt NPs, i.e., the reaction temperature, the molar ratios of HAuCl4/H2PtCl6, and the amount of GA. When polyvinylpyrrolidone K-30 (PVP) was used as a protecting agent, the Au@Pt core-shell NPs obtained using this green synthesis method were better dispersed and smaller in size. The as-prepared Au@Pt NPs exhibited better catalytic activity in the reaction where NaBH4 reduced p-nitrophenol to p-aminophenol. However, the results showed that the Au@Pt bimetallic NPs had a lower catalytic activity than the pure Au NPs obtained by the same method, which confirmed the formation of Au@Pt core-shell nanostructures because the active sites on the surfaces of the Au NPs were covered with a Pt shell.

  5. Synthesis of Au@Pt bimetallic nanoparticles with concave Au nanocuboids as seeds and their enhanced electrocatalytic properties in the ethanol oxidation reaction

    NASA Astrophysics Data System (ADS)

    Tan, Lingyu; Li, Lidong; Peng, Yi; Guo, Lin

    2015-12-01

    Herein, a new type of uniform and well-structured Au@Pt bimetallic nanoparticles (BNPs) with highly active concave Au nanocuboids (NCs) as seeds was successfully synthesized by using the classic seed-mediated method. Electrochemical measurements were conducted to demonstrate their greatly enhanced catalytic performance in the ethanol oxidation reaction (EOR). It was found that the electrochemical performance for Au@Pt BNPs with the concave Au NCs as seeds, which were enclosed by {611} high-index facets, could be seven times higher than that of the Au@Pt bimetallic nanoparticles with regular spherical Au NPs as seeds. Furthermore, our findings show that the morphology and electrocatalytic activity of the Au@Pt BNPs can be tuned simply by changing the compositional ratios of the growth solution. The lower the amount of H2PtCl6 used in the growth solution, the thinner the Pt shell grew, and the more high-index facets of concave Au NCs seeds were exposed in Au@Pt BNPs, leading to higher electrochemical activity. These as-prepared concave Au@Pt BNPs will open up new strategies for improving catalytic efficiency and reducing the use of the expensive and scarce resource of platinum in the ethanol oxidation reaction, and are potentially applicable as electrochemical catalysts for direct ethanol fuel cells.

  6. Synthesis of Au@Pt bimetallic nanoparticles with concave Au nanocuboids as seeds and their enhanced electrocatalytic properties in the ethanol oxidation reaction.

    PubMed

    Tan, Lingyu; Li, Lidong; Peng, Yi; Guo, Lin

    2015-12-18

    Herein, a new type of uniform and well-structured Au@Pt bimetallic nanoparticles (BNPs) with highly active concave Au nanocuboids (NCs) as seeds was successfully synthesized by using the classic seed-mediated method. Electrochemical measurements were conducted to demonstrate their greatly enhanced catalytic performance in the ethanol oxidation reaction (EOR). It was found that the electrochemical performance for Au@Pt BNPs with the concave Au NCs as seeds, which were enclosed by {611} high-index facets, could be seven times higher than that of the Au@Pt bimetallic nanoparticles with regular spherical Au NPs as seeds. Furthermore, our findings show that the morphology and electrocatalytic activity of the Au@Pt BNPs can be tuned simply by changing the compositional ratios of the growth solution. The lower the amount of H2PtCl6 used in the growth solution, the thinner the Pt shell grew, and the more high-index facets of concave Au NCs seeds were exposed in Au@Pt BNPs, leading to higher electrochemical activity. These as-prepared concave Au@Pt BNPs will open up new strategies for improving catalytic efficiency and reducing the use of the expensive and scarce resource of platinum in the ethanol oxidation reaction, and are potentially applicable as electrochemical catalysts for direct ethanol fuel cells.

  7. Facile self-assembly synthesis of PdPt bimetallic nanotubes with good performance for ethanol oxidation in an alkaline medium.

    PubMed

    Huang, Zhongyuan; Zhou, Haihui; Sun, Feifei; Fu, Chaopeng; Zeng, Fanyan; Li, Tianqi; Kuang, Yafei

    2013-10-01

    PdPt bimetallic nanotubes were prepared by the self-assembly of Pt and Pd on Te nanowires at room temperature. The morphologies of the as-prepared PdPt nanotubes were investigated by scanning electron microscopy and transmission electron microscopy, and the results display a large amount of PdPt bimetallic nanotubes with a diameter of 10-20 nm and a length of several micrometers. The composition and structure of the nanotubes were characterized by X-ray diffraction, high-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy spectrum analysis, and the results display uniform compositional distributions of both elements (Pd and Pt). The mechanism of the formation of the nanotube structure was supposed. The electrocatalytic performance of PdPt nanotubes were studied by cyclic voltammetry and chronoamperometry. Electrochemical results show that the as-prepared PdPt nanotube catalysts have not only high activity but also good stability for ethanol oxidation in alkaline medium.

  8. Core-shell Au-Pd nanoparticles as cathode catalysts for microbial fuel cell applications

    NASA Astrophysics Data System (ADS)

    Yang, Gaixiu; Chen, Dong; Lv, Pengmei; Kong, Xiaoying; Sun, Yongming; Wang, Zhongming; Yuan, Zhenhong; Liu, Hui; Yang, Jun

    2016-10-01

    Bimetallic nanoparticles with core-shell structures usually display enhanced catalytic properties due to the lattice strain created between the core and shell regions. In this study, we demonstrate the application of bimetallic Au-Pd nanoparticles with an Au core and a thin Pd shell as cathode catalysts in microbial fuel cells, which represent a promising technology for wastewater treatment, while directly generating electrical energy. In specific, in comparison with the hollow structured Pt nanoparticles, a benchmark for the electrocatalysis, the bimetallic core-shell Au-Pd nanoparticles are found to have superior activity and stability for oxygen reduction reaction in a neutral condition due to the strong electronic interaction and lattice strain effect between the Au core and the Pd shell domains. The maximum power density generated in a membraneless single-chamber microbial fuel cell running on wastewater with core-shell Au-Pd as cathode catalysts is ca. 16.0 W m‑3 and remains stable over 150 days, clearly illustrating the potential of core-shell nanostructures in the applications of microbial fuel cells.

  9. Core-shell Au-Pd nanoparticles as cathode catalysts for microbial fuel cell applications

    PubMed Central

    Yang, Gaixiu; Chen, Dong; Lv, Pengmei; Kong, Xiaoying; Sun, Yongming; Wang, Zhongming; Yuan, Zhenhong; Liu, Hui; Yang, Jun

    2016-01-01

    Bimetallic nanoparticles with core-shell structures usually display enhanced catalytic properties due to the lattice strain created between the core and shell regions. In this study, we demonstrate the application of bimetallic Au-Pd nanoparticles with an Au core and a thin Pd shell as cathode catalysts in microbial fuel cells, which represent a promising technology for wastewater treatment, while directly generating electrical energy. In specific, in comparison with the hollow structured Pt nanoparticles, a benchmark for the electrocatalysis, the bimetallic core-shell Au-Pd nanoparticles are found to have superior activity and stability for oxygen reduction reaction in a neutral condition due to the strong electronic interaction and lattice strain effect between the Au core and the Pd shell domains. The maximum power density generated in a membraneless single-chamber microbial fuel cell running on wastewater with core-shell Au-Pd as cathode catalysts is ca. 16.0 W m−3 and remains stable over 150 days, clearly illustrating the potential of core-shell nanostructures in the applications of microbial fuel cells. PMID:27734945

  10. Copper Modified Magnetic Bimetallic Nano-catalysts Ligand Regulated Catalytic Activity

    EPA Science Inventory

    Postsynthetic modification of magnetic nano ferrites (Fe3O4) has been accomplished by anchoring glutathione and dopamine on the surface. The Cu nano particles immobilized over these surfaces were investigated for the coupling and cyclo addition reactions. The Fe3O4-DOPA-Cu (na...

  11. Electrochemistry of cholesterol biosensor based on a novel Pt-Pd bimetallic nanoparticle decorated graphene catalyst.

    PubMed

    Cao, Shurui; Zhang, Lei; Chai, Yaqin; Yuan, Ruo

    2013-05-15

    A new electrochemical biosensor with enhanced sensitivity was developed for detection of cholesterol by using platinum-palladium-chitosan-graphene hybrid nanocomposites (PtPd-CS-GS) functionalized glassy carbon electrode (GCE). An electrodeposition method was applied to form PtPd nanoparticles-doped chitosan-graphene hybrid nanocomposites (PtPd-CS-GS), which were characterized by scanning electron microscopy (SEM) and electrochemical methods. The presence of the PtPd-CS-GS nanocomposites not only accelerated direct electron transfer from the redox enzyme to the electrode surface, but also enhanced the immobilized amount of cholesterol oxidase (ChOx). Under optimal conditions, the fabricated biosensor exhibited wide linear ranges of responses to cholesterol in the concentration ranges of 2.2×10(-6) to 5.2×10(-4)M, the limit of detection was 0.75 μM (S/N=3). The response time was less than 7s and the Michaelis-Menten constant (Km(app)) was found as 0.11 mM. In addition, the biosensor also exhibited excellent reproducibility and stability. Along with these attractive features, the biosensor also displayed very high specificity to cholesterol with complete elimination of interference from UA, AA, and glucose. PMID:23618155

  12. Structural studies of hydrodesulfurization catalysts

    SciTech Connect

    Sanchez, A.

    1983-01-01

    Hydrodesulfurization (HDS) is a catalytic process used to remove sulfur from S-containing compounds by converting it to hdyrogen sulfide in the presence of dihydrogen. Catalysts used in HDS are mainly made of molybdenum and cobalt sulfides supported on ..gamma..-alumina. The objective of this work was to correlate changes in the HDS activity of these catalysts with structural information obtained by X-ray absorption spectroscopy (XAS). Two series of catalysts were prepared, one by incipient wetness impregnation and the other by bulk impregnation. The catalysts had approximately the same Mo content and varying Co content, and were tested for thiophene HDS in a fixed bed reactor at 573 K and atmospheric pressure. Extended X-ray absorption fine structure (EXAFS) and X-ray absorption edge spectroscopy (XAES) were used at the Mo and Co K-edges. The catalysts were treated in a mixture of hydrogen sulfide/dihydrogen. For both series of catalysts, HDS activity increased with atomic ratio r = Co/(Co + Mo), reached a maximum and declined with further increase in r. Catalysts prepared by incipient wetness impregnation showed higher HDS activity. From EXAFS and XAES, it appears that molybdenum has a local environment similar to that of molybdenum disulfide, very dispersed on the surface of the alumina. Cobalt has sulfur atoms as nearest neighbors. The number N(S) of sulfur neighbors of Mo, determined from EXAFS, depends on r like HDS activity, and shows a linear correlation with HDS activity that holds for both series of catalysts. It seems reasonable that as r increases, the sulfur binding energy of Mo increases until the maximum value of N(S) is reached, and then declines.

  13. CO2 Hydrogenation over Oxide-Supported PtCo Catalysts: The Role of the Oxide Support in Determining the Product Selectivity.

    PubMed

    Kattel, Shyam; Yu, Weiting; Yang, Xiaofang; Yan, Binhang; Huang, Yanqiang; Wan, Weiming; Liu, Ping; Chen, Jingguang G

    2016-07-01

    By simply changing the oxide support, the selectivity of a metal-oxide catalysts can be tuned. For the CO2 hydrogenation over PtCo bimetallic catalysts supported on different reducible oxides (CeO2 , ZrO2 , and TiO2 ), replacing a TiO2 support by CeO2 or ZrO2 selectively strengthens the binding of C,O-bound and O-bound species at the PtCo-oxide interface, leading to a different product selectivity. These results reveal mechanistic insights into how the catalytic performance of metal-oxide catalysts can be fine-tuned.

  14. Growth of Single-Walled Carbon Nanotubes by High Melting Point Metal Oxide Catalysts

    NASA Astrophysics Data System (ADS)

    Qian, Yang; Xiang, Rong; An, Hua; Inoue, Taiki; Chiashi, Shohei; Maruyama, Shigeo

    We report on the growth of single-walled carbon nanotubes (SWNTs) from Co oxide catalysts. The concept is using the relatively lower mobility of metal oxide (than metal) to suppress catalyst aggregation at high temperatures. Compared to the SWNTs grown by pre-reduced catalysts, SWNTs grown from oxidized Co catalysts have shown narrower diameter distribution and smaller average diameter. Different growth parameters are discussed regarding the resulting morphology of SWNTs. Transmission electron microscopy (TEM) investigations reveal the information that Co catalysts are transformed to Co3O4 after reduction-calcination process. X-ray photoelectron spectroscopy (XPS) investigations indicate that Co3O4 has decomposed to CoO before growth at a typical growth temperature (800 ºC) in Ar atmosphere. We propose that CoO has higher melting point than Co and thus is more stable during the growth. Our results indicate that besides the bimetallic catalysts, monometallic catalytic system could also be useful in stabilizing the catalysts to grow chirality-specific SWNTs by transforming the relatively low melting point metal catalysts to high melting point metal oxide catalysts. Yang Qian was supported through ``Global Leader Program for Social Design and Management''.

  15. Catalyst activator

    DOEpatents

    McAdon, Mark H.; Nickias, Peter N.; Marks, Tobin J.; Schwartz, David J.

    2001-01-01

    A catalyst activator particularly adapted for use in the activation of metal complexes of metals of Group 3-10 for polymerization of ethylenically unsaturated polymerizable monomers, especially olefins, comprising two Group 13 metal or metalloid atoms and a ligand structure including at least one bridging group connecting ligands on the two Group 13 metal or metalloid atoms.

  16. Dechlorination of Polychlorinated Biphenyls by Pd/Mg Bimetallic Corrosion Nano-Cells

    EPA Science Inventory

    Polychlorinated biphenyls (PCBs), manufactured until mid-1970's for use as electrical insulators, were banned in 1979 due to their toxicity and persistence in the environment (1). Dechlorination of PCBs using bimetallic systems is a promising technology wherein enhanced corrosio...

  17. Levelling the playing field: screening for synergistic effects in coalesced bimetallic nanoparticles.

    PubMed

    Tan, Rachel Lee Siew; Song, Xiaohui; Chen, Bo; Chong, Wen Han; Fang, Yin; Zhang, Hua; Wei, Jun; Chen, Hongyu

    2016-02-14

    Depending on the synthetic methods, bimetallic nanoparticles can have either core-shell, phase segregated, alloy, or partially coalesced structures, presenting different degrees of atomic mixing on their surface. Along with the variations of size and morphology, the structural differences make it difficult to compare the catalytic activity of bimetallic nanoparticles. In this article, we developed a facile screening method that can focus on the synergistic effects rather than structural differences. Prefabricated nanoparticles are mixed together to form linear aggregates and coalesced to form bimetallic junctions. Their hollow silica shells allow materials transport but prevent further aggregation. With a level playing field, this screening platform can identify the best bimetallic combination for a catalytic reaction, before optimizing the synthesis. This approach is more advantageous than the conventional approaches where structural difference may have dominant effects on the catalytic performance. PMID:26797095

  18. Chemistry of Bimetallic Linked Cyclopentadienyl Complexes: Progress Report, 1 December 1986 --30 November 1989

    DOE R&D Accomplishments Database

    Schrock, R. R.

    1989-01-01

    Research continued on the chemistry and preparation of bimetallic cyclopentadienyl complexes containing up to two tungsten or one tungsten and a cobalt, rhodium, or ruthenium. The general method for preparation and analysis of polyenes is also discussed. (CBS)

  19. Nonchromophoric halide ligand variation in polyazine-bridged Ru(II),Rh(III) bimetallic supramolecules offering new insight into photocatalytic hydrogen production from water.

    PubMed

    Rogers, Hannah Mallalieu; White, Travis A; Stone, Brittany N; Arachchige, Shamindri M; Brewer, Karen J

    2015-04-01

    The new bimetallic complex [(Ph2phen)2Ru(dpp)RhBr2(Ph2phen)](PF6)3 (1) (Ph2phen = 4,7-diphenyl-1,10-phenanthroline; dpp = 2,3-bis(2-pyridyl)pyrazine) was synthesized and characterized to compare with the Cl(-) analogue [(Ph2phen)2Ru(dpp)RhCl2(Ph2phen)](PF6)3 (2) in an effort to better understand the role of halide coordination at the Rh metal center in solar H2 production schemes. Electrochemical properties of complex 1 display a reversible Ru(II/III) oxidation, and cathodic scans indicate multiple electrochemical mechanisms exist to reduce Rh(III) by two electrons to Rh(I) followed by a quasi-reversible dpp(0/-) ligand reduction. The weaker σ-donating ability of Br(-) vs Cl(-) impacts the cathodic electrochemistry and provides insight into photocatalytic function by these bimetallic supramolecules. Complexes 1 and 2 exhibit identical light-absorbing properties with UV absorption dominated by intraligand (IL) π → π* transitions and visible absorption by metal-to-ligand charge transfer (MLCT) transitions to include a lowest energy Ru(dπ) → dpp(π*) (1)MLCT transition (λ(abs) = 514 nm; ε = 16 000 M(-1) cm(-1)). The relatively short-lived, weakly emissive Ru(dπ) → dpp(π*) (3)MLCT excited state (τ = 46 ns) for both bimetallic complexes is attributed to intramolecular electron transfer from the (3)MLCT excited state to populate a low-energy Ru(dπ) → Rh(dσ*) triplet metal-to-metal charge transfer ((3)MMCT) excited state that allows photoinitiated electron collection. Complex 1 outperforms the related Cl(-) bimetallic analogue 2 as a H2 photocatalyst despite identical light-absorbing and excited-state properties. Additional H2 experiments with added halide suggest ion pairing plays a role in catalyst deactivation and provides new insight into observed differences in H2 production upon halide variation in Ru(II),Rh(III) supramolecular architectures.

  20. Zircon Supported Copper Catalysts for the Steam Reforming of Methanol

    NASA Astrophysics Data System (ADS)

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

    2008-03-01

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

  1. Levelling the playing field: screening for synergistic effects in coalesced bimetallic nanoparticles

    NASA Astrophysics Data System (ADS)

    Tan, Rachel Lee Siew; Song, Xiaohui; Chen, Bo; Chong, Wen Han; Fang, Yin; Zhang, Hua; Wei, Jun; Chen, Hongyu

    2016-02-01

    Depending on the synthetic methods, bimetallic nanoparticles can have either core-shell, phase segregated, alloy, or partially coalesced structures, presenting different degrees of atomic mixing on their surface. Along with the variations of size and morphology, the structural differences make it difficult to compare the catalytic activity of bimetallic nanoparticles. In this article, we developed a facile screening method that can focus on the synergistic effects rather than structural differences. Prefabricated nanoparticles are mixed together to form linear aggregates and coalesced to form bimetallic junctions. Their hollow silica shells allow materials transport but prevent further aggregation. With a level playing field, this screening platform can identify the best bimetallic combination for a catalytic reaction, before optimizing the synthesis. This approach is more advantageous than the conventional approaches where structural difference may have dominant effects on the catalytic performance.Depending on the synthetic methods, bimetallic nanoparticles can have either core-shell, phase segregated, alloy, or partially coalesced structures, presenting different degrees of atomic mixing on their surface. Along with the variations of size and morphology, the structural differences make it difficult to compare the catalytic activity of bimetallic nanoparticles. In this article, we developed a facile screening method that can focus on the synergistic effects rather than structural differences. Prefabricated nanoparticles are mixed together to form linear aggregates and coalesced to form bimetallic junctions. Their hollow silica shells allow materials transport but prevent further aggregation. With a level playing field, this screening platform can identify the best bimetallic combination for a catalytic reaction, before optimizing the synthesis. This approach is more advantageous than the conventional approaches where structural difference may have dominant

  2. Studies of Heterogeneous Catalyst Selectivity and Stability for Biorefining Applications

    NASA Astrophysics Data System (ADS)

    O'Neill, Brandon J.

    The conversion of raw resources into value-added end products has long underlain the importance of catalysts in economic and scientific development. In particular, the development of selective and stable heterogeneous catalysts is a challenge that continues to grow in importance as environmental, sociological, and economic concerns have motivated an interest in sustainability and the use of renewable raw materials. Within this context, biomass has been identified as the only realistic source of renewable carbon for the foreseeable future. The development of processes to utilize biomass feedstocks will require breakthroughs in fundamental understanding and practical solutions to the challenges related to selectivity and stability of the catalysts employed. Selectivity is addressed on multiple fronts. First, the selectivity for C-O bond scission reactions of a bifunctional, bimetallic RhRe/C catalyst is investigated. Using multiple techniques, the origin of Bronsted acidity in the catalyst and the role of pretreatment on the activity, selectivity, and stability are explored. In addition, reaction kinetics experiments and kinetic modeling are utilized to understand the role of chemical functional group (i.e. carboxylic acid versus formate ester) in determining the decarbonylation versus decarboxylation selectivity over a Pd/C catalyst. Finally, kinetic studies over Pd/C and Cu/gamma-Al2O3 were performed so that that may be paired with density functional theory calculations and microkinetic modeling to elucidate the elementary reaction mechanism, identify the active site, and provide a basis for future rational catalyst design. Next, the issue of catalyst stability, important in the high-temperature, liquid-phase conditions of biomass processing, is examined, and a method for stabilizing the base-metal nanoparticles of a Cu/gamma-Al2O 3 catalyst using atomic layer deposition (ALD) is developed. This advancement may facilitate the development of biorefining by enabling

  3. Transformation of sodium bicarbonate and CO2 into sodium formate over NiPd nanoparticle catalyst

    PubMed Central

    Wang, Mengnan; Zhang, Jiaguang; Yan, Ning

    2013-01-01

    The present research systematically investigated, for the first time, the transformation of sodium bicarbonate and CO2 into sodium formate over a series of Ni based metal nanoparticles (NPs). Ni NPs and eight NiM (M stands for a second metal) NPs were prepared by a facile wet chemical process and then their catalytic performance were evaluated in sodium bicarbonate hydrogenation. Bimetallic NiPd NPs with a composition of 7:3 were found to be superior for this reaction, which are more active than both pure Ni and Pd NPs. Hot filtration experiment suggested the NPs to be the truly catalytic active species and kinetic analysis indicated the reaction mechanism to be different than most homogeneous catalysts. The enhanced activity of the bimetallic nanoparticles may be attributed to their smaller size and improved stability. PMID:24790945

  4. Transformation of Sodium Bicarbonate and CO2 into Sodium Formate over NiPd Nanoparticle Catalyst

    NASA Astrophysics Data System (ADS)

    Wang, Mengnan; Zhang, Jiaguang; Yan, Ning

    2013-09-01

    The present research systematically investigated, for the first time, the transformation of sodium bicarbonate and CO2 into sodium formate over a series of Ni based metal nanoparticles (NPs). Ni NPs and eight NiM (M stands for a second metal) NPs were prepared by a facile wet chemical process and then their catalytic performance were evaluated in sodium bicarbonate hydrogenation. Bimetallic NiPd NPs with a composition of 7:3 were found to be superior for this reaction, which are more active than both pure Ni and Pd NPs. Hot filtration experiment suggested the NPs to be the truly catalytic active species and kinetic analysis indicated the reaction mechanism to be different than most homogeneous catalysts. The enhanced activity of the bimetallic nanoparticles may be attributed to their smaller size and improved stability.

  5. Preparation of Supported Metal Catalysts by Atomic and Molecular Layer Deposition for Improved Catalytic Performance

    NASA Astrophysics Data System (ADS)

    Gould, Troy D.

    Creating catalysts with enhanced selectivity and activity requires precise control over particle shape, composition, and size. Here we report the use of atomic layer deposition (ALD) to synthesize supported Ni, Pt, and Ni-Pt catalysts in the size regime (< 3 nm) where nanoscale properties can have a dramatic effect on reaction activity and selectivity. This thesis presents the first ALD synthesis of non-noble metal nanoparticles by depositing Ni on Al2O3 with two half-reactions of Ni(Cp)2 and H2. By changing the number of ALD cycles, Ni weight loadings were varied from 4.7 wt% to 16.7 wt% and the average particle sizes ranged from 2.5 to 3.3 nm, which increased the selectivity for C 3H6 hydrogenolysis by an order of magnitude over a much larger Ni/Al2O3 catalyst. Pt particles were deposited by varying the number of ALD cycles and the reaction chemistry (H2 or O 2) to control the particle size from approximately 1 to 2 nm, which allowed lower-coordinated surface atoms to populate the particle surface. These Pt ALD catalysts demonstrated some of the highest oxidative dehydrogenation of propane selectivities (37%) of a Pt catalyst synthesized by a scalable technique. Dry reforming of methane (DRM) is a reaction of interest due to the recent increased recovery of natural gas, but this reaction is hindered from industrial implementation because the Ni catalysts are plagued by deactivation from sintering and coking. This work utilized Ni ALD and NiPt ALD catalysts for the DRM reaction. These catalysts did not form destructive carbon whiskers and had enhanced reaction rates due to increased bimetallic interaction. To further limit sintering, the Ni and NiPt ALD catalysts were coated with a porous alumina matrix by molecular layer deposition (MLD). The catalysts were evaluated for DRM at 973 K, and the MLD-coated Ni catalysts outperformed the uncoated Ni catalysts in either activity (with 5 MLD cycles) or stability (with 10 MLD cycles). In summary, this thesis developed a

  6. Selective hydrogenation of butadiene over TiO2 supported copper, gold and gold-copper catalysts prepared by deposition-precipitation.

    PubMed

    Delannoy, Laurent; Thrimurthulu, Gode; Reddy, Padigapati S; Méthivier, Christophe; Nelayah, Jaysen; Reddy, Benjaram M; Ricolleau, Christian; Louis, Catherine

    2014-12-28

    Oxide supported copper and gold catalysts are active for the selective hydrogenation of polyunsaturated hydrocarbons but their low activity compared to palladium catalysts and the deactivation of copper catalysts limit their use. There are only a very limited number of studies concerned with the use of bimetallic Au-Cu catalysts for selective hydrogenation reactions and the aim of this work was to prepare TiO2-supported monometallic Au and Cu and bimetallic AuCu (Cu/Au atomic ratio of 1 and 3) catalysts and to evaluate their catalytic performance in the selective hydrogenation of butadiene. Small gold, copper and gold-copper nanoparticles (average particle size < 2 nm) were obtained on TiO2 using the preparation method of deposition-precipitation with urea followed by reduction under H2 at 300 °C. Very small clusters were observed for Cu/TiO2 (∼1 nm) which might result from O2 induced copper redispersion, as also supported by the XPS analyses. The alloying of copper with gold was found to inhibit its redispersion and also limits its reoxidation, as attested by XPS. The bimetallic character of the AuCu nanoparticles was confirmed by XPS and EDX-HAADF. Cu/TiO2 was initially more active than Au/TiO2 in the selective hydrogenation of butadiene at 75 °C but it deactivated rapidly during the first hours of reaction whereas the gold catalyst was very stable up to 20 hours of reaction. The bimetallic AuCu/TiO2 catalysts displayed an activation period during the first hours of the reaction, which was very pronounced for the sample containing a higher Cu/Au atomic ratio. This initial gain in activity was tentatively assigned to copper segregation at the surface of the bimetallic nanoparticles, induced by the reactants. When the AuCu/TiO2 catalysts were pre-exposed to air at 75 °C before butadiene hydrogenation, surface copper segregation occurred, leading to higher initial activity and the suppression of the activation period. Under the same conditions, Cu/TiO2 totally

  7. Chemisorption effects on the spatial atomic distribution of bimetallic nanostructures

    NASA Astrophysics Data System (ADS)

    Montejano-Carrizales, J. M.; Morán-López, J. L.

    1992-04-01

    The spatial atomic distribution in icosahedral and cubo-octahedral bimetallic clusters with a total number of atoms, N=55 and 147, in the presence of chemisorbed species, is studied. The equilibrium atomic configuration is obtained by calculating the free energy within the regular solution model and by assuming that the surface of the cluster is covered by chemisorbed atoms. Depending on the interaction between chemisorbed species and the cluster components, the atomic distribution in the cluster can be completely modified as compared to the case of clusters with a clean surface. Applications to the chemisorption of H and O on CuNi, CuPd, and NiPt clusters are discussed. We present results for the temperature dependence of the concentration at the different shells around the central atom.

  8. Segregation and shape stability in small bimetallic particles

    NASA Astrophysics Data System (ADS)

    Morán-López, J. L.; Balseiro, C. A.

    1986-04-01

    The equilibrium atomic spatial distribution of a 55-atom bimetallic particle is studied within the regular solution model. As a consequence of the large surface-to-volume ratio, the criterion for phase separation versus long-range ordering in small particles and in infinite systems differs considerably. With the comparison of the total energies in cubo-octahedral (C) and icosahedral (I) particles, a phase diagram for the ground state is obtained. As a function of temperature the particle may change its shape from C to I. We applied the theory, based on estimations from bulk properties, to the CuPd and the IrPd particles, and present results for the temperature dependence of the average concentrations at the different shells around the central atom. On the same basis some predictions for the NiPt, CuPt, AuPt, and the CuNi systems are made.

  9. Synthesis and characterization of carboxyethylene-bridged bimetallic compounds

    SciTech Connect

    Gibson, D.H.; Franco, J.O.; Mehta, J.M.; Harris, M.T.; Ding, Y.; Mashuta, M.S.; Richardson, J.F.

    1995-11-01

    The synthesis and characterization of carboxyethylene-bridged bimetallic complexes Cp{sup *}Re(CO)(NO)CO{sub 2}CH{sub 2}CH{sub 2}M (4, M = Mo(CO){sub 3}Cp; 7, M = W(CO){sub 3}Cp; 9, M = Fe(CO){sub 2}Cp) and CpFe(CO)(PPh{sub 3})CO{sub 2}CH{sub 2}CH{sub 2}W(CO){sub 3}Cp (11) are described. Thermolysis of 4, in solution or in the solid state, yields the CO{sub 2}-bridged compound Cp{sup *}Re(CO)(NO)(CO{sub 2} )Mo(CO){sub 2}Cp (3) as the major product. Compound 11 has been structurally characterized. Crystal data for 11 are reported. 16 refs., 1 fig., 3 tabs.

  10. Reduced graphene oxide nanosheets decorated with Au-Pd bimetallic alloy nanoparticles towards efficient photocatalytic degradation of phenolic compounds in water

    NASA Astrophysics Data System (ADS)

    Darabdhara, Gitashree; Boruah, Purna K.; Borthakur, Priyakshree; Hussain, Najrul; Das, Manash R.; Ahamad, Tansir; Alshehri, Saad M.; Malgras, Victor; Wu, Kevin C.-W.; Yamauchi, Yusuke

    2016-04-01

    Reduced graphene oxide nanosheets decorated with Au-Pd bimetallic alloy nanoparticles are successfully prepared via a chemical approach consisting of reducing the metal precursors using ascorbic acid as reductant at an elevated temperature. The prepared nanocomposite is employed as a photocatalyst for the degradation of organic contaminants such as phenol, 2-chlorophenol (2-CP), and 2-nitrophenol (2-NP). The complete degradation of phenol is achieved after 300 min under natural sunlight irradiation whereas the degradation of 2-CP and 2-NP is completed after 180 min. The activity of the photocatalyst is evaluated considering several parameters such as the initial phenol concentration, the photocatalyst loading, and the pH of the solution. The degradation kinetics of all the compounds is carefully studied and found to follow a linear Langmuir-Hinshelwood model. Furthermore, the reusability of the photocatalyst is successfully achieved up to five cycles and the catalyst exhibits an excellent stability.Reduced graphene oxide nanosheets decorated with Au-Pd bimetallic alloy nanoparticles are successfully prepared via a chemical approach consisting of reducing the metal precursors using ascorbic acid as reductant at an elevated temperature. The prepared nanocomposite is employed as a photocatalyst for the degradation of organic contaminants such as phenol, 2-chlorophenol (2-CP), and 2-nitrophenol (2-NP). The complete degradation of phenol is achieved after 300 min under natural sunlight irradiation whereas the degradation of 2-CP and 2-NP is completed after 180 min. The activity of the photocatalyst is evaluated considering several parameters such as the initial phenol concentration, the photocatalyst loading, and the pH of the solution. The degradation kinetics of all the compounds is carefully studied and found to follow a linear Langmuir-Hinshelwood model. Furthermore, the reusability of the photocatalyst is successfully achieved up to five cycles and the catalyst

  11. Catalyst suppliers consolidate further, offer more catalysts

    SciTech Connect

    Rhodes, A.K.

    1995-10-02

    The list of suppliers of catalysts to the petroleum refining industry has decreased by five since Oil and Gas Journal`s survey of refining catalysts and catalytic additives was last published. Despite the consolidation, the list of catalyst designations has grown to about 950 in this latest survey, compared to 820 listed in 1993. The table divides the catalysts by use and gives data on their primary differentiating characteristics, feedstock, products, form, bulk density,catalyst support, active agents, availability, and manufactures.

  12. Fine particle clay catalysts for coal liquefaction

    SciTech Connect

    Olson, E.S.

    1991-01-01

    The efficient production of environmentally acceptable distillate fuels requires catalysts for hydrogenation and cleavage of the coal macromolecules and removal of oxygen, nitrogen, and sulfur heteroatoms. The goal of the proposed research is to develop new catalysts for the direct liquefaction of coal. This type of catalyst consists of fine clay particles that have been treated with reagents which form pillaring structures between the aluminosilicate layers of the clay. The pillars not only hold the layers apart but also constitute the active catalytic sites for hydrogenation of the coal and the solvent used in the liquefaction. The pillaring catalytic sites are composed of pyrrhotite, which has been previously demonstrated to be active for coal liquefaction. The pyrrhotite sites are generated in situ by sulfiding the corresponding oxyiron species. The size of the catalyst will be less than 40 nm in order to promote intimate contact with the coal material. Since the clays and reagents for pillaring and activating the clays are inexpensive, the catalysts can be discarded after use, rather than regenerated by a costly process. The proposed work will evaluate methods for preparing the fine particle iron-pillared clay dispersions and for activating the particles to generate the catalysts. Characterization studies of the pillared clays and activated catalysts will be performed. The effectiveness of the pillared clay dispersion for hydrogenation and coal liquefaction will be determined in several types of testing.

  13. Fine particle clay catalysts for coal liquefaction

    SciTech Connect

    Olson, E.S.

    1991-01-01

    The efficient production of environmentally acceptable distillate fuels requires catalysts for hydrogenation and cleavage of the coal macromolecules and removal of oxygen, nitrogen, and sulfur heteroatoms. The goal of the proposed research is to develop new catalysts for the direct liquefaction of coal. This type of catalyst consists of fine clay particles that have been treated with reagents which form pillaring structures between the aluminosilicate layers of the clay. The pillars not only hold the layers apart but also constitute the active catalytic sites for hydrogenation of the coal and solvent used in the liquefaction. The pillaring catalytic sites are composed of pyrrhotite, which has been previously demonstrated to be active for coal liquefaction. The pyrrhotite sites are generated in situ by sulfiding the corresponding oxyiron species. The size of the catalyst will be less than 40 nm in order to promote intimate contact with the coal material. Since the clays and reagents for pillaring and activating the clays are inexpensive, the catalysts can be discarded after use, rather than regenerated by a costly process. The proposed work will evaluate methods for preparing the fine particle iron-pillared clay dispersions and for activating the particles to generate the catalysts. Characterization studies of the pillared clays and activated catalysts will performed. The effectiveness of the pillared clay dispersion for hydrogenation and coal liquefaction will be determined in several types of testing. 5 refs., 1 tab.

  14. Ocular dispersion

    NASA Astrophysics Data System (ADS)

    Hammer, Daniel X.; Noojin, Gary D.; Thomas, Robert J.; Stolarski, David J.; Rockwell, Benjamin A.; Welch, Ashley J.

    1999-06-01

    Spectrally resolved white-light interferometry (SRWLI) was used to measure the wavelength dependence of refractive index (i.e., dispersion) for various ocular components. The accuracy of the technique was assessed by measurement of fused silica and water, the refractive indices of which have been measured at several different wavelengths. The dispersion of bovine and rabbit aqueous and vitreous humor was measured from 400 to 1100 nm. Also, the dispersion was measured from 400 to 700 nm for aqueous and vitreous humor extracted from goat and rhesus monkey eyes. For the humors, the dispersion did not deviate significantly from water. In an additional experiment, the dispersion of aqueous and vitreous humor that had aged up to a month was compared to freshly harvested material. No difference was found between the fresh and aged media. An unsuccessful attempt was also made to use the technique for dispersion measurement of bovine cornea and lens. Future refinement may allow measurement of the dispersion of cornea and lens across the entire visible and near-infrared wavelength band. The principles of white- light interferometry including image analysis, measurement accuracy, and limitations of the technique, are discussed. In addition, alternate techniques and previous measurements of ocular dispersion are reviewed.

  15. Development of Novel Supported Gold Catalysts: A Materials Perspective

    SciTech Connect

    Dai, Sheng; Ma, Zhen

    2011-01-01

    Since Haruta et al. discovered that small gold nanoparticles finely dispersed on certain metal oxide supports can exhibit surprisingly high activity in CO oxidation below room temperature, heterogeneous catalysis by supported gold nanoparticles has attracted tremendous attention. The majority of publications deal with the preparation and characterization of conventional gold catalysts (e.g., Au/TiO{sub 2}), the use of gold catalysts in various catalytic reactions, as well as elucidation of the nature of the active sites and reaction mechanisms. In this overview, we highlight the development of novel supported gold catalysts from a materials perspective. Examples, mostly from those reported by our group, are given concerning the development of simple gold catalysts with single metal-support interfaces and heterostructured gold catalysts with complicated interfacial structures. Catalysts in the first category include active Au/SiO{sub 2} and Au/metal phosphate catalysts, and those in the second category include catalysts prepared by pre-modification of supports before loading gold, by post-modification of supported gold catalysts, or by simultaneous dispersion of gold and an inorganic component onto a support. CO oxidation has generally been employed as a probe reaction to screen the activities of these catalysts. These novel gold catalysts not only provide possibilities for applied catalysis, but also furnish grounds for fundamental research.

  16. Fabrication of Cu-Ag core-shell bimetallic superfine powders by eco-friendly reagents and structures characterization

    SciTech Connect

    Zhao Jun; Zhang Dongming; Zhao Jie

    2011-09-15

    Superfine bimetallic Cu-Ag core-shell powders were synthesized by reduction of copper sulfate pentahydrate and silver nitrate with eco-friendly ascorbic acid as a reducing agent and cyclodextrins as a protective agent in an aqueous system. The influence of Ag/Cu ratio on coatings was investigated. Ag was homogeneously distributed on the surface of Cu particles at a mole ratio of Ag/Cu=1. FE-SEM showed an uniformity of Ag coatings on Cu particles. Antioxidation of Cu particles was improved by increasing Ag/Cu ratio. TEM-EDX and UV-vis spectra also revealed that Cu cores were covered by Ag nanoshells on the whole. The surface composition analysis by XPS indicated that only small parts of Cu atoms in the surface were oxidized. It was noted that the hindrance of cyclodextrins chemisorbed on particles plays an important role in forming high quality and good dispersity Cu-Ag (Cu-Ag) core-shell powders. - Graphical abstract: Mechanism of fabricating Cu-Ag particles with good dispersibility using {beta}-CDs as a protective agent was studied because of its special structure. Highlights: > Green supramolecular {beta}-CD used as a protective agent and ascorbic acid(Vc) as a reducing agent to fabricate Cu-Ag powders. > Particles are monodisperse and the diameter is close to nanoscale(100-150 nm). > Resistance of Cu particles to oxidation was higher. > Formation mechanism explained.

  17. DNA-templated synthesis of PtAu bimetallic nanoparticle/graphene nanocomposites and their application in glucose biosensor

    PubMed Central

    2014-01-01

    In this paper, single-stranded DNA (ss-DNA) is demonstrated to functionalize graphene (GR) and to further guide the growth of PtAu bimetallic nanoparticles (PtAuNPs) on GR with high densities and dispersion. The obtained nanocomposites (PtAuNPs/ss-DNA/GR) were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDS), and electrochemical techniques. Then, an enzyme nanoassembly was prepared by self-assembling glucose oxidase (GOD) on PtAuNP/ss-DNA/GR nanocomposites (GOD/PtAuNPs/ss-DNA/GR). The nanocomposites provided a suitable microenvironment for GOD to retain its biological activity. The direct and reversible electron transfer process between the active site of GOD and the modified electrode was realized without any extra electron mediator. Thus, the prepared GOD/PtAuNP/ss-DNA/GR electrode was proposed as a biosensor for the quantification of glucose. The effects of pH, applied potential, and temperature on the performance of the biosensor were discussed in detail and were optimized. Under optimal conditions, the biosensor showed a linearity with glucose concentration in the range of 1.0 to 1,800 μM with a detection limit of 0.3 μM (S/N = 3). The results demonstrate that the developed approach provides a promising strategy to improve the sensitivity and enzyme activity of electrochemical biosensors. PMID:24572068

  18. DNA-templated synthesis of PtAu bimetallic nanoparticle/graphene nanocomposites and their application in glucose biosensor

    NASA Astrophysics Data System (ADS)

    Leng, Jing; Wang, Wen-Min; Lu, Li-Min; Bai, Ling; Qiu, Xin-Lan

    2014-02-01

    In this paper, single-stranded DNA (ss-DNA) is demonstrated to functionalize graphene (GR) and to further guide the growth of PtAu bimetallic nanoparticles (PtAuNPs) on GR with high densities and dispersion. The obtained nanocomposites (PtAuNPs/ss-DNA/GR) were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectrometer (EDS), and electrochemical techniques. Then, an enzyme nanoassembly was prepared by self-assembling glucose oxidase (GOD) on PtAuNP/ss-DNA/GR nanocomposites (GOD/PtAuNPs/ss-DNA/GR). The nanocomposites provided a suitable microenvironment for GOD to retain its biological activity. The direct and reversible electron transfer process between the active site of GOD and the modified electrode was realized without any extra electron mediator. Thus, the prepared GOD/PtAuNP/ss-DNA/GR electrode was proposed as a biosensor for the quantification of glucose. The effects of pH, applied potential, and temperature on the performance of the biosensor were discussed in detail and were optimized. Under optimal conditions, the biosensor showed a linearity with glucose concentration in the range of 1.0 to 1,800 μM with a detection limit of 0.3 μM (S/N = 3). The results demonstrate that the developed approach provides a promising strategy to improve the sensitivity and enzyme activity of electrochemical biosensors.

  19. Activation of catalysts for synthesizing methanol from synthesis gas

    DOEpatents

    Blum, David B.; Gelbein, Abraham P.

    1985-01-01

    A method for activating a methanol synthesis catalyst is disclosed. In this method, the catalyst is slurried in an inert liquid and is activated by a reducing gas stream. The activation step occurs in-situ. That is, it is conducted in the same reactor as is the subsequent step of synthesizing methanol from a methanol gas stream catalyzed by the activated catalyst still dispersed in a slurry.

  20. Dehalogenation of Polybrominated Diphenyl Ethers and Polychlorinated Biphenyl by Bimetallic, Impregnated, and Nanoscale Zerovalent Iron

    PubMed Central

    Zhuang, Yuan; Ahn, Sungwoo; Seyfferth, Angelia L.; Masue-Slowey, Yoko; Fendorf, Scott; Luthy, Richard G.

    2011-01-01

    Nanoscale zerovalent iron particles (nZVI), bimetallic nanoparticles (nZVI/Pd), and nZVI/Pd impregnated activated carbon (nZVI/Pd-AC) composite particles were synthesized and investigated for their effectiveness to remove polybrominated diphenyl ethers (PBDEs) and/or polychlorinated biphenyls (PCBs). Palladization of nZVI promoted the dehalogenation kinetics for mono- to tri-BDEs and 2,3,4-trichlorobiphenyl (PCB 21). Compared to nZVI, the iron-normalized rate constants for nZVI/Pd were about 2-, 3-, and 4-orders of magnitude greater for tri-, di-, and mono-BDEs, respectively, with diphenyl ether as a main reaction product. The reaction kinetics and pathways suggest an H-atom transfer mechanism. The reaction pathways with nZVI/Pd favor preferential removal of para-halogens on PBDEs and PCBs. X-ray fluorescence mapping of nZVI/Pd-AC showed that Pd mainly deposits on the outer part of particles, while Fe was present throughout the activated carbon particles. While BDE 21 was sorbed onto activated carbon composites quickly, debromination was slower compared to reaction with freely dispersed nZVI/Pd. Our XPS and chemical data suggest about 7% of the total iron within the activated carbon was zero-valent, which shows the difficulty with in-situ synthesis of a significant fraction of zero-valent iron in the micro-porous material. Related factors that likely hinder the reaction with nZVI/Pd-AC are the heterogenous distribution of nZVI and Pd on activated carbon and/or immobilization of hydrophobic organic contaminants at the adsorption sites thereby inhibiting contact with nZVI. PMID:21557574

  1. Nickel/ruthenium catalyst and method for aqueous phase reactions

    DOEpatents

    Elliott, Douglas C.; Sealock, John L.

    1998-01-01

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

  2. Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials.

    PubMed

    Bedford, Nicholas M; Showalter, Allison R; Woehl, Taylor J; Hughes, Zak E; Lee, Sungsik; Reinhart, Benjamin; Ertem, S Piril; Coughlin, E Bryan; Ren, Yang; Walsh, Tiffany R; Bunker, Bruce A

    2016-09-27

    Bimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when two different metallic species are mixed at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesized with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy, and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods was then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence dependence in both surface structure and surface composition. Replica exchange with solute tempering molecular dynamics simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces via different mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be leveraged

  3. Kinetics and mechanism of the heterogeneous catalyzed oxidative decolorization of Acid-Blue 92 using bimetallic metal-organic frameworks

    NASA Astrophysics Data System (ADS)

    El-sharkawy, Rehab G.; El-din, Ahmed S. Badr; Etaiw, Safaa El-din H.

    2011-09-01

    The kinetics study of the oxidative decolorization of Acid-Blue 92 has been investigated by hydrogen peroxide catalyzed with bimetallic metal-organic frameworks. The used metal-organic frameworks (MOF) are [Ph 3SnCu(CN) 2·L] where L = pyrazine (pyz) 1, methylpyrazine (mepyz) 2, 4,4'-bipyridine (bpy) 3, trans-1,2-bis(4-pyridyl)ethene (tbpe) 4 or 1,2-bis(4-pyridyl)ethane (bpe) 5. The reaction was followed by conventional UV-Vis spectrophotometer at λmax = 571 nm. The reaction exhibited first-order kinetics with respect to [dye] and [H 2O 2]. The reactivity of the catalysts depends on the type of the medium and thereafter decreases in strong alkaline media. Addition of NaCl enhances the reaction rate. Also, the irradiation of the reaction with UV-light enhanced the rate of AB-92 mineralization by about 86.9%. The reaction was entropy-controlled as confirmed by the isokinetic relationship. A reaction mechanism was proposed with the formation of free radicals as an oxidant.

  4. Fe-Mn bi-metallic oxides loaded on granular activated carbon to enhance dye removal by catalytic ozonation.

    PubMed

    Tang, Shoufeng; Yuan, Deling; Zhang, Qi; Liu, Yameng; Zhang, Qi; Liu, Zhengquan; Huang, Haiming

    2016-09-01

    A Fe-Mn bi-metallic oxide supported on granular activated carbon (Fe-Mn GAC) has been fabricated by an impregnation-desiccation method and tested in the catalytic ozonation of methyl orange (MO) degradation and mineralization. X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy characterizations revealed that Fe-Mn oxides were successfully loaded and uniformly distributed on the GAC, and nitrogen adsorption isotherms showed that the supported GAC retained a large surface area and a high pore volume compared with the pristine GAC. The catalytic activity was systematically assessed by monitoring the MO removal efficiencies at different operational parameters, such as catalyst dosage, initial solution pH, and ozone flow rate. The Fe-Mn GAC exhibited better catalytic activity relative to ozone alone and GAC alone, improving the TOC removal by 24.5 and 11.5 % and COD removal by 13.6 and 7.3 %, respectively. The reusability of the hybrid was examined over five consecutive cyclic treatments. The Fe-Mn GAC catalytic activity was only a slight loss in the cycles, showing good stability. The addition of Na2CO3 as hydroxyl radicals (•OH) scavengers proved that the catalytic ozonation mechanism was the enhanced generation of •OH by the Fe-Mn GAC. The above results render the Fe-Mn GAC an industrially promising candidate for catalytic ozonation of dye contaminant removal.

  5. Fe-Mn bi-metallic oxides loaded on granular activated carbon to enhance dye removal by catalytic ozonation.

    PubMed

    Tang, Shoufeng; Yuan, Deling; Zhang, Qi; Liu, Yameng; Zhang, Qi; Liu, Zhengquan; Huang, Haiming

    2016-09-01

    A Fe-Mn bi-metallic oxide supported on granular activated carbon (Fe-Mn GAC) has been fabricated by an impregnation-desiccation method and tested in the catalytic ozonation of methyl orange (MO) degradation and mineralization. X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy characterizations revealed that Fe-Mn oxides were successfully loaded and uniformly distributed on the GAC, and nitrogen adsorption isotherms showed that the supported GAC retained a large surface area and a high pore volume compared with the pristine GAC. The catalytic activity was systematically assessed by monitoring the MO removal efficiencies at different operational parameters, such as catalyst dosage, initial solution pH, and ozone flow rate. The Fe-Mn GAC exhibited better catalytic activity relative to ozone alone and GAC alone, improving the TOC removal by 24.5 and 11.5 % and COD removal by 13.6 and 7.3 %, respectively. The reusability of the hybrid was examined over five consecutive cyclic treatments. The Fe-Mn GAC catalytic activity was only a slight loss in the cycles, showing good stability. The addition of Na2CO3 as hydroxyl radicals (•OH) scavengers proved that the catalytic ozonation mechanism was the enhanced generation of •OH by the Fe-Mn GAC. The above results render the Fe-Mn GAC an industrially promising candidate for catalytic ozonation of dye contaminant removal. PMID:27316651

  6. Ion irradiation synthesis of Ag–Au bimetallic nanospheroids in SiO{sub 2} glass substrate with tunable surface plasmon resonance frequency

    SciTech Connect

    Meng, Xuan; Yu, Ruixuan; Takayanagi, Shinya; Shibayama, Tamaki; Watanabe, Seiichi

    2013-08-07

    Ag–Au bimetallic nanospheroids with tunable localized surface plasmon resonance (LSPR) were synthesized by 100 keV Ar–ion irradiation of 30 nm Ag–Au bimetallic films deposited on SiO{sub 2} glass substrates. A shift of the LSPR peaks toward shorter wavelengths was observed up to an irradiation fluence of 1.0 × 10{sup 17} cm{sup −2}, and then shifted toward the longer wavelength because of the increase of fragment volume under ion irradiation. Further control of LSPR frequency over a wider range was realized by modifying the chemical components. The resulting LSPR frequencies lie between that of the pure components, and an approximate linear shift of the LSPR toward the longer wavelength with the Au concentration was achieved, which is in good agreement with the theoretical calculations based on Gans theory. In addition, the surface morphology and compositions were examined with a scanning electron microscope equipped with an energy dispersive spectrometer, and microstructural characterizations were performed using a transmission electron microscope. The formation of isolated photosensitive Ag–Au nanospheroids with a FCC structure partially embedded in the SiO{sub 2} substrate was confirmed, which has a potential application in solid-state devices.

  7. [Catalyst research]. Final Report

    SciTech Connect

    Ian P Rothwell; David R McMillin

    2005-03-14

    Research results are the areas of catalyst precursor synthesis, catalyst fluxionality, catalyst stability, polymerization of {alpha}-olefins as well as the chemistry of Group IV and Group V metal centers with aryloxide and arylsulfide ligands.

  8. Probing hydrodesulfurization over bimetallic phosphides using monodisperse Ni2-xMxP nanoparticles encapsulated in mesoporous silica

    NASA Astrophysics Data System (ADS)

    Danforth, Samuel J.; Liyanage, D. Ruchira; Hitihami-Mudiyanselage, Asha; Ilic, Boris; Brock, Stephanie L.; Bussell, Mark E.

    2016-06-01

    Metal phosphide nanoparticles encapsulated in mesoporous silica provide a well-defined system for probing the fundamental chemistry of the hydrodesulfurization (HDS) reaction over this new class of hydrotreating catalysts. To investigate composition effects in bimetallic phosphides, the HDS of dibenzothiophene (DBT) was carried out over a series of Ni-rich Ni2-xMxP@mSiO2 (M = Co, Fe) nanocatalysts (x ≤ 0.50). The Ni2-xMxP nanoparticles (average diameters: 11-13 nm) were prepared by solution-phase arrested precipitation and encapsulated in mesoporous silica, characterized by a range of techniques (XRD, TEM, IR spectroscopy, BET surface area, CO chemisorption) and tested for DBT HDS activity and selectivity. The highest activity was observed for a Ni1.92Co0.08P@mSiO2 nanocatalyst, but the overall trend was a decrease in HDS activity with increasing Co or Fe content. In contrast, the highest turnover frequency (TOF) was observed for the most Co- and Fe-rich compositions based on sites titrated by CO chemisorption. IR spectral studies of adsorbed CO on the Ni2-xMxP@mSiO2 catalysts indicate that an increase in electron density occurs on Ni sites as the Co or Fe content is increased, which may be responsible for the increased TOFs of the catalytic sites. The Ni2-xMxP@mSiO2 nanocatalysts exhibit a strong preference for the direct desulfurization pathway (DDS) for DBT HDS that changes only slightly with increasing Co or Fe content.

  9. Single walled carbon nanotube growth and chirality dependence on catalyst composition

    NASA Astrophysics Data System (ADS)

    Orbaek, Alvin W.; Owens, Andrew C.; Crouse, Christopher C.; Pint, Cary L.; Hauge, Robert H.; Barron, Andrew R.

    2013-09-01

    Vertical arrays of single walled carbon nanotubes (VA-SWNTs) were grown using bi-metallic nanoparticle pro-catalysts. Iron oxide particles were doped with varying quantities of first row transition metals (Mn, Co, Ni, and Cu) for a comparative study of the growth of nanotubes. VA-CNT samples were verified using scanning electron microscopy, and characterized using resonance Raman spectroscopy. The length of the VA-CNTs is used as a measure of catalyst activity: the presence of dopants results in a change in the CNT length and length distribution. Cross correlation of the Raman spectra reveal variations in the distribution of radial breathing mode peaks according to the pro-catalyst composition. The formation of various chirality nanotubes is constant between repetitive runs with a particular catalyst, but may be controlled by the identity and concentration of the metal dopants within the iron catalyst. These results demonstrate that the composition of the catalyst is a major driving force toward type selective growth of nanotubes.Vertical arrays of single walled carbon nanotubes (VA-SWNTs) were grown using bi-metallic nanoparticle pro-catalysts. Iron oxide particles were doped with varying quantities of first row transition metals (Mn, Co, Ni, and Cu) for a comparative study of the growth of nanotubes. VA-CNT samples were verified using scanning electron microscopy, and characterized using resonance Raman spectroscopy. The length of the VA-CNTs is used as a measure of catalyst activity: the presence of dopants results in a change in the CNT length and length distribution. Cross correlation of the Raman spectra reveal variations in the distribution of radial breathing mode peaks according to the pro-catalyst composition. The formation of various chirality nanotubes is constant between repetitive runs with a particular catalyst, but may be controlled by the identity and concentration of the metal dopants within the iron catalyst. These results demonstrate that the

  10. Sol-gel based oxidation catalyst and coating system using same

    NASA Technical Reports Server (NTRS)

    Watkins, Anthony N. (Inventor); Leighty, Bradley D. (Inventor); Oglesby, Donald M. (Inventor); Ingram, JoAnne L. (Inventor); Schryer, Jacqueline L. (Inventor)

    2010-01-01

    An oxidation catalyst system is formed by particles of an oxidation catalyst dispersed in a porous sol-gel binder. The oxidation catalyst system can be applied by brush or spray painting while the sol-gel binder is in its sol state.

  11. Catalyst mixture for the catalytic reduction of nitrogen oxides in gaseous mixtures

    SciTech Connect

    Ginger, E.

    1981-03-24

    A physical mixture of a first and second catalyst is described. The first catalyst comprises copper or a copper compound, preferably copper sulfate supported on a porous carrier material. The second catalyst is a combination of metals or compounds thereof, preferably sulfates of vanadium and iron or tungsten and iron, also dispersed on a porous carrier material.

  12. EFFECT OF PRETREATMENT ON PT-CO/C CATHODE CATALYSTS FOR THE OXYGEN-REDUCTION REACTION

    SciTech Connect

    Fox, E.

    2009-05-13

    In order to reduce the precious metal loading without sacrificing activity and stability, a new method for the preparation of bimetallic catalysts is proposed. Currently, Pt-alloy particles, with 2 to 3 nm in diameter, are loaded on high surface area carbon supports. Of the Pt loaded, only the surface atoms interact with the reactants. In order to increase the Pt utilization per metal particle the new process for catalyst preparation will incorporate a non-noble transition metal core coated with a skin layer of Pt deposited on high surface area carbon. The effect of reducing agent strength during synthesis was also explored. It was determined that the Co addition has a higher impact on catalyst when used with NaBH4 as reducing agent as compared to NaCOOH.

  13. Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts

    PubMed Central

    Sahraie, Nastaran Ranjbar; Kramm, Ulrike I.; Steinberg, Julian; Zhang, Yuanjian; Thomas, Arne; Reier, Tobias; Paraknowitsch, Jens-Peter; Strasser, Peter

    2015-01-01

    Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here we report a successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and 57Fe Mössbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the active-site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity. PMID:26486465

  14. Nickel-tungsten carbide catalysts for the production of 2,5-dimethylfuran from biomass-derived molecules.

    PubMed

    Huang, Yao-Bing; Chen, Meng-Yuan; Yan, Long; Guo, Qing-Xiang; Fu, Yao

    2014-04-01

    The development of new catalytic systems for the conversion of biomass-derived molecules into liquid fuels has attracted much attention. We propose a non-noble bimetallic catalyst based on nickel-tungsten carbide for the conversion of the platform molecules 5-(hydroxymethyl)furfural into the liquid-fuel molecule 2,5-dimethylfuran (DMF). Different catalysts, metal ratios and reaction conditions have been tested and give rise to a 96% yield of DMF. The catalysts have been characterized and are discussed. The reaction mechanism is also explored through capture of reaction intermediates. The analysis of the reaction mixture over different catalysts is presented and helps to understand the role of nickel and tungsten carbide during the reaction. PMID:24574062

  15. Fracture evaluations of fusion line cracks in nuclear pipe bimetallic welds

    SciTech Connect

    Scott, P.; Francini, R.; Rahman, S.; Rosenfield, A.; Wilkowski, G.

    1995-04-01

    In both BWRs and PWRs there are many locations where carbon steel pipe or components are joined to stainless steel pipe or components with a bimetallic weld. The objective of the research described in this report was to assess the accuracy of current fracture analyses for the case of a crack along a carbon steel to austenitic weld fusion line. To achieve the program objective, material property data and data from a large-diameter pipe fracture experiment were developed to assess current analytical methods. The bimetallic welds evaluated in this program were bimetallic welds obtained from a cancelled Combustion Engineering plant. The welds joined sections of the carbon steel cold-leg piping system to stainless steel safe ends that were to be welded to stainless steel pump housings. The major conclusion drawn as a result of these efforts was that the fracture behavior of the bimetallic weld evaluated in this program could be evaluated with reasonable accuracy using the strength and toughness properties of the carbon steel pipe material in conjunction with conventional elastic-plastic fracture mechanics or limit-load analyses. This may not be generally true for all bimetallic welds, as discussed in this report.

  16. Melting phenomena: effect of composition for 55-atom Ag-Pd bimetallic clusters.

    PubMed

    Cheng, Daojian; Wang, Wenchuan; Huang, Shiping

    2008-05-14

    Understanding the composition effect on the melting processes of bimetallic clusters is important for their applications. Here, we report the relationship between the melting point and the metal composition for the 55-atom icosahedral Ag-Pd bimetallic clusters by canonical Monte Carlo simulations, using the second-moment approximation of the tight-binding potentials (TB-SMA) for the metal-metal interactions. Abnormal melting phenomena for the systems of interest are found. Our simulation results reveal that the dependence of the melting point on the composition is not a monotonic change, but experiences three different stages. The melting temperatures of the Ag-Pd bimetallic clusters increase monotonically with the concentration of the Ag atoms first. Then, they reach a plateau presenting almost a constant value. Finally, they decrease sharply at a specific composition. The main reason for this change can be explained in terms of the relative stability of the Ag-Pd bimetallic clusters at different compositions. The results suggest that the more stable the cluster, the higher the melting point for the 55-atom icosahedral Ag-Pd bimetallic clusters at different compositions.

  17. Characterization of Bimetallic Fe-Ru Oxide Nanoparticles Prepared by Liquid-Phase Plasma Method

    NASA Astrophysics Data System (ADS)

    Lee, Sung-Jin; Lee, Heon; Jeon, Ki-Joon; Park, Hyunwoong; Park, Young-Kwon; Jung, Sang-Chul

    2016-07-01

    The bimetallic Fe-Ru oxide nanoparticles were synthesized in the liquid-phase plasma (LPP) method which employed iron chloride and ruthenium chloride as precursors. The active species (OH·, Hα, Hβ, and OI) and the iron and ruthenium ions were observed in the plasma field created by the LPP process. The spherical-shaped bimetallic Fe-Ru oxide nanoparticles were synthesized by the LPP reaction, and the size of the particles was growing along with the progression of the LPP reaction. The synthesized bimetallic Fe-Ru oxide nanoparticles were comprised of Fe2O3, Fe3O4, RuO, and RuO2. Ruthenium had a higher reduction potential than iron and resulted in higher ruthenium composition in the synthesized bimetallic nanoparticles. The control of the molar ratio of the precursors in the reactant solution was found to be employed as a means to control the composition of the elements in bimetallic nanoparticles.

  18. Effect of Synthesis Techniques on Crystallization and Optical Properties of Ag-Cu Bimetallic Nanoparticles

    NASA Astrophysics Data System (ADS)

    Xiong, Ziye; Qin, Fen; Huang, Po-Shun; Nettleship, Ian; Lee, Jung-Kun

    2016-04-01

    Silver (Ag)-copper (Cu) bimetallic nanoparticles (NPs) were synthesized by the reduction of silver nitrate and copper (II) acetate monohydrate using ethylene glycol in a microwave (MW) heating system with controlled reaction times ranging from 5 min to 30 min. The molar ratio Ag/Cu was varied from 1:1 to 1:3. The effect of reaction conditions on the bimetallic NPs structures and compositions were characterized by x-ray photoelectron spectroscopy, x-ray diffraction and transmission electron microscopy. The average particle size was approximately 150 nm. The surface plasmon resonance (SPR) of Ag-Cu bimetallic NPs was investigated by monitoring the SPR band peak behavior via UV/Vis spectrophotometry. The resonance peak positions and peak widths varied due to the different structures of the bimetallic NPs created under the synthesis conditions. In the MW heating method, the reduction of Cu was increased and Cu was inhomogeneously deposited over the Ag cores. As the composition of Cu becoming higher in the Ag-Cu bimetallic NPs, the absorption between 400 nm to 600 nm was greatly enhanced.

  19. Polymer nanocomposite membranes with hierarchically structured catalysts for high throughput dehalogenation

    NASA Astrophysics Data System (ADS)

    Crock, Christopher A.

    Halogenated organics are categorized as primary pollutants by the Environmental Protection Agency. Trichloroethylene (TCE), which had broad industrial use in the past, shows persistence in the environment because of its chemical stability. The large scale use and poor control of TCE resulted in its prolonged release into the environment before the carcinogenic risk associated with TCE was fully understood. TCE pollution stemmed from industrial effluents and improper disposal of solvent waste. Membrane reactors are promising technology for treating TCE polluted groundwater because of the high throughput, relatively low cost of membrane fabrication and facile retrofitting of existing membrane based water treatment facilities with catalytic membrane reactors. Compared to catalytic fluidized or fixed bed reactors, catalytic membrane reactors feature minimal diffusional limitation. Additionally, embedding catalyst within the membrane avoids the need for catalyst recovery and can prevent aggregation of catalytic nanoparticles. In this work, Pd/xGnP, Pd-Au/xGnP, and commercial Pd/Al2O3 nanoparticles were employed in batch and flow-through membrane reactors to catalyze the dehalogenation of TCE in the presence of dissolved H2. Bimetallic Pd-Au/xGnP catalysts were shown to be more active than monometallic Pd/xGnP or commercial Pd/Al 2O3 catalysts. In addition to synthesizing nanocomposite membranes for high-throughput TCE dehalogenation, the membrane based dehalogenation process was designed to minimize the detrimental impact of common catalyst poisons (S2-, HS-, and H2S -) by concurrent oxidation of sulfide species to gypsum in the presence of Ca2+ and removal of gypsum through membrane filtration. The engineered membrane dehalogenation process demonstrated that bimetallic Pd-Au/xGnP catalysts resisted deactivation by residual sulfide species after oxidation, and showed complete removal of gypsum during membrane filtration.

  20. Rapid transformation of 1,2,3,4-TCDD by Pd/Fe catalysts.

    PubMed

    Wang, Zhiyuan; Huang, Weilin; Peng, Ping'an; Fennell, Donna E

    2010-01-01

    This study investigated reductive dechlorination of 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) in the presence of Pd/Fe, Cu/Fe and Ni/Fe bimetallic catalysts or zero-valent iron (ZVI) under aqueous and ambient temperature conditions. It was found that the Pd/Fe catalyst can rapidly transform 1,2,3,4-TCDD to chlorine-free dibenzo-p-dioxin (DD) with >95% of conversion and half lives on the order of 5h, whereas Cu/Fe, Ni/Fe and ZVI were not reactive over 10d. The dechlorination of 1,2,3,4-TCDD in the Pd/Fe systems was found to be stepwise, with 1,2,3-tri (TrCDD), 1,2-di (DCDD), and mono-(MCDD) chlorodibenzo-p-dioxins as the three intermediate products at low concentrations and DD as the final and dominant product. The reaction rate of 1,2,3,4-TCDD dechlorination appeared to decrease as the coverage of palladium on iron particle surface increases from 0.0060 mol% to 0.0228 mol%. Compared to our prior study of reductive dechlorination of 1,2,3,4-TCDD with zero valent zinc (ZVZ) as the reductant, the reactions with Pd/Fe bimetallic materials were relatively slower for TCDD, but much faster for TrCDDs and DCDDs, yielding DD as the major product. The study suggested that Pd/Fe bimetallic catalyst-based reactions may be suitable for rapid decontamination of polychlorinated dibenzo-p-dioxin/dibenzofuran (PCDD/F) polluted soils and sediments.