Showing papers on "Dehydrogenation published in 2005"

Reversible storage of hydrogen in destabilized LiBH4.

Abstract: Destabilization of LiBH4 for reversible hydrogen storage has been studied using MgH2 as a destabilizing additive. Mechanically milled mixtures of LiBH4 + 1/2MgH2 or LiH + 1/2MgB2 including 2−3 mol % TiCl3 are shown to reversibly store 8−10 wt % hydrogen. Variation of the equilibrium pressure obtained from isotherms measured at 315−400 °C indicate that addition of MgH2 lowers the hydrogenation/dehydrogenation enthalpy by 25 kJ/(mol of H2) compared with pure LiBH4. Formation of MgB2 upon dehydrogenation stabilizes the dehydrogenated state and, thereby, destabilizes the LiBH4. Extrapolation of the isotherm data yields a predicted equilibrium pressure of 1 bar at approximately 225 °C. However, the kinetics were too slow for direct measurements at these temperatures.

Facile Conversion of Alcohols into Esters and Dihydrogen Catalyzed by New Ruthenium Complexes

Abstract: An efficient, environmentally benign method for the preparation of esters from alcohols under mild, neutral conditions without the need for carboxylic acid derivatives and condensing agents was developed. Catalyst design, based on new Ru(II) hydrido carbonyl complexes incorporating electron-rich PNP and PNN ligands has resulted in the novel complex (I) which is an outstanding catalyst for the dehydrogenation of primary alcohols to esters and H2 under neutral conditions.

Metal Oxides : Chemistry and Applications

Abstract: Molecular Structures of Surface Metal Oxide Species: Nature of Catalytic Active Sites in Mixed Metal Oxides I.E. Wachs Nanostructured Supported Metal Oxides M.S. Wong Defect Chemistry and Transport in Metal Oxides A. Thursfield, A. Kruth, J.T.S Irvine, and I.S. Metcalfe Cation Valence States of Transitional Metal Oxides Analyzed by Electron Energy-Loss Spectroscopy Z..L. Wang Surface Processes and Composition of Metal Oxide Surfaces B. Pawelec The Electronic Structure of Metal Oxides P.M. Woodward, H. Mizoguchi, Y.-I. Kim, and M.W. Stoltzfus Optical and Magnetic Properties of Metal Oxides S. Ishihara Redox Properties of Metal Oxides B.M. Reddy The Surface Acidity and Basicity of Solid Oxides and Zeolites G. Busca Optical Basicity: A Scale of Acidity/Basicity of Solids and Its Application to Oxidation Catalysis E. Bordes-Richard and P. Courtine Investigation of the Nature and Number of Surface Active Sites of Supported and Bulk Metal Oxide Catalysts through Methanol Chemisorption L.E. Briand Combinatorial Approaches to Design Complex Metal Oxides F. Schuth and S.A. Schunk Propane Selective Oxidation to Propene and Oxygenates on Metal Oxides E.K. Novakova and J.C. Vedrine Methane Oxidation on Metal Oxides R.M. Navarro, M.A. Pena, and J.L.G. Fierro Oxidative Dehydrogenation (ODH) of Alkanes over Metal Oxide Catalysts G. Deo, M. Cherian, and T.V.M. Rao Metathesis of Olefins on Metal Oxides J.L.G. Fierro and J.C. Mol Applications of Metal Oxides for Volatile Organic Compound Combustion D.P. Dissanayake Hydrogenation of Carbon Oxides on Metal Oxides J.L.G. Fierro Photocatalysis: Photocatalysis on Titanium Oxide-Based Catalysts M. Anpo, S. Dohshi, M. Kitano, and Y. Hu Photocatalytic Activity forWater Decomposition of RuO2-Dispersed p-Block Metal Oxides with d10 Electronic Configuration Y. Inoue Selective Catalytic Reduction (SCR) Processes on Metal Oxides G. Centi and S. Perathoner Gas Sensors Based on Semiconducting Metal Oxides A. Gurlo, N. Barsan, and U. Weimar Fuel Electrodes for Solid Oxide Fuel Cells S.W. Tao and J.T.S. Irvine Index

Experimental and DFT Studies of the Conversion of Ethanol and Acetic Acid on PtSn-Based Catalysts†

Abstract: Reaction kinetics studies were conducted for the conversions of ethanol and acetic acid over silica-supported Pt and Pt/Sn catalysts at temperatures from 500 to 600 K. Addition of Sn to Pt catalysts inhibits the decomposition of ethanol to CO, CH4, and C2H6, such that PtSn-based catalysts are active for dehydrogenation of ethanol to acetaldehyde. Furthermore, PtSn-based catalysts are selective for the conversion of acetic acid to ethanol, acetaldehyde, and ethyl acetate, whereas Pt catalysts lead mainly to decomposition products such as CH4 and CO. These results are interpreted using density functional theory (DFT) calculations for various adsorbed species and transition states on Pt(111) and Pt3Sn(111) surfaces. The Pt3Sn alloy slab was selected for DFT studies because results from in situ 119Sn Mossbauer spectroscopy and CO adsorption microcalorimetry of silica-supported Pt/Sn catalysts indicate that Pt−Sn alloy is the major phase present. Accordingly, results from DFT calculations show that transition-...

Mechanisms of methanol decomposition on platinum: A combined experimental and ab initio approach.

Abstract: The dual path mechanism for methanol decomposition on well-defined low Miller index platinum single crystal planes, Pt(111), Pt(110), and Pt(100), was studied using a combination of chronoamperometry, fast scan cyclic voltammetry, and theoretical methods. The main focus was on the electrode potential range when the adsorbed intermediate, CO(ad), is stable. At such "CO stability" potentials, the decomposition proceeds through a pure dehydrogenation reaction, and the dual path mechanism is then independent of the electrode-substrate surface structure. However, the threshold potential where the decomposition of methanol proceeds via parallel pathways, forming other than CO(ad) products, depends on the surface structure. This is rationalized theoretically. To gain insights into the controlling surface chemistry, density functional theory calculations for the energy of dehydrogenation were used to approximate the potential-dependent methanol dehydrogenation pathways over aqueous-solvated platinum interfaces.

Efficient Ruthenium‐Catalyzed Aerobic Oxidation of Amines by Using a Biomimetic Coupled Catalytic System

Abstract: Efficient aerobic oxidation of amines was developed by the use of a biomimetic coupled catalytic system involving a ruthenium-induced dehydrogenation. The principle for this aerobic oxidation is that the electron transfer from the amine to molecular oxygen occurs stepwise via coupled redox systems and this leads to a low-energy electron transfer. A substrate-selective ruthenium catalyst dehydrogenates the amine and the hydrogen atoms abstracted are transported to an electron-rich quinone (2a). The hydroquinone thus formed is subsequently reoxidized by air with the aid of an oxygen-activating [Co(salen)]-type complex (27). The reaction can be used for the preparation of ketimines and aldimines in good to high yields from the appropriate corresponding amines. The reaction proceeds with high selectivity, and the catalytic system tolerates air without being deactivated. The rate of the dehydrogenation was studied by using quinone 2a as the terminal oxidant. A catalytic cycle in which the amine promotes the dissociation of the dimeric catalyst 1 is presented.

Metal-Catalysed Reactions of Hydrocarbons

Abstract: Metals and Alloys.- Small Metal Particles and Supported Metal Catalysts.- Chemisorption and Reactions of Hydrogen.- The Chemisorption of Hydrocarbons.- Introduction to the Catalysis of Hydrocarbon Reactions.- Exchange of Alkanes with Deuterium.- Hydrogenation of Alkenes and Related Processes.- Hydrogenation of Alkadienes and Polyenes.- Hydrogenation of Alkynes.- Hydrogenation of the Aromatic Ring.- Hydrogenation of Small Alicyclic Rings.- Dehydrogenation of Alkanes.- Reactions of the Lower Alkanes with Hydrogen.- Reactions of Higher Alkanes with Hydrogen.- Index.

In situ XPS investigations of Cu1−xNixZnAl-mixed metal oxide catalysts used in the oxidative steam reforming of bio-ethanol

Abstract: A series of CuNiZnAl-multicomponent mixed metal oxide catalysts with various Cu/Ni ratios were prepared by the thermal decomposition of Cu1−xNixZnAl-hydrotalcite-like precursors and tested for oxidative steam reforming of bio-ethanol. Dehydrogenation of EtOH to CH3CHO is favored by Cu-rich catalyst. Introduction of Ni leads to C C bond rupture and producing CO, CO2 and CH4. H2 yield (selectivity) varied between 2.6–3.0 mol/mol of ethanol converted (50–55%) for all catalysts at 300 °C. The above catalysts were subjected to in situ XPS studies to understand the nature of active species involved in the catalytic reaction. Core level and valence band XPS as well as Auger electron spectroscopy revealed the existence of Cu2+, Ni2+ and Zn2+ ions on calcined materials. Upon in situ reduction at reactions temperatures, the Cu2+ was fully reduced to Cu0, while Ni2+ and Zn2+ were partially reduced to Ni0 and Zn0, respectively. On reduction, the nature of ZnO on Cu-rich catalyst changes from crystalline to amorphous, relatively inert and highly stabilized electronically. Relative concentration of the Ni0 and Zn0 increases upon reduction with decreasing Cu-content. Valence band results demonstrated that the overlap between 3d bands of Cu and Ni was marginal on calcined materials, and no overlap due to metallic clusters formation after reduction. Nonetheless, the density of states at Fermi level increases dramatically for Ni-rich catalysts and likely this influences the product selectivity.

In situ XAFS and NMR study of rhodium-catalyzed dehydrogenation of dimethylamine borane.

Abstract: In situ X-ray absorption fine structure spectroscopy (XAFS) and 11B NMR were used to study the rhodium-catalyzed dimerization reaction of dimethylaminoborane, (CH3)2NHBH3 or DMAB. XAFS spectra show that the active form of the rhodium catalyst is most likely composed of a six-atom Rh core surrounded by tightly bound external ligands. NMR results show the presence of monomeric dimethylamine borane (CH3)2NBH2, providing evidence that hydrogen formation from the homogeneous Rh species occurs by an intramolecular pathway. This is in contrast to thermal pathways that involve intermolecular B−N concurrent with hydrogen formation. This work shows that in situ XAFS spectroscopy offers a unique experimental tool to differentiate between heterogeneous and homogeneous catalysis.

The chemistry of selective ring-opening catalysts

Abstract: Bitumen-derived crude and heavy oils require severe processing and produce middle distillate product with poor ignition quality. This becomes a concern to refiners as tighter specifications on transportation fuel are promulgated. One process to address this issue is selective ring opening of cycloparaffins to reduce the number of ring structures, while retaining the carbon number of a product molecule. The process involves bifunctional catalysts, both metal and acid sites, working in high-pressure, high-temperature reactor systems in the presence of hydrogen. The acidic sites catalyze dehydrogenation, cracking, isomerization and dealkylation, while the metal sites promote hydrogenation, hydrogenolysis and isomerization. Various compounds containing single, double and multiple rings have been used to model the ring-opening reactions and a number of mechanisms have been proposed. The five-membered ring readily undergoes ring-opening reaction on either acid or metal catalysts with the selectivity and activity dependent on the nature of the supported metal catalyst. The ring opening of six-membered ring compounds is secondary, requiring an acidic function to isomerize a six-membered ring cycloparaffin to a five-membered ring. A balanced metallic-acidic function catalyst is necessary to achieve optimal performance. A system dominated by acid function results in excess cracking, while a catalytic system with high concentration of metals leads to mainly hydrogenation. Commercial hydrocracking catalysts using transition metal sulfides on acidic supports usually require severe operating conditions due to their low activities of the metal sulfide compared to metal sites, leading to extensive cracking of cycloparaffin side chains. Noble metals supported on acidic oxides are the most active catalysts for selective ring opening, but these catalysts are very sensitive to poisoning by sulfur compounds in petroleum feedstocks. An understanding of the chemistry of selective ring-opening catalysts, combined with theoretical studies of structure–activity relationships and high throughput experimentation methods, provides opportunities in searching for new generations of selective ring-opening catalysts with high-performance and sulfur resistance.

Selective Oxidation of Methanol and Ethanol on Supported Ruthenium Oxide Clusters at Low Temperatures

Abstract: RuO2 domains supported on SnO2, ZrO2, TiO2, Al2O3, and SiO2 catalyze the oxidative conversion of methanol to formaldehyde, methylformate, and dimethoxymethane with unprecedented rates and high comb...

Catalytic steam reforming of ethanol to produce hydrogen and acetone

Abstract: Steam reforming of ethanol over CuO/CeO2 was studied. Acetaldehyde and hydrogen were mainly produced at 260degreesC. At 380degreesC, acetone was the main product, and 2 mol of hydrogen was produced from 1 mol of ethanol. The formation of hydrogen accompanied by the production of acetone was considered to proceed through the following, consecutive reactions: dehydrogenation of ethanol to acetaldehyde. aldol condensation of the acetaldehyde, and the reaction of the aldol with the lattice oxygen [O(s)] on the catalyst to form a surface intermediate, followed by its dehydrogenation and decarboxylation. The overall reaction was expressed by2C(2)H(5)OH + H2O --> CH3COCH3 + CO2 + 4H(2). Ceria played an important role as an oxygen supplier. The addition of MgO to CuO/CeO2 resulted in the production of hydrogen at lower temperatures by accelerating aldol condensation. (C) 2004 Elsevier B.V. All rights reserved.

Destabilization of LiBH4 by mixing with LiNH2

Abstract: It was revealed that LiBH4 is destabilized by mixing with LiNH2 and the mixture desorbs a large amount of hydrogen. First-principles calculations predicted that the enthalpies of dehydrogenation for LiBH4 alone and the mixture of LiBH4 + 2 LiNH2 are 75 kJ/molH2 and 23 kJ/molH2, respectively. Motivated by this prediction, we experimentally examined the dehydrogenation properties for LiBH4 and the mixture under hydrogen pressure. The amounts of desorbed hydrogen from LiBH4 and the mixture at 703 K and 522 K were 10.6 mass % and 7.8 mass %, respectively. The dehydrogenation pressure of the mixture was much higher than that of LiBH4 alone, although the mixture was measured at approximately 180 K lower temperature. This result suggests that the mixture is much unstable as compared with LiBH4 alone.

Development and application of oxygen permeable membrane in selective oxidation of light alkanes

Abstract: In this paper, oxygen permeable membrane used in membrane reactor for selective oxidation of alkanes will be discussed in detail. The recent developments for the membrane materials will be presented, and the strategy for the selection of the membrane materials will be outlined. The main applications of oxygen permeable membrane in selective oxidation of light alkanes will be summarized, which includes partial oxidation of methane (POM) to syngas and partial oxidation of heptane (POH) to produce H2, oxidative coupling of methane (OCM) to C2, oxidative dehydrogenation of ethane (ODE) to ethylene and oxidative dehydrogenation of propane (ODP) to propylene. Achievements for the membrane material developments and selective oxidation of light alkanes in membrane reactor in our group are highlighted.

Unraveling the surface reactions during liquid-phase oxidation of benzyl alcohol on Pd/Al2O3: An in situ ATR-IR study

Abstract: The palladium-catalyzed liquid-phase reaction of benzyl alcohol to benzaldehyde was investigated in the presence and absence of oxygen by attenuated total reflection infrared (ATR−IR) spectroscopy. The 5 wt % Pd/Al2O3 catalyst was fixed in a flow-through ATR−IR cell serving as a continuous-flow reactor. The reaction conditions (cyclohexane solvent, 323 K, 1 bar) were set in the range commonly applied in the heterogeneous catalytic aerobic oxidation of alcohols. The in situ ATR−IR study of the solid−liquid interface revealed a complex reaction network, including dehydrogenation of benzyl alcohol to benzaldehyde, decarbonylation of benzaldehyde, oxidation of hydrogen and CO on Pd, and formation of benzoic acid catalyzed by both Pd and Al2O3. Continuous formation of CO and its oxidative removal by air resulted in significant steady-state CO coverage of Pd during oxidation of benzyl alcohol. Unexpectedly, benzoic acid formed already in the early stage of the reaction and adsorbed strongly (irreversibly) on th...

Oxidative dehydrogenation of ethane and propane over vanadia and molybdena supported catalysts

Abstract: The catalytic performance of vanadia and molybdena catalysts with monolayer coverage supported on alumina and titania in the oxidative dehydrogenation (ODH) of ethane and propane was investigated. The surface structure of the MO x species (M = Mo, V) was investigated with laser Raman spectroscopy, while the acidity and reducibility of the materials were probed by temperature programmed NH 3 desorption and H 2 reduction, respectively. Testing of the materials showed that in both ethane and propane oxidative dehydrogenation, vanadia catalysts were much more active than the molybdena ones, irrespective of the support used. Comparison of the catalysts based on the support used, showed that titania-supported catalysts exhibit superior activity but inferior selectivity than the corresponding alumina-supported ones. Taking into account that the oxygen involved in the M O-support bonds is kinetically relevant, the behavior of each catalytic system can be explained based on the electronegativity of each cation involved in these bonds. The apparent activation energies for ethane and propane ODH, derived from kinetic measurements, follow the reactivity of the samples. Despite the higher reactivity of propane at same reaction conditions, similar values of activation energy were calculated. The pre-exponential factors could be responsible for the lower reaction rates in ethane ODH.

Hydrogen storage by decalin/naphthalene pair and hydrogen supply to fuel cells by use of superheated liquid-film-type catalysis

Abstract: A catalytic reaction pair of decalin dehydrogenation/naphthalene hydrogenation has been proposed as a storage medium for fuel-cell hydrogen in mobile modes. The hydrogen capacities with decalin (7.3 wt.%, 64.8 kg-H2 m3) are higher than the target values of the Department of Energy, USA (6.5 wt.%, 62.0 kg-H2 m3). Platinum–rhenium composite catalysts supported on granular activated carbon in “superheated liquid-film” states gave excellent reactivities for decalin dehydrogenation, where the conversion of almost 100% from decalin to naphthalene was attained within 1 h by heating at 280 °C in a batch-wise reactor. “Superheated liquid-film” conditions were also realized in a continuous-type reactor at the same temperature (280 °C). With the goal of maintaining rapid evolution of hydrogen stationarily, a rather wide range of decalin feed rates was allowable with use of platinum particles supported on activated carbon cloth. Decalin should be evaluated as an organic chemical hydride not only because of its storage densities but also because of its potential power densities for fuel-cell vehicles.

Modified borohydrides for reversible hydrogen storage

Abstract: This paper reports the results in the effort to destabilize lithium borohydride for reversible hydrogen storage. A number of metals, metal hydrides, metal chlorides and complex hydrides were selected and evaluated as the destabilization agents for reducing dehydriding temperature and generating dehydriding-rehydriding reversibility. It is found that some additives are effective. The Raman spectroscopic analysis shows the change of B-H binding nature.

XPS and EXAFS study of supported PtSn catalysts obtained by surface organometallic chemistry on metals: Application to the isobutane dehydrogenation

Abstract: In this work, well defined alumina and silica supported Pt and PtSn catalysts were prepared by surface organometallic reactions and were characterized by TEM, XPS and EXAFS. These catalysts were tested in the catalytic dehydrogenation of isobutane. XPS results show that tin is found under the form of Sn(0) and Sn(II,IV), being the percentage of Sn(0) lower for alumina supported than for silica supported catalysts. Tin modified platinum catalysts, always show a decrease of approximately 1 eV in the BE of Pt, what would be indicative of an electron charge transfer from tin to platinum. When the concentration of Sn(0) is high enough, in our case Sn(0)/Pt ∼ 0.3, EXAFS experiments demonstrated the existence of a PtSn alloy diluting metallic Pt atoms, for both PtSn/γ-Al2O3 and PtSn/SiO2. This PtSn alloy seems to be not active in the dehydrogenation reaction; however, it is very important for selectivity and stability, inhibiting cracking and coke formation reactions. The ensemble of our catalytic, XPS and EXAFS results, show that bimetallic PtSn/γ-Al2O3 catalysts, prepared via SOMC/M techniques, can be submitted to several sequential reaction–regeneration cycles, recovering the same level of initial activity each time and that the nature of the catalytic surface remains practically without modifications.

Mesoporous material with active metals

Abstract: A process for treating organic compounds includes providing a composition which includes a substantially mesoporous structure of silica containing at least 97% by volume of pores having a pore size ranging from about 15 Å to about 30 Å and having a micropore volume of at least about 0.01 cc/g, wherein the mesoporous structure has incorporated therewith at least about 0.02% by weight of at least one catalytically and/or chemically active heteroatom selected from the group consisting of Al, Ti, V, Cr, Zn, Fe, Sn, Mo, Ga, Ni, Co, In, Zr, Mn, Cu, Mg, Pd, Pt and W, and the catalyst has an X-ray diffraction pattern with one peak at 0.3° to about 3.5° at 2θ. The catalyst is contacted with an organic feed under reaction conditions wherein the treating process is selected from alkylation, acylation, oligomerization, selective oxidation, hydrotreating, isomerization, demetalation, catalytic dewaxing, hydroxylation, hydrogenation, ammoximation, isomerization, dehydrogenation, cracking and adsorption.

Oxygen-Induced Ligand Dehydrogenation of a Planar Bis-μ-Chloronickel(I) Dimer Featuring an NHC Ligand

Abstract: Planar bis-μ-chloronickel(I) dimers undergo rapid aerobic oxidation to yield bis-μ-hydroxonickel(II) dimers with concomitant ligand dehydrogenation.

Dehydrogenation of Cyclohexane Over Ni Based Catalysts Supported on Activated Carbon using Spray-pulsed Reactor and Enhancement in Activity by Addition of a Small Amount of Pt

Abstract: Dehydrogenation of cyclohexane to benzene has been carried out over Ni supported on activated carbon cloth ACC (Ni/ACC) catalysts under spray-pulsed mode reactor to study hydrogen evolution for hydrogen storage and supply system applications. The maximum rate of hydrogen evolution using monometallic Ni/ACC catalysts was 8.5 mmol g−1cat min−1 for Ni loading of 20% by weight. A small amount of Pt (0.5 wt%) was added to the Ni based catalysts. A synergistic effect was observed in the case of the promoted catalysts the hydrogen production was enhanced by ca. 1.5 times as compared to the 20 wt% Ni only catalyst. As compared to 0.5 wt% monometallic Pt catalyst, the 20 wt% Ni–0.5 wt% Pt bimetallic catalyst exhibits ca. 60 times higher hydrogen production rates. Selectivity towards dehydrogenation observed to be enhanced by addition of Pt into Ni/ACC catalysts.

Intensities of IR stretching bands as a criterion of polarization and initial chemical activation of adsorbed molecules in acid catalysis. Ethane adsorption and dehydrogenation by zinc ions in ZnZSM-5 zeolite.

Abstract: A DRIFT study of ethane adsorbed by zinc cations in ZnZSM-5 prepared by chemical reaction of the hydrogen form of the zeolite with zinc vapor at 770 K, or by wet ion exchange, reveals unusual spect...