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Showing papers on "Catalysis published in 1994"


Journal ArticleDOI
24 Mar 1994-Nature
TL;DR: The use of the templating approach to synthesize mesoporous silica-based molecular sieves partly substituted with titanium—large-pore analogues of titanium silicalite find that these materials show selective catalytic activity towards the oxidation of 2,6-ditert-butyl phenol to the corresponding quinone and the conversion of benzene to phenol.
Abstract: Titanium silicalite is an effective molecular-sieve catalyst for the selective oxidation of alkanes, the hydroxylation of phenol and the epoxidation of alkenes in the presence of H2O2 (refs 1-3). The range of organic compounds that can be oxidized is greatly limited, however, by the relatively small pore size (about 0.6 nm) of the host framework. Large-pore (mesoporous) silica-based molecular sieves have been prepared recently by Kresge et al. and Kuroda et al.; the former used a templating approach in which the formation of an inorganic mesoporous structure is assisted by self-organization of surfactants, and the latter involved topochemical rearrangement of a layered silica precursor. Here we describe the use of the templating approach to synthesize mesoporous silica-based molecular sieves partly substituted with titanium--large-pore analogues of titanium silicalite. We find that these materials show selective catalytic activity towards the oxidation of 2,6-di-tert-butyl phenol to the corresponding quinone and the conversion of benzene to phenol.

1,672 citations


Journal ArticleDOI
24 Jun 1994-Science
TL;DR: Several examples of enzymatic reactions that appear to use this principle are presented, and a weak hydrogen bond in the enzyme-substrate complex in which the pKa's do not match can become a strong, low-barrier one if the p Ka's become matched in the transition state or enzyme-intermediate complex.
Abstract: Formation of a short (less than 2.5 angstroms), very strong, low-barrier hydrogen bond in the transition state, or in an enzyme-intermediate complex, can be an important contribution to enzymic catalysis. Formation of such a bond can supply 10 to 20 kilocalories per mole and thus facilitate difficult reactions such as enolization of carboxylate groups. Because low-barrier hydrogen bonds form only when the pKa's (negative logarithm of the acid constant) of the oxygens or nitrogens sharing the hydrogen are similar, a weak hydrogen bond in the enzyme-substrate complex in which the pKa's do not match can become a strong, low-barrier one if the pKa's become matched in the transition state or enzyme-intermediate complex. Several examples of enzymatic reactions that appear to use this principle are presented.

1,007 citations


Journal ArticleDOI
TL;DR: In this paper, the average stacking heights of poorly crystalline MoS2 powders are estimated by X-ray crystallography and for the first time correlated with the selectivity of the catalyst for hydrogenation versus HDS (hydrodesulfurization).

667 citations



Journal ArticleDOI
TL;DR: Manganese oxides of different crystallinity, oxidation state and specific surface area have been used in the selective catalytic reduction (SCR) of nitric oxide with ammonia, indicating a relation between the SCR process and active surface oxygen.
Abstract: Manganese oxides of different crystallinity, oxidation state and specific surface area have been used in the selective catalytic reduction (SCR) of nitric oxide with ammonia between 385 and 575 K. MnO2 appears to exhibit the highest activity per unit surface area, followed by Mn5O8, Mn2O3, Mn3O4 and MnO, in that order. This SCR activity correlates with the onset of reduction in temperature-programmed reduction (TPR) experiments, indicating a relation between the SCR process and active surface oxygen. Mn2O3 is preferred in SCR since its selectivity towards nitrogen formation during this process is the highest. In all cases the selectivity decreases with increasing temperature. The oxidation state of the manganese, the crystallinity and the specific surface area are decisive for the performance of the oxides. The specific surface area correlates well with the nitric oxide reduction activity. The nitrous oxide originates from a reaction between nitric oxide and ammonia below 475 K and from oxidation of ammonia at higher temperatures, proven by using 15NH3. Participation of the bulk oxygen of the manganese oxides can be excluded, since TPR reveals that the bulk oxidation state remains unchanged during SCR, except for MnO, which is transformed into Mn3O4 under the applied conditions. In the oxidation of ammonia the degree of oxidation of the nitrogen containing products (N2, N2O, NO) increases with increasing temperature and with increasing oxidation state of the manganese. A reaction model is proposed to account for the observed phenomena.

634 citations


Book
01 Oct 1994
TL;DR: In this paper, the authors present an overview of the history of catalytic components in diesel engines and their application in a variety of applications, such as catalytic converter, catalytic converters, and catalytic monoliths.
Abstract: Preface. ACKNOWLEDGEMENTS. ACKNOWLEDGEMENTS, FIRST EDITION. ACKNOWLEDGEMENTS, SECOND EDITION. I. FUNDAMENTALS. 1. Catalyst Fundamentals. 1.1 Introduction. 1.2 Catalyzed Verses Non-Catalyzed Reactions. 1.3 Catalytic Components. 1.4 Selectivity. 1.5 Promoters and their Effect on Activity and Selectivity. 1.6 Dispersed Model for Catalytic Component on Carrier: Pt on Al 2 O 3 . 1.7 Chemical and Physical Steps in Heterogeneous Catalysis. 1.8 Practical Significance of knowing the Rate-Limiting Step. 2. The Preparation of Catalytic Materials: Carriers, Active Components, and Monolithic Substrates. 2.1 Introduction. 2.2 Carriers. 2.3 Making the Finished Catalyst. 2.4 Nomenclature for Dispersed Catalysts. 2.5 Monolithic Materials as Catalyst Substrates. 2.6 Preparing Monolithic Catalysts. 2.7 Catalytic Monoliths. 2.8 Catalyzed Monoliths Nomenclature. 2.9 Precious Metal Recovery from Monolithic Catalysts. 3. Catalyst Characterization. 3.1 Introduction. 3.2 Physical Properties of Catalysts. 3.3 Chemical and Physical Morphology Structures of Catalytic Materials . 3.4 Techniques for Fundamental Studies. 4. Monolithic Reactors for Environmental Catalysis. 4.1 Introduction. 4.2 Chemical Kinetic Control. 4.3 The Arrhenius Equation and Reaction Parameters. 4.4 Bulk Mass Transfer. 4.5 Reactor Bed Pressure Drop. 4.6 Summary. 5. Catalyst Deactivation. 5.1 Introduction. 5.2 Thermally Induced Deactivation. 5.3 Poisoning. 5.4 Washcoat Loss. 5.5 General Comments on Deactivation Diagnostics in Monolithic Catalysts for Environmental Applications. II. MOBILE SOURCE. 6. Automotive Catalyst. 6.1 Emissions and Regulations. 6.2 The Catalytic Reactions for Pollution Abatement. 6.3 The Physical Structure of the Catalytic Converter. 6.4 First-Generation Converters: Oxidation Catalyst (1976-1979). 6.5 NOx, CO and HC Reduction: The Second Generation: The Three Way Catalyst (1979 - 1986). 6.6 Vehicle Test Procedures (U.S., European and Japanese). 6.7 NOx, CO and HC Reduction: The Third Generation (1986 - 1992). 6.8 Palladium TWC Catalyst: The Fourth Generation (Mid-1990s). 6.9 Low Emission Catalyst Technologies. 6.10 Modern TWC Technologies for the 2000s. 6.11 Towards a Zero-Emission Stoichiometric Spark-Ignit Vehicle. 6.12 Engineered Catalyst Design. 6.13 Lean-Burn Spark-Ignited Gasoline Engines. 7. Automotive Substrates. 7.1 Introduction to Ceramic Substrates. 7.2 Requirements for Substrates. 7.3 Design Sizing of Substrates. 7.4 Physical Properties of Substrates. 7.5 Physical Durability. 7.6 Advances in Substrates. 7.7 Commercial Applications. 7.8 Summary. 8. Diesel Engine Emissions. 8.1 Introduction. 8.2 Worldwide Diesel Emission Standards. 8.3 NO x -Particulate Tradeoff. 8.4 Analytical Procedures for Particulates. 8.5 Particulate Removal. 8.6 NOX Reduction Technologies. 8.7 2007 Commercial System Designs (PM Removal Only). 8.8 2010 Commercial System Approaches under Development (PM and NO x Removal). 8.9 Retrofit and Off-Highway. 8.10 Natural Gas Engines. 9. Diesel Catalyst Supports and Particulate Filters. 9.1 Introduction. 9.2 Health Effects of Diesel Particulate Emissions. 9.3 Diesel Oxidation Catalyst Supports. 9.4 Design/Sizing of Diesel Particulate Filter. 9.5 Regeneration Techniques. 9.6 Physical Properties and Durability. 9.7 Advances in Diesel Filters. 9.8 Applications. 9.9 Summary. 10. Ozone Abatement within Jet Aircraft. 10.1 Introduction. 10.2 Ozone Abatement. 10.3 Deactivation. 10.4 Analysis of In-Flight Samples. 10.5 New Technology. III. STATIONARY SOURCES. 11. Volatile Organic Compounds . 11.1 Introduction. 11.2 Catalytic Incineration. 11.3 Halogenated Hydrocarbons. 11.4 Food Processing. 11.5 Wood Stoves. 11.6 Process Design. 11.7 Deactivation. 11.8 Regeneration of Deactivated Catalysts. 12. Reduction of NO x . 12.1 Introduction. 12.2 Nonselective Catalytic Reduction of NOx. 12.3 Selective Catalytic Reduction of NOx. 12.4 Commercial Experience. 12.5 Nitrous Oxide (N 2 O). 12.6 Catalytically Supported Thermal Combustion. 13. Carbon Monoxide and Hydrocarbon Abatement from Gas Turbines. 13.1 Introduction. 13.2 Catalyst for CO Abatement. 13.3 Non-Methane Hydrocarbon (NMHC) Removal. 13.4 Oxidation of Reactive Hydrocarbons. 13.5 Oxidation of Unreactive Light Paraffins. 13.6 Catalyst Deactivation. 14. Small Engines. 14.1 Introduction. 14.2 Emissions. 14.3 EPA Regulations. 14.4 Catalyst for Handheld and Nonhandheld Engines. 14.5 Catalyst Durability. IV. NEW AND EMERGING TECHNOLOGIES. 15. Ambient Air Cleanup. 15.1 Introduction. 15.2 Premair (R) Catalyst Systems. 15.3 Other Approaches. 16. Fuel Cells and Hydrogen Generation. 16.1 Introduction. 16.2 Low-Temperature PEM Fuel Cell Technology. 16.3 The Ideal Hydrogen Economy. 16.4 Conventional Hydrogen Generation. 16.5 Hydrogen Generation from Natural Gas for PEM Fuel Cells. 16.6 Other Fuel Cell Systems. INDEX.

619 citations


Journal ArticleDOI
26 Aug 1994-Science
TL;DR: A fundamental microkinetic model is proposed, which accounts for the observed industrial kinetics performance and suggests a catalytic cycle that consists of both acid and redox reactions and involves both surface V-OH (Brønsted acid sites) and V=O species.
Abstract: The selective catalytic reduction reaction of nitric oxide bv ammonia over vanadia-titania catalysts is one of the methods of removing NOx pollution. In the present study, it has been possible to identify the reaction mechanism and the nature of the active sites in these catalysts by combining transient or steady-state in situ (Fourier transform infrared spectroscopy) experiments directly with on-line activity studies. The results suggest a catalytic cycle that consists of both acid and redox reactions and involves both surface V-OH (Bronsted acid sites) and V=O species. A fundamental microkinetic model is proposed, which accounts for the observed industrial kinetics performance.

612 citations


Journal ArticleDOI
01 Mar 1994-Nature
TL;DR: The use of a supercritical phase, in which hydrogen is highly miscible, leads to a very high initial rate of reaction up to 1,400 moles of formic acid per mole of catalyst per hour as discussed by the authors.
Abstract: THE use of carbon dioxide as a starting material for the synthesis of organic compounds has long been a goal for synthetic chemists. The hydogenation of carbon dioxide to formic acid, methanol and other organic substances is particularly attractive, but has remained difficult. This route to formic acid has been described recently, based on the use of organometallic rhodium catalysts in dimethyl sulphoxideII and aqueous2 solvents. We report here the efficient production of formic acid in a supercritical mixture of carbon dioxide and hydrogen containing a catalytic ruthenium() phosphine complex. The use of a supercritical phase, in which hydrogen is highly miscible, leads to a very high initial rate of reaction up to 1,400 moles of formic acid per mole of catalyst per hour. The same reaction under identical conditions but in liquid organic solvents is much slower. Our results suggest that supercritical fluids represent a promising medium for homogeneous catalysis.

611 citations


Journal ArticleDOI
TL;DR: In this article, the authors discuss the rates of formation and dissociation of complexes with nitrogen donors, their relationship to the rate of product formation, and presents the factors which induce homolytic cleavage of MC bonds.
Abstract: Homogeneous catalysis has been responsible for many major recent developments in synthetic organic chemistry. The combined use of organometallic and coordination chemistry has produced a number of new and powerful synthetic methods for important classes of compounds in general and for optically active substances in particular. For this purpose, complexes with optically active ligands have been used, most of them coordinating through phosphorus. More recent developments have highlighted the use of “nitrogen-donors”, particularly as they are easily obtained from the “chiral pool”. However, the remarkable achievements in this area have been based on an empirical approach. This article attempts to bridge the gap between the synthetic and the coordination chemist. The first section discusses the rates of formation and dissociation of complexes with nitrogen donors, their relationship to the rates of product formation, and presents the factors which induce homolytic cleavage of MC bonds. It also provides a summary of the main types of organometallic complexes formed by metal centers coordinated to nitrogen donors and their reactivity patterns. The second section highlights the most significant, homogeneously catalyzed reactions involving complexes with nitrogen ligands. Foremost among them are the asymmetric aspects of hydrogenation (particularly those involving boranes as reducing agents), hydrosilylation, cyclopropanations, Diels-Alder reactions, aldol condensations, alkylation of aldehydes, conjugate addition reactions, Grignard cross-coupling reactions, allylic alkylations, oxidation reactions, olefin epoxidations, and di-hydroxylation of olefins.

603 citations


Journal ArticleDOI
TL;DR: In this paper, 13C-Methanol and 12C ethene were co-reacted over SAPO-34 in a flow system at 400°C using argon as a carrier (diluent) gas.

597 citations


Journal ArticleDOI
TL;DR: In this article, the authors measured the kinetics of methanol electro-oxidation on well-characterized Pt-Ru alloy surfaces as a function of temperature and found that the activity of Ru towards the dissociative adsorption of Methanol is a strong function of the temperature.
Abstract: The kinetics of methanol electro-oxidation on well-characterized Pt-Ru alloy surfaces were measured in sulfuric acid solution as a function of temperature. The alloy surfaces were prepared in ultrahigh vacuum with the surface composition determined by low energy ion scattering. It was found that the activity of Ru towards the dissociative adsorption of methanol is a strong function of temperature. This change in the adsorptive nature of the Ru sites with temperature produced a variation in the optimum surface composition with temperature. The optimum surface had an Ru content which increased with increasing temperature, from close to [approximately]10 atomic percent (a/o) Ru at 25 C to a value in the vicinity of [approximately]30 a/o at 60 C. The shift in optimum composition with temperature was attributed to a shift in the rate-determining step from methanol adsorption/dehydrogenation at low temperature to the surface reaction between the dehydrogenated intermediate and surface oxygen at high temperature. The apparent activation energies were consistent with this change in the rate-determining step.

Journal ArticleDOI
TL;DR: In this paper, the aziridination of olefins was evaluated and found to be both catalyst and substrate dependent, and it was concluded that the olefin selectivity profile for the reaction is independent of the oxidation state of the copper catalyst employed.
Abstract: Soluble Cu(1) and Cu(I1) triflate and perchlorate salts are efficient catalysts for the aziridination of olefins employing (N-@-tolylsulfonyl)imino)phenyliodinane, PhI=NTs, as the nitrene precursor. Electron-rich as well as electron-deficient olefins undergo aziridination with this reagent in 55-958 yields, at temperatures ranging from -20 OC to +25 OC. The catalyzed nitrogen atom-transfer reaction to enol silanes and silylketene acetals has also been developed to provide facile syntheses of a-amino ketones. Other metal complexes were found to be less effective at catalyzing the reaction, while PhI=NTs proved to be superior to other imido group donors as the nitrene precursor. Reaction rates and yields are enhanced in polar aprotic solvents such as MeCN and MeN02. Reaction stereospecificity in the aziridination of cis and trans disubstituted olefins was evaluated and found to be both catalyst and substrate dependent. Intermolecular competition experiments between pairs of monoand disubstituted olefins indicate that the olefin selectivity profile for the reaction is independent of the oxidation state of the copper catalyst employed. It is concluded that these reactions are proceeding through the 2+ catalyst oxidation state under the conditions employed

Journal ArticleDOI
TL;DR: In this article, the specific properties of dispersed and promoted ZrO 2 are presented for the photocatalytic total decomposition of water and a novel application for photocatalysis of water is presented.

Journal ArticleDOI
TL;DR: In this article, the surface vanadium oxide phase on all the oxide supports is essentially independent of the loading below monolayer coverage, which suggests that a structural difference is not responsible for the difference in reactivity of the various supported vanadium dioxide catalysts.

Journal ArticleDOI
TL;DR: In this paper, a review of the application of biand multi-metallic catalysts in the aqueous phase oxidation of alcohols with molecular oxygen is presented, focusing on the transformation of primary alcohols to aldehydes or carboxylic acids.

Journal ArticleDOI
TL;DR: In this article, temperature-programmed reduction (TPR), Raman spectroscopy, X-ray photo-electron spectrography (XPS), and infrared spectrograms were used to characterize the reduction properties of manganese oxide catalysts.

Journal ArticleDOI
TL;DR: In this article, the authors investigated carbon dioxide reforming of methane to synthesis gas using Ni catalysts in the temperature range of 500-850°C and showed that the overall reaction can be described by a Langmuir-Hinshelwood mechanistic scheme, assuming that methane dissociation is the rate determining step.

Journal ArticleDOI
23 Jun 1994-Nature
TL;DR: In this paper, it was shown that manganese complexes derived from l,4,7-trimethyl-l, 4,4-7-triazacyclononane and related ligand systems act as highly effective catalysts for the bleaching of stains by hydrogen peroxide at low temperatures.
Abstract: THE detergents of the next century will be routinely required to contain bleaching agents that are not only more active than those currently available but also environmentally safe and cost-effective. Hydrogen peroxide, the traditional bleaching agent1, loses its activity as the washing temperature decreases. Peroxyacetic acid maintains acceptable bleaching activity down to 40–60 °C (ref. 2), but still lower temperatures are desirable. It is generally recognized that manganese and iron complexes are less environmentally damaging reagents than other transition-metal compounds, and such complexes have received considerable attention as bleaching catalysts3–11. Here we show that manganese complexes derived from l,4,7-trimethyl-l,4,7-triazacyclononane and related ligand systems act as highly effective catalysts for the bleaching of stains by hydrogen peroxide at low temperatures. These complexes also catalyse the epoxidation of alkenes and the oxidation of poh phenolic substrates by hydrogen peroxide. Our results demonstrate the considerable potential of these systems for clean and efficient low-temperature bleaching.

Journal ArticleDOI
TL;DR: In this article, the complete oxidation of methane by supported Pd was studied in a reaction mixture of 2% CH4 in air at 550 K, and atmospheric pressure, where the catalysts were Pd supported on Al2O3 and ZrO2 deposited from PdCl2 or Pd(NH3)2(NO2)2 precursors.

Journal ArticleDOI
TL;DR: In this article, the authors studied a catalytic decomposition of methanol on low Miller index platinum surfaces, Pt(111), Pt(110), and Pt(100) in perchloric, sulfuric, and phosphoric acids at room temperature.
Abstract: We have studied a catalytic decomposition of methanol on low Miller index platinum surfaces, Pt(111), Pt(110), and Pt(100) in perchloric, sulfuric, and phosphoric acids at room temperature. The instantaneous methanol oxidation current is unaffected by the methanolic CO formation (surface poisoning) and depends on platinum surface structure and composition of supporting electrolyte with respect to the anions. The highest oxidation current, 156 mA-cm[sup [minus]2], is observed with the Pt(110) electrode in perchloric acid solution at 0.200 V vs Ag/AgCl reference. In terms of turnover, this current translates to 163 molecules-(Pt site)[sup [minus]1][center dot]s[sup [minus]1], a high rate exceeding previous expectations in methanol electrode kinetics. Overall, the oxidation current changes by 3 orders of magnitude between the extreme cases examined in this study. Breaking up the total effect into individual components shows that the surface geometry and anionic effects are roughly comparable. Therefore, we have an evidence that anion-platinum interactions are as important in determining the methanol oxidation rate as is the surface geometry of the Pt catalyst. 52 refs., 13 figs., 4 tabs.


Book
30 Jun 1994
TL;DR: In this paper, phase-transfer catalysis is used to transfer anion-anion pairs between an organic phase and an aqueous phase containing hydroxide ion and the effect of hydration of the transferred anion.
Abstract: Preface. Part 1: Basic concepts in phase-transfer catalysis: Phase-transfer-catalyzed reactions Basic steps of phase-transfer catalysis The PTC reaction rate matrix Anion transfer and anion activation Effect of reaction variables on transfer and intrinsic rates Outline of compounds used as phase-transfer catalysts. Part 2: Phase-transfer catalysts -- Fundamentals I: Introduction Structural factors affecting the distribution of anions between aqueous and organic phases Structural factors affecting the distribution of phase-transfer catalyst cations between the aqueous and organic phases Effects of the organic phase polarity on the distribution of phase-transfer cation-anion pairs Effects of changes in organic phase polarity during reaction Factors affecting the distribution of phase-transfer catalyst cation-anion pairs between an organic phase and an aqueous phase containing hydroxide ion Effect of hydration of the transferred anion and the effect of inorganic salt and/or hydroxide concentration in the aqueous phase. Part 3: Phase-transfer catalysis -- Fundamentals II: Introduction Liquid-liquid PTC Solid-liquid PTC. Part 4: Phase-transfer catalysts: Introduction Use of quaternary salts as phase-transfer catalysts Macrocyclic and macrobicyclic ligands PEGs, Tris (3, 6-dioxahepty)amine (TDA-1), and related ethoxylated compounds as phase-transfer catalysts Other soluable polymers and related multifunctional compounds as phase-transfer catalysts Use of dual PTC catalysts or use of cocatalysts in phase-transfer systems Catalysts for transfer of species other than anions Separation and recovery of phase-transfer catalysts. Part 5: Insoluable phase-transfer catalysts: Introduction PTC catalysts bound to insoluable resins Phase-transfer catalysts bound to inorganic solid supports PTC catalysts contained in a separate liquid phase (Third-liquid-phase catalyst). Part 6: Variables in reaction design for laboratory and industrial applications of phase-transfer catalysis: Choice of catalyst Choice of solvent Presence of water Agitation Choice of anion, leaving group, and counteranion Choice of base Guidelines for exploring new PTC applications. Part 7: Phase-transfer catalysis displacement reactions with simple anions: General considerations Behavior of various anions in PTC displacement reactions. Part 8: Phase-transfer catalysis reaction with strong bases: C-Alkylation N-Alkylation O-Alkylation -- Etherification S-Alikylation -- Thioetherification Dehydrohalogenation Carbene reactions Condensation reactions Deuterium exchange, isomerization, and oxidation. Part 9: Phase-transfer catalysis -- Polymerization and polymer modification: Introduction Polymer synthesis Chemical modification of polymers. Part 10: Phase-transfer-catalyzed oxidations: Introduction Permanganate oxidations Oxidations with hyperchlorite and hypobromite PTC oxidations with hydrogen peroxide PTC air or oxygen oxidations Oxidations by persulfates PTC oxidations with nitric acid PTC carbon tetrachloride/sodium hydroxide oxidations PTC oxidations with perborate PTC oxidations with ferrate and ferricyanide PTC oxidations with superoxide PTC electrochemical oxidations PTC oxidations with other oxidents. Part 11: Phase-transfer-catalyzed reductions: Sodium borohydride reductions Lithium aluminum hydride reductions Reductions with sodium formate Reductions with sulfur-containing anions Hydrogenation Reductions with formaldehyde Electrochemical reduction Photochemical reduction Wolff-Kishner reduction Reduction by dodecarbonyltriiron and related species. Part 12: Phase-transfer catalysis -- Chiral phase-transfer catalyzed formation of carbon-carbon bonds: Introduction Alkylation reactions. Part 13: Phase-transfer catalysis - Transition metal cocatalyzed reactions: Introduction Carbonylation and reactions with carbon monoxide PTC reduction and hydrogenation

Journal ArticleDOI
TL;DR: A range of alumina-supported platinum catalysts have been prepared and investigated for the selective reduction of nitrogen monoxide in the presence of a large excess of oxygen in steady state microreactor experiments.
Abstract: A range of alumina-supported platinum catalysts have been prepared and investigated for the selective reduction of nitrogen monoxide in the presence of a large excess of oxygen. Steady-state microreactor experiments have demonstrated that these catalysts are very active and selective for the reduction of nitrogen monoxide by propene at temperatures as low as 200°C. There does not appear to be a simple correlation between the activity for nitrogen monoxide reduction and the platinum surface area. Instead it is found that there is a very good inverse correlation between the maximum nitrogen monoxide reduction activity and the temperature. The most active catalysts for selective nitrogen monoxide reduction are those that generate activity at the lowest temperature. The technique of temporal analysis of products (TAP) has been used to obtain detailed mechanistic data about the selective nitrogen monoxide reduction reaction on an alumina-supported platinum catalyst. Using carbon monoxide, hydrogen or propene as reductant it has been demonstrated that the predominant mechanism for selective nitrogen monoxide reduction involves the decomposition of nitrogen monoxide on reduced platinum metal sites, followed by the regeneration of the active platinum sites by the reductant. In the decomposition step it has been shown that oxygen from nitrogen monoxide is retained on the surface of the platinum and blocks the surface for further adsorption/reaction of nitrogen monoxide; it has been observed that oxidised platinum catalysts are not active for the nitrogen monoxide reduction reaction. Under typical operating conditions, propene is a far more efficient reductant than either carbon monoxide or hydrogen. The greater efficiency of propene as a reductant is explained on the basis of the additional reducing power of the propene molecule, which can react with as many as nine adsorbed oxygen atoms, ensuring that 'patches' of reduced platinum are available for nitrogen monoxide adsorption/reaction. A small additional activity of reduced platinum in the presence of propene, which is not observed when carbon monoxide or hydrogen is used as reductant, has been explained on the basis of a second mechanism involving the carbon-assisted decomposition of nitrogen monoxide at sites on the reduced platinum adjacent to adsorbed carbon-containing moieties, believed to be fragments from adsorbed propene molecules. A model for the selective reduction of nitrogen monoxide on alumina-supported platinum catalysts is presented which is capable of explaining all the results obtained in this work and in the published literature on this subject.

Journal ArticleDOI
TL;DR: In this paper, the reactions of organometallic zirconium compounds are reviewed and a specific interest is placed on reactions where C-C bonds are formed, where the authors focus on the reactions where the C-c bond is formed.
Abstract: The authors review the reactions of organometallic zirconium compounds. Specific interest is placed on reactions where C-C bonds are formed.

Journal ArticleDOI
15 Jul 1994-Science
TL;DR: With individual stoichiometric steps observed and combined, and with intermediates isolated and fully characterized (including crystal structures), these systems demonstrate the effectiveness of a rational approach to catalytic design.
Abstract: Homogeneous catalytic activation of the strong carbon-fluorine bonds under mild conditions was achieved with the use of rhodium complexes as catalysts. The catalytic reactions between polyfluorobenzenes and hydrosilanes result in substitution of fluorine atoms by hydrogen atoms and are chemo- and regioselective. With individual stoichiometric steps observed and combined, and with intermediates isolated and fully characterized (including crystal structures), these systems demonstrate the effectiveness of a rational approach to catalytic design.

Journal ArticleDOI
TL;DR: In this article, model oxygenated compounds were used, namely 4-methylacetophenone, diethyldecanedioate and guaiacol, and their reactivity and conversion scheme were determined.
Abstract: The elimination of specific oxygenated groups of biomass-derived pyrolysis oils (bio-oils) is necessary for improving their stability. These are mainly unsaturated groups like alkene, carbonyl and carboxylic functions, as well as guaiacyl groups. For practical applications, it is desirable that the reactions are performed selectively in order to avoid excessive hydrogen consumption. The reactions must be done at relatively low temperature in order to limit competitive thermal condensation reactions. In this study, model oxygenated compounds were used, namely 4-methylacetophenone, diethyldecanedioate and guaiacol. They were tested simultaneously in one reaction test in the presence of sulfided cobalt-molybdenum and nickel-molybdenum supported on gamma-alumina catalysts in a batch system. Their reactivity and conversion scheme were determined. The ketonic group is easily and selectively hydrogenated into a methylene group at temperatures higher than 200 degrees C. Carboxylic groups are also hydrogenated to methyl groups, but a parallel decarboxylation occurs at comparable rates. A temperature around 300 degrees C is required for the conversion of carboxylic groups as well as for the conversion of the guaiacyl groups. The main reaction scheme of guaiacol is its transformation in hydroxyphenol which is subsequently converted to phenol. But in batch reactor conditions, guaiacol gives a high proportion of heavy products. CoMo and NiMo catalysts have comparable activities and selectivities. However, the NiMo catalyst has a higher decarboxylating activity than CoMo and also leads to a higher proportion of heavy products during the conversion of guaiacol.

Journal ArticleDOI
TL;DR: In this article, the authors describe the disadvantages of the three-way catalytic reduction process in V,OS-TiO,-W03 with ammonia as a reductant.

Journal ArticleDOI
TL;DR: In this article, several supported nickel catalysts were tested for the methane reforming reaction at 700°C and the initial activity depended essentially on the state of the nickel phase (reduction and dispersion) and little on its environment (support, additive).

Journal ArticleDOI
TL;DR: In this paper, the importance of acid-base bifunctional catalysis by ZrO2 and its mixed oxides is emphasized, and industrial applications of Zr O2 catalysts are demonstrated.

Journal ArticleDOI
TL;DR: In this article, the catalytic activity of the Ti-Beta catalyst for selective oxidation by H 2 O 2 of alkanes and alkenes with different molecular sizes was measured and compared with that of TS-1 under the same experimental conditions.