Catalysis

About: Catalysis is a research topic. Over the lifetime, 400924 publications have been published within this topic receiving 8702469 citations.

Cu-ZSM-5 Zeolites for the Formation of Methanol from Methane and Oxygen: Probing the Active Sites and Spectator Species

Abstract: A series of Cu-ZSM-5 zeolites was prepared by varying nature of the charge compensating cation, copper precursor, copper loading, and pH. The materials were tested for the oxidation of methane to methanol using oxygen. A linear relationship between the amount of methanol produced over Cu-ZSM-5 zeolites from methane and oxygen and a UV-Vis-NIR DRS charge transfer band at 22,700 cm -1 is reported irrespective of the synthesis route used. The absolute intensity of the 22,700 cm -1 band is always low, indicating a low number of active sites in the samples. In all studied Cu-ZSM-5 zeolites at least two copper species were present: (a) Cu-O clusters dispersed on the outer surface of ZSM-5 and (b) highly dispersed copper-oxo species inside the channels, a minority fraction in the sample. By relating catalytic activity to FT-IR data of adsorbed pivalonitrile, visualizing Cu-O particles on the outer surface of the zeolite, and subsequently adsorbed NO, indicative of the Cu-O species inside the zeolite channel, it was concluded that Cu-O species on the outer surface are not involved in the oxidation reaction, while copper inside the channels are responsible for the selective conversion of methane to methanol.

Chemistry In Alternative Reaction Media

Abstract: Preface.Abbreviations and Acronyms.1 Chemistry in Alternative Reaction Media.1.1 Economic and Political Considerations.1.2 Why Do Things Dissolve?1.3 Solvent Properties and Solvent Classification.1.3.1 Density.1.3.2 Mass Transport.1.3.3 Boiling Point, Melting Point and Volatility.1.3.4 Solvents as Heat-Transfer Media.1.3.5 Cohesive Pressure, Internal Pressure, and Solubility Parameter.1.4 Solvent Polarity.1.4.1 Dipole Moment and Dispersive Forces.1.4.2 Dielectric Constant.1.4.3 Electron Pair Donor and Acceptor Numbers.1.4.4 Empirical Polarity Scales.1.4.5 ENT and ET(30) Parameters.1.4.6 Kamlet-Taft Parameters.1.4.7 Hydrogen Bond Donor (HBD) and Hydrogen Bond Acceptor (HBA) Solvents.1.5 The Effect of Solvent Polarity on Chemical Systems.1.5.1 The Effect of Solvent Polarity on Chemical Reactions.1.5.2 The Effect of Solvent Polarity on Equilibria.1.6 W hat is Required from Alternative Solvent Strategies?References.2 Multiphasic Solvent Systems.2.1 An Introduction to Multiphasic Chemistry.2.1.1 The Traditional Biphasic Approach.2.1.2 Temperature Dependent Solvent Systems.2.1.3 Single- to Two-Phase Systems.2.1.4 Multiphasic Systems.2.2 Solvent Combinations.2.2.1 Water.2.2.2 Fluorous Solvents.2.2.3 Ionic Liquids.2.2.4 Supercritical Fluids and Other Solvent Combinations.2.3 Benefits and Problems Associated with Multiphasic Systems.2.3.1 Partially Miscible Liquids.2.4 Kinetics of Homogeneous Reactions.2.4.1 Rate is Independent of Stoichiometry.2.4.2 Rate is Determined by the Probability of Reactants Meeting.2.4.3 Rate is Measured by the Concentration of the Reagents.2.4.4 Catalysed Systems.2.5 Kinetics of Biphasic Reactions.2.5.1 The Concentration of Reactants in Each Phase is Affected by Diffusion.2.5.2 The Concentration of the Reactants and Products in the Reacting Phase is Determined by Their Partition Coefficients.2.5.3 The Partition Coefficients of the Reactants and Products May Alter the Position of the Equilibrium.2.5.4 Effect of Diffusion on Rate.2.5.5 Determining the Rate of a Reaction in a Biphasic System.2.6 Conclusions.References.3 Reactions in Fluorous Media.3.1 Introduction.3.2 Properties of Perfluorinated Solvents.3.3 Designing Molecules for Fluorous Compatibility.3.4 Probing the Effect of Perfluoroalkylation on Ligand Properties.3.5 Partition Coefficients.3.6 Liquid-Liquid Extractions.3.7 Solid Separations.3.8 Conclusions.References.4 Ionic Liquids.4.1 Introduction.4.1.1 The Cations and Anions.4.1.2 Synthesis of Ionic Liquids.4.2 Physical Properties of Ionic Liquids.4.3 Benefits and Problems Associated with Using Ionic Liquids in Synthesis.4.4 Catalyst Design.4.5 Conclusions.References.5 Reactions in Water.5.1 The Structure and Properties of Water.5.1.1 The Structure of Water.5.1.2 Near-Critical Water.5.1.3 The Hydrophobic Effect.5.1.4 The Salt Effect.5.2 The Benefits and Problems Associated with Using Water in Chemical Synthesis.5.3 Organometallic Reactions in Water.5.4 Aqueous Biphasic Catalysis.5.4.1 Ligands for Aqueous-Organic Biphasic Catalysis.5.5 Phase Transfer Catalysis.5.5.1 The Transfer of Nucleophiles into Organic Solvents.5.5.2 Mechanisms of Nucleophilic Substitutions Under Phase Transfer Conditions.5.5.3 The Rates of Phase Transfer Reactions.5.5.4 Using Inorganic Reagents in Organic Reactions.5.6 Organometallic Catalysis under Phase Transfer Conditions.5.7 Triphase Catalysis.5.7.1 Mixing Efficiency in Solid-Liquid Reactions.5.8 Conclusions.References.6 Supercritical Fluids.6.1 Introduction.6.2 Physical Properties.6.3 Local Density Augmentation.6.4 Supercritical Fluids as Replacement Solvents.6.5 Reactor Design.6.6 Spectroscopic Analysis of Supercritical Media.6.6.1 Vibrational Spectroscopy.6.6.2 NMR Spectroscopy.6.7 Reactions in Supercritical Media.6.8 Conclusions.References.7 Diels-Alder Reactions in Alternative Media.7.1 Diels-Alder Reactions in Water.7.2 Diels-Alder Reactions in Perfluorinated Solvents.7.3 Diels-Alder Reactions in Ionic Liquids.7.4 Diels-Alder Reactions in Supercritical Carbon Dioxide.7.5 Conclusions.References.8 Hydrogenation and Hydroformylation Reactions in Alternative Solvents.8.1 Introduction.8.2 Hydrogenation of Simple Alkenes and Arenes.8.2.1 Hydrogenation in Water.8.2.2 Hydrogenation in Ionic Liquids.8.2.3 Hydrogenation in Fluorous Solvents.8.2.4 Hydrogenation in Supercritical Fluids.8.3 Hydroformylation Reactions in Alternative Media.8.3.1 Hydroformylation in Water.8.3.2 Hydroformylation in Ionic Liquids.8.3.3 Hydroformylation in Fluorous Solvents.8.3.4 Hydroformylation in Supercritical Fluids.8.4 Conclusions.References.9 FromAlkanestoCO2: Oxidation in Alternative Reaction Media.9.1 Oxidation of Alkanes.9.2 Oxidation of Alkenes.9.3 Oxidation of Alcohols.9.4 Oxidation of Aldehydes and Ketones.9.5 Destructive Oxidation.9.6 Conclusions.References.10 Carbon-Carbon Bond Formation, Metathesis and Polymerization.10.1 Carbon-Carbon Coupling Reactions.10.1.1 Heck Coupling Reactions.10.1.2 Suzuki Coupling Reactions.10.1.3 Reactions Involving the Formation of C=C Double Bonds.10.2 Metathesis Reactions.10.2.1 Ring Opening Metathesis Polymerization.10.2.2 Ring Closing Metathesis.10.3 Polymerization Reactions in Alternative Reaction Media.10.3.1 Polymerization Reactions in Water.10.3.2 Polymerization Reactions in Supercritical Carbon Dioxide.10.3.3 Polymerization in Fluorous Solvents.10.4 Conclusions.References.11 Alternative Reaction Media in Industrial Processes.11.1 Obstacles and Opportunities for Alternative Media.11.2 Reactor Considerations for Alternative Media.11.2.1 Batch Reactors.11.2.2 Flow Reactors.11.2.3 New Technology Suitable for Multiphasic Reactions.11.3 Industrial Applications of Alternative Solvent Systems.11.3.1 The Development of the First Aqueous-Organic Biphasic Hydroformylation Plant.11.3.2 Other Examples of Processes Using Water as a Solvent.11.3.3 Scale-Up of PTC Systems.11.3.4 Thomas Swan Supercritical Fluid Plant.11.3.5 Other Applications of Supercritical Carbon Dioxide.11.4 Outlook for Fluorous Solvents and Ionic Liquids.11.5 Conclusions.References.Index.

Deactivation of PdO–Al2O3 oxidation catalyst in lean-burn natural gas engine exhaust: aged catalyst characterization and studies of poisoning by H2O and SO2

Abstract: A palladium oxide on alumina oxidation catalyst was employed to remove combustible pollutants from the exhaust of a spark-ignited, lean-burn natural gas engine. Rapid deactivation was seen for the oxidation of methane and ethane. Characterization results are consistent with sulfur as the primary source of catalyst activity loss. In microreactor studies, deactivation of the engine aged catalysts was only apparent if water was present in the feed stream. In dry feed gas, the activity of fresh and engine aged samples was the same. SO2 in dry gas was shown to cause both inhibition and deactivation for methane oxidation. This deactivation is partly reversible at 733 K and completely reversible at 793 K. Water inhibits the rate of methane oxidation and causes some permanent activity loss. Activity studies at 733 and 793 K indicate that activity loss is greater when both water and SO2 are present. Sulfur oxide groups on the surface increase both the amount of water sorbed and the water desorption temperature in TPD experiments. It is proposed that water and SO2 compete for adsorption sites on the alumina surface. Enhanced activity loss in the presence of both poisons is attributed to enhanced water inhibition and spillover of sorbed SO2 and SO3 species from alumina to the PdO surface.

Catalysis of heteropoly acids entrapped in activated carbon.

Abstract: Activated carbon was found to be able to entrap a certain amount of heteropoly acids, resulting in solid acid catalysts. Heteropoly acids thus entrapped were hardly removed even by extraction with hot water or hot methanol. The entrapped catalysts offer convenient methods for liquid-phase etherification of alcohols and vapor-phase selective esterification.