Showing papers in "Advances in Catalysis in 1966"

Chemical Identification of Surface Groups

Abstract: Publisher Summary The properties of a surface are influenced by the surface groups and the knowledge of their existence and of their chemistry are important for many technological processes This chapter examines the surface compounds on carbon—microcrystalline carbon, graphite, and diamond—on silica, on titania, and on alumina and silica–alumina Most important and best known among the surface compounds of carbon are those with oxygen and with sulfur Thus, two kinds of surface oxides are known Basic surface oxides are formed always when a carbon surface is freed from all surface compounds by heating in a vacuum or in an inert atmosphere and comes into contact with oxygen only after cooling to low temperatures Acidic surface oxides are formed when carbon is treated with oxygen a temperatures near its ignition point Unambiguous identification of carboxyl groups has been achieved by two reactions of the acyl chlorides: Friedel–Crafts reaction and Schmidt rearrangement

Stereochemistry and the Mechanism of Hydrogenation of Unsaturated Hydrocarbons

Abstract: Publisher Summary This chapter discusses the stereochemistry and the mechanism of hydrogenation of unsaturated hydrocarbons. The chapter reviews the development of the concepts and methods pertinent to the application of stereochemistry to the study of the mechanism of the surface-catalyzed reactions of hydrogen with unsaturated hydrocarbons. Explanations of the stereochemistry of hydrogenation have been dominated by ideas concerning the manner in which a given unsaturated compound may best be fitted onto a planar surface from which hydrogen is abstracted. The chapter discusses the development of techniques that permit the identification of different product-controlling reactions that directs one to consider the stereochemical consequences of various postulated reaction sequences. The similarity between heterogeneous and homogeneous catalytic hydrogenation has been emphasized recently by the demonstration that platinum–tin complexes catalyze the homogeneous hydrogenation of acetylene and ethylene at room temperature and certain complexes of rhodium are effective for the hydrogenation of 1-hexene.

π Complex Adsorption in Hydrogen Exchange on Group VIII Transition Metal Catalysts

Abstract: Publisher Summary This chapter reviews π complex adsorption that has been proposed in catalytic reaction mechanisms. The main evidence for this intermediate has been obtained from isotopic hydrogen exchange reactions with aromatic compounds where an interpretation according to classical theories has met with increasing difficulties. Group VIII transition metal catalyzed hydrogen exchange reactions are important in providing useful information concerning the fundamental processes of bond rupture and bond formation on catalyst surfaces. The chapter discusses the limitations of the classical associative and dissociative exchange mechanisms. The chapter also discusses quantum mechanical treatment of π complex adsorption in terms of charge-transfer theory including a description of two new exchange mechanisms formulated on this new mode of interaction. The advantages of an interpretation of catalytic exchange reactions in terms of π complex adsorption are outlined with a summary of available evidence to support the theory. The possible role of π complex adsorption in hydrogenation and related reactions is also discussed.

The Homogeneous Catalytic Isomerization of Olefins by Transition Metal Complexes

Abstract: Publisher Summary This chapter discusses the homogeneous catalytic isomerization of olefins by transition metal complexes Transition metal hydrides play a key role in the catalytic homogeneous isomerization of olefins The pure hydrides, such as HCo(CO) 4 can function as the catalyst or transition metals complexed to stabilizing ligands can function as catalysts The catalysis almost certainly proceeds through hydride intermediates in many cases The most attractive mechanism for olefin isomerization consists of initial complexing between olefin and metal, addition of H–M across the double bond to generate a σ carbon-metal bond, and then elimination of H–M in the opposite direction with eventual release of the isomerized olefin The evidence for such a mechanism is compelling, especially with the heavier transition metals However, when some σ-alkyl metals of cobalt and iron have been treated with olefins under conditions appropriate for isomerization, no transfer of the metal to the olefin occurred

Machines and Systems: A Preface

Abstract: Publisher Summary The book, “Advances in catalysis and related subjects, volume 16,” reviews the recent developments on mechanisms involved in several different classes of catalytic reactions: isomerization of olefins, dehydration of alcohols, hydrogen exchange, and hydrogenation of unsaturated hydrocarbons. The book discusses the courses of the kinetic processes and the electronic features of specific reaction complexes of the catalytic systems. The chapters in the book distinguish two major levels of machines and systems—the mechanism of kinetic course of the over-all reaction and the mechanism of electronic interaction in a specific reaction step.