Showing papers in "Advances in Catalysis in 1968"

Organic Catalysis over Crystalline Aluminosilicates

Abstract: Publisher Summary This chapter focuses on organic catalysis over crystalline alumiosilicates. Zeolites are crystalline aluminosilicates composed of SiO4 and AlO4 tetrahedra arranged in various geometric patterns. The chapter discusses reactions over a wide variety of crystalline aluminosilicates and emphasizes on catalysis over X- and Y-type faujasites. Unusual opportunities for organic catalysis were found to exist when these were base exchanged to substantially eliminate their alkali metal content. It is shown that catalytic activity in ion-exchanged faujasites is influenced by cation type, cation location in the lattice, zeolite Si/Al ratio, and the presence of proton donors. The existence of several crystallographically distinct cation locations provides the basis for a potential heterogeneity of sites in catalytic reactions. The Linde workers made calculations for the electrostatic field strengths of surface cations near SII and SIII in an X-type zeolite of Si/Al ratio 1.0 and in a Y-type zeolite of Si/Al ratio 2.0. In both cases, the fields has been significantly larger near SIII than SII at a distance of 2 Ǻ from the center of the cation for the univalent cation-exchanged systems, provided both sites are occupied.

Stereochemistry and Mechanism of Hydrogenation of Naphthalenes on Transition Metal Catalysts and Conformational Analysis of the Products

Abstract: Publisher Summary This chapter discusses the stereochemistry and mechanism of hydrogenation of naphthalenes on transition metal catalysts. The chapter discusses the mechanism of saturation of naphthalene, as a stepwise process of two-by-two additions of hydrogen. The reaction scheme gives no hint of the mechanisms of adsorption and desorption, the extent and manner of the hydrogen exchange that always accompanies saturation, and whether each pair of hydrogen is added simultaneously or in separate steps. The hydrogenation of naphthalene to decalins has been known to proceed by way of tetralin as an intermediate. Two kinds of mechanisms have been proposed for formation of trans-decalin. One suggestion is that trans isomers may be formed by direct trans addition of hydrogen at the two bridgehead positions. The other mechanism involves cis addition in a more complicated process that involves turning over of some sort of intermediate, with or without intervening desorption.

On Transition Metal-Catalyzed Reactions of Norbornadiene and the Concept of π Complex Multicenter Processes

Abstract: Publisher Summary This chapter focuses on bicyclo[22l]heptadiene-2,5 (norbornadiene), a new versatile substrate for catalytic studies The chapter describes its transition metal-catalyzed reactions and discusses the mechanism of these reactions and the function of transition metals in catalytic processes of this kind The chemistry of norbornadiene is characterized by strain and homoconjugation Hence, the olefin undergoes a series of addition reactions that are frequently accompanied by the formation of the nortricyclene system—the direction of electrophilic attack being usually exo Transition metal complexes, such as nickel carbonyl or bisacrylonitrile nickel have been found to greatly promote the reaction of acrylonitrile with norbornadiene Norbornadiene may be carbonylated essentially under the conditions of Reppe's acrylic ester synthesis

The Effects of Ionizing Radiation on Solid Catalysts

Abstract: Publisher Summary This chapter discusses the effects of ionizing radiation on solid catalysts. The study of a catalyst by irradiation consists of four steps: (1) damage to the solid by irradiation, (2) the characterization of the defects produced, (3) the measurement of changes in catalytic activity or chemisorptions brought about by the irradiation, and (4) the attribution of any such changes to specific types of defect. Radiation has been observed to produce effects, such as alteration of surface area, desorption under radiation, and modification of physical adsorptivity. Because they show less variability from substance to substance than do catalysis and chemisorption, they are classed together as “nonspecific effects.” A special method for the irradiation of a catalyst is to incorporate in it atoms of a radioactive isotope. There is a connection between the preirradiation technique and the simultaneous irradiation of catalyst and substrate. Several adsorption experiments have been done under irradiation. Such experiments are simpler than radiolysis in the presence of a solid and helps in understanding the more complex systems.