Structural amd Physicochemical Aspects of Acidic Catalysis in Zeolites

Abstract

Publisher Summary This chapter describes the various aspects of acidity related to catalytic properties by discussing the influence and importance of the framework constituents in view of localized sites and of overall properties. Mainly protonic sites, the more important in carbonium ions formation, are considered in the chapter. Three important main points for catalysis with zeolites are related to the cation field: modification of molecule in cation fields, increase in the acid strength, and formation of new acid sites. There are at least two adsorption site types in zeolites: cationic and acidic sites. Catalysis on acid sites acts while the reactant is simultaneously being adsorbed on the cations. The polarizing power of the cations plays a role in acidic catalysis by acting on the number of potential acidic sites through an adsorption equilibrium (if the surface is not fully covered—that is, for non–zero order reactions). When the reactant can be transformed on cations and on acid sites, the selectivity of the reaction will depend, among other parameters, upon the importance of the adsorption not only on cation and proton sites acting independently but, for a major part, on the competitive weight of each of these sites in the overall rate of reactant consumption.