Zeolite acid strength and reaction mechanisms in catalysis

Abstract

The heterogeneous catalysts of greatest practical importance are acidic zeolites, and these cannot be studied using the traditional methods of UHV surface science. As recently as 1994 there was near universal agreement that zeolites were superacids, and that many of the most important reaction mechanisms in catalysis were based upon simple carbenium ions and other exotic high-energy intermediate species. This Paper reviews a series of investigations, many of them using solid-state NMR, that led to the reclassification of zeolite acidity and a theoretical basis for understanding carbenium ion stability in these fascinating solids. Building on this better understanding of zeolite acid strength and the types of carbenium ions that are reasonable intermediates in zeolites, it was possible to elucidate many of the features of a challenging mechanistic problem: methanol to hydrocarbon catalysis.