THE ROLES OF BRONSTED AND LEWIS SURFACE ACID SITES IN ACID-TREATED MONTMORILLONITE SUPPORTED ZNCL2 ALKYLATION CATALYSTS

The catalyst known as ''clayzic'' (ZnCl2 supported on acid-treated mon tmorillonite) exhibits both Bronsted and Lewis surface acidities. The relative catalytic activities of these two types of acid site have bee n determined in a range of reactions, by comparing the activities of c layzic with those of related catalysts which exhibit only one type of surface acidity. Acid-treated montmorillonite has been used as the Bro nsted acid catalyst in this comparison, and ZnCl2 supported on a mesop orous silica has been used as the Lewis acid catalyst. The results con firm that the relative activities of the two types of acid site depend on both the nature of the reaction and the polarity of the reaction m edium. They will be of value in optimising the choice of support and t he ZnCl2 loading in clayzic-type catalysts for specific reactions.