Effect of degree of H⁺ exchange on the acidity distribution of HNa---ZSM---5

Abstract

The acidity distribution of the HNa---ZSM---5 zeolites was investigated by the adsorption and desorption of pyridine using the two gas chromatographic methods, viz. T.p.d. (temperature programmed desorption) under chromatographic conditions and stepwise thermal desorption (STD), at temperatures close to those employed in the catalytic reactions and also by studying the model reactions, viz. cracking of cumene and isomerization of o-xylene, catalysed by protonic acid sites in a pulse microreactor. The acidity has been found to be strongly dependent on the degree of H⁺-exchange of the zeolite. When the degree of H⁺-exchange is increased, an increase is observed not only in the number of strong acid sites, but also in the ratio of strong acid sites to the exchanged H⁺ and in the catalytic activity for both the cumene cracking and o-xylene isomerization reactions.