ACIDITY OF ZSM-5 ZEOLITES - A COMPARISON OF RESULTS OBTAINED USING DIFFERENT EXPERIMENTAL METHODS

Abstract

Acidity of HZSM-5 zeolites with varying silica/alumina ratios has been studied by different techniques. Total acidity decreases with increase in silica/alumina ratio as expected, but the concentration of strong acid sites increases in the same direction. High temperature peak in TPD of ammonia alone does not account for total structural acidity. A linear relationship has been established between the concentration of moderately strong acid sites in ZSM-5 and its catalytic activity in EB disproportionation reaction. Infrared spectra of adsorbed pyridine on various zeolite samples indicate that strength of both Bronsted and Lewis acid sites increases with silica/alumina ratio, but Lewis acidity is generally weaker than Bronsted acidity.