Esterification of acetic acid with methanol to methyl acetate on Pd-modified zeolites: effect of Bronsted acid site strength on activity

Abstract

The effect of the amount of Bronsted acid sites with their strengths on bare and palladium-modified H-ZSM5 and H-Ferrierite on the catalytic activity in the esterification of acetic acid with methanol was investigated by comparing the variation of Bronsted acid site strength. The strong acid sites on zeolites are responsible for the low reaction rate of esterification and low selectivity to methyl acetate by the strong adsorption properties of reactants. The stronger Bronsted acid site strengths, which are more abundant on bare H-Ferrierite than H-ZSM5, were properly modified with Pd promoter without significant loss of total acid sites. The esterification rates were largely increased with a concomitant increase of methyl acetate selectivity after Pd modification. The strongly adsorbed methoxy species by forming surface dimeric alcohols can be attributed to the suppressed rate of esterification. The roles of Bronsted acid sites and their strengths to catalytic activity were verified through NH3-TPD and adsorbed pyridine or methanol through FT-IR analyses.