Dehydroxylation of NaHY zeolites studied by infrared spectroscopy

Abstract

The dehydroxylation of NaHY zeolites of various exchange degrees was studied by i.r. spectroscopy. The quantitative i.r. studies of pyridine adsorption enabled us to determine the concentrations of OH groups and Lewis-acid sites in partially dehydroxylated zeolites. The concentration of Lewis-acid sites in completely dehydroxylated NaHY zeolites is half the initial concentration of OH groups. Experiments on the thermodesorption of pyridine provided information concerning the acid strength of the acid sites. The partial dehydroxylation of NaHY zeolites results in a decrease in the acid strength of both OH groups and Lewis-acid sites. The acid strength of the Lewis-acid sites in a dehydroxylated NaHY zeolite having a higher exchange degree is higher than in the case of an NaHY zeolite whose degree of exchange is lower.