Isopropylamine adsorption for the characterization of acid sites in silica-alumina catalysts

Abstract

The adsorption and reaction of isopropylamine has been studied using temperature-programmed desorption (TPD) and thermogravimetric analysis (TGA) on a series of silica-alumina catalysts as a function of alumina content, and the results have been correlated with cracking activities for n-hexane. The TPD-TGA curves on the amorphous silica-aluminas exhibit similar features to that observed on high-silica zeolites in that a well-defined feature is observed which desorbs as propene and ammonia between 575 and 650 K. This desorption feature appears to be due to strong Bønsted sites which are not present on either pure silica or alumina. The concentration of these sites increases in a regular manner with Al content and correlates well with the n-hexane cracking activity. This suggests that the TPD-TGA measurement of isopropylamine is a useful probe of the catalytically active sites on amorphous silica-aluminas.