Catalytic activity of SAPO5 for cracking of butane and hexane

Abstract

The catalytic properties of three SAPO5 samples for cracking of n-hexane and n-butane have been investigated. For characterization, both adsorption and temperature-programmed desorption of ammonia and pyridine were used. Only bridging hydroxyl groups (strong Brønsted-acid sites wre found to be active for both reactions. The catalytic activities of these sites were the same for all samples investigated. Differences exist with respect to the accessibility of n-butane and n-hexane. The variatios of the turnover frequencies suggest that n-butane was converted over all Brønsted-acid sites) were the same for all samples investigated. Differences exist with respetc the accessibility of n-butane and n-hexane. The variations ofthe turnover frequencies suggest that n-butane was converted over all Bronsted-acid sites to adsorb pyridine. The prodcuct distribution and the apparent enerties of activatio suggest the prevalence of a monomolecular mechanism for cracking. As both molecules, an-butenes and n-hexan,e have nearly identical kinetic diameters, the transition state for n-hexane must be more bulky than that for n-butane.