Reactions of 3-methylpentane and 2,3-dimethylbutane on aluminosilicate catalysts

Abstract

Catalytic reactions of 3-methylpentane and 2,3-dimethylbutane on HY, amorphous silica-alumina, and HZSM-5 have been studied at 500°C. Both kinetic phenomena and product selectivities have been reported. Cracking reactions on HZSM-5 can be attributed to initiation through protonation occurring at Bronsted sites. Bimolecular processes leading to chain reactions via hydride transfer are restricted within the narrow pore pentasil zeolite. On HY and amorphous silica-alumina, initiation of cracking also occurs at Brønsted sites. No direct evidence was found for participation of Lewis acid sites on the catalyst framework itself. Following initiation, reactions on these catalysts are accelerated through a chain process occurring at Lewis sites generated by adsorption of product olefins at Brønsted sites. The resulting change in the dominant cracking mechanism is reflected in the product selectivity, illustrated here by a falling off in formation of molecular hydrogen as conversion increases.