ROLES OF BRONSTED AND LEWIS SITES DURING CRACKING OF N-OCTANE ON H-MORDENITE

Catalytic reactions of n-octane on H-mordenite at 400-degrees-C have been studied. Evidence from changes in activity and selectivity with catalyst pretreatment temperature show that the dominant cracking processes leading to formation of acyclic alkanes and alkenes take place on Bronsted sites. Formation of aromatics and coke, associated with hydrogen transfer and cyclization processes are, however, enhanced by the presence of Lewis sites on the catalyst surface. Ratios of branched to linear alkane cracking fragments cannot be correlated with the ratio of Lewis to Bronsted sites present. Ratios of alkanes to alkenes can be correlated with changes in the ratio of Bronsted to Lewis sites present, at a given reaction temperature. However, this correlation cannot be further extended to give a ratio of cracking processes via protolytic and beta-scission mechanisms.