Insight into Catalytic Cracking Pathways of N-Pentane over Bifunctional Catalysts to Produce Light Olefins

Revealing the reaction mechanism to guide the industrial production of targeted products still remains a grand challenge for catalytic cracking of light alkanes to olefins over metal-acid bifunctional catalyst. Herein, we systematically investigated the reaction mechanism of n-pentane cracking on the Ag/ZSM-5 bifunctional catalyst featuring both dehydrogenation and cracking capabilities. Specifically, overall cracking network of n-pentane was comprehensively constructed to show the roles of metal dehydrogenation sites and acid sites respectively, in which metal Ag could substitute the H of the Br & oslash;nsted acid site to form the Al-O-Ag linkage with enhanced adsorption and activation of n-pentane, while Br & oslash;nsted acid site with weak acid strength relay to promote cracking reaction. Thanks to this synergy of the two active sites, the apparent activation energy of n-pentane cracking to light olefins was decreased from 82.77 KJ/mol to 68.26 KJ/mol and the proportion of specific path (C5H12 -> H-2 + C5H10) in n-pentane monomolecular cracking reaction increased from 14.62% to 69.24%. In addition, 0.57Ag/ZSM-5 catalyst exhibited the conversion of n-pentane up to 67.55 wt%, which improved the performance of the parent ZSM-5 by 13.42 wt%. These analysis results of reaction mechanism may provide some insights for the rational design of catalysts and the full utilization of petrochemical resources.