Reaction pathways of n-butane cracking over the MFI, FER and TON zeolites: Influence of regional differences in Brønsted acid sites

Abstract

Three zeolites ZSM-5, ZSM-35 and ZSM-22 are applied in n -butane cracking to reveal the influence of regional differences in Brønsted acid sites on reaction pathways. The Brønsted acid sites located in the channels of ZSM-5 exhibit a higher catalytic activity and yields to light olefins (especially the ethylene), which can be attributed to more relative contribution of bimolecular pathway. In comparison, more Brønsted acid sites are situated on the external surface or micropore mouths of ZSM-35 and ZSM-22, which are beneficial to propylene production. Note-worthily, almost no propane production on the two zeolites implies the predomination of monomolecular pathway. In situ FTIR technique further discloses that the difference in the reaction pathways is tailored by adsorption configurations of n -butane at two types of Brønsted acid sites. Under comparable conditions, the ZSM-5 performs a relatively good catalytic stability through bimolecular pathway. Furthermore, the correlation between deactivation rate and light olefins reveals that the enhancement of propylene selectivity accelerates the deactivation of ZSM-35 and ZSM-22. While, promotion on the ethylene selectivity is a significant inducement for the deactivation of ZSM-5. Reaction pathways of n-butane cracking tailored by the influence of regional differences in Brønsted acid sites. • Three typical 10-member ring zeolites ZSM-5, ZSM-35 and ZSM-22 are prepared. • Reaction pathways of n -butane cracking over the zeolites are investigated. • Regional differences in Brønsted acid sites tailor the selectivities to propylene and ethylene. • ZSM-5 zeolite exhibits high catalytic activity and stability compared to ZSM-35 and ZSM-22. • Catalyst deactivation mechanisms are revealed on different reaction pathways.