Moderation of textural properties in hierarchical ZSM-5 to enhance the yield of olefins in catalytic cracking of hydrocarbons

Abstract

A dual-template method was adopted to prepare hierarchical ZSM-5 zeolite and used for catalytic cracking of n-pentane to produce light olefins. Through regulation of the content of tetrapropylammonium hydroxide (TPAOH) and tetrabutylphosphonium hydroxide (TBPOH), ZSM-5 zeolites with tuneable proportions of micropores to mesopores are hydrothermally synthesized. In cracking reactions, mesopores provide spatial diffusion which enhances the conversion of reactants, and micropores confirm the cracking depth of the intermediate products. With TPAOH/TBPOH of 20/1 (molar ratio), the prepared catalyst (SP-1T) gives a yield of light olefins (ethylene and propylene) up to 48.2 wt% at 600 °C. The hierarchy factors (HFs) calculated from the textural properties show a positive correlation with TOFs based on the reactant conversion, but not with the yield of olefins. Moreover, the deep secondary reaction is inhibited over the SP-1T catalyst, thus leading to excellent catalytic stability.