Urea-induced platelike ZSM-5 zeolites with Si zoning for efficient alkylation of toluene with ethanol to para-ethyltoluene†

Abstract

Platelike zeolites with a short diffusion pathway are promising catalysts due to mass transfer advantages. Herein, platelike ZSM-5 with a reduced b-axis thickness (∼90 nm) was synthesized using a urea-assisted crystallization strategy. We disclose the significant application of this platelike catalyst in the toluene alkylation reaction with ethanol to produce para-ethyltoluene (p-ET). The reaction results demonstrate that this platelike ZSM-5 exhibits a higher toluene conversion (58.3%) and ET selectivity (88.7%) than conventional ZSM-5. This improvement is primarily due to the shortened straight channels of platelike ZSM-5, which facilitate mass transport and increase the accessibility to acid sites. Nevertheless, the shortened b-axis of platelike ZSM-5 seems to have no significant positive impact on para-selectivity for p-ET. Hence, we constructed a Si-zoned external surface on the platelike ZSM-5 by means of the surface modification strategy to accurately passivate the surface acid sites, thereby inhibiting the isomerization reaction, and achieving higher selectivity for p-ET (>95%) and extended catalytic stability (>100 h) in the reaction of toluene alkylation with ethanol.