Ultrathin ZSM-5 Shell Constructed on an S-1 Crystal Surface for Prins Reaction to Boost Methanol Aromatization with High Catalytic Stability

Abstract

The conversion of methanol to aromatic over acid zeolite is a promising route to increase the supply of aromatic via a nonpetroleum route. However, the low conversion rate of the hydrogen transfer route between olefins over conventional ZSM-5 leads to a low efficiency of the aromatization process. Herein, a thin ZSM-5 shell with high Lewis/Brønsted was coated on the silicalite-1 surface by seed-induced stepwise crystallization. The thin ZSM-5 shell and Lewis acid sites promoted the formation of formaldehyde by hydrogen transfer between methanol and the olefin. Formaldehyde underwent a Prins reaction with olefin to generate long-chain unsaturated hydrocarbons, which accelerated the aromatization process of olefins. The aromatic selectivity increased to 33.9% from 26.6% of hydrogen transfer routes between olefins, and the alkene selectivity decreased from 16.1% to 9.4%. The diffusion promoted by ultrathin shell slowed down the formation of polycyclic aromatic, achieving stable conversion of methanol to aromatics. Appropriately increasing the amount of Brønsted acid in the catalyst or introducing additional olefin into the reaction system could promote the formation of dimethylcyclopentene intermediates and the conversion to aromatic, further improving the aromatic selectivity. This study extended insights into the regulation of acidity and diffusion length over ZSM-5 for promoting aromatic production.