Synthesis of layered ZSM-5 zeolites with stable self-supported structure for enhanced catalytic cracking of cycloalkane aromatics

Abstract

High diffusion resistance of conventional microporous ZSM-5 zeolites greatly inhibits the effective conversion of cycloalkane aromatics into BTX, ethylene, and propylene over acid sites during the catalytic cracking of diesel. Herein, we successfully synthesized self-supported layered ZSM-5 with enhanced diffusion ability and specific acid site distribution through pre-crystallization and hydrothermal synthesis to boost the catalytic cracking of tetralin. Assisted by pre-synthesized crystal seeds as nuclei and quaternary ammonium salts, a unique 2 nm thick layer was stably spread over the surface of the crystal seeds. Even after the templating agents are removed at high temperatures, the robust self-supported layered structure could still maintain the thermal stability of MFI structure with excess 50 % acid sites distributed on the external surface. Such specific acidic distribution greatly resisted the formation of coke in the zeolite pore channels. Moreover, thanks to the reduced diffusion resistance of the mesoporous structure, the self-supported layered ZSM-5 zeolites exhibited enhanced tetralin conversion of 47.3 %, nearly 38 % higher than that of traditional ZSM-5 zeolites (9.7 %). This work could provide a reference for the design of efficient zeolite catalysts with multi-level pore structure for catalytic cracking of diesel.