Size Effect of ZSM-5 on Diffusion and Catalytic Performance in Syngas Conversion to Aromatics over MnCrOx-ZSM-5 Catalyst

The combination of metal oxide and ZSM-5 zeolite (OXZEO) composite catalysts provides a promising route for direct syngas conversion to aromatics with a high selectivity. The diffusion of guest molecules in zeolites plays a key role in catalysis, but it is not well understood in the OXZEO syngas reaction. Herein, we showed that both the diffusion in the micropore and on the external surface of ZSM-5 depend on the ZSM-5 particle size. A larger particle size could lead to a longer retention time of olefins in the micropores, which are the key precursors of aromatics, thus promoting aromatization. A larger ZSM-5 particle also exhibits a lower diffusion barrier of aromatics on the external surface, which inhibits further methylation of BTX. Therefore, a higher aromatization capacity and higher BTX selectivity have been obtained over larger ZSM-5 particles in the OXZEO-catalyzed syngas reaction.