Catalytic properties and deactivation behavior of modified H-ZSM-5 in the conversion of methanol-to-aromatics

Abstract A comparative study on the effects of SiO2 modification and mesoporous structures on catalytic performances over ZSM-5 zeolites in MTA conversion both theoretically and experimentally was done. Experimental results showed that hierarchical pores increased the production of aromatics. However, DFT calculation proved that energy barriers for producing aromatics over mesoporous ZSM-5 were larger than that of parent ZSM-5 due to decreasing acid strength after alkali treatment which significantly influenced rate-determining step. Furthermore, diffusion behaviors of toluene were studied by Molecular Dynamics. Larger pores led to the improvement of diffusion behaviors over hierarchical ZSM-5 owing to the decrease of collision frequency between molecules. Therefore, the formation of aromatics was mainly determined by diffusion limitation over hierarchical ZSM-5. The lowest BTX selectivity was obtained over SiO2 deposited mesoporous ZSM-5 due to decreasing acid strength and blockage of pore mouth. Additionally, the deactivation of ZSM-5 serial catalysts in MTA was attributed the formation of insoluble coke. Moreover, the introduction of mesopores and silylation on external surface alleviated the deactivation of catalysts.