A theoretical insight into diffusion mechanism of benzene-methanol alkylation reaction in ZSM-5 zeolite

Alkylation reaction of benzene and methanol produces desirable product p-xylene, thus understanding the structure-performance relationship in alkylation reaction is significant. Herein, the diffusion behavior of representative components (i.e. benzene, methanol, olefin and alkylbenzene) involved in the alkylation reaction catalyzed by Al-substituting ZSM-5 (H-ZSM-5) zeolite at 673 K was studied based on molecular dynamics simulations. As a result, the self-diffusion coefficients (Ds) of methanol and benzene at 673 K in H-ZSM-5 zeolite are 2.97 × 10−8 and 6.50 × 10−12 m2 s−1, respectively; while in CH3-ZSM-5 zeolite, the presence of CH3O- intermediates does favor to the diffusion of benzene and alkylbenzene, especially p-xylene. Furthermore, due to the distinguished dynamic diameters compared with pore sizes, the reaction species exhibit anisotropic diffusion along x-, y- and z-direction of zeolite channel. This work may not only provide an insight into the diffusion mechanism for alkylation reaction of benzene and methanol, but also help guide the design of zeolite catalysts.