Methanol diffusion in H-ZSM-5 catalysts as a function of loading and Si/Al ratio: A classical molecular dynamics study

Abstract

Methanol diffusion in H-ZSM-5 was studied using classical molecular dynamics at 373 –423 K, using loadings of 3 and 5 molecules per unit cell, in frameworks with Si/Al = 15, 47, 95 191 and a fully siliceous system. While the lower loading exhibits higher diffusivity, self-diffusivities increase at both loadings between Si/Al = 15 and 95, after which they are independent of composition. The trend in diffusivity with Si/Al ratio is explained in terms of methanol-acid site interactions, while the trend with loading is explained in terms of methanol-methanol interactions and the resulting methanol structure in the catalyst pores.

Keywords

• Methanol-to-hydrocarbons
• ZSM-5
• Molecular dynamics
• Zeolites