Theoretical Insights into Intracrystalline Diffusion of Olefins in MTO Catalysts

Abstract

Diffusion process plays a decisive role in MTO reactions over zeolite catalysts. In this work, a theoretical approach was developed for modelling olefins diffusion in two typical zeolites, HZSM-5 and HSAPO-34. Activation barrier between large cavities and channels was determined using Lennard–Jones (LJ) potentials, where electrostatic potential was inserted to account for the induced dipole force that had been ignored in previous studies. Six typical products of MTO were selected as probe molecules. Detailed insights into the variation of activation barrier and diffusivity were obtained via comparative analysis between the two zeolites. Transition from Knudsen diffusion to configurational diffusion was also discriminated, and probe molecules were found to fall basically either in configurational regime or near transition regime. This work provides a submodel for further modeling of the complete reaction system, and ultimately contributes to a rational design of zeolite catalysts.