Molecular Dynamics Simulations of Self-Diffusivities, Corrected Diffusivities, and Transport Diffusivities of Light Gases in Four Silica Zeolites To Assess Influences of Pore Shape and Connectivity

Abstract

We have used equilibrium molecular dynamics (EMD) to study the influences of pore shape and connectivity on single component diffusion of several gases in silica zeolites using atomically detailed models of these materials. Results are presented for CH 4, CF 4, SF 6, Ar, and Ne in silicalite, CH 4, Ar, and Ne in ITQ-3, CH 4, CF 4, Ar, and SF 6 in ITQ-7, and CH 4, CF 4, Ar, and H 2 in ZSM-12 at room temperature. This set of four silica zeolites includes one, two, and three-dimensional pore topologies and pore volumes of several different shapes. EMD can be used to simultaneously determine the self-diffusivities and corrected diffusivities as a function of pore loading, and this has been done for every example. In combination with adsorption isotherms computed using grand canonical Monte Carlo, EMD results can also determine the transport diffusivity as a function of pore loading. The resulting transport diffusivities are reported for every example. The broad data set presented here is useful for considering the variety of diffusion behaviors that can occur for small molecules adsorbed in zeolite pores.