A theory for two-component diffusion in zeolites

Abstract

This chapter discusses the assumptions underlying modern atomistic and lattice approaches, and details the techniques and applications of modeling both rapid dynamics and activated diffusion. Practical applications of zeolites are typically run under steady-state conditions, making the relevant transport coefficient the Fickian diffusivity or other related permeability coefficient. However, modeling such steady-state transport through zeolites with atomistic models is challenging, prompting many researchers to simulate self-diffusion, which is the stochastic motion of tagged particles at equilibrium. The wide range of diffusional timescales encountered by molecules in zeolites presents unique challenges to the modeler, requiring that various simulation tools, each with its own range of applicability, be brought to bear on modeling dynamics in zeolites. The goals of simulating molecular dynamics in zeolites with atomistic detail are two-fold: to predict the transport coefficients of adsorbed molecules and to elucidate the mechanisms of intracrystalline diffusion. The chapter summarizes the major findings discovered over the last several years and enumerates future needs for the frontier of modeling dynamics in zeolites. With a rich variety of interesting properties and industrial applications, and with over 100 zeolite framework topologies synthetically available, each with its own range of compositions, zeolites offer size, shape, and electrostatically selective adsorption, diffusion, and reaction up to remarkably high temperatures.