The Maxwell-Stefan formulation, as applied to zeolites such as ZSM-5 that contained both weak and strong adsorption sites, was compared to dynamic Monte Carlo simulations for the limiting case of single-component self-diffusion. The study was intended as a consistency check, and as a step towards an analytical or semi-analytical theory for self-diffusion in zeolites with multiple types of site. When it was assumed that ζ, the ratio of the self-exchange coefficient to the corrected diffusivity, was equal to unity, the Maxwell-Stefan formulation performed well for silicalite. Because ζ was generally occupancy-dependent, the theory was unsuitable as a fully predictive one for self-diffusion in heterogeneous microporous solids until a theory for ζ was derived. As several studies had demonstrated that the Maxwell-Stefan formulation was able to predict multi-component diffusivities from single-component diffusivities for zeolites with one type of site, an extension to zeolites with multiple types of sites was required.

Testing the Consistency of the Maxwell-Stefan Formulation When Predicting Self-Diffusion in Zeolites with Strong Adsorption Sites. M.O.Coppens, V.Iyengar: Nanotechnology, 2005, 16[7], S442-8