Self-diffusion in zeolites was studied using a simple mean-field theory and dynamic Monte Carlo simulations of diffusion on a lattice model of the zeolite pore space. The method was powerful, and able to probe the influence of the topology of the pore network, the fraction of strong adsorption sites, the relative strengths of weak and strong sites, the number of sites per zeolite cage and the ratio of intra-cage to extra-cage hopping probabilities. The results confirmed the qualitative trends observed in pulsed-field gradient NMR experiments and were able to explain them. For ZSM-5, a new possible type of functional dependence of the diffusivity upon occupancy, with two inclination points, was found.

Dynamic Monte-Carlo and Mean-Field Study of the Effect of Strong Adsorption Sites on Self-Diffusion in Zeolites. M.O.Coppens, A.T.Bell, A.K.Chakraborty: Chemical Engineering Science, 1999, 54[15-16], 3455-63