Diffusion and reaction in high-occupancy zeolite catalysts—I. A stochastic theory

Abstract

The theory of Markov pure jump processes is employed to model zeolitic diffusion and reaction as a sequence of elementary jump events taking place in a finite periodic lattice. Monte Carlo and approximate analytical solutions to the derived Master equation are developed to examine the effect of intracrystalline occupancy on the macroscopic diffusional behavior of the system. It is shown that, in the absence of soft intermolecular interactions, the Wicke—Kallenbach and uptake diffusivities for a single-component system are independent of intracrystalline occupancy, but the self-diffusivity decreases with increases with occupancy if these interaction are attractive, and decreases if they are repulsive. For a multicomponent system, the diffusivity matrix is nondiagonal and occupancy-dependent, giving rise to interesting competitive diffusion and entertainment phenomena.