DIFFUSION BEHAVIOR OF BINARY-MIXTURES IN RESTRICTED REGIONS OF ZEOLITE NAY FROM MOLECULAR-DYNAMICS CALCULATIONS

Diffusion coefficients D-1 and D-2 of a binary mixture of adsorbates of diameters sigma(1) and sigma(2) in the restricted regions of zeolite NaY have been obtained from molecular dynamics simulations. The results suggest that the ratio of the diffusion coefficients zeta = D-1/D-2 exhibit unusual behaviour with an increase in the ratio of diameters eta = sigma(1)/sigma(2):D-1 > D-2 even when sigma(1) > sigma(2). Calculations on a single component adsorbate in zeolite NaY suggest that the diffusion coefficient shows an anomaly when the adsorbate diameter approaches the diameter of the window, the narrowest portion of the porous network. It is shown that the latter result explains the unexpected behaviour in the ratio of diffusion coefficients observed for the binary mixture.