Diffusion behaviour of binary mixtures in restricted regions of zeolite NaY from molecular dynamics calculations

Diffusion coefficients D1 and D2 of a binary mixture of adsorbates of diameters σ1 and σ2 in the restricted regions of zeolite NaY have been obtained from molecular dynamics simulations. The results suggest that the region of the diffusion coefficients ζ = D1/D2 exhibit unusual behaviour with an increase in the ratio of diameters η = σ1/σ2: D1 > D2 even when σ1 > σ2. 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.