Normal, single-file, and dual-mode diffusion of binary adsorbate mixtures in AlPO4-5

Abstract

We have used molecular simulations to examine the diffusion of Ne, Ar, Kr, Xe, ${\mathrm{CH}}_{\mathrm{4}},$ ${\mathrm{CF}}_{\mathrm{4}},$ ${\mathrm{CCl}}_{\mathrm{4}},$ ${\mathrm{SF}}_{\mathrm{6}},$ ${\mathrm{SnCl}}_{\mathrm{4}},$ and ${\mathrm{SnBr}}_{\mathrm{4}}$ in the molecular sieve ${\mathrm{AlPO}}_{\mathrm{4}}\mathrm{-5},$ both as single species and as coadsorbed mixtures. Single adsorbed species exhibit a transition from normal to single-file diffusion as a function of increasing adsorbate size. In addition to normal and single-file diffusion, coadsorbed mixtures exhibit a qualitatively new diffusion mode in which one species performs normal diffusion while the other undergoes single-file diffusion. We discuss the prospects for experimental verification of this phenomenon, and present measurements of the loading dependence of diffusion rates during the dual-mode diffusion of ${\mathrm{Ne/CF}}_{\mathrm{4}}$ mixtures.