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

We have used molecular simulations to examine the diffusion of Ne, Ar, Kr, Xe, CH₄, CF₄, CCl₄, SF₆, SnCl₄, and SnBr₄ in the molecular sieve AlPO₄-5, 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 Ne/CF₄ mixtures.