DIFFUSION OF A MIXTURE OF METHANE AND XENON IN SILICALITE - A MOLECULAR-DYNAMICS STUDY AND PULSED-FIELD GRADIENT NUCLEAR-MAGNETIC-RESONANCEEXPERIMENTS

The diffusion of a mixture of methane and xenon in the zeolite silical ite is studied by use of molecular dynamics (MD) simulations and pulse d field gradient (PFG) nuclear magnetic resonance (NMR). For a fixed t otal number of guest molecules, the ratio of xenon to methane is varie d in order to examine the special properties of diffusion in a mixture . High xenon concentrations were found to slow the methane diffusivity in the mixture, while the diffusion of xenon is nearly unaffected by high methane concentrations. The reason for the dominance of xenon is the larger local heat of adsorption of xenon and the larger mass of xe non compared to methane in combination with channel size and topology in silicalite. Simulated and experimental data are in very good agreem ent with each other. Diffusion anisotropy as resulting from the MD sim ulations is discussed in terms of the correlation rule for diffusion i n the interconnected pore system of ZSM-5 (Karger, J. J. Phys. Chem. 1 991, 98, 5558).