The diffusion of a mixture of methane and xenon in the zeolite silicalite is studied by use of molecular dynamics (MD) simulations and pulsed field gradient (PFG) nuclear magnetic resonance (NMR). For a fixed total number of guest molecules, the ratio of xenon to methane is varied 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 xenon compared to methane in combination with channel size and topology in silicalite. Simulated and experimental data are in very good agreement with each other. Diffusion anisotropy as resulting from the MD simulations is discussed in terms of the correlation rule for diffusion in the interconnected pore system of ZSM-5 (Ka ¨rger,

A probe system is described which allows the application of magnetic field gradient pulses with amplitudes up to 24 T/m for self-diffusion measurements by means of a PFG NMR spectrometer operating at a proton resonance frequency of 400 MHz. It is demonstrated that PFG NMR measurements in the high field of a superconducting magnet necessitate precautions which are of minor relevance for measurements with iron magnets. Taking advantage of the large gradient intensity and the high sensitivity in signal detection of the described system, attenuation patterns of the NMR spin echo are observed for the first time that represent the PFG NMR analogue of the diffraction pattern of a sphere.

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