ANOMALOUS BEHAVIOR OF CAGE-TO-CAGE DIFFUSION OF METHANE IN ZEOLITE-A AND ZEOLITE-Y

Computer simulation studies of methane in zeolites NaY and NaCaA are reported. Rates of cage-to-cage crossovers are found to be significantly higher through the narrower window of zeolite NaCaA. These results suggest that such behaviour first observed for noble gases may be widely prevalent in many sorbate-zeolite systems and therefore need to be taken into account as an important factor influencing the diffusion coefficient. Variation of the rate of cage-to-cage diffusion with temperature has been obtained. The observed variation with temperature is shown to be consistent with the surface-mediated and centralized diffusion mechanisms previously reported for cage-to-cage diffusion. At high temperatures, the influence of the sorbate-zeolite interactions is minimal.