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 r eported. Rates of cage-to-cage crossovers are found to be significantl y higher through the narrower window of zeolite NaCaA. These results s uggest that such behaviour first observed for noble gases may be widel y prevalent in many sorbate-zeolite systems and therefore need to be t aken into account as an important factor influencing the diffusion coe fficient. Variation of the rate of cage-to-cage diffusion with tempera ture has been obtained. The observed variation with temperature is sho wn to be consistent with the surface-mediated and centralized diffusio n mechanisms previously reported for cage-to-cage diffusion. At high t emperatures, the influence of the sorbate-zeolite interactions is mini mal.