Dependence of diffusion properties in zeolites Y and A: a search in the sorbate interaction parameter space

Molecular dynamics simulations have been carried out at room temperature on spherical monatomic sorbates in zeolites Y and A. A search has been made in the sorbate LennardJones εss-σss parameter space to see the variation of three properties, namely, rate of intercage diffusion (kc), rate of cage visits (kv) and diffusion coefficient (D). The results suggest that the three properties show a decrease with increase in εss for all values of σss except for kc at the value of σss corresponding to the tight fit parameter γ≈1. These results for kc are consistent with earlier work indicating the existence of a diffusion anomaly or a levitation effect. The absence of such behaviour on the part of kv and D seems to suggest that a diffusion anomaly may be strongly temperature dependent