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

Abstract

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 ε_ss-σ_ss parameter space to see the variation of three properties, namely, rate of intercage diffusion (k_c), rate of cage visits (k_v) and diffusion coefficient (D). The results suggest that the three properties show a decrease with increase in ε_ss for all values of σ_ss except for k_c at the value of σ_ss corresponding to the tight fit parameter γ≈1. These results for k_c 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 k_v and D seems to suggest that a diffusion anomaly may be strongly temperature dependent.