Influence of orientational disorder in the adsorbent on the structure and dynamics of the adsorbate: MD simulations of SO2 in ZSM-22

Abstract

Structural and dynamical behavior of SO2 molecules within ZSM-22 is studied using molecular dynamics simulations, to understand the influence of orientational disorder (OD) and inter – crystalline spacing in ZSM-22 as a function of adsorbate loading. Addition of inter-crystalline space provides connectivity of isolated pores in ZSM-22 and is shown to suppress both translational and rotational motion of SO2. We infer that geometry and dimensionality of the connecting space are important factors in determining the effects of pore connectivity on the adsorbed species behavior. As a function of OD, decrease in self-diffusion coefficient of SO2 in ZSM-22 is observed. An increase in rotational correlation time and a decrease in libration angle with OD is observed, ascribed to the restriction imposed on the orientational freedom of the adsorbate by an increase in OD. The behavior of SO2 results from an interplay of guest-host interactions and the dimensionality and geometry of confinement.