Molecular dynamics simulation of carbon dioxide diffusion in NaA zeolite: assessment of surface effects and evaluation of bulk-like properties

Abstract

Molecular dynamics simulations were carried out for a finite sample of NaA zeolite in contact with bulk carbon dioxide in a wide range of temperatures and CO₂ contents. Density and diffusion profiles were obtained to estimate the depth at which the external surfaces of the zeolite affect CO₂ diffusion in porous space. The approximate depth of surface effects for NaA zeolite was estimated as ca. 2 nm, though this figure may vary depending on temperature and adsorbed gas density. Diffusion coefficients and diffusion activation energies were calculated for CO₂ and Na⁺ in the bulk-like region of the zeolite. Diffusion activation energy for carbon dioxide demonstrated a non-monotonic dependence on the amount of adsorbed gas.