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

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.