Reference Potentials for Adsorption of Helium, Argon, Methane, and Krypton in High-Silica Zeolites

Quantitative agreement with experimental data for adsorption of argon, krypton, and methane in high-silica zeolites is achieved with a molecular model, which (1) assumes pairwise additivity of intermolecular forces; (2) ignores partially concealed silicon atoms and lumps their dispersion energy with the oxygen atoms; (3) neglects energy induced by the weak electric field inside silicalite; (4) uses the Lennard-Jones 12-6 potential for gas-gas and gas-solid interactions. The parameters of the Ar-O gas-solid potential are ε/k=93.0 K and σ=3.335 Å. The gas-solid potential parameters for krypton and methane were calculated from the Ar-O reference potential using Lorentz-Berthelot mixing rules and the principle of corresponding states. The pore volume of silicalite determined from the He-O potential is 0.175 cm3 g-1. The local density of gases adsorbed in the pores varies with the strength of the gas-solid potential; at 306 K and 10 bar, the maximum absolute density of methane is about one half the density of liquid methane at its normal boiling point. Copyright © 2001 Elsevier Science B.V