Reference potentials for adsorption of helium, argon, methane, and kryptonin high-silica zeolites

Quantitative agreement with experimental data for adsorption of argon, kryp ton, and methane in high-silica zeolites is achieved with a molecular model , which (1) assumes pairwise additivity of intermolecular forces; (2) ignor es partially concealed silicon atoms and lumps their dispersion energy with the oxygen atoms; (3) neglects energy induced by the weak electric field i nside 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 epsilon /k = 93.0 K and sigma = 3.335 Angstrom. The gas-solid potential pa rameters for krypton and methane were calculated from the Ar-O reference po tential using Lorentz-Berthelot mixing rules and the principle of correspon ding states. The pore volume of silicalite determined from the He-O potenti al is 0.175 cm(3) g(-1). The local density of gases adsorbed in the pores v aries with the strength of the gas-solid potential; at 306 K and 10 bar, th e maximum absolute density of methane is about one half the density of liqu id methane at its normal boiling point. (C) 2001 Elsevier Science B.V. All rights reserved.