Intermolecular potential for methane in zeolite A and Y: adsorption isotherm and related properties

Abstract

Based on energies derived from ab initio calculations on methane in zeolite A and Y a more accurate intermolecular potential is proposed for hydrocarbon-zeolite interaction. We then employ the proposed potential POTJI (consisting of sets ABCHA and ABCHY) as well as another potential (termed KDMG) based on the work of Kiselev and Du and Murad and Gubbins in grand canonical Monte Carlo simulations to obtain adsorption isotherms and molecular dynamics simulations to obtain self-diffusion coefficients. For methane in zeolite A we show that the derived potential predicts accurately adsorption isotherm, heats of sorption and diffusion coefficients. For methane in zeolite Y a somewhat less accurate reproduction of adsorption isotherm is obtained. In general, these potentials predict values that are closer to experimentally obtained values than existing potential. Radial distribution function is more structured than for existing KDMG potential. Translational diffusion coefficients are generally lower than KDMG potential while the rotational diffusion coefficients are actually higher than seen for KDMG potential. Further, it is seen that the set of potential parameters derived for zeolites A and Y are similar suggesting that it might be possible to derive one unified set of parameters that would perform reasonably across a large set of zeolite structures. Similar transferability of potentials across the range of hydrocarbons may also be possible. Finally, these results suggest that it may be possible to derive accurate classical potentials for interaction between organic and inorganic systems based on ab initio calculations.