The adsorption of non polar (argon, methane) and quadrupolar (carbon dioxide, nitrogen) gases on siliceous Faujasite at ambient temperature and high pressure conditions up to 50 bar, is investigated both experimentally and theoretically by combining Microcalorimetry and Grand Canonical Monte Carlo techniques. The aim of this present work is to evaluate the adsorption isotherms as well as the evolution of the differential enthalpies of adsorption as a function of coverage, for each of the gases under study, and to compare directly results of simulations with our own experimental data. To this purpose, the choice of reliable interatomic potentials required to describe both the adsorbate/framework and adsorbate/adsorbate interactions is crucial. This work is thus based on new transferable pair potential models for methane and carbon dioxide, recently developed by one of the authors using quantum mechanical methods. Finally, we propose a simplified model which can relate the differential enthalpy of adsorption at low coverage to the polarisability of the gases.

Adsorption microcalorimetry of non-polar argon and quadrupolar nitrogen gases was carried out at 77 K and 302 K on two chemically different faujasite type zeolites (DAY and NaX). Considering absolute quantities adsorbed, the differential enthalpies of adsorption at zero coverage obtained with each system do not vary with temperature. Similarities in the differential enthalpies with increasing coverage are observed only if one considers non-specific adsorption phenomena either with a non-polar probe or on a non-polar surface. Where "specific" polar interactions occur for the nitrogen-NaX system, significant differences are observed. This experimental study is the first to compare microcalorimetric measurements of adsorption in such a wide range of temperature.

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