Effect of Water Adsorption on Cation-Surface Interaction Energy in the Na-Mordenite of 5.5 : 1 Si/Al Ratio

The mobility of the Na+ cations localized at the inner surface of the studied mordenite zeolite depends on the material surface properties. In this work, we show that the activation energy, ΔEhop, relating to the Na+ cation hopping displacement is associated to the surface potential and therefore can be used to get a better insight into the zeolite surface properties. Indeed, when molecules as water are adsorbed at the surface, they modify the surface potential energy and hence influence the value of ΔEhop. If the adsorbed molecules are polar they directly interact with the cations which become more mobile. The more the ΔEhop value is, the less the amount of adsorbed water molecules is. Alterations of the ΔEhop value with respect to the amount of adsorbed water molecules are interpreted using the Dubinin model which is based on simple adsorption principle