Effect of Water Adsorption on the Thermodynamics and Dynamics of the Extra-Framework Cations in Zeolite Systems

1. Introduction This work consisted of exploring the effect of water on both the distribution of the extra-framework cations and on their interactions with the framework in zeolite systems. From a practical point of view, this study was performed because water plays a key role in many applications involving adsorption and, more particularly, in ion-exchange which is carried out in aqueous solution. It is thus well known that water improves the efficiency of this process by coordinating the cations and hence increasing their mobility [1]. Dielectric Relaxation Spectroscopy (DRS) experiments performed on different types of aluminosilicate zeolites characterised by various Si/Al ratios, recently showed that the cations are progressively de-trapped from their initially occupied sites in the dehydrated state, as the number of water molecules per unit cell increases [2,3]. Furthermore, it was also pointed out a weakening of the interactions between the extra-framework cations and the zeolite framework with increasing water content.