A microscopic description of the effect of hydration on the behavior of extraframework cations in zeolite Na + -mordenite is reported. Energy minimization techniques, combined with appropriate interatomic potentials to describe the potential energy surface of this complex system, have been used to determine the site selectivity of both cations and water molecules as a function of the hydration level. We have thus shown that the positions of the cations in the main channels are substantially perturbed upon the sorption of water molecules whereas those of the cations located in the small side channels are only slightly shifted. This modeling has been successfully compared with experimental data obtained by dielectric relaxation spectroscopy.

The evolution of thermally stimulated depolarization current (TSDC) measured on a mordenite Na zeolite is examined as a function of the Na+ exchange degree. According to this investigation, the dipolar reorientation is due to Na+, and the TSDC signal analysis leads to an assessment of the interaction energies between the hopping Na+ ions and the zeolitic lattice. The values of these energies are found to be between 0.7 and 0.9 eV. According to the Na+ exchange degree and the nature of the occupied Na+ sites, a quantitative and qualitative characterization of each site is given.