Location and de-trapping energy of sodium ions in dehydrated X and Y faujasites determined by dielectric relaxation spectroscopy

Both the location and the de-trapping energy ΔE of the extraframework sodium cations embedded in Na56Y and Na96X zeolites are investigated by means of dielectric relaxation spectroscopy (DRS). It is shown that the Na+ cations are distributed into three different types of crystallographic sites, with a respective occupancy established by comparing our DRS data to those previously obtained from simulation. Then, the de-trapping energy of the Na+ cations embedded in each crystallographic site is determined and analysed in the light of the structural feature of the site. The difference between the de-trapping energy of the different crystallographic sites in Na56Y and Na96X is thus interpreted using simple qualitative models based on electronegativity and cation/cation repulsion. It is thus shown that the consideration of this later parameter is essential to explain the rearrangement of the energy level of each cation site when a critical Si/Al ratio is reached.