Cation Dynamics upon Adsorption of Methanol in Na−Y Faujasite Type Zeolites: A Dielectric Relaxation Spectroscopy Investigation

Abstract

Dielectric relaxation experiments are carried out to address the question of cation location upon adsorption of methanol in a Na-Y faujasite system. They allow us to probe both the evolutions of the number of extraframework sodium ions in the different crystallographic sites and of their de-trapping energy as a function of the adsorbate loading. Redistributions of the cation positions are explained in light of previous molecular dynamic results. It is shown that SI cations remain mainly trapped in their initial sites whatever the methanol loading. At low and intermediate loadings, SII cations migrate within the supercage, due to strong interaction with the adsorbate molecules. They are followed by hopping of SI' cations from the sodalite cage toward the supercage to fill vacant SII sites. At higher loading, the cation motions are hindered due to steric effects induced by absorbates within the supercage. These cation motions are shown to be consistent with the evolution of the de-trapping energy of Na + .