Cation Migration upon Adsorption of Methanol in NaY and NaX Faujasite Systems:  A Molecular Dynamics Approach

Abstract

Molecular dynamics simulations have been carried out to address the question of cation migration upon adsorption of methanol in NaY and NaX faujasite systems as a function of the loading. For NaY, it has been shown that, at low and intermediate loadings, SII cations can migrate toward the center of the supercage due to strong interactions with the adsorbates, followed by a hopping of SI' from the sodalite cage into the supercage to fill the vacant SII site. A SI' cation can also migrate across the double six ring and takes a SI' vacant position. SI cations mainly remain trapped in their initial sites whatever the loading. At high loading, only limited motions are observed for SII cations due to steric effects induced by the presence of adsorbates within the supercage. For NaX, the SIII' cations which occupy the most accessible adsorption sites are significantly moving upon coordination to the methanol molecules; the extent of this mobility exhibits a maximum for 48 methanol molecules per unit cell before decreasing at higher loadings due to steric hindrance. In addition, the SI' and SII cations remain almost trapped in their initial sites whatever the loading. Indeed, the most probable migration mechanism involves SIII' cation displacements into nearby SIII' sites.

Quantum chemical investigation of the adsorption of methanol on a cluster model of faujasite

“…The cation mobility is known to play an important role in adsorption processes [12,13] and to depend considerably on the adsorbate species [26,27]. The decomposition of the interaction energy can thus help to elucidate the role of the cation in sorption processes.…”

Modelling of Physisorption in Porous Solids

“…A statistical approach based on Monte Carlo (MC) techniques is commonly used to properly describe this feature . It has also been evidenced that the adsorption of certain molecules induces a significant redistribution of the extra-framework cations (Beauvais et al, 2004;Maurin et al, 2006). Another aspect consists of modelling via MC simulations the location of the extra-framework cations and their distribution within the porosity of these materials when the crystallographic sites and their occupancies are not experimentally available (Vitale et al, 1997).…”

IR and ESR study of copper(II) complexes with 15N-labelled lysine and ornithine

“…The immobilized monomeric species of CuðAAÞ 2þ 2 compounds in the supercages (III type sites [47]) of the NaY zeolite (Figs. 6b, 7a) which has cavity diameters $13 Å and an water content of 26.4%, have a tetragonal elongated octahedral symmetry (stereochemistry) due to the coordination of two water molecules at Cu 2+ ion along the O z axis (apical positions).…”

“…The second species from HY zeolite are located on the walls of the cavities, in the S II sites [47], and their OH(OH 2 ) groups are stronger coordinated to Cu 2+ ion than other water molecules from inner of the cavities, resulting in a slight distorted C 4v (squarepyramidal) local symmetry.…”