title: Molecular simulation studies of water physisorption in zeolites.
abstract: We report a series of Grand Canonical Monte Carlo simulations of water adsorption in NaY and NaX faujasite, as well as in silicalite-1. Computed adsorption isotherms and heats of adsorption were in good agreement with the available experiments. The existence of cyclic water hexamers in NaX located in the 12-ring windows, recently disclosed by neutron diffraction experiments (Hunger et al., J. Phys. Chem. B, 2006, 110, 342-353) was reproduced in our simulations. Interestingly enough, such cyclic hexamer clusters were also observed in the case of NaY, in which no stabilizing cation is present in the 12-ring window. We also report cation redistribution upon water adsorption for sodium faujasite with varying cation contents (Si ratio Al ratio in the range 1.53-3). A simple and transferable forcefield was used, that enabled to reproduce the different aspects of water physisorption in stable zeolites. The high pressure water condensation in hydrophobic silicalite-1 was reproduced without any parameter readjustment. The method and forcefield used here should be useful for engineering oriented applications such as the prediction of multi-component mixture adsorptive separations in various stable zeolites. It allows to address the issue of the effect of the small amounts of water that are almost inevitably present in zeolite-based separation processes.
authors.affiliation: Laboratoire de Chimie Physique, Bâtiment 349, UMR 8000 CNRS and Université Paris-Sud, F-91405, Orsay, France.
authors.forename: Angela
authors.initials: A
authors.lastname: Di Lella
authors.forename: Nicolas
authors.initials: N
authors.lastname: Desbiens
authors.forename: Anne
authors.initials: A
authors.lastname: Boutin
authors.forename: Isabelle
authors.initials: I
authors.lastname: Demachy
authors.forename: Philippe
authors.initials: P
authors.lastname: Ungerer
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bellat
authors.forename: Alain H
authors.initials: AH
authors.lastname: Fuchs