Water dynamics in chabazite

• Published in: Microporous and mesoporous materials 2011-12, Vol.146 (1), p.106-118
• Main Authors: Chanajaree, R., Bopp, Ph.A., Fritzsche, S., Kärger, J.
• Format: Article
• Language: English
• Subjects: Diffusion; Molecular dynamics simulations; Rotation; Water; Zeolites
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2011.01.028

Water molecules and cations within the MD simulation box. [Display omitted] ► The density dependence pattern of self-diffusion for water in chabazite is explained. ► A model for the anisotropy of self-diffusion is revised and corrected. ► Rotational dynamics under geometrical confinement is investigated. Self-diffusion, libration and reorientation of water molecules in the zeolite chabazite are examined by molecular dynamics (MD) computer simulations at different temperatures and loadings. Comparison with experiment provides satisfactory agreement of the self-diffusivities and excellent agreement of the anisotropy factors and explains the failure of their prediction by the concept of structure-correlated diffusion anisotropy. Long-range electrostatic interactions are found to affect self-diffusion at high loadings and temperatures. Spectral densities of librational motion are similar to those in aqueous salt solutions, while reorientation is much slower and much more anisotropic. The vector in direction of the molecular dipole moment reorients only very slowly, as a consequence of the attraction by the almost immobile Ca + + -ions and by the walls of the zeolite. The other two vectors seem to reorient by jumps rather than by rotational diffusion.