Inelastic neutron scattering study of NH4Y zeolites

An inelastic neutron scattering study of NH4Y zeolites is presented 2-350 meV (16-2800 cm-1). The spectra are interpreted in terms of translational and librational motions of ammonium ions and NH3 and H2O mols. For the hydrated samples, the translational modes of H2O species are obsd. at 12 meV and librational modes are found at .gtorsim. 50 meV. The translational and librational modes of the ammonium ions also depend on the cation locations. Ammonium species give rise to (ion-lattice) translational modes at 10-15 meV and at 15-25 meV for species localized in sodalite cages and supercages, resp. The corresponding librational modes are obsd. at .apprx. 8 meV and in the region 3-6 meV, resp. Strongly hindered librations are obsd. at 50-70 meV and 30-50 meV, resp., for the ions in the 2 different cages. Low-frequency as well as high-frequency librational modes of the ammonium species may occur caused by the presence of different ammonium species. Differences in reorientational motions are obsd. for hydrated zeolites and for reammoniated zeolites. For the latter, a stronger interaction of the ammonium ions with the zeolitic lattice is present and the low-frequency librational modes are shifted to higher energy-transfer values. When increasing the loading with NH3, librational and translational motions of NH3 species can be obsd. A heterogeneity in the reorientational barriers is present, indicating the presence of different NH3 species. [on SciFinder (R)]