NMR Study of Local and Long Range Dynamics of Adsorbed Water in Zeolite NaY(Br)

The dynamics of partially deuterated water in zeolite NaY(Br) are investigated by a combination of several NMR methods for two different loadings, 4 water molecules and 18 water molecules per supercage. Information on local dynamics is obtained by H-1 and H-2 NMR spin-lattice relaxation, H-2 NMR solid-echo spectra and H-2 NMR stimulated echo decay curves. The water long range diffusion has been studied by H-1 NMR static field gradient experiments. The most important findings are as follows: The mechanism of water dynamics depends strongly on the degree of loading. This is clearly reflected in both, local and long range motion. The intermediate H-2 NMR spectra might be explained referring to a model proposed by O'Hare et al.: It is based on two different populations of water molecules performing tetrahedral jumps respectively C-2-flips of their OH bonds. Alternative models for the local water dynamics, distorted tetrahedral jumps and a distribution of correlation times, are also discussed.