Multinuclear Solid-State NMR Study of Dehydration of Na–Y Type Zeolites

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Abstract
High-resolution solid-state NMR spectra of 23Na, 27Al, and 29Si nuclei were measured for dehydrated Na–Y type zeolites as well as undehydrated and rehydrated samples using magic angle sample spinning technique. 1H NMR spectra, X-ray diffraction patterns, and thermal properties were measured as well. 23Na NMR results indicate that there are three types of Na sites with different symmetries in the faujasite framework; two types with high and slightly low symmetries are detected by NMR, while the third cannot because of its very low symmetry. Na ions in high-symmetry sites are moved into slightly-low and very-low-symmetry sites by the dehydration. On the other hand, the Na ions in the amorphous region are located in low and very-low-symmetry sites. 27Al and 29Si NMR lines are broadened by the dehydration, due to the distortion of AlO4 tetrahedra and the interaction with 27Al nuclei, respectively. The 29Si spin-lattice relaxation time becomes longer by the dehydration, which indicates that water molecules play some role in the relaxation.