LOW-TEMPERATURE AND ECHO H-1 MAGIC-ANGLE-SPINNING NUCLEAR-MAGNETIC-RESONANCE STUDIES OF DEALUMINATED AND WEAKLY REHYDRATED ZEOLITES H-Y

Low-temperature H-1 magic-angle spinning nuclear magnetic resonance (M AS NMR) and various rotor-synchronous spin echo H-1 MAS NMR experiment s have been applied to characterize partially dealuminated and weakly rehydrated zeolites H-Y. The signal caused by water adsorption on Lewi s acid sites does not change at 160 K in comparison to room temperatur e. Spin echo H-1 MAS NMR experiments with dipolar dephasing by means o f high-power Al-27 irradiation confirm that the water molecules must b e close to aluminium sites. Two models of water adsorption on Lewis ac id sites are discussed.