DETERMINATION OF GALLIUM IN H(GA)ZSM5 ZEOLITES BY GA-71 MAS NMR-SPECTROSCOPY

Ga-71 and Si-29 magic angle spinning (MAS) NMR and some H-1 NMR (CRAMPS) investigations have been carried out on H(Ga)ZSM5 zeolites. Quantification of the Ga-71 NMR responses, obtained for the acid form of the zeolite, showed that about 70 +/- 2% of the theoretical signal intensity was measured, based on the total gallium content of the samples. Only signals from tetrahedral gallium were observed in a reproducible manner. The lack of gallium NMR response, which is ascribed to the presence of large electric field gradients on part of the gallium nuclei, has been found to depend on the nature of the counterion in the zeolite. Maximum NMR signal intensities were obtained for Rb+- and Cs+- exchanged zeolites. A model to explain these phenomena is presented. The gallosilicates were found to be thermally stable up to a temperature of 600-degrees-C, but in the presence of steam a loss of framework gallium was observed above 550-degrees-C.