A GA-69 AND GA-71 MAS NMR-STUDY OF THE GALLIUM ANALOG ZEOLITE ZSM-5

Ga-69 and Ga-71 magic-angle-spinning (MAS) NMR spectra of a series of gallium analogue zeolites H-(Ga)ZSM-5, with varying Si/Ga ratios, were obtained at 14.1 and 7.1 T. The quadrupole coupling constant e2qQ/h was deduced from the shift difference of the centre of gravity of the Ga-69 and Ga-71 resonance. An analysis of the linewidth as a function of the magnetic field shows that the width is not only determined by the second-order quadrupolar broadening, but also by a distribution of chemical shifts. The values obtained for the quadrupole coupling constant and chemical shift distribution are compared to those found for Al-27 in H-(Al)ZSM-5. It is argued that the observed differences are related to the different NMR properties of the isotopes, and do not point to any structural changes of the ZSM-5 lattice.