XE-129 NUCLEAR-MAGNETIC-RESONANCE STUDIES OF H-GA-MFI ZEOLITES

Xe-129 Nuclear magnetic resonance (NMR) studies of H-Ga-MFI samples having a range of lattice and extralattice gallium contents have shown that the Xe-129 NMR technique can be used as an estimate of the lattice gallium content and the extent of charge on the extralattice gallium species. The xenon chemical shift extrapolated to zero xenon coverage can be used to estimate the lattice gallium content and the extent of charge on the extralattice gallium species. The xenon chemical shift extrapolated to zero xenon coverage is linearly dependent on the lattice gallium content as determined by Si-29 magic-angle spinning (MAS) NMR spectroscopy. Samples containing high concentrations of extralattice gallium showed a marked upward curvature in plots of xenon chemical shift versus xenon density at low xenon density. Steaming of the zeolites reduces the lattice gallium content and the upward curvature in the xenon chemical shift plots, consistent with hydrolysis of extralattice Ga3+ to uncharged oxide or oxyhydroxide gallium species within the zeolite pores.