A MAS NMR and DRIFT study of the Ga species in Ga/H-ZSM5 catalysts and their effect on propane ammoxidation

71Ga, 27Al and 29Si MAS-NMR and DRIFT spectroscopies were used to characterize the state of gallium in Ga/H-ZSM5 catalysts tested for their ability to catalyse the ammoxidation of propane. Ga-species were observed in two different possible environments: octahedrally-coordinated gallium in small Ga2O3 particles at the external surface of the zeolite crystals, octahedrally-coordinated gallium in GaO(OH) or related species, and tetrahedrally-coordinated gallium in cationic-exchange positions inside the zeolite. Redox (H2-O2) cycles promote the migration of gallium from the GaO(OH) or Ga2O3 species at the external surface of the zeolite crystals to cationic-exchange sites within the zeolite channels. The redox treatment definitely had a beneficial effect on its catalytic performance for the ammoxidation of propane, which is known to occur via a bifunctional mechanism. The main product was acetonitrile at high Ga and Al contents while acrylonitrile was also observed as a side product at high Ga and low Al contents