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.Key words: ZSM5, MFI, in situ studies, MAS NMR, DRIFT, propane activation, ammoxidation.