Effect of nitridation on the electronic environment of vanadium in VAlO(N) powder catalysts, used for the ammoxidation of propane

VAlO(N) oxynitrides are promising novel catalysts for the ammoxidation of propane to acrylonitrile. These catalysts are obtained after nitridation of a VAlO oxide precursor in NH3 or during the reaction in a NH3/C3H8/O2 mixture. The local structure around the vanadium atoms in the oxide precursor and in several catalysts that have been used in catalytic tests is studied by X-ray absorption spectroscopy (XAS). The nitridation in NH3 was followed with in situ XAS. The oxide precursors have tetrahedral co-ordinated vanadium, while after full nitridation octahedrons are found and a small decrease in vanadium oxidation state occurs. The catalysts used in the ammoxidation reaction consist of a mixture of these tetrahedrons and octahedrons.