XANES study of hydrothermal Mo-V-Based mixed oxide M1-phase catalysts for the (Amm)oxidation of propane

The hydrothermal Mo-V-based mixed oxide catalysts possessing the M1-phase structure were investigated by XANES and in situ X-ray diffraction under ambient and dynamic redox conditions in the presence of O₂ and H₂ at 693 K. Under ambient conditions, XANES, with the use of model compounds, suggested oxidation states of Nb, Te, Mo, and V close to 5+, 4+, 6+, and 4+, respectively, in the bulk Ml phase. The oxidation state changes of Nb, Te, and Mo were not detected under the dynamic redox conditions employed, while the pre-edge peak of vanadium in the Ml phase exhibited small, reproducible shifts, suggesting that VO_x is the active catalytic species in the bulk Ml-phase catalysts for selective (amm)oxidation of propane.