Solid state chemistry of bulk mixed metal oxide catalysts for the selective oxidation of propane to acrylic acid

Syntheses of Mo-V-Sb-Nb-O bulk materials, which are candidate catalyst systems for the selective oxidation of propane to acrolein and acrylic acid, were made using soluble precursor materials. The products were characterized by X-ray powder diffraction and Raman spectroscopic studies. The objectives of this work were to explore the utility of liquid phase automated synthesis for the preparation of bulk mixed metal oxides, and the identification of the oxide phases present in the system. This is the first published study of the phase composition for these materials. After calcination of these bulk oxides under flowing nitrogen at 600 degreesC, and using stoichiometric ratios of Mo-V-Sb-Nb (1:1:0.4:0.4) and Mo-V-Sb-Nb (3.3:1:0.4:0.4) it was demonstrated that a mixture of phases were obtained for the syntheses. X-ray powder diffraction studies distinguished SbVO4, MO6V9O40, MoO3, and a niobium-stabilized defect phase of a vanadium-rich molybdate, Mo0.61-0.77V0.31Nb0.19Nb0.08-0.04Ox, as the major phases present. Complementary data were provided by the Raman spectroscopic studies, which illustrated the heterogeneity of the phases present in the mixture. Raman also indicated bands attributable to the presence of phases containing terminal M=O bonds as well as M-O-M polycrystalline phases. Previous studies on this system have identified SbVO4 and niobium-stabilized vanadium molybdate species as the active phases necessary for the selective oxidation of alkanes. (C) 2001 Elsevier Science B.V. All rights reserved.