Synthesis of Vanadium Phosphorus Oxide Catalysts by Aerosol Processing

The use of an aerosol process to prepare vanadium phosphorus oxide (VPO) catalysts for butane oxidation to maleic anhydride was investigated. Heating an aerosol created with air of an aqueous solution of NH₄VO₃ and H₃PO₄ with phosphorus to vanadium atomic ratio P/V = 1.2 at 700 °C resulted in a material that had an average vanadium oxidation state of 4.7–5.0. After activation in a butane and oxygen mixture, a stable catalyst was obtained which showed selectivities to maleic anhydride (MA) of up to 48% at 475 °C. X-ray diffraction and laser Raman spectroscopic characterization of the catalyst showed that the as-prepared sample was mostly VOPO₄·2H₂O, which was converted to α_I-VOPO₄ under reaction conditions. The catalyst was much more active than a VPO catalyst with P/V = 1.1 or 1.2 prepared by the conventional method in an aqueous medium. Thus, in spite of its lower surface area and selectivity for MA, it produced a higher yield of MA even on the basis of the weight of catalyst.