This is a study of the effects of catalyst preparation and treatment on the structure and reactivity of VPO (vanadium phosphorus oxide or "vanadium phosphate") catalysts for the partial oxidation of n-butane to maleic anhydride. The core strategy is the incorporation of silicon into the VPO system, influencing the morphology, redox potential, and acidity of the catalyst; silicon should stabilize the vanadyl pyrophosphate phases, considered beneficial for the desired catalytic effect. Catalyst materials prepared are characterized by X-ray diffraction, Fourier-transform photoacoustic spectroscopy, X-ray photoelectron spectroscopy, chemisorption, and kinetic measurements to establish structure, morphology, and activity. Also examined is the effect of water vapor on the acidity, activity, and selectivity of the catalysts. Maleic anhydride is an important industrial product as a chemical intermediate in the production of a number of important monomers, drugs, and pesticides. It is now made by catalytic oxidation of butane; the low cost of the feedstock makes this feasible despite the limited yield. The objective of this work is to identify the cause of the yield limitation; if it can be circumvented, the economic impact would be major.
