A comparison study on the partial oxidation of n-butane and propane over VPO catalysts supported on SBA-15, MCM-41, and fumed SiO₂

A desorption-precipitation method was used to prepare VPO catalysts supported on SBA-15, MCM-41, and fumed SiO₂ for the partial oxidation of n-butane and propane. Techniques such as N₂ adsorption-desorption measurements, XRD, XPS, Raman, and H₂-TPR were adopted to explore the nature of the catalysts as well as the characters of the supported VPO species. For all the samples, the VPO components were present predominantly in the form of well-crystallized (VO)₂P₂O₇ phase, and the VOPO₄-like phases were absent. The interaction between VPO and support was significant for the samples activated under n-butane/air but not so much for those activated in the atmosphere of water vapor/propane/air. Hence, the key factors that influenced the catalytic activity in n-butane and propane oxidation should be VPO-support interaction and VPO dispersion. Generally speaking, the VPO catalysts supported on the three silica-based materials showed fairly good performance for n-butane oxidation (i.e. high in butane conversion and MA selectivity). The three catalysts are less active for propane oxidation but show fairly good selectivity to propylene and acid products at low propane conversion. The discrepancies in the reaction behavior suggest that VPO-type catalysts are rather structure specific towards the reactant molecules.