Sol-Gel Synthesis of Vanadium Phosphorus Oxides as Catalyst for the Partial Oxidation of Butane to Maleic Anhydride
Juan M. Salazar, Vishwamitra Research Institute, Center for Uncertain Systems: Tools for Optimization and Management, 368 56th Street, Clarendon Hills, IL 60514 and Keith L. Hohn, Kansas State University, 105 Durland Hall, Manhattan, KS 66506-5102.
The partial oxidation of butane to maleic anhydride is catalyzed industrially by vanadium phosphorous oxides (VPO). These catalysts have the potential to be improved if synthesized as nanostrutured materials since small crystallite sizes have been reported as improved materials for this application. VPO are traditionally manufactured from solid vanadium oxides by synthesizing VOHPO4∙0.5H2O (the precursor) and subsequently dehydrating and reducing it to produce (VO)2P2O7 (the active phase). This work discusses an alternative synthesis method based on sol-gel techniques, which is capable of producing high surface area materials (small crystallite size) as precursors. Vanadium(V) triisopropoxide oxide was reacted with ortho-phosphoric acid in an aprotic solvent. The products were dried at high pressure in an autoclave with a controlled excess of solvent and 2-propanol. After the autoclave drying, the surface area of the obtained materials was between 50 and 120 m2/g and the crystallite size between 300 and 700 nm depending on the excess of solvent that was employed. The precursors were tested as catalysts for the partial oxidation of butane at 673 K and the sol-gel prepared precursors showed higher selectivity (41%) when compared with the traditionally prepared materials (30%) at the same level of conversion (35%). All precursors and catalysts were characterized by IR, XRD, SEM and BET and the products of the catalytic tests were analyzed by GC.