Partial Oxidation of n-Butane over a Sol-Gel Prepared Vanadium Phosphorous Oxide

Abstract: Vanadium phosphorous oxide (VPO) is traditionally manufactured from solid vanadium oxides by synthesizing VOHPO₄∙0.5H₂O (the precursor) followed by in situ activation to produce (VO)₂P₂O₇ (the active phase). This paper discusses an alternative synthesis method based on sol-gel techniques. 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. This procedure produced a gel of VOPO₄ with interlayer entrapped molecules. The surface area of the obtained materials was between 50 and 120 m²/g. Alcohol produced by the alkoxide hydrolysis reduced the vanadium during the drying step, thus VOPO₄ was converted to the precursor. This procedure yielded non-agglomerated platelets, which were dehydrated and evaluated in a butane-air mixture. Catalysts were significantly more selective than the traditionally prepared materials with similar intrinsic activity. It is suggested that the small crystallite size obtained increased their selectivity towards maleic anhydride.