(185d) Sol-Gel Synthesis Of Nanostructured Vanadium Phosphorus Oxides As Catalyst For The Partial Oxidation Of Butane To Maleic Anhydride

The partial oxidation of n-butane to maleic anhydride is catalyzed industrially by vanadium phosphorous oxides (VPO). These catalysts considerably improve their performance when prepared as nanostructured materials. This work discusses an alternative synthesis method based on sol-gel techniques, which is capable of producing nanostructured catalysts. Vanadium(V) triisopropoxide oxide was reacted with ortho-phosphoric acid in tetrahydrofuran (THF). The wet products were dried at high pressure in an autoclave with a controlled excess and composition of a THF-2-propanol mixture. After the autoclave drying the solid was identified as VOHPO₄?0.5H₂O (the precursor). The use of 2-propanol during the drying process increased the amount of precursor in the powder but reduced its surface area and increased its crystallite size. However, when the materials were activated for the partial oxidation of n-butane the surface area increased and the particle size decreased considerably. The evaluation of these materials as catalysts for the partial oxidation of n-butane at 673 K under mixtures of 1.5% n-butane in air yielded selectivity of 40% at 50% conversion compared to 25% selectivity at similar level of conversion produced by the traditionally prepared catalysts. Interestingly, when the concentration of oxygen was reduced to 17% (when air is used oxygen concentration is about 20%) selectivity increased up to 90%. The concentration of oxygen affects the performance of a nanostructured VPO catalyst more drastically than a traditionally prepared material. All precursors and catalysts were characterized by IR, XRD, SEM and BET and the products of the catalytic tests were analyzed by GC.