n-Butane oxidation using VO(H2PO4)2 as catalyst derived from an aldehyde/ketone based preparation method

Abstract

A detailed study of n-butane oxidation over vanadium phosphate catalysts derived from in situ activation of VO(H₂PO₄)₂ is described and discussed. New methods of preparation of VO(H₂PO₄)₂ are described using the reaction of V₂O₅ and H₃PO₄ or VOPO₄ ·2H₂O with an aldehyde or ketone as a reducing agent. It is proposed that the enol form of the aldehyde and ketone act as the reducing agent. VO(H₂PO₄)₂ can also be obtained by reduction of VOPO₄ phases with alcohols. The catalysts derived from VO(H₂PO₄)₂ by in situ activation in 1.5% butane in air at 400°C for 72 h are largely disordered and, by detailed powder X-ray diffraction and laser Raman spectroscopy, are shown to be comprised mainly of disordered material containing some untransformed VO(H₂PO₄)₂, VOPO₄ phases and possibly some VO(PO₃)₂. The catalysts derived from all the forms of VO(H₂PO₄)₂ investigated are found to exhibit maleic anhydride selectivities in the range 20–30% and it is concluded that the low selectivity is due to the presence of VOPO₄ phases in the activated catalysts.