Partial Oxidation of n-Pentane over Vanadium Phosphorus Oxide supported on Hydroxyapatites

Abstract

The selective oxidation of n-pentane to value-added products, maleic anhydride or phthallic anhydride by vanadium phosphorus oxide loaded on hydroxyapatites as catalysts and oxygen as oxidant was investigated. Hydroxyapatite (HAp) and cobalthydroxyapatite (Co-HAp) were prepared by the co-precipitation method and VPO with varying weight percentages (2.5–15.0 %) were loaded on the hydroxyapatite supports by the wet impregnation technique. The catalyst materials were characterized by surface area measurements, elemental analysis, powder X-ray diffraction (XRD), infrared spectroscopy (IR) and temperatureprogrammed reduction (TPR).VPOis present in two phases, viz. (VO)2P2O7 andVOPO4.With increase in theVPOloading on the hydroxyapatites, the (VO)2P2O7 phase also increased. From catalytic results, a conversion of 75 % of n-pentane and selectivity towards maleic anhydride, about 50 % and phthalic anhydride, about 25 %, were consistently achieved with loadings of 5.0 and 7.5 wt.%VPOat 360 °C forGHSVsof 1900 and 2300 h–1. Under optimum conditions, product yields of up to 40%maleic anhydride and 20 % phthalic anhydride were obtained. It is proposed that the products formed through the diene intermediate.

KEYWORDS Selective oxidation, n-pentane, vanadium phosphorus oxide, hydroxyapatite, maleic anhydride, phthalic anhydride.