Selective oxidation of C₄ hydrocarbons to maleic anhydride over Bi-doped VPO catalysts

The Bi-doped vanadium-phosphorus-oxygen(VPO)catalysts(VPOBi)were prepared. Effects of Bi dopant dosage on activities of the prepared catalysts in selective oxidation of C₄ hydrocarbons to maleic anhydride were investigated with n-butane or mixed C₄ as feedstocks. Under the optimal conditions: reaction temperature 653 K, GHSV 2000 h^-1 and VPOBi as catalyst, yield of maleic anhydride was 40.4% with n-butane as feedstock and 0.3%(mole fraction)Bi as dopant of the catalyst, and its yield reached 49. 2% with mixed C₄ as feedstock and 0.2% Bi as dopant of the catalyst. The catalysts were characterized by means of XRD, BET, SEM and H₂-TPR. The results showed that introduction of Bi dopant obviously promoted increase of the exposed(020)crystal faces of the catalysts, modified their morphology, and increased their specific surface areas. The activity of lattice oxygen in the catalysts also increased after Bi doping, so that the lattice oxygen could be reduced by H₂ at low temperature. These changes improved the catalyst activity in the selective oxidation of C₄ hydrocarbons to maleic anhydride.