VPO catalyst doped with Ce-Zr composite oxide for n-butane selective oxidation to maleic anhydride

A new VPO catalyst was prepared by doping with an appropriate amount of Ce-Zr composite oxide. The doped-catalyst possesses significantly improved catalytic performance compared with the pure VPO catalyst. In the n-butane/air co-feed reaction, the mole yield of maleic anhydride over the doped catalyst is doubled as compared with that over the pure VPO catalyst. In the absence of gas-phase oxygen, the amount of lattice oxygen in the doped catalyst that is selective to maleic anhydride is 1.2 times higher than that in the pure VPO catalyst. The results of the BET surface area measurement, X-ray diffraction, average vanadium valence measurement, arid temperature-programmed experiments show that a small quantity of Ce-Zr composite oxide present in active phases of the catalyst takes part in the redox process of the VPO system. The addition of the Ce-Zr composite oxide has two functions: (1) to promote the formation Of (VO)(2)P(2)O7 phase and maintain the average vanadium valence, which are in favor of obtaining the VPO catalyst with a good phase structure and stable catalytic performance; (2) to improve the redox property of the VPO catalyst remarkably and thereby increase the amount of reversible lattice oxygen stored in the catalyst dramatically.