The Effect of Cobalt Doping on the Structural Transformation Sequences Occurring During the Activation of Vanadium Phosphorus Oxide Catalysts

Vanadium phosphorus oxide (VPO) is commercially used to catalyse the oxidation of n-butane to maleic anhydride (MA). The catalyst itself is formed by activating the hemihydrate precursor VOHPO4.0.5H2O in an n-butane/air mixture at about 400°C for at least 100 hours [1]. Although many authors believe that this reaction is dependent solely on the presence of the crystalline (VO)2P2O7 phase [2], Hutchings et al have argued that the initial reaction step requires a V5+ phase and that selectivity and activity improve if a significant amount of a disordered V4+-V5+ phase is present [3].