Investigation of the nature of the oxidant (selective and unselective) in/on a vanadyl pyrophosphate catalyst

Abstract

The anaerobic oxidation of CO by a (VO)₂P₂O₇ catalyst has been used to investigate the nature of the oxidant (selective and unselective) in/on that material. Three peaks were observed in the rate of production of CO₂ - at 993, 1073 and 1093 K. The temperature of the maximum in the rate of production of the first CO₂ peak and the amount of oxygen associated with it are the same as that observed in the selective anaerobic oxidation of n-butane to butene and butadiene, but-1-ene to butadiene and furan and but-1,3-diene to dihydrofuran, furan and maleic anhydride. The interaction of CO with the (VO)₂P₂O₇ catalyst forming CO₂ at 993 K is therefore concluded to be with the selective oxygen. The total amount of oxygen removed by the CO from the (VO)₂P₂O₇ lattice (>5 monolayers) is about six times greater than that of the selective oxygen. The higher activation energies for the removal of the unselective oxygen accounts for the high selectivities (~80%) encountered commercially for the anaerobic oxidation of n-butane to maleic anhydride. Re-oxidation of the CO reduced (VO)₂P₂O₇ by N₂O quantitatively replaces all of the lattice oxygen removed by the formation of CO₂, but does not restore the original morphology.