Oxidation of vanadium pyrophosphate (VPO) to the orthophosphate was investigated by temperature programmed oxidation (TPO) and by weight gain measurements in a TGA unit as a model for the re-oxidation of a catalyst in a two-bed process in the partial oxidation of butane to maleic anhydride (MA). It was demonstrated by FTIR observations that the weight gain corresponds to the VPO oxidation. The results of separate measurements of a catalyst alternatively exposed to oxygen and to a stream containing butane should also be applicable to a VPO catalyst employed in a two-bed process. The VPO oxidation measurements demonstrate that re-oxidation of a VPO catalyst in a two-bed process should be carried out at a higher temperature than the butane partial oxidation. When this is carried out, significant performance improvements in the two-bed process are observed.