Preparation of vanadium phosphorus oxide catalysts. Influence of macroscopic P:V ratio in determining phase composition after calcination

Three series of vanadium phosphorus oxide (VPO) catalysts with nominal P:V ratios in the range 0.8-1.2:1 were prepared using alcohol based preparation procedures. The influence of reflux time and nature of the alcohol on the phases observed in the final catalyst as well as the susceptibility of the precursor to oxidation were assessed. Residual V₂O₅ entrained in the precursor was the primary factor which determined the resistance to oxidation of the V⁴⁺ containing phases in the temperature range 350-450°C. V₂O₅ added to a pure V⁴⁺ phase also induced susceptibility to oxidation. These findings indicate a high degree of ionic mobility within the VPO system and that the macroscopic P:V ratio is important in determining the eventual stability of the V⁴⁺ oxidation state during calcination.