The mechanism of surface doping in vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride: The role of Au promoter

This paper studies the role of Au as a promoter for vanadyl pyrophosphate, catalyst for n-butane oxidation to maleic anhydride. Samples were prepared with a stoichiometric P/V ratio (P/V = 1.0), and then doped with increasing amounts of Au. It was found that the addition of the Au promoter had a profound influence on its catalytic behaviour, as samples containing the greater amount of Au (3 wt%) showed a behaviour that was similar to that of optimal catalysts which were prepared with a slight excess of P. In fact, the presence of Au allowed all the phenomena that typically lead to the worst catalytic behaviour of stoichiometric vanadyl pyrophosphate to be minimised, i.e. both the over-oxidation of vanadium and the development of the very active but poorly selective I-VOPO4. This was attributed to the enhanced reducibility of V5+ that was observed in Au-doped samples, as compared to the undoped ones.