New Aspects of the Cooperation Between Phases in Vanadium Phosphate Catalysts

The possibility of a cooperation between two different phases in the phosphorous vanadium catalysts during the oxidation of butane to maleic anhydride is discussed. The results deal with mechanical mixtures of separately prepared catalysts. A conspicuous synergy is observed between a phosphorous poor and a phosphorous rich VPO catalyst, as well as between a VPO and Sb2O4 or BiPO4. Both activities and selectivities are increased. The synergy corresponds to a decrease of sintering during the catalytic reaction, an increase of acidity, and a higher oxido-reduction rate. Our results lead to speculate that in phosphorous vanadium catalysts. at least two separate phases could cooperate during the catalytic reaction. This cooperation would take place thanks to mobile oxygen species. one of these phases (probably that corresponding to a low P/V ratio) acts as activator (or donor) of oxygen and the other (probably that with a high P/V ratio) plays the role of acceptor of oxygen.