Physicochemical properties of catalysts based on aqueous solutions of Mo–V–phosphoric heteropoly acids Original Research Article

Various organic substrates can be selectively oxidized with O2 in two stages using aqueous solutions of Mo–V–phosphoric heteropoly acids (HPA) as catalysts. In stage (1), a substrate is oxidized with a HPA solution to the desired product that is separated from the reduced form of HPA. The latter is oxidized with O2 in stage (2) closing a catalytic cycle. All physicochemical properties of the homogeneous catalysts based on HPA solutions continuously alter during these redox processes. Using as an example a solution of the modified high-vanadium HPA having gross composition H16P3Mo17V7O84 (HPA-7′), it was shown that viscosity and pH of this solution reach their maxima after reaction (1) and attain their minima after reaction (2). The reverse situation is observed for redox potential of the HPA-7′ solution. Many-cycled testing of 1-butene oxidation in stages (1) + (2) in the presence of the Pd + HPA-7′ catalyst confirms that the alterations of physicochemical properties of the catalyst are completely reversible.