Polyoxometalate-based heterogeneous catalysts for liquid phase selective oxidations: Comparison of different strategies

Recent achievements in the preparation of polyoxometalate-based heterogeneous catalysts using different immobilization techniques, such as embedding into a silica matrix by sol–gel method, irreversible adsorption on active carbon, electrostatic attachment to NH2-modified mesoporous silica, and incorporation within nanocages of the metal-organic framework MIL-101 are surveyed. The catalyst characterization is reported, and their catalytic performances in liquid phase selective oxidations are compared, with special attention being paid to the questions of catalyst stability to leaching, nature of catalysis and catalytic properties after recycling. The scope and limitations of the POM-based heterogeneous catalysts are discussed.