ABSTRACT
Alumina (Al2O3) is widely used as a support for industrial catalysts due to its mechanical strength, thermal stability, surface property and strong interaction with metals and metal oxides Although the property and activity of alumina strongly depend on surface aluminum sites, construction of well-defined aluminum structures is insufficient even when conditions are controlled during preparations. Particularly, the introduction of metal ions as heteroatoms to the vacant sites of lacunary polyoxometalates is one of the unprecedented effective technologies for constructing well-defined, active metal sites. Polyoxometalate-supported complexes have great potential to develop polyoxometalate chemistry. In addition to the Lewis acidic polyoxometalates used as comparisons above, several compounds have been reported to show Lewis acid catalysis. For the classical MPV reduction catalyzed by metal alkoxide, the reaction mechanism involved a reversible hydride transfer from a secondary alcohol to a carbonyl substrate via a six-membered transition state, initiated by the activation of the carbonyl groups by coordination to the Lewis acidic metal center.
