Vanadium-polyoxometalate catalyst

Marchal-Roch, C. Bayer, R. Moisan, J.F. Teze, A. Herve, G. Oxidative dehydrogenation of isobu-tyric acid Characterization and modeling of vanadium containing polyoxometalate catalysts. Top. Catal. 1996, 5,407-419. 

NomiyaK, Nemoto Y, HasegawaT, Matsuoka S (2000) Multicenter active sites of vanadium-substituted polyoxometalate catalysts on benzene hydroxylation with hydrogen peroxide and two reaction types with and without an induction period. J Mol Catal A Chem 152 55-68 Ono Y (1992) Perspectives in catalysis. In Thomas JM, Zamaraev KI (eds). Blackwell scientific publications, Oxford... 

Methacryhc acid is a major chemical conunodity produced annually via a multistep route that does, unfortunately, produce many environmentally undesirable by-products.Methacrylic acid, however, can also be direcily formed by oxidation of isobutane over polyoxometalate Keggin catalysts (e.g. H3PM012O40 and its vanadium-substituted analogs H3+xPMoi2-xVx04o) and such a green process has been investigated by several researchers. This possibility has resulted in many oxidation studies with polyoxometalate catalysts over the past two decades. 

Enantioselective oxidation catalysis to yield chiral products from prochiral substrates using polyoxometalate catalysts has not been observed until recently. However, in a combined effort of several research groups it has been shown that the racemic vanadium-substituted sandwich type polyoxometalate, [(V 0)2ZnW(ZnW9034)2] , is an extremely effective catalyst (up to 40 000 turnovers) at near ambient temperatures, for the enantioselective epoxidation of aUyHc alcohols to the 2R,3R-ejx)xyalcohol with the sterically crowded chiral hydroperoxide, TADOOH, as oxygen donor [31], Scheme 8.6. 

An isopolyoxovanadate catalyst, [C8Hi7N(CH3)3]3H3Vio028, showed high catalytic activity in the oxidation of dibenzothiophene to its corresponding sulfone using molecular oxygen as oxidant under mild reaction conditions. A radical chain mechanism has been ruled out. Lewis bases suppress the vanadium-polyoxometalate catalysed dioxygenase reaction and catalysed the oxidation reaction of 3,5-di-t-butylcatechol selectively. The rate of autoxidation is increased by the polyoxometalate catalyst. ... 

Other classes of catalysts investigated include supported Keggin-type P/Mo/V/O polyoxometalates [14-16], and titania-supported vanadium oxide or V/P/(Mo)/0... 

Polyoxometalates are important catalysts but they are also finding application in optical, electrical, and magnetic devices. Mixed-metal polyoxometalates with vanadium(V) in the polyoxoanion core confers enhanced properties to such structures, principally in their ability to form essentially infinite networks that can be utilized as coatings or as other thin film materials. Additionally, these materials have tunable electromagnetic and photochromic properties. In combination with organic polymers, so-called hybrid polymers, special electrochemical properties are conferred, making possible such electrical storage devices such as capacitors and batteries that utilize the redox properties of the polyoxometalate [7],... 

Another catalyst type is the heterogeneous catalyst, which remains as a solid and promotes chemistry at the surface. To function well, they require high surface areas per unit mass. Metal oxides and hydroxides are common examples. A vanadium(V) oxide is employed in the formation of ammonia from nitrogen and hydrogen under elevated temperature and pressure, for example. Polyoxometallate metal clusters, which are oxo-ligand coordination complexes employing dominantly 02 and HO as ligands, have some catalytic roles. 

Systems based on Keggin-type polyoxometalates (POMs) (phosphomolybdic acid derivatives) have been the most effective and widely used catalysts in gas-phase isobutane selective oxidation research. This Keggin POM catalyst application was hrst claimed in 1981 by Rohm and Haas, and after several catalyst mod-ihcations has been patented by other companies such as Asahi Kasei, Sumitomo, Mitshubishi, etc. However, in addition to a Keggin phosphomolybdate, vanadium must also be present in the anion structure in order to obtain a catalyst effective in the selective oxidation of isobutane. Moreover, the addition of - -3 metal cations to the phosphomolybdate anion increases the thermal stability of the catalyst, significantly minimizing its deactivation. " ... 

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