Green Oxidation Reactions by Polyoxometalate-Based Catalysts: From Molecular to Solid Catalysts

Abstract

This article summarizes our recent developments for H 2 O 2 -and O 2 -based green oxidation reactions by polyoxometalates (POMs) and related compounds. POMbased structurally controlled molecular catalysts exhibit high catalytic performance for epoxidation and sulfoxidation with H 2 O 2 . These molecular catalysts can be immobilized on the organic-inorganic hybrid support with covalently anchoring N-octyldihydroimidazolium cation fragments via the anion exchange. In addition, we have developed supported metal hydroxide catalysts such as Ru(OH) x /Al 2 O 3 and Cu(OH) x /TiO 2 on the basis of the information of the catalytically active sites with POMs. By using these supported metal hydroxide catalysts, novel aerobic oxidative synthesis of nitriles and amides, and efficient aerobic oxidative homocoupling of alkynes can be realized.

Encapsulation of Keggin-type phosphotungstic acid into the mesopores of SBA-16 as a reusable heterogeneous catalyst for the epoxidation of olefins

“…The major utilization of these compounds is in the area of catalysis where soluble POMs exhibit the role of homogeneous catalysts in the oxidation of organic compounds [5][6][7][8][9][10][11][12][13]. It is well-known that POMs have fast and reversible redox properties, which make them hopeful catalysts for the oxidation of ole ns, aromatics, and alcohols [14,15].…”

Oxidation of Cyclohexanol on Phosphotungstic Acid Anion Intercalated Layered Double Hydroxides With Aqueous H2o2 as Oxidant

“…(POMs) [6][7][8][9] have widely been used in the catalytic oxidation reaction due to their oxidative stability and high efficiency. [10][11][12] The homogeneous catalysis is green, highly efficient and environmentally pollution-free, 13,14 but there are inherent problems existing with this method such as the difficult separation of the product and thus the catalyst is easily lost in the process. Hence, it is absolutely necessary to heterogenize the soluble POMs.…”

Classical Keggin Intercalated into Layered Double Hydroxides: Facile Preparation and Catalytic Efficiency in Knoevenagel Condensation Reactions

“…[4][5][6] One the POMs' important properties is their superior catalytic performance in numerous processes which has been exploited in industrial processes. [7][8][9][10][11][12][13] However, the industrial application of POMbased homogeneous catalytic systems has been largely restricted by the poor solubility of POMs in common organic solvents due to their crystalline nature, high negative charge, low energy lattice [14] , contamination/separation and decomposition issues. Consequently, design of POM-based heterogeneous catalysts is a potentially alternative way to overcome the above limitations and fine control of the POMbased material's functionality.…”