Redox properties and oxidation catalysis of potassium salts of transition metal-substituted I-2-K8P2W17O61(MADTOH2) (M = MnII, ZnII, FeII, CoII, CuII, and NiII) Wells-Dawson heteropolyacids

Potassium salts of transition metal-substituted I-2-K8P2W17O61(MADTOH2) (M = MnII, ZnII, FeII, CoII, CuII, and NiII) Wells-Dawson heteropolyacids were prepared to investigate their redox properties and oxidation catalysis. Successful formation of I-2-K8P2W17O61(MADTOH2) catalysts was confirmed by FT-IR, 31P NMR, and ICP-AES measurements. Reduction potential and absorption edge energy of I-2-K8P2W17O61(MADTOH2) catalysts were determined by an electrochemical method and UV-vis spectroscopy in solution, respectively. Absorption edge energy of I-2-K8P2W17O61(MADTOH2) catalysts decreased with increasing reduction potential of the catalysts. It was also found that reduction potential of I-2-K8P2W17O61(MADTOH2) catalysts increased and absorption edge energy of the catalysts decreased with decreasing Tanaka electronegativity of substituted transition metal. Vapor-phase benzyl alcohol oxidation was also carried out as a model reaction in order to probe oxidation catalysis of I-2-K8P2W17O61(MADTOH2) catalysts. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of I-2-K8P2W17O61(MADTOH2) catalysts. Reduction potential and absorption edge energy of I-2-K8P2W17O61(MADTOH2) catalysts could be utilized as a probe of oxidation catalysis of the catalysts.