Redox properties and oxidation catalysis of potassium salts of transition metal-substituted α2-K8P2W_(17)O_(61)(M·OH2) (M = Mn~(II), Zn~(II), Fe~(II), Co~(II), Cu~(II), and Ni~(II)) Wells-Dawson heteropolyacids

摘要

Potassium salts of transition metal-substituted α2-K8P2W_(17)O_(61)(M·OH2) (M = Mn~(II), Zn~(II), Fe~(II), Co~(II), Cu~(II), and Ni") Wells-Dawson heteropolyacids were prepared to investigate their redox properties and oxidation catalysis. Successful formation of α2-K8P2W_(17)O_(61)(M·OH2) catalysts was confirmed by FT-IR, ~(31)P NMR, and ICP-AES measurements. Reduction potential and absorption edge energy of α2-K8P2W_(17)O_(61)(M·OH2) catalysts were determined by an electrochemical method and UV-vis spectroscopy in solution, respectively. Absorption edge energy of α2-K8P2W_(17)O_(61)(M·OH2) catalysts decreased with increasing reduction potential of the catalysts. It was also found that reduction potential of α2-K8P2W_(17)O_(61)(M·OH2) 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 α2-K8P2W_(17)O_(61)(M·OH2) catalysts. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of α2-K8P2W_(17)O_(61)(M·OH2) catalysts. Reduction potential and absorption edge energy of α2-K8P2W_(17)O_(61)(M·OH2) catalysts could be utilized as a probe of oxidation catalysis of the catalysts.