Redox properties and oxidation catalysis of transition metal-substituted α-K5PW11O39(M•OH2) (M = MnII, CoII, NiII, and ZnII) Keggin heteropolyacid catalysts for liquid-phase oxidation of 2-propanol

alpha-K5PW11O39(M center dot OH2) (M = Mn-II, Co-II, Ni-II, and Zn-II) Keggin heteropolyacid catalysts were prepared in order to investigate their redox properties and oxidation catalysis. Successful formation of alpha-K5PW11O39(M center dot OH2) heteropolyacid catalysts was confirmed by FT-IR, P-31 NMR, and ICP-AES analyses. Reduction potentials and absorption edge energies of alpha-K5PW11O39(M center dot OH2) heteropolyacid catalysts were determined by electrochemical method and UV-vis spectroscopy, respectively. It was found that absorption edge energy of the catalysts decreased with increasing reduction potential. Liquid phase oxidation of 2-propanol with hydrogen peroxide over alpha-K5PW11O39(M center dot OH2) heteropolyacid catalysts was carried out as a model reaction to examine their oxidation catalysis. It was revealed that yield for acetone over the catalysts increased with increasing reduction potential and with decreasing absorption edge energy of the catalysts. Thus, reduction potential and absorption edge energy of alpha-K5PW11O39(M center dot OH2) heteropolyacid catalysts could be utilized as a correlating parameter to track the oxidation catalysis of the catalysts. (C) 2013 Elsevier B.V. All rights reserved.