The oxidation of benzothiophene using the Keggin-type lacunary polytungstophosphate as catalysts in emulsion

A series of emulsion catalysts were successfully synthesized with quarternary ammonium cations and heteropolyanions, and they were characterized by TG/DTA, FTIR, P-31 MAS NMR and EPR. The emulsion catalyst with intact Keggin-structure, [C18H37N(CH3)(3)]H-2[PW12O40] (PW12), is inactive for benzothiophene (BT) oxidation with H2O2 as oxidant under atmospheric pressure at 30 C. Moreover, the metal-substituted catalysts PW11M (M =Ti, Mn, Fe, Co, Ni and Cu) show rather low activity with the conversion less than 15% for BT oxidation. Whereas, the catalyst with mono-lacunary Keggin-structures, [C18H37N(CH3)(3)](5)Na-2[PW11O39] (PW11), could completely catalytic oxidize BT into the corresponding sulfone under the same conditions. After careful characterizations of the catalysts, it is found that only PW11 catalyst could effectively transform into the active polyperoxometalates species in the presence of hydrogen peroxide in non-polar solvent. (C) 2010 Elsevier B.V. All rights reserved.