TRANSITION-METAL SUBSTITUTED 12-TUNGSTOPHOSPHATES - CHARACTERIZATION AND EVALUATION OF THEIR PERFORMANCE AS OXIDATION CATALYSTS

Tetrabutylammonium salt of [PW12O40](3-) and its transition metal (Mn2 +, Fe2+, Co2+ and Cu2+) substituted compounds are characterized by ele mental analysis, thermogravimetric and spectroscopic techniques. Therm al stability of these compounds decreases after metal ion substitution , but the cobalt substituted compound is relatively more stable. The c obalt substituted compound is found to be a good catalyst for the oxid ation of cyclohexanol and the catalytic activity of the transition met al substituted compounds decreases in the order: Co2+ much greater tha n Mn2+ > Fe2+ greater than or equal to Cu2+. Detailed studies of the r eaction in the presence of Co2+ and Mn2+ substituted compounds reveal that the transition metal ions are initially oxidized to a higher oxid ation state which then act as the catalytic centre for the reaction. T he enhanced catalytic activity of Co2+ substituted compound is due its oxidation to Co4+ in the presence of H2O2 which is evidenced from EPR and UV-VIS spectroscopic studies.