CATALYTIC BEHAVIORS OF THE HETEROPOLYTUNGSTOLANTHANATE (LNW10, LN CERIUM, NEODYMIUM, AND SAMARIUM) ANION ON THE DECOMPOSITION OF HYDROGEN-PEROXIDE AND CYCLOHEXANOL OXIDATION WITH H2O2 IN A HOMOGENEOUS SYSTEM

In the presence of the heteropolytungstolanthanate anion (Ce(IV)W10O36 -9, and Nd(III)W10O36-9, Sm(III)W10)36-9; LnW10) the kinetic behaviors of hydrogen peroxide decomposition and cyclohexanol oxidation with H2 O2 were investigated. In CeW10 the H2O2 decomposition rate tended to r each almost a limited value with increasing H2O2 concentration, while in NdW10 and SmW10 it decreased considerably after reaching the maximu m value in high H2O2. The kinetic behavior of LnW10 was reasonably exp lained by a reaction scheme in which an intermediate species is initia lly formed (IS1) and then reacts further with H2O2 molecules to change the inactive species and, thus, to be removed from the catalytic cycl e. Cyclohexanol was selectively oxidized with H2O2 to cyclohexanone ac cording to the reaction order 0.6-0.8 on the H2O2 concentration until the high H2O2 region in the presence of all LnW10. The Arrhenius law c oncerning the overall rates of both reactions of H2O2 decomposition an d cyclohexanol oxidation was maintained in any LnW1O; further, a good compensation effect between the Arrhenius parameters, preexponential f actor (log V0) and apparent activation energy (E(ap)), was found for b oth reactions in the series of LnW10. However, the empirical points co ncerning the log V0 vs. E(ap) plot in the oxidation alined in an inver se manner to those in H2O2 decomposition, that is, the order is CeW10< SmW10<NdW10 in the former and NdW10<SmW10<CeW10 in the latter. From th is finding, both reactions were suggested to proceed via a common-inte rmediate species. Furthermore, it was elucidated that the more stable is the species, the more favorably are the alcohol molecules activated to the final products in the oxidation reaction.