A novel manganese tungstate nanorod catalyst for the oxidation of styrene with tert-butyl hydroperoxide as oxidant

Catalyst,solvent and process parameters are the keys for the selective oxidation of styrene and other olefins to value added intermediates.Hence MnWO4 was synthesized by the one-pot hydrothermal method using Pluronic F127 as a surfactant,characterized and evaluated for the oxidation of styrene and different olefins,using tert-butyl hydroperoxide（TBHP） as oxidant.X-ray diffractogram confirmed the phase purity of MnWO4 which became further evident from the near surface equimolar proposition of Mn and W in+2 and+6 oxidation states,respectively,as inferred from X-ray photoelectron spectra.N2 sorption followed type Ⅳa isotherm with H3 hysteresis loop,starting at the relative pressure（P/P_o） of 0.9,typically of mesoporous materials containing macropores as further confirmed by pore-size distribution.Transmission electron microscope images of MnWO4 revealed its nanorod morphology.In the absence of catalyst,styrene conversion was 35%with benzaldehyde as the sole product and addition of 75 g of MnWO4 increased the styrene conversion to 97.3%,and the styrene oxide selectivity from 0% to 85% demonstrated its activity and selectivity.For the maximum conversion and styrene oxide selectivity optimum temperature,styrene:TBHP molar ratio,catalyst amount and solvent were found to be 70 ℃,1:2,75 mg,and acetonitrile,respectively.MnWO4 catalyst retained its activity and selectivity for five recycles,confirming its recoverability and reusability.From the kinetic studies,pre-exponential factor and apparent activation energy were found to be 0.206 s-1 and 31.5 kJ·mol-1,respectively,and a reaction mechanism was proposed.MnWO4 catalyst was active for oxidation of alkenes,cycloolefins and alkenyl aromatics with high selectivity for epoxides.