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/Po ) 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 degrees C, 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<middle dot>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.