Epoxidation of olefins with molecular oxygen as the oxidant using gold catalysts supported on polyoxometalates
We report a highly efficient green process for the epoxidation of various olefins using polyoxometalate-supported gold nanoparticles as catalysts and using oxygen as the terminal oxidant. The nanoparticles were prepared through thermal reduction of Au(III) and were characterised by TEM and XPS. The elemental composition of the catalyst was also determined using ICP. The results show that higher calcination temperatures give a higher degree of reduction, but also result in some sintering of the particles. The catalytic epoxidation reaction may be carried out with or without a solvent and with air or molecular oxygen as the stoichiometric oxidant and using t-butyl hydroperoxide as an initiator. The method shows consistently high conversions and >90% selectivity to epoxide formation for norbornene and cyclooctene oxidation. The catalysts show little deactivation with time and are easily recovered by filtration and can be reused with little or no loss in activity and selectivity.