Epoxidation of styrene by t-butyl hydroperoxide over gold nanoparticles supported on Yb₂O₃: Effect of gold deposition method, gold loading, and calcination temperature of the catalyst on its surface properties and catalytic performance

Surface properties and epoxidation performance of Au/Yb₂O ₃ catalyst are influenced by the method of gold deposition [viz. deposition-precipitation (DP), homogeneous deposition-precipitation (HDP) or impregnation], gold loading (0.9-6.6 wt%), and the catalyst calcination temperature (400-900°C)]. The catalyst showed the best epoxidation performance when it was prepared by the HDP method and calcined at 500 °C. The Au/Yb₂O₃ catalyst even after calcination at 900 °C showed good activity and epoxide selectivity. Both Au⁰ and Au ³⁺ surface species were found in the catalyst calcined at 800 °C, but only Au⁰ species were observed at the lower calcination temperatures (<600 °C). The selectivity for styrene oxide increased continuously with the reaction temperature (from 75 °C to 97 °C) and time (1-5 h), indicating that styrene oxide did not undergo secondary reactions under these conditions.