Epoxidation of styrene by anhydrous t-butyl hydroperoxide over reusable gold supported on MgO and other alkaline earth oxides

Abstract

Gold nanoparticles deposited on MgO, CaO, SrO, and BaO by homogeneous deposition-precipitation using urea are, for the first time, reported to be novel highly active/selective and reusable catalysts in the epoxidation of styrene to styrene oxide (SO) by anhydrous t-butyl hydroperoxide. Au/MgO prepared by deposition-precipitation using NaOH is also studied in styrene epoxidation. The slightly poorer performance of Au/MgO prepared by deposition-precipitation in epoxidation of styrene (conversion: 44.6%, SO selectivity: 36.1%), as compared with to the gold catalysts prepared on alkaline earth oxides by homogeneous deposition-precipitation (styrene conversion: ≥ 53%, SO selectivity: 45-60%), is attributed to the lower loading (4.1 wt%), larger particle size (D_Au = 17.9 nm), and possible presence of trace impurities (Na⁺ and Cl^-;) in the former. Higher gold loading (4.7-7.5 wt%) and smaller gold particles (D_Au ≅ 8.0 nm) were observed in the alkaline earth-supported Au catalysts prepared by homogeneous deposition-precipitation.