Tuning the olefin-VOCs epoxidation performance of ceria by mechanochemical loading of coinage metal

Under the background of carbon dioxide emission reduction, how to realize the treatment and the high value-added conversion of typical olefin volatile organic compounds (olefin-VOCs), such as styrene, is a big challenge. In this contribution, the ceria-supported coinage metal catalysts (M/CeO2, M = Au, Ag, and Cu) are successfully synthesized by a dry mechanochemical method, and their catalytic performance for styrene-VOC epoxidation with tert-butyl hydrogen peroxide (TBHP) as an oxidant to prepare high-value styrene oxide (SO) is investigated. The oxygen vacancies of ceria play a key role in the anchoring of metal nanoparticles. After ball milling, Au(III) is partially reduced and coexists on ceria in two valence states (Au3+ and Au0), and the reactive oxygen species of the as-prepared catalyst are enhanced. The catalytic behaviors, including solvents effect, substrate concentration, oxidant ratio, catalyst dosage, reaction time, and temperature, are systematically investigated. Au/CeO2 exhibits good styrene epoxidation performance with a total styrene conversion of 94% and a SO yield of 63%, along with good reusability and substrate scalability. Thermodynamics and kinetics show that Au/CeO2 was more favorable for styrene epoxidation and this reaction is dominated by the rate of intrinsic chemical reactions on the surface of the catalyst. Based on experimental discussions and a set of characterizations (XPS, XRD, in-situ FT-IR, ESR, ESI-HSMS, etc.), the mechanism is revealed as the synergistic catalysis between the reactive oxygen species of Au/CeO2 and the peroxide radicals generated by the homolysis of TBHP.