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/CeO, 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 (Au and Au), 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/CeO 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/CeO 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/CeO and the peroxide radicals generated by the homolysis of TBHP.