Efficient Olefins Epoxidation on Ultrafine H₂O–WO_x Nanoparticles with Spectroscopic Evidence of Intermediate Species

Design and synthesis of high-performance heterogeneous catalysts are of immense interest in chemical industries. Herein, ultrafine H₂O coordinated WO_x nanoparticles (H₂O–WO_x, average diameter 2.24 nm) embedded into porous carbon matrix have been obtained via space-confinement pyrolysis with postmodification oxidation approach. The synthesized H₂O–WO_x nanoparticles exhibit high activities toward olefin epoxidation reaction using H₂O₂ as oxidant. In epoxidation of cis-cyclooctene, the turnover frequency of the catalyst can achieve as high as 949 h^–1, an activity comparable to the highest of all reported early transition-metal based catalysts. UV–vis spectra and controlled catalytic experiments have been performed to ascertain the possible active site in the catalyst: compared with traditional WO₃ and peroxide coordinated W-(η²-O₂) species, the water coordinated H₂O–WO_x can transform to hydroperoxide HOO–WO_x in the presence of H₂O₂, and the HOO–WO_x species can be further activated by proton acid to enhance its catalytic activities.