Efficient Olefins Epoxidation on Ultrafine H₂O–WO_<i>x</i> Nanoparticles with Spectroscopic Evidence of Intermediate Species

Abstract

Design and synthesis of high-performance heterogeneous catalysts are of immense interest in chemical industries. Herein, ultrafine H2O coordinated WOx nanoparticles (H2O–WOx, average diameter 2.24 nm) embedded into porous carbon matrix have been obtained via space-confinement pyrolysis with postmodification oxidation approach. The synthesized H2O–WOx 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–WOx can transform to hydroperoxide HOO–WOx in the presence of H2O2, and the HOO–WOx species can be further activated by proton acid to enhance its catalytic activities.