Regulation of the oxygen vacancies of WOx for highly efficient catalytic epoxidation of cyclooctene†

Oxygen vacancies of the WO_x catalyst play a critical role in the epoxidation of cyclooctene. However, the main factor restricting the industrial application of oxygen vacancy-enriched tungsten oxide is deactivation due to oxidation of oxygen vacancies. Herein, WO_x with tunable oxygen vacancies was prepared through simple reduction and regeneration of inactivated WO_2.72, which exhibited 97.3% conversion of cyclooctene and 99.0% selectivity toward epoxyoctane. The catalytic performance of the catalyst was not significantly reduced after five repeated regeneration cycles. SEM, XRD and XPS characterization presented the variation in the morphology, structure and component of a series of WO_x regenerated with different reduction temperatures and times and verified the regeneration of WO_2.72 and the presence of abundant oxygen vacancies. In situ DRIFTS demonstrated that appropriate oxygen vacancies improved the adsorption and activation of H₂O₂ to the hydroperoxide-coordinated HOO–WO_x species, which greatly promoted the performance of cyclooctene epoxidation. This paper not only provides a simple, green, and cost-effective approach for the regeneration of the WO_2.72 catalyst as an industrial catalyst using oxygen vacancy-enriched tungsten oxide but also sheds light on the mechanism of olefin epoxidation.