Crystal Phase Transformation of Tungsten Oxide: A Novel Route to Oxygen Vacancy Engineering for Highly Active Epoxidation Catalysts

Abstract

Modulation of oxygen vacancies through defect engineering plays a critical role in improving the catalytic performance of transition metal oxide crystal catalysts. Herein, we report a crystal phase transition (CPT) strategy for precisely controlling oxygen vacancies in tungsten oxide. The WO3·H2O was first synthesized via a solvothermal process, and then gradually transformed into W18O49, with the phase transition deliberately halted at the intermediate stage to form a biphasic WO3·H2O/W18O49 composite, which possesses a high oxygen vacancy concentration (15.62%) and simultaneously has a large specific surface area (87.81 m2·g-1). Such a tailored architecture demonstrates exceptional high activity in the epoxidation of cyclooctene (96% yield at 60 ℃ for 4 h) and exhibits remarkable stability, attributed to the synergistic effects arising from the aforementioned structural advantages, mainly including the oxygen vacancies in the W18O49 and longer W-H2O bond jointly promote the activation of H2O2 into W-OOH. This CPT defect engineering provides an effective approach to optimize performance of transition metal oxide catalysts and deepens understanding of oxygen vacancy-mediated reaction mechanism.