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 transformation (CPT) strategy for precisely controlling oxygen vacancies in tungsten oxide. 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 exceptionally high activity in the epoxidation of cyclooctene (96% yield at 60 °C for 4 h) and exhibits remarkable stability, attributed to the synergistic effects arising from the aforementioned structural advantages, mainly including oxygen vacancies in W₁₈O₄₉ and a longer W–H₂O bond, which jointly promote the activation of H₂O₂ into W–OOH. This CPT defect engineering provides an effective approach for optimizing the performance of transition metal oxide catalysts and deepens the understanding of the oxygen vacancy-mediated reaction mechanism.