Operando Identification of Dynamic Photoexcited Oxygen Vacancies as True Catalytic Active Sites

The complex structural evolution of catalysts under realistic reaction conditions causes great difficulty in identifying true active sites and further understanding the correlations between the dynamic behavior and the catalytic property. Herein, we developed a set of operando electron paramagnetic resonance (EPR) measurements to investigate the dynamic behavior of true active sites, particularly the atomic surface structures and interfacial processes under reaction conditions. By constructing reduced TiO2 as the catalyst model, supported by the developed operando EPR and multiple in situ characterization results, we confirm the generation of previously unrevealed active sites of photoexcited oxygen vacancies (Vo) and further dissect the formation, rebirth, and evolvement of dynamic Vo at the electronic level. Subsequently, the consistent theoretical and experimental results comprehensively justify the dynamic photoexcited Vo as the true active site directly determining the catalytic performance, subverting the classical perception of predesigned Vo as the active site. The relationship between dynamic active site evolution and catalytic performance during operation enables us to understand the interfacial mechanisms at work and design better catalysis systems.