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Identifying the dynamic structural changes of the active sites in a catalytic reaction under realistic working conditions is a great challenge. In this work, we demonstrate that in situ electron paramagnetic resonance (EPR) technology is an important technique for the electronic-level recognition of the dynamic evolution of active sites over a defective BiOCl catalyst during the gas–solid photocatalytic reaction. The formation and recovery of photoexcited oxygen vacancies (PE-OVs) with or without UV light irradiation are experimentally verified, and these vacancies can be defined as photoswitchable OVs. The photoexcited dynamic OVs could function as genuine active sites to activate the O2 molecules via directional single-electron transfer from px or pz of Bi 6p to π2py* of the O2 molecules. In situ FT-IR spectra elucidate that the dynamic PE-OVs were available to promote the conversion of reaction intermediates to the final product. Thus, PE-OVs are identified as dynamic active sites for photocatalysis reactions, challenging the common view of the static OVs as active sites. This work provides an innovative concept of dynamic defects as real active sites for catalysis reactions.
Ren et al. (Mon,) studied this question.