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

Abstract

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.

Dynamic Metal–Support Interaction-Activated Sub-Nanometer Pt Clusters on FeOx Supports for Aqueous Phase Reforming and Hydrogenolysis of Glycerol

“…At the same time, the peak area ratio corresponding to Fe 2+ enlarged with the reduction temperature (≤200 °C), which implies that more Fe 3+ species are reduced to Fe 2+ species, forming more oxygen vacancy defects (i.e., O v –Fe 2+ sites) . In addition, in situ EPR characterization was used to further probe the effect of reduction temperature on the O v defects, as shown in Figure d. , The signals at a g -factor of 2.003 were attributed to the surface Fe 2+ defect and O v . The increase of the O v signal with reduction temperature depicted that O v –Fe 2+ defect sites were directly related to the Pt δ− species.…”

“…25 In addition, in situ EPR characterization was used to further probe the effect of reduction temperature on the O v defects, as shown in Figure 3d. 26,27 The signals at a g-factor of 2.003 were attributed to the surface Fe 2+ defect and O v . The increase of the O v signal with reduction temperature depicted that O v −Fe 2+ defect sites were directly related to the Pt δ− species.…”

Synthesis of Petitjeanite Bi3O(OH)(PO4)2 Photocatalytic Microparticles: Effect of Synthetic Conditions on the Crystal Structure and Activity toward Degradation of Aqueous Perfluorooctanoic Acid (PFOA)

“…It should be noted that as the reaction proceeded, there was a noticeable increase in activity. This is likely due to in situ V O generation under UV irradiation …”

“…This is likely due to in situ V O generation under UV irradiation. 66 Since catalyst activity has been correlated to surface V O content, we further investigated BOHP oxygen occupancy via EDS analysis (Table S6). The results show that the ratio of oxygen to bismuth (O:Bi) and oxygen to phosphate (O:P) decreased as the NH 4 OH volume increased, suggesting increased V O concentrations near the particle surfaces.…”

Oxygen vacancies meet partial S substitution: an effective strategy to achieve obvious synergistic effects and adjustable electrochemical behavior in NiFe-LDH for enhanced OER and capacitive performance

“…Moreover, another reason for the gradual decrease in ECSA values could be the S filling O v behavior, due to O v being considered to be the active site in the electrochemical process. 60,69 Interestingly, the ECSA value of NiFe-LDHS was not the largest, indirectly suggesting that the intrinsic activity of electrochemical sites played a dominant role in electrochemical performance. Thus, it can be concluded that the synergistic effect of O v and S was mainly reflected by the intrinsic activity of electroactive materials, which essentially determined the electrochemical performance.…”