Real-Time Observation of the Defect Dynamics in Working Au/CeO₂ Catalysts by Combined Operando Raman/UV–Vis Spectroscopy

Abstract

Supported gold catalysts are highly active for a variety of reactions including low-temperature CO oxidation. It has been shown that reducible support materials, e.g., ceria or titania, may significantly alter the catalytic performance. In this contribution, we provide the first direct evidence for ceria (CeO2) support dynamics and its relevance in Au/CeO2 catalysts during room temperature CO oxidation. In particular, combined operando Raman and UV–vis spectroscopy are employed to monitor the surface and subsurface defect dynamics of ceria quantitatively and in real time. The results clearly show a dependence of catalytic activity on the reduction state of the ceria support. In fact, the prereduced CeO2 catalyst support increases the activity during CO oxidation initially by 100%. The reduction is not limited to the CeO2 surface but also affects the CeO2 subsurface due to oxygen mobility and charge transfer in CeO2–x . Our results highlight the enormous importance of the support properties for a mechanistic understanding of oxidation reactions over metal/ceria catalyst materials.

Chemical and Electronic Changes of the CeO2 Support during CO Oxidation on Au/CeO2 Catalysts: Time-Resolved Operando XAS at the Ce LIII Edge

“…The data furthermore demonstrate that, in good agreement with the previous Raman spectroscopy data [22,33,39], there are (at least) two different types of O-vacancies/Ce 3+ species, one which is in the surface region and can easily be formed and replenished at 80 • C, and another one which is formed only at higher temperatures (400 • C) and cannot be replenished upon exposure to CO/O 2 mixtures at 80 • C, at least not on the time scale of these experiments.…”

New Insights on the Dynamic Role of the Protecting Agent on the Reactivity of Supported Gold Nanoparticles

“…Therefore, the MW‐assisted loss of atomic oxygen and the simultaneous Ce 3+ formation during reaction resulted in a contained decrease of the crystal size of the catalyst, as already indicated by XRD. Combined operando Raman and UV‐Vis spectroscopies were employed to perform real‐time observations of the dynamic of defects in Au/CeO 2 catalysts under working conditions . It was found that the reduction state of the ceria support strongly affects the catalytic activity.…”

“…It was found that the reduction state of the ceria support strongly affects the catalytic activity. Moreover, oxygen mobility and charge transfer processes induce the reduction at both surface and subsurface of the catalyst …”

“…Combined operando Raman and UV-Vis spectroscopies were employed to perform real-time observations of the dynamic of defects in Au/CeO 2 catalysts under working conditions. [39] It was found that the reduction state of the ceria support strongly affects the catalytic activity. Moreover, oxygen mobility and charge transfer processes induce the reduction at both surface and subsurface of the catalyst.…”

“…Moreover, oxygen mobility and charge transfer processes induce the reduction at both surface and subsurface of the catalyst. [39][40][41] Basing on the catalytic tests and the characterization data, it can be proposed that 2-FA esterification to Me-2-F followed two reaction paths. According to Scheme 3, 2-FA can follow Path 1 and be directly converted to the ester by involving the formation of the hemiacetal to Me-2-F.…”