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

Abstract

While being highly active for the CO oxidation reaction already at low temperatures, Au/CeO2 catalysts suffer from continuous deactivation with time on stream, with the activity and deactivation depending on the initial catalyst activation procedure. In previous X-ray absorption measurements at the Au LIII edge, which focused on changes in the electronic and geometric changes of Au, we found a modest increase of the Au particle size during reaction, with the Au nanoparticles (NPs) present in a dominantly metallic state during reaction, regardless of the pretreatment. Here we aim at expanding on these insights by examining the changes in electronic and chemical composition of the CeO2 support induced by different pretreatment procedures and during subsequent CO oxidation at 80 °C, by following changes at the Ce LIII near edge region in time-resolved operando X-ray absorption measurements. The results indicate a strong dependence of the initial concentration of Ce3+ ions on the pretreatment, while during subsequent reaction this rapidly approaches a steady-state value which depends on the oxidative/reductive character of the reaction gas mixture, but is largely independent of the pretreatment. These results are discussed and related to earlier finding on the electronic properties of Au nanoparticles under identical reaction conditions.

Fundamental Aspects of Ceria Supported Au Catalysts Probed by In Situ/Operando Spectroscopy and TAP Reactor Studies

“…In the next step, the as prepared Au/CeO 2 catalyst precipitate was washed with deionized water and subsequently dried at room temperature overnight (≥12 h). Different loadings of Au in the range between 2 and 5 wt.% were used [28,36,38,46,47,54] . It should be mentioned that the proper selection of the surface morphology of CeO 2 is also an additional parameter that can be controlled in the catalyst synthesis to steer the catalytic properties of resulting Au/CeO 2 catalysts.…”

“…Focusing first on the pretreatment effect we can also see a pronounced effect of the treatment gas on the resulting chemical properties of CeO 2 . While the oxidative pretreatment (O400) resulted in about perfect CeO 2 structure (Ce exists mainly as Ce 4+ ), with a negligible Ce 3+ ions concentration, XANES spectra at the Ce L III edge showed a notable reduction of CeO 2 both after the reductive CO400 and the H400 pretreatments [54] …”

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

“…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 …”

Recent Advances of Ceria‐Based Materials in the Oxidation of Carbon Monoxide

“…In addition, the reducibility of the support is also an important criterion for evaluating catalyst performance. [ 48 ] Both phenomena are affected by the type, size, and distribution of oxygen vacancies on the CeO 2 surface, [ 49 ] so‐called oxygen vacancies, including single, double, and multiple oxygen vacancies, as well as surface, subsurface, and bulk vacancies. The amount of oxygen vacancies depends on the reduction degree of the catalyst, which is related not only to the environment, but also to the nanostructure of the catalyst.…”