NAP-XPS and In Situ DRIFTS of the Interaction of CO with Au Nanoparticles Supported by Ce_1–xEu_xO₂ Nanocubes

Abstract

Control of metal–support interactions is one of the major challenges in heterogeneous catalysis. In this study, we explored the effect of Eu doping on the metal–support interactions in Au/Ce1–x Eu x O2 catalysts applied in the oxidation of CO. We probe the catalysts with CO under realistic conditions by near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). NAP-XPS allows in situ investigation of the surface reducibility of the ceria support and charging of the Au nanoparticles. Both parameters are crucial, as they are responsible for the efficiency of Au/ceria catalysts in the CO oxidation. We found that doping of the ceria support with Eu decreases the reducibility of Ce4+ in the Au/Ce1–x Eu x O2 system and the population of Auδ+ sites. We identified the available CO adsorption sites on Au/ceria (Auδ−, Au0, and Auδ+) in the typical temperature window of the CO oxidation reaction by in situ DRIFTS. We found that the difference in the catalytic activity of Au/CeO2 and Au/Ce0.80Eu0.20O2 does not origin from an electronic effect of the Eu dopant or different adsorption sites but from the size of the Au nanoparticles. The most active Au nanoparticles are very small, reactive Au nanoparticles, which are exclusively present on the undoped ceria support.

Tiny Species with Big Impact: High Activity of Cu Single Atoms on CeO2–TiO2 Deciphered by Operando Spectroscopy

“…This suggests that oxygen from Ce–O–Cu–O–Ce (−Ce–□–Cu–O–Ce) bridge is used for oxidation of CO to CO 2 , which agrees with the observed reduction of Ce 4+ to Ce 3+ as evident from Figure . A similar effect has been reported by Bezkrovnyi et al, who observed that Au nanoparticles facilitate the surface reduction of ceria in Au-doped CeO 2 under CO flow conditions …”

“…Figure illustrates the corresponding Ce 3d region. The spectra can be deconvoluted into three doublets for Ce 4+ ( u ‴/ v ‴ at about 917 and 898.3 eV, u / v at 901.1 and 882.5 eV, and u ″/ v ″ at 907.7 and 887.6 eV, marked in red) and two doublets for Ce 3+ ( u ′/ v ′ at 903.6 and 884.8 eV and u 0 / v 0 at 899.2 and 880.6 eV, marked in blue). , The surface percentage of Ce 3+ (indicated on the right of the spectra in Figure ) was determined from the area of the subpeaks using eq . − The surface of the bare support at 25 °C in He contains already 16.1% of Ce 3+ , confirming its surface reducibility in agreement with previously reported results. ,, This is also supported by the axial EPR signal with g ⊥ = 1.963 and g || = 1.941 in the bare support, assigned to electrons trapped in vacancies next to Ce 3+ (Figure ). Incorporation of Cu in Cat2 raises the Ce 3+ content to 29.5%.…”

“…The spectra can be deconvoluted into three doublets for Ce 4+ (u‴/ v‴ at about 917 and 898.3 eV, u/v at 901.1 and 882.5 eV, and u″/v″ at 907.7 and 887.6 eV, marked in red) and two doublets for Ce 3+ (u′/v′ at 903.6 and 884.8 eV and u 0 /v 0 at 899.2 and 880.6 eV, marked in blue). 124,125 The surface percentage of Ce 3+ (indicated on the right of the spectra in Figure 12) was determined from the area of the subpeaks using eq 3. 124…”

The Sintering of Au Nanoparticles on Flat {100}, {111} and Zigzagged {111}-Nanofacetted Structures of Ceria and Its Influence on Catalytic Activity in CO Oxidation and CO PROX

“…It remains an open question about the presence/absence of highly active subnanometer Au clusters in these samples. However, we observed the presence of such Au clusters in Au/CeO 2 (NC) annealed at 300 °C [32,33]. There are no objective reasons which can prevent thermally induced redispersion (e.g., strong anchoring on oxygen vacancies) in all investigated samples (annealed in the air only).…”

“…It can be explained by the presence of highly active sub-nanometer Au nanoclusters in pre-treated samples (both at 300 and 500 °C). In our previous works, we observed, using (S)TEM technique, such Au clusters in Au/ CeO 2 (NC) annealed at 300 °C [32,33]. The second possible explanation is the presence of pseudo-single sites, i.e., gold ions slightly abstracted from a gold clusters, which exhibit lower activation energy in the rate-determining step of COoxidation [34].…”