Role of Two-Electron Defects on the CeO₂ Surface in CO Preferential Oxidation over CuO/CeO₂ Catalysts

Abstract

Owing to the peculiar synergistic interaction between CuO and CeO 2 at the interface, CuO/CeO 2 is one of the most efficient catalysts to purify a H 2 source, which is used in a proton exchange membrane fuel cell by preferential oxidation (PROX) of CO. The defective structure in CeO 2 is considered to be a crucial factor affecting the synergistic interaction. However, the defect−interaction relationship has not been well established due to the complex variation in different types of defects. Therefore, in this study, a novel ultrasound-assisted precipitation method was used to separately modulate diverse types of defects. The structural variation was explored by characterization techniques and theoretical calculations. It was found that the synergistic interaction was mainly related to two-electron defects on the CeO 2 surface. The two-electron defects could absorb O 2 to form the η 2 peroxide, and Cu ions could incorporate with the η 2 peroxide. Then, the two additional electrons in the two-electron defects would induce the electronic redispersion in CuO/CeO 2 , synchronously producing Cu + and Ce 3+ . The resulting Cu + and Ce 3+ were related to unsaturated CuO and redox capacity, which intimately affected the CO adsorption and oxygen activation. Thus, the catalytic performance was significantly promoted by increasing the amount of twoelectron defects in CeO 2 . Our study not only demonstrates a feasible way to finely control the synergistic interaction between CuO and CeO 2 but also deeply reveals the direct influence of two-electron defects on the CeO 2 surface on PROX.

Synthesis of CuO‐Loaded Ceria Hollow Spheres for Catalytic CO Oxidation

“…In Figure 5c, the spectrum with typical six binding energy peaks at 882.1, 898.5, 916.8 eV are in agreement with Ce 4+ in previous report [21] . The 3d 5/2 and 3d 3/2 spin‐orbit components of Ce 4+ are marked in Figure 5c, referring to Ce 4+ v and u spin‐orbit doublets [8,18] . In comparison to pure sample and Ce in CHS (Figure S5c), binding energy Ce3d 5/2 at 882.1 eV and the six peaks overlap well with these of pure sample without any shift, indicating the majority state of Ce in CHS‐CuO are Ce IV oxide.…”

“…These two typical reflections are characteristic for the presence of Tenoirte (CuO) phase [5c] . The diffraction peaks attributed to CuO are visible, indicating that CuO species are highly dispersed on the surface [8,18] . The peaks are reasonably weak for two reasons.…”

Recent Advances on the Rational Design of Non-Precious Metal Oxide Catalysts Exemplified by CuOx/CeO2 Binary System: Implications of Size, Shape and Electronic Effects on Intrinsic Reactivity and Metal-Support Interactions

“…Interestingly, ethanol washing during the preparation of CuO x /CeO 2 oxides leads to decreased particle sizes, as it affects the dehydration process between precursors particles, resulting in decreased adsorbed water and improved dispersion [272]. Very recently, a novel ultrasound-assisted precipitation method was employed to adjust the defective structure of CeO 2 and in turn, the CO-RPOX activity [273]. By means of characterization techniques and theoretical calculations, it was shown that only two-electron defects on ceria surface (i.e., defects adsorbing oxygen to form peroxides instead of superoxide species which are formed on one-electron defects) were responsible for the formation of Cu + and Ce 3+ species, which were intimately involved in the CO adsorption and oxygen activation processes [273].…”

“…Very recently, a novel ultrasound-assisted precipitation method was employed to adjust the defective structure of CeO 2 and in turn, the CO-RPOX activity [273]. By means of characterization techniques and theoretical calculations, it was shown that only two-electron defects on ceria surface (i.e., defects adsorbing oxygen to form peroxides instead of superoxide species which are formed on one-electron defects) were responsible for the formation of Cu + and Ce 3+ species, which were intimately involved in the CO adsorption and oxygen activation processes [273]. In particular, the adsorption of O 2 on two-electron defects resulted in peroxides formation, followed by Cu ions incorporation towards the development of Cu-O-Ce structure.…”

Engineering CuOx–ZrO2–CeO2 nanocatalysts with abundant surface Cu species and oxygen vacancies toward high catalytic performance in CO oxidation and 4-nitrophenol reduction

“…25,26 As reported in several relevant studies, six peaks labeled as V, V″, V‴, U, U″ and U‴ are the evidence of the presence of Ce 4+ , [25][26][27] while other four peaks denoted as V 0 , V′ and U 0 , U′ are assigned to the final Ce 3+ states which can be used as an indicator of the existence of oxygen vacancies. 14,25,28 The increase of the intensity of V 0 and U 0 peaks indicates the increase of Ce 3+ content on the surface of CeO 2 . The surface composition has been also confirmed by XPS quantitative analysis shown in Table 2.…”