Identifying the active redox oxygen sites in a mixed Cu and Ce oxide catalyst by in situ X-ray absorption spectroscopy and anaerobic reactions with CO in concentrated H2

The active redox oxygen site of a mixed copper cerium oxide catalyst (Cu0.07Ce0.93O2) and the active copper species for CO preferential oxidation in rich H2 were investigated by in situ X-ray absorption spectroscopy (XAS) at Cu K-edge during anaerobic reaction along with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible–near infrared (UV–Vis–NIR) diffuse reflectance spectroscopy. During anaerobic reaction, the absorption edge energy of in situ X-ray absorption near edge spectroscopy (XANES) spectra shifts to lower energy and the white-line intensity decreases, suggesting the reduction of Cu(II) to Cu(I) via the removal of surface lattice oxygen to oxidize CO. In addition, the first shell Cu–O peak intensity decrease of a series of Fourier transformed extended X-ray absorption fine structure (EXAFS) spectra during anaerobic reaction indicates the loss of copper’s first oxygen neighbor to oxidize CO. These provided for the first time the experimental evidence that the active/labile oxygen in copper cerium oxide catalysts is the first oxygen neighbor of Cu(II) species, which is further supported by UV–Vis studies on the reduction of the optical absorption edge energy of copper in the catalyst.

Graphical abstractThe active redox oxygen sites in a mixed Cu and Ce oxide catalyst (Cu0.07Ce0.93O2) have been for the first time identified to be the first oxygen neighbor of active Cu ions by coupling the in situ XAS with anaerobic titration experiments.Figure optionsDownload full-size imageDownload high-quality image (152 K)Download as PowerPoint slideHighlights► For the first time, in situ XAS was coupled with anaerobic titration to identify active oxygen sites. ► The first oxygen neighbor of active copper ions is the active redox oxygen. ► The active redox oxygen site is highly re-generable and structurally stable. ► In situ XANES spectra show that Cu(II) was reduced to Cu(I) during anaerobic titration. ► Active Cu(II) ions strongly interact with CeO2 forming a mixed copper cerium oxide.