Redox behaviour of copper(II) species on CuCe oxide catalysts: electron paramagnetic resonance (EPR) study

Effects of Ni-Doping of Ceria-Based Materials on Their Micro-Structures and Dynamic Oxygen Storage and Release Behaviors

“…The component showing the main band at 855.2 eV with two satellites is attributed to NiOc 2? , where the octahedral coordinated Ni species has the oxygen species with the similar local environment to that of CeO 2 [21]. For Ni 2p XPS spectra of Ni 0.1 Ce 0.6 Zr 0.3 O x , the band energies are higher than those measured for Ni 0.1 Ce 0.9 O x , implying that the introduction of zirconia influences the top-surface nickel species [7].…”

“…Furthermore, the bands at 339.4, 468.0, and 649.3 cm -1 provide the evidence of the presence of the similar cubic phase, where Ce 0.67 Zr 0.33 O 2 solid solution can characterized with the bands at 313.7, 473.8, and 605.6 cm -1 . These bands have been claimed to be corresponding to internal tetragonal symmetry of the pseudocubic phase [21]. After Ni-doping, the featuring peaks at 313.7 and 605.6 cm -1 shift to higher frequencies.…”

Flame‐Synthesized Ceria‐Supported Copper Dimers for Preferential Oxidation of CO

“…This feature has been previously ascribed to either superoxide species adsorbed on Ce 4þ ions (O 2 À -Ce 4þ ) [37] or partially reduced (Cu 2þ -Ce 3þ ) species. [38] The simultaneous existence of signals K and D detected at higher Cu concentrations in FSP-prepared catalysts can be rationalized by the following argument: while K originates from two oxygen-bridged Cu nuclei, [36] these dimers facilitate the formation of doubly charged oxygen vacancies in the CeO 2 lattice, as indicated by the XPS and Raman results. It is proposed the electrons localized at these vacancies can react with nearby Ce 4þ , which subsequently leads to an intensification of the D-type signal.…”

“…As Cu content increases, these spectral features are gradually replaced by a doublet centered at g ¼ 2.05 (labeled K1 and K2), which has been reported to result from a dimer consisting of two equivalent and axially symmetric Cu atoms. [38] As depicted in Scheme 1, oxo-bridged dimer formation effectively condenses the number of Cu 2þ residing on a fixed number of surface sites, allowing for higher concentrations of Cu ions to be accommodated over a limited number of terminal O. To satisfy the fourfold coordination for a Cu atom substituted in the place of a surface Ce, [25] an oxygen vacancy is also generated.…”

“…While heightened surface reducibility has been separately ascribed to dimeric [17] and highly ionic [43] Cu-CeO 2 species, the results of this combined experimental and theoretical study are the first to suggest these two previously disparate phenomena are in fact contingent upon one another. Importantly, FSP-synthesized Cu-CeO 2 spontaneously generates these desirable structural/electronic properties without the need for additional high-temperature [38] or evacuation [37] treatments. Despite reduction by CO occurring readily over Cu-CeO 2 materials at comparatively low temperatures (T ¼ 300 K), [44] Sedmak et al [41] determined, through kinetic studies, that reoxidation of the catalytic support was the ratelimiting step in the overall reaction mechanism.…”