Highly resolved electron paramagnetic resonance spectrum of copper(II) ion pairs in CuCe oxide

Abstract

Avenue Albert Einstein, 69626 Vi/leurbanne, France A copper-cerium oxide sample prepared with an atomic ratio, Cu : Ce, of 0.01 has been studied by electron paramagnetic resonance (EPR) spectroscopy. A well resolved spectrum of copper(11) ion pairs has been evi denced and the hyperfine structure of the perpendicular components clearly appears. The high resolution can be explained by the presence of two nearly equivalent Cu2+ ions separated by an oxygen ion. A correlation in EPR parameters has been found between the signal corresponding to a single Cu2+ ion, a precursor of the dimer, and the copper(11) ion pair spectrum.

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.…”

“…This is due to interaction between the nuclear spins of two Cu 2þ ions. [36] For FSP catalysts, hyperfine splitting is resolvable at all Cu concentrations, indicating a high degree of crystallization between the Cu and CeO 2 components is achieved. [36] Hyperfine splitting has previously been reported in Cu-CeO 2 systems subject to prolonged periods at elevated temperatures and under vacuum.…”

“…At lower loadings (0.5-2.0 wt%), the feature A and the triplet states at g-values of 2.50, 2.38, and 2.28 (labeled C1, C2, and C3, respectively) indicate the Cu component is present as monomers. [36] The differing g-values for C-type signals indicate different degrees of distortion from the ideal octahedral coordination geometry, with C3 being previously ascribed to Cu 2þ occupying subsurface lattice positions. [37] It is thought that, at lower Cu loadings, the comparatively low Cu ion concentration promotes monomer dispersion throughout the lattice and across the surface, with minimal electronic interaction with adjacent Cu atoms.…”

“…At intermediate Cu concentrations (4-8 wt%), a series of wellresolved hyperfine splittings, labeled D, develop at around www.afm-journal.de Oxygen-bridged dimers [36] FULL PAPER g ¼ 2.05. 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.…”

Emf Measurements on Nanocrystalline Copper-Doped Ceria

“…However, the solubility of copper in the CeO -fluorite lattice must be expected to be low due to the difference in ionic radii. Electron paramagnetic resonance studies (7) showed that CeO containing 1% Cu exhibited surface segregation with an enrichment factor of 25, which supports the assumption of a rather low solubility in the CeO structure. In the related Cu-Zrsystem (8) no ternary compound and a very small solid solubility of copper in the cubic ZrO modification have been reported.…”