| Abstract
| - The structure and chemical environment of Cu in Cu/CeO2 catalysts synthesized by thesolution combustion method have been investigated by X-ray diffraction (XRD), transmissionelectron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, X-rayphotoelectron spectroscopy (XPS), cyclic voltammetry (CV), and extended X-ray fine structure(EXAFS) spectroscopy. High-resolution XRD studies of 3 and 5 atom % Cu/CeO2 do not showCuO lines in their respective patterns. The structure could be refined for the compositionCe1-xCuxO2-δ (x = 0.03 and 0.05; δ ∼ 0.13 and 0.16) in the fluorite structure with 5−8%oxide ion vacancy. High-resolution TEM did not show CuO particles in 5 atom % Cu/CeO2.EPR as well as XPS studies confirm the presence of Cu2+ species in the CeO2 matrix. Redoxpotentials of Cu species in the CeO2 matrix are lower than those in CuO. EXAFSinvestigations of these catalysts show an average coordination number of 3 around the Cu2+ion in the first shell at a distance of 1.96 Å, indicating the O2- ion vacancy around the Cu2+ion. The Cu−O bond length also decreases compared to that in CuO. The second and thirdshell around the Cu2+ ion in the catalysts are attributed to −Cu2+−O2-−Cu2+− at 2.92 Åand −Cu2+−O2-−Ce4+− at the distance of 3.15 Å, respectively. The present results providedirect evidence for the formation of a Ce1-xCuxO2-δ type of solid solution phase having −□−Cu2+−O−Ce4+− kind of linkages.
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