Structural Investigation of Combustion Synthesized Cu/CeO2 Catalysts by EXAFS and Other Physical Techniques: Formation of a Ce1-xCuxO2-δ Solid Solution

• DOI: 10.1021/cm0201706
• Publication Date: 2002-09-17T20:41:22Z
• Authors: Parthasarathi Bera; K. R. Priolkar; P. R. Sarode; M. S. Hegde; S. Emura; R. Kumashiro; N. P. Lalla
• Keywords: Solid State & Structural Chemistry Unit; 02 engineering and technology; 540; 0210 nano-technology

The structure and chemical environment of Cu in Cu/CeO2 catalysts synthesized by the solution combustion method have been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, X-ray photoelectron 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 show CuO lines in their respective patterns. The structure could be refined for the composition Ce1-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. Redox potentials of Cu species in the CeO2 matrix are lower than those in CuO. EXAFS investigations of these catalysts show an average coordination number of 3 around the Cu2+ ion in the first shell at a distance of 1.96 A, indi...