Evidence for different copper species in precursors of copper–cerium oxide catalysts for hydrogenation reactions. An X-ray diffraction, EPR and X-ray photoelectron spectroscopy study

Conditions for preparing copper–cerium mixed oxides by coprecipitation have been examined. X-Ray diffraction (XRD), electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the oxides calcined at different temperatures up to 1073 K. In all cases, a solid solution is formed by the insertion of Cu2+ ions in substitutional positions in the ceria lattice; this occurs at the coprecipitation step, and is maintained during calcination. Four Cu2+ signals were found by EPR and attributed to monomers, dimers, clusters and small particles of CuO. Taking into account the eventual presence of additional crystallized CuO and the reduction in copper at the surface detected by XPS, a model for these oxides is proposed.