Physico-chemical study of impregnated Cu and V species on CeO₂ support by thermal analysis, XRD, EPR, ⁵¹V-MAS-NMR and XPS

CuVCe oxides were prepared by impregnation of copper and/or vanadium precursors on ceria support. The solids freshly prepared were calcined under air between 400 and 700 °C. Physico-chemical properties of these oxides were then studied using different techniques: Thermal Analysis (DSC/TG), X Ray Diffraction (XRD), Electron Paramagnetic Resonance (EPR), ⁵¹V Magic Angle Spinning Nuclear Magnetic Resonance (⁵¹V-MAS-NMR) and X-Ray Photoelectron Spectroscopy (XPS). X-ray diffraction and thermal analysis revealed cerium orthovanadate phase formation during the calcination of the 1Cu1V10Ce solid. This CeVO₄ phase is not observed for the 10Cu1V10Ce sample. The EPR study revealed two well-resolved copper signals: the first corresponds to isolated Cu²⁺ species and the second to Cu²⁺ dimers. The ⁵¹V-MAS-NMR confirmed the presence of CeVO₄ phase for 1Cu1V10Ce sample and revealed polymeric V–O–V chains in interaction with a copper ceria matrix for 10Cu1V10Ce sample. Finally, the XPS study indicated high vanadium content on the solid surface. This phenomenon is enhanced by the copper content in the solid and could explain the absence of the CeVO₄ phase in 10Cu1V10Ce sample. Thus the ceria orthovanadate phase formation is inhibited by the presence of a high copper content in the solid.