Investigation of binary and ternary Cu-V-Ce oxides by X-ray diffraction, thermal analysis, and electron paramagnetic resonance

The influence of vanadyl and copper precursors, impregnated on ceria, was e valuated by X-ray diffraction (XRD), thermal analysis (TG-DSC), and electro n paramagnetic resonance (EPR) of binary and ternary oxides. The formation of a copper oxalate phase from copper nitrate and vanadyl oxalate was revea led during the preparation of the ternary oxide (1Cu1V10Ce). Three types of Cu(II) species in the dried copper containing solids were evidenced: (i) C u(II) cations with an elongated octahedral symmetry attributed to the coppe r nitrate precursor, (ii) a copper oxalate phase with a compressed octahedr al symmetry and (iii) well-dispersed CU2+ ions on the ceria surface, locate d in a tetragonally distorted octahedral crystal field and surrounded by le ss than six ligands. The dispersion of the copper(II) cations over the ceri a support surface was facilitated by the copper nitrate precursor. The EPR intensities clearly show that the increase of the oxalate precursor content induces a large fraction of copper that escapes detection by EPR and could be consistent with the presence of large Cu(II) agglomerates. After the ca lcination of the solids at 300 degreesC, only one copper species was eviden ced and assigned to CU2+ ions located in octahedral sites tetragonally dist orted. The distortion was more pronounced in the presence of vanadium than in the case of the copper cerium oxide samples. The high dispersion of the copper(II) cations over the ceria support surface, owing to the copper nitr ate precursor, was confirmed even after its thermal decomposition.