Investigation of Binary and Ternary Cu−V−Ce Oxides by X-ray Diffraction, Thermal Analysis, and Electron Paramagnetic Resonance

Abstract

The influence of vanadyl and copper precursors, impregnated on ceria, was evaluated by X-ray diffraction (XRD), thermal analysis (TG-DSC), and electron paramagnetic resonance (EPR) of binary and ternary oxides. The formation of a copper oxalate phase from copper nitrate and vanadyl oxalate was revealed during the preparation of the ternary oxide (1Cu1V10Ce). Three types of Cu(II) species in the dried copper containing solids were evidenced: (i) Cu(II) cations with an elongated octahedral symmetry attributed to the copper nitrate precursor, (ii) a copper oxalate phase with a compressed octahedral symmetry and (iii) well-dispersed Cu2+ ions on the ceria surface, located in a tetragonally distorted octahedral crystal field and surrounded by less than six ligands. The dispersion of the copper(II) cations over the ceria 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 calcination of the solids at 300 °C, only one copper species was evidenced and assigned to Cu2+ ions located in octahedral sites tetragonally distorted. 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 nitrate precursor, was confirmed even after its thermal decomposition.

Nature of the vanadia?ceria interface in V5+/CeO2 catalysts and its relevance for the solid-state reaction toward CeVO4 and catalytic properties

“…Similar signals have previously been detected in V 2 O 5 /CeO 2 materials treated at temperatures lower than those required for the formation of CeVO 4 [21][22][23]. In addition, the samples that contain CeO 2 typically show a sharp axial signal with g ⊥ = 1.965 and g = 1.940.…”

“…In addition, the samples that contain CeO 2 typically show a sharp axial signal with g ⊥ = 1.965 and g = 1.940. These features have been previously related with either quasi-free electrons or with Ce 3+ cations located in distorted sites of the fluorite lattice [21][22][23][24]. A recent study has assigned this signal to Cr 3+ impurities of CeO 2 at the ppb level [25].…”

“…The EPR spectra of the VCe samples calcined and outgassed at 300 • C present a series of very weak lines near g = 1.94 and A = 13 × 10 −3 cm −1 , which can be attributed to the hyperfine structure of residual isolated VO 2+ groups ( 51 V nuclear spin I = 7/2; natural abundance 99.75%) [20][21][22][23]. Similar signals have previously been detected in V 2 O 5 /CeO 2 materials treated at temperatures lower than those required for the formation of CeVO 4 [21][22][23].…”

Structural and catalytic investigation of vanadia supported on ceria promoted with high surface area rice husk silica

“…Signals observed for CeO 2 and g values calculated (f 1 ions: g e > g ⊥ > g || ) are attributed to the presence of two different types of Ce 3+ ions. Signal A is due to Ce 3+ species with removable ligands and signal B is with Ce 3+ ions stabilized by some lattice defects located in distorted sites of the fluorite structure [35]. Silica promotion reduces the intensity of Ce 3+ species and only signal B is observed suggesting some interaction between ceria surface and silica.…”

EPR, ENDOR, and HYSCORE Study of the Structure and the Stability of Vanadyl−Porphyrin Complexes Encapsulated in Silica: Potential Paramagnetic Biomarkers for the Origin of Life

“…All of the data are taken from the literature 35,[61][62][63][64][65][66][67][68][69][70][71][72][73][74][75]. The gray area corresponds to V(IV) in octahedral sites of the oxides.…”