Transition-metal ion dimers formed in CeO₂: an EPR study

Abstract

MeCeO oxides (Me = Cu2+, Mn2+, V4+, Mo5+), with an atomic ratio Me/Ce = 0.1, have been prepared by impregnation of ceria (CeO,) with the corresponding Me salt. Subsequently, the solids were oxidized or reduced at given temperatures. An EPR study evidenced the presence of dimers in the solids. A fine structure was obtained for CuCeO and MoCeO oxides. The signal at half magnetic field intensity (Am, = f2), characteristic of dimers, was present in all the MeCeO oxides with a hyperfine structure for Cu2+, Mn2+ or V4+ ions. From the relative intensity of the half-field and the normal-field signals characterizing the dimer spectrum, the distance between the Me ions has been calculated. For CuCeO and MoCeO oxides, monomer ions have been evidenced as precursors of the dimers. The dimer spectrum of Mo5+ ions has been observed only at 77 K and not at room temperature. In all cases, the dimers are located in oxygen vacancies near Ce3+ ions, present in the solid before the introduction of transition-metal ions.

Decoupling the Impacts of Engineering Defects and Band Gap Alignment Mechanism on the Catalytic Performance of Holey 2D CeO2−x‐Based Heterojunctions

“…Since surfaces have higher energies than the bulk, [ 56 ] the g factors have been differentiated between surface and bulk phenomena. Consequently, although g factor for Mo 5+ has been identified, [ 57 ] this can be assigned to the surface since it is not present in the bulk, as shown in Figure 3f. Similarly, there is no g factor for Mo 6+ because this valence does not bond with CeO 2− x .…”

EPR study of nanocrystalline CeO2 exhibiting ferromagnetism at room temperature

“…The EPR detection of Ce 3+ ions in CeO 2 is discussed in many publications and relates mainly to the line with g ∼ 1.96, that is observed at room and up to very high temperatures, which is not typical for rare‐earth ions except S‐state ions. In addition g ∼ 1.96 is rather close to the g value of cubic site position of Ce 3+ in CaF 2 that can be equal to 2 or 3.1 .…”

Morphology Modulated Photocatalytic Activity of CeO2 Nanostructures for Selective Oxidation of Biobased Alpha‐Pinene to Oxygenates

“…The EPR signal of the CeO 2 nanostructures with different morphologies are presented in Figure 7. The Ce‐NPs exhibited a large O 2 − signal attributed to the available electrons arising from Ce 3+ ions in lattice positions capable of being transferred to O 2 molecules and O 2 − species are located on surface Ce 4+ ions with both oxygen equidistant from the surface [38] . Ce‐NPs are enclosed by the (111) and (100) crystal planes which are oxygen‐terminated surfaces and could be responsible for the large O 2 EPR signal.…”

“…The Ce-NPs exhibited a large O 2 À signal attributed to the available electrons arising from Ce 3 + ions in lattice positions capable of being transferred to O 2 molecules and O 2 À species are located on surface Ce 4 + ions with both oxygen equidistant from the surface. [38] Ce-NPs are enclosed by the (111) and (100) crystal planes which are oxygen-terminated surfaces and could be responsible for the large O 2 EPR signal. As the morphology changes to Ce-NCs, the O 2 signal decreased significantly compared to that of Ce-NPs, while the Ce 3 + EPR signal increased slightly.…”