Influence of the Ce–F interaction on cerium photoelectron spectra in CeO F layers

Anion-mediated electronic effects in reducible oxides: Tuning the valence band of ceria via fluorine doping

“…The most obvious electronic effect of this substitution is the addition to the system of one electron per fluoride ion; the excess electron localizes in a 4f orbital of a single Ce ion, reducing the nominal oxidation state of the ion from 4+ to 3+. 19,22,23 As we have shown previously, the Ce 3+ ion associated with an F − substituent is not spectroscopically identical to that in pure ceria, as is directly evident from Ce 3d core-level photoemission spectra, where both the ratio and position of the final state components differ. 22 A careful deconvolution of the Ce 3d spectra can isolate the Ce 3+ -F interaction components and utilize the difference for the determination of the extent of fluorination of the sample.…”

“…19,22,23 As we have shown previously, the Ce 3+ ion associated with an F − substituent is not spectroscopically identical to that in pure ceria, as is directly evident from Ce 3d core-level photoemission spectra, where both the ratio and position of the final state components differ. 22 A careful deconvolution of the Ce 3d spectra can isolate the Ce 3+ -F interaction components and utilize the difference for the determination of the extent of fluorination of the sample. The presence of characteristic Ce 3+ -F interaction components in the Ce 3d spectra also implies a distinct screening response to the 3d core hole.…”

“…The Ce-F area is considered as containing Ce 3+ ions only because it is directly derived from the spectrum of CeF 3 . 22 Density functional theory calculations were carried out using the projector augmented wave (PAW) method, 41 as implemented in the Vienna Ab initio Simulation Package (VASP), version 5.3.5. [42][43][44][45] We used the standard Perdew-Burke-Ernzerhof (PBE) potentials distributed with this version of VASP, which incorporate the [Xe]4d electrons of Ce atoms and the 1s electrons of O and F atoms into the cores, with a plane-wave cutoff energy of 400 eV, and a 4 × 4 × 1, Γ centred k-point mesh which was generated according to the Monkhorst-Pack scheme.…”

“…This suggestion is supported by the results of theoretical calculations, 19 as well as by the observation that exposing CeO 2 to F 2 gas above 130 ○ C leads to fluorine incorporation without any change to the cubic structure, up to the conversion to the hexagonal CeF 3 phase around 270 ○ C. 20 Furthermore, it has also been shown that fluorine can be incorporated into ceria on contact with fluorine-containing materials, such as Nafion® or CaF 2 . 9,21,22 Even commercially available ceria single crystals have been found to be contaminated with fluorine, although the origin of the contamination is unclear. 11 Importantly, experiments on the contaminated single crystals reveal that fluorine tends to accumulate close to the surface, with a gradient decreasing into the bulk.…”

HKUST-1-Supported Cerium Catalysts for CO Oxidation

“…Normally, the existence of Ce 3+ and Ce 4+ is evidenced by doublets that are bound together, and their splitting is at around 18.4 eV. The Ce 3+ presence is also shown by three singlets [37]. In the presented case, the peaks corresponding to Ce 3+ predominate, whereas only two doublets for Ce 4+ are observed.…”