Fig. 1. Raman spectra of ceria with different particle sizes, showing 464 cm-1 peak shift to lower energy and its asymmetric broadening with decreasing particle size. Adapted with permission from Ref. [32]. Copyright 2002 AIP Publishing.

Fig. 2. UV-Vis absorption spectrum (a) and UV and visible Raman spectra (b) of a ceria sample annealed at 1000 °C for 5 h. Adapted with permission from Ref. [40]. Copyright 2009 American Chemical Society.

Fig. 3. (a) A typical XAS spectrum at the Ce LIII edge for a powder sample of CeO2; (b) The expanded XANES range of the absorption spectrum of CeO2; (c) The Fourier transform magnitude of the data (black curve) and theoretical fit (dotted red curve) for the first coordination shell of cerium of the CeO2 EXAFS data. Adapted from Ref. [20]. Copyright 2020 Royal Chemical Society.

Fig. 4. Evolution with temperature of the concentration fraction of Ce3+ present within the sample during exposure to hydrogen. Results were obtained from linear combination fitting performed on the time-resolved XAS measurements. Ce3+ concentration fraction during the heating and cooling phases plotted in black and red, respectively. Reprinted from Ref. [61]. Copyright 2019 American Chemical Society.

Fig. 5. IR spectra in the OH region for a ceria sample treated three times under H2 (13 kPa) for 0.5 h at 573 (a), 623 (b), 673 (c) and 773 K (d). Reprinted with permission from Ref. [68]. Copyright 1996 Royal Society of Chemistry.

Fig. 6. Infrared reflection absorption spectra of 1 ML CO adsorption on oxidized and reduced single crystal ceria(110) and (111) surfaces at around 80 K. Reprinted with permission from Ref. [78]. Copyright 2017 John Wiley and Sons.

Fig. 7. (a) Deconvolution of the Ce 3d core level XPS spectrum (923.1-876.0 eV of ~18 L) after subtracting the Shirley background where the green lines correspond to the Gaussian-Lorentzian peaks; (b) change in the intensity ratio of Ce3+/Ce4+ with increasing the exposure of atomic hydrogen, where the line is for eye-guide only. Adapted with permission from Ref. [89]. Copyright 2014 Elsevier B.V.

Fig. 8. INS spectra of CeO2 collected at 10 K after H2-treated at 533 K (a), 623 K (b), 673 K (c), 393 K (d) vacuum after (c); (e) exposure to O2 at RT and then 393 K vacuum after (d). All spectra are difference spectra using the spectrum of CeO2 after 673 K O2-treatment as background. Adapted from Ref. [63]. Copyright 2017 American Chemical Society.

Scheme 1. Schematic description of H2 interaction with CeO2 with the formation of surface OH and Ce-H. Adapted from Ref. [63]. Copyright 2017 American Chemical Society.

Scheme 2. A stepwise mechanism of oxygen reduction on ceria, i.e., the reoxidation of reduced ceria by O2.

Fig. 9. (a) Raman spectra of O2 adsorption on oxidized CeO2. The CeO2 pellet was heated under 10% O2 in He flow from 93 to 673 K at a rate of 5 K min-1, and the spectra were collected at each of the specified temperatures. Adapted with permission from Ref. [102]. Copyright 2006 John Wiley and Sons; (b) Raman spectra from O2 adsorption at different temperatures on 673 K reduced ceria rods, cubes and octahedra. Adapted from Ref. [38]. Copyright 2010 American Chemical Society.

Fig. 10. IR spectra of adsorbed dioxygen on CeO2 at 298 K after admission of 16O2 (18O2) for 1 min (a), and pre-reduced CeO2-x (673 K in H2) at 210 K (b); (c) pre-reduced CeO2-x (673 K in H2) in presence of 16O2 at elevated temperature from 200 to 473K with a heating rate of 2.5 K/min. Adapted from Ref. [106]. Copyright 1989 American Chemical Society.

Fig. 11. (a) 17O NMR (14.1 T) spectra of 17O enriched CeO2 nanoparticles mixed with the TEKPol radical in TCE, with and without microwave irradiation, using a presaturated Hahn echo experiment. The spectra were recorded at 95 K. The OFF spectrum was recorded at 12.5 kHz MAS, whereas the ON spectrum was recorded at 10 kHz in order to separate the spinning sidebands from the signal arising from the first layer. Spinning sidebands are labelled according to the layer of the signal from which they arise. (b) The indirect DNP 17O NMR (14.1 T) spectra of 17O enriched CeO2 nanoparticles impregnated with TEKPol in TCE, recorded at 12.5 kHz MAS with a recycle delay of 4.3 s, 320 scans and variable contact times for the 1H-17O cross polarisation. The 17O magnetisation was pre-saturated to avoid the direct DNP signal. Adapted from with permission Ref. [112]. Copyright 2017 Royal Society of Chemistry.

Fig. 12. EPR spectra of CeO2 sample (recorded after 30 min at 77 K) under increasing PO2. Reprinted with permission from Ref. [115]. Copyright 2013 Springer Publishing.

Fig. 13. IR spectra from pyridine adsorbed on ceria nanoshapes that were calcined at 673 K. Spectra were obtained after pyridine adsorption at room temperature followed by desorption at 423 K. Reprinted from Ref. [137]. Copyright 2015 American Chemical Society.

Fig. 14. TMP-31P NMR spectra of CeO2 with different morphologies. Reprinted from Ref. [144]. Copyright 2020 American Chemical Society.

Scheme 3. Proposed structure of typical adsorbed carbonate species on metal oxides.

Fig. 15. Proposed assignment of IR bands to different (hydrogen)carbonate species on ceria. Ce (yellow), O (red), C (dark gray), H (white). (a) hydrogen carbonate; (b) monodentate carbonate; (C) bidentate-type carbonate; and (d) tridentate carbonate. Adapted from Ref. [162]. Copyright 2011 American Chemical Society.

Scheme 4. Possible adsorption modes of CHCl3 species on an oxide surface. M stands for metal cation.

Fig. 16. IR spectra from CHCl3 adsorbed at room temperature on dehydrated ceria with three different morphologies. Adapted from Ref. [137]. Copyright 2011 American Chemical Society.