The Study of Nanocrystalline Cerium Oxide by X-Ray Absorption Spectroscopy

Valence of Highly Dispersed Cerium Oxide Species on Silica Quantitatively Estimated by Ce L<SUB>III</SUB>-edge XANES

“…10,11) During the fitting analysis of CeO 2 spectrum, the shoulder can not be discarded and it is treated as Ce(III) in this work because it was the same energy position as that of Ce(III). It can be considered that CeO 2 is an insulating mixed valence or interatomic intermediate-valence system having a mixture of multielectrons configurations 4f 0 and 4f 1 in the ground state.…”

“…Ce L III -edge XANES spectroscopy has been proposed as a useful method for the quantitative determination of the ratio of Ce(III) and Ce(IV), since both species exhibit each distinguishable absorption peaks. [10][11][12][13][14][15][16][17][18][19][20][21][22] In the present study, a series of SiO 2 -CeO 2 samples were prepared by impregnation method followed by calcination in air and studied by Ce L IIIedge XANES through a curve fitting analysis in order to know the ratio of Ce(III) and Ce(IV) and assignment of the UV absorption band for these species on silica.…”

Techniques for the Study of the Electronic Properties

“…A general feature shared by all nanostructured oxide materials with size typically below 10-15 nm is that they display broader CRs with respect to well-crystallized references. 19,21,24,25,26,31,33,39 This can be observed in the inset of Figure 6.1; the derivative spectra give evidence of a larger overlap between CRs. The reason for this can be understood in terms of the f-rule.…”

Techniques for the Study of the Structural Properties

“…Inclusion of the third cumulant would mainly influence coordination distance while the fourth would influence coordination number and/or (second order) Debye-Waller factor. A point to stress is that, as mentioned throughout the text, nanocrystalline phases prepared by chemical methods are commonly accompaigned by amorphous ones 43,46 and different techniques may in fact be selective to one of them (XRD) while others (as XAFS) inform over the whole system. Although EXAFS studies of dispersed surface species are not the main target of this review, it can be mentioned here that revisions of related papers can be found in refs.…”

“…The presence of surface hydroxyl-coordinated centers has been also mentioned in ZrO 2 but detected by using other techniques 42 . The case of cerium-containing nanostructured oxides is still under study due the fact that the series of samples with increasing size are obtained by calcining at progressively higher temperatures solids from Ce(III) precursors and this influences the presence and concentration of two oxidation states Ce(III)/Ce(IV) in materials with small particle size 43,44 .…”