Ceria and Its Defect Structure: New Insights from a Combined Spectroscopic Approach

Abstract

Ceria is an interesting component for a variety of catalytic and fuel cell applications. In the study described here, ten different commercial ceria samples as well as synthesized ceria samples were investigated in detail regarding their (defect) structure and characteristic properties using XRD, N2 adsorption–desorption, and optical spectroscopy (Raman, DRIFTS, UV–vis). The investigations revealed correlations of surface defect features (Raman, DRIFTS) as well as those of bulk defects (Raman, UV–vis). The Raman feature at around 250 cm–1 was demonstrated to be related to surface defects rather than a 2TA vibration as described in the literature. A correlation between UV–vis band gap values and the presence of Raman bulk defects was established based on the observed decrease of the band gap energy with increasing number of defects. Detailed Raman analysis revealed that the frequently mentioned linear equation for the determination of the crystal size from the half-width of the F 2g Raman feature is erroneous, since the F 2g half-width depends on ceria bulk defects. Apart from these universal observations, differences in the properties depending on synthesis conditions were observed. In particular, it is shown that the type and quantity of ceria defects are influenced not only by crystal size but also by the preparation method.

Outstanding Methane Oxidation Performance of Palladium‐Embedded Ceria Catalysts Prepared by a One‐Step Dry Ball‐Milling Method

“…Furthermore,t he better Pd distribution of PdCeM is maintained after stability tests.T his is also confirmed by comparing the Raman spectra obtained by mapping 144 mm 2 of the surface of PdCeM and PdCeIW (Supporting Information, Figure S13). Ab road Raman signal covering the region between 550-600 cm À1 is also detected in PdCeM;peaks in this region are attributed to surface defects in ceria [15] that might include those generated by close interaction and inclusion of Pd into CeO 2 lattice. Collecting several spectra, it is clearly seen that the intensity ratio between the two signals is rather constant for PdCeM (Supporting Information, Figure S13), indicating am ore homogeneous spreading of Pd over CeO 2 , as it can be expected from its distribution within the surface layer.…”

Nanostructured Ceria-Based Materials: Effect of the Hydrothermal Synthesis Conditions on the Structural Properties and Catalytic Activity

“…fluorite lattice [25], and three weaker Raman peaks at 261 cm −1 , 598 cm −1 , and 1165 cm −1 . The first and the third ones can be assigned to the higher order modes of ceria, namely to the second order transverse acoustic mode, that is, 2TA [24] (although a different assignment to a Ce-OH related vibration has recently been suggested [26]), and to the second overtone of the longitudinal optical band (2LO) [26]. The Raman peak at 598 cm −1 is instead a disorder induced mode arising from Frenkel-type anion defects, consisting of a vacancy, originated by the motion of an O 2− ion to an interstitial octahedral site [17,23].…”

Cerium(III) Nitrate Derived CeO2 Support Stabilising PtOx Active Species for Room Temperature CO Oxidation

“…In the Raman spectrum of the “PtO x /CeO 2 ‐220” catalyst taken after CO+O 2 reaction, two new signals at 660 and 570 cm −1 are registered in comparison with the spectrum of the “CeO 2 ‐220” support (Figure S7A). According to the previously reported data these bands correspond to the Pt−O and the bridging Pt−O−Ce vibrations of highly dispersed PtO x entities bonded with the ceria surface . It should be noted that, in the spectrum of the as‐prepared “PtO x /CeO 2 ‐220” catalyst the 570 cm −1 peak is absent and in the range of Pt−O vibrations a diffuse peak is observed.…”

“…The scalable methods of preparation of CeO 2 supports vary from the cerium salts solution hydrolysis to the flame spray pyrolysis . Among these methods the simplest and most straightforward one is the thermal decomposition of cerium salts, such as Ce(NO 3 ) 3 ⋅ 6H 2 O, Ce 2 (C 2 O 4 ) 3 , (NH 4 ) 2 [Ce(NO 3 ) 6 ], and Ce 2 (CO 3 ) 2 O ⋅ H 2 O . Despite its apparent simplicity, a variety of parameters including composition of the precursor, temperature, ramping rate, gaseous atmosphere, and precursor pre‐treatment, can be used to control the key characteristics of the resulting ceria materials.…”