Effect of Crystallinity on the Photoreduction of Cerium Oxide:  A Study of CeO₂ and Ce/Al₂O₃ Catalysts

Abstract

The effect of crystallinity on the photoreduction of cerium oxide (Ce4+ to Ce3+) during X-ray photoelectron spectroscopy (XPS) analysis of CeO2 and Ce/Al2O3 catalysts has been determined. Cerium oxide samples were prepared by calcining cerium(IV) methoxyethoxide in air at different temperatures. The structure of the resulting metal oxides was determined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The oxide obtained from calcination at 200 °C consisted primarily of amorphous cerium oxide, while the material produced at 750 °C contained large CeO2 crystallites. XPS Ce 3d spectra obtained for the samples showed that the amorphous cerium oxide sample was reduced more extensively than the crystalline material during XPS analysis. Ce/Al2O3 catalysts (5.1 wt % CeO2) were prepared by incipient wetness impregnation using ammonium cerium(IV) nitrate and cerium(IV) methoxyethoxide precursors. XRD and XPS analyses of the Ce/Al2O3 catalyst derived from the nitrate precursor (designated CeN) indicated that most of the cerium was present as poorly dispersed CeO2 crystallites. The catalyst prepared using the alkoxide precursor (designated CeA) also contained poorly dispersed cerium oxide; however, XRD data suggested that very little of the cerium oxide phase was crystalline. The XPS Ce 3d spectrum obtained for the CeN catalyst was typical of Ce(IV) oxide while the spectrum collected for the CeA catalyst was similar to a Ce(III) compound. These results have been attributed to enhanced photoreduction of the amorphous cerium oxide present in the CeA catalyst.

Characterization and activity of visible-light-driven TiO2 photocatalyst codoped with nitrogen and cerium

“…According to the diffraction angle of Peak B, it was confirmed to be relevant to CeO 2 [16][17][18][19][20], implying a significant portion of Ce 3+ ions were oxidized into Ce 4+ during heating treatment. The average crystal size can be estimated by the Scherrer's formula, D=(Kl)/(b cos y), from the integral width of XRD peaks, where K is the Scherrer constant (K=0.9), l is the wavelength of XRD (l=0.15418 nm), and b is the full-width at half-maximum (FWHM) of the 1 0 1 plane (in radians) [23]. The crystalline structure and crystal size of the prepared TiO 2 were summarized in …”

“…4d. Since Burroughs [27] made his first attempt, much effort has been made to interpret these peaks qualitatively or quantitatively [16,23,[28][29][30][31][32]. It was reported that the Ce 3d spectra could be assigned to two sets of spin-orbital multiplets, i.e., 3d 5/2 and 3d 3/2 [16,32] which are denoted as v and u in Fig.…”

Preparation, characterization of a ceria loaded carbon nanotubes nanocomposites photocatalyst and degradation of azo dye Acid Orange 7

“…5b, the peaks at 882, 898, 900.5, 907.3 and 916.5 eV can be attributed to Ce (IV), and the peaks at 882 and 898eV correspond to the Ce (IV) 3d 9 4f 1 and 3d 9 4f 0 fi nal state, respectively. The spin-orbit splitting appears at 900.5, 907.3 and 916.5 eV, which corresponds to 3 u peaks of Ce (3d) 3/2 , indicating that the Ce species in the nanocomposites photocatalyst has a IV valence and exists as CeO 2 (Mei et al 2010, Park et al 1996, Zhang et al 2010. In addition, the O 1s spectrum of the prepared CeO 2 /CNTs is shown in Fig.…”

Separation technology meets green chemistry: development of magnetically recoverable catalyst supports containing silica, ceria, and titania

“…The peak at 461.3 eV is related to the X-ray emission source. The deposition of CeO 2 and TiO 2 was performed using ammonium cerium(IV) nitrate and titanium(IV) isopropoxide, and the presence of Ce 3+ and Ti 3+ is an consequence of the long time X-ray irradiation [32].…”