Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

Catalytic Properties of Ceria and CeO2-Containing Materials

Oxygen vacancies in transition metal and rare earth oxides: Current state of understanding and remaining challenges

Magnetic nanoscaled Fe3O4/CeO2 composite was prepared by the impregnation method and characterized as a heterogeneous Fenton-like catalyst for 4-chlorophenol (4-CP) degradation. The catalytic activity was evaluated in view of the effects of various processes, pH value, catalyst addition, hydrogen peroxide (H2O2) concentration, and temperature, and the pseudo-first-order kinetic constant of 0.11 min–1 was obtained for 4-CP degradation at 30 °C and pH 3.0 with 30 mM H2O2, 2.0 g L–1 Fe3O4/CeO2, and 0.78 mM 4-CP. The high utilization efficiency of H2O2, calculated as 79.2%, showed a promising application of the catalyst in the oxidative degradation of organic pollutants. The reusability of Fe3O4/CeO2 composite was also investigated after six successive runs. On the basis of the results of metal leaching, the effects of radical scavengers, intermediates determination, and X-ray photoelectron spectroscopic (XPS) analysis, the dissolution of Fe3O4 facilitated by CeO2 played a significant role, and 4-CP was decom...

Magnetic Nanoscaled Fe3O4/CeO2 Composite as an Efficient Fenton-Like Heterogeneous Catalyst for Degradation of 4-Chlorophenol

Electron spectroscopy of single crystal and polycrystalline cerium oxide surfaces

This article presents an XPS study of Ce 3d emission spectra dominated by atomic multiplet effects in core level spectroscopy of rare earth compounds (Ce oxides). Core level spectroscopy has been used to study the electronic states of Ce 3d5/2 and Ce 3d3/2 levels in Ce4+ and Ce3+ states. The well-resolved components of Ce 3d5/2 and Ce 3d3/2 spin-orbit components, due to various final states (4f0, 4f1, 4f2 configurations), were determined on 3d XPS spectra from commercial powders (CeO2, CePO4).

These results were used to study the 3d spin-orbit component of mixed cerium-titanium oxide.

This compound was prepared by co-melting commercial powders of CeO2 and TiO2 at 1800 K under air using a solar furnace with a flux density of 16 MW.m−2 at the focal point of the parabolic concentrator. The mixed oxide Ce2Ti2O7 was produced and contained Ce(III) species which may be reactive with water to give back the initial metal oxides and generate hydrogen, a valuable product considered as a promising energy carrier in the future in replacement of oil.

The 3d photoemission spectra revealed the presence of mixed components attributed to mainly Ce(III) and Ce(IV) species. Copyright © 2008 John Wiley & Sons, Ltd.

Ce 3d XPS investigation of cerium oxides and mixed cerium oxide (CexTiyOz)

A study of the core-electron X-ray photoelectron (X-p.e.) spectra of the f0 compounds La2O3, LaMO3(M = Fe and Co), CeO2, and BaCeO3 is described. Results on the chelate species [La(tmhd)3] and [Ce(tmhd)4](tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato) are included for comparison. Special precautions have been taken to ensure an optimal degree of surface purity of the samples. Satellite structure has been observed for the 4p, in addition to the 3d and 4d, signals in both the lanthanum(III) and cerium(IV) compounds. These satellites arc discussed in terms of coexcitations of the charge-transfer type, principally O 2p→ metal 4f transitions. In the cerium(IV) oxides the satellites are apparently due to energy-gain (representing ‘ shake-down ’) rather than energy-loss (shake-up) processes.

Satellite structure in the X-ray photoelectron spectra of some binary and mixed oxides of lanthanum and cerium

He(I), He(II) and valence region X-ray photoelectron spectra are reported for the Group VIA hexacarbonyls and are assigned on the basis of published molecular orbital calculations A pronounced increase in intensity of the first photoelectron band is observed on descending the group, and multiplet structure is clearly discernible on this band in the case of W(CO)6

Photoelectron studies of metal carbonyls. Part 2.—The valence region photoelectron spectra of the group VIA hexacarbonyls

Photoelectron spectra excited in the gas phase with He-I radiation are reported for the tetroxides, RuO4 and OsO4, and for the oxychloride species VOCl3, CrO2Cl2 and MoO2Cl2. The X-ray photoelectron spectrum of OsO4 has also been measured. The nature of the metal-oxygen bonding in these molecules, as inferred from the spectrometric data, is discussed.

He-I photoelectron spectra of some d0 transition metal compounds

The results of a study of the reduction of some platinum(IV) compounds during the course of X-ray photoelectron measurements are presented. All the compounds investigated suffered reduction though the observed rates varied considerably. Kinetic analysis of the peak intensities in the X-ray photoelectron spectra reveal that the reduction process is invariably first order, and a model is proposed to account for this finding. Platinum(II) compounds studied were stable to X-radiation.

Radiation damage in some platinum(IV) complexes produced during soft X-ray photoelectron spectroscopic studies

It is shown that the presence of distinct SbIII and SbV atoms in the mixed-valency compound Cs2SbCl6 can be directly demonstrated by X-ray photoelectron spectroscopy. The surface purity of the material can be checked by supplementary studies using argon ion bombardment.

Peter Burroughs

Papers

Satellite structure in the X-ray photoelectron spectra of some binary and mixed oxides of lanthanum and cerium

Photoelectron studies of metal carbonyls. Part 2.—The valence region photoelectron spectra of the group VIA hexacarbonyls

He-I photoelectron spectra of some d0 transition metal compounds

Radiation damage in some platinum(IV) complexes produced during soft X-ray photoelectron spectroscopic studies

A study of the mixed-valency compound Cs2SbCl6 by X-ray photoelectron spectroscopy