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

The infrared spectral performance of the N x O y species observed on oxide surfaces [N2O, NO−, NO, (NO)2, N2O3, NO+, NO2 − (different nitro and nitrito anions), NO2, N2O4, N2O5, NO2, and NO3 − (bridged, bidentate, and monodentate nitrates)] is considered. The spectra of related compounds (N2, H-, and C-containing nitrogen oxo species, C─N species, NH x species) are also briefly discussed. Some guidelines for spectral identification of N x O y adspecies are proposed and the transformation of the nitrogen oxo species on catalyst surfaces are regarded.

Identification of Neutral and Charged N x O y Surface Species by IR Spectroscopy

The analysis of various parameters of metal oxides and the search of criteria, which could be used during material selection for solid-state gas sensor applications, were the main objectives of this review. For these purposes the correlation between electro-physical (band gap, electroconductivity, type of conductivity, oxygen diffusion), thermodynamic, surface, electronic, structural properties, catalytic activity and gas-sensing characteristics of metal oxides designed for solid-state sensors was established. It has been discussed the role of metal oxide manufacturability, chemical activity, and parameter's stability in sensing material choice as well.

Metal oxides for solid-state gas sensors: What determines our choice?

Automotive catalytic converters: current status and some perspectives

Importance of the Relationship between Surface Phases and Photocatalytic Activity of TiO2

FT-IR characterization of the surface acidity of different titanium dioxide anatase preparations

The structure and stability of sulfated alumina and titania

The oxidative adsorption of SO 2 on ceria has been studied using gravimetry and IR spectroscopy. SO 2 oxidation gives rise to two main types of sulfates: surface and bulklike species. The former are characterized by IR bands in the 1400-1340 cm −1 range while the latter lead to a very broad band near 1200 cm −1 . Their relative amount depends on the sample surface area and the total sulfate amount formed. The sulfate thermal stability and reducibility are compared to those of sulfate species formed on other oxides. It is also found that oxidation of SO 2 adsorbed species into sulfate can occur without O 2 addition, a concomitant ceria reduction then being evidenced by UV-visible reflectance spectroscopy.

Study of ceria sulfation

This review article deals with the development of sulfur recovery from the Claus process to H2S selective oxidation. Governments are constantly tightening regulations to limit the emission of sulfur compounds into the air. This makes it necessary to constantly enhance the level of sulfur recovery from natural, refinery, or coal gasification geses, and many improvements in the Claus process have been introduced to this end. In this review, emphasis has been put on the mechanism of reactions occurring in most of the sulfur recovery units, reactions between H2S and SO2 or O2 and side reactions such as hydrolysis of COS and CS2 or sulfation of the catalyst.

Odette Saur

Papers

FT-IR characterization of the surface acidity of different titanium dioxide anatase preparations

The structure and stability of sulfated alumina and titania

Study of ceria sulfation

Claus catalysis and H2S selective oxidation

An infrared study of sulfated zirconia