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

Ceria in automotive exhaust catalysts: I. Oxygen storage

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Use of CeO2-based oxides in the three-way catalysis

Automotive catalytic converters: current status and some perspectives

The effects of SO2 on the oxidation of hydrocarbons and carbon monoxide over Ptγ-Al2O3 catalysts

Metal-support interaction in automotive exhaust catalysts: Rh-washcoat interaction

Surface interaction in the MoO3γ-Al2O3 system

Chemisorption of CO on a 0.92 wt. % Rh/γ‐Al2O3 catalyst gave three species of adsorbed CO molecules: Species RhCO, at about 2000 cm−1; species Rh(CO)2, showing a doublet with peak frequencies at 2100 and 2030 cm−1; and a bridged species Rh2CO, leading to a very broad band peaked between 1850 and 1900 cm−1. The thermostability of these adsorbed species is in the sequence Rh2CO≳RhCO≳Rh(CO)2. Only the doublet band of Rh(CO)2 and the very broad band of the bridged species Rh2CO were found on well dispersed Rh metal in its δ phase. The band contours of the RhCO and Rh(CO)2 species were Fourier transformed into the time domain. The result showed that the configuration RhCO was spread over an approximately four times wider distribution of adsorption sites (surface–adsorbed CO interactions) than that of the Rh(CO)2 species. Furthermore, it was shown that the CO molecules adsorbed as RhCO species are ’’floppy,’’ undergoing some type of fast (probably librational) motion with a characteristic time of 0.1×10−12 sec. On the contrary, the CO molecules adsorbed as RH(CO)2 obey a slow modulation regime, with a characteristic time of about 3×10−12 sec. It is pointed out that this greatly different behavior may be of significance with regard to the selectivity and activity of the different catalytic sites as well as to the directional properties of the metal–carbon bond orbitals.

H.C. Yao

Papers

Ceria in automotive exhaust catalysts: I. Oxygen storage

The effects of SO2 on the oxidation of hydrocarbons and carbon monoxide over Ptγ-Al2O3 catalysts

Metal-support interaction in automotive exhaust catalysts: Rh-washcoat interaction

Surface interaction in the MoO3γ-Al2O3 system

Infrared spectra of chemisorbed CO on Rh/γ–Al2O3: Site distributions and molecular mobility