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 open literature concerning chemical and mechanistic aspects of the selective catalytic reduction of NO by ammonia (SCR process) on metal oxide catalysts is reviewed. Catalytic systems based on supported V2O5 (including the industrial TiO2-supported V2O5–WO3 and/or V2O5–MoO3 catalysts) and catalysts containing Fe2O3, CuO, MnOx and CrOx are considered. The results of spectroscopic studies of the adsorbed surface species, adsorption–desorption measurements, flow reactor and kinetic experiments are analyzed. The proposed reaction mechanisms are described and critically discussed. Points of convergence and of disagreement are underlined.

Chemical and mechanistic aspects of the selective catalytic reduction of NOx by ammonia over oxide catalysts: A review

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

Automotive catalytic converters: current status and some perspectives

Catalytic removal of NO

This review covers the literature through 1991 on nitric oxide catalysis as applied to automobile exhaust systems. Attention is given to the threeway catalyst system which simultaneously promotes the reduction of nitrogen oxides and the oxidation of carbon monoxide and hydrocarbons. These systems have been used on most passenger cars in the United States since 1982. Prior to 1980, emission control catalysts were oxidation catalysts, and reduction in exhaust nitric oxide was achieved using engine modifications (i.e., exhaust gas recirculation). This review focuses on catalytic control of NO, for gasoline-fueled vehicles (not diesels and alternate fuels) and primarily on developments reported since 1982. The term NO, refers to both NO and NOz. The reader is referred to an earlier publication by the author for a general review of automobile catalytic converters [1] and to a review by Egelhoff [2] on the nitric oxide literature through 1980. The recent literature on NO, reduction in lean exhaust is c...

Nitric oxide catalysis in automotive exhaust systems

Catalysts have been widely used to lower the emissions of carbon monoxide (CO) and hydrocarbons (HC) in the exhaust of automobiles in the United States since the introduction of 1975 models in the fall of 1974 These catalysts, contained in so-called catalytic converters in the exhaust system of automobiles, promote the oxidation of CO and HC to CO2 and H2O under net oxidizing conditions (eg A/F > 1461): Until 1978, emission control requirements for nitrogen oxide (NO x ) emissions were met through noncatalyst technology, primarily exhaust gas recirculation (EGR) [1, 2] Starting with some vehicles sold in California in 1977, NO x emissions from gasoline engines have been subject to catalytic control The catalyst here has the additional function to promote the reduction of NO to N2 via reaction of NO with hydrogen or CO Catalyst systems designed to reduce NO x are considerably more complex than the earlier control systems For example, the control system introduced by General Motors on some 1978 model year cars has closed-loop air-fuel ratio control (closed-loop fuel metering system, exhaust gas oxygen sensor, and an electronic control unit) as well as a three-way catalyst which simultaneously promotes the conversion of HC, CO, and NO x [3] Stringent federally mandated emission control requirements of 1 gram per mile (g mi−1) for NO x have led to the further application of three-way catalysts This review will emphasize the state-of-the-art of catalytic control of automobile exhaust emissions since 1978, specifically three-way catalysts A recent review by J Kummer covers part of this period and earlier years [4] Other reviews of this subject are listed in the reference section [5–14]

Kathleen C. Taylor

Papers

Nitric oxide catalysis in automotive exhaust systems

Automobile Catalytic Converters

Selective reduction of nitric oxide over noble metals

Determination of ruthenium surface areas by hydrogen and oxygen chemisorption

Platinum and palladium addition to supported rhodium catalysts for automotive emission control