Toward Understanding Automotive Exhaust Conversion Catalysis at the Atomic Level

This review focuses on the reactions and catalysts used for control of emissions of exhaust gases for gasoline-fueled automobiles with emphasis on fundamental understanding of the surface processes. Attention is paid to three-way catalysts, which simultaneously enhance the conversion of CO, hydrocarbons, and nitrogen oxides. The mechanisms of the CO oxidation and nitrogen oxide reactions, the specific differences in behavior of Pt, Pd, and Rh, the effect of alloy formation, and the role of ceria used as additive in three-way catalysts are discussed. Results of surface science studies are compared with results reported for supported catalysts. For CO oxidation, there is excellent agreement between results obtained for single crystal surfaces and supported catalysts. The kinetics of the reactions on pure metals can be understood on the basis of the kinetics parameters obtained from single-crystal studies. For the NO reduction reactions, there is qualitative agreement between results obtained with single-crystal and supported catalysts. The major effects of alloy formation can be understood on the basis of the surface composition.