| abstract |
Provided are exhaust systems and components suitable for use in conjunction with gasoline engines to treat gaseous emissions such as hydrocarbons, nitrogen oxides, and carbon monoxides. Layered three-way conversion (TWC) catalysts comprise an outer layer whose rhodium is supported by an oxygen storage component, such as a ceria-zirconia composite, and the outer layer is substantially free from alumina as a support. The rhodium-containing layer can be free of all other precious metals, such as platinum and palladium. A lower palladium layer is provided where the palladium is supported by a refractory metal oxide. The lower palladium layer can be free of rhodium and platinum and can contain an oxygen storage component that is the same or different from that in the rhodium-containing layer. Methods of making and using these catalysts are also provided. |