Development of Innovative Three-Way Catalysts Containing Ceria–Zirconia Solid Solutions with High Oxygen Storage/Release Capacity

Innovative three-way catalysts containing ceria-zirconia solid solutions (CZ) with a ZrO 2 content ranging from 5 to 75 mol% were developed. Such catalysts have very high oxygen storage/release capacity (OSC). The OSC of'catalysts containing first-generation CZ was found to increase linearly with the amount of zirconia dissolved in the solid solution in the 0-20 mol%( ZrO 2 range. The thermal stability of the catalyst containing first-generation CZ was higher than that containing ceria. Second-generation CZ with greater OSC than first-generation CZ was developed by a homogeneous coprecipitation process, followed by heat-treatment below 1000 °C, enabling dissolution of zirconia into ceria up to 75 mol% zirconia as estimated by XRD. Third-generation CZ, CZ-doped alumina (ACZ), was developed by homogeneous coprecipitation based on the "diffusion barrier concept". The OSC of ACZ was 23 times larger than that of pure ceria. The NOx emission over the catalyst containing ACZ was reduced by about a factor of five compared with that containing pure ceria. Toyota Motor Corp. has put three-way catalysts containing first-, second-, and third-generation CZ into practical use globally.