2. Three-Way Catalyst Containing Second-Generation CZHow can we develop a new process to prepare a nearly per-fectly homogeneous solid solution of ceria–zirconia? This wasone of the most important themes for improvement in three-way catalysts in the early 1990s. In addition, the prepared ce-ria–zirconia solid solution should be of a single phase, prefera-bly a cubic phase, rather than a double or mixed phase. Theassumption was that a single phase solid solution would notexperience a large volume change and fragment, and wouldbe retained in the same phase under cycling of oxygen-richand oxygen-lean conditions at high temperature. We also as-sumed that it would be easier to store oxygen in, and releaseoxygen from, the lattice of a cubic phase oxide than from thatof a tetragonal or monoclinic phase oxide.The thermodynamically stable cubic phase of the ceria–zirconia solid solution has already been identified in theZrO 2 –CeO 2 system. 42–44,64–66 The phase diagrams reveal thatzirconia is almost 100% soluble in ceria when a 50/50 mixtureof Ce/Zr is heated to approximately 1600? C in air. These sol-id solutions exhibit a high OSC. 67 However, their specific sur-face area is too low to allow their use as automotive catalystsbecause, as mentioned earlier, a low specific surface area re-stricts the rate of oxygen storage/release.
2. Three-Way Catalyst Containing Second-Generation CZHow can we develop a new process to prepare a nearly per-fectly homogeneous solid solution of ceria–zirconia? This wasone of the most important themes for improvement in three-way catalysts in the early 1990s. In addition, the prepared ce-ria–zirconia solid solution should be of a single phase, prefera-bly a cubic phase, rather than a double or mixed phase. Theassumption was that a single phase solid solution would notexperience a large volume change and fragment, and wouldbe retained in the same phase under cycling of oxygen-richand oxygen-lean conditions at high temperature. We also as-sumed that it would be easier to store oxygen in, and releaseoxygen from, the lattice of a cubic phase oxide than from thatof a tetragonal or monoclinic phase oxide.The thermodynamically stable cubic phase of the ceria–zirconia solid solution has already been identified in theZrO 2 –CeO 2 system. 42–44,64–66 The phase diagrams reveal thatzirconia is almost 100% soluble in ceria when a 50/50 mixtureof Ce/Zr is heated to approximately 1600? C in air. These sol-id solutions exhibit a high OSC. 67 However, their specific sur-face area is too low to allow their use as automotive catalystsbecause, as mentioned earlier, a low specific surface area re-stricts the rate of oxygen storage/release.<br>
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