Improvement of oxygen storage capacity of CeO2-ZrO2 solid solution by heat treatment in reducing atmosphere

The function of oxygen storage capacity (OSC) is very important to improve a performance for an automobile exhaust catalyst. CeO2-ZrO2 solid solution has an excellent OSC, and is available for a catalytic promoter. In this paper, OSC of the CO reduced CeO2-ZrO2 solid solution having various composition loaded with Pt was estimated by thermo gravimeter, and the phases and the crystalline structure of the reduced CeO2-ZrO2 solid solution were studied by X-ray diffraction method. The maximum total OSC-value of the reduced material occurs at the composition of 50 mol% CeO2-50 mol% ZrO2. The maximun value is about 753 mumol O-2/g-solid solution, which is about twice the value (416 mumol O-2/g-solid solution) of the attrition-milled CeO2-ZrO2 solid solution, and 5 times higher than that (150 mumol O-2/g-solid solution) of the material synthesized by conventional impregnation. The reduced material consists of Ce2Zr2O8 and CeO2 solid solution in the composition range from 30 to 50 mol% ZrO2. The reduced material consists of the mixture. Ce2Zr2O8 and ZrO2 in the composition range from 50 mol% ZrO2 to 100 mol% ZrO2. The presence of Zr4+ near Ce4+ makes the expansion easier enhancing further valence change, because Zr4+ is very small in volume. Regular distribution of Cc and Zr ions would make it possible to place Zr4+ in the nearest position to Cc ion. This would be the reason why the partial OSC of Ce2Zr2O8 is much higher than the complete solid solution.