Improvement of Oxygen Storage Capacity of CeO2-ZrO2 Solid Solution by Heat Treatment in Reducing Atmosphere.

Abstract

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 50mol% CeO2-50mol% ZrO2. The maximun value is about 753μmol O2/g-solid solution, which is about twice the value (416μmol O2/g-solid solution) of the attritionmilled CeO2-ZrO2 solid solution, and 5 times higher than that (150μmol O2/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 50mol% ZrO2. The reduced material consists of the mixture, Ce2Zr2O8 and ZrO2 in the composition range from 50mol% ZrO2 to 100mol% 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 Ce and Zr ions would make it possible to place Zr4+ in the nearest position to Ce ion. This would be the reason why the partial OSC of Ce2Zr2O8 is much higher than the complete solid solution.