Thermal stability of oxygen storage properties in a mixed CeO₂-ZrO₂ system

CeO₂ and CeO₂/ZrO₂ supports were prepared by two low temperature (500°C) routes: calcination of hydroxide precipitates and firing mixtures of acetates. The supports were loaded with 0.5% Pt and characterized both fresh and aged (at 800 and 1000°C). X-ray diffraction analyses show that a CeO₂/ZrO₂ solid solution is formed in the samples prepared by precipitation of the hydroxides and calcination at 500°C. To our knowledge this is the lowest temperature chemical route (not including high energy ball milling) to CeO₂/ZrO₂ solid solutions yet reported. Samples prepared by firing the acetate mixtures had almost exclusively CeO₂ and ZrO₂ in separated phases. Oxygen storage measurements showed that the addition of zirconia increased the oxygen storage capacities (on a per gram of catalyst basis) over ceria alone for both preparation methods. In the phase separated materials the amount of reversibly stored oxygen was 1.7-2.5 times more per gram catalyst than that of ceria only. The beneficial effects of zirconia are most pronounced in the solid solutions which had oxygen storage 3-5 times higher than ceria. When the Zr concentration is optimized, the solid solution materials aged at 1000°C showed higher oxygen storage than fresh CeO₂. For both preparation methods, the optimal (per gram catalyst) Zr concentration was found to be 25 mol% Zr for samples aged at 1000°C, however, the performance of the solid solution materials was somewhat insensitive to Zr loading between 15 and 50 mol% Zr.