THERMAL-STABILITY OF OXYGEN STORAGE PROPERTIES IN A MIXED CEO2-ZRO2 SYSTEM

CeO2 and CeO2/ZrO2 supports were prepared by two low temperature (500 degrees C) routes: calcination of hydroxide precipitates and firing mi xtures of acetates. The supports were loaded with 0.5% Pt and characte rized both fresh and aged (at 800 and 1000 degrees C). X-ray diffracti on analyses show that a CeO2/ZrO2 solid solution is formed in the samp les prepared by precipitation of the hydroxides and calcination at 500 degrees C. To our knowledge this is the lowest temperature chemical r oute (not including high energy ball milling) to CeO2/ZrO2 solid solut ions 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 am ount of reversibly stored oxygen was 1.7-2.5 times more per gram catal yst than that of ceria only. The beneficial effects of zirconia are mo st pronounced in the solid solutions which had oxygen storage 3-5 time s higher than ceria. When the Zr concentration is optimized, the solid solution materials aged at 1000 degrees C showed higher oxygen storag e than fresh CeO2. For both preparation methods, the optimal (per gram catalyst) Zr concentration was found to be 25 mol% Zr for samples age d at 1000 degrees C, however, the performance of the solid solution ma terials was somewhat insensitive to Zr loading between 15 and 50 mol% Zr. (C) 1998 Elsevier Science B.V.