Effect of preparation method and redox treatment on the reducibility and structure of supported ceria-zirconia mixed oxide

An Al2O3-supported Ce0.45Zr0.55O2 was prepared with a modified sol-gel procedure designed to maximize the interaction between ceria and zirconia and promote thermal stability of alumina. Its properties, characterized in detail with XRD, TPR, and laser Raman spectroscopy, were compared with those of more conventional preparations. This sample consisted of finely dispersed CexZr1-xO2 and had a high fraction of easily reducible Ce4+. Complete insertion of Zr into the ceria fluorite structure was observed after 900degreesC oxidation. After reduction at 980degreesC and reoxidation at 900degreesC, the mixed oxide particles remained small and furthermore still remained single phase and homogeneous by XRD characterization.Redox treatment enhanced the reducibility of Ce4+ in this sample. One feature of the enhancement, similar to that in bulk mixed oxide of similar composition, was an increase in the ratio of Ce4+ that was reducible at similar to491degreesC relative to the ones at similar to577degreesC. A new low-temperature reduction feature appeared at 320degreesC. This was attributed to the segregation of a small fraction of Ce3+ from the mixed oxide upon reduction and the subsequent formation of a finely dispersed ceria-rich phase on the surface of mixed oxide crystallites upon reoxidation. This phenomenon was particular to the supported samples because Al2O3 was able to stabilize the particle size of the mixed oxide during severe redox and thermal treatincrits. (C) 2002 Elsevier Science (USA).