AN XRD AND TEM INVESTIGATION OF THE STRUCTURE OF ALUMINA-SUPPORTED CERIA-ZIRCONIA

Dispersed CeO2-ZrO2 is of interest as a thermally stable oxygen-storag e component of automotive catalysts. Alumina-supported CeO2-ZrO2 sampl es were prepared by coimpregnation in order to maximize the interactio n between Zr and Ce. The phases present, their particle sizes and the interactions among the phases of fresh, steam-aged and reduced samples were investigated by XRD and TEM. In the fresh samples, a particulate solid solution phase ZrxCe1-xO2 of cubic symmetry was identified. How ever, the zirconium concentration of this particulate phase was found to be smaller than that expected from the Zr loading. This suggests th e existence of finely dispersed zirconia on the Al2O3 surface. For the steam-aged samples, a second Ce-Zr oxide solid solution phase of high er Zr concentration and tetragonal symmetry was found in addition to t he original CeO2-based cubic solid solution. The appearance of this se cond phase may have resulted from sintering of the highly dispersed zi rconia. The highly dispersed zirconia may also be responsible for prev enting reaction between CeO2 and the Al2O3 support, since CeAlO3 was f ound only in high-temperature reduced samples without zirconia. The pa rticle sizes of the various phases were measured by XRD and TEM. The p article size of the supported particulate phase decreased with increas ing zirconium loading, but a discrepancy was noted between the XRD and the TEM results. This discrepancy is discussed in terms of compositio nal inhomogeneity in the ZrxCe1-xO2 solid solution phase. (C) 1997 Aca demic Press.