Ce-Zr-Ca ternary mixed oxides:: Structural characteristics and oxygen handling properties

The structural/morphological and oxygen handling properties of Ce-Zr-Ca ternary mixed oxides prepared by a microemulsion method with a Zr:Ce atomic ratio close to 1 and with a Ca atomic content of 10 and 33 at% have been analyzed by using X-ray diffraction, transmission electron microscopy, infrared and Raman spectroscopies, electron spin resonance, and mass spectrometry using labeled (CO2)-O-18 as reactant probe. The ternary oxides synthesized are nanostructured, with an average crystalline particle size around 2 nm, and always display tetragonal t" symmetry. Their homogeneity in terms of chemical composition is reasonably good, although it decreases with the Ca content of the specimen. Ca introduction in a ceria-zirconia oxidic network strongly modifies surface and bulk oxygen handling properties. Surface properties are mainly modified by the depletion of Ce centers from the outermost layer and their concomitant electronic modification. Bulk oxygen diffusion is strongly altered and its behavior as a function of the Ca content slightly decays for low Ca doping and displays a large enhancement for the sample with the highest Ca concentration. (C) 2002 Elsevier Science (USA).