HREM study of the reoxidation of heavily reduced Ce-La mixed oxides of interest in environmental catalysis.

HREM, in combination with structural modelling, image processing and image simulation, has been applied to characterise in detail the nanostructure of different Ce-La mixed oxides reduced in hydrogen at 1223K and further reoxidised in oxygen at room temperature. The formation of a thin, protective, surface layer on top of hexagonal-Ln₂0₃ (Ln: Ce,La) mixed oxide crystals has been evidenced after this treatment. The chemical nature and orientation relationships between the surface and bulk phases are discussed on the basis of the reactivity of these mixed oxides against oxidation and hydration/carbonation processes.