Advanced Electron Microscopy Investigation of Ceria-Zirconia-Based Catalysts

The potentials of advanced transmission and scanning transmission electron microscopy in nanostructural studies of ceria–zirconia mixed oxides are overviewed. The crystallographic criteria that allow us to discriminate the different CeO2–ZrO2 polymorphs and the nanocrystal size range within which they can be applied are discussed. The combined use of high resolution electron microscopy (HREM) and high‐angle annular dark field scanning transmission electron microscopy (HAADF‐STEM) to detect disorder–order transitions in the cation sublattice of this family of oxides and the size limit down to which each of them can be used for that purpose are also analyzed. Criteria to discriminate, on the basis of HREM images, the oxygen arrangement of the so called κ‐Ce2Zr2O8 phase from that of an oxidized pyrochlore Ce2Zr2O8 phase are presented and applied to the interpretation of experimental HREM images. HAADF‐STEM tomography studies and detailed analysis of HAADF‐STEM images establish both the crystallographic and compositional features of the surfaces of the mixed oxides that give enhanced redox activity. These findings allow deeper understanding of the influence of different thermal ageing pretreatments on the redox behavior of this family of mixed oxides. Novel characterization data do evidence that this model does not only fruitfully apply to binary ceria–zirconia oxides but also to more complex ternary oxides containing terbium. Hail Ce–Zr: Advanced electron microscopies are systematically applied to the 2D and 3D structural and chemical characterization of ceria–zirconia systems of current interest in environmental catalysis. Relevant details concerning both the bulk and the surface of these materials are obtained, which allows us to establish a rational model to correlate redox properties, nanostructure, and thermochemical treatments.