Specific features of the defect structure of metastable nanodisperse ceria, zirconia, and related materials

Models of the defect structure and microstructure of the CeO2, ZrO2, Ce-Me-1-O (Me-1 = La, Sm, Zr), and Zr-Me-2-O (Me-2 = Ca, Sr, Ba) nanomaterials are discussed. For ceria-based fluorite, the appearance of weakly bound oxygen and the mobility of bulk oxygen are due to distortions in the Ce-O coordination sphere and the appearance of interstitial oxygen atoms. For pure and doped zirconia, the phases forming in the intermediate temperature range are characterized by metastable structural networks differing from those observed in the equilibrium phases. The change in the local environment of the Zr cations (eight-atom coordination sphere) from a square antiprism in the initial salts to a distorted fluorite-like polyhedron in zirconia and the principle of structural conformity between hydrolyzed cations and the terminal hydroxyls of the Zr complexes in solution are the factors determining the genesis and structural features of the metastable phases. The defect structure and microstructure of the complex fluorite-like oxides have an effect on the state of the supported active component, favoring the formation of clustered species in the vicinity of extended defects in the support. Some examples of this effect in different types of reactions are provided.