Surfaces of doped nanophase cerium oxide catalysts

Solid solutions of nanophase cerium oxides have been prepared and the relat ionship between their bulk crystal structure and surface characteristics ha s been studied at room temperature with X-ray diffraction (XRD) and X-ray p hotoelectron spectroscopy (XPS). Dopants with a valence lower than +4, such as Ca2+, Nd3+, and Pb2+, introduce structural defects (oxygen vacancies) i n the cerium oxide Lattice, which has been found to affect the redox cataly tic activity of the materials. The introduction of oxygen vacancies leads t o the appearance of an O1s core level peak with a shift of 2.0-2.5 eV to hi gher binding energies as compared to the care level peak of the lattice oxy gen in CeO2. The intensity of this high binding energy Ols peak varies with the expected concentration of oxygen vacancies in the surface, the type of dopant cation and its concentration in the solid solution. It was found th at carbonate and hydroxide species are responsible for the appearance of th is O1s peak, presumably as a result of capping of oxygen vacancies at the s urface. The implications of these surface groups on the catalytic activity of the materials are discussed. (C) 2000 Acta Metallurgica Inc.