Abstract:

A series of Ce_xTi_1-xO₂ oxide composites were synthesized using a coprecipitation method, and their structures were investigated using X-ray diffraction, N₂ adsorption-desorption isotherms, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, H₂ temperature-programmed reduction, selective chemisorption of methyl orange, and isoelectric point measurements. The selective chemisorption of methyl orange and isoelectric point measurements successfully characterized the outmost surface structures of the Ce_xTi_1-xO₂ oxide composites, and the term "equivalent CeO₂ surface coverage" in a monolayer was introduced to describe the outmost surface compositions. Ce_xTi_1-xO₂ oxide composites with x ≥ 0.7 form a cubic fluorite phase solid solution, the Ce_0.3Ti_0.7O₂ oxide composite is a pure monoclinic compound, and the other oxide composites have mixed phase structures. The outmost surface structure evolves in a different way from the bulk structure. A cubic fluorite Ce_0.7Ti_0.3O₂ solid solution partially undergoes cubic fluorite solid solution-to-monoclinic Ce_0.3Ti_0.7O₂ phase transition on its outmost surface, and Ce_0.3Ti_0.7O₂ on the outmost surface of Ce_0.7Ti_0.3O₂ grows from the surface to the bulk. Cubic fluorite Ce_xTi_1-xO₂ solid solutions exhibit good reducibilities at relatively low temperatures, whereas Ce_0.3Ti_0.7O₂ exhibits good reducibility at relatively high temperatures. These results provide comprehensive and in-depth structural information for important Ce_xTi_1-xO₂ oxide composites.

Key words: Titania, Ceria, Oxide composite, Phase structure, Surface structure, X-ray absorption spectroscopy, Selective chemisorption, Isoelectric point