CexTi1-xO2复合氧化物表面结构和体相结构的演变

利用X射线衍射、N₂吸附等温线、X射线光电子能谱、X射线吸收谱、H₂-程序升温还原、甲基橙选择化学吸附和等电点测定等方法研究了共沉淀方法制备的一系列Ce_xTi_1-xO₂复合氧化物的结构. 成功发展了甲基橙选择化学吸附和等电点方法研究Ce_xTi_1-xO₂复合氧化物的最外层表面结构, 并定义了“等价CeO₂表面覆盖度”来描述Ce_xTi_1-xO₂复合氧化物的最外层表面结构. Ce_xTi_1-xO₂复合氧化物 (x ≥ 0.7)形成立方萤石相固溶体, Ce_0.3Ti_0.7O₂表现出纯的单斜相, 而其它复合氧化物表现出混合相. Ce_xTi_1-xO₂复合氧化物最外层表面结构的演变行为不同于其体相结构.Ce_0.7Ti_0.3O₂立方萤石相固溶体最外层表面已经部分形成了单斜相Ce_0.3Ti_0.7O₂, 随Ce含量的降低, 单斜相Ce_0.3Ti_0.7O₂从最外层表面向体相生长. Ce_xTi_1-xO₂复合氧化物立方萤石相固溶体和单斜相Ce_0.3Ti_0.7O₂分别在相对较低和较高的温度表现出好的还原性能. 上述结果提供了全面和深层次的Ce_xTi_1-xO₂复合氧化物结构信息.

Evolution of surface and bulk structures of CexTi1-xO2 oxide composites

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.