前驱体CeOHCO_3的结构对CeO_2催化性能的影响(英文)

Effect of Structure of CeOHCO_3 Precursor of CeO_2 on Its Catalytic Performance

以尿素替代水为溶剂,采用改良的尿素水解法制备不同结构的CeOHCO3和CeO2,并运用N2吸附-脱附、X射线衍射、H2程序升温还原、O2程序升温脱附、X射线光电子能谱、扫描电镜及甲烷燃烧反应对CeO2催化剂进行表征和催化性能测试.结果表明,CeO2催化性能和前驱体CeOHCO3的晶相结构(六方相或八面体相)存在直接关系.与以八面体为前驱体制得的颗粒状CeO2相比,以六方相为前驱体制得的棒状CeO2具有比表面积大、氧化还原能力强、表面氧空缺浓度高以及催化甲烷燃烧活性高的特点.

A modified hydrothermal process method based on using urea instead of water as the solvent was used to prepare CeOHCO3. Pure CeOHCO3 with a single crystalline structure was produced by varying the experimental conditions. CeO2 particles obtained from these CeOHCO3 precursors were tested for CH4 oxidation. The temperatures for 90% methane conversion were 604 and 647 ~C for CeO2 catalysts obtained from hexagonal and orthorhombic CeOHCO3, respectively, indicating that the CeO2 catalyst from hexagonal CeOHCO3 （CeO2-A） was more active than that from the orthorhombie form （CeOz-D）. The specific surface area and pore volume of CeO2-A were 45 m2/g and 0.35 cm3/g, respectively, which were higher than those of CeOz-D. Hz-TPR showed a much lower reduction temperature and enhanced re- ducibility with CeO2-A. XPS and O2-TPD results demonstrated there were more oxygen vacancies on the surface of CeOz-A than on CeO2-D, which implied increased oxygen mobility. The CeOHCO3-structure dependent activity was investigated and found to originate from the morphologies of the CeOHCO3 precursors. Hexagonal CeOHCO3 had a rod-like shape while orthorhombic CeOHCO3 had a sphere-like morphology. After calcination, the obtained CeO2 had the morphology of the precursor. The difference in morphology gave CeO2 catalysts with different texture, structure, reducibility, and thus catalytic activity.