Reddy Benjaram M, Khan Ataullah, Lakshmanan Pandian, Aouine Mimoun, Loridant Stéphane, Volta Jean-Claude
Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500007, India.
J Phys Chem B. 2005 Mar 3;109(8):3355-63. doi: 10.1021/jp045193h.
Structural characteristics of nanosized ceria-silica, ceria-titania, and ceria-zirconia mixed oxide catalysts have been investigated using X-ray diffraction (XRD), Raman spectroscopy, BET surface area, thermogravimetry, and high-resolution transmission electron microscopy (HREM). The effect of support oxides on the crystal modification of ceria cubic lattice was mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahighly dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO(2)-SiO(2) sample primarily consists of nanocrystalline CeO(2) on the amorphous SiO(2) surface. Both crystalline CeO(2) and TiO(2) anatase phases were noted in the case of CeO(2)-TiO(2) sample. Formation of cubic Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) (at 1073 K) were observed in the case of the CeO(2)-ZrO(2) sample. Raman measurements disclose the fluorite structure of ceria and the presence of oxygen vacancies/Ce(3+). The HREM results reveal well-dispersed CeO(2) nanocrystals over the amorphous SiO(2) matrix in the cases of CeO(2)-SiO(2), isolated CeO(2), and TiO(2) (anatase) nanocrystals, some overlapping regions in the case of CeO(2)-TiO(2), and nanosized CeO(2) and Ce-Zr oxides in the case of CeO(2)-ZrO(2) sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO(2) is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of the mixed oxide systems is more than that of pure CeO(2) and is system dependent.
采用X射线衍射（XRD）、拉曼光谱、BET比表面积、热重分析和高分辨率透射电子显微镜（HREM）等方法，研究了纳米氧化铈-二氧化硅、氧化铈-二氧化钛和氧化铈-氧化锆混合氧化物催化剂的结构特征。主要关注了载体氧化物对氧化铈立方晶格晶体改性的影响。所研究的氧化物通过软化学路线由超高稀释溶液制得，并在773至1073 K的温度下进行热处理。XRD结果表明，CeO(2)-SiO(2)样品主要由非晶态SiO(2)表面的纳米晶CeO(2)组成。在CeO(2)-TiO(2)样品中，同时观察到了结晶态的CeO(2)和TiO(2)锐钛矿相。在CeO(2)-ZrO(2)样品中，观察到了立方Ce(0.75)Zr(0.25)O(2)和Ce(0.6)Zr(0.4)O(2)（在1073 K时）的形成。拉曼测量揭示了氧化铈的萤石结构以及氧空位/Ce(3+)的存在。HREM结果显示，在CeO(2)-SiO(2)、孤立的CeO(2)和TiO(2)（锐钛矿）纳米晶体的情况下，CeO(2)纳米晶体在非晶态SiO(2)基质上分散良好；在CeO(2)-TiO(2)的情况下，存在一些重叠区域；在CeO(2)-ZrO(2)样品的情况下，存在纳米级的CeO(2)和Ce-Zr氧化物。通过对HREM实验图像进行数字衍射分析确定的这些晶体的确切结构特征表明，CeO(2)主要呈立方萤石几何形状。热重分析测定的储氧能力（OSC）表明，混合氧化物体系的OSC大于纯CeO(2)，且与体系有关。
