Reddy Benjaram M, Lakshmanan Pandian, Khan Ataullah, Loridant Stéphane, López-Cartes Carlos, Rojas Teresa C, Fernandez Asunción
Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500007, India.
J Phys Chem B. 2005 Jul 21;109(28):13545-52. doi: 10.1021/jp051438u.
Ce(x)Zr(1)(-)(x)O(2) solid solutions deposited over silica surface were investigated by X-ray diffraction (XRD), Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HREM) techniques in order to understand the role of silica support and the temperature stability of these composite oxides. For the purpose of comparison, an unsupported Ce(x)Zr(1)(-)(x)O(2) was also synthesized and subjected to characterization by various techniques. The Ce(x)Zr(1)(-)(x)O(2)/SiO(2) (CZ/S) (1:1:2 mole ratio based on oxides) was synthesized by depositing Ce(x)Zr(1)(-)(x)O(2) solid solution over a colloidal SiO(2) support by a deposition precipitation method and unsupported Ce(x)Zr(1)(-)(x)O(2) (CZ) (1:1 mole ratio based on oxides) was prepared by a coprecipitation procedure, and the obtained catalysts were subjected to thermal treatments from 773 to 1073 K. The XRD measurements disclose the presence of cubic phases with the composition Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) in CZ samples, while CZ/S samples possess Ce(0.75)Zr(0.25)O(2), Ce(0.6)Zr(0.4)O(2), and Ce(0.5)Zr(0.5)O(2) in different proportions. The crystallinity of these phases increased with increasing calcination temperature. The cell a parameter estimations indicate contraction of ceria lattice due to the incorporation of zirconium cations into the CeO(2) unit cell. Raman measurements indicate the presence of oxygen vacancies, lattice defects, and displacement of oxygen ions from their normal lattice positions in both the series of samples. The HREM results reveal, in the case of CZ/S samples, a well-dispersed nanosized Ce-Zr-oxides over the surface of amorphous SiO(2). The structural features of these crystals as determined by digital diffraction analysis of experimental images reveal that the Ce-Zr-oxides are mainly in the cubic geometry and exhibit high thermal stability. Oxygen storage capacity measurements by a thermogravimetric method reveal a substantial enhancement in the oxygen vacancy concentration of CZ/S sample over the unsupported CZ sample.
通过X射线衍射（XRD）、拉曼光谱（RS）和高分辨率透射电子显微镜（HREM）技术研究了沉积在二氧化硅表面的Ce(x)Zr(1)(-)(x)O(2)固溶体，以了解二氧化硅载体的作用以及这些复合氧化物的温度稳定性。为了进行比较，还合成了无载体的Ce(x)Zr(1)(-)(x)O(2)并通过各种技术进行表征。通过沉积沉淀法将Ce(x)Zr(1)(-)(x)O(2)固溶体沉积在胶体SiO(2)载体上合成了Ce(x)Zr(1)(-)(x)O(2)/SiO(2)（CZ/S）（基于氧化物的摩尔比为1:1:2），通过共沉淀法制备了无载体的Ce(x)Zr(1)(-)(x)O(2)（CZ）（基于氧化物的摩尔比为1:1），并将所得催化剂在773至1073K下进行热处理。XRD测量结果表明，CZ样品中存在组成Ce(0.75)Zr(0.25)O(2)和Ce(0.6)Zr(0.4)O(2)的立方相，而CZ/S样品中不同比例地含有Ce(0.75)Zr(0.25)O(2)、Ce(0.6)Zr(0.4)O(2)和Ce(0.5)Zr(0.5)O(2)。这些相的结晶度随煅烧温度的升高而增加。晶胞a参数估计表明，由于锆阳离子掺入CeO(2)晶胞中，氧化铈晶格收缩。拉曼测量表明，在这两个系列的样品中都存在氧空位、晶格缺陷以及氧离子从其正常晶格位置的位移。HREM结果表明，在CZ/S样品的情况下，纳米尺寸的Ce-Zr-氧化物在无定形SiO(2)表面上分散良好。通过对实验图像进行数字衍射分析确定的这些晶体的结构特征表明，Ce-Zr-氧化物主要为立方几何形状并表现出高热稳定性。通过热重法进行的储氧能力测量表明，CZ/S样品的氧空位浓度比无载体的CZ样品有显著提高。
