Wang Xianqin, Rodriguez José A, Hanson Jonathan C, Gamarra Daniel, Martínez-Arias Arturo, Fernandez-García Marcos
Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
J Phys Chem B. 2005 Oct 27;109(42):19595-603. doi: 10.1021/jp051970h.
The structural and electronic properties of Ce(1-x)Cu(x)O(2) nano systems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Cu atoms embedded in ceria had an oxidation state higher than those of the cations in Cu(2)O or CuO. The lattice of the Ce(1)(-x)Cu(x)O(2) systems still adopted a fluorite-type structure, but it was highly distorted with multiple cation-oxygen distances with respect to the single cation-oxygen bond distance seen in pure ceria. The doping of CeO(2) with copper introduced a large strain into the oxide lattice and favored the formation of O vacancies, leading to a Ce(1-x)Cu(x)O(2-y) stoichiometry for our materials. Cu approached the planar geometry characteristic of Cu(II) oxides, but with a strongly perturbed local order. The chemical activities of the Ce(1-x)Cu(x)O(2) nanoparticles were tested using the reactions with H(2) and O(2) as probes. During the reduction in hydrogen, an induction time was observed and became shorter after raising the reaction temperature. The fraction of copper that could be reduced in the Ce(1-x)Cu(x)O(2) oxides also depended strongly on the reaction temperature. A comparison with data for the reduction of pure copper oxides indicated that the copper embedded in ceria was much more difficult to reduce. The reduction of the Ce(1-x)Cu(x)O(2) nanoparticles was rather reversible, without the generation of a significant amount of CuO or Cu(2)O phases during reoxidation. This reversible process demonstrates the unusual structural and chemical properties of the Cu-doped ceria materials.
采用基于同步加速器的X射线衍射、X射线吸收光谱、拉曼光谱和密度泛函计算等方法，对通过反相微乳液法制备的Ce(1-x)Cu(x)O(2)纳米体系的结构和电子性质进行了表征。嵌入二氧化铈中的铜原子的氧化态高于Cu(2)O或CuO中阳离子的氧化态。Ce(1)(-x)Cu(x)O(2)体系的晶格仍采用萤石型结构，但相对于纯二氧化铈中单一的阳离子-氧键距离，它因多个阳离子-氧距离而发生了高度畸变。用铜掺杂CeO(2)会在氧化物晶格中引入较大应变，并有利于氧空位的形成，导致我们的材料具有Ce(1-x)Cu(x)O(2-y)化学计量比。铜接近Cu(II)氧化物的平面几何特征，但局部有序性受到强烈扰动。以与H(2)和O(2)的反应为探针，测试了Ce(1-x)Cu(x)O(2)纳米颗粒的化学活性。在氢气还原过程中，观察到一个诱导期，升高反应温度后诱导期变短。Ce(1-x)Cu(x)O(2)氧化物中可还原的铜的比例也强烈依赖于反应温度。与纯铜氧化物还原数据的比较表明，嵌入二氧化铈中的铜更难还原。Ce(1-x)Cu(x)O(2)纳米颗粒的还原相当可逆，在再氧化过程中不会生成大量的CuO或Cu(2)O相。这一可逆过程证明了铜掺杂二氧化铈材料具有非同寻常的结构和化学性质。
