Key Laboratory of Mesoscopic Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China.
J Colloid Interface Sci. 2011 Feb 1;354(1):341-52. doi: 10.1016/j.jcis.2010.10.043. Epub 2010 Oct 23.
The present work focuses on the combination of ceria with another oxide of different ionic valences from period 3 (Mg(2+), Al(3+), and Si(4+)) using coprecipitation method, followed by calcination at 450 and 750°C, respectively. The textural, structural, morphological and redox properties of nanosized ceria-magnesia, ceria-alumina and ceria-silica mixed oxides have been investigated by means of N(2) physisorption, XRD, Raman, HRTEM, DRS, FT-IR, and H(2)-TPR technologies. XRD results of these mixed oxides reveal that only nanocrystalline ceria (ca. 3-6nm for the 450°C calcined samples) could be observed. The grain size of ceria increases with the increasing calcination temperature from 450 to 750°C due to sintering effect. The highest specific surface area is obtained at CeO(2)-Al(2)O(3) mixed oxides when calcination temperature reaches 750°C. Raman spectra display the cubic fluorite structure of ceria and the existence of oxygen vacancies, and displacement of oxygen ions from their normal lattice positions in the ceria-based mixed oxides. DRS measurements confirm that the smaller the grain size of the ceria, the higher indirect band gap energy. H(2)-TPR results suggest that the reductions of surface and bulk oxygen of ceria were predominant at low and high calcination temperature, respectively. Finally, CO oxidation were performed over these ceria-based mixed oxides, and the combination of CeO(2)-Al(2)O(3) exhibited highest activity irrespective of calcination temperature, which may due to excellent textural/structural properties, good homogeneity, and redox abilities.
本工作重点研究了铈与来自第 3 周期的另一种不同价态氧化物（Mg(2+)、Al(3+)和 Si(4+)）的复合，采用共沉淀法，分别在 450 和 750°C 下煅烧。通过 N(2)物理吸附、XRD、Raman、HRTEM、DRS、FT-IR 和 H(2)-TPR 技术研究了纳米尺寸的铈-氧化镁、铈-氧化铝和铈-氧化硅混合氧化物的结构、形貌和氧化还原性能。这些混合氧化物的 XRD 结果表明，仅观察到纳米晶氧化铈（对于 450°C 煅烧的样品约为 3-6nm）。由于烧结效应，随着煅烧温度从 450°C 升高到 750°C，氧化铈的晶粒尺寸增大。当煅烧温度达到 750°C 时，CeO(2)-Al(2)O(3)混合氧化物具有最高的比表面积。拉曼光谱显示氧化铈的立方萤石结构和氧空位的存在，以及氧离子在基于氧化铈的混合氧化物中从其正常晶格位置的位移。DRS 测量证实，氧化铈的晶粒尺寸越小，间接带隙能越高。H(2)-TPR 结果表明，表面和体相氧的还原分别在低温和高温下占主导地位。最后，在这些基于氧化铈的混合氧化物上进行了 CO 氧化反应，无论煅烧温度如何，CeO(2)-Al(2)O(3)的组合都表现出最高的活性，这可能归因于优异的结构/结构性质、良好的均一性和氧化还原能力。
