Wang Xu, Du Lin-Ying, Du Meng, Ma Chao, Zeng Jie, Jia Chun-Jiang, Si Rui
Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China.
Phys Chem Chem Phys. 2017 Jun 7;19(22):14533-14542. doi: 10.1039/c7cp02004j.
A low-concentration cobalt (∼6 at%) and manganese (∼3 at%) bimetallic oxide catalyst supported on ceria nanorods (CoMnO/CeO), as well as its related single metal oxide counterparts (CoO/CeO and MnO/CeO) was synthesized via a deposition-precipitation approach. The fresh samples after air-calcination at 400 °C were tested under the reaction conditions of CO oxidation, and showed the following order of reactivity: CoMnO/CeO > CoO/CeO > MnO/CeO. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data identified that the structure of the CeO support was maintained during deposition of metal (Co, Mn) ions while the corresponding vis-Raman spectra verified that more oxygen vacancies were created after deposition-precipitation than those in pure ceria nanorods. Aberration-corrected, high-angle, annular dark-field scanning transmission electron microscopy (HAADF-STEM) images with the help of electron energy loss spectroscopy (EELS) analyses determined two types of cobalt species, i.e. ultra-fine clusters (<2 nm) and smaller nanocrystals (up to 5 nm) in CoO/CeO while only bigger nanostructures (∼10 nm) of cobalt-manganese oxides in CoMnO/CeO. X-ray absorption fine structure (XAFS) measurements demonstrated the presence of a cubic CoO phase in all the cobalt-based catalysts. The fitting results of the extended X-ray absorption fine structure (EXAFS) indicated that the introduction of the secondary metal (Mn) oxide significantly enhanced the two-dimensional growth of cobalt oxide nanostructures on the surface of CeO. Therefore, the enhanced activity of CO oxidation reaction over the bimetallic cobalt-manganese oxide nanocatalyst can be attributed to the higher crystallinity of the CoO phase in this work.
通过沉积沉淀法合成了负载在二氧化铈纳米棒上的低浓度钴（约6原子%）和锰（约3原子%）双金属氧化物催化剂（CoMnO/CeO）及其相关的单金属氧化物对应物（CoO/CeO和MnO/CeO）。在400℃空气煅烧后的新鲜样品在CO氧化反应条件下进行了测试，反应活性顺序如下：CoMnO/CeO＞CoO/CeO＞MnO/CeO。X射线衍射（XRD）和透射电子显微镜（TEM）数据表明，在金属（Co、Mn）离子沉积过程中，CeO载体的结构得以保持，而相应的可见拉曼光谱证实，沉积沉淀后产生的氧空位比纯二氧化铈纳米棒中的更多。借助电子能量损失谱（EELS）分析的像差校正高角度环形暗场扫描透射电子显微镜（HAADF-STEM）图像确定了两种钴物种，即CoO/CeO中的超细团簇（<2nm）和较小的纳米晶体（最大5nm），而CoMnO/CeO中只有较大的钴锰氧化物纳米结构（约10nm）。X射线吸收精细结构（XAFS）测量表明，所有钴基催化剂中均存在立方CoO相。扩展X射线吸收精细结构（EXAFS）的拟合结果表明，引入第二金属（Mn）氧化物显著增强了CeO表面氧化钴纳米结构的二维生长。因此，在双金属钴锰氧化物纳米催化剂上CO氧化反应活性的增强可归因于本工作中CoO相的更高结晶度。
