%0 Journal Article
%T <br>
%A 徐倩
%A 朱俊发
%A 李雄
%A 王岩
%A 胡善玮
%A 鞠焕鑫
%J 物理化学学报
%D 2018
%R 10.3866/PKU.WHXB201804092
%X 利用扫描隧道显微镜、X射线光电子能谱和同步辐射光电子能谱研究了CeO2(111)，部分还原的CeO2-x(111) (0＜x＜0.5)以及Ca掺杂的CeO2模型催化剂的形貌、电子结构以及它们与CO2分子间的相互作用。CeO2(111)和部分还原的CeO2-x(111)薄膜外延生长于Cu(111)单晶表面。不同Ca掺杂的CeO2薄膜是通过在CeO2(111)薄膜表面室温物理沉积金属Ca及随后真空退火到不同温度而得到的。不同的制备过程导致样品具有不同的表面组成，化学态和结构。CO2吸附到CeO2和部分还原的CeO2-x表面后导致表面羧酸盐的形成。此外，相比于CeO2表面，羧酸盐物种更易在部分还原的CeO2-x表面生成，而且更加稳定。而在Ca掺杂的氧化铈薄膜表面，Ca2+离子的存在有利于CO2的吸附，且探测到碳酸盐物种的形成。<br>CeO2-based catalysts are promising for use in various important chemical reactions involving CO2, such as the dry reforming of methane to produce synthesis gas and methanol. CeO2 has a superior ability to store and release oxygen, which can improve the catalytic performance by suppressing the formation of coke. Although the adsorption and activation behavior of CO2 on the CeO2 surface has been extensively investigated in recent years, the intermediate species formed from CO2 on ceria has not been clearly identified. The reactivity of the ceria surface to CO2 has been reported to be tuned by introducing CaO, which increases the number of basic sites for the ceria-based catalysts. However, the mechanism by which Ca2+ ions affect CO2 decomposition is still debated. In this study, the morphologies and electronic properties of stoichiometric CeO2(111), partially reduced CeO2-x(111) (0 < x < 0.5), and calcium-doped ceria model catalysts, as well as their interactions with CO2, were investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy, and synchrotron radiation photoemission spectroscopy. Stoichiometric CeO2(111) and partially reduced CeO2-x(111) films were epitaxially grown on a Cu(111) surface. STM images show that the stoichiometric CeO2 film exhibits large, flat terraces that completely cover the Cu(111) surface. The reduced CeO2-x film also has a flat surface and an ordered structure, but dark spaces are observed on the film. Different Ca-doped ceria films were prepared by physical vapor deposition of metallic Ca on CeO2(111) at room temperature and subsequent annealing to 600 or 800 K in ultrahigh vacuum. The different preparation procedures produce samples with various surface components, oxidation states, and structures. Our results indicate that the deposition of metallic Ca on CeO2 at room temperature leads to a partial reduction of Ce from the +4 to the +3 state, accompanied by the oxidation of Ca to Ca2+. Large CaO nanofilms are observed on CeO2 upon annealing to 600 K. However, small CaO nanoislands appear near the step edges and more Ca2+ ions migrate into the subsurface of CeO2 upon annealing to 800 K. In addition, different surface-adsorbed species
%U http://www.whxb.pku.edu.cn/CN/Y2018/V34/I12/1381