CeO2(110)表面上CO氧化反应的密度泛函理论研究

利用密度泛函理论系统研究了O2与CO在CeO2(110)表面的吸附反应行为. 研究表明, O2在洁净的CeO2(110)表面吸附热力学不利, 而在氧空位表面为强化学吸附, O2分子被活化, 可能是重要的氧化反应物种. CO在洁净的CeO2(110)表面有化学吸附与物理吸附两种构型, 前者形成二齿碳酸盐物种, 后者与表面仅存在弱的相互作用. 在氧空位表面, CO可分子吸附或形成碳酸盐物种, 相应吸附能均较低. 当表面氧空位吸附O2后(O2/Ov), CO可吸附生成碳酸盐或直接生成CO2, 与原位红外光谱结果相一致. 过渡态计算发现，O2/Ov/CeO2(110)表面的三齿碳酸盐物种经两齿、单齿过渡态脱附生成CO2. 利用扩展休克尔分子轨道理论分析了典型吸附构型的电子结构, 说明表面碳酸盐物种三个氧原子电子存在离域作用, 物理吸附的CO及生成的CO2电子结构与相应自由分子相似.

A Density Functional Theory Study of CO Oxidation on CeO2(110) Surface

CO adsorption and oxidation reaction on the CeO2(110) surface were systematically investigated using density functional theory (DFT). It was found that O2 adsorption on the clean CeO2(110) surface is thermodynamically unfavorable. When surface oxygen vacancy exists, strong adsorption occurs and the O2/Ov species forms, which might be one of the most important oxygen species for oxidative reaction. Two types of CO adsorption structures on the clean CeO2(110) surface were observed. The strong chemisorbed configurations form a bidentate carbonate intermediate; while only weak interactions occur between CO and CeO2(110) surface for the physisorbed one. On the CeO2(110) surface with oxygen vacancy, both carbonate species and molecular CO were obtained with low adsorption energies. When O2 adsorbs on the surface with oxygen vacancy (O2/Ov), CO might strongly adsorb on the surface to form carbonate intermediate, or directly form CO2. It was very interesting to find that the carbonate species on the O2/Ov/CeO2(110) surface desorbs to CO2 through the bidentate and monodentate intermediates. According to the extended Hückel (eH) theory, it was indicated that the electrons of three oxygen atoms of the carbonate intermediate are partial delocalization. The electronic structures of the physisorbed CO and CO2 product on the CeO2(110) are much similar to those of free molecules.