CO在CeO2(111)表面的吸附与氧化

采用密度泛函理论计算了CO在CeO2(111)表面的吸附与氧化反应行为. 结果表明, O2在洁净的CeO2(111)表面为弱物理吸附, 而在氧空位表面是强化学吸附, 且O2分子活化程度较大, O—O键长为0.143 nm. CO在CeO2(111)表面吸附行为的研究表明, CO在洁净表面及氧空位表面上为物理吸附, 吸附能均小于0.42 eV; 当表面氧空位吸附O2后, CO可吸附生成二齿碳酸盐中间体或直接生成CO2, 与原位红外光谱结果相一致. 表面碳酸盐物种脱附生成CO2的能垒仅为0.28 eV. 计算结果表明, 当CeO2表面存在氧空位时, Hubbard参数U对CO吸附能有一定的影响. CeO2载体在氧化反应中可能的催化作用为, 在氧气氛下, CeO2表面氧空位吸附O2分子, 形成活性氧物种, 参与CO催化氧化反应.

Adsorption and Oxidation of CO over CeO2(111)Surface

Adsorption and oxidation of CO on a CeO2(111) surface terminated by bridging oxygen atoms were systematically investigated using density functional theory (DFT). We found that O2 adsorption on a clean CeO2(111) surface was weak physisorption; while strong chemical adsorption occurred and the O—O bond was activated with a bond length of 0.143 nmin the present of surface oxygen vacancy. CO adsorption onto a clean CeO2(111) surface and a surface with oxygen vacancies occurred through physisorption with both adsorption energies being less than 0.42 eV. With O2 adsorption onto a surface with oxygen vacancies (O2/Ov), CO might absorb strongly on the surface to form a bidentate carbonate intermediate or directly produce CO2 without an energy barrier. The carbonate intermediate might desorb as CO2 with an energy barrier of 0.28 eV using a climbing nudged elastic band (CNEB). We also found that the values of the Hubbard U parameter affected the CO adsorption energy in the presence of surface oxygen vacancies. Our results indicate that a possible effect of the ceria support on catalytic oxidation consists of O2 adsorbing onto the CeO2(111) surface with oxygen vacancies which can be easily activated to form reactive oxygen species and then take part in the CO oxidation reaction.