Department of Energy, Environmental and Chemical Engineering, Washington University, St. Louis, Missouri 63130, USA.
J Chem Phys. 2013 Jan 7;138(1):014702. doi: 10.1063/1.4773248.
Ceria (CeO(2)) is a promising catalyst for the reduction of carbon dioxide (CO(2)) to liquid fuels and commodity chemicals, in part because of its high oxygen storage capacity, yet the fundamentals of CO(2) adsorption, activation, and reduction on ceria surfaces remain largely unknown. We use density functional theory, corrected for onsite Coulombic interactions (GGA+U), to explore various adsorption sites and configurations for CO(2) on stoichiometric and reduced ceria (110), the latter with either an in-plane oxygen vacancy or a split oxygen vacancy. We find that CO(2) adsorption on both reduced ceria (110) surfaces is thermodynamically favored over the corresponding adsorption on stoichiometric ceria (110), but the most stable adsorption configuration consists of CO(2) adsorbed parallel to the reduced ceria (110) surface at a split oxygen vacancy. Structural changes in the CO(2) molecule are also observed upon adsorption. At the split vacancy, the molecule bends out of plane to form a unidentate carbonate with the remaining oxygen anion at the surface; this is in stark contrast to the bridged carbonate observed for CO(2) adsorption at the in-plane vacancy. Also, we analyze the pathways for CO(2) conversion to CO on reduced ceria (110). The subtle difference in the energies of activation for the elementary steps suggest that CO(2) dissociation is favored on the split vacancy, while the reverse process of CO oxidation may favor the formation of the in-plane vacancy. We thus show how the structure and properties of the ceria catalyst govern the mechanism of CO(2) activation and reduction.
氧化铈（CeO2）是一种很有前途的催化剂，可将二氧化碳（CO2）还原为液体燃料和大宗商品化学品，部分原因是其具有较高的储氧能力，但 CO2 在氧化铈表面的吸附、活化和还原的基本原理在很大程度上仍然未知。我们使用密度泛函理论，结合局域库仑相互作用校正（GGA+U），来探索 CO2 在化学计量氧化铈（110）和还原氧化铈（110）表面的各种吸附位和构型，后者具有面内氧空位或分裂氧空位。我们发现，CO2 在还原氧化铈（110）表面的吸附在热力学上比在化学计量氧化铈（110）表面上的吸附更有利，但最稳定的吸附构型是 CO2 平行于还原氧化铈（110）表面在分裂氧空位处吸附。吸附后 CO2 分子的结构也发生了变化。在分裂的空位处，分子偏离平面，与表面上剩余的氧阴离子形成单齿碳酸盐；这与在面内空位处观察到的桥连碳酸盐形成鲜明对比。此外，我们还分析了 CO2 在还原氧化铈（110）上转化为 CO 的途径。基本步骤的活化能的细微差异表明，CO2 解离在分裂空位处更有利，而 CO 氧化的逆过程可能有利于形成面内空位。因此，我们展示了氧化铈催化剂的结构和性质如何控制 CO2 活化和还原的机制。
