Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania 16802, United States.
Langmuir. 2013 Aug 13;29(32):10120-31. doi: 10.1021/la401747n. Epub 2013 Jul 30.
MnO(x)-CeO(x) mixed oxide systems exhibit interesting sulfur adsorption capacities and catalytic activity. We examined the electronic structure of Mn-doped fluorite CeO2 bulk solid and surface using density functional theory (DFT) with the Hubbard U term or the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. We specifically evaluate the reducibility and formation energies of Mn-doped CeO2 surfaces. The use of a U value on the d-states of Mn is examined, and a value of 4 eV is chosen based upon results from DFT+U calculations on bulk MnO(x),1 XANES characterization of oxidation states in calcined and reduced Mn-doped CeO2, and comparison with HSE06 hybrid functional results. Electronic structure impacts of the U inclusion are discussed. The concentration and orientation of Mn atoms doped into the surface of CeO2 have a great influence on the reducibility of the surface. Based upon formation energies, Mn will not favor doping into the surface of CeO2 in a fully oxidized system (Mn(4+)). Under reducing environments, Mn will dope into the surface with oxygen vacancies present (Mn(3+) and Mn(2+)). The first oxygen vacancy is not likely catalytically important in fluorite MnO(x)-CeO(x) systems as formation of the fully oxidized surface is not stable. A greater degree of reduction would occur during a catalyzed redox reaction.
MnO(x)-CeO(x) 混合氧化物系统表现出有趣的硫吸附能力和催化活性。我们使用密度泛函理论 (DFT) 结合 Hubbard U 项或 Heyde-Scuseria-Ernzerhof (HSE06) 混合泛函，研究了 Mn 掺杂萤石 CeO2 体相和表面的电子结构。我们特别评估了 Mn 掺杂 CeO2 表面的还原能力和形成能。我们研究了 Mn 的 d 态上 U 值的使用，根据 DFT+U 计算在体相 MnO(x)上的结果、在煅烧和还原的 Mn 掺杂 CeO2 中氧化态的 XANES 表征以及与 HSE06 混合泛函结果的比较，选择了 4 eV 的 U 值。讨论了包含 U 对电子结构的影响。掺杂到 CeO2 表面的 Mn 原子的浓度和取向对表面的还原能力有很大影响。根据形成能，在完全氧化体系（Mn(4+)）中，Mn 不会优先掺杂到 CeO2 表面。在还原环境下，Mn 将掺杂到存在氧空位的表面（Mn(3+)和 Mn(2+)）。在萤石 MnO(x)-CeO(x) 体系中，第一个氧空位可能在催化方面并不重要，因为完全氧化表面的形成不稳定。在催化氧化还原反应中，会发生更大程度的还原。
