Pd（100）薄结构上Pd氧化物膜上吸附氧介导的氧化还原功能：第一性原理研究
Redox functionality mediated by adsorbed oxygen on a Pd-oxide film over a Pd(100) thin structure: A first-principles study
摘要：
采用第一性原理电子结构计算方法，在广义梯度近似下，确定了Pd（100）薄膜上的稳定氧位，其表面晶胞为（sqrt {5} × sqrt{5}）R27 ^circ.吸附的单原子氧进入桥接两个2-重配位的Pd原子的位点或进入桥接2-重配位的Pd原子和4-重配位的Pd原子的位点。CO氧化PdO膜还原和N_2O氧化PdO膜还原的反应能均为放热反应。使用轻推弹性带方法，其中吸附的氧的平移运动的能量势垒可以成为SIM 0.45 eV，这是足够低，以允许在高温下的表面氧的流动性之间的吸附的氧原子的运动进行评估。PdO膜上存在2-折叠配位的Pd原子，其局部结构与用于Suzuki-Miyaura交叉偶联的Pd催化剂的结构相似，从而允许氧的流动性。虽然NO_x（包括NO_2和NO）的还原并不总是由PdO膜催化的，但我们认为，当NO_x和CO的流入持续进行时，当反应循环保持在一个设计良好的氧表面上时，在Pd表面结构上吸附氧的PdO膜可能会发生连续的氧化还原反应。
英文摘要：
Stable oxygen sites on a PdO film over a Pd(100) thin structures with a (sqrt{5} times sqrt{5}) R27^circ surface-unit cell are determined using the first-principles electronic structure calculations with the generalized gradient approximation. The adsorbed monatomic oxygen goes to a site bridging two 2-fold-coordinated Pd atoms or to a site bridging a 2-fold-coordinated Pd atom and a 4-fold-coordinated Pd atom. Estimated reaction energies of CO oxidation by reduction of the oxidized PdO film and N_2O reduction mediated by oxidation of the PdO film are exothermic. Motion of the adsorbed oxygen atom between the two stable sites is evaluated using the nudged elastic band method, where an energy barrier for a translational motion of the adsorbed oxygen may become sim 0.45 eV, which is low enough to allow fluxionality of the surface oxygen at high temperatures. The oxygen fluxionality is allowed by existence of 2-fold-coordinated Pd atoms on the PdO film, whose local structure has similarity to that of Pd catalysts for the Suzuki-Miyaura cross coupling. Although NO_x (including NO_2 and NO) reduction is not always catalyzed only by the PdO film, we conclude that there may happen continual redox reactions mediated by oxygen-adsorbed PdO films over a Pd surface structure, when the influx of NO_x and CO continues, and when the reaction cycle is kept on a well-designed oxygen surface.
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