Department of Chemistry, Key Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of Education, Xiangtan University, Hunan Province 411105, People's Republic of China.
J Am Chem Soc. 2013 Feb 20;135(7):2583-95. doi: 10.1021/ja309460v. Epub 2013 Feb 8.
We have systematically studied the CO oxidation on various nanosized gold clusters with sizes ranging from 0.3 to 0.8 nm on the basis of density functional theory (DFT) calculations. A hitherto unreported trimolecular Langmuir-Hinshelwood (LH) mechanism is proposed, which offers new insights into the fundamental mechanism for CO oxidation on nanosized gold clusters. Specifically, we find that the coadsorbed CO molecule at a unique triangular Au(3) active site can act as a promoter for the scission of an O-O bond, leading to the spontaneous formation (due to extremely low energy barrier) of two CO(2) molecules as product. The key step to the O-O bond scission in the OCOO* intermediate is significantly accelerated due to the electrophilic attack of the coadsorbed neighboring CO molecule on the triangular Au(3) site. This new mechanism is called CO self-promoting oxidation, which can be visualized in real time from the trajectory of a Born-Oppenheimer molecular dynamics (BOMD) simulation. We also find that such CO self-promoting oxidation is quite universal, as long as the triangular Au(3) reaction site is available. This is demonstrated in two prototype metal oxide supported gold nanostructure systems: namely, Au(n)/MgO and bilayer-Au/TiO(2). The coadsorbed CO can not only serve as a promoter for its own oxidation but also promote other oxidation reactions such as styrene oxidation through expediting O-O scission on gold nanostructures.
我们基于密度泛函理论（DFT）计算系统地研究了尺寸范围在 0.3 至 0.8nm 的各种纳米金簇上的 CO 氧化。我们提出了一种迄今尚未报道的三分子 Langmuir-Hinshelwood（LH）机制，该机制为纳米金簇上 CO 氧化的基本机制提供了新的见解。具体来说，我们发现独特的三角形 Au(3)活性位上共吸附的 CO 分子可以作为促进 O-O 键断裂的促进剂，导致两个 CO(2)分子自发形成（由于极低的能量势垒）作为产物。在 OCOO*中间体中 O-O 键断裂的关键步骤由于共吸附相邻 CO 分子对三角形 Au(3)位的亲电攻击而显著加速。这种新的机制被称为 CO 自促进氧化，可以通过 Born-Oppenheimer 分子动力学（BOMD）模拟的轨迹实时观察到。我们还发现，只要存在三角形 Au(3)反应位，这种 CO 自促进氧化就相当普遍。这在两个原型金属氧化物负载金纳米结构体系中得到了证明：即 Au(n)/MgO 和双层-Au/TiO(2)。共吸附的 CO 不仅可以作为自身氧化的促进剂，还可以通过加速金纳米结构上的 O-O 断裂来促进其他氧化反应，如苯乙烯氧化。
