Activated Methane on Small Cationic Platinum Clusters
Activated Methane on Small Cationic Platinum Clusters
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DOI：
10.1002/anie.201107042
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Fielicke, Andre
中科院分区：
文献类型：
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作者：
Harding, Dan J.;Kerpal, Christian;Fielicke, Andre
催化活化小分子碳氢化合物中的CH键，特别是甲烷，是一种具有重大技术意义的反应，因为它允许从大量廉价的原料中制备有价值的官能化产品。然而，即使在表征良好的铂表面上，确定甲烷活化的细节，特别是最早的步骤仍然是困难的。[1，2]挑战包括甲烷分子在铂表面上的弱物理吸附，它容易解离，以及在许多表面实验中确定H原子位置的困难，因为H原子是X射线或电子的弱散射体，并且没有电子核心能级。[3]尽管存在这些挑战，Yoshinobu等人还是提出了这些挑战。用红外反射吸收光谱研究了吸附在铂(111)面上的甲烷最多具有C3v对称性。已经用X射线吸收光谱确定了甲烷在铂(977)[5]上的吸附几何形状，报告说甲烷通过一个氢原子结合，尽管他们无法确定它是结合在顶部还是在中空位置。对包括甲基、亚甲基和亚甲基的部分脱氢反应中间体/产物进行了广泛的研究(例如，见[6])。对甲烷与铂原子和簇合物的反应进行了较详细的研究。[7]在小离子簇合物与CH4在单一碰撞条件下反应的情况下，发现PtN[C，2H]+络合物是有利的产物。[8-10]已经有许多计算研究了铂簇合物[11-13]和表面[5，14，15]与甲烷的相互作用，主要是用密度泛函理论(DFT)。由于系统的大小、电子的数目和可能的路径，以及可能需要处理的几个电子态和它们之间的交叉，这种计算是具有挑战性的。[13]这些物种的实验光谱表征，特别是反应中间产物。
The catalytic activation of CH bonds in small hydrocarbons, particularly methane, is a reaction which is of significant technological interest, as it allows valuable, functionalized products to be made from plentiful, cheap feedstocks. However, even on well characterized platinum surfaces determination of the details of methane activation, in particular the earliest steps, remains difficult.[1, 2] Challenges include the weak physisorption of molecular methane on platinum surfaces, its ready dissociation and the difficulty associated with determining H atom positions in many surface experiments, as H atoms are weak scatterers of X-rays or electrons and have no electronic core levels.[3] Despite these challenges, Yoshinobu et al. have used infrared reflection absorption spectroscopy to show that CH4 adsorbed on Pt (111) has at most C3v symmetry.[4] Oström et al. have determined the adsorption geometry of methane on Pt (977)[5] using X-ray absorption spectroscopy, reporting methane to bind via a single H atom, though they were unable to determine whether it was bound atop or in hollow sites. Partially dehydrogenated reaction intermediates/products including methyl, methylene and methylidyne have been extensively studied (see for example [6]). The reactions of methane with platinum atoms and clusters have been studied in some detail.[7] In the case of small ionic clusters reacting with CH4 under single collision conditions Ptn [C, 2H]+ complexes were found to be the favored products.[8–10] There have been a number of computational studies of the interactions of platinum clusters [11–13] and surfaces [5, 14, 15] with methane, primarily using density functional theory (DFT). Such calculations are challenging, due to the large system size, number of electrons and possible paths, and the fact that several electronic states and crossings between them may need to be treated.[13] Experimental spectroscopic characterization of these species, particularly the reaction intermedi-