Ring-Opening Reactions of Methylcyclopentane over Metal Catalysts, M = Pt, Rh, Ir, and Pd: A Mechanistic Study from First-Principles Calculations
Ring-Opening Reactions of Methylcyclopentane over Metal Catalysts, M = Pt, Rh, Ir, and Pd: A Mechanistic Study from First-Principles Calculations
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DOI：
10.1021/cs3005924
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发表时间：
2013-01
期刊：
影响因子：
12.9
通讯作者：
Zhi-Jian Zhao;L. Moskaleva;N. Rösch
中科院分区：
文献类型：
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作者：
Zhi-Jian Zhao;L. Moskaleva;N. Rösch
用密度泛函方法研究了甲基环戊烷转化为各种开环产物，支链和不支链的己烷，即2-甲基戊烷和3-甲基戊烷，以及正己烷。我们用平坦的M(111)面和阶梯状的M(211)面的平板模型考察了四种金属催化剂，M=Pt，Rh，Ir和Pd，分别描述了富平台的大颗粒和富缺陷的小颗粒M。由于C-H键的活化和形成与颗粒结构无关，因此我们将重点放在C-C键的断裂上，这可能是结构敏感的。在这些金属表面的不同位置上，C-C键的断裂势垒确实从∼20kJmol-1到∼140kJmol-1不等。总的来说，Rh和Ir表面的活化能较低，这与这两种金属比铂和钯具有更高的实验活性是一致的。根据计算的C-C键断裂势垒，我们能够合理地解释不同开环产物的选择性。
Using density functional calculations we studied the conversion of methylcyclopentane to its various ring-opening products, branched and unbranched hexanes, that is, 2-methylpentane and 3-methylpentane, as well as n-hexane. We examined four metal catalysts, M = Pt, Rh, Ir, and Pd, using slab models of flat M(111) and stepped M(211) surfaces, to describe terrace-rich large and defect-rich small M particles, respectively. As C–H bond activation and formation is rather independent of the particle structure, we focused on C–C bond scission which is expected to be structure sensitive. The barriers of C–C bond scission indeed vary from ∼20 kJ mol–1 to ∼140 kJ mol–1 on various sites of these metal surfaces. In general, lower activation energies were calculated for Rh and Ir surfaces, in agreement with the higher experimental activity of these two metals compared to Pt and Pd. From the calculated C–C bond breaking barriers, we were able to rationalize the selectivity toward different ring-opening products, as obs...