Reaction mechanism on the activation of ethane C–H and C–C bonds by a diplatinum cluster
Reaction mechanism on the activation of ethane C–H and C–C bonds by a diplatinum cluster
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DOI：
10.1007/s00214-013-1387-z
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发表时间：
2013-08
影响因子：
1.7
通讯作者：
Ting Ju;Huaqing Yang;Fangchen Li;Xiangyuan Li;Changwei Hu
中科院分区：
文献类型：
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作者：
Ting Ju;Huaqing Yang;Fangchen Li;Xiangyuan Li;Changwei Hu
在BPW 91/aug-cc-pvtz，Lanl 2 tz水平上，在单重态和三重态势能面上对Pt 2团簇与C2 H6的反应机理进行了理论研究.脱乙烯通道（Pt 2 H2 + C2 H4）在动力学上是有利的，速率常数（单位dm 3 mol − 1 s −1）为，而脱氢通道（Pt 2C 2 H4 + H2）在热力学上是优选的。Pt 2团簇催化乙烷二次脱氢制乙炔的反应动力学和热力学与乙烷一次脱氢制乙烯的反应动力学基本相当。此外，C-H裂解中间体（H）_2Pt_2C_2H_4和C-C裂解中间体CH_3HPtPtCH_2在Pt_2 + C_2H_6反应中均具有优先选择性。此外，（H）2 Pt 2C 2 H4是动力学优选的，而CH 3 HPtPtCH 2是动力学受阻的。根据活化应变模型分析，稳定化作用有利于C-H键断裂，而活化应变有利于C-C键断裂。从C-C键断裂到C-H键断裂，活化能垒的降低主要是由于过渡态相互作用变得更加稳定。与单个Pt原子相比，Pt 2原子簇表现出更好的催化性能，因为Pt 2原子簇的同步效应使C2 H6中的两个C-H键同时断裂，从而使C2 H4从C2 H6中快速释放出来。这一结果与实验观察相吻合。此外，Pt 2簇表现出更有效的双重脱氢乙烷。
The reaction mechanism of Pt2cluster with C2H6has been theoretically investigated on the singlet and triplet potential energy surfaces at BPW91/aug-cc-pvtz, Lanl2tz level. The deethylenation channel (Pt2H2+ C2H4) is kinetically favorable with the rate constant (in dm3mol−1s−1) of, while the dehydrogenation channel (Pt2C2H4+ H2) is thermodynamically preferable. The twofold dehydrogenation of ethane to acetylene by Pt2cluster is both thermodynamically and kinetically almost equivalent to the single dehydrogenation to ethylene. In addition, both the C–H cleavage intermediate (H)2Pt2C2H4and the C–C cleavage intermediate CH3HPtPtCH2are thermodynamically favored in the Pt2+ C2H6reaction. Furthermore, (H)2Pt2C2H4is kinetically preferred, while CH3HPtPtCH2is kinetically hindered. According to analysis of activation strain model, the stabilizing interactionprefers the C–H bond cleavage, while the activation strainfavors the C–C bond cleavage. From C–C to C–H bond cleavage, the lowering of activation barrier is mainly caused by the transition states interactionbecoming more stabilizing. Compared with mononuclear Pt atom, Pt2cluster exhibits a more promising catalyst, because the synchronous effect of the atoms of Pt2cluster makes two C–H bonds of C2H6break simultaneously and then kinetically releases C2H4readily from C2H6. This result is in good agreement with the experimental observation. Moreover, Pt2cluster exhibits more efficient twofold dehydrogenation from ethane.