Key Lab of Colloid and Interface Chemistry, Ministry of Education, Institute of Theoretical Chemistry, Shandong University, Jinan 250100, People's Republic of China.
J Mol Model. 2012 Jul;18(7):3051-60. doi: 10.1007/s00894-011-1318-7. Epub 2011 Dec 13.
The density functional theory (DFT) calculations are carried out to study the mechanism details and the ensemble effect of methanol dehydrogenation over Pt(3) and PtAu(2) clusters, which present the smallest models of pure Pt clusters and bimetallic PtAu clusters. The energy diagrams are drawn out along both the initial O-H and C-H bond scission pathways via the four sequential dehydrogenation processes, respectively, i.e., CH(3)OH → CH(2)OH → CH(2)O → CHO → CO and CH(3)OH → CH(3)O → CH(2)O → CHO → CO, respectively. It is revealed that the reaction kinetics over PtAu(2) is significantly different from that over Pt(3). For the Pt(3)-mediated reaction, the C-H bond scission pathway, where an ensemble composed of two Pt atoms is required to complete methanol dehydrogenation, is energetically more favorable than the O-H bond scission pathway, and the maximum barrier along this pathway is calculated to be 12.99 kcal mol(-1). In contrast, PtAu(2) cluster facilitates the reaction starting from the O-H bond scission, where the Pt atom acts as the active center throughout each elementary step of methanol dehydrogenation, and the initial O-H bond scission with a barrier of 21.42 kcal mol(-1) is the bottom-neck step of methanol decomposition. Importantly, it is shown that the complete dehydrogenation product of methanol, CO, can more easily dissociate from PtAu(2) cluster than from Pt(3) cluster. The calculated results over the model clusters provide assistance to some extent for understanding the improved catalytic activity of bimetal PtAu catalysts toward methanol oxidation in comparison with pure Pt catalysts.
采用密度泛函理论（DFT）计算研究了甲醇在 Pt(3)和 PtAu(2)团簇上脱氢的反应机理细节和整体效应，Pt(3)和 PtAu(2)团簇分别为纯 Pt 团簇和双金属 PtAu 团簇的最小模型。分别沿着初始的 O-H 和 C-H 键断裂途径，通过四个连续的脱氢过程，即 CH(3)OH → CH(2)OH → CH(2)O → CHO → CO 和 CH(3)OH → CH(3)O → CH(2)O → CHO → CO，绘制出能量图。结果表明，PtAu(2)上的反应动力学与 Pt(3)上的显著不同。对于 Pt(3)介导的反应，需要两个 Pt 原子组成的整体来完成甲醇脱氢，C-H 键断裂途径在能量上比 O-H 键断裂途径更有利，并且沿着这条途径的最大势垒计算为 12.99 kcal mol(-1)。相比之下，PtAu(2)团簇有利于从 O-H 键断裂开始的反应，其中 Pt 原子在甲醇脱氢的每个基本步骤中都充当活性中心，初始 O-H 键断裂的势垒为 21.42 kcal mol(-1)，是甲醇分解的底部瓶颈步骤。重要的是，结果表明甲醇的完全脱氢产物 CO 更容易从 PtAu(2)团簇中解离出来，而不是从 Pt(3)团簇中解离出来。模型团簇上的计算结果在一定程度上有助于理解与纯 Pt 催化剂相比，双金属 PtAu 催化剂对甲醇氧化的催化活性提高。
