Comprehensive mechanism and structure-sensitivity of ethanol oxidation on platinum: New transition-state searching method for resolving the complex reaction network
Comprehensive mechanism and structure-sensitivity of ethanol oxidation on platinum: New transition-state searching method for resolving the complex reaction network
复制标题
铂上乙醇氧化的综合机理和结构敏感性：解决复杂反应网络的新过渡态搜索方法
DOI：
10.1021/ja801648h
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发表时间：
2008-08-20
影响因子：
15
通讯作者：
Liu, Zhi-Pan
中科院分区：
文献类型：
--
作者：
Wang, Hui-Fang;Liu, Zhi-Pan
乙醇在Pt上的氧化是一个典型的多步多选择性多相催化过程。对这一基本反应的全面理解将极大地有利于直接乙醇燃料电池催化剂的设计和生物质含氧化合物的降解。本文采用一种有效的反应路径搜索方法，将我们的新的过渡态搜索技术与周期性密度泛函理论计算相结合，对乙醇氧化在不同Pt表面（包括密排Pt{111}、台阶Pt{211}和开放Pt{100}）上的反应网络进行了深入的研究.我们的新技术使过渡态和鞍点的位置，大多数表面反应简单，有效地通过优化局部极小值。我们发现，乙醇氧化的选择性明显依赖于Pt的表面结构，这可以归因于两个关键反应步骤的结构敏感性：（i）乙醇的初始脱氢和（ii）乙酰基（CH（3）CO）的氧化。在开放的表面位点上，乙醇倾向于通过强吸附的中间体（CH（2）CO或CHCO）裂解C-C键，这导致完全氧化为CO（2）。然而，在Pt{111}上仅部分氧化为CH（3）CHO和CH（3）COOH。我们的机制指出，开放的表面Pt{100}是最好的方面，充分氧化乙醇在低覆盖率，这揭示了来源的显着催化性能的Pt四面体纳米晶体最近发现。结构选择性的物理起源是合理的热力学和动力学方面。确定了两个基本量，决定乙醇氧化的选择性：（i）表面金属原子与不饱和含C片段键合的能力和（ii）相对于其他网站的表面顶部网站的羟基的相对稳定性。
Ethanol oxidation on Pt is a typical multistep and multiselectivity heterogeneous catalytic process. A comprehensive understanding of this fundamental reaction would greatly benefit design of catalysts for use in direct ethanol fuel cells and the degradation of biomass-derived oxygenates. In this work, the reaction network of ethanol oxidation on different Pt surfaces, including close-packed Pt{111}, stepped Pt{211}, and open Pt{100}, is explored thoroughly with an efficient reaction path searching method, which integrates our new tran siti on-state searching technique with periodic density functional theory calculations. Our new technique enables the location of the transition state and saddle points for most surface reactions simply and efficiently by optimization of local minima. We show that the selectivity of ethanol oxidation on Pt depends markedly on the surface structure, which can be attributed to the structure-sensitivity of two key reaction steps: (i) the initial dehydrogenation of ethanol and (ii) the oxidation of acetyl (CH(3)CO). On open surface sites, ethanol prefers C-C bond cleavage via strongly adsorbed intermediates (CH(2)CO or CHCO), which leads to complete oxidation to CO(2). However, only partial oxidizations to CH(3)CHO and CH(3)COOH occur on Pt{111}. Our mechanism points out that the open surface Pt{100} is the best facet to fully oxidize ethanol at low coverages, which sheds light on the origin of the remarkable catalytic performance of Pt tetrahexahedra nanocrystals found recently. The physical origin of the structure-selectivity is rationalized in terms of both thermodynamics and kinetics. Two fundamental quantities that dictate the selectivity of ethanol oxidation are identified: (i) the ability of surface metal atoms to bond with unsaturated C-containing fragments and (ii) the relative stability of hydroxyl at surface atop sites with respect to other sites.