Velocity-resolved kinetics of site-specific carbon monoxide oxidation on platinum surfaces
Velocity-resolved kinetics of site-specific carbon monoxide oxidation on platinum surfaces
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DOI：
10.1038/s41586-018-0188-x
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发表时间：
2018-06-14
期刊：
影响因子：
64.8
通讯作者：
Kitsopoulos, Theofanis N.
中科院分区：
文献类型：
--
作者：
Neugebohren, Jannis;Borodin, Dmitriy;Kitsopoulos, Theofanis N.
催化剂被广泛用于提高反应速率。它们的作用是稳定反应在其活性部位的过渡态，在活性部位，原子排列确保了有利的相互作用（1）。然而，当催化剂具有多个活性位点时，例如与无机纳米颗粒的台阶边缘或紧密堆积的梯田相关的位点（2-4），其具有无法同时测量的不同活性时，机械理解通常是有限的。一个例子是一氧化碳在铂表面上的氧化，这是最古老和研究得最好的多相反应之一。1824年，这种反应被认为是戴维安全灯功能的关键，今天它被用于优化燃烧，氢气生产和燃料电池操作（5，6）。二氧化碳产物以双峰动能分布形成（7-13）;然而，尽管进行了广泛的研究（5），但仍不清楚这是否反映了在多个活性位点发生的不止一种反应机制的参与（12，13）。在这里，我们表明，在不同的活性位点的反应速率可以同时测量，使用分子束可控地引入反应物和切片离子成像（14，15）映射的产物分子的速度矢量，这反映了对称性和活性位点的取向（16）。我们使用这种速度分辨动力学方法来绘制一氧化碳在铂表面台阶边缘和平台位置的氧化速率，并发现反应通过两个不同的通道进行（11-13）：它在低温下由更活跃的台阶位置主导，在高温下由更丰富的平台位置主导。我们希望我们的方法是适用于广泛的非均相反应，并提供不同的活性位点，这应该是有用的改进催化剂的设计中的贡献改进的机械理解。
Catalysts are widely used to increase reaction rates. They function by stabilizing the transition state of the reaction at their active site, where the atomic arrangement ensures favourable interactions(1). However, mechanistic understanding is often limited when catalysts possess multiple active sites-such as sites associated with either the step edges or the close-packed terraces of inorganic nanoparticles(2-4)-with distinct activities that cannot be measured simultaneously. An example is the oxidation of carbon monoxide over platinum surfaces, one of the oldest and best studied heterogeneous reactions. In 1824, this reaction was recognized to be crucial for the function of the Davy safety lamp, and today it is used to optimize combustion, hydrogen production and fuel-cell operation(5,6). The carbon dioxide products are formed in a bimodal kinetic energy distribution(7-13); however, despite extensive study(5), it remains unclear whether this reflects the involvement of more than one reaction mechanism occurring at multiple active sites(12,13). Here we show that the reaction rates at different active sites can be measured simultaneously, using molecular beams to controllably introduce reactants and slice ion imaging(14,15) to map the velocity vectors of the product molecules, which reflect the symmetry and the orientation of the active site(16). We use this velocity-resolved kinetics approach to map the oxidation rates of carbon monoxide at step edges and terrace sites on platinum surfaces, and find that the reaction proceeds through two distinct channels(11-13): it is dominated at low temperatures by the more active step sites, and at high temperatures by the more abundant terrace sites. We expect our approach to be applicable to a wide range of heterogeneous reactions and to provide improved mechanistic understanding of the contribution of different active sites, which should be useful in the design of improved catalysts.