Chemical Imaging of Elementary Steps in Hydrogenation Reactions of Surfaces

表面氢化反应基本步骤的化学成像

• 批准号: 1608568
• 负责人: Udo Schwarz
• 金额: $ 15万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2018-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1608568&HistoricalAwards=false
• 关键词: Chemical; Imaging; Elementary; Steps; Hydrogenation

With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professors Schwarz and Altman at Yale University are developing a new approach for the visualization and characterization of single molecule surface chemistry. This new approach offers dramatic advances over existing pathways to explore surface chemistry over large ensembles of molecules and reactions; instead each step of a reaction is individually induced by the tip of a scanning probe microscope, the specific and unique reaction pathway is chosen at will, and energy barriers between potential minima on that pathway are quantified. During each step, the interactions responsible to drive the reaction are characterized with unprecedented precision, which has the potential to reveal the influence of nearby surface defects or other molecules, thereby opening a whole new avenue to the study of surface chemistry and catalysis. The technique and the novel results it can generate are being illustrated using hydrogenation, dehydrogenation, and carbon-carbon bond formation in aromatic compounds as examples. These reactions are chosen because of their extraordinary technological importance for the world's chemical and petrochemical industry. The ability to "see chemistry in action" combined with controlling and quantifying every detail of it is expected to facilitate outreach to the general public.More specifically, the new approach builds on recent advances in scanning probe microscopy, which have made it possible to not only image molecules on surfaces, but also to 1) map the entire surface potential around the molecule, thereby uncovering sites of enhanced local reactivity; 2) translate molecules, atoms, and clusters while measuring the diffusion barrier between sites, thereby detecting these barriers as a function of the chemical environment; 3) split molecules (dissociation) using energy provided by the tip; and 4) form molecules and molecular bonds through voltage pulses induced by the tip after the reactants have been arranged properly on the surface. This research, for the first time, combines these elements to achieve a complete quantitative picture of all of the elementary steps involved in surface reactions. The new approach is centered on measuring the force needed to push molecules and/or atoms together so that they can react; by integrating along the path, the energy barriers and depths of the potential minima can be recovered. To achieve the necessary stability of the molecules on the surface, all investigations take place at low temperatures using a home-built combined scanning tunneling/atomic force microscope. First, benzene, iodobenzene, and hydrogen are deposited on the (111) surface of platinum. Subsequently, individual H and I atoms are produced by applying voltage pulses and the resulting radicals and atoms are manipulated to determine possible manipulation paths and diffusion barriers between potential minima while the potential energy landscapes are being mapped. Finally, biphenyl are produced by linking two benzyl radicals or benzene by hydrogenating benzyl, either spontaneously or through the application of bias voltage pulses once the species are brought close together. As a result, complete energetic information is obtained on a single-molecule level.

在化学测量和成像计划的支持下，耶鲁大学的施瓦​​茨和奥特曼教授正在开发一种新的方法，用于可视化和表征单分子表面化学。这种新方法为现有的途径提供了巨大的进步，以探索大型分子和反应的大型综合体。取而代之的是，反应的每个步骤都是由扫描探针显微镜的尖端单独诱导的，并随意选择特定和独特的反应途径，并且该途径上电势最小值之间的能屏障进行了量化。在每个步骤中，负责驱动反应的相互作用都以前所未有的精度来表征，这有可能揭示附近表面缺陷或其他分子的影响，从而为研究表面化学和催化的研究打开了一个全新的途径。它可以用芳香族化合物中的氢化，脱氢和碳碳键形成来说明该技术及其可以产生的新型结果。之所以选择这些反应，是因为它们对世界化学和石化工业的技术重要性非常重要。预计“看到化学作用”的能力与控制和量化的每个细节相结合，有望促进向公众宣传。更具体地说，新方法是基于扫描探针显微镜的最新进展，这不仅可以在表面上进行图像分子，而且还可以绘制整个局部局部反应，从而增强本地局部的反应; 2）在测量位点之间的扩散屏障的同时翻译分子，原子和簇，从而检测到这些障碍是化学环境的函数； 3）使用尖端提供的能量分裂分子（解离）； 4）在反应物正确排列在表面上后，通过尖端诱导的电压脉冲形成分子和分子键。这项研究首次将这些元素结合在一起，以实现表面反应中所有基本步骤的完整定量图片。新方法集中在测量将分子和/或原子推在一起所需的力，以便它们可以反应。通过沿路径的整合，可以回收潜在极小的能量屏障和深度。为了达到表面上分子的必要稳定性，所有研究都使用自制的扫描隧道/原子力显微镜在低温下进行。首先，将苯，碘和氢沉积在铂（111）表面上。随后，单个H和I原子是通过施加电压脉冲来产生的，并操纵所得的自由基和原子，以确定可能的操纵路径和潜在最小值之间的可能的操纵路径和扩散屏障，同时映射了势能景观。最后，双苯基是通过自发的氢化苄基或苯二苯甲酸连接或苯连接产生的，或者一旦将物种近距离连接起来。结果，在单分子水平上获得完整的能量信息。