Ligand-directed heterogeneous catalysis for controlling chemoselectivity of multi-pathway surface reactions: towards mechanistic understanding via surface science approach.

多途径表面反应的选择性取决于竞争反应活化势垒的细微差异，这是难以控制的。克服这个问题的最有希望的策略之一是在反应物和催化活性位点之间引入特定的选择性相互作用，将化学转化引向所需的路线。这种相互作用可以通过催化剂与配体的官能化来施加，通过空间约束或电子效应促进所需的途径。近年来，一系列高选择性的配体功能化粉末催化剂的开发，开辟了配体导向多相催化的新领域。微观层面的理解的潜在的表面过程，但是，仍然在很大程度上missing.With拟议的研究，我们的目标是在原子级的理解发生在金属表面的有机配体组件功能化的配体定向多相催化。本研究的重点将是在原子水平上表征配体组装体的几何和化学结构，以及探索在这些复杂界面上发生的多途径反应的分子反应机制和动力学。我们将在定义明确的配体功能化模型催化剂上应用独特的表面敏感技术组合-金属单晶和金属纳米粒子支撑在模型氧化物上-在原子水平上探索配体定向催化的起源。我们的实验方法包括结合扫描隧道显微镜的结构表征的配体层;红外光谱使化学鉴定和表面物种的操作监测和分子束技术允许高度控制的动力学研究。我们将系统地改变配体组装的化学和几何结构，以调整表面限制和电子效应，并找到精确的配体层的这些结构和化学性质与吸附和反应过程之间的相关性，例如反应物和反应中间体在配体层上的吸附几何形状、反应机理、对竞争反应途径的活性和选择性以及反应动力学。两种类型的反应将被调查：多不饱和羰基化合物和炔的部分选择性氢化，这些国家的最先进的实验技术的组合将首次采用在基础水平的研究模型配体导向催化，并将允许获得新的原子水平的见解基本表面过程。这项研究的结果具有很大的潜力，为开发新的概念，以合理的设计与定制的催化性能的表面。

The selectivity of multi-pathway surface reactions depends on subtle differences in the activation barriers of competing reactions, which is difficult to control. One of the most promising strategies to overcome this problem is to introduce a specific selective interaction between the reactant and the catalytically active site, directing the chemical transformations towards the desired route. This interaction can be imposed via functionalization of a catalyst with ligands, promoting the desired pathway via steric constrain or electronic affects. Recently, a number of highly selective ligand-functionalized powdered catalysts was developed, opening up a new field of ligand-directed heterogeneous catalysis. The microscopic-level understanding of the underlying surface processes, however, is still largely missing.With the proposed research we are aiming at an atomistic-level understanding of ligand-directed heterogeneous catalysis occurring at the metal surfaces functionalized with organic ligand assemblies. The focus of this study will be at the atomistic-level characterization of the geometric and chemical structure of the ligand assemblies as well as at the exploring the molecular reaction mechanisms and kinetics of multi-pathway reactions occurring at these complex interfaces.We will apply a unique combination of surface-sensitive techniques on well-defined model catalysts functionalized with ligands – both metal single crystals and metallic nanoparticles supported on model oxides– to explore the origins of ligand-directed catalysis at the atomistic level. Our experimental approach includes a combination of scanning tunneling microscopy for structural characterization of the ligand layers; infrared spectroscopy enabling the chemical identification and in operando monitoring of the surface species and molecular beam techniques allowing for highly controlled kinetic studies.We will systematically change the chemical and the geometric structure of the ligand assemblies to tune the surface confinement and electronic effects and find exact correlations between these structural and chemical properties of the ligand-layer and the adsorption and reactive processes, such as the adsorption geometries of the reactants and the reaction intermediates over a ligand-layer, the reaction mechanisms, the activity and selectivity towards competing reaction pathways and reaction kinetics. Two types of reactions will be investigated: partial selective hydrogenation of multi-unsaturated carbonyl compounds and alkynes.The combination of these state-of-the-art experimental techniques will be employed for the first time in the fundamental-level studies on the model ligand-directed catalysis and will allow to obtain new atomistic-level insights into the underlying elementary surface processes. The outcome of this research holds a great potential for developing new concepts towards rational-based design of surfaces with tailor-made catalytic properties.