Study on surface chemical reactions by real-time tracing with atomic-resolution microscope and x-ray spectroscopy

这个项目的目的是开发一种结合微观技术获得的表面物种空间分布的方法，以及从同步加速器光谱和反应模拟提供的动力学信息，以了解固体表面上进行的表面反应机理，并将其应用于实际表面反应的机理研究。在这种方法的基础上进行的机理研究揭示了如下所示的几个重要表面过程的微观机制，并证实了它的用处。CO氧化铂(111)是汽车催化的模型反应，当表面氧原子形成二维岛时，反应速率显著降低。结果表明，这种速率的降低是由于岛内CO分子的氧化过渡态由于与邻近CO分子的大排斥作用而发生强烈的失稳所致。对于汽车催化的模型反应--Rh(111)上的NO还原，我们发现了一条新的反应途径，即从气相撞击NO分子形成NO二聚体，并与表面氮反应。结果表明，NO二聚体对N-N键面向表面的表面氮的攻击在该反应中起着关键作用。利用铂(111)表面的H_2O+OH覆盖层，研究了在铂燃料电池催化剂中起重要作用的表面质子转移。结果发现，不仅有简单的质子从H_2O到OH的转移，而且通过H_3O+向次最近的OH中心的质子转移也有很大的贡献。我们还首次估算了这两个质子转移过程的时间尺度。

The aim of this project is developing a combined approach of spatial distribution of surface species obtained from microscopic techniques and kinetics information provided from synchrotron-based spectroscopies and reaction simulations to understand the mechanisms of surface reactions proceeding on solid surfaces and its application to mechanistic studies on actual surface reactions. The mechanistic studies on the basis of this approach revealed the microscopic mechanisms for several important surface processes as shown below and led to confirm its usefulness.1. CO oxidation Pt(111), which is a model reaction for the automobile catalysis, exhibits a significant decrease in reaction rate when surface oxygen atoms form two-dimensional islands. It was clarified that this rate reduction is caused by strong destabilization of the transition state for oxidation of CO molecules inside the islands due to large repulsive interactions with neighbor CO molecules.2. For NO reduction on Rh(111), which is a model reaction for the automobile catalysis, we found a new reaction path where impinging NO molecules from gas phase form a NO dimer and react with surface nitrogen. It was revealed that attack of the NO dimer to surface nitrogen with N-N bond facing to the surface plays a key role in this reaction.3. Proton transfer at surfaces, which is considered to act an important role on the Pt fuel-cell catalysts, was studied using H_2O+OH overlayers on Pt(111). As a result, we found not only the simple proton transfer from H_2O to OH but also significant contribution of proton transfer via formation of H_3O+ to the next-nearest OH site. We also estimated the time scale of the two proton transfer processes for the first time.