Scanning Tunneling Microscopic Studies on Model Molybdenum Sulfide Catalysts

本文利用最先进的扫描隧道显微镜(STM)和扫描隧道光谱(STS)技术研究了促进和非促进二硫化钼晶体的拓扑和电子行为。为了跟踪催化剂表面的变化，在超高真空和常压条件下都进行了测量。本工作的目的是(1)用扫描隧道显微镜(STM)表征溅射前后的二硫化钼单晶表面，并与硫化钼(100)和石墨上的二硫化钼进行对比：(2)研究不同负载下钴对二硫化钼表面形貌和电子结构的影响；(3)研究了硫化钼、钴促进的二硫化钼和石墨上的二硫化钼等探针分子的吸附和解离特性；(4)跟踪了钼(100)和氧化钼在石墨上的硫化过程。根据加氢脱硫(HDS)催化反应中心的性质和反应机理对数据进行了解释。这项研究涉及将一系列新技术(隧道显微镜)应用于一个经典问题(氢硫化)，这对两者都有潜在的好处。尽管在过去20年里，HDS几乎没有取得什么进展，但环境压力正迫使它再次成为人们关注的焦点。虽然这一过程得到了广泛的实践，但人们对此仍然知之甚少，即使是渐进式的改进也可能产生重大影响。

This an investigation of the topological and electronic behavior of promoted and unpromoted molybdenum disulfide crystals using state-of-the-art scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) techniques. Measurements are made both under ultrahigh vacuum and under atmospheric conditions in order to follow changes in the catalyst surface. The goals of the effort are (1) using STM, to characterize the molybdenum disulfide single-crystal surface before and after sputtering, and to contrast this to sulfided molybdenum(100) and molybdenum disulfide on graphite; (2) to investigate the effect of cobalt on the morphology and on the electronic structure of molybdenum disulfide under various loadings; (3) to study the adsorption and dissociation characteristics of probe molecules such as thiophene, dithiophene, and benzothiophene on molybdenum disulfide, cobalt-promoted molybdenum disulfide, and molybdenum disulfide on graphite; and (4) to follow the sulfidation process of molybdenum(100) and molybdenum oxide on graphite. The data are interpreted in terms of nature of reaction sites and reaction mechanisms in hydrodesulfurization (HDS) catalysis. This study involves the application of a new battery of techniques (tunnelling microscopy) to a classical problem (hydrosulfurization) with potential benefits for both. Although there has been little advance in HDS in the last two decades, environmental pressures are forcing it to the forefront of interest again. Although widely practiced, the process is still poorly understood, and even incremental improvements could have a major impact.