Atomic-Scale Edge Structures on Industrial-Style MoS2 Nanocatalysts
Atomic-Scale Edge Structures on Industrial-Style MoS2 Nanocatalysts
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DOI：
10.1002/anie.201103745
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Helveg, Stig
中科院分区：
文献类型：
--
作者：
Hansen, Lars P.;Ramasse, Quentin M.;Helveg, Stig
目前，人们对从二硫化钼中提取的功能纳米结构非常感兴趣，如富勒烯、纳米管/纳米线和血小板作为血小板，二硫化钼被用作工业炼油、析氢和光氧化的催化剂。[2-5]二硫化钼纳米催化剂基本上由不同程度堆叠的二维S-Mo-S层组成。S-Mo-S层的催化活性与其边缘有关，因此，为了了解催化活性位点的性质，关于边缘结构的详细信息是必不可少的通过扫描隧道显微镜（STM）和密度泛函理论（DFT）计算，在超高真空条件下在平面衬底上制备模型催化剂，获得了前所未有的原子尺度对MoS2边缘结构和反应性的深入了解。这些信息大大提高了对结构依赖的催化性能[6]的理解，并且当与工业型MoS2纳米催化剂的高分辨率电子显微镜相结合时，可能会导致催化剂性能的进一步改进。[7-10]最近，由于像差校正的高分辨率（扫描）透射电子显微镜（HR (S) TEM）技术的进步，成像对比度和分辨率达到了前所未有的水平，这将极大地有利于工业型二硫化钼纳米催化剂边缘结构的研究通过HRTEM，我们证明了在（001）投影中可以获得工业型石墨支撑的MoS2纳米催化剂的单原子敏感图像，这有助于明确识别单层和双层MoS2结构，以及两种主要的低指数边缘类型的晶体学指数化详细的结构信息是从相位图像中获得的，该相位图像代表了样品的通过聚焦的HRTEM图像系列的重建。然而，由于在获取连续图像期间进行边缘重建，无法直接确定催化重要的最外层边缘的原子尺度结构。这些边缘重建很可能是由入射电子束（动能为80 keV）引起的撞击损伤引起的，而由于样品的导电性，电离损伤预计可以忽略不计。将初级电子能量降低到其阈值能量[13]以下，即MoS2约为66keV（见支持信息），可以减少撞击损伤。直到最近，在这样的条件下进行HRSTEM才成为可能在此，我们报告了在低光束能量（60 keV）下获得的HRSTEM图像，以获得有关工业型MoS2纳米催化剂边缘结构的原子尺度信息，并将图像与模型催化剂研究和DFT计算预测的边缘结构进行了比较。
Currently, considerable interest is directed toward functional nanostructures, such as fullerenes, nanotubes/wires, and platelets, derived from molybdenum disulfide.[1] As platelets, MoS2 is employed as catalyst for industrial oil refining, hydrogen evolution, and photooxidation.[2–5] The MoS2 nanocatalyst basically consists of 2-dimensional S–Mo–S layers that are stacked to various degrees. The catalytic reactivity of the S–Mo–S layers is associated with their edges and detailed information about the edge structures is thus essential in order to understand the nature of the catalytically active sites.[6] Unprecedented atomic-scale insight into the MoS2 edge structure and reactivity was obtained from scanning tunnelling microscopy (STM) of model catalysts, prepared under ultra-high-vacuum conditions on planar substrates, and from density functional theory (DFT) calculations. Such information has significantly improved the understanding of the structural-dependent catalytic properties [6] and may lead to further improvement in the formulation of the catalyst properties when combined with high-resolution electron microscopy of industrial-style MoS2 nanocatalysts.[7–10] Recently, unprecedented levels of imaging contrast and resolution became available due to advances in aberrationcorrected high-resolution (scanning) transmission electron microscopy (HR (S) TEM)[11] and should benefit tremendously the study of edge structures on industrial-style MoS2 nanocatalysts.[12] By HRTEM, we demonstrated that single-atomsensitive images of industrial-style graphite-supported MoS2 nanocatalysts, viewed in the (001) projection, may be obtained facilitating an unambiguous identification of single-and double-layer MoS2 structures as well as a crystallographic indexation of the two predominant lowindexed edge types.[12] The detailed structural information was obtained from a phase image representing a reconstruction of a through-focus series of HRTEM images of the sample. However, due to edge reconstructions during the acquisition of the consecutive images, a determination of the atomic-scale structure of the catalytically important outermost edges was not directly possible. These edge reconstructions are most likely caused by knock-on damage induced by the incident electron beam (with a kinetic energy of 80 keV), whereas ionization damage is expected to be negligible due to the electrical conductivity of the sample. The knock-on damage may be reduced by lowering of the primary electron energy below its threshold energy,[13] which is approximately 66keV for MoS2 (see the Supporting Information). Only quite recently, HRSTEM under such conditions became possible.[14] Herein, we report HRSTEM images, acquired at low beam energy (60 keV), to obtain atomic-scale information about the edge structure of the industrial-style MoS2 nanocatalysts and we compare the images with edge structures predicted by model catalyst studies and DFT calculations.