Imaging MoS2 Nanocatalysts with Single-Atom Sensitivity

摘要

Materials derived from layered dichalcogenides, such as MoS2, are of wide nanotechnological interest for instance as nanocatalysts for industrial oil refinement, hydrogen evolution, and photooxidation. The MoS2 structure basically consists of two-dimensional S-Mo-S slabs (Figure 1a), which are stacked to various degrees. However, direct information on the atomic-scale structure of MoS2 nanocatalysts that are used in industry can be difficult to obtain. Information was previously obtained from scanning tunneling microscopy of model catalysts prepared under ultra-high vacuum conditions on planar, single-crystalline supports, and from density functional theory calculations.The information from the model studies is difficult to relate to technologically relevant catalysts because the morphology and distribution of the catalytically important edge sites of the MoS2 slabs are found to be sensitive to the preparation conditions, edge-attached promoter atoms, and interactions with support media. For a long time, a key goal has therefore been to obtain high-resolution microscopy images on industrial-style MoS2 nanocatalyst systems. Although high-resolution microscopy provides a powerful means for imaging industrial catalysts at different length scales, atomically resolved images of the supported MoS2 slabs in a (001) projection have not been available because of insufficient image contrast or resolution. Recently advances in high-resolution transmission electron microscopy (HRTEM) have made it possible to obtain images of unsupported one-atom-thick films with single-atom sensitivity. Herein, we report how the imaging technique was applied to obtain atomically resolved information on the shape and structure of MoS2 nanocatalysts prepared in an industrial style.