Quantitative Two-Dimensional (2D) Morphology–Selectivity Relationship of CoMoS Nanolayers: A Combined High-Resolution High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HR HAADF-STEM) and Density Functional Theory (DFT) Study

Cobalt-promoted and nonpromoted MoS2 nanolayers supported on alumina are prepared and activated under various sulfidation (temperature/pressure (T, P)) conditions which induce the formation of nanolayers with two-dimensional (2D) morphology of MoS2 tuned by the presence of the promoter and by the sulfidation conditions. An unprecedented high selectivity is found for the CoMoS nanolayers. The origin of this selectivity is explained by 2D morphology effects quantified by high-resolution scanning transmission electron microscopy in high-angle annular dark field mode (HR HAADF-STEM) and density functional theory (DFT) calculations. A quantitative structure–selectivity relationship is identified between the 2D shape index of CoMoS nanolayers and their selectivity performances. This 2D shape index is determined by statistical analysis of the CoMoS nanolayers identified after principal component analysis processing of HR HAADF-STEM images. It is shown that this shape index, reflecting the isotropic/anisotropic d...