Atomic-scale insight into structure and morphology changes of MoS_2 nanoclusters in hydrotreating catalysts

摘要

High-resolution scanning tunneling microscopy (STM) is used in combination with density-functional theory (DFT) to provide new insight into the morphology and atomic-scale structure of MoS_2 nanoclusters in hydrodesulfurization (HDS) catalysts.Atom-resolved STM images of gold-supported single-layer MoS_2 nanoclusters reveal that first direct evidence that both the detailed atomic-scale structure of the catalytically important edges and the overall morphology of the nanoparticles are sensitive to sulfiding and reaction conditions.Specifically,it is shown that synthesis of H_2S:H_2=500 results in MoS_2 nanoclusters with a triangular morphology,whereas sulfiding in H_2S:H_2=0.07 leads to hexagonally truncated nanoclusters.For both morphologies we identify the exact geometric edge structure of the MoS_2 nanoclusters edges,the hexagonal MoS_2 structures exhibit completely different edge structures with a lower sulfur coverage on the Mo edges and S edges with adsorbed S-H groups.A thermodynamic model based on DFT is employed to construct phase diagrams which can predict the stability of different MoS_2 edge structures under different conditions.The present results thus provide new insight into the atomic structure of the HDS catalysts and how it may change with reaction conditions.