atomic-scale investigation of carbon in MoS₂ hydrotreating catalysts sulfided by organosulfur compounds

From an interplay of Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS) experiments, and density functional theory (DFT) calculations, we investigate the fundamental effect of the use of organosulfur compounds for the sulfidation of MoS₂ nanoclusters in the hydrotreating catalyst. Our results reveal that incorporation of carbon in MoS₂-based hydrotreating catalysts as carbide-type phase is not favorable when synthesized with or exposed to dimethyl disulfide (DMDS) or dimethyl sulfide (DMS). These results suggest that substitution of sulfur with carbon on the predominant type of edge structures in MoS₂ nanoclusters is thermodynamically unfavorable, a result that is confirmed by DFT to be valid for all edge structures of MoS₂ exposed under catalytically relevant conditions. However, the results show that the choice of the sulfiding agent can strongly influence the morphology and dispersion of the sulfided phase, and such effects are therefore expected to be of major importance for the activity of the freshly sulfided catalyst.