Combined Experimental and Theoretical Molecular Approach of the Catalytically Active Hydrotreating MoS2 Phases Promoted by 3d Transition Metals

High-throughput synthesis combined with a surface organometallic (coordination) chemistry approach is used to prepare in a systematic way a series of 40 metal-promoted (Me)-MoS2 active phases supported on amorphous silica alumina with various Me/Mo ratios (0-0.5). The intrinsic catalytic activity in a model reaction, namely, toluene hydrogenation, evaluated also by a high-throughput method shows a well-marked Me/Mo optimal ratio corresponding to an improved catalytic activity with respect to the MoS2 reference for Me = Fe, Co, and Ni. In contrast, no impact is observed for Zn, while a negative impact on the activity is observed for Ti and Cu. To rationalize these results, the thermodynamic stabilities, local structures, and magnetic properties of the Me atoms at the edges of the MoS2 nanocrystallite are examined by the density functional theory (DFT) calculations. The calculated edge energy descriptor unambiguously categorizes the different types of MeMoS mixed phases. Optimal intermediate edge energies are found for CoMoS, NiMoS, and to a lesser extent for FeMoS, whereas too high or too low edge energies are found for Me = Ti, V, Cu, and Zn, which is consistent with the observed catalytic trends with the varying Me/Mo ratio. The location of Fe in close vicinity of the MoS2 phase is highlighted by scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy analysis which is in agreement with the DFT prediction of the stability of Fe at MoS2 edges. Finally, we propose to extend the edge energy descriptor to WS2-based catalysts and to other sulforeductive conditions.