Impact of diverse active sites on MoS₂ catalyst: Competition on active site formation and selectivity of thiophene hydrodesulfurization reaction

MoS₂ is an efficient catalyst widely used in hydrodesulfurization (HDS) reaction. Coordinatively unsaturated active sites (CUS) on defective MoS₂ clusters are the most active positions for HDS reaction. In this study, we investigated CUS formation competition and thiophene HDS reaction mechanism at diverse active sites on MoS₂ nanoclusters by using density functional theory. First, we constructed five defective MoS₂ clusters with different CUSs. The calculated formation energies and Gibbs free energies of these CUSs indicated that the MoS₂ clusters with single-corner or -edge CUSs were the favorable structures under HDS condition, especially the former type. Subsequently, thiophene adsorption configurations and HDS reactions at the corner and edge CUSs on MoS₂ clusters were elucidated. Results showed that the corner CUS was more beneficial for thiophene adsorption than the edge CUS due to the smaller steric hindrance effect. For HDS process at the corner CUS, reaction via hydrogenation route was more competitive, and the reaction formed 2-butene as a product and tetrahydrothiophene as an impurity. By contrast, at the edge CUS, the direct desulfurization route with butadiene production was more energetically favorable, indicating an enhanced catalytic HDS property. This work provides theoretical basis in screening catalyst active sites and catalytic reaction products in industrial HDS processes.