A theoretical study on reaction mechanisms and kinetics of thiophene hydrodesulfurization over MoS2 catalysts

In the present work, thiophene hydrodesulphurization (HDS) over the Mo-edge, the S-edge, and the Mo-S connection edge of MoS2 catalyst with 50% sulfur coverage was studied using first-principles based microkinetic modeling. Two parallel HDS routes, i.e., direct desulfurization (DDS) and hydrogenation (HYD) were taken into account. It has been found that the major reaction route of thiophene HDS on the Mo-and the Mo-S edges is temperature dependent. In the low temperature range of 500-600 K, the HYD route is dominant, leading to the C4H8 formation. As the temperature increases, the DDS route becomes competitive with the HYD route. At the temperature above 650 K, the DDS route will be the dominant HDS reaction route on the Mo-and the Mo-S edges. The DDS route leading to the formation of C4H6 is the major thiophene HDS reaction route on the S-edge in the entire temperature range of 500-750 K. The microkinetic modeling results show the overall HDS activity on the S-edge is lower than it on the Mo-and the Mo-S edges. The Mo-S edge also provides a preferential reaction pathway, which facilitates 2-hydrothiophene migration from the Mo-edge to the S-edge, followed by remaining elementary steps with lower activation barriers in the DDS route.