Computational Chemistry Analysis of Hydrodesulfurization Reactions Catalyzed by Molybdenum Disulfide Nanoparticles

Molybdenum disulfide, MoS2, is a very versatile material used in several applications of science and engineering. In particular, when supported on alumina, it is a widely used catalyst for hydrotreating processes in petroleum refineries. Stringent environmental norms and uncertainty in import of low sulfur crude oil put pressure on refiners worldwide to develop more efficient catalysts to meet the demand of clean fuel. The hydrodesulfurization of thiophene and dibenzothiophene on both unpromoted and nickel-promoted MoS2 catalyst is analyzed using a multiscale approach including classical molecular dynamics (MD) and density functional theory (DFT). MD simulations are performed on a hydrocarbon mixture containing sulfur compounds to determine relative positions of thiophene and dibenzothiophene molecules with respect to the MoS2 catalytic surface previous to possible reactions that are then studied with DFT. The sample box contains a total of 57 515 atoms and is able to represent a realistic size of the nanocatalyst process. Under typical hydrodesulfurization conditions, vacancies are needed for adsorption of sulfur compounds and therefore activation of hydrogen becomes an important step. In addition, complexes of MoS2 with graphene and boron nitride, BN, surfaces are also analyzed. MoS2 graphene complexes show improvement in the efficiency of adsorption of thiophene on the catalyst edge. Both hydrogenation and direct desulfurization pathways are presented on pristine MoS2 clusters as well as under typical hydrodesulfurization conditions.