MoS2 single slab as a model for active component of hydrodesulfuration catalyst: a quantum chemical study 1. Molecular and electronic structure of Mo12S24 macromolecule and its adsorption complex with H2S

Abstract

The molecular and electronic structure of Mo12S24 macromolecule as the MoS2 single slab structure was calculated by the density functional theory (DFT) method with the B3P86 hybrid exchange-correlation functional. The results of calculations point to slight relaxation of coordinatively unsaturated Mo and S atoms, which is consistent with the published data. The calculated width of the forbidden band (0.85–0.98 eV) is comparable with the experimental value (1.30 eV) and similar to that obtained from DFT calculations with periodic boundary conditions (0.89 eV). The surface Mo centers in the Mo12S24 macromolecule are more reduced than the internal (MoIV) atoms. In order to characterize the adsorption capacity of coordinatively unsaturated Mo centers, a Mo12S24·6H2S adsorption complex was calculated. The structure and energy characteristics of the adsorption complex point to a weak donor-acceptor interaction of the π-lone pair of H2S molecule with the surface (reduced) Mo centers. The active center of thiophene hydrodesulfuration catalysts is formed as a result of the oxidative addition of hydrogen followed by occlusion of hydrogen into the MoS2 matrix.