307化 学 学 报 Abstract Recently, transition metal sulfides (TMS) have played an important role in many catalytic reactions. In particular, they are widely used in the petrochemical industry, such as the hydrodesulfurization (HDS) and the hydrodenitrogenation (HDN) processes. In this work, density functional theory (DFT) and coupled cluster theory [CCSD(T)] calculations were used to study the niobium-mixed di-nuclear molybdenum sulfide clusters NbMoS n -/0 (n=3~7). In our calculations, their ground-state structures were determined and the effects of doping metal, adjusting the sulfur content (n) and changing the charge states of clusters were discussed on the geometries, electronic structures and chemical bonding of NbMoS n -/0 (n= 3~7). NbMoS n -/0 (n=3~7) clusters can be viewed as linking different sulfur ligands to the NbMoS 2 four-membered rings. Among them, diverse poly-sulfur ligands, such as bridging S 2 , terminal S 2 and terminal S 3 groups, emerged in the sulfur-rich clusters. Generalized Koopmans' Theorem was employed to predict the vertical detachment energies (VDEs), and simulate the corresponding anionic photoelectron spectra (PES). The first VDEs (VDE 1st ) of NbMoS n -(n=3~6) increased gradually as a function of n, and then decreased suddenly when the sulfur content (n) reached 7. The VDE 1st reached the maximum by 4.69 eV when the sulfur content equaled to 6. The driving forces (-ΔG) of the reduction reactions between NbMoS n -/0 (n =3~7) and H 2 were evaluated. The NbMoS-anion with the terminal 2 2 S -group yielded the negative value of ΔG, which indicated that the reaction is thermodynamically favored even at the room temperature. We predicted that doping niobium into the molybdenum sulfides may improve the emergence of S 2 group which may be helpful in producing the coordinatively unsaturated sites (CUS) under the H 2 /H 2 S atmosphere. Molecular orbital analyses are performed to improve our understanding on the structural evolution and the chemical bonding of NbMoS n -/0 (n=3~7) clusters.
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