Theoretical Studies On The Ternary Niobium-Molybdenum Sulfide Doped Clusters

Group VB/VIB transition metal sulfides have a wide range of applications in many fields,such as solid lubricants,industrial catalysis,electrode materials,magnetic materials and hydrogen storage and so forth.Particularly,in a series of catalytic reactions,the doped niobium-molybdenum sulfides exhibit a good synergistic effect.In order to further study the factors that affect their catalytic performances,Gas-phase clusters can be used as molecular model to gain the effective information,which may be helpful to provide some theoretical guidance for designing better catalysts with higher activity and selectivity.In this paper,density functional theory(DFT)and coupled cluster theory CCSD(T)calculations were used to study the ternary niobium-molybdenum sulfide doped clusters.Effects of the cluster size,the sulfur content,the doping ratio of Nb and Mo and the charge states on their geometries,electronic structures,chemical bonding and reactivity were investigated.A summary of our work is given as follows:1.Theoretical calculations are carried out to study the niobium-mixed di-nuclear molybdenum sulfide clusters NbMoSrn-/0(n = 3-7).Generalized Koopmans' theorem is applied to predict the vertical detachment energies(VDEs),and simulate the corresponding anionic photoelectron spectra(PES).Our calculations show that NbMoSn-/0(n = 3-7)clusters can be viewed as linking different sulfur ligands to the NbMoS2 four-membered rings.The various sulfide ligands appear successively.In addition,the coordinately unsaturated NbMoSs shows the higher stability and greater Lewis acidity which may indicate better electrophilic ability.2.Theoretical calculations are carried out to investigate the tri-nuclear niobium-molybdenum sulfide clusters NbxMo3-xS62-/-/0/+(x = 1,2).Our calculations show that the NbxMo3-xS62-/-/0/+(x = 1,2)ground states can be viewed as linking different sulfur ligands to the NbxMo3-xS3(x = 1,2)six-membered rings.The remaining three sulfur atoms are attached to the six-membered rings in the form of two terminal S atoms and a caping S atom.We also calculated the vertical detachment energies(VDEs)of the NbMo2S6-and Nb2MoS6-ground state and compared their VDEs values to theMo3S6-and Nb3S6-clusters.3.Based on the work studied above,we carry out an investigation on the reactivity of the Mo2S5 and NbMoS5-clusters with the H2S.Our calculations show that NbMoS5-ground state shows higher reactivity,because the activation energy of the reaction can be significantly reduced.It infers that the reactivity of molybdenum sulfides may be enhanced by doping the niobium atom.Our work may bring some insight into the future improvement of the relevant catalysts.