烷基噻吩在MoS_2团簇上吸附行为的密度泛函理论研究

Density Functional Theory Studies of Alkylthiophene Adsorption on a MoS_2 Cluster

运用密度泛函理论(DFT),采用Mo16S32团簇模型,在PW91/DNP水平上研究了噻吩(TP)及一系列烷基噻吩类硫化物如2-甲基噻吩(2-MT)、3-甲基噻吩(3-MT)、2,3-二甲基噻吩(2,3-DMT)、2,4-二甲基噻吩(2,4-DMT)、2,5-二甲基噻吩(2,5-DMT)及3,4-二甲基噻吩(3,4-DMT)等在加氢脱硫催化剂MoS2上的吸附行为.结果表明,在η1S吸附构型中,Mo16S32团簇对烷基噻吩吸附能力的顺序为2,5-DMT>2,4-DMT≈2,3-DMT>2-MT>3,4-DMT>3-MT>TP.通过键长、Mayer键级、Mulliken电荷分析可知,当噻吩环的2-或5-位不含甲基时,吸附能随硫原子电荷密度的增加而增大;2-或5-位含甲基时,甲基与团簇上相邻的Mo原子发生了弱的相互作用,使吸附能增大;虽然2,5-DMT的2-和5-位均含有甲基,但甲基离团簇上相邻的Mo较远,相互作用较小,吸附能较2,3-DMT和2,4-DMT增加的较少.文中还对各硫化物在MoS2催化剂上的加氢脱硫反应进行了讨论.

Adsorption properties of thiophene（TP） and alkylthiophene（2-methylthiophene（2-MT）,3-methylthiophene（3-MT）,2,3-dimethylthiophene（2,3-DMT）,2,4-dimethylthiophene（2,4-DMT）,2,5-dimethylthiophene（2,5-DMT） and 3,4-dimethylthiophene（3,4-DMT）） on a MoS2 catalyst for hydrogenation desulfurization（HDS） have been investigated by the first-principle DFT calculations which were based on a Mo16S32 cluster model and performed with PW91 function and DNP basis set.The calculated interaction energies indicate that the adsorption ability of the Mo16S32 cluster for the alkylthiophene molecules in η1S adsorption mode decreases in the order of 2,5-DMT2,4-DMT≈2,3-DMT2-MT3,4-DMT3-MTTP.According to the bond length,Mayer bond orders and Mulliken charge analysis,the adsorption energies are consistent with the electron density of the sulfur atom for the thiophenic compounds without any substituent in 2-and 5-positions.When 2-or 5-position is replaced by a methyl group,a weak interaction can be found between the methyl and the adjacent Mo atom and the adsorption energies increase compared with above sulfur compounds.For 2,5-DMT in which both 2-and 5-positions are substituted,the distance between the methyl groups and the adjacent Mo atom enlarges,leading weak interactions between them,The adsorption energy of 2,5-DMT on the Mo16S32 cluster does not increase as much as those for 2,4-DMT and 2,3-DMT molecules.The HDS reactions of all the sulfur compounds on the catalyst are also discussed in this paper.