合成气中的硫对Ni(111)表面上CO甲烷化的影响

EFFECT OF SULFUR IN SYNGAS ON CO METHANATION ON Ni(111)SURFACE

基于密度泛函理论的方法,对硫覆盖度为0.22的Ni(111)表面上合成气甲烷化的反应机理进行了研究.描述了Ni(111)含硫表面上各种反应分子和可能中间体的稳定构型,相对于Ni(111)表面,反应物CO的吸附能降低了0.30eV,而重要中间体CH2,CH3和HCO吸附能分别下降了0.11eV,0.24eV和0.23eV.得出在0.22mL硫覆盖度的Ni(111)表面上CO通过加氢反应生成甲烷的最优路径为:CO+4H→HCO+3H→CH_2O+2H→CH_3O+H→CH_3+H→CH_4,而在Ni(111)洁净表面甲烷化时,HCO的进一步加氢则容易生成CHOH,这说明表面S原子的存在使CO甲烷化的路径发生了改变.

Based on DFT method,the purpose of this study is to investigate the reaction mechanism during the CO methanation on the Ni（111）surface with sulfur coverage of 0.22.The equilibrium geometries of reactants and all possible intermediates are represented,and the possible elementary reactions from HCO species are listed.Compared with clean Ni（111）surface,the adsorption energy of CO on sulfide surface decreased 0.3eV,such as CH_2,CH_3 and HCO,the adsorption energy of these important intermediates decreased respectively 0.11 eV,0.24 eV and 0.23 eV.By analyzing the energy barriers of six reaction paths on the Ni（111）surface with sulfur coverage of 0.22 mL,it is concluded that the favorable reaction path of CO methanationis：CO＋4H→HCO＋3H→CH_2O＋2H→CH_3O＋ H →CH_3 ＋ H→CH_4.However,on clean Ni（111）surface the HCO species tend to be hydrogenated by forming CHOH,this change of methanation route is due to the effect of sulfur.