催化学报

催化学报 ›› 2009, Vol. 30 ›› Issue (12): 1269-1275.

• 研究论文 • 上一篇    下一篇

甲烷在清洁 Pd(111) 及氧改性的 Pd(111) 表面解离的密度泛函理论研究

吕存琴1,2, 凌开成1, 王贵昌3   

  1. 1 太原理工大学化学化工学院, 山西太原 030024; 2 山西大同大学化学化工学院, 山西大同 037009; 3 南开大学化学学院, 天津 300071;
  • 收稿日期:2009-12-25 出版日期:2009-12-25 发布日期:2013-09-29

Density Functional Theoretical Study of Decomposition of Methane on Clean Pd(111) and Oxygen-Modified Pd(111) Surfaces

LÜ Cun-Qin12, LING Kai-Cheng1, WANG Gui-Chang3   

  1. 1College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China; 2College of Chemistry and Chemical Engineering, Shanxi Datong University, Datong 037009, Shanxi, China; 3College of Chemistry, Nankai University, Tianjin 300071, China;
  • Received:2009-12-25 Online:2009-12-25 Published:2013-09-29

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摘要： 采用广义梯度近似 (GGA) 的密度泛函理论 (DFT) 并结合平板模型, 研究了 CH4 在清洁 Pd(111) 及 O 改性的 Pd(111) 表面发生 C朒 键断裂的反应历程. 优化了裂解过程中反应物、过渡态和产物的几何构型, 获得了反应路径上各物种的吸附能及反应的活化能. 结果表明, CH4 采用一个 H 原子指向表面的构型在 Pd(111) 表面的顶位吸附, CH3 的最稳定的吸附位置为顶位, OH, O 和 H 的最稳定吸附位置均为面心立方. CH4 在清洁 Pd(111) 表面裂解的活化能为 0.97 eV, 低于它在 O 原子改性 (O 没有参与反应) 的 Pd(111) 表面的活化能 1.42 eV, 说明表面氧原子抑制了 CH4 中 C朒 键的断裂. 当亚表面 O 原子和表面 O 原子 (O 参与反应) 共同存在时, C朒 键断裂的活化能为 0.72 eV, 低于只有表层氧存在时的活化能 (1.43 eV), 说明亚表面的 O 原子对 CH4 分子的活化具有促进作用. CH4 在 O 原子改性的 Pd(111) 表面裂解生成 CH3 和 H, 以及生成 CH3 和 OH 的反应活化能分别为 1.42 和 1.43 eV, 说明 CH4 在 O 原子改性的 Pd(111) 表面发生这两种反应的难易程度相当.

Abstract: The reaction pathway of C–H bond breaking of methane on the clean Pd(111) and O-modified Pd(111) surfaces was investigated by the first-principles density functional theory generalized gradient approximation calculations with the slab model. Geometries of reactants, transition states, and products were calculated. Adsorption energy of possible species and activation energy barriers of the reaction were also obtained. The calculated results show that methane favors such a configuration that one hydrogen points towards the surface in the top site. Methyl is adsorbed in the top site, and hydroxyl, oxygen, and hydrogen are all adsorbed in the fcc site. On the clean Pd(111) surface, the activation energy of 0.97 eV is smaller than that of 1.42 eV in the case of oxygen-modified (oxygen atom acts as a “spectator”) Pd(111) surface, which indicates that the presence of oxygen atom inhibited the C–H bond cleavage. Compared with the case that only the surface oxygen atom exists (oxygen atom participates in the reaction), the activation energy decreased from 1.43 to 0.72 eV when the subsurface oxygen atom exists. This suggests that the subsurface oxygen atom promotes the activation of methane molecule. On the oxygen-modified Pd(111), the activation energy of the reactions forming methyl and hydrogen, and methyl and hydroxyl is 1.42 and 1.43 eV, respectively, which indicates that the reaction possibility is equivalent.

Key words: methane, decomposition, palladium, oxygen atom modification, density functional theory, generalized gradient approximation, slab model