物理化学学报 >> 2008, Vol. 24 >> Issue (11): 2025-2031.doi: 10.3866/PKU.WHXB20081115

研究论文 上一篇    下一篇

甲醛在CeO2(111)表面吸附的密度泛函理论研究

蒋仕宇; 滕波涛; 鲁继青; 刘雪松; 杨培芳; 杨飞勇; 罗孟飞   

  1. 浙江师范大学物理化学研究所, 浙江省固体表面反应化学重点实验室, 浙江 金华 321004
  • 收稿日期:2008-05-14 修回日期:2008-07-21 发布日期:2008-11-10
  • 通讯作者: 滕波涛 E-mail:tbt@zjnu.cn

A Density Functional Theory Study of Formaldehyde Adsorption on CeO2(111) Surface

JIANG Shi-Yu; TENG Bo-Tao; LU Ji-Qing; LIU Xue-Song; YANG Pei-Fang; YANG Fei-Yong; LUO Meng-Fei   

  1. Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua 321004, Zhejiang Province, P. R. China
  • Received:2008-05-14 Revised:2008-07-21 Published:2008-11-10
  • Contact: TENG Bo-Tao E-mail:tbt@zjnu.cn

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摘要： 采用基于第一性原理的密度泛函理论和周期平板模型, 研究了甲醛在以桥氧为端面的CeO2(111)稳定表面上的吸附行为. 通过对不同覆盖度, 不同吸附位的甲醛吸附构型、吸附能及电子态密度的分析发现, 甲醛在CeO2(111)表面存在化学吸附与物理吸附两种情况. 化学吸附结构中甲醛的碳、氧原子分别与表面的氧、铈原子发生相互作用, 形成CH2O2物种; 吸附能随着覆盖度的增加而减小. 与自由甲醛分子相比, 物理吸附的甲醛构型变化不大, 其吸附能较小. 利用CNEB(climbing nudged elastic band)方法计算了甲醛在CeO2(111)表面的初步解离反应活化能(约1.71 eV), 远高于甲醛脱附能垒, 这与甲醛在清洁CeO2(111)表面程序升温脱附实验中产物主要为甲醛的结果相一致.

关键词: 二氧化铈, 甲醛, 密度泛函理论, 周期平板模型, 态密度

Abstract: Formaldehyde adsorption on CeO2(111) surface terminated by bridge O atom was systematically investigated by periodic density functional theory (DFT) with the generalized gradient approximation (GGA) developed by projector augmented wave (PAW). According to the analysis of the optimized structures of adsorbed formaldehyde, adsorption energies at different coverages and different adsorption sites, it is found that there are two types of adsorbed formaldehyde on CeO2(111) surface. For the chemisorbed formaldehyde, the carbon and oxygen atoms of formaldehyde interact with the corresponding oxygen and cerium atoms of CeO2(111) surface, and form chemical bonds. The adsorption energies decrease with the increase of formaldehyde coverage on CeO2(111) surface. However, the optimized structures of the physically adsorbed formaldehyde are almost unchanged compared with the free formaldehyde molecule. The corresponding adsorption energies are generally lower than -27 kJ·mol-1. It is learned from the density of states of the chemically adsorbed formaldehyde that the energy of the highest occupied molecular orbital (HOMO), nO, shifts downward greatly, while the oxygen electrons of CeO2(111) surface transfer to the lowest unoccupied molecular orbital (LUMO) of formaldehyde, π*CO . Therefore, newCe—O2 bonds formand the corresponding C—O1 bonds of formaldehyde are elongated. Based on the investigation above, the potential energy for the first H atom dissociation reaction of formaldehyde was calculated using climbing nudged elastic band (CNEB) to be ca 1.71 eV, which was much higher than that of the barrier for the desorption of formaldehyde, 0.80 eV. It is indicated that the main reaction for the temprature programmed desorption (TPD) of formaldehyde over clean CeO2 (111) surface is the desorption of formaldehyde instead of its dissociation reaction, which is well consistent with experimental data.

Key words: Ceria, Formaldehyde, Density functional theory, Periodical slab model, Density of states

MSC2000: 

  • O641