物理化学学报 >> 2005, Vol. 21 >> Issue (12): 1343-1346.doi: 10.3866/PKU.WHXB20051203

研究论文 上一篇    下一篇

N2在Pd金属表面的吸附行为

朱瑜;蒋刚;于桂凤;朱正和;王和义;傅依备   

  1. 四川大学原子与分子物理研究所, 成都 610065;西南核物理与化学研究所, 四川 绵阳 621900
  • 收稿日期:2005-05-09 修回日期:2005-06-16 发布日期:2005-12-15
  • 通讯作者: 蒋刚 E-mail:gjiang@scu.edu.cn

Adsorption Behavior of N2 on Pd Surface

ZHU Yu;JIANG Gang;YU Gui-Feng;ZHU Zheng-He;WANG He-Yi;FU Yi-Bei   

  1. Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065; Southwest Institute of Nuclear Physics and Chemistry, Mianyang 621900
  • Received:2005-05-09 Revised:2005-06-16 Published:2005-12-15
  • Contact: JIANG Gang E-mail:gjiang@scu.edu.cn

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摘要： 对Pd原子采用相对论有效原子实势(RECP/SDD), N原子采用AUG-cc-pVTZ基函数, 利用B3LYP方法计算了PdN和PdN2分子的微观结构以及不同温度下的热力学函数. 以气态分子总能量中的振动能EV代替该分子处于固态时的振动能量, 以电子运动和振动运动熵SEV代替分子处于固态的熵的近似方法, 计算了不同温度下金属Pd与N2反应的ΔHӨ、ΔSӨ、ΔGӨ及氮化反应平衡压力, 导出了氮化反应平衡压力与温度的关系. 由此可看出, 在常压及298.15～998.15 K温度条件下, N2在金属Pd表面的吸附过程以Pd(s) + N2 = PdN2(s)反应进行. 计算得出在标准条件下, PdN(s)的生成焓为254.37 kJ·mol-1, PdN2(s)的生成焓为－80.59 kJ·mol-1. 并与Pd氢化反应平衡压力比较, 得到平衡常数Kp(N2)比Kp(H2)约小两个数量级, 说明N2较难被金属Pd表面吸附, 在热力学上有利于氢置换氮.

关键词: PdN, PdN2, 密度泛函理论, 热力学函数, 平衡压力, 吸附行为

Abstract: Based on the relativistic effective core potential (RECP/SDD) for Pd atom and AUG-cc-pVTZ basis function for N atom, the structure of PdN and PdN2 have been optimized using B3LYP method, and the thermodynamic functions for PdN and PdN2 have been calculated. The vibrational energy, electronic and vibrational entropy of the molecules in their solid states are assumed, ΔHӨ, ΔSӨ and ΔGӨ and nitrogen equilibrium pressures of the nitrogenating reaction have been calculated based on this approximation. It is deduced that at 1.01325×105 Pa and 298.15～998.15 K, adsorption of N2 on Pd surface proceeds as Pd(s) + N2 = PdN2(s). The formation enthalpy for PdN(s) at 298.15 K is 254.37 kJ·mol-1, and the formation enthalpy for PdN2(s) at 298.15 K is －80.59 kJ·mol-1. The nitrogen equilibrium pressure is about 100 times of the hydrogen equilibrium pressure, so it is difficult for Pd to adsorb N2.

Key words: PdN, PdN2, Density functional theory, Thermodynamic function, Equilibrium pressure, Adsorption behavior