CO在Pt低指数面上吸附行为的理论研究

用密度泛函理论(DFT)中的广义梯度近似(GGA)方法对CO-Pt低指数面吸附体系进行了结构优化, 并对吸附体系的吸附热、C—O键和C—Pt键的键长、布居数分析、电子态密度进行了研究. 计算结果表明, 在0.25 ML(monolayer)的覆盖率下, CO最容易在Pt(100)晶面的桥位、Pt(110)晶面的短桥位、Pt(111)晶面的hcp三重位吸附, 吸附热分别达到了2.11、2.37、1.96 eV; CO在吸附成键过程中伴有电子在CO分子和Pt之间的转移. 吸附后, C—O键被削弱, 键长变长, 金属内部的作用亦被削弱, 其表层Pt 原子的布居数明显降低; 态密度分析表明, CO在吸附过程中, 其4σ、1π、5σ、2π轨道均参与成键.

Theoretical Study on the Behavior of CO Chemisorption on Low-index Platinum Surfaces

Generalized gradient approximation (GGA) of the density function theory (DFT) was applied to investigate the structure of CO chemisorption on low-index platinum surfaces. Many properties including chemisorption energy, bond lengths of C—O and C—Pt, population analysis, and density of state were calculated by CASTEP-module of Materials Studio package. It was shown that when the coverage was 0.25 ML (monolayer), the preference sites of CO chemisorption on Pt were the bridge site of Pt(100), short bridge site of Pt(110) and hcp hollowsite of Pt(111), the chemisorption energies were 2.11, 2.37 and 1.96 eV, respectively. There existed electron transfer between CO molecule and Pt atoms during the adsorption. After adsorption, C—O bond was weaken, its bond length was longer than before, the interactions of inner Pt atoms were weaken too. The population of the first layer Pt atoms on surface was reduced obviously. According to DOS analysis, some mixing of the 4σ, 1π, 5σ, 2π molecular orbitals with metal states was observed.