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采用密度泛函理论方法系统地研究了Pd/Au(100)表面上乙烯气相氧化法合成乙酸乙烯酯的催化活性.对关键反应物种在该表面的吸附、共吸附性质及耦合基元反应进行了计算和讨论.乙烯在Pd/Au(100)表面上存在π-,2σ-两种稳定吸附构型,为弱化学吸附;乙酸根物种存在Pd-Au与Pd-Pd两种二位啮合(bi-dentate)构型,为强化学吸附.Pd/Au(100)表面的吸附作用使两个关键反应物种分子轨道能量靠近.共吸附构型中最高占据和最低未占据分子轨道的能级差(HOMO-LUMO-gap)随表面相邻Pd原子数目的增多而增大,表明由HOMO向LUMO分子轨道发生电子转移的能力变弱.耦合基元反应过渡态能垒的分析结果与HOMO-LUMO-gap定性分析结果一致,说明连续相邻的表面Pd原子不利于反应的进行.
The catalytic activity of ethylene gas-phase oxidation on the surface of Pd / Au (100) was systematically investigated by means of density functional theory. The adsorption, co-adsorption and coupling reaction of the key reactive species on the surface were investigated Calculated and discussed. There are π-, 2σ- stable adsorption configurations on the Pd / Au (100) surface and weak chemisorption. There are two kinds of bi- -dentate structure, which is a strong chemisorption.Adsorption on the Pd / Au (100) surface brings the molecular orbital energies of the two key species closer together.Homogeneous and lowest unoccupied molecular orbital in the co-adsorption configuration -LUMO-gap) increases with the increase of the number of Pd atoms on the surface, which indicates that the ability of electron transfer from HOMO to LUMO molecular orbitals becomes weaker.The analysis results of the energy barrier of the transition state between the coupling elementary reactions and HOMO-LUMO-gap Qualitative analysis of the results are consistent, indicating that the continuous adjacent Pd atoms on the surface is not conducive to the reaction.