摘要
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.
A density functional theory （DFF） study has been conducted to investigate the catalyst reactivity of Pd/ Au（100） surface, which is well performed for the production of vinyl acetate （VAc） from acetoxylation of ethylene. The adsorption and co-adsorption properties of the key reagents as well as their coupling reaction were calcu-lated and discussed. Ethylene species are weakly chemical-adsorbed on Pd/Au（100） with w- and 2or- configuration; while acetate species are strongly chemical-absorbed on the surface with Pd-Au and Pd-Pd hi-dentate configurations. As the number of first-neighbor Pd atoms decreases, the molecular orbitals of the two reagents become closer due to the adsorption of.the Pd/Au（100）. The gap between the highest occupied and the lowest unoccupied molecular orbital （HOMO-LUMO-gap） becomes larger in the co-adsorption system, which implies that the electron transfer from HOMO to LUMO becomes more difficult. Energy barrier results of the elementary reaction are in good agreement with the previous molecular orbital analysis, demonstrating that more first-neighbor Pd atoms on Pd/Au （100） surface is not favor of the VAc synthesis.
出处
《分子催化》
EI
CAS
CSCD
北大核心
2013年第2期173-180,共8页
Journal of Molecular Catalysis(China)
