Vinyl Chloride Selectivity during Epoxidation on Oxygen Pre-adsorbed Ag(100): A Density-Functional Theory Study

Vinyl chloride selectivity during epoxidation on an atomic oxygen pre-adsorbed Ag(100) surface using density functional theory (DFT) with the periodic slab model was investigated. The reaction mechanism is a two-step process where chloroethylene oxametallacycle intermediate (OMMC) is first formed and then converted to the products. Because of the asymmetry of vinyl chloride, two competitive reaction pathways are evident. The reaction energies and the activation energies of the processes were determined by the DFT calculations. Compared with the reaction activity energy, in one pathway the formation of chloroethylene epoxide (CE) is more favorable than the formation of chloroacetaldehyde (CA) whereas in the other pathway, the formation of CA is more favorable than the formation of CE and acetyl chloride. To further understand the reason for the selectivity difference in these different paths the projected density of states of the C atom and the Ag atom involved in the OMMC was calculated.

摘要： 采用密度泛函理论和周期性平板模型对氯乙烯在预吸附氧原子的 Ag(100) 面上选择性环氧化反应进行了模拟计算. 结果表明, 该反应首先由反应物生成中间体, 再由中间体生成产物. 由于氯乙烯是一种不对称的分子, 所以该反应存在两种可能的途径. 比较反应活化能可以发现, 在一个反应通道中环氧氯乙烷要比氯乙醛的生成更容易; 而在另一反应通道中, 氯乙醛要易于环氧氯乙烷和乙酰氯的生成. 同时还研究了中间体中碳原子和银原子的投影态密度 (PDOS), 以期更深入地了解两种不同反应途径活化能差异的原因.

The mechanism and projected density of states of the vinyl chloride epoxidation reaction were investigated by periodic density functional theory. The detailed selective oxidation mechanism for the asymmetric molecules was explored.Figure optionsDownload as PowerPoint slide