Department of Chemical Engineering, Middle East Technical University, 06800, Ankara, Turkey and Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, 5600 MB, Eindhoven, The Netherlands.
Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, 5600 MB, Eindhoven, The Netherlands.
Phys Chem Chem Phys. 2018 Nov 7;20(41):26681-26687. doi: 10.1039/c8cp04210a. Epub 2018 Oct 15.
Propylene oxide (PO) is one of the 50 most produced chemicals according to the production volume. Environmental and economic drawbacks of conventional PO production processes necessitate new production methods. Among the new production alternatives, direct epoxidation of propylene to propylene oxide by molecular oxygen is a highly desired method and seen as the holy grail of propylene epoxidation studies. In this study, the propylene epoxidation mechanism on an AgO(001) surface is investigated computationally by means of density functional theory (DFT) calculations using the Vienna Ab-initio Simulation Package (VASP). A perfect AgO(001) surface and a surface with one O vacancy are utilized for this purpose. It is found that propylene oxide can be directly formed on an AgO(001) surface whether there is an oxygen vacancy or not. The rate controlling step is PO desorption from both surfaces. PO isomers, i.e. acetone and propanal, can also be formed on these surfaces. However, activation barriers do exist for these molecules. Direct allyl formation on the AgO(001) surface is found to be unfavorable unlike what is proposed in the literature. On the other hand, it is observed that an allyl radical can be formed either via an oxametallocycle path or after the formation of propylene oxide. In fact, the discovered allyl radical formation pathway from propylene oxide is found as the most probable successive reaction pathway because of the high desorption barrier of PO.
环氧丙烷（PO）是根据产量排名前 50 的最常见化学品之一。传统的 PO 生产工艺在环境和经济方面存在缺陷，因此需要开发新的生产方法。在新的生产方法中，丙烯直接用分子氧环氧化生成 PO 是一种非常理想的方法，被视为丙烯环氧化研究的圣杯。在这项研究中，通过使用维也纳从头算模拟包（VASP）的密度泛函理论（DFT）计算，研究了在 AgO(001)表面上丙烯环氧化的反应机理。为此目的，使用了完美的 AgO(001)表面和具有一个 O 空位的表面。研究发现，无论是否存在氧空位，PO 都可以直接在 AgO(001)表面上形成。控制步骤是从两个表面上脱附 PO。这些表面上也可以形成 PO 的异构体，即丙酮和丙醛。然而，这些分子存在着活化能垒。与文献中提出的观点不同，在 AgO(001)表面上直接形成丙烯是不利的。另一方面，观察到可以通过氧杂环戊二烯途径或在 PO 形成后在 AgO(001)表面上形成烯丙基自由基。实际上，由于 PO 的脱附势垒较高，发现从 PO 形成的烯丙基自由基的形成途径是最可能的连续反应途径。
