Li Hao, Abraham Christina Susan, Anand Megha, Cao Ang, Nørskov Jens K
Catalysis Theory Center, Department of Physics, Technical University of Denmark, Lyngby 2800, Denmark.
Advanced Institute for Materials Research (WPI-AIMR), Tohoku University, Sendai 980-8577, Japan.
J Phys Chem Lett. 2022 Mar 10;13(9):2057-2063. doi: 10.1021/acs.jpclett.2c00257. Epub 2022 Feb 25.
Propylene oxide (PO) is an important chemical. So far, its synthesis protocol relies on expensive oxidants. In contrast, direct epoxidation of propylene (DEP) using molecular oxygen is considered ideal for PO synthesis. Unfortunately, DEP has not met industrial demands due to the low propylene conversion and high side-product selectivity for known catalysts. Instead of a thermal process using molecular oxygen, electrolytic propylene oxidation can synthesize PO at room temperature, using the atomic oxygen generated from water-splitting. Herein, using density functional theory, surface Pourbaix analysis, scaling relation analysis, and microkinetic modeling, we show that (i) propylene epoxidation is facile on weak-binding catalysts if reactive atomic oxygen preexists; (ii) electrolytic epoxidation is facile to provide atomic oxygen for epoxidation, while hydroperoxyl formation does not overwhelm the epoxidation process at the potential of interest; (iii) propylene dehydrogenation is a competing step that forms side products. Finally, we discuss the opportunities and challenges of this green PO synthesis method.
环氧丙烷（PO）是一种重要的化学品。到目前为止，其合成方案依赖于昂贵的氧化剂。相比之下，使用分子氧对丙烯进行直接环氧化（DEP）被认为是合成PO的理想方法。不幸的是，由于已知催化剂的丙烯转化率低和副产物选择性高，DEP尚未满足工业需求。与使用分子氧的热过程不同，电解丙烯氧化可以在室温下利用水分解产生的原子氧合成PO。在此，我们使用密度泛函理论、表面Pourbaix分析、标度关系分析和微观动力学建模表明：（i）如果存在活性原子氧，丙烯环氧化在弱结合催化剂上是容易的；（ii）电解环氧化易于为环氧化提供原子氧，而过氧羟基的形成在感兴趣的电位下不会使环氧化过程不堪重负；（iii）丙烯脱氢是形成副产物的竞争步骤。最后，我们讨论了这种绿色PO合成方法的机遇和挑战。
