Sun Ben, Wang Gui-Chang
Frontiers Science Center for New Organic Matter, Tianjin key Lab and Molecule-based Material Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China.
Phys Chem Chem Phys. 2023 Nov 15;25(44):30612-30626. doi: 10.1039/d3cp04362b.
The direct epoxidation of propylene is one of the most important selective oxidation reactions in industry. The development of high-performance copper-based catalysts is the key to the selective oxidation technology and scientific research of propylene. The mechanism of propylene's partial oxidation catalyzed by Cu(111) under different oxygen coverage conditions was studied using density functional theory calculations and microkinetic modeling. We report here in detail two parallel reaction pathways: dehydrogenation and epoxidation. The transition states and energy distributions of the intermediates and products were calculated. The present results showed that propylene oxide (PO) selectivity was high under low oxygen coverage, and increasing the oxygen coverage would decrease the PO selectivity but increase the PO activity, and there was an inverse relationship between PO selectivity and activity. Increasing oxygen coverage would reduce the energy barrier for the C-O bond formation of CHO due to the weaker adsorption strength of CH, thus decreasing the PO formation selectivity. On the other hand, increasing oxygen coverage would reduce the energy barrier for the possible reaction steps of propylene epoxidation in general, and thus increasing the catalytic activity. It might be proposed that the active site for propylene epoxidation is the metallic copper or partially oxidized copper in terms of the change of PO formation selectivity with oxygen coverage.
丙烯的直接环氧化是工业中最重要的选择性氧化反应之一。开发高性能铜基催化剂是丙烯选择性氧化技术和科研的关键。利用密度泛函理论计算和微观动力学模型研究了不同氧覆盖条件下Cu(111)催化丙烯部分氧化的机理。在此，我们详细报道了两条平行反应途径：脱氢和环氧化。计算了中间体和产物的过渡态及能量分布。目前的结果表明，在低氧覆盖下环氧丙烷（PO）选择性较高，增加氧覆盖会降低PO选择性但提高PO活性，且PO选择性和活性之间存在反比关系。增加氧覆盖会由于CH吸附强度较弱而降低CHO形成C-O键的能垒，从而降低PO生成选择性。另一方面，增加氧覆盖总体上会降低丙烯环氧化可能反应步骤的能垒，从而提高催化活性。从PO生成选择性随氧覆盖的变化来看，可能提出丙烯环氧化的活性位点是金属铜或部分氧化的铜。
