Madsen Monica R, Rønne Magnus H, Heuschen Marvin, Golo Dusanka, Ahlquist Mårten S G, Skrydstrup Troels, Pedersen Steen U, Daasbjerg Kim
Carbon Dioxide Activation Center (CADIAC), Interdisciplinary Nanoscience Center, Department of Chemistry, Aarhus University, Gustav Wieds Vej 14, 8000 Aarhus C, Denmark.
Department of Theoretical Chemistry & Biology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, 10691 Stockholm, Sweden.
J Am Chem Soc. 2021 Dec 8;143(48):20491-20500. doi: 10.1021/jacs.1c10805. Epub 2021 Nov 23.
Urgent solutions are needed to efficiently convert the greenhouse gas CO into higher-value products. In this work, -Mn(bpy)(CO)Br (bpy = 2,2'-bipyridine) is employed as electrocatalyst in reductive CO conversion. It is shown that product selectivity can be shifted from CO toward HCOOH using appropriate additives, i.e., EtN along with PrOH. A crucial aspect of the strategy is to outrun the dimer-generating parent-child reaction involving -Mn(bpy)(CO)Br and [Mn(bpy)(CO)] and instead produce the Mn hydride intermediate. Preferentially, this is done at the first reduction wave to enable formation of HCOOH at an overpotential as low as 260 mV and with faradaic efficiency of 59 ± 1%. The latter may be increased to 71 ± 3% at an overpotential of 560 mV, using 2 M concentrations of both EtN and PrOH. The nature of the amine additive is crucial for product selectivity, as the faradaic efficiency for HCOOH formation decreases to 13 ± 4% if EtN is replaced with EtNH. The origin of this difference lies in the ability of EtN/PrOH to establish an equilibrium solution of isopropyl carbonate and CO, while with EtNH/PrOH, formation of the diethylcarbamic acid is favored. According to density-functional theory calculations, CO in the former case can take part favorably in the catalytic cycle, while this is less opportune in the latter case because of the CO-to-carbamic acid conversion. This work presents a straightforward procedure for electrochemical reduction of CO to HCOOH by combining an easily synthesized manganese catalyst with commercially available additives.
需要紧急解决方案来有效地将温室气体一氧化碳转化为更高价值的产品。在这项工作中，-Mn(bpy)(CO)Br（bpy = 2,2'-联吡啶）被用作还原一氧化碳转化的电催化剂。结果表明，使用适当的添加剂，即EtN和PrOH，可以使产物选择性从一氧化碳转向甲酸。该策略的一个关键方面是超越涉及-Mn(bpy)(CO)Br和[Mn(bpy)(CO)]的二聚体生成的母子反应，而是生成锰氢化物中间体。优先在第一个还原波处进行此操作，以在低至260 mV的过电位下形成甲酸，法拉第效率为59±1%。使用2 M浓度的EtN和PrOH，在560 mV的过电位下，后者可提高到71±3%。胺添加剂的性质对产物选择性至关重要，因为如果用EtNH代替EtN，甲酸形成的法拉第效率会降至13±4%。这种差异的根源在于EtN/PrOH能够建立碳酸异丙酯和一氧化碳的平衡溶液，而对于EtNH/PrOH，更有利于形成二乙氨基甲酸。根据密度泛函理论计算，在前一种情况下一氧化碳可以顺利参与催化循环，而在后一种情况下则不太合适，因为发生了一氧化碳到氨基甲酸的转化。这项工作通过将易于合成的锰催化剂与市售添加剂相结合，提出了一种将一氧化碳电化学还原为甲酸的直接方法。
