Promoting Selective Generation of Formic Acid from CO 2 Using Mn(bpy)(CO) 3 Br as Electrocatalyst and Triethylamine/Isopropanol as Additives

作者：Monica R. Madsen, Magnus H. Rønne, Marvin Heuschen, Dusanka Golo, Mårten S. G. Ahlquist, Troels Skrydstrup, Steen Uttrup Pedersen, Kim Daasbjerg · 发表于：Journal of the American Chemical Society · 年份：2021 · DOI：10.1021/jacs.1c10805 · 被引用次数：68 · 研究领域：CO2 Reduction Techniques and Catalysts、Carbon dioxide utilization in catalysis、Ionic liquids properties and applications

Urgent solutions are needed to efficiently convert the greenhouse gas CO 2 into higher-value products. In this work, fac -Mn(bpy)(CO) 3 Br (bpy = 2,2′-bipyridine) is employed as electrocatalyst in reductive CO 2 conversion. It is shown that product selectivity can be shifted from CO toward HCOOH using appropriate additives, i.e., Et 3 N along with i PrOH. A crucial aspect of the strategy is to outrun the dimer-generating parent-child reaction involving fac -Mn(bpy)(CO) 3 Br and [Mn(bpy)(CO) 3 ] − 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 Et 3 N and i PrOH. The nature of the amine additive is crucial for product selectivity, as the faradaic efficiency for HCOOH formation decreases to 13 ± 4% if Et 3 N is replaced with Et 2 NH. The origin of this difference lies in the ability of Et 3 N/ i PrOH to establish an equilibrium solution of isopropyl carbonate and CO 2, while with Et 2 NH/ i PrOH, formation of the diethylcarbamic acid is favored. According to density-functional theory calculations, CO 2 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 2 -to-carbamic acid conversion. This work presents a straightforward procedure for ...