In a comparative study of the electrocatalytic CO2 reduction, cobalt meso‐tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In ...the former case, employing N,N‐dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO2 becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO2. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone.
Heterogeneous vs. homogeneous: When cobalt meso‐tetraphenylporphyrin (CoTPP) is immobilized on carbon nanotubes, a remarkably enhanced catalytic activity in CO2 electroreduction is observed, with CoITPP− serving as the active species. The simple approach for heterogenization enables facile screening and evaluation of molecular catalysts under heterogeneous conditions.
The selective and efficient reduction of carbon dioxide represents a key solution to producing non‐fossil‐fuel‐based feedstocks for the chemical industry, while alleviating the increasing atmospheric ...concentration of this greenhouse gas. A variety of catalytic methods for the CO2 reduction reaction (CO2RR) have been developed, including hydrogenations and electrochemical or photochemical reductions. For many of the most significant breakthroughs reported in the last decade, we realized that amines or closely related functional groups play a critical role for such transformations, and in several cases, are directly associated with the catalyst as a pendant group. Amines play multiple roles, such as CO2 trapping agents, proton shuttles, electron donors, or facilitators of CO2 reductions through formamide derivatives. In this Viewpoint, we compile some of these recent findings, and discuss their significance in a broader context in an attempt to provide guidelines for the design of new catalysts with enhanced activity and selectivity.
Within the last decade, several of the most significant breakthroughs in the homogeneous electrochemical or photochemical reduction and hydrogenation of carbon dioxide have been driven by the introduction of amines or amine‐derived moieties in the reaction mixture. These amines play multiple roles, which are discussed herein to provide guidelines for the design of new catalysts with enhanced activity and selectivity.
Electrocatalysis is a promising tool for utilizing carbon dioxide as a feedstock in the chemical industry. However, controlling the selectivity for different CO2 reduction products remains a major ...challenge. We report a series of manganese carbonyl complexes with elaborated bipyridine or phenanthroline ligands that can reduce CO2 to either formic acid, if the ligand structure contains strategically positioned tertiary amines, or CO, if the amine groups are absent in the ligand or are placed far from the metal center. The amine-modified complexes are benchmarked to be among the most active catalysts for reducing CO2 to formic acid, with a maximum turnover frequency of up to 5500 s–1 at an overpotential of 630 mV. The conversion even works at overpotentials as low as 300 mV, although through an alternative mechanism. Mechanistically, the formation of a Mn–hydride species aided by in situ protonated amine groups was determined to be a key intermediate by cyclic voltammetry, 1H NMR, DFT calculations, and infrared spectroelectrochemistry.
Significant efforts have been devoted over the last few years to develop efficient molecular electrocatalysts for the electrochemical reduction of carbon dioxide to carbon monoxide, the latter being ...an industrially important feedstock for the synthesis of bulk and fine chemicals. Whereas these efforts primarily focus on this formal oxygen abstraction step, there are no reports on the exploitation of the chemistry for scalable applications in carbonylation reactions. Here we describe the design and application of an inexpensive and user-friendly electrochemical set-up combined with the two-chamber technology for performing Pd-catalysed carbonylation reactions including amino- and alkoxycarbonylations, as well as carbonylative Sonogashira and Suzuki couplings with near stoichiometric carbon monoxide. The combined two-reaction process allows for milligram to gram synthesis of pharmaceutically relevant compounds. Moreover, this technology can be adapted to the use of atmospheric carbon dioxide.Electroreduction of CO
to CO is a potential valorisation pathway of carbon dioxide for fine chemicals production. Here, the authors show a user-friendly device that couples CO
electroreduction with carbonylation chemistry for up to gram scale synthesis of pharmaceuticals even under atmospheric CO
.
Carbon dioxide utilization through electrocatalysis is a promising pathway toward a more sustainable future. In this work the electrocatalytic reduction of carbon dioxide by ReI and RuII bipyridine ...complexes bearing pendant amines (N,N′-((2,2′-bipyridine-6,6′-diylbis(2,1-phenylene))bis(methylene))bis(N-ethylethanamine) (dEAbpy)) is evaluated. In both cases, the major reduction product is carbon monoxide accompanied by some formic acid, although the yield of the latter never reaches the predominant level known from the corresponding Mn(dEAbpy)(CO)3Br complex. This demonstrates the profound effect of the identity of the metal center, in addition to the ligand, for the product distribution. In this work, we report the synthesis procedures and X-ray diffraction studies along with electrochemical and infrared spectroelectrochemical studies of Re(dEAbpy)(CO)3Cl and Ru(dEAbpy)(CO)2Cl2 to propose a mechanism for the CO2 reduction reaction.
Urgent solutions are needed to efficiently convert the greenhouse gas CO2 into higher-value products. In this work, fac-Mn(bpy)(CO)3Br (bpy = 2,2′-bipyridine) is employed as electrocatalyst in ...reductive CO2 conversion. It is shown that product selectivity can be shifted from CO toward HCOOH using appropriate additives, i.e., Et3N along with iPrOH. A crucial aspect of the strategy is to outrun the dimer-generating parent-child reaction involving fac-Mn(bpy)(CO)3Br 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 Et3N and iPrOH. The nature of the amine additive is crucial for product selectivity, as the faradaic efficiency for HCOOH formation decreases to 13 ± 4% if Et3N is replaced with Et2NH. The origin of this difference lies in the ability of Et3N/iPrOH to establish an equilibrium solution of isopropyl carbonate and CO2, while with Et2NH/iPrOH, formation of the diethylcarbamic acid is favored. According to density-functional theory calculations, CO2 in the former case can take part favorably in the catalytic cycle, while this is less opportune in the latter case because of the CO2-to-carbamic acid conversion. This work presents a straightforward procedure for electrochemical reduction of CO2 to HCOOH by combining an easily synthesized manganese catalyst with commercially available additives.
Development of new catalytic approaches for reduction of small molecules is an aspiring technology to alleviate increasing energy demands without use of fossil fuels. One of the most promising ...molecular catalysts for reduction of CO2 is fac‐Mn(bpy)(CO)3Br (bpy=2,2’‐bipyridine). In this work, the mechanism of electrochemical reduction of this complex is elucidated using cyclic voltammetry along with digital simulations. It is revealed that the dimer complex, Mn2(bpy)2(CO)6, is not, as often assumed, formed by dimerization of the singly reduced manganese complex, Mn(bpy)(CO)3., but instead from its reduction to Mn(bpy)(CO)3−, followed by further reaction with Mn(bpy)(CO)3Br (rate constant=1.75×105 M−1 s−1). On the basis of cyclic voltammetry, infrared‐spectroelectrochemistry, and 1H NMR spectroscopy, we establish that this parent‐child reaction involving Mn(bpy)(CO)3Br as electrophile can be diverted by adding either acids or iodomethane as substituting electrophiles. This demonstrates that Mn(bpy)(CO)3−, which is the central catalyst for CO2 reduction, can be formed at less extreme potentials than previously believed by suppressing the parent‐child reaction.
Parent‐child reaction: The mechanism for electroreduction of Mn(bpy)(CO)3Br is examined by digital simulation of cyclic voltammetry responses. After initial reduction forming Mn(bpy)(CO)3, further reduction to Mn(bpy)(CO)3− outruns the, otherwise, favorable dimerization. Nevertheless, the dimeric complex is formed through a parent‐child reaction involving Mn(bpy)(CO)3Br and Mn(bpy)(CO)3−. The anion can be trapped using protons or iodomethane.
The selective and efficient reduction of carbon dioxide represents a key solution to producing non‐fossil‐fuel‐based feedstocks for the chemical industry, while alleviating the increasing atmospheric ...concentration of this greenhouse gas. A variety of catalytic methods for the CO2 reduction reaction (CO2RR) have been developed, including hydrogenations and electrochemical or photochemical reductions. For many of the most significant breakthroughs reported in the last decade, we realized that amines or closely related functional groups play a critical role for such transformations, and in several cases, are directly associated with the catalyst as a pendant group. Amines play multiple roles, such as CO2 trapping agents, proton shuttles, electron donors, or facilitators of CO2 reductions through formamide derivatives. In this Viewpoint, we compile some of these recent findings, and discuss their significance in a broader context in an attempt to provide guidelines for the design of new catalysts with enhanced activity and selectivity.
Within the last decade, several of the most significant breakthroughs in the homogeneous electrochemical or photochemical reduction, and hydrogenation of carbon dioxide have been driven by the introduction of amines or amine‐derived moieties in the reaction mixture. These amines play multiple roles, which are discussed herein to provide guidelines for the design of new catalysts with enhanced activity and selectivity.
In a comparative study of the electrocatalytic CO
reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the ...former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO
becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO
. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone.
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