Mn-Based Molecular Catalysts for the Electrocatalytic Disproportionation of CO₂ into CO and CO₃^2–

Abstract

This work studies the electrocatalytic disproportionation of CO2 into CO and CO3 2– mediated by a [Mn-2,6-bis­(1-(alkyl)­imidazol-2-ylidene)­pyridine]Br pincer complex. We identify three mechanistic scenarios involving one or two catalytically active metal centers in the activation of carbon dioxide and use density functional theory to map out the energy landscape for each of the mechanistic steps. Experimentally determined second-order kinetics in CO2 consumption, the formation of CO and CO3 2– together with an observed order in catalyst of 0.5 determined by cyclic voltammetry using the Burés normalized timescale method, suggest a turnover-limiting CO3 2– loss through the scission of a bimetallic species. Faradaic efficiencies for the reduction of CO2 to CO of 86 ± 4% are observed. Given the reaction mass balance, we estimate a Faradaic efficiency from the conversion of CO2 to CO3 2– of 93 ± 4%. Our combined experimental−theoretical approach suggests that two sequential CO2 insertions are followed by a rearrangement to produce carbon monoxide and carbonate from two molecules of CO2 at singly reduced catalyst molecules. The disproportionation reaction reported herein combines the power of catalytic CO2 conversion with sequestration and provides a new chemical avenue for the conversion of carbon dioxide.

Transition metal-based catalysts for the electrochemical CO2reduction: from atoms and molecules to nanostructured materials

“…N-Heterocyclic carbenes (NHC) also represent an important class of organic molecules effectively employed to improve the CO 2 RR catalytic performances of metal NPs. 448 Chelating multidentate NHC ligands have been successfully used for CO 2 electroreduction in homogeneous molecular catalysts [449][450][451][452] and polycrystalline metallic surfaces (vide infra). 453 The strong s-donating character of the NHC ligands is particularly attractive for CO 2 RR, leading to electron-rich metal surfaces with an enhanced reactivity towards CO 2 .…”

Chemical and Electrochemical Recycling of End-Use Poly(ethylene terephthalate) (PET) Plastics in Batch, Microwave and Electrochemical Reactors

“…Given our experience in the field of electrolytic hydrogen production [ 31 , 32 , 33 ] and reductive electrocatalysis [ 34 , 35 ], we investigated the electrochemical generation of the necessary basic conditions using current passage through a protic medium ( Scheme 1 ). We hypothesized that this methodology would have a distinct advantage over the batch and microwave methods occurring at room temperature in neutral salted media, with the necessary base generated in situ ( Scheme 1 ) at rates that one can control by dialing in the delivery of charge in coulombs/s.…”

Redox-Active Manganese Pincers for Electrocatalytic CO2 Reduction

“…Further CV experiments determined a second order in CO 2 by using the resulting currents from varying CO 2 concentrations as relative rates and a half-order in catalyst by varying catalyst concentration. The latter determination was the first example of the Burés normalized timescale method [50] being used to determine the order in catalyst from voltammetry data. The proposed mechanism (Scheme 4) begins with the reduction of two equivalents of the metal complex 7 followed by the loss of two CO each to form a square planar Mn 0 species 7a.…”

“…Inorganics 2020, 8, x FOR PEER REVIEW 9 of 12 example of the Burés normalized timescale method [50] being used to determine the order in catalyst from voltammetry data. The proposed mechanism (Scheme 4) begins with the reduction of two equivalents of the metal complex 7 followed by the loss of two CO each to form a square planar Mn 0 species 7a.…”

“…This behavior is unlike previous studied group VII catalysts, as discussed above. Density Functional Theory (DFT) calculations showed that between the reduced forms (7a for Mn) of the two complexes, the Mn complex demonstrates increased metalloradical character (66%) while the Re has a much lower radical character on the metal (38%), suggesting that the reduced Re complex may not be sufficiently nucleophilic for CO 2 reduction [50]. A second explanation for this observation would be that the CO ligands are too strongly bound to allow coordination of a new CO 2 ligand.…”