Role of Bimetallic Interactions in the Enhancement of Catalytic CO₂ Reduction by a Macrocyclic Cobalt Catalyst

Abstract

The use of two metal centers in a CO 2 reduction catalyst that work together synergistically, with similar or complementary functions, can potentially lead to a significant reduction in overpotential, enhance catalytic activity and/or selectivity, and/or enable access to cascade strategies where each metal center catalyzes a different step in the conversion of CO 2 to a fuel. Here, the bimetallic reactivity of two metal centers has been identified as the primary route for the reduction of CO 2 to CO promoted by the macrocycle, [Co(HMD)] 2+ (HMD = 5,7,7,12,14,4,8,, based on the experimental characterization of all major steps of the proposed catalytic cycle using pulse radiolysis time-resolved IR (PR-TRIR) spectroscopy, corroborated by density functional theory (DFT) calculations and IR spectroelectrochemistry (IR-SEC). A bimetallic intermediate is formed in situ from two singly reduced [Co(HMD)] + species bridged by a CO 2 molecule, and the presence of a coordinating species, e.g., formate anion, appears to assist in the formation of such an intermediate. It has been demonstrated that this reactivity enables access to elementary steps with lower energy requirements, resulting in overall catalysis being kinetically more facile compared to the mononuclear pathway. A two-step approach that combines chemical reduction followed by PR-TRIR has been successfully used for probing the structure and reactivity of reactive intermediates involved in the advanced stages of a catalytic cycle, which are rarely interrogated using experimental techniques.

Photocatalytic C–N coupling towards urea synthesis with a palladium-supported CeO2 catalyst

“…15,16 On the other hand, carbon dioxide (CO 2 ) is the main greenhouse gas leading to serious environmental concerns. 17 Thus, converting both N 2 and CO 2 into value-added urea molecules via photocatalytic C-N coupling reaction is a feasible approach for not only achieving effective utilization of CO 2 but also mitigating environmental concerns and energy crisis. Nevertheless, the photocatalytic urea production process still suffers from extremely serious challenges.…”

A Dicationic fac-Re(bpy)(CO)3Cl for CO2 Electroreduction at a Reduced Overpotential

“…Water is a weak acid in acetonitrile (p K a 38–41), and the apparent p K a of wet, CO 2 -saturated CH 3 CN is a somewhat lower 23.4 . The long-known participation of Bu 4 N + as a proton source via Hoffman degradation to tri- n -butyl amine and butene must be considered as well. ,, The computed apparent p K a of Bu 4 N + , which is present in abundance, is ∼17, but it is plausibly slow due to the poorly accessibly acidic C H 2 protons and the complication of breaking the N–C bond . The involvement of Bu 4 N + as an acid was probed by repeating the water titration CVs in the presence of 0.1 M Me 4 NPF 6 (Figure B).…”

Dinuclear metal synergistic catalysis for energy conversion

“…Electrocatalytic CO 2 reduction into valuable fuels and chemicals over dinuclear metallic complex catalysts has also attracted considerable research interest. [135][136][137][138][139] In 2018, we designed and synthesized a dinuclear Ni complex, which can serve as an electrocatalyst for the reduction of CO 2 to CO. The TON and TOF values reached as high as 4.1 Â 10 6 and 190.0 s À1 , respectively, which are 38-fold improvement of that of the corresponding mononuclear Ni complex.…”

“…A series of experimental characterizations and DFT calculations revealed that a bimetallic intermediate was in situ generated from two reduced mononuclear Co species bridged by a CO 2 molecule, which is more beneficial for the CO 2 reduction to CO compared with the mononuclear pathway. 136 In addition to transition metal centers, the DMSC effect between dinuclear noble metal sites in the electrocatalytic CO 2 RR has also been studied. For example, Jurss et al designed and synthesized two anthracene-bridged dinuclear Re complexes with cis-and trans-conformers, as well as a mononuclear Re complex for electrocatalytic CO 2 reduction.…”

“…A series of experimental characterizations and DFT calculations revealed that a bimetallic intermediate was in situ generated from two reduced mononuclear Co species bridged by a CO 2 molecule, which is more beneficial for the CO 2 reduction to CO compared with the mononuclear pathway. 136…”