Elucidating the Mechanism of CO2 Reduction by Mn/Re Catalysts: A Time-resolved Spectroscopic Investigation
Title: Elucidating the Mechanism of CO2 Reduction by Mn/Re Catalysts: A Time-resolved Spectroscopic Investigation
DNr: NAISS 2023/22-1046
Project Type: NAISS Small Compute
Principal Investigator: Samir Chattopadhyay <samir.chattopadhyay@kemi.uu.se>
Affiliation: Uppsala universitet
Duration: 2023-10-09 – 2024-11-01
Classification: 10402
Homepage: https://www.katalog.uu.se/profile/?id=N21-780


Electrocatalytic and photocatalytic CO2 reduction (CO2RR) hold great promise for addressing climate change and reducing the reliance of the chemical and transportation sectors on fossil fuels. Molecular CO2RR catalysts offer benefits like tunability, selectivity, and efficiency, but enhancing their suitability for industrial use requires a more profound understanding of their underlying mechanisms, an area where current CO2RR research falls short. Re and Mn bipyridine tricarbonyl complexes (M(bpy)(CO)3X, X= -Cl/-Br, M= Re/Mn) are known for their CO2 reduction capabilities. The Re complex can reduce CO2 to CO without the need for a Br√łnsted acid, whereas the Mn counterpart requires an acid source to activate CO2. Current renewable energy research is focused on developing molecular CO2RR catalysts with 2nd sphere residues (providing H+ transfer, electrostatic interaction, H-bonding, and Lewis acid residues for intermediates stabilization) around their active sites. This approach enhances efficiency and product selectivity. To design efficient catalysts for producing formate, CO, CH4, and other products from CO2, understanding the mechanistic cycle is crucial. However, there remains a lack of comprehensive understanding of the CO2RR mechanistic cycle catalyzed by Re/Mn-bipyridine complexes. A recently proposed cycle combines density functional theory calculations with experimental evidence (J. Am. Chem. Soc. 2014, 136, 46, 16285). This project work aims to uncover the mechanistic cycle by synthesizing intermediates independently and examining the effects of adding reducing equivalents and protons. We will employ time-resolved FTIR/UV-Vis and a stopped-flow mixing system to track the changes in the CO vibrational frequency (or electronic spectra of the intermediates) within the catalysts at a sub-millisecond scale. Few in-depth analyses of intermediate formation and decay exist. Our objective is to explore the catalytic cycle through various intermediates, thoroughly investigating their kinetics. I plan to do some DFT and TDDFT calculations to obtain the predicted vibrational frequencies, electronic absorption spectra, energetics of the reaction, possible transition states, and pKa values of the crucial intermediates (with/without 2nd sphere proton transfer residues). I plan to use both Gaussian and ORCA for the same. These calculated properties and their experimental counterpart will help us to decipher the overall mechanistic cycle and the role of the 2nd coordination sphere during CO2RR. This insight will help to develop catalysts that can reduce CO2 selectively and efficiently at a lower applied potential.