Group 6 transition metal-based molecular complexes for sustainable catalytic CO2 activation

Abstract

The alarming growth in atmospheric CO₂ has emerged as one of the prime concerns in the context of climate change. Power, petroleum, and construction sectors are the major contributors to CO₂ emissions worldwide. The global imbalance of the present-day carbon cycle must be rectified for sustainable energy harvesting with modifications in existing CO₂ capture, utilization, and sequestration (CCUS) methodologies. A rational link between hydrocarbon/CO₂ and the water/H₂ cycles can pave the way for a model net zero-emission energy infrastructure. The success of this net zero-emission energy scheme depends on the successful deployment of CO₂ reduction reaction (CO₂RR) and H₂ evolution reaction (HER) catalysts that can be operated under broad chemical conditions in aqueous solutions. The associated thermodynamic factors have posed serious challenges for the scientific community to develop sustainable and economically viable catalysts for CO₂RR. In this perspective, we have specifically essayed the generation of different variants of CO₂ activating molecular catalysts based on group 6 transition elements [chromium (Cr), molybdenum (Mo), and tungsten (W)]. Their high natural abundance coupled with access to a wide range of redox states have poised these elements for utilization in the multielectron CO₂RR process. These elements have also found their usage in biology in versatile oxidoreductase enzymes' active sites, including CO₂ activating ones. The blueprint of such enzymes has prompted the inception of several molecular catalysts for CO₂ activation following both chemical and electrochemical pathways. Close control of the ligand environment around these complexes was found crucial for the catalytic efficiency and product specificity. Despite these initial successes, group 6 transition metal-based molecular electrocatalysts are yet to match the remarkable catalytic efficiency of natural CO₂ reduction enzymes. The rational incorporation of enzyme-inspired outer coordination sphere features (interactive peripheral functionalities) around the synthetic core can improve the catalytic response of Cr/Mo/W-based complexes further by assisting CO₂ binding, creating a proton relay, and inducing superior water solubility. Hence, the enzyme-inspired catalyst design will possibly provide a new leeway in developing sustainable CO₂RR catalysts, where the best of the metalloenzyme and organometallic complex can be brought together.