Co-Catalyst-Free Chemical Fixation of CO₂ into Cyclic Carbonates by using Metal-Organic Frameworks as Efficient Heterogeneous Catalysts

The concentration of carbon dioxide (CO₂ ) in the atmosphere is increasing at an alarming rate resulting in undesirable environmental issues. To mitigate this growing concentration of CO₂ , selective carbon capture and storage/sequestration (CCS) are being investigated intensively. However, CCS technology is considered as an expensive and energy-intensive process. In this context, selective carbon capture and utilization (CCU) as a C1 feedstock to synthesize value-added chemicals and fuels is a promising step towards lowering the concentration of the atmospheric CO₂ and for the production of high-value chemicals. Towards this direction, several strategies have been developed to convert CO₂ , a Greenhouse gas (GHG) into useful chemicals by forming C-N, C-O, C-C, and C-H bonds. Among the various CO₂ functionalization processes known, the cycloaddition of CO₂ to epoxides has gained considerable interest owing to its 100% atom-economic nature producing cyclic carbonates or polycarbonates in high yield and selectivity. Among the various classes of catalysts studied for cycloaddition of CO₂ to cyclic carbonates, porous metal-organic frameworks (MOFs) have gained a special interest due to their modular nature facilitating the introduction of a high density of Lewis acidic (LA) and CO₂ -philic Lewis basic (LB) functionalities. However, most of the MOF-based catalysts reported for cycloaddition of CO₂ to respective cyclic carbonates in high yields require additional co-catalyst, say tetra-n-butylammonium bromide (TBAB). On the contrary, the co-catalyst-free conversion of CO₂ using rationally designed MOFs composed of both LA and LB sites is relatively less studied. In this review, we provide a comprehensive account of the research progress in the design of MOF based catalysts for environment-friendly, co-catalyst-free fixation of CO₂ into cyclic carbonates.