Co-Catalyst-Free Chemical Fixation of CO2into 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 CO(2)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 CO(2)functionalization processes known, the cycloaddition of CO(2)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 CO(2)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 CO(2)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 CO(2)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 CO(2)into cyclic carbonates.