The non-volatility, structure-tunability, and high CO 2 uptake capacity render ionic liquids (ILs) the most exciting materials for the carbon dioxide (CO 2) capture and fixation to value-added chemicals. The aim of this mini-review is to give a brief idea about the development of the potential ILs for CO 2 capture, the mechanism involved in the CO 2 binding and the application of ILs in the conversion of CO 2 to useful chemicals. The mechanisms and nature of interactions in between IL-CO 2 have been discussed in terms of the nature of cation, anion, presence of functional group, and the extent of interaction between the components of ILs. The fixation of CO 2 to linear and cyclic carbonates and electroreduction of CO 2 to carbon-rich fuels in ILs has been accounted in detail. At the end, future challenges in terms of commercializing the ILs for CO 2 capture and utilization technology are discussed.

Herein we report the application of polyamine pentaethylenehexamine (PEHA, 3,6,9,12-tetraazatetradecane-1,14-diamine) in CO2 absorption with both neat PEHA and aqueous solutions thereof. The absorption of molecular CO2 in pure PEHA and in PEHA-water systems resulted in the formation of two chemical species, namely, PEHA carbamate and bicarbonate. It was observed that, upon formation of these species, both the CO2 absorption capacity and CO2 absorption rate were controlled by the amount of water in the system. During the CO2 absorption, the neat PEHA and 92 wt % PEHA were capable of forming carbamate species only while other aqueous analogues with higher dilution allowed for the formation of both carbamate and bicarbonate species upon exceeding 8 wt % water in the mixture. The CO2 uptake steadily increased with an increase in the water concentration in the solvent mixture and reached the maximum value of 0.25 g of CO2/(g of solvent) in the case of 56 wt % PEHA in water. However, in the case of more dilute systems (i.e., <56 wt % PEHA in water), the trend reversed and the CO2 loading decreased linearly to 0.05 g of CO2/(g of solvent) for 11 wt % PEHA in water. Meanwhile, it usually took shorter time to achieve the full CO2 absorption capacity (equilibrium) with increasing water content in all cases. The 13C NMR analysis was used to quantify the relative amount of PEHA carbamate and bicarbonate, respectively, in reaction mixtures. The Kamlet–Taft parameters (α, β, and π*) of aqueous solutions for different concentrations of PEHA were also studied taking advantage of various solvatochromic dyes and correlated with the CO2 absorption capacity. The thermally induced switchable nature of CO2-saturated neat and aqueous PEHA solutions for transformation of ionic PEHA carbamate and bicarbonate moieties to molecular PEHA is also represented. A comparison between aqueous PEHA and aqueous monoethanolamine (industrial solvent) for CO2 capture is reported. Hence, most importantly, a switchable PEHA system is demonstrated for reversible CO2 absorption processes.

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Herein, we report the application of inexpensive mesoporous melamine-formaldehyde resins (MMFR and MMFR250) obtained by a novel template-free and organosolvent-free hydrothermal method as efficient heterogeneous catalysts for direct synthesis of cyclic carbonates from CO2 and epoxides (epichlorohydrin, butylene oxide, and styrene oxide). The catalytic activities of the melamine resins were attributed to the abundant Lewis basic N-sites capable of activating CO2 molecules. Based on CO2-temperature programmed desorption, the concentrations of surface basic sites for MMFR and MMFR250 were estimated to be 172 and 56 μmol/g, while the activation energies of CO2 desorption (strength of basic sites) were calculated to be 92.1 and 64.5 kJ/mol. We also observed considerable differences in the catalytic activities and stabilities of polymeric catalysts in batch and in continuous-flow mode due to the existence of a synergism between adsorption of CO2 and cyclic carbonates (poison). Our experiments also revealed the important role of catalyst surface chemistry and CO2 partial pressure upon catalyst poisoning. Nevertheless, owing to their unique properties (large specific surface area, large mesoporous, and CO2 basicity), melamine resins presented excellent activities (turnover frequency 207–2147 h–1) and selectivities (>99%) for carbonation of epoxides with CO2 (20 bar initial CO2 or CO2:epoxide mole ratio ∼1.5) under solvent-free and co-catalyst-free conditions at 100–120 °C. Most importantly, these low-cost polymeric catalysts were reusable and demonstrated exceptional stability in a flow reactor (tested up to 13 days of time on stream, weight hourly space velocity 0.26–1.91 h–1) for continuous cyclic carbonate production from gaseous CO2 with different epoxides (conversion 76–100% and selectivity >99%) under industrially relevant conditions (120 °C, 13 bar, solvent-free/co-catalyst-free) confirming their superiority over the previously reported catalytic materials.