Abstract
The effective conversion of carbon dioxide (CO2) into cyclic carbonates requires porous materials with high ionic content and large specific surface area. Herein, we developed a new systematic post-synthetic modification strategy for synthesizing imidazolium-based hypercrosslinked ionic polymers (HIPs) with high ionic content (up to 2.1 mmol g−1) and large specific surface area (385 m2 g−1) from porous hypercrosslinked polymers (HCPs) through addition reaction and quaternization. The obtained HIPs were efficient in CO2 capture and conversion. Under the synergistic effect of high ionic content, large specific surface area, and plentiful micro/mesoporosity, the metal-free catalyst [HCP-CH2-Im][Cl]-1 exhibited quantitative selectivities, high catalytic yields, and good substrate compatibility for the conversion of CO2 into cyclic carbonates at atmospheric pressure (0.1 MPa) in a shorter reaction time in the absence of cocatalysts, solvents, and additives. High catalytic yields (styrene oxide, 120 °C, 8 h, 94% yield; 100 °C, 20 h, 93% yield) can be achieved by appropriately extending the reaction times at low temperature, and the reaction times are shorter than other porous materials under the same conditions. This work provides a new strategy for synthesizing an efficient metal-free heterogeneous catalyst with high ionic content and a large specific surface area from HCPs for the conversion of CO2 into cyclic carbonates. It also demonstrates that the ionic content and specific surface area must be coordinated to obtain high catalytic activity for CO2 cycloaddition reaction.
Highlights
The exploitation of effective strategies for CO2 capture, sequestration, and utilization is crucial for the sustainable development of human society
A large number of homogeneous and heterogeneous catalysts have been used for the CO2 cycloaddition reaction, including ionic liquids (ILs) [8,9,10,11], metal complexes [12,13,14,15], metal-organic frameworks (MOFs) [16,17,18,19,20,21], and porous organic polymers (POPs) [1,2,3,6,22,23,24,25,26]
We developed a new strategy for synthesizing hypercrosslinked ionic polymers (HIPs) with high ionic content and large specific surface area from hypercrosslinked polymers (HCPs) through addition reaction and quaternization
Summary
The exploitation of effective strategies for CO2 capture, sequestration, and utilization is crucial for the sustainable development of human society. The best active catalyst HP-[BZPhIm]Cl-DCX-1 has a large specific surface area (763 m2 g−1) and moderate IL content (0.762 mmol g−1) It can convert epichlorohydrin into cyclic carbonates with 99% yield and 98% selectivity at 120 ◦C, 0.1 MPa CO2 in 11 h. We developed a new strategy for synthesizing HIPs with high ionic content and large specific surface area from HCPs through addition reaction and quaternization. The optimal addition reaction conditions were identified as follows: the mass ratio of allyl chloride to HCP (5), the mass ratio of H2SO4/HCP (1.5), reaction time (24 h), and temperature (50 ◦C); the chloromethyl content and specific surface area of HCP-CH2-Cl-1 can reach 2.1 mmol g−1 and 385 m2 g−1, respectively.
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