Amine-Impregnated Porous Organic Polymers with Chemisorption Sites for Highly Efficient CO2 Chemical Conversion under Ambient Conditions

CO2 cycloaddition with epoxides is an important chemical process for CO2 conversion to generate cyclic carbonates, which are major sources and intermediates of fine chemicals and electrolytes. Unfortunately, the catalytic efficiency of various porous organic polymers (POPs) for the CO2 cycloaddition process remains poor and necessitates severe conditions or a prolonged reaction time at mild temperature and pressure. Only a few reports have emphasized the improvement of the interaction among POP heterogeneous catalysts with CO2, in addition to many attempts to boost efficiency by increasing the adsorption capacity of POPs for CO2. Furthermore, chemisorption, which can efficiently adsorb and activate CO2, could be used to establish a high binding affinity and interaction among POPs and CO2. Herein, we report amine-impregnated porous organic polymers, i.e., hyper-cross-linked polymer (HCP)-tetraphenylporphyrin (TPP), using a wet impregnation method that differentiates itself from the chemical grafting method due to the simplicity of sample preparation and high amine loading to create abundant CO2 chemisorption sites to effectively adsorb and activate CO2 for easier cycloaddition reactions under mild conditions. The amine-functionalized heterogeneous catalysts HCP-TPP-Co-EDA-10 and HCP-TPP-Co-PEI-5 showed a strong binding affinity with CO2 (Qst value of 31.8 and 52.5 kJ mol-1) and high catalytic yield (reaching up to 99%) under mild temperature and pressure. Interestingly, the turnover number (TON) and turnover frequency (TOF) could reach up to 6930 and 193 h-1, respectively, which are one of the highest values reported so far under mild conditions. Furthermore, HCP-TPP-Co-EDA-10 and HCP-TPP-Co-PEI-5 have excellent recyclability and stability (more than five recycling times) for CO2 conversion. Additionally, a possible mechanism is also proposed for the catalytic conversion reaction. This simple strategy of utilizing amines as chemisorption sites for CO2 is demonstrated as an approach to designing highly efficient functionalized hyper-cross-linked polymers (HCPs) for CO2 capture and chemical conversion.