Achieving carbon neutrality through conversion of CO2 to cyclic carbonates using bifunctional benzimidazolium-based pyridine hypercrosslinked polymers

Abstract

Carbon capture, utilization, and storage strategies have emerged as critical and practical solutions for mitigating excessive carbon emissions. This study introduced the synthesis of 1,3-disubstituted imidazolium salt-functionalized hypercrosslinked polymer (HCPs) through Friedel-Crafts alkylation reaction. By manipulating the substituent group structure of the imidazole salts, the materials with a hierarchical pore structure and a moderate specific surface area was obtained, reaching up to 492 m²·g⁻¹. The catalytic efficacy of HCPs materials in converting CO₂ into cyclic carbonates was evaluated in the absence of metals, solvents, or additives. Among these, HCPs-1 demonstrated exceptional catalytic performance in CO₂-epoxide cycloaddition reaction, achieving yields as high as 99 % under 1.0 MPa CO₂ at 100°C over 10 h. Additionally, epoxides bearing various substituent groups were converted into cyclic carbonates using HCPs-1. The recyclability tests indicated that HCPs-1 retained its catalytic activity with no significant degradation after 6 cycles. Furthermore, the results of density functional theory (DFT) calculations revealed that benzimidazolium salts enhance the activation of both CO₂ and epoxides through CO₂-philic N atoms and strong H-bonding interactions, thereby facilitating the cycloaddition process. Consequently, this work introduces a novel approach to the design and synthesis of imidazolium-functionalized heterogeneous catalysts, integrating heteroatoms to enhance catalytic activity.