N-Heterocyclic Carbene Moiety in Highly Porous Organic Hollow Nanofibers for Efficient CO2 Conversions: A Comparative Experimental and Theoretical Study

Global warming and climate change are two severe environmental dangers brought on by the steady rise in the carbon dioxide (CO2) concentration in the atmosphere. Thus, in order to reduce this problem, it is essential to find an efficient material for high CO2 capture that can simultaneously exhibit good catalytic activity for CO2 utilization into useful chemicals. Herein, we report the synthesis of N-heterocyclic carbene-based porous organic polymers (NHC-01 and NHC-02) using the Friedel–Crafts reaction with the imidazolium salt and bi-phenyl. Among the two porous polymers, NHC-01 exhibited outstanding stability, high flexibility, and high BET surface area (1298 m2 g–1). NHC-01 material displayed a high CO2 uptake capacity of 2.85 mmol g–1 under 1.0 bar pressure at 273 K. NHC-01/02 has been utilized as a metal-free organocatalyst for the CO2 conversion reaction due to its high surface area, high CO2 absorption capacity, and as it bears the NHC moiety in the organic network. NHC-01 selectively reduced CO2 to methanol via hydrosilylation with complete conversion of silane under atmospheric CO2 pressure. Furthermore, the catalyst also shows good catalytic activity toward N-formylation and reductive cyclization reactions, which showed good yields up to at least four catalytic cycles. The reaction mechanisms are also studied by theoretical simulation using density functional theory (DFT), which shows that intermediates have the appropriate free energy level for the catalyst to promote the reaction with a low energy barrier.