Toward sustainable catalysis: Anion-engineered metal-/halogen-free catalysts for efficient chemical fixation of low concentration CO2

The efficient conversion of atmospheric CO 2 into high value-added chemicals remains a persistent challenge. In this study, a heterogeneous catalyst PD x BpyOH with both metal-free and halogen-free properties and nucleophilic hydroxyl sites was developed for the cycloaddition reaction of CO 2 with epoxides. This catalyst was constructed by incorporating a bipyridine complex and a imidazolium salt into an organic polymer matrix, followed by anion exchange. The porosity structure of these catalysts were optimized by tuning the crosslinker DVB ratio (x = 0, 2, 3, 4). A series of characterizations confirmed that it had a hierarchical micro-mesoporous structure, and the specific surface area regulated by DVB improved the physical adsorption capacity of CO 2 . Under the optimal conditions (80 mg catalyst, 60 °C, 1 atm CO 2 , 48 h), PD 2 BpyOH achieved 89 % conversion of epichlorohydrin. Furthermore, it maintained 85 % conversion in 96 h under simulated industrial flue gas (15 % CO 2 /85 % N 2 ), demonstrating robust recyclability and activity for various epoxides. This catalytic system provides a new metal-free and halogen-free heterogeneous catalytic strategy for the utilization of low-concentration CO 2 . A metal- and halogen-free heterogeneous catalysts were synthesized and used for the efficient transformation of low concentration CO 2 into cyclic carbonate. • Metal and halogen-free heterogeneous catalysts were synthesized. • The porosity structure of these catalysts can be finely tuned. • The catalyst is active for cycloaddition of CO 2 with epoxides in the absence of co-catalyst. • The catalyst show excellent catalytic activity at low CO 2 concentration.