A composite metal–organic framework/carbon aerogel for enhanced CO2 adsorption and catalytic conversion

Abstract

The chemical conversion of carbon dioxide (CO₂) into chemicals offers opportunities to utilize CO₂ as a sustainable carbon source. Metal–organic frameworks (MOFs) are important CO₂ adsorption catalysts. To enhance the affinity for CO₂, a composite adsorption catalyst, formed by combining MOFs with carbon aerogels (CCAs), was used to adsorb CO₂ from simulated flue gas and directly catalyze its conversion into cyclic carbonates with epichlorohydrin. CCAs were prepared from a sodium alginate/kappa–carrageenan/chitosan mixture using a wet-spinning technique. On the surface of CCA, glutamic acid and copper salt were used to synthesize the composite adsorption catalyst (GluCu–CCA) via a co-precipitation method. GluCu–CCA was characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. Adsorption experimental results indicated that GluCu–CCA had excellent adsorption capacity, with a pure CO₂ uptake of 292 mg g⁻¹ (6.64 mmol g⁻¹) and a pseudo-first-order kinetic rate constant of 0.074 min⁻¹. For 15% CO₂, the adsorption capacity reached 233 mg g⁻¹ (5.30 mmol g⁻¹). During the adsorption–catalysis process, GluCu–CCA effectively catalyzed the ring addition reaction, achieving CO₂ conversion rates of 87.8%. In cyclic adsorption–desorption tests, the adsorption capacity of GluCu–CCA showed only a slight reduction after 20 cycles (94% retention). Furthermore, in the catalytic conversion cycling experiments, there was virtually no decrease in CO₂ conversion efficiency in 3 cycles, demonstrating GluCu–CCA's excellent cycling stability for adsorption and catalysis. The adsorption mechanism revealed that the N site in GluCu–CCA served as a critical adsorption site, while Cu(I) acted as a crucial active site in both the adsorption and catalytic reaction processes. The simple synthesis of GluCu–CCA offers a competitive approach for the integrated adsorption and catalytic conversion of CO₂.