Revealing the competitive effect of N2 and H2O towards CO 2 adsorption in N-rich ordered mesoporous carbons

The incorporation of heteroatoms improves CO ₂ adsorption on carbon-based materials, but it can also provide some hydrophilic character to the bare-carbon frameworks, making the hypothesis of competitive CO ₂/H ₂O adsorption not negligible. In this respect, the CO ₂ capture is here evaluated through a deep characterization of the sorption properties of N-rich ordered mesoporous carbons under dry and moisture conditions, and in CO ₂/N ₂ gas mixtures. The nanocasting strategy is used to obtain N-rich CMK-3-type carbons in one pot by impregnating D-glucosamine hydrochloride, a carbon/nitrogen source, into an SBA-15 silica template followed by pyrolysis treatment at 600, 750, and 900 °C. The fine-tuning of the pyrolysis treatment aims to find the right proportion of micropores and N content, which are important features for selective CO ₂ adsorption. The highest surface amount of N (11.3 at.%), in particular of the pyridinic type, enhances the CO ₂/N ₂ selectivity (1.03 mmol/g of adsorbed CO ₂ from a 20% CO ₂ in N ₂), but also the undesired increment in the H ₂O uptake. CO ₂ uptake under competitive CO ₂/H ₂O conditions is better preserved with 8.3 at.% of surface nitrogen (1.55, 1.52, 0.61, and 0.89 mmol/g of CO ₂ at a relative humidity of 0, 25, 50, and 75%, respectively). Interestingly, the N-CMK-3 materials retain their capture properties over repetitive adsorption-desorption cycles in pure CO ₂. In this respect, a TGA-FTIR study is performed to monitor the reusability of the sorbents after CO ₂ capture from moist flue gases to assess the effectiveness of the reactivation procedure towards the removal of the adsorbed species.