Hard coal- and lignite-derived N-doped carbons: Structure–performance relationship in CO ₂ capture, CH ₄ and H ₂ storage

In this study, nitrogen-doped activated carbons (N-ACs) were synthesized in a single step from Zonguldak hard coals (& Uuml;z & uuml;lmez, Kozlu, Karadon) and Soma lignite using LiOH and urea as activating and nitrogen-doping agents, respectively. The produced N-ACs were characterized for their surface area, pore structure, and morphology, and evaluated for CO2 and CH4 adsorption at 298 K and H-2 adsorption at 77 K under low-pressure conditions. Among the samples, the N-AC from & Uuml;z & uuml;lmez coal (UAC) exhibited the highest BET surface area (1945 m(2)/g), micropore volume (0.79 cm(3)/g), and superior CO2 (16.65 wt%) and CH4 (2.51 wt%) uptake. In contrast, the Soma lignite-derived sample (SAC) showed much lower adsorption due to its poor porosity. The best H2 performance was achieved by KAC and KOAC, indicating the importance of micropore volume and pore accessibility. Although UAC had the highest surface area, its H2 uptake was moderate (2.41 wt%), suggesting surface chemistry also plays a role. CO2/N-2 selectivity analysis revealed that UAC maintained high selectivity under varying temperatures and gas mixtures, indicating its potential for post-combustion CO2 capture. These results highlight the importance of coal precursor type, activation method, and nitrogen doping in developing efficient porous carbons for gas storage applications.