Porous carbon-based materials are promising candidates for CO2 adsorption, but their performance under realistic flue gas conditions remains a major challenge. This study focuses on the synthesis of Ca-modified biochar, BC(Ca), using a microwave-assisted method for enhanced CO2 capture under post-combustion conditions. BC(Ca) was thoroughly characterized and evaluated as a CO2 adsorbent across a range of operating conditions, including changes in temperature, pressure and humidity. The macroporous texture of the biochar (BC) promoted uniform Ca dispersion without significant pore blockage, which is attributed to the microwave-assisted synthesis. BC(Ca), containing 4.6 at.% Ca, mainly as CaO and Ca(OH)2, and having a BET area of 445 m2 g−1, exhibited a CO2 adsorption capacity of 2.42 mmol g−1 and a CO2/N2 selectivity of 36 under 15 % vol. of CO2 in N2, at 1 bar and 25 °C. This performance was maintained at elevated pressure, up to 25 bar, highlighting the potential of BC(Ca) for industrial applications. Under humid conditions, with pre-loaded relative humidity (RH) of up to 50 %, BC and BC(Ca) decreased their CO2 uptake, whereas BC(Ca) showed superior stability. BC(Ca) retained 66 % of its CO2 uptake, achieving 1.13 mmol g−1 and outperforming comparable carbon-based sorbents under particularly harsh conditions (50 °C, 30 % RH). The improved humidity tolerance was attributed to synergistic effects between physical adsorption, surface basicity enhancement, and water-assisted chemisorption, highlighting the robustness of BC(Ca) for CO2 capture in humid flue gas streams.

P. Arjona-Jaime acknowledges CONAHCYT-Mexico (CVU 901672) for her scholarship and the financial support of COPOCYT (Fideicomiso 23871, 2024-01). [...]. V. Fierro and A. Celzard acknowledge the support of the CATALPA project (ANR-22-PESP-0007) funded by the ANR France 2030 program.

9 figures, 2 tables.-- Under a Creative Commons BY 4.0 license.

Peer reviewed