Do N-doped activated carbons truly outperform N-free activated carbons for CO2 separation in humid conditions?

This study aims to evaluate whether N-doping of activated carbons (ACs) can improve CO2 separation in a realworld post-combustion scenario. A high-surface-area, N-free AC was synthesized and subsequently N-doped by blending it with urea and subjecting it to heat treatment at 623 K in air. The potential of this N-doped AC for environmental gas separation was assessed, focusing on its CO2 capture performance in the presence of increasing relative humidity (RH) levels. High-pressure adsorption isotherms for CO2 and N2 were obtained and fitted, using the Dual-Site Langmuir model to calculate selectivity. The results indicate that the N-doping posttreatment with urea reduces the AC textural properties, particularly affecting larger micropores and mesopores. Despite this, N-doping enhances CO2 selectivity, and dynamic breakthrough simulations for CO2/N2 separation suggest that N-doped AC can perform better than undoped samples under dry conditions due to their increased tap density. However, N-doping also increases water affinity, which may be undesirable for applications involving undried flue gas streams. The pristine AC exhibited a nearly stable CO2 adsorption capacity up to 40 % relative humidity (RH), whereas the CO2 capacity of the N-doped AC progressively decreased from 10 % RH.