Influence of ammonia treatment on the CO2 adsorption of activated carbon

Abstract

The objectives of this study were to prepare an adsorbent with high-CO2 adsorption performance (CO2-AP) and to clarify the effect of N-doping on the CO2-AP of activated carbon (AC). First, N-doped AC was prepared by alkaline activation of biomass and subsequent treatment with NH3 (NH3-AC), and its CO2-AP was evaluated (665 mg-CO2/g). Next, chemical and pore property analyses of the prepared NH3-AC were conducted to investigate the effect of N-species on the CO2-AP. NH3-AC with improved CO2-AP was produced by NH3 treatment at 400 °C or lower. In contrast, the CO2-AP of NH3-AC prepared at 500 °C or higher decreased as the treatment temperature increased. The N content increased when the treatment temperature was < 200 and 700–800 °C, and N1s XPS analysis showed that NH3 was mainly incorporated into the AC as pyridinic-N. Pore analysis showed that the quantity of 0.55–0.85 nm micropores, which were CO2 adsorption sites, decreased when the treatment temperature was > 500 °C, and it was concluded that the decrease in CO2-AP was due to the reduction in micropores. However, no significant change was observed in the pore properties of NH3-AC at 200–400 °C, suggesting that the increase in CO2-AP was due to the formation of basic sites by the pyridinic-N introduced during NH3 treatment.