Synergistic activation mechanism of CO2 and H2O during preparation of Zhundong coal-based activated carbons for adsorption and reduction of NO

Adsorption and reduction of NO by coal-based activated carbon has the advantages of cleanliness, wide distribution of raw materials and low cost. In this paper, activated carbons with 30, 50 and 70 wt% burn-off rates were prepared via physical activation of Zhundong coal by CO2, H2O and 40 % H2O/60 % CO2 at 700 degrees C, and NO removal rates were tested in both temperature-programmed and isothermal experiments. The synergistic effects of CO2/H2O co-activation on the morphology, pore and chemical structures of activated carbons and the adsorption and reduction of NO by activated carbon are systematically investigated for the first time. The results show that the pore size distribution and functional group contents of activated carbons varied with the burn-off rate. At a low burn-off rate of 30 wt%, the H2O/CO2 co-activated carbon exhibits the best adsorption and reduction performance for NO among all samples, which may be attributed to its largest microporous area and abundant oxygen-containing functional groups. As the burn-off rate increased, the micropores were deeply etched, enlarged and/or merged to form mesoporous structures, leading to a decrease in the number of micropores and the NO conversion. At the same burn-off rate and similar specific surface area, the NO conversion increases with increasing C - O content, suggesting that NO reduction is encouraged by C - O enrichment. Coalbased porous carbons from H2O/CO2 co-activation at a low burn-off rate has the advantage of high adsorption and reduction performance for NO. In addition, the effect of active metal elements in coal-based activated carbon on the catalytic reduction of NO was briefly discussed. A novel synergistic activation method was used to prepare activated carbon for reduction of NO at moderate temperatures and the synergistic mechanism is proposed.