Investigations of NO reduction by coal-based activated carbon with KOH activation: Performance and mechanism

Selective catalytic reduction of ammonia is the most widely used technology for NOx removal, but there have been serious ammonia leaks and a narrow reaction temperature window. To overcome these limitations, a coal-based activated carbon (CAC) approach using KOH activation for the ammonia-free reduction of NO was investigated in this work. A preparation process was investigated by evaluating the De-NOx performance at different mass ratios (KOH:coal = 0–3:1), and activation temperatures (700–900 °C). The optimum conditions were an activation temperature of 700 °C and a 1:1 ratio of KOH/coal, named CAC-1:1-700. Between 330 and 500 °C, the NO conversion efficiency is maintained at 100% within 90 min. The CAC-1:1-700 showed excellent denitrification performance and SO2 resistance. Based on BET, SEM, XRD, Raman, FT-IR, and XPS characterization analysis, it was found showed that KOH activation could increase the amorphous carbon, pore structure, and C(O) functional groups in CAC, which had positive effects on the denitrification performance. Furthermore, the evolution of char structures and surface species before and after the Char-NO-O2 reaction was evaluated by Raman and XPS, and the possible reaction mechanisms was proposed. Aliphatic structures and small aromatic rings can play the same role in De-NOx, O2 is adsorbed on the carbon to form an oxygen-containing functional group, generating more C–O groups and creating reactive sites C*. NO then interacts with these reactive sites and is reduced to N2. This research prepared CAC as a promising potential alternative to ammonia reductants due to its excellent denitration performance over a medium temperature range and complex flue gas environments, while providing the high-value utilization of coal resources.