Transformation of functional groups in the reduction of NO with NH3 over nitrogen-enriched activated carbons

In recent years, activated carbon technology has been applied in various industrial flue gas purifications, with a high desulfurization efficiency but a relatively low denitrification efficiency. To strengthen the denitrification performance and further clarify which physicochemical property factor dominates the reduction of NO over activated carbon, this study used four kinds of nitrogen-enriched additives to modify the activated carbon, and the denitrification efficiency increased. The results from porosity analysis and Raman spectra showed that modification reduced the specific surface area and total pore volume of the activated carbon but promoted the disorder of graphite microcrystalline structure providing the adsorption and reaction active center for NO and NH3. The oxygen-containing and nitrogen-containing functional groups were detected by X-ray photoelectron spectrometry before and after the reaction. The results revealed that the phenolic hydroxyl oxygen was transformed to carbonyl oxygen of quinone, and pyridine, pyrrole and quaternary nitrogen functional groups were converted to pyridine N-oxides and amines. The transient response experiment was employed to investigate the adsorption state of NO and NH3 in denitrification reaction by abruptly cutting off the intake of NO or NH3 under steady-state reaction. The results revealed that the reduction of NO with NH3 at 110 °C follows the Langmuir-Hinshelwood (L-H) mechanism, while at 150 °C with Elay-Rideal (E-R) mechanism and L-H mechanism. The pyridine, pyrrole and quaternary amine groups can adsorb NO in the gaseous state, and the phenolic hydroxyl group acts as the adsorption site of NH3 to produce quinones and N2 and complete the SCR reaction.