Mechanism of O2-promoted NO adsorption on activated carbon: An experimental and computational study

Activated carbon can be used to control NO x emissions in low-temperature flue gas, while improving its performance is challenging. NO adsorption on activated carbon was found significantly promoted with the presence of O 2 . Based on the analysis of NO adsorption characteristics under different atmospheres and corresponding desorption characteristics, NO oxidation, NO 2 migration and further conversion on activated carbon are proposed to cause the significant increase in NO adsorption capacity. Quantum chemical calculations conducted on the adsorption and reaction pathways of NO, O 2 , and NO 2 on different carbonaceous models clarified that the pathway of O 2 -promoted NO adsorption on activated carbon can be divided into two stages. In the first stage, O 2 adsorbs on active carbon atoms near the hydroxyl functional group and undergoes an oxidation reaction with gaseous NO to generate NO 2 . In the second stage, the desorbed NO 2 is re-absorbed on the saturated carbon atoms; the N-down adsorption configuration of NO 2 will not convert, while the O-down adsorption configuration of NO 2 will oxidize the active site to form C-O and release NO; the C-O further reacts with the gaseous NO 2 to form NO 3 - which stably remains. There are two types of active sites involved in the pathway. The active carbon atoms near the hydroxyl functional groups mainly play a catalytic role in the oxidation of NO, while the saturated carbon atoms mainly store nitrogen-containing components. The results can help improve the performance of activated carbon in adsorbing NO in low-temperature flue gas.