Effect of N-doping on NO2 adsorption and reduction over activated carbon: An experimental and computational study

Due to high adsorption capacity, NO 2 adsorption using activated carbon has become a potential denitration technology. A correlation between N-doping and NO 2 adsorption process on activated carbon is pointed out by previous studies but lacks a clear explanation. The main objective of this work is to clarify the influencing mechanism of N-doping on NO 2 adsorption and reduction over activated carbon. N-doped activated carbons were synthesized by melamine impregnation followed by calcination and tested as NO 2 adsorbents. Experimental results showed that AC600 with highest N content possessed highest NO 2 adsorption capacity and lowest NO release percentage. NO 2 adsorption on activated carbon is a complex process, including NO 2 adsorption, NO 2 reduction to NO, and NO release. Density functional theory calculations results showed that N-doping affected all steps mentioned above. Firstly, N-doping increased NO 2 physisorption energies, meaning that NO 2 was easier to be adsorbed. Thus, NO 2 adsorption capacities increased with the increase of N content experimentally. Secondly, N-doping increased the energy barrier of the rate-determining step of NO 2 reduction. Thus, the reduction of NO 2 to NO was harder. Thirdly, N-doping increased NO desorption energies, implying that the release of generated NO was harder. The inhibition of NO 2 reduction and NO desorption results in the decrease of NO release percentage due to N-doping jointly. This work elucidates the influencing mechanism of N-doping on NO 2 adsorption and NO 2 reduction on theoretical level, which fills up the research gap and guides the design of activated carbon for efficient NO 2 adsorption.