Role of nitrogen functional groups and manganese oxides on the reduction of NO over modified semi-coke catalyst at low temperature

Modified semi-coke catalysts loaded melamine (M) and/or manganese oxides (MnO_x) were prepared by the impregnation method for the reduction of NO at low temperature. A fixed-bed reactor, XRD, Raman and XPS were used for the catalytic activity measurement and characterization of modified semi-coke catalysts. The highest denitration rate of 5M–10Mn–ASC was 91.6% at 225 °C and kept the highest level within 200–300 °C. The results of characterization revealed the changes of nitrogen functional groups on the surface of modified semi-coke catalysts. Pyrrolic-like nitrogen (N-5) appeared on the surface of semi-coke catalysts only with M. After loading M and MnO_x simultaneously, quaternary nitrogen (N–Q) appeared and the contribution of nitro type complexes (–NO₂) declined sharply. During the whole reaction process, melamine as a nitrogen species source can adjust both the contribution of acidic and basic functional groups. The acidic functional groups, like C=O and N–Q, could provide active sites to adsorb NH₃ and the basic functional groups, like pyridinic-like nitrogen (N-6) and N-5, could adsorb some O₂ and NO. Meanwhile, the sufficient oxygen vacancies and surface chemical oxygen provided by MnO_x reinforced denitration efficiency of modified semi-coke catalysts as well. Different modified conditions would result in the changing roles of nitrogen functional groups constantly, which could be beneficial to improve the denitration rate. Based on the results of catalytic activity measurements and analysis of different characterization, the possible denitrification mechanism of modified semi-coke catalysts was built.