Insights into the mechanism for the selective catalytic reduction of NOx with NH3 on (MnO)2+ ZSM-5: A DFT study

In this work, the reaction mechanisms for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with NH3 on a (MnO)(2+)/ ZSM-5 catalyst were investigated based on the density functional theory (DFT) method. Our calculations showed that the NH3 could strongly adsorb on the (MnO) 2+/ ZSM-5 catalyst as compared to NO. The proposed reaction pathway, NH3(ads)-> NH2+H -> NH2(ads) + NO(ads) -> NH2NO -> NHNO + H -> N-2+H2O, was more favorable with smaller activation barrier (1.40 eV) of the rate-determining step. The compared reaction process that the adsorbed NH3 reacted directly with adsorbed NO was difficult to happen for the higher activation barrier. Meanwhile, the framework oxygen participated in the oxidation process from ammonia to NH2, thereby increasing its availability for the reaction. In addition, the regeneration process of active site in the presence of NH3 and NO2 was explored, and the rate-limiting step possessed an activation barrier of 1.46 eV. The NH2NO species was formed as the crucial intermediate and subsequently decomposed into the N-2 and H2O.