Elucidating the role and enhancement mechanisms of CH4 on the coupling abatement of N2O & NO over Fe-SSZ-13 catalysts

Abstract

CH4 + NH3 + NOx + N2O coupling system was proposed for high-effective simultaneous catalytic reduction of both NO and N2O from flue gas generated by nitric or adipic acid industries. The Fe-SSZ-13 catalyst performed both elegant activity for NOx and N2O at 400–600 °C. Based on experimental studies, the active Fe species were illustrated and the transforming of Fe species during the N2O decomposition (deN2O) and selective catalytic reduction (SCR) processes was clarified. It found that deN2O could cause the main active sites of [Fe-O2-Fe]2+ transform to [Fe-O-Fe]2+ and consequently inhibited the NH3-SCR process over the Fe-SSZ-13 catalyst. Meanwhile, the αO* generated via N2O decomposition would strengthen NO oxidation to NO2, which is advantageous to NH3-SCR. More importantly, the functions of CH4 for deN2O and NH3-SCR were also investigated. CH4 could work as reductant to convert N2O over the Fe-SSZ-13. CH4 could also facilitate the reduction of NO; however, NH3 has stronger activity to NO than that of CH4. And CH4 was easily oxidized by O2 rather than N2O or NO, which significantly limit the CH4-SCR for N2O with present of O2. At the same time, CH4 can also accelerate αO* consumption that somehow enhance deN2O efficiency. Moreover, the consumption of αO* by CH4 prevent the transforming of [Fe-O2-Fe]2+ to [Fe-O-Fe]2+, and CH4 play an important role on turnover rates of [Fe-O2-Fe]2+ and [Fe-O-Fe]2+ active sites, guaranteeing both satisfactory purifying efficiency for NO and N2O. This work reveals the positive promoting effect of CH4 on simultaneous reduction of NOx and N2O, and proposes a potential catalyst for implementation.