Mechanism of catalytic sites participating in N2O formation over Fe-BEA and Cu-SSZ-13 NH3-SCR catalysts

Abstract

N2O as a potent greenhouse gas, is increasingly emphasized in automotive exhausts. The mechanism of N2O formation over Fe-BEA and Cu-SSZ-13 catalysts was investigated by experiments and density functional theory (DFT) calculations to elucidate the effect of NO2/NOx ratios and water. An updated detailed experimental phenomenon was exhibited to DRIFTs, NH3-TPD and catalytic performance and the results showed that N2O formation increased with the rising NO2/NOx ratio, the NH3 absorbed on Lewis acid sites provided the N atom on N2O formation. The DFT calculation identified that the side reaction of NO2 with NH3 on active sites generated N2O. The NH2 and HONO bonded to Fe sites to form H2NNO and OH, and then the H atom of H2NNO migrated toward HNNO and H2O over Fe-BEA catalyst, while activated HONO reacted with NH2 to generate HNNOOH on Cu sites, then desorbed into N2O and H2O over Cu-SSZ-13 catalyst.