Evolution mechanism of NOx in NH3-SCR reaction over Fe-ZSM-5 catalyst: Species-performance relationships

[Display omitted] •NH3-SCR activity partly depends on relative amount of the active species.•The coexistence of “L-H” and “E-R” pathway was suggested by DRIFT studies.•[Fe-NO2] with three geometries was an important intermediate species in Slow SCR.•[Fe-NO2]-1/[FeO-NO] formation was the rate limiting steps in Fe/NO2/NH3 reaction. Fe-based zeolites are known for desired high-temperature activity in the selective catalytic reduction of NOx by NH3, and species-performance relationships over Fe-ZSM-5 were systematically investigated in this study. Via activity tests, characterization and TOF calculation, it was found that both the relative amount and the real content of active Fe species played vital roles in the catalytic activity. The weakened high-temperature acid sites and stronger NH3 oxidation caused by oligomeric Fe and FexOy species could account for the decreased high-temperature activity over Fe-ZSM-5 with a high Fe loading. N2O formation via nitrate decomposition was barely found over Fe-ZSM-5 with Fe content of 1.0 wt%, the “L-H” and “E-R” pathway could coexist in the SCR reaction as suggested by DRIFT studies. DFT calculation showed that [Fe-NO2]-1 was the most easily generated and the formation of [Fe-NO2]-1/[FeO-NO] was the rate limiting step in the calculated reaction pathways of NO2 and NH3.