Elucidating redox pathways for N2O selective catalytic reduction with NO and NH3 over Fe-chabazite zeolites

We combined kinetics and in situ X-ray absorption spectroscopy to investigate redox pathways of N2O-selective catalytic reduction (SCR) by NH3 and NO over Fe-exchanged Chabazite zeolites, a strategy to mitigate emissions of greenhouse gas N2O and toxic NOx from sources such as NH3 engines. N2O-SCR occurs via Fe-II/Fe-III redox cycles with N2O as the oxidant, and parallel reactions involving NO+NH3 or NH3 as reductants, where in situ XAS shows that most Fe ions are redox-active. NO co-reduces Fe-III with NH3 rather than oxidizing to NO2. Net rates of N2O-SCR in gas mixtures containing NH3 versus NO+NH3 are both limited by Fe-II oxidation, resulting in similar apparent activation energies. In contrast, reduction pathway selectivity reflects the intrinsic kinetics of Fe-III reduction steps with NO+NH3 versus NH3, implying that reduction involving NO+NH3 dominates at lower temperatures and higher NO pressures. This work provides fundamental insights into kinetics and mechanisms of N2O-SCR.