Iron-catalysed cooperative redox mechanism for the simultaneous conversion of nitrous oxide and nitric oxide

Abstract

Iron-exchanged zeolites are often deployed industrially to remediate nitric oxide (NO) and nitrous oxide (N₂O) emissions. The nature of the active site and the reaction mechanism involved in the simultaneous removal of NO and N₂O remain largely unknown, primarily because of the heterogeneity of Fe species. Here we combined catalytic experiments with transient operando X-ray absorption spectroscopy, electron paramagnetic resonance and diffuse reflectance infrared Fourier transform spectroscopy to disentangle the nature of Fe species and elementary reaction steps. We identified spectroscopically the square-planar Fe²⁺ sites in the β-cationic position responsible for N₂O activation and the related redox cycle. These sites communicate with tetrahedrally coordinated Fe²⁺ sites in the adjacent γ-cationic position, accounting for adsorption and redox-mediated oxidation of NO. The availability of NH₃ adsorbed on neighbouring Brønsted acid sites regulates the overall reaction rate of this dual-site mechanism by intercepting the NO oxidation sequence. The cooperation between these redox processes ensures enhanced conversion of both NO and N₂O.