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

Iron-exchanged zeolites are often deployed industrially to remediate nitric oxide (NO) and nitrous oxide (N 2 O) emissions. The nature of the active site and the reaction mechanism involved in the simultaneous removal of NO and N 2 O 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 Fe 2+ sites in the β-cationic position responsible for N 2 O activation and the related redox cycle. These sites communicate with tetrahedrally coordinated Fe 2+ sites in the adjacent γ-cationic position, accounting for adsorption and redox-mediated oxidation of NO. The availability of NH 3 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 N 2 O. Fe-exchanged zeolite catalysts are known for their ability to remediate NO x and N 2 O emissions, but their reactivity in mixed streams of NO and N 2 O remains unclear. Now a suite of operando spectroscopies reveals the active Fe species involved in the process and their synergistic effect during the simultaneous conversion of these pollutants.