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 (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 beta-cationic position responsible for N2O activation and the related redox cycle. These sites communicate with tetrahedrally coordinated Fe2+ sites in the adjacent gamma-cationic position, accounting for adsorption and redox-mediated oxidation of NO. The availability of NH3 adsorbed on neighbouring Br & oslash;nsted 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. Fe-exchanged zeolite catalysts are known for their ability to remediate NOx and N2O emissions, but their reactivity in mixed streams of NO and N2O 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.