DRIFTS study of the catalytic N2O reduction by SO2 on FeZSM-5

SO2 has been recognized as an effective reducing agent for N2O over iron-containing zeolite catalysts, lowering the operation temperature up to 100 K with respect to the direct N2O decomposition. This unique behavior contrasts with the common poisoning effect of SO2 over other active de-N2O metals (e.g. Co, Cu, Rh, and Ru). The formation of surface sulfates has been generally posed as the main cause for catalyst deactivation by SO2. Through the use of in situ infrared spectroscopy (DRIFTS), we show that steam-activated FeZSM-5 indeed builds up stable sulfate species during the N2O + SO2 reaction. Significant amounts of sulfur were detected in the used catalyst by elemental analysis and X-ray photoelectron spectroscopy. However, the enhanced N2O conversion is remarkably stable, indicating that the reducing action by SO2 and the sulfation of the surface are decoupled. The resulting sulfate species are thus spectators in the catalytic process and do not block or alter the structure of the active sites for N2O reduction and decomposition.