Catalytic N2O decomposition and reduction by NH3 over Fe/Beta and Fe/SSZ-13 catalysts

Abstract

Fe/zeolites are important N2O abatement catalysts, efficient in direct N2O decomposition and (selective) catalytic N2O reduction. In this study, Fe/Beta and Fe/SSZ-13 materials were synthesized via solution ion-exchange and used to catalyze these two reactions. The nature of the Fe species was probed with UV–vis, Mössbauer and EPR spectroscopies and H2-TPR. These characterizations collectively indicate that primarily isolated and dinuclear Fe sites are present in Fe/SSZ-13, whereas Fe/Beta contains higher concentrations of oligomeric FexOy species. H2-TPR results suggest that Fe-O interactions are weaker in Fe/SSZ-13, as evidenced by the lower reduction temperatures by H2 and higher extents of autoreduction during high-temperature pretreatments in inert gas. Kinetic measurements show that Fe/SSZ-13 has higher normalized reaction rates in catalytic N2O decomposition, thus demonstrating a positive correlation between reaction rate and Fe-O binding, consistent with O2 desorption being rate-limiting for this reaction. However, Fe/Beta was found to display higher reaction rates in catalyzing N2O reduction by NH3. This latter result indicates that larger active ensembles (i.e., oligomers) are responsible for this reaction, consistent with the fact that both N2O and NH3 need to be activated in this case.