Finely Iron-Dispersed Particles on beta Zeolite from Solvated Iron Atoms: Promising Catalysts for NH3-SCO

beta zeolite has been functionalized with 2 wt % Fe to obtain catalysts for the ammonia selective catalytic oxidation (NH3SCO) reaction. Iron deposition was performed on the zeolite surface by solvated metal atom dispersion (SMAD) and ion exchange (IE) procedures. ZSM-5 was selected as the reference structure known to assure high dispersion of isolated centers when functionalized with iron by IE. Transmission electron microscopy techniques combined with element maps enlightened on the iron-species distribution and dimension on the two zeolites. As expected, highly homogeneous dispersed iron species were present on the ZSM-5 sample prepared by IE, while with beta zeolite, the same deposition method led to the formation of FeOx aggregates (2.5-10 nm) together with isolated iron species. On the other hand, by the SMAD approach, well-formed FeOx nanoparticles ranging from 1.0 to 4.5 nm were revealed on beta zeolite. NH3-SCO on iron-containing zeolites started at approximately 300 degrees C, without any clear effect of the size of Fe on the reaction activity/selectivity. Ammonia conversion regularly increased with temperature with always very high selectivity to nitrogen (98-100%), without any NOx or N2O formation, on iron-containing beta zeolites, in particular. Only a very limited increase of iron particle dimensions was observed on the used Fe catalysts, in any case. The collected experimental results indicated that isolated well-dispersed iron species are associated with high activity and selectivity in the NH3-SCO reaction. SMAD-derived iron nanoparticles worked with excellent performances in the ammonia oxidation reaction with high activity in terms of conversion, selectivity to nitrogen, and stability.