Finely Iron-dispersed Particles on beta Zeolite solvated iron atoms: promising catalysts for NH3-SCO

Beta zeolite has been functionalized with ca. 2 wt.% Fe to obtain catalysts for the NH3-SCO reaction. Iron deposition was performed on the zeolite surface by solvated metal atom dispersion (SMAD) and ionic-exchange (IE) procedures. ZSM-5 was selected as 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 hands, by SMAD approach, well-formed FeOx-nanoparticles ranging 1.0 – 4.5 nm were revealed on Beta zeolite. Ammonia oxidation activity (NH3-SCO) on iron-containing zeolites started at ca. 300°C, without no clear effect of the size of Fe on the reaction activity/selectivity. Ammonia conversion regularly increased with temperature with always very high selectivity to dinitrogen (98-100%), without any NOx or N2O formation, on iron containing Beta zeolites, in particular. Only very limited increase of iron particle dimensions were observed on the used Fe-catalysts, in any case. The collected experimental results indicated that not only 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 dinitrogen, and stability.