Characterization of Fe Substitution into La-Hexaaluminate Systems and the Effect on N₂O Catalytic Decomposition

Compared to Ba-hexaaluminates with β-Al 2 O 3 structure, La-hexaaluminates with magnetoplumbite (MP) structure have more substituted Al sites in the preferentially exposed mirror plane, which should favor N 2 O decomposition. In this regard, LaFe x Al 12– x O 19 catalysts with x = 1 and 5 were herein prepared using the coprecipitation method. 57 Fe Mössbauer spectroscopy and X-ray diffraction structure refinements revealed that Fe 3+ ions originating in Fe 2 O 3 species mainly entered tetrahedral Al(2) and trigonal bipyramidal Al(5) sites. Meanwhile, Fe 3+ ions in octahedral sites of perovskite-type LaFeO 3 intermediates preferentially accommodated in octahedral Al(3) sites in the mirror plane of La-hexaaluminates. Correlation of normalized rates (moles of N 2 O per hour per square meter) of the catalysts at 500 °C with the occupancy of Fe ions in different Al crystallographic sites of the MP phase indicated that Fe 3+ ions in the Al(3) and Al(5) sites were highly active for N 2 O decomposition. In contrast, Fe 2+ derived from a Fe 3+ → Fe 2+ reduction under high-temperature calcination played a negative role.