Effect of Ir crystallographic site on the catalytic performance of Ir-substituted barium hexaferrites for N2O decomposition

Ir-substituted barium hexaferrites (BaIrxFe12−xO19, x ≤ 0.6) were prepared using the carbonates route and investigated for high-concentration N2O decomposition. It was found that BaIrxFe12−xO19 offered a better dispersion of iridium by incorporating Ir into the hexaferrite structure. The crystallographic sites of Ir in BaIrxFe12−xO19 were identified through the analysis of Fe occupancy in the matrix by sensitive 57Fe Mössbauer spectroscopy. Framework iridium preferentially occupied the octahedral sites in the order of 2a, 12k, and 4f2 as increasing x value. When x = 0.1 and 0.4, the substitution of Ir for Fe3+ occurred in the 2a and 12k sites in the rigid spinel block with a comparable N2O decomposition activity, while this substitution in the 4f2 sites in the mirror plane at x = 0.6 resulted in a remarkable enhancement of activity. Ir ions in the octahedral 4f2 sites in the loosely packed mirror plane were highly active for N2O decomposition.

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► The crystallographic sites of Ir in barium hexaferrites were identified.
► Ir preferentially occupied the octahedral sites.
► The occupation follows the order of 2a, 12k, and 4f2 as increasing Ir content.
► Ir ions in 4f2 sites in the mirror plane were more active for N2O decomposition.