Abstract:  LaFe_xMn_yAl_12-x-yO₁₉ hexaaluminate catalyst samples were prepared by a coprecipitation method and tested for N₂O decomposition with high concentration (30%, V/V). The catalyst samples were characterized by X-ray diffraction, scanning electron microscopy, N₂ adsorption-desorption, ultraviolet-visible spectroscopy, and Mössbauer spectroscopy. The results showed that the partial substitution by Mn led to easier formation of phase-pure hexaaluminate compared with that by Fe under the investigated conditions. Fe³⁺ occupied both tetrahedral sites in spinel block and trigonal bipyramid sites in mirror plane for LaFe_xAl_12-xO₁₉ (x = 0.5, 1) hexaaluminate. Mn²⁺ preferentially entered tetrahedral sites at low Mn content (y = 0.5) for LaMn_yAl_12-yO₁₉ hexaaluminate, whereas Mn³⁺ entered octahedral sites in spinel block at y = 1. The activity tests for N₂O decomposition with high concentration demonstrated that Fe³⁺ in trigonal bipyramid sites of LaFe_xAl_12-xO₁₉ and Mn³⁺ in octahedral sites of LaMn_yAl_12-yO₁₉ were the main active centers.

Key words: iron, manganese, hexaaluminate, nitrous oxide, decomposition, propellant, M鰏sbauer spectroscopy