Influence of Chemical States of Fe and Mn on N2O Decomposition over LaFexMnyAl12-x-yO19 Catalysts

LaFexMnyAl12-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, N-2 adsorption-desorption, ultraviolet-visible spectroscopy, and Mossbauer 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 LaFexAl12-xO19(x = 0.5, 1) hexaaluminate. Mn2+ preferentially entered tetrahedral sites at low Mn content (y = 0.5) for LaMnyAl12-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 LaFexAl12-xO19 and Mn3+ in octahedral sites of LaMnyAl12-yO19 were the main active centers.