铁和锰的化学状态对 LaFexMnyAl12-x-yO19 催化剂上 N2O 分解的影响

 以共沉淀法制备了 LaFexMnyAl12-x-yO19 六铝酸盐催化剂, 并用 X 射线衍射、扫描电镜、N2 吸附-脱附、紫外-可见漫反射光谱和穆斯堡尔谱对催化剂进行了表征, 考察了催化剂上高浓度 N2O 分解反应的性能. 结果表明, 在所考察的条件下, Mn 比 Fe 更有利于促进六铝酸盐晶相的形成. LaFexAl12-xO19 (x = 0.5, 1) 中 Fe 以 Fe3+位于六铝酸盐尖晶石结构中的四面体位和镜面层结构中的三角双锥位, 其中后者为 N2O 分解的主要活性中心. LaMnyAl12-yO19 (y = 0.5, 1) 中 Mn 优先以 Mn2+进入四面体位, 然后以 Mn3+进入尖晶石结构中的八面体位, 并成为 N2O 分解的主要活性中心.

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

 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.