Thermal Evolution Crystal Structure and Fe Crystallographic Sites in LaFexAl12–xO19 Hexaaluminates
Thermal Evolution Crystal Structure and Fe Crystallographic Sites in LaFexAl12–xO19 Hexaaluminates
复制标题
DOI：
10.1021/jp500682d
复制
发表时间：
2014-05
影响因子：
3.7
通讯作者：
Yan Zhang;Xiaodong Wang;Yanyan Zhu;Xin Liu;Tao Zhang
中科院分区：
文献类型：
--
作者：
Yan Zhang;Xiaodong Wang;Yanyan Zhu;Xin Liu;Tao Zhang
与BaFe_（12）O_（19）铁氧体相比，高取代浓度的La-磁铅石（MP）六铝酸盐的研究较少。通过共沉淀法合成了不同Fe负载量（x = 0-12）的LaFexAl 12-xO 19催化剂。从700到1400摄氏度的样品的热演化之后，X射线衍射。通过Rietveld精修和室温及低温Fe-57穆斯堡尔谱，阐明了最终MP结构中不同晶位的Fe分布。结果表明，Fe掺杂（x = 1-9）降低了La-六铝酸盐的阈值温度。当x >= 6时，LaFeO 3中间相的偏析阻碍了MP相的形成，当x = 12时，甚至导致MP相的消失。与未取代的样品相比，Fe取代的La-六铝酸盐（x = 4，Al（1）和Al（4）位在尖晶石块体中开始系统地被占据直到x = 11。N_2O催化分解的转化率为（0.16 ~ 0.47）× 10 ~（2）h ~（-1）m ~（-2）），表明Fe ~（3+）与N_2O催化分解性能之间存在一定的相关性。镜面中的离子（Al（3），Al（5））。
Compared with BaFe12O19 hexaferrite, La-magnetoplumbite (MP) hexaaluminates with a high-substituted concentration have rarely been investigated. LaFexAl12-xO19 catalysts at various Fe loadings (x = 0-12) were synthesized by coprecipitation. Thermal evolution of the samples from 700 up to 1400 degrees C has been followed by X-ray diffractometry. Fe distribution in different crystallographic sites in the final MP structure was clarified by means of Rietveld refinement and room-temperature and low-temperature Fe-57 Mossbauer spectroscopy. The results showed that Fe doping (x = 1-9) lowered the threshold temperature of La-hexaaluminates. When x >= 6, the segregation of LaFeO3 intermediates essentially hindered the formation of monophasic MP phase and even led to the absence of the MP structure when x = 12. Compared with the unsubstituted sample, Fe-substituted La-hexaaluminates (x = 4, Al(1) and Al(4) sites in the spinel block started to be systematically occupied up to x = 11. The reasonably constant turnover frequencies ((0.16 to 0.47) x 10(2) h(-1) m(-2)) indicated a correlation between the N2O catalytic decomposition performance and Fe3+. ions in the mirror plane (Al(3), Al(5)).