铁基超细粒子催化剂结构与还原行为的Mssbauer谱研究

铁基超细粒子催化剂具有优良的F-T反应性能。本工作利用原位Mssbauer谱辅以XRD技术研究了含有钾助剂的F-T合成铁基超细粒子催化剂的结构与还原行为,考察了催化剂组成和第二金属组分(Mn,Zn,Mg)的影响。“纯”铁超细粒子催化剂在氢气中很容易经Fe_3O_4还原为零价铁。第二金属组分的引入,一方面阻碍了催化剂的还原,另一方面稳定了Fe~(2+)的存在而使其成为还原的主要中间相,这有利于反应条件下形成类尖晶石结构的活性相。对于Fe-Mn催化剂,上述效应随锰含量的增加而更趋显著。铁基超细粒子催化剂在氢气中的还原能力依“纯”Fe>Fe-Zn>Fe-Mn>Fe-Mg的顺序递减,这在一定程度上反映了铁与第二金属组分之间相互作用的强弱。

A MSSBAUER SPECTROSCOPIC STUDY ON THE STRUCTURE AND REDUCTION BEHAVIOR OF IRON BASED UITRAFINE PARTICLE CATALYSTS

Iron based ultrafine particle catalysts have been found to exhibit excellent performance for F-T synthesis.In this work, the effects of the second metal component and the catalyst composition on the structure and reduction behavior of K-promoted Fe-M ultrafine particle catalysts for F-T synthesis were studied by Mssbauer spectroscopy in combination with X-ray diffraction (XRD)techniques. It was found that the incorporation of a second metal component (Mn, Zn or Mg) into the catalyst makes the chemical environment around iron atoms markedly deviate from cubic symmetry, and also makes the particle size of ironcontaining phase in the catalyst even still smaller. "Pure" iron ultrafine particle catalyst can be easily reduced to zero-valent iron via Fe_3O_4. The incorporation of a second metal component hinders the reduction of iron-containing phase in the catalyst, and stabilizes divalent iron oxide as an intermediate in the reduction. This favors the formation of the active phase with spinel-like structure under typical F-T synthesis condition. For Fe-Mn catalysts, the effects are more pronounced with increasing Mn content.The reducibility of iron based ultrafine particle catalysts follows the order of "pure" Fe>Fe-Zn>Fe-Mn>Fe-Mg. This is, in certain extent, an indication of the interaction between iron and the second metal component.