超微粒子碳化铁催化剂在F—T合成中表面形态的研究

Surface Characterization of Ultrafine Particle Iron-carbonid Catalysts in F-T Synthesis

应用光电子能谱研究催化剂表面化学状态的变化，属当前催化领域的新课题．文中用ＸＰＳ和ＸＲＤ技术研究了超微粒子碳化铁催化剂在Ｆ－Ｔ合成过程中表面形态和体相结构的变化．由于超微粒子催化剂表面具有极高的化学活性，尽管其体相结构是α－Ｆｅ和碳化铁．但仍有部分氧化物复盖在催化剂表面．经Ｈ２处理，体相内碳化铁被全部还原的同时，伴随烃化物的生成，而表面仍有极少量的氧和碳以各种不同的复杂形式吸附在Ｆｅ的表面．再经ＣＯ和Ｈ２混合气处理，体相内得到Ｆ－Ｔ合成过程中具有稳定化学结构的α－Ｆｅ，碳化铁和γ－Ｆｅ２Ｏ３，其表面则是大量碳和氧以及碳氢化合物、羰基化合物以固定形式吸附在催化剂Ｆｅ的表面．然而这种形式又是一个动态平衡。伴随着烯烃、烷烃及含氧的碳氢化合物从催化剂表面脱附下来形成产物；然后再解离吸附ＣＯ和Ｈ２，再脱附，构成Ｆ—Ｔ合成催化剂表面的动态平衡．文中进一步论证了Ｆ－Ｔ合成的碳化物机理．

Surface characterization and bulk phase change for ultrafine particle iron-carbonide catalyst in F-T synthesis have been studied by XPS and XRD techniques. Although the bulk phase of the iron-carbonid catalyst conaists of α-Fe and iron-carbonide, the presence of oxides and carbide layer on its surface can be observed. With H2 pre-treatment of the catalyst iron-carbonid in the bulk were completely reduced, while there were still a little amount or complex compoundes formed by oxygen and carbon and adsorbed on iron surface. After retreatment with the mixture CO and H2α-Fe,iron-carbonid and γ-Fe2O3 were formed in the bulk phase, which possess stable chemical structure in the F-T reaction. On the surface, significant amount of carbon, oxygen and hydrocarbon which atdsorbed on the catalyst. Thus a dynamic equilibrium in F-T synthesis can be reched by taking the dole in which the prodicts of olefine,alkane and oxygen comaing hydrocarbons were desorbed from the catalyst dissodated to adsorb CO and H2, and desorbed again. It provids a proof og thr catalytical mechanism orCarbide.