Pérez-Alonso F J, Granados M López, Ojeda M, Herranz T, Rojas S, Terreros P, Fierro J L G, Gracia M, Gancedo J R
Instituto de Catálisis y Petroleoquímica, (CSIC), Marie Curie 2, 28049 Madrid, Spain.
J Phys Chem B. 2006 Nov 30;110(47):23870-80. doi: 10.1021/jp064575f.
A series of Fe-Ce mixed oxides (95 atom % Fe-5 atom % Ce) has been prepared by different methods: coprecipitation, impregnation, and physical mixture of Ce and Fe oxides. These solids have been tested in the Fischer-Tropsch synthesis. The characterization of the catalytic precursors was carried out by X-ray diffraction (XRD), Raman, Mössbauer, and X-ray photoelectron (XPS) spectroscopic techniques. When the preparation method ensures a microscopic contact between Fe and Ce cations in the solid, several types of Fe-Ce interactions are present in the calcined solids. The interactions take the shape of Fe-O-Ce bridges that can exist either in the hematite-like solid solution or in the interphase between the Fe oxide covered by microcrystals of Ce oxide. In the case of the hematite-like solid solution, Ce(IV) cations are dissolved in the alpha-Fe2O3 network. The promotion by Ce of the catalytic properties observed in the final catalysts can be directly related with the detection of these Fe-O-Ce bridges in the calcined solids. The Ce promotion results in a larger yield to hydrocarbons, a higher production of olefins, and a higher selectivity to medium and large chain hydrocarbons (larger than six carbon atoms). It is proposed that the Ce promotion is due to the presence of Fe0-Ce(III) ensembles in the final catalysts arising from the initial Fe-O-Ce bridges developed in the parent calcined samples.
通过不同方法制备了一系列铁铈混合氧化物（95原子%铁 - 5原子%铈）：共沉淀法、浸渍法以及铈和铁氧化物的物理混合物法。这些固体已在费托合成中进行了测试。通过X射线衍射（XRD）、拉曼光谱、穆斯堡尔光谱和X射线光电子能谱（XPS）技术对催化前驱体进行了表征。当制备方法确保固体中Fe和Ce阳离子之间存在微观接触时，煅烧后的固体中存在几种类型的Fe - Ce相互作用。这些相互作用呈现为Fe - O - Ce桥的形式，其可存在于类赤铁矿固溶体中或存在于被Ce氧化物微晶覆盖的Fe氧化物之间的界面中。在类赤铁矿固溶体的情况下，Ce(IV)阳离子溶解在α - Fe₂O₃网络中。Ce对最终催化剂中观察到的催化性能的促进作用可直接与煅烧后固体中这些Fe - O - Ce桥的检测相关。Ce的促进作用导致烃类产率更高、烯烃产量更高以及对中长链烃（大于六个碳原子）的选择性更高。有人提出，Ce的促进作用是由于最终催化剂中存在Fe⁰ - Ce(III)组合，这是由母体煅烧样品中最初形成的Fe - O - Ce桥产生的。
