title: Relevance in the Fischer-Tropsch synthesis of the formation of Fe-O-Ce interactions on iron-cerium mixed oxide systems.
abstract: 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.
authors.affiliation: Instituto de Catálisis y Petroleoquímica, (CSIC), Marie Curie 2, 28049 Madrid, Spain.
authors.forename: F J
authors.initials: FJ
authors.lastname: Pérez-Alonso
authors.forename: M López
authors.initials: ML
authors.lastname: Granados
authors.forename: M
authors.initials: M
authors.lastname: Ojeda
authors.forename: T
authors.initials: T
authors.lastname: Herranz
authors.forename: S
authors.initials: S
authors.lastname: Rojas
authors.forename: P
authors.initials: P
authors.lastname: Terreros
authors.forename: J L G
authors.initials: JL
authors.lastname: Fierro
authors.forename: M
authors.initials: M
authors.lastname: Gracia
authors.forename: J R
authors.initials: JR
authors.lastname: Gancedo