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Abstract: Two model spherical iron catalysts (100Fe/0Al2O3 and 100Fe/15Al2O3) with free Cu and K promoters were prepared by the combination of co-precipitation and spray drying method for the application of slurry Fischer–Tropsch synthesis (FTS). The effect of Fe–Al2O3 interaction on the reduction/carburization behavior in H2/CO/syngas, surface basicity and the change of phase structure were comparatively studied by means of H2 or CO temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD) and Mössbauer effect spectroscopy (MES). The results showed that the catalyst incorporated with Al2O3 exhibits a strong Fe–Al2O3 interaction, which obviously weakens the surface basicity, stabilizes the FeO phase and inhibits the reduction of iron catalyst in H2 or syngas. Furthermore, Fe–Al2O3 interaction also restrains the carburization of iron catalyst in CO or syngas. In slurry FTS process, it was found that the strong Fe–Al2O3 interaction decreases the FTS activity and suppresses the water gas shift (WGS) reaction, but can stabilize the active sites of iron catalyst and improve its run stability. Due to the strong Fe–Al2O3 interaction, the weak surface basicity on the catalyst incorporated with Al2O3 greatly decreases the selectivity of heavy hydrocarbon products. [Copyright &y& Elsevier]

Abstract: The effect of adding SiO2 to a precipitated iron-based Fischer–Tropsch synthesis (FTS) catalyst was investigated using N2 physical adsorption, H2 differential thermogravimetric analysis, temperature-programmed reduction/desorption (TPR/TPD) and Mössbauer spectroscopy. The FTS performances of the catalysts with or without SiO2 were compared in a fixed bed reactor. The characterization results indicated that SiO2 facilitates the high dispersion of Fe2O3 and significantly influences the Fe/Cu and Fe/K contacts, which play an important role in the surface basicity, reduction and carburization behaviors, as well as the FTS performances. The incorporation of SiO2 enhances the Fe/Cu contact, further enlarges the H2 adsorption and promotes the reduction of Fe2O3 →FeO x , while the transformation of FeO x →Fe is suppressed probably due to the strong Fe–SiO2 interaction. SiO2 indirectly weakens the surface basicity and severely suppresses the carburization and CO adsorption of the catalyst. In the FTS reaction, it was found that SiO2 decreases the FTS initial activity but improves the catalyst stability. Due to the lower surface basicity than the catalyst without SiO2, the catalyst incorporated with SiO2 has higher selectivity to light hydrocarbons and methane and decreased selectivity to the olefins and heavy hydrocarbons. [Copyright &y& Elsevier]

Abstract: The structural properties and iron–silica interaction of the precipitated iron catalysts incorporated with or without silica have been investigated by powder X-ray diffraction (XRD), Mössbauer spectroscopy, and temperature-programmed reduction (TPR) with H2 consumption quantitative analysis. The Fischer–Tropsch synthesis (FTS) performances of the catalysts were carried out in a slurry-phase continuously stirred tank reactor (CSTR). It was found that, for as-prepared samples, nano-particles of iron oxide mixtures (α- and/or γ-Fe2O3) formed on the silica-incorporated catalyst, whereas well-crystallized hematite (α-Fe2O3) is the only phase on the silica-free catalyst. After reduction in H2, the observed phase in the silica-free catalyst is α-Fe, whereas wüstite (Fe x O) and iron (II) silicate (Fe2SiO4) are the main phases in the silica-incorporated catalyst. In H2-TPR, the Fe3+ ions in the silica-incorporated catalyst are reduced to Fe (0) via Fe2+ ions as intermediate and the reduction extent of iron oxides obviously decreased comparing with the silica-free catalyst. The differences in structural properties and reduction behavior between the silica-free and the silica-incorporated catalysts may be due to the high dispersion effect of silica and the iron–silica interaction. The iron–silica interaction also decreases the FTS activity and improves the light hydrocarbon selectivity. [Copyright &y& Elsevier]

Abstract: A systematic study was undertaken to investigate the effects of Al2O3/SiO2 ratio on reduction, carburization and catalytic behavior of iron-based Fischer–Tropsch synthesis (FTS) catalysts promoted with potassium and copper. The catalysts were characterized by N2 physical adsorption, CO2 temperature-programmed desorption (TPD), H2 temperature-programmed reduction (TPR) and Mössbauer effect spectroscopy (MES). CO2-TPD indicated that Al2O3 binder has stronger acidity than SiO2 binder and weakens the surface basicity of the catalysts. H2-TPR profiles suggested that the lower Al2O3/SiO2 ratio promotes the reduction of Fe2O3→Fe3O4. With further increasing Al2O3/SiO2 ratio, the transformation of Fe2O3→Fe3O4 shifts to higher temperatures. The MES results showed that the increase of Al2O3/SiO2 ratio leads to the relatively large crystallite size of α-Fe2O3 and inhibits carburization of the catalyst. During reaction tests in a fixed bed reactor it was found that a maximum in catalyst activity is noted at the Al2O3/SiO2 ratio of 5/20 (weight basis). The selectivity to olefins shows a rapid decrease and the formations of methane and light hydrocarbons are promoted with increasing Al2O3/SiO2 ratio. The oxygenate selectivity in total products increases with increasing Al2O3/SiO2 ratio. [Copyright &y& Elsevier]

Abstract: FeCu/SiO2 catalysts, in which K or Na promoter is incorporated respectively, are prepared by a combination method of continuous co-precipitation and spray drying technology. The catalysts were characterized by temperature-programmed desorption and Mössbauer spectroscopy. The Fischer–Tropsch synthesis (FTS) performance of the catalysts was studied in a continuously stirred tank slurry reactor. The basicity of the K-promoted catalyst is enhanced, as demonstrated by CO2-TPD results. MES results show that sodium can weaken the dispersion of α-Fe2O3 phase; either potassium or sodium can promote carburization of the catalyst, while the effect of sodium is weaker. FTS results indicate that the addition of K or Na can improve the catalyst activity, and shift the product distribution to heavy hydrocarbons to the different extent. [Copyright &y& Elsevier]