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An industrial manganese-promoted ultrafine particle (UFP) iron catalyst for slurry phase Fischer–Tropsch synthesis was examined in a 1 dm3 stirred tank slurry reactor under various reaction conditions as a representative of industrial practice (533–573 K, 1.5–2.5 MPa, 1.0–2.5 l (STP)/g-cat h, H2/CO=0.65–2.0). The Fe–Mn UFP catalyst showed high CO conversion and gave high yields of C2–C4 alkenes, partially attributed to less secondary hydrogenation of alkenes during the slurry reaction. The catalyst displayed a slow deactivation rate with time on stream. The effects of reaction conditions on the catalytic activity, hydrocarbon product distribution and the ratio of alkene/alkane were discussed. [Copyright &y& Elsevier]

Abstract: Kinetic Monte Carlo simulations were carried out for Fischer–Tropsch synthesis in a wide range of industrially relevant reaction conditions. The macroscopic performance of different reaction conditions obtained from simulations quite agrees with experimental trends. In all examined conditions, H and CO are dominant species on catalyst surface. The rest intermediates only exist in small amount, and are controlled by H and CO coverages. Activity and selectivity for Fischer–Tropsch synthesis and water gas shift reaction are determined by surface H/CO ratio. Reaction conditions can directly change surface coverage of H, CO, and vacant sites, and consequently exert an influence on macroscopic performance of iron catalyst. [Copyright &y& Elsevier]

Abstract: Mechanisms and kinetics for the reduction of a precipitated iron-based Fischer–Tropsch catalyst in H2 have been investigated using in situ Mössbauer effect spectroscopy (MES) and thermogravimetric (TG) method in the temperature range of 250–350°C. In situ MES results indicate that the reduction of paramagnetic (PM) α-Fe2O3 (70%) and superparamagnetic (spm) Fe3+ (30%) in the fresh catalyst proceed via different steps. PM α-Fe2O3 is firstly reduced to magnetite and then to metallic iron, while the reduction of spm Fe3+ proceeds in three consecutive steps: it is first reduced to magnetite with a significantly rapid rate, then to non-stoichiometric wüstite, and finally to metallic iron. The reduction of PM α-Fe2O3 to Fe3O4 can be described by a two-dimensional Avrami–Erofe’ ev phase change model (formation and growth of nuclei). However, the corresponding overall reduction, which includes the reduction of PM α-Fe2O3 and spm Fe3+ to Fe3O4, can be described by a three-dimensional phase-boundary-controlled reaction model based on the overall extraction ratio of oxygen. The difference between the two models selected for the PM α-Fe2O3 reduction and the corresponding overall reduction is attributed to the rapid reduction of spm Fe3+ to Fe3O4. For the reduction of PM magnetite to α-Fe and its corresponding overall reduction (including the reduction of PM and spm Fe3O4 to α-Fe), it is found that both of them follow the Avrami–Erofe’ ev phase change model (two-dimensional or three-dimensional). The value of apparent activation energy for the overall reduction has been calculated and compared with the literature data. [Copyright &y& Elsevier]

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: An industrial iron-based catalyst (100Fe/5Cu/6K/16SiO2, by weight) was characterized after reduction at different temperatures and after Fischer–Tropsch synthesis (FTS) in a stirred tank slurry reactor (STSR). The BET surface area and pore volume of the catalyst decreases with increasing reduction temperature, and the contrary trend was found for pore size. The iron phase compositions of catalysts reduced with syngas were strongly dependent on pretreatment conditions employed. Pretreatment with syngas at lower temperature prevents iron catalyst activation. Carburization was intensified with the increase in reduction temperature. The formation of iron carbides in reduced catalyst was necessary for obtaining stable high FTS activity. The relationship between the amount of CO2 in tail gas during activation and the Fe3+ (spm) content in the reduced catalyst was observed. The rapid carburization at high reduction temperature resulted in the formation of a superparamagnetic Fe3+ core and an iron carbide layer of the reduced catalyst. FTS activity decreased with the increase in the reduction temperature, but the stability distinctly improved. It was found that the working catalyst loss in the heavier waxy products resulted in higher deactivation rate of the catalyst reduced at lower temperature. With the increase in the reduction temperature, the product distribution shifted towards the lower molecular weight products. [Copyright &y& Elsevier]