Study on Fe–Al2O3 interaction over precipitated iron catalyst for Fischer–Tropsch synthesis

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.