Fischer–Tropsch Synthesis: Influence of Support Incorporation Manner on Metal Dispersion, Metal–Support Interaction, and Activities of Iron Catalysts

Precipitated Fe/Cu/K Fischer–Tropsch Synthesis (FTS) catalysts incorporated with precipitated and binder Al2O3 were characterized by N2 physical adsorption, Temperature-Programmed Reduction/Desorption (TPR/TPD), and Mössbauer Effect Spectroscopy (MES). It was found that the Al2O3 incorporation manner plays an important role on metal dispersion and metal–support interaction, which dramatically influence the H2/CO adsorption, reduction, and carburization, as well as FTS performances of iron catalysts. Specifically, the incorporation of Al2O3 during precipitation (i.e., precipitated Al2O3) leads to high Fe2O3 dispersion and strengthens the Fe–Cu and Fe–K contacts, which in turn promote the reduction and increase the surface basic sites as well as H2 and CO adsorptions. In sharp contrast, Al2O3 added either after precipitation or after heat treatment of the iron precursor (i.e., binder Al2O3) is likely to form a strong metal–support interaction (i.e., Fe–Al2O3 interaction) and decrease the surface basicity, thereby inhibiting CO adsorption. Correspondingly, in slurry-phase FTS reaction, it was observed that the addition of precipitated Al2O3 facilitates catalyst carburization and improves the FTS activity. As expected with the presence of binder Al2O3, the reduced catalysts contain small amounts of iron carbides and show low FTS activity as well as water gas shift (WGS) reactivity. Further, presumably because of more basic sites than binder Al2O3 supported catalysts, the catalyst incorporated with precipitated Al2O3 shows lower selectivity to light hydrocarbons (methane, C2–C4, C5–C11, and C12–C18) but remarkably higher selectivity to heavy hydrocarbons (C19+). These observations were explained in terms of the influence of the Al2O3 incorporation manner on the promotional effects of Cu and K.