Fischer–Tropsch synthesis on Co/ZnO catalyst—Effect of pretreatment procedure

The effect of catalyst pretreatment, using hydrogen or carbon monoxide, on the activity and selectivity of cobalt on ZnO catalyst (10 wt% Co/ZnO) during Fischer–Tropsch synthesis was studied in a fixed bed reactor. Catalyst reduced with hydrogen had higher activity and higher olefin content, and produced less methane than the CO activated catalyst. Catalysts were characterized by means of Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR), and hydrogen chemisorption (H2-TPD) with pulse re-oxidation. Reduction of Co3O4 occurs in two stages during H2-TPR and CO-TPR. In the latter case CoO, metallic cobalt, cobalt carbides (CoxC; x = 2 or 3) and carbon (from CO disproportionation) are formed during the reduction process. The existence of Co0 along with CoO and CoxC, indicates a possibility of two reaction paths for formation of CoxC from CoO: the direct path (CoO → CoxC) and a series reaction via Co0 (i.e. CoO → Co0 → CoxC).

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► H2-activated Co/ZnO catalyst was more active than the CO-activated catalyst.
► H2-activated catalyst had higher olefin content and lower methane selectivity.
► Both cobalt carbide (CoxC; x = 2 or 3) and metallic cobalt were found after CO pretreatments.