Fischer-Tropsch synthesis on Co/ZnO catalyst-Effect of pretreatment procedure
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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 (H 2 -TPD) with pulse re-oxidation. Reduction of Co 3 O 4 occurs in two stages during H 2 -TPR and CO-TPR. In the latter case CoO, metallic cobalt, cobalt carbides (Co x C; x = 2 or 3) and carbon (from CO disproportionation) are formed during the reduction process. The existence of Co 0 along with CoO and Co x C, indicates a possibility of two reaction paths for formation of Co x C from CoO: the direct path (CoO Co x C) and a series reaction via Co 0 (i.e. CoO Co 0 Co x C). 2011 Elsevier B.V. All rights reserved.