Effects of preparation method on the properties of cobalt supported β-zeolite catalysts for Fischer-Tropsch synthesis

The effect of preparation method on the properties of Co supported β-zeolite catalysts was examined in this study. Co-supported β-zeolite catalysts (20wt.% Co as Co₃O₄) were prepared by impregnation (IMP20), incipient wetness (IW20), physical mixing (PHY20) and precipitation (PCT20) methods and were characterized by various methods including N₂ adsorption (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂ thermal programmed reduction (H₂-TPR), and transmission electron microscopy (TEM). Fischer-Tropsch (FT) synthesis was carried out over these catalysts at 230°C and 1MPa in a fixed-bed flow-type reactor. XPS and H₂-TPR analyses suggest that the catalysts can be ranked in terms of metal-support interactions: PCT20>IMP20≅IW20>PHY20. On the other hand, based on reducibility, the catalysts were ordered as follows: PHY20>IMP20≅IW20>PCT20. The catalytic activity and product selectivity during FT synthesis were also found to depend on the catalyst preparation method. The catalyst prepared by the incipient wetness method exhibited the highest CO conversion with high liquid production, whereas the physically mixed catalyst showed the lowest CO conversion. All the catalysts produced gasoline-range liquid hydrocarbons (C₅-C₁₁) mainly and the selectivity towards i-paraffins was more than 60% in the case of the catalyst prepared by precipitation. Furthermore, the composition of liquid products produced over catalysts prepared by the impregnation and incipient wetness methods were similar to each other. Thus, the results of the study clearly show that the physico-chemical properties of the catalysts as well as catalytic activities and product selectivity during the FT reaction strongly depend on the catalyst preparation method.