Fischer-Tropsch synthesis: the influence of various cobalt compounds applied in the preparation of supported cobalt catalysts on their performance

摘要

The dependence of the activity of cobalt-based catalysts for Fischer-Tropsch synthesis on the type of cobalt precursor and support material was studied. Titania-supported catalysts were prepared by means of incipient wetness impregnation (IW), precipitation (PR) and spreading (SP) techniques. All catalysts were characterised by XRD, XPS , TPR and CO pulse experiments. The catalytic performance of the catalysts was examined at a total pressure of 20 bar, a temperature of 200 deg C, a space velocity (GHSV) of 1200 h~(-1) and using a syngas having a H_2 to CO ratio equal to 2. For titania-supported catalysts, the use of oxalate, acetate and acetyl acetonate as cobalt precursors resulted in a higher activity compared with the reference catalyst prepared from nitrate. The activities determined can be slightly correlated with an increasing cobalt dispersion, which was affected by the preparation procedure and type of precursor. The range of chain growth probabilities increased in the following order: cobalt-EDTA (#alpha#= 0.71) < cobalt acetate (#alpha#= 0.74) < cobalt(II) acetyl acetronate, cobalt oxalate, cobalt nitrate, cobalt-EDTA (#alpha#= 0.82-0.84). On adding 0.1 wt% Ru to the catalyst made from cobalt(III) acetyl acetonate, #alpha# increased from 0.71 to 0.80. For catalysts prepared by incipient wetness impregnation, ceria and zirconia were additionally used as supports. The activity changed in the following order: ZrO_2 < TiO_2 < CeO_2. The #alpha#-value for ceria-and zirconia-supported cobalt catalysts amounted to 0.81 and 0.69., respectively.