Ru promoted cobalt catalyst on γ-Al2O3: Influence of different catalyst preparation method and Ru loadings on Fischer-Tropsch reaction and kinetics

Ruthenium promoted cobalt catalysts supported on γ-Al2O3 were prepared by stepwise and co-impregnation methods. The effects of impregnation order on activity and selectivity of the Fischer-Tropsch synthesis (FTS) were investigated using fixed bed microreactor. The catalysts were characterized by TPR, XRD and TEM. The selected Ru loading was 0.15 wt.% while that of Co was 15.0 wt.% in all of the prepared samples by different order of impregnation. The catalyst prepared by co-impregnation method shifted both steps of cobalt oxide reduction temperatures to lower temperatures by about 100 °C. However, temperature shift was lower for the catalyst prepared by stepwise impregnation method. The highest CO conversion and C5+ selectivity and the lowest methane selectivity were obtained for the catalyst synthesized by co-impregnation method. Two other catalysts with 0.3 and 0.6 wt.% of Ru loadings on 15.0 wt.% Co were synthesized by co-impregnation and its effect on the FTS was investigated. The prepared catalysts showed an increase in CO conversion with the increase of Ru from 0 to 0.30 wt.%. However, further increase in Ru led to lower CO conversion for a Ru loading of 0.6 wt.%. The effects of temperature and H2/CO ratio for all catalysts were examined and their performance modeled by a Langmuir-Hinshelwood-Hougen-Watson (LHHW) rate expression.