Ru promoted cobalt catalyst on γ-Al2O3 support: Influence of different impregnation method in catalyst preparation on Fischer-Tropsch Reaction

Cobalt supported γ-Al2O3 catalysts were prepared by stepwise impregnation and co-impregnation of γ-Al2O3 with well mixed aqueous solution of cobalt nitrate and ruthenium chloride as precursors of cobalt and ruthenium respectively. In the stepwise impregnation method the support was first impregnated with the solution of one precursor, dried, calcined and followed by impregnation with the solution of the second precursor, dried and calcined, whereas, in the so-called co-impregnation method, the support is impregnated with the solution of both precursors simultaneously. The selected ruthenium loading was 0.15 wt% while that of cobalt was 15.0 wt% in all of the prepared samples. The effects of impregnation order of the catalysts on activity and selectivity of the Fischer-Tropsch synthesis were investigated in a fixed bed reactor. The catalysts were characterized by temperature programmed reduction (TPR). The addition of a small amount of ruthenium promoter to Co/Al2O3, by co-impregnation method, shifted both steps of cobalt reduction temperatures to lower temperatures by about 100oC. This effect is less pronounced for the catalyst which is 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. This catalyst shows; up to 2 times higher conversion, 4.5% improvement in C5+ selectivity and 15.5% suppression of methane selectivity

Keywords:

Fischer–Tropsch synthesis , Co–Ru/γ-Al2O3 catalyst , promoter , stepwise impregnation , co-impregnation