Performances of promoted cobalt catalysts supported on mesoporous alumina for Fischer-Tropsch synthesis

Noble metals (Ru, Re, Pt, Ir) and transition metals (Mn, Y) with their atomic ratio of 0.01 to cobalt were used as promoters on the cobalt catalysts supported on mesoporous alumina. The cobalt loading was 15 wt% and all catalysts were tested for Fischer-Tropsch synthesis in a fixed -bed reactor. The process conditions for activity test were: 230 degrees C and 400 psi, GHSV = 900 h(-1), and H-2/CO= 2.0. The selectivity test for the promoted and unpromoted catalysts was performed at CO conversion approximate to 50% by adjusting the syngas flowrate. Addition of promoters increased the cobalt dispersion on mesoporous alumina support. The highest increase in dispersion from 4.7% to 7.6% resulted from addition of Ru. Promoters positively impacted the cobalt dispersion in the decreasing order of: Ru < Re < Pt < Ir < Mn < Y. The reduction temperature for all promoted catalysts were shifted to lower temperature. The maximum decrease in temperature happened with platinum by Delta T similar to -150 degrees C for the 1st reduction temperature and Delta T similar to - 270 degrees C for the 2nd reduction temperature. The reducibility of the CoOx species on mesoporous alumina was extensively improved by noble metals addition and modestly enhanced by Mn and Y. Significant increase in CO conversion and C5+ of the promoted catalysts were observed. CO conversion was increased from similar to 60% to similar to 86, 84, 82, 80% as a result of Ru, Re, Ir, Pt addition. Addition of Ru and Re promoters favored the heavy molecular weight hydrocarbons' (C5+) selectivity and improved it from 81.7% to 84.2 and 83.1%, respectively.