The effects of the addition of Ag, Au, or Rh to a 15 wt% Co/SiO(2) catalyst on the Fischer-Tropsch (FT) synthesis were studied. Both Au and Rh showed a promoting effect on the FT activity, whereas the addition of Ag decreased the activity. The addition of a small amount of Rh (0.1-0.5 wt%) increased the CO conversion by 50% without affecting the selectivity. It was found that Rh catalyzed the reduction of cobalt oxides, but it did not change the number of surface cobalt atoms. It is proposed that the higher activity of Rh-promoted catalysts is due to the hydrogen spillover from Rh to Co during FT synthesis. (C) 2010 Elsevier B.V. All rights reserved.