This study focuses on the state of nickel as promotor in cobalt Fischer–Tropsch synthesis catalysts. Both catalyst material and promotor were monitored during reduction and under Fischer–Tropsch synthesis conditions with X-ray absorption spectroscopy and X-ray powder diffraction. The study was carried out on catalysts with varying amounts of metal and promotor in order to elucidate interactions between support, catalyst and promotor metal. Nickel acts as a reduction promotor for cobalt, with a low percentage of nickel interacting with the alumina support to form unreducible nickel aluminate. Furthermore, in a two-step impregnation procedure nickel behaves as seeds for the cobalt particles with the subsequent formation of a solid solution between the two metals.