Noble metals, such as platinum or gold, may promote the reduction of cobalt in supported cobalt catalysts either by direct contact or indirectly via hydrogen spill-over. The synthesis go gold nano-particles using THPC in the presence of a calcined Co/TiO2-catalyst precursor results in a broadening of the gold particle size distribution possibly due to the association of gold with Co3O4. This was not observed for platinum and platinum-gold alloys synthesized in the same manner. Platinum-gold alloys are less effective than platinum as a reduction promoter, possibly due to the presence of gold on the surface of the alloy particles.