Pt/SiO2 and Ca-promoted Pt/SiO2 catalysts were prepared from three different Pt precursors and tested for CO hydrogenation at 280 degrees C and 25 bar. Changing the Pt precursor affects both the activity and selectivity of the resulting catalyst. The measure of activity enhancement for methanol on addition of the promoter increases in the order [Pt(NH3)(4)](OH)(2) < H-2[Pt(OH)9] < H-2[PtCl6]. A correlation between the activity enhancement on Ca addition and the extent of metal-promoter interaction, as measured by the change in the temperature-programmed reduction profile and loss of chemisorption capacity, was observed. This suggests that the dopant needs to be located on the metal particle in order to promote the reaction.