Combined temperature programmed reaction (TPR) and infrared (IR) spectroscopic studies for Fischer-Tropsch reaction have been performed over Ru/SiO 2 and Ru-Ag/SiO 2 supported catalysts. Reaction of linearly absorbed CO with hydrogen starts at 375 K over Ru/SiO 2 catalyst and reaches maximum at 420 K accompanied with an intensity decrease of linear CO absorption. The reaction with bridged absorbed CO peaks around 510-535 K. Addition of Ag yields mixed Ru-Ag bimetallic sites while it suppresses the formation of bridged bonded CO. Formation of methane on this modified surface occurs at 390 K and reaches maximum at 444 K. Suppression of hydrogen on the Ag-doped surface also occurs resulting in the formation of unsaturated hydrocarbons and of CH, intermediates not observed with Ru/SiO 2 catalyst. Such intermediates are believed to be the building blocks of higher hydrocarbons during the Fischer-Tropsch synthesis. Linearly absorbed CO is found to be more reactive as compared to bridged CO. The Ag-modified surface also produces CO 2 and carbon. On this surface, hydrogenation of CO begins at 390 K and reaches maximum at 494 K. The high temperature for hydrogenation of absorbed CO and C over Ru-Ag/SiO 2 catalyst as compared to Ru/SiO 2 catalyst is due to the formation of Ru-Ag bimetallic surfaces impeding hydrogen adsorption.