Combined FTIR and Temperature Programmed Fischer-Tropsch Synthesis over Ru/SiO2 and Ru-Ag/SiO2 Supported Catalysts

摘要

Combined temperature programmed reaction (TPR) and infrared (IR) spectroscopic studies for Fischer-Tropsch reaction have been performed over Ru/SiO2 and Ru-Ag/SiO2 supported catalysts.Reaction of linearly absorbed CO with hydrogen starts at 375 K over Ru/SiO2 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_x intermediates not observed with Ru/SiO2 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 CO2 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/SiO2 catalyst as compared to Ru/SiO2 catalyst is due to the formation of Ru-Ag bimetallic surfaces impeding hydrogen adsorption.