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The hydrogenation of CO2 to methane has been investigated over Ru catalysts supported on zeolite (H-ZSM-5) and on silica. Supported Ru catalysts were very active for the hydrogenation of CO2. Ru/ZSM-5 was more selective to methane than Ru/SiO2. On the basis of FT-IR spectra of CO and CO2 adsorbed on the catalysts, it has been suggested that this behaviour can be related to a higher positive polarization of ruthenium on the zeolite. This leads to a weaker Ru–CO bond on the H-ZSM-5-supported sample with a corresponding increase of the hydrogen surface coverage that favours the transformation of the intermediate CO to methane. [ABSTRACT FROM AUTHOR]