FTIR SPECTROSCOPIC STUDY OF THE INTERACTION OF CO2 AND CO2+H-2 OVER PARTIALLY OXIDIZED RU TIO2 CATALYST

At least three distinct linearly bound carbonyl species are identified in the adsorption of CO2 or CO2 + H-2 over Ru-RuO(x)/TiO2 catalyst. The relative concentration and the growth of these species depend on metal oxidation state, presence of hydrogen, reaction temperature, and duration of exposure. The presence of preadsorbed or coadsorbed hydrogen promotes formation of [GRAPHICS] type species, the RuO(x)-(CO)ad species develop only on prolonged exposure to a dose of CO2 or CO2 + H-2. The oxygen or the hydrogen ligand bonded to ruthenium facilitates C-O bond scission. The widely reported lower temperature requirement for the CO2 methanation reaction as compared to that of CO is attributed to the high reactivity of nascent carbonyl species which give methane directly via ''active'' carbon formation. As shown earlier (Gupta et al., J. Catal. 137, 437 (1992)), the CO methanation requires multistep transformations, making the process energy intensive, particularly in the 300-450 K temperature range. The studies using H-2 and C-13 labeled adsorbates helped in the identification of oxygenated surface species having vibrational bands in the 1000-1800 cm-1 region. These species are regarded as inactive side products formed on the support and/or at the Ru-support interfaces. (C) 1994 Academic Press, Inc.