In-situ DRIFTS experiments under CO2/H2 mixture were performed to probe the surface intermediate species on the reduced catalysts and possibly obtain information about the active sites, comparing Ru/SiO2 and Ru/12%Ti-SiO2. A detailed discussion can be found below Fig. in the Supporting Information. Focusing on the region of carbonyl bands at 2045-1960 cm - 1 in Fig. (b) and (c), we perceive that carbonyl species are formed at the temperature as low as 100 C for Ru/12%Ti-SiO2. The bands at 2000-1993 cm -1 and 2045 cm -1 in the spectra of Ru/SiO2 and Ru/12%Ti-SiO2, respectively, can be ascribed to CO linearly adsorbed on Ru sites (Ru-CO). It has been proposed that the wavenumber of this linearly-bonded CO is coveragedependent. A shift to higher wavenumber is indicative of a larger CO coverage . There is also a marked difference in band intensities at 1975-1960 cm -1 between the two catalysts. These bands can be assigned to bridged-bonded CO at the metal-support interface (Ruif-CO) . This indicates that for Ru/12%Ti-SiO2, CO adsorption could be facilitated at interfacial sites between Ru and TiO2. Several studies discuss that interfacial adsorbed carbonyl species are more active intermediates than linear carbonyl and multi-carbonyl species in CO/CO2 methanation reactions either via direct or H-assisted dissociation of adsorbed CO .