Adsorption and Reaction of CO2 on the RuO2(110) Surface

The interaction of CO2 with the bare RuO2(110) surface, exposing unsaturated Ru and oxygen atoms, was studied using high-resolution electron energy-loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). At 85 K, CO2 is found to adsorb only on coordinatively unsaturated Ru-cus sites giving rise to three different species: physisorbed CO2, chemisorbed CO2 δ-, and CO2·CO2 δ- dimers. A complete assignment of the vibrational spectra is reached which allows us to gain insight into the reactions involved. Upon annealing, two channels open up for physisorbed CO2: desorption or further reaction with chemisorbed CO2 δ- forming CO2·CO2 δ- dimers. At 175 K, a bidentate carbonate is observed because of the reaction of CO2 δ- with an O bridge. Further annealing induces a thermally activated conversion from the bidentate to a CO3 δ- monodentate species. The latter is stable up to about room temperature and then decomposes into CO2 and Oad. The adsorption geometries of the different species are discussed in detail. The activation of CO2 to form a chemisorption bond occurs only on the Ru-cus site. This gives further evidence for the key role played by Ru-cus in the catalytic activity of the bare RuO2(110) surface.