Adsorption and interaction of CO2 on rutile TiO2(110) surfaces: a combined UHV-FTIRS and theoretical simulation study

CO2 adsorption and interaction on rutile TiO2(110) surfaces was studied by UHV-FTIRS combined with theoretical simulations. With increasing CO2 exposure, CO2 adsorbs in succession at the oxygen vacancy (Vo) sites, on the five-coordinated Ti cation (Ti-5c) sites and the bridging oxygen (O-br) sites at low temperature. The coupling has occurred between neighboring CO2 adsorbed on Ti-5c sites from rather low CO2 coverage (similar to 0.5 ML), leading the nu(3)(OCO) asymmetric stretching vibrations to split into two absorption bands in IR spectra. Two kinds of coupled geometries of adjacent CO2 on Ti-5c sites are determined by theoretical simulations. For the higher CO2 coverage (similar to 1.5 ML), the horizontal adsorption configuration along the [1 (1) over bar0] azimuth of CO2 adsorbed on O-br sites is identified for the first time using polarization-and azimuth-resolved RAIRS in experiments. The significant deviation of CO2 from the top of O-br sites demonstrates the strong coupling between CO2 adsorbed on O-br and Ti-5c sites.