Low-temperature scanning tunnelling microscopy was used to study the adsorption of CO2 on rutile (110) from 80 to 180K. For low CO2 doses, two molecular adsorption sites with different binding energies were identified, which were effectively isolated from one another by an apparent activation barrier to their interconversion. The less tightly bound adsorption site was identified as being CO2 adsorbed atop 5-fold coordinated titanium surface atoms (Ti5f), without binding preferentially near oxygen vacancies. CO2 desorption from Ti5f occurred at about 140K. The more strongly bound site involved molecular CO2 binding at bridging oxygen vacancies (VO,br). Two distinct configurations of VO,br bound CO2 molecules were observed. Despite its being bound to the vacancy, CO2 did not dissociate thermally but remained intact up to the desorption temperature of about 175K. At an elevated tunnelling bias, the scanning tunnelling microscope tip could selectively dissociate these CO2 molecules and thus trigger the healing of individual VO,br. At higher coverages, CO2 adsorption occurred predominantly at the more abundant Ti5f sites, with the distribution of CO2 molecules being determined by interactions along both the [001] and [1¯10] directions.

CO2 Adsorption, Diffusion, and Electron-Induced Chemistry on Rutile TiO2(110): a Low-Temperature Scanning Tunneling Microscopy Study. Acharya, D.P., Camillone, N., Sutter, P.: Journal of Physical Chemistry C, 2011, 115[24], 12095-105