CO2 as a probe for monitoring the surface defects on TiO2(110) -: Temperature-programmed Desorption

The adsorption and thermal desorption of CO2 bound to both oxidized and reduced TiO2(110) surfaces has been studied using temperature-programmed desorption. For the stoichiometric and fully oxidized surface, a single thermal desorption feature (E-d = 48.5 kJ/mol) is measured and attributed to CO2 bound to regular fivefold coordinated Till atoms. For the fully reduced TiO2(110) surface, CO2 binds not only to regular sites, but also to oxygen vacancy sites (E-d = 54.0 kJ/mol), created by thermal annealing. The variation in the characteristic CO2 desorption kinetics was measured as a function of the surface reduction temperature, and the systematic production of increasing levels of surface defects is observed in the temperature range of 600-1100 K. This investigation was complimented by a comparison of the characteristic CO2 desorption features from a TiO2(110) surface which was prepared by sputtering and direct annealing, without annealing in O-2 flux. It was found that after annealing to temperatures above 900 K, the CO2 thermal desorption is very similar for surfaces prepared by the two methods, regardless of surface preparation.