UHV-FTIRS studies on molecular competitive adsorption: 12CO, 13CO and CO2 on reduced TiO2(110) surfaces.

Competitive adsorption of prototype molecules such as (12)CO, (13)CO and CO2 at the two typical fivefold coordinated Ti5c(4+) cation sites of reduced rutile TiO2(110) surfaces was studied in a newly designed UHV-FTIR system. The measured binding energies of (12)CO, (13)CO or CO2 adsorbed at two kinds of Ti5c(4+) sites are different. The molecular occupying probability at these sites depends on the binding energy of the adsorbed molecules; while, the molecular exchanging probability at these sites depends on their binding energy difference due to the presence of competitive adsorption. A simple thermodynamic equilibrium model was proposed to qualitatively interpret the adsorption and competitive adsorption mechanisms. These results will contribute to the elucidation of the (photo)catalytic process on TiO2(110) surfaces.