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

Abstract

Competitive adsorption of prototype molecules such as ¹²CO, ¹³CO and CO₂ at the two typical fivefold coordinated Ti_5c⁴⁺ cation sites of reduced rutile TiO₂(110) surfaces was studied in a newly designed UHV-FTIR system. The measured binding energies of ¹²CO, ¹³CO or CO₂ adsorbed at two kinds of Ti_5c⁴⁺ 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.