Adsorption of CO2 on oxidized, defected, hydrogen and oxygen covered rutile (1 × 1)-TiO2(110)

Abstract

Presented are initial, S₀ and coverage, Θ, dependent S(Θ), adsorption probability measurements of CO₂ as a function of impact energy, E_i = 0.12–1.3 eV, adsorption temperature, T_s = 85–300 K, hydrogen and oxygen pre-exposure, as well as density of defects, Γ, as varied by annealing (T = 600–900 K) and Ar⁺ ion sputtering (dose χ_Ar at 600 eV at 85 K) of a rutile (1 × 1) TiO₂(110) surface. The defect densities were qualitatively characterized by thermal desorption spectroscopy (TDS) of CO₂. The CO₂ TDS curves consisted of two structures that can be assigned to adsorption on pristine and oxygen vacancy sites, in agreement with earlier studies. S₀ decreased linearly with E_i and was independent of T_s. The adsorption dynamics were dominated by the effect of precursor states leading to Kisliuk-like shapes over the E_i and T_s range studied. Oxygen vacancy sites reduced S₀ of CO₂. Preadsorbed oxygen blocked preferentially defect sites, which led to an increase in S₀. Hydrogen preadsorption results in physical site blocking with decreased S₀ as H-preexposure increased, while the shape of S(Θ) curves was conserved. In contrast to oxygen, hydrogen does not adsorb preferentially on defect sites. The adsorption probability data were parameterized by analytic functions (Kisliuk model) and by Monte Carlo simulations (MCSs).