The hydrated layer and the adsorption of carbon monoxide at the surface of titania (anatase)

The vacuum thermal dehydration of TiO2 has been investigated by FTIR spectroscopy and revealed that the surface hydrated layer is made up of hydroxyls and coordinated water mols. The thermal elimination of the two components of the surface hydrated layer gives rise to 2 different families of strong Lewis acid centers, at which CO adsorbs at ambient temp., yielding two σ-coordinated species characterized by different coverages, adsorption isotherms, νCO stretching frequencies and heats of adsorption. The properties of adsorbed CO are influenced, through inductive effects, by the nature and concn. of charge-releasing and/or withdrawing species present at the surface. On sulfate-contaminated TiO2 only one CO adsorbed species is obsd., consistent with the virtually substitution of surface hydroxyls with sulfate residues. The charge-withdrawing nature of the latter strongly affects the properties of adsorbed CO, in agreement with the proposed model.