ESCA Studies of the Adsorptions of CH₃OH, HCOOH and HCHO on Polycrystalline Ti and Tio₂(100) Surfaces

The Surfaces of polycrystalline titanlum and TiO₂ (100) were characterised by XPS and UPS. For clean polycrystalline titanium surfaces, the Ti(2p) peaks appeared at 453.7eV and 460.8eV binding energies, corresponding to the 3/2 and 1/2 signals. The HeⅠ or HeⅡ induced Ti (3d) band appeared at 0.8eV below the Fermi level. For order TiO₂(100) surfaces, the Ti(2p) peaks were at 458.6eV and 464.4eV with no band at 0.8eV observeable in the UPS spectra. Ar⁺ bombardment would caule defects on the surfaces. Ti(2p) peaks corresponding to the formation of Te²⁺ and Te³⁺ were observed. The existance of the 0.8eV band below the Fermi level in the UPS spectra also showed that the surfaces were reduced. O₂⁺ bombardment and annealing at 700K would re-oxidised the defect surface to Tio₂(100).
Metallic titanium is a strong Lewis base. On polycrystalline Ti surfaces, CH₃OH, HCOOH and HCHO adsorbed dissociatively at 295K to give surface carbide, oxide, OH, CH_x and CH_xO (x<3). In the case of HCOOH adsorption, surface formate was formed as well. Order TiO₂(100) surfaces are of mild bascity. CH₃OH adsorption only gave surfaces OH, CH_x and CH_xO. Adsorption of HCHO at 295K gave similar species but at 700K, formate was obsenved. On defect TiO₂(100) surfaces, oxygen vacancies faciliated C-O bond eleavage. HCOOH adsorbed mainly as HCO and the adsorption of HCHO did not form formate at 700K.