Surface modification of platinum by titanium dioxide overlayers: A case of simple site blocking

Abstract

The suppression of CO and H 2 chemisorption on Pt surfaces when supported on TiO 2 carriers is well established. Recently, it has been suggested that migration of the support material onto the Pt surface is responsible for this effect. To test this hypothesis, the suppression of CO chemisorption on TiO 2 modified Pt foil has been studied. A combination of X-ray photoelectron spectroscopy (XPS), low energy inelastic ion scattering (LEISS) and temperature programmed desorption were used to fully characterize the composition, electronic structure and chemisorption properties of the modified surface. Surface TiO 2 was prepared by in situ evaporation of Ti from TaTi alloy in a background of 1 × 10 −6 mbar O 2. Subsequent annealing (770 K) of this surface produced a stoichiometric TiO 2. When oxygen vacancies (Ti 3+ centers) were introduced by chemical treatment, an ohmic contact was formed between the reduced TiO 2 and the Pt surface. However, no new major chemisorption states were observed in CO TPD on this modified Pt surface. Rather, a simple suppression of the total amount of chemisorption was observed. Combining LEISS with TPD established a clear linear relationship between the extent of chemisorption suppression and the number of sites physically blocked by the TiO 2.