Evidence of correlation between electronic density and surface acidity of sulfated TiO2

Correlation between the electronic structure and surface acidity of TiO2-SO42- with different SO42- amounts has been investigated by means of NH3-TPD, NH3-FT-IR and XPS. With the increase of sulfate loadings, the shift of binding energies of O 1s in hydroxyl and Ti 2p(2/3) increases and is proportional to total acidity. A linear relation is obtained between Ti 2p binding energy shift and Lewis acid sites, while the shift in O 1s binding energy is attributed both to the generation of NH3 hydrogen bond and of Bronsted acid sites. Accordingly, the results obtained from XPS measurements provide evidence that the ammonia adsorption sites are attributed to the decrease of electron density of O 1s in hydroxyl (Bronsted type and H bonded) and Ti 2p(2/3) (Lewis type) by inductive effect of the neighboring sulfate ion