Benzene–ammonia coadsorption on TiO2(anatase)

Abstract

The adsorption of benzene on clean and ammonia-covered titania samples has been studied by FTIR spectroscopy. Special attention has been paid to the stretching vibrations of surface hydroxy groups. The presence of coordinated ammonia does not affect the ν(OH) bands of free surface TiOH groups, although surface Ti—O stretching modes (1100–1000 cm^–1) are perturbed. The ν(OH) bands shift and broaden upon benzene adsorption both on clean and ammonia-covered surfaces. However, the extent of this shift for clean surfaces is twice that for ammonia covered surfaces. This is interpreted as a weakening effect of coordinated ammonia on the Brønsted acidity of surface hydroxy groups. The adsorption of benzene also causes a perturbation of the spectrum of coordinated ammonia, revealing a direct interaction between these two adsorbates.