FTIR study of adsorption, thermal reactions and photochemistry of benzene on powdered TiO2

The adsorption, thermal reactions, and photochemistry of benzene on powdered TiO2 have been investigated using Fourier-transform infrared spectroscopy. Benzene is adsorbed with its π electrons interacting with the surface Ti4+ ions, and is stable even when the TiO2 temperature is increased to 400°C. However, it is subject to thermal decomposition to H2O(g), CO(g) and CO2(g) in the presence of O2 and the dissociation occurs below ∽225°C. With the aid of an adsorption study of phenol and iodobenzene, it is found that phenoxy groups are generated on the surface in the photooxidation of benzene on TiO2 and the amount greatly increases in the presence of H2O or O2. Other surface products containing carbonyl or carboxylate groups are produced as well for benzene photoreaction in O2. The present in situ study shows that the products extracted using solvents from TiO2 catalysts after photooxidation of benzene in previous investigations may not reveal the real products formed on the surface during photoillumination processes.