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.