Fourier transform infrared study of the performance of nanostructured TiO2particles for the photocatalytic oxidation of gaseous toluene

Thermal and hydrothermal treatments have been applied to an amorphous TiO2 precursor for obtaining nanosized TiO2 particles (P11t and P11h, respective ly) of different photocatalytic properties. The activity of these catalysts has been tested by performing the toluene oxidation in gas phase in a cont inuous photoreactor. A Fourier transform infrared (FTIR) investigation of t he catalysts under conditions prevailing during the test photoreaction has also been carried out. The photoreactivity results showed that CO2 was the main oxidation product and benzaldehyde a stable intermediate. Anatase P11t photoactivity was similar to that observed for commercial photocatalysts, while anatase P11h presented a marked improvement. The FTIR study on these samples indicate that P11h has a higher number of hydrogen-bonded hydroxyl groups that are more stable under RT outgassing than P11t. The higher photo activity of P11h is attributed to the participation of these hydrogen-bonde d hydroxyls in the toluene conversion to CO2. FTIR spectra also suggest tha t benzaldehyde, the minor oxidation product, originates from toluene adsorb ed on isolated hydroxyls. Benzaldehyde is more strongly adsorbed on P11h th an on P11t; the presence of water vapor in the reacting mixture, however, f acilitates its desorption and/or photooxidation. (C) 2001 Academic Press.