Enhancing selectivity in photocatalytic formation of p-anisaldehyde in aqueous suspension under solar light irradiation via TiO₂ N-doping

The photocatalytic partial oxidation of 4-methoxybenzyl alcohol to the corresponding aldehyde (p-anisaldehyde) was performed under simulated solar irradiation by using home prepared N-doped TiO₂ catalysts. The photocatalysts were prepared by a sol-gel method, using TiCl₄ as TiO₂ precursor and NH₄Cl, urea or NH₄OH as N-doping sources. A commercial TiO₂ (Degussa P25) was also used for comparison aims. The prepared catalysts were characterized by BET specific surface area, XRD, ESEM and UV-vis spectroscopy. The reactivity results show that (i) the doped catalysts are predominantly amorphous, and they show selectivity values far higher than those of the corresponding undoped ones and of well crystallized catalysts - even if the last ones show a higher activity - and (ii) exploitation of solar light significantly increases the reaction selectivity. In addition, different light sources were also used in order to investigate the effect of radiation wavelength ranges on the reactivity and selectivity to aldehyde.