Selective photocatalytic oxidation of aromatic alcohols in solar-irradiated aqueous suspensions of Pt, Au, Pd and Ag loaded TiO2 catalysts

Abstract

The photocatalytic partial oxidation of 4-methoxybenzyl alcohol (MBA) and 4-nitrobenzyl alcohol (NBA) to corresponding aldehydes or acids was performed in water under simulated solar light at different pH's by using Pt, Au, Pd and Ag loaded Degussa P25 TiO2 catalysts, prepared by photoreduction. Bare Degussa P25 TiO2 was also used as a reference. The metal loaded TiO2 photocatalysts were characterized by XRD, TEM, ESEM and DRS techniques. The best activity and selectivity results were obtained with Pt loaded TiO2. The reactivity results show that metal loading on Degussa P25 sharply promotes the photoactivity and product selectivity towards aldehydes. Moreover, at low pH's very high aldehyde selectivities were determined for both alcohols. MBA oxidation rate was very high at low pH's, whereas an opposite trend was observed for NBA, due to the difference of the substituent group. Only from NBA a significant amount 4-nitrobenzbic acid (ca. 50%) was obtained at high pH values