Reaction mechanism and pathway for the selective photocatalytic hydrogenation of nitroaromatics over TiO2 in alcohols

Abstract

This research investigated the mechanism and photocatalytic performance of the selective photocatalytic hydrogenation of different nitroaromatics (Ar-NO2) in several alcohols under UV light using P25-TiO2 at room temperature and atmospheric pressure. The effect of Pt-deposited P25-TiO2 on the photocatalytic performance was also studied. Ar-NO2 was converted to aminoaromatics (Ar-NH2) with high Ar-NO2 conversion and Ar-NH2 selectivity at nearly 100%. The amounts of Ar-NH2 were proportional with carbonyl compounds at the ratio around 1:3. Acetaldehyde, acetone, and butanone were produced by oxidation of ethanol, 2-propanol, and butanol, respectively. Ethanol exhibited the fastest completed Ar-NO2 conversion due to the most efficient formation of hydrogen ions (H+). Moreover, Pt/P25 exhibited higher photocatalytic activity than P25-TiO2, which was in good agreement with the UV-Vis, XPS, and PL results. Pt/P25 promoted electron transfer and retard electron-hole recombination. Accordingly, the photocatalytic activity was influenced by hydrogen donor and charge separation efficiency of the catalyst. From varying the substrate, the concentration of substrate, alcoholic solvents, and the catalyst, this suggested that the photocatalytic performance of this reaction did not rely on the substrate but depended on H+ formation rate from the oxidation of alcohol by hole (h+).