Surface processes in selective photocatalytic oxidation of hydroxybenzyl alcohols by TiO2 P25

Aryl aldehydes and acids are important industrial intermediates, but their synthesis from the corresponding alcohols often requires the use of high temperatures and harmful solvents and oxidant agents. Heterogeneous photocatalysis represents an interesting option for the partial oxidation of alcohols to aldehydes at room temperature using water as solvent. In this work, the partial photocatalytic oxidation of 2-hydroxybenzyl alcohol (salicyl alcohol) and 4-hydroxybenzyl alcohol to the corresponding aldehydes and acids has been compared, under environmental-friendly conditions, employing TiO2 P25 as photocatalyst in water. The selectivity to the corresponding aldehydes and acids, under the same experimental conditions, was higher for 4-hydroxybenzyl alcohol than for 2-hydroxybenzyl alcohol owing to its greater stability with respect to oxidant attacks and to the lower adsorption of 4-hydroxybelzaldehyde and 4-hydroxybenzoic acid on the photocatalyst surface. The processes occurring at the oxide surface during the reaction were monitored at the molecular level by FT-IR spectroscopy under in situ UV irradiation to get deeper insights into the different behavior of the two alcohols.