Photocatalytic Reforming of Aqueous Acetic Acid into Molecular Hydrogen and Hydrocarbons over Co-catalyst-Loaded TiO₂: Shifting the Product Distribution

Abstract

Acetic acid in aqueous suspensions of co-catalyst-loaded TiO2 was photocatalytically converted into carbon dioxide, molecular hydrogen, methane, and ethane. The formed amounts of CO2 were found to increase in the order Ag/TiO2 < Au/TiO2 < Rh/TiO2 < RuO2/TiO2 < IrO2/TiO2 < Pt/TiO2, thus indicating that the metal oxides employed here are suitable co-catalysts to promote the photocatalytic conversion of acetic acid. The same sequence of activities was found for methane evolution but not for the formation of H2. The evolved amounts of these products as well as the amount distribution were found to be strongly affected by the initial concentration of the organic acid and by the co-catalyst. A large value of the work function of the employed co-catalyst seems to favor H2 evolution. Gaseous mixtures rich in hydrocarbons are photocatalytically produced at sufficiently high initial concentrations of acetic acid employing a composite photocatalyst, where the co-catalyst has a low value of the work function, such as IrO2 and Ag.