Efficient utilization of glycerol as a hydrogen source for partial hydrogenation of alkynes over a Cu-loaded TiO2 photocatalyst

Abstract

The utilization of biomass glycerol would contribute to the fight against global warming by reducing greenhouse gas emissions; however, efficient utilization of glycerol in water is still a challenge. In this study, partial hydrogenation of alkynes over a titanium(IV) oxide photocatalyst with a copper cocatalyst (Cu/TiO2) was investigated in the presence of glycerol in an acetonitrile-water solvent. Glycerol worked efficiently as a hydrogen source and alkynes were converted to corresponding alkenes. Glycolic acid and formic acid, which are formed as oxidation products of glycerol, cause a decrease of recyclability due to the partial dissolution of Cu nanoparticles. The stability of the Cu/TiO2 photocatalyst is improved by the addition of NaOH, although the reaction rate decreases. A slight increase in the reaction temperature restores the reaction rate of partial hydrogenation, and preferably, the H2 yield becomes smaller. The results provide a new application of biomass glycerol in water, i.e., a hydrogen source for photocatalytic reactions.