Selective Hydrogen Peroxide Formation by Titanium Dioxide Photocatalysis with Benzylic Alcohols and Molecular Oxygen in Water

Photocatalytic production of hydrogen peroxide (H2O2) on semiconductor catalysts with alcohol as a hydrogen source and molecular oxygen (O-2) as an oxygen source has attracted much attention as a potential method for safe H2O2 synthesis, because the reaction can be carried out without the use of explosive H-2/O-2 mixed gases. Early reported photocatalytic systems with aliphatic alcohol as a hydrogen source, however, produce only a,few millimolar levels of H2O2. We found that benzylic alcohols, when used as a hydrogen source for photoreaction in water with titanium dioxide (TiO2) photocatalyst, produce a very high concentration of H2O2 (ca. 40 mM). Raman spectroscopy and electron spin resonance analysis revealed that the enhanced H2O2 formation is due to the efficient formation of side on coordinated peroxo species on the photoactivated TiO2 surface, via the reaction of benzylic alcohol and O-2. The peroxo species is readily transformed to H2O2, thus facilitating highly efficient H2O2 production.