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 (O2) 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 H2/O2 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 O2. The peroxo species is readily transformed to H2O2, thus facilitating highly efficient H2O2 production.