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

Photocatalytic production of hydrogen peroxide (H 2 O 2 ) 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 H 2 O 2 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 H 2 O 2 . We found that benzylic alcohols, when used as a hydrogen source for photoreaction in water with titanium dioxide (TiO 2 ) photocatalyst, produce a very high concentration of H 2 O 2 (ca. 40 mM). Raman spectroscopy and electron spin resonance analysis revealed that the enhanced H 2 O 2 formation is due to the efficient formation of side-on coordinated peroxo species on the photoactivated TiO 2 surface, via the reaction of benzylic alcohol and O 2 . The peroxo species is readily transformed to H 2 O 2, thus facilitating highly efficient H 2 O 2 production.