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We examine in detail the roles of Ti 3+ defects and the associated oxygen vacancies in the activity and selectivity of TiO 2 -supported Au catalysts (Au@TiO 2 ) for renewable hydrogen production by photoreforming of ethanol. A series of Au@TiO 2 catalysts was synthesized using varied exposure to reducing agent NaBH 4 . The electronic structure of the series of Au@TiO 2 catalysts was examined spectroscopically and showed that increased exposure to NaBH 4 increased the concentration of Ti 3+ defects and the associated oxygen vacancies in TiO 2 , and increased the amount of electron-rich Au. The activity and selectivity of the catalysts increased as the concentration of defect sites increased. During ethanol photoreforming, the Au@TiO 2 catalyst with the highest concentration of defects produced highpurity H 2 at a record rate of ∼7093 μmol g cat −1 h −1 and the carbon−carbon bond (C−C) cleavage of ethanol to form CH 4 and CO 2 was significantly inhibited. Extensive spectroscopic data support the conclusion that TiO 2 surface oxygen vacancies adjacent to Au may be active catalytic sites that assist the adsorption and activation of ethanol as well as the delivery of photogenerated charge carriers to the activated species during the photoreforming of ethanol.

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