Photocatalytic hydrogen production from ethanol over Au/TiO₂ anatase and rutile nanoparticles: Effect of Au particle size

Solar hydrogen production from renewables such ethanol and water is one of the promising methods for fuel generation either for direct combustion or to power fuel cells. Gold catalysts with finite nanoparticle size have been shown active for many dark catalytic reactions and in particular for oxidation reactions. Their potential as active materials for photoreactions has received sporadic attention, however. In this work we have prepared Au catalysts deposited on anatase and rutile TiO₂ nanoparticles of similar sizes in order to study their activity for the photo-production of hydrogen from ethanol alone as well as in presence of varying amounts of water. The catalysts have been studied by BET, XRD, HRTEM, XPS, and TPD while their catalytic reaction was followed in liquid slurry under UV illumination. Au mean particle size between ca. 3 and 30 nm size were prepared on both supports. Our study indicates that while small Au particle catalysts were more active than larger ones the photocatalytic activity tracks the amount of Au without particle size effect in contrast to dark reactions. The rate of the photocatalytic reaction was largely determined by the bulk electron-hole recombination of the TiO₂ support. For the same Au particle size and the same TiO₂ particle size the rate of hydrogen production on anatase was about 100 times faster than that observed on rutile. Extraction of reaction rates indicates that a production of ca. 5 L of H₂ min^-1 kg^-1 Catal. can be obtained. This production rate puts these catalysts as promising materials for hydrogen generation for applied devices.