Sonochemical hydrogen production efficiently catalyzed by Au/TiO ₂

Au/TiO₂ was used as a highly efficient sonocatalyst to produce H₂ from water or aqueous solutions. Au/TiO₂ significantly increased the yields of H• and •OH radicals in the sonolysis of water. Product analysis and isotope evidence indicated that hydrogen molecules derived from methanol/water solutions were formed by three pathways: (1) recombination of two H• atoms from the cleavage of water molecules, (2) H-abstraction from methanol by H• generated by water cleavage, and (3) thermal reforming of methanol. The relative importance of each pathway was assessed by carefully analyzing the hydrogen-isotope composition of the evolved hydrogen gas using a modified gas chromatograph. The source of hydrogen in the H₂ evolved from methanol/water solutions during sonolysis was also addressed. Data showed that, although the addition of methanol in the presence of Au/TiO₂ resulted in a 12-fold increase in the rate of H₂ evolution, nearly half of the hydrogen atoms were nevertheless derived from water molecules. Control studies of H₂ formation in the presence of bare TiO ₂ and in the absence of a catalyst were also performed. In both cases, the compositions of evolved hydrogen gas were similar to that of the Au/TiO₂ system, although hydrogen evolution was much slower. These findings reveal that Au nanoparticles on the TiO₂ surface effectively catalyze water cleavage and methanol reforming.