Sonochemical Hydrogen Production Efficiently Catalyzed by Au/TiO2

Au/TiO2 was used as a highly ellicient sonocatalyst to produce H-2 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: (I) 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 leach 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 H-2 evolved from meethanol/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 H-2 evolution, nearly half of the hydrogen atoms were nevertheless derived from water molecules. Control studies of H-2 formation in the presence of bare TiO2 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.