Zeolite-supported ruthenium oxide catalysts for photochemical reduction of water to hydrogen

Ruthenium oxide on zeolite Y was made by thermal decarbonylation of Ru-3(CO),2 followed by heating in air. The morphology of the RuO2 was strongly dependent on the temperature at which oxidation was carried out. The size of the RuO2 particles increased from 2-5 to >50 nm as temperature was increased from 100 to 400 degreesC. Particle shape was also altered, being spherical at low temperatures and fibrous-like with specific crystals faces (101) exposed at higher temperatures. The photocatalytic activity of RuO2/zeolite Y for H-2 formation from H2O was examined using the system Ru(bpy)(3)(2+), Na-2 EDTA and methylviologen (MV2+). The rate of hydrogen evolution peaked with the RuO2/zeolite Y generated at 200-300 degreesC. The initial catalytic activity of RuO2/zeolite Y was poorer than Pt, but better than powder RuO2. However, the extent of MV2+ decomposition was less with the RuO2 catalysts allowing for longer term use. The decomposition of MV2+ was due to the photochemical instability of the methylviologen radical. By attaching the Ru(bpy)(3)(2+)-Moiety covalently to the RuO2-zeolite surface, the viologen radical is generated close to the catalyst. This system also resulted in H-2 production, but with no detectable MV2+ decomposition. (C) 2003 Elsevier Inc. All rights reserved.