Photolysis of water over metallized powdered titanium dioxide

Photolysis of gas-phase water has been carried out on NaOH-coated Rh/TiO2 and Pd/TiO2 catalysts. Hydrogen and oxygen were simultaneously produced on both catalysts and the stoichiometric composition (H2/O2= 2) was obtained for most of the catalysts. The rate of water photolysis strongly depended upon the amount of NaOH loaded and the pressure of water vapour. The photolysis rate on the Rh/TiO2 catalyst was maximized at 15 wt % of NaOH coating and at ca. 2 Torr of water-vapour pressure. The photocatalytic activity depended upon the kind of metal deposited as well as the source of TiO2. Rh was more active but Pd was less active than Pt, which was tested previously. The highest formal quantum yield was ca. 29% when the Rh/TiO2 catalyst was used. The dependences of the photolysis rate on light intensity, wavelength and thermal back reaction rate have also been studied.