Hydrogen production by photo-catalytic steam reforming of methanol on noble metal-modified titanium dioxide

The photocatalytic production of hydrogen by methanol steam reforming was studied over a series of pristine or noble metal - modified TiO2 photocatalysts, synthesized by flame spray pyrolysis or by deposition of preformed noble metal nanoparticles on TiO2. A closed recirculation apparatus was employed, with the photocatalyst bed continuously fed with methanol/water vapors. Methanol underwent oxidation up to CO2 through the formation of formaldehyde and formic acid. Hydrogen evolved at constant rate, which significantly increased upon noble metal addition, Pt being the most effective co-catalyst, followed by gold and silver, according to their work function values. The steady-state formaldehyde, formic acid and carbon dioxide production rates, plotted vs. the methanol molar fraction in the aqueous solution generating the gaseous reaction mixture, were successfully fitted on the basis of a reaction scheme, in which each elementary oxidation step may occur through OH radical mediated or hole-mediated direct paths.