Room temperature hydrogen production from aliphatic alcohols over uv-illuminated powder Ni/TiO2 catalysts

The dependence of the room temperature H₂ production from liquid methanol or propan-1-ol on the degree of reduction of Ni and on the Ni content (0.03–13.8 wt%) of UV (λ ? 297 nm) illuminated Ni/TiO₂ catalysts has been studied. A complete reduction of Ni was found beneficial and an optimum rate of H₂ production from methanol (quantum yield ～0.05) was observed for ～5 wt% Ni. Magnetic measurements indicated that the mean Ni crystallite size varied with the content and was in the 6.5–18 nm range, as compared with ～2 nm for Pt particles on the same support. At least the highest Ni percentages induced a decrease in the anatase photoconductance under vacuum, which can be attributed to an electron transfer from the semiconductor grains (～25 nm dia.) to the Ni particles. The optimum in the photocatalytic H₂ production was considered as resulting from a compromise between the Ni catalytic properties and this electron transfer either because of a decrease in the number or strength of the TiO₂ basic sites or an increase in the electron-hole recombination at the Ni particles. Finally, the difference in the optimum metal content for Ni and Pt(0.1–1 wt%) was attributed mainly to the distinct particle sizes.