Photocatalytic hydrogen production over titania modified by gold – Metal (palladium, nickel and cobalt) catalysts

The photocatalytic production of hydrogen on modified Au/TiO₂-based photocatalysts by using water/methanol mixtures was studied. The main goal was to study the effect of surface modification of Au/TiO₂ with Pd, Ni and Co on H₂ production under UV light irradiation (λ ca. 254 nm). Catalysts were produced by depositing Pd, Ni or Co precursors (nitrates hydrated salts) on TiO₂ (Evonik, P25) by incipient wetness impregnation followed by thermal treatment under H₂ (Pd and Co) or air (Ni). Thereafter, Au was incorporated by deposition-precipitation with urea (DPU method) and then the catalysts were thermally activated again under air flow. The photocatalysts were characterized by UV–Vis diffuse reflectance, HAADF-TEM, EDXS, FTIR CO adsorption, XPS and photoluminescence. In order to obtain detailed information about the composition of the nanoparticles, high-resolution elemental analyses (EDXS line scans) were performed. The Au-Pd, Au-Ni and Au-Co on TiO₂ photocatalysts showed higher performance for H₂ production (266, 256 and 171 mmol H₂ mmol_Au⁻¹ h⁻¹, respectively) compared to the Au/TiO₂ material (106 mmol H₂ mmol_Au⁻¹ h⁻¹). PL results showed that the improved H₂ production rate could be explained by an enhanced charge separation. The highest H₂ production showed by the Au-Pd/TiO₂ sample could be attributed to synergistic effects, derived from the interaction between Au and Pd particles. For the Au-Ni/TiO₂ and Au-Co/TiO₂ samples it is proposed that nickel or cobalt oxides worked as promoters (with additives effects) because of the formation of a p–n heterojunction.