This work addresses photocatalytic generation of hydrogen (H2) from water and methanol over semiconductor-supported metal catalysts, such as Au, Ag and Cu, allowing proton reduction under visible light. Structure-reactivity relationships were assessed by applying suitable in situ spectroscopic techniques and by varying the composition of the semiconductor as well as of the metal component. It was shown that the ability of charge-carrier formation and transfer was strongly affected by the support properties, such as surface area, defects or surface-trapping sites.