The role of the support in catalyzing the gas-phase H2 production onto Pd-C3N4/TiO2 assisted by light

H 2 production through gas-phase photocatalysis remains limited by the poor light-harvesting ability and insufficient thermal activity of many conventional photocatalysts. In this work, Pd-loaded TiO 2 /C 3 N 4 composites were prepared to investigate the complementary role of both semiconductors under photothermal conditions. The results show that C 3 N 4 is mainly responsible for the photocatalytic contribution, improving visible-light absorption and enhancing H 2 production from methanol and water under illumination. The catalyst containing 10 wt% C 3 N 4 in TiO 2 reached the highest light-induced H 2 production rate of 7.2 mmol·g CAT −1 ·h −1 , confirming its superior photoactive properties. In contrast, TiO 2 provides higher thermocatalytic activity, favoring H 2 production under thermal conditions. STEM-EDX and XPS analyses revealed support-dependent Pd distributions and metal-support interactions. In the composite, Pd preferentially localized at the C 3 N 4 /TiO 2 interface, while XPS indicated stronger Pd-C 3 N 4 interactions, helping to explain the different catalytic behaviors. These results demonstrate the complementary roles of TiO 2 and C 3 N 4 in gas-phase photothermal H 2 production.