Photoinduced Ammonia Synthesis over Lanthanum Oxyhydride-Supported Metal Nanoparticle Catalysts

Hydride materials have a significant ability to promote ammonia synthesis over supported transition metal (TM) nanoparticles due to the unique properties of lattice H^- ions. Here, we report that lanthanum oxyhydride (LaH_3-2xO_x) facilitates ammonia synthesis on the supported TM catalyst under visible light irradiation. Ru-loaded LaH_3-2xO_x exhibited an order of magnitude higher ammonia synthesis rate at 180 °C with an ∼18 kJ mol^-1 lower activation energy under visible light irradiation (λ = 405 nm, 1.04 W cm^-2) than that under dark conditions. The enhanced catalytic performance can be explained by photoionization of H^- (H^- → H⁰ + e^-) constituting the valence band maximum (VBM) of LaH_3-2xO_x, in which photogenerated electrons are transferred to supported Ru, and neutral hydrogen (H⁰) facilitates the hydrogenation of nitrogen species. Moreover, the photoexcitation of LaH_3-2xO_x enables shifting of the optimum TM catalyst from Ru to Ni in the volcano-shaped relationship between ammonia synthesis activity and metal-nitrogen binding energy.