Robustness of Ru/SiO₂ as a Hydrogen-Evolution Catalyst in a Photocatalytic System Using an Organic Photocatalyst

Effects of various metal oxide supports (SiO₂, SiO₂–Al₂O₃, TiO₂, CeO₂, and MgO) on the catalytic reactivity of ruthenium nanoparticles (RuNPs) used as a hydrogen-evolution catalyst have been evaluated in photocatalytic hydrogen evolution using 2-phenyl-4-(1-naphthyl)­quinolinium ion (QuPh⁺–NA) and dihydronicotinamide adenine dinucleotide (NADH) as a photocatalyst and an electron donor, respectively. The 3 wt % Ru/SiO₂ catalyst freshly prepared by an impregnation method exhibited the highest catalytic reactivity among RuNPs supported on various metal oxides, which was nearly the same as that of commercially available Pt nanoparticles (PtNPs) with the same metal weight. However, the initial catalytic reactivity of 3 wt % Ru/SiO₂ was lost after repetitive use, whereas the catalytic reactivity of PtNPs was maintained under the same experimental conditions. The recyclability of the 3 wt % Ru/SiO₂ was significantly improved by employing the CVD method for preparation. The initial catalytic reactivity of 0.97 wt % Ru/SiO₂ prepared by the CVD method was higher than that of 2 wt % Ru/SiO₂ prepared by the impregnation method despite the smaller Ru content. The total amount of evolved hydrogen normalized by the weight of Ru in 0.97 wt % Ru/SiO₂ was 1.7 mol g_Ru^–1, which is now close to that normalized by the weight of Pt in PtNPs (2.0 mol g_Pt^–1). Not only the preparation method but also the morphology of SiO₂ supports affected significantly the catalytic activity of Ru/SiO₂. The Ru/SiO₂ catalyst using nanosized SiO₂ with undefined shape exhibited higher catalytic activity than Ru/SiO₂ catalysts using mesoporous SiO₂ or spherical SiO₂. The kinetic study and TEM observation of the Ru/SiO₂ catalysts suggest that the microenvironment of RuNPs on SiO₂ surfaces plays an important role to exhibit the high catalytic performance in the photocatalytic hydrogen production

Protonation Equilibrium and Hydrogen Production by a Dinuclear Cobalt–Hydride Complex Reduced by Cobaltocene with Trifluoroacetic Acid

A dinuclear Co complex with bis­(pyridyl)­pyrazolato (bpp^–) and terpyridine (trpy) ligands, [Co^III₂(trpy)₂(μ-bpp)­(OH)­(OH₂)]⁴⁺ (<b>1</b>⁴⁺), undergoes three-electron reduction by cobaltocene in acetonitrile to produce <b>1</b>⁺, which is in the protonation equilibrium with the Co^IICo^III–hydride complex, and the further protonation of the hydride by trifluoroacetic acid yields hydrogen quantitatively. The kinetic study together with the detection of the Co^IICo^III-hydride complex revealed the mechanism of the hydrogen production by the reaction of <b>1</b>⁺ with trifluoroacetic acid

Mesoporous Nickel Ferrites with Spinel Structure Prepared by an Aerosol Spray Pyrolysis Method for Photocatalytic Hydrogen Evolution

Submicron-sized mesoporous nickel ferrite (NiFe₂O₄) spheres were prepared by an aerosol spray pyrolysis method using Pluronic F127 as a structure-directing agent, and their photocatalytic performance for hydrogen (H₂) evolution was examined in an aqueous MeOH solution by visible light irradiation (λ > 420 nm). The structure of the spherical mesoporous nickel ferrites was studied by transmission electron microscopy, powder X-ray diffraction, and N₂ adsorption–desorption isotherm measurements. Mesoporous NiFe₂O₄ spheres of high specific surface area (278 m² g^–1) with a highly crystalline framework were prepared by adjusting the amount of structure-directing agent and the calcining condition. High photocatalytic activity of mesoporous NiFe₂O₄ for H₂ evolution from water with methanol was achieved due to the combination of high surface area and high crystallinity of the nickel ferrites