Noble metal

About: Noble metal is a research topic. Over the lifetime, 15113 publications have been published within this topic receiving 337947 citations.

Two-dimensional gold nanostructures with high activity for selective oxidation of carbon-hydrogen bonds

Abstract: Efficient synthesis of stable two-dimensional (2D) noble metal catalysts is a challenging topic. Here we report the facile synthesis of 2D gold nanosheets via a wet chemistry method, by using layered double hydroxide as the template. Detailed characterization with electron microscopy and X-ray photoelectron spectroscopy demonstrates that the nanosheets are negatively charged and [001] oriented with thicknesses varying from single to a few atomic layers. X-ray absorption spectroscopy reveals unusually low gold-gold coordination numbers. These gold nanosheets exhibit high catalytic activity and stability in the solvent-free selective oxidation of carbon-hydrogen bonds with molecular oxygen.

Imine hydrogenation with simple alkaline earth metal catalysts

Abstract: Hydrogenation of unsaturated bonds is dominated by transition metal catalysis. Compared with transition metals, the use of other metals is less explored, especially so for the s-block elements despite their ready availability and low cost. Here, we show that group 2 metal amides (M[N(SiMe3)2]2, M = Mg, Ca, Sr, Ba) unexpectedly catalyse the hydrogenation of aldimines with H2 at 80 °C and a remarkably low H2 pressure of 1–6 bar. Conversion rates increase with metal size: Mg < Ca < Sr < Ba (for Ba, quantitative conversion is reached within 15 min). The key to this catalysis is the unanticipated formation of metal hydride species by deprotonation of H2 (pK a ≈ 49) with a weak base M[N(SiMe3)2]2 (HN(SiMe3)2: pK a ≈ 25.8). Density functional theory calculations suggest that the most favourable pathway indeed involves metal hydride intermediates. The efficient alkaline earth metal-catalysed hydrogenation of imines with molecular hydrogen at remarkably low pressure provides an attractive alternative to transition metal catalysis. Hydrogenation is one of the most common catalytic processes on both laboratory and industrial scales, and typically is carried out with a noble metal catalyst. Here, the authors show that alkaline earth metal amides are capable of hydrogenating imines under mild conditions.

Photocatalytic Hydrogen Evolution from Water Using Copper Gallium Sulfide under Visible-Light Irradiation

Abstract: Copper gallium sulfide with a chalcopyrite-type structure (CuGa3S5) and a band gap of ca. 2.4 eV was prepared by a solid-state reaction. The as-prepared CuGa3S5 exhibited photocatalytic hydrogen evolution activity in an aqueous solution containing Na2S and Na2SO3 as sacrificial electron donors under visible-light irradiation (λ > 420 nm), even without a cocatalyst, such as platinum (Pt). The photocatalytic activity, however, was improved by the deposition of noble metal cocatalysts. Among the noble metals tested, rhodium (Rh) was found to be the most effective cocatalyst to improve the H2 evolution activity, which was 2.5 times that achieved without a cocatalyst. Dispersion of base sulfides, including nickel sulfide (NiS) and iron sulfide (FeS), into the reactant solution containing CuGa3S5 also increased the activity. The activity under optimized conditions (5.0 wt % NiS/CuGa3S5) was 3 times that of a similarly optimized Rh/CuGa3S5. The results of electrochemical measurements and photocatalytic reactions...