Noble metal

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

Redox preparation of mixed-valence cobalt manganese oxide nanostructured materials: highly efficient noble metal-free electrocatalysts for sensing hydrogen peroxide

Abstract: High-performance hydrogen peroxide sensors provide valuable signals of biological interactions, disorders, and developing of diseases. Low-cost metal oxides are promising alternatives but suffer from low conductivity and sensing activity. Multi-component metal oxides are excellent candidates to accomplish these challenges, but the composition inhomogeneity is difficult to manage with conventional material preparation. We demonstrated redox preparation strategies to successfully synthesize highly homogeneous, noble metal-free H2O2 sensors of spinel nanostructured cobalt manganese oxides with enhanced conductivity, multiple mixed-valence features, and efficient H2O2 sensing activities. The designed redox reactions accompanied with material nucleation/formation are the key factors for compositional homogeneity. High conductivity (1.5 × 10−2 S cm−1) and H2O2 sensing activity (12 times higher than commercial Co3O4) were achieved due to the homogeneous multiple mixed-valence systems of Co(II)/(III) and Mn(III)/(IV). A wide linear detection range (from 0.1 to 25 mM) with a detection limit of 15 μM was observed. Manganese species assist the formation of large surface area nanostructures, enhancing the H2O2 reduction activities, and inhibit the sensing interference. The material controls of hierarchical nanostructures, elemental compositions, porosity, and electrochemical performances are highly associated with the reaction temperatures. The temperature-dependent properties and nanostructure formation mechanisms based on a reaction rate competition are proposed.

Highly reactive and selective Sn-Pd bimetallic catalyst supported by nanocrystalline ZSM-5 for aqueous nitrate reduction

Abstract: A new bimetallic catalyst supported by environmentally benign nanocrystalline ZSM-5 (NZSM-5), was developed to reduce nitrate completely and selectively to nitrogen gas without producing nitrite. The catalyst was optimized by use under a variety of conditions (i.e., promoter metal type (Sn, Cu, Ag, Ni)), noble metal type (Pd, Pt, Au), promoter metal concentration (0–3.4 wt%), noble metal concentration (0–2.8 wt%), catalyst calcination temperature (0–550 °C), H2 flow rate (0–60 mL/min), and CO2 flow rate (0–60 mL/min). Complete nitrate removal with the highest nitrogen selectivity (91%) was achieved using 1%Sn-1.6%Pd-NZSM-5 catalyst under optimized conditions that included: initial nitrate concentration: 30 mg/L NO3-N; calcination temperature: 350 °C; H2 flow rate: 30 mL/min; and CO2 flow rate: 60 mL/min for 60 min. The estimated kinetic rate constant of the catalyst is 16.40 × 10−2 min−1, the catalyst-loading normalized rate constant is 65.60 × 10−2 min−1 gcat−1, while Pd-loading normalized rate constant is 410 × 10−2 L/min gPd−1. The catalyst showed remarkable nitrate removal (100%) and nitrogen selectivity (>88%) for up to five successive reactions with consistent kinetics. A 100% nitrate removal and >81% nitrogen selectivity was also achieved by the catalyst for five repeated cycles. However, the kinetics gradually slowed down to 4.36 × 10−2 min−1 over five repeated cycles, (still superior to fresh catalysts already reported in the literature). Characterization tests confirmed that the used catalyst was chemically stable, and that the decrease in its reactivity was due mainly to the sintering of metallic nano particles during the regeneration process.

Gasification of Alkylphenols with Supported Noble Metal Catalysts in Supercritical Water

Abstract: Gasification of alkylphenols as lignin model compounds was examined in the presence of supported noble metal catalysts in supercritical water without hydrogen donor at 673 K. The activity of the catalyst was in the order of Ru/γ-alumina > Ru/carbon, Rh/carbon > Pt/γ-alumina, Pd/carbon, and Pd/γ-alumina. The effect of water density with the Ru/γ-alumina catalyst was examined in detail. The main gas products were methane, carbon dioxide, and hydrogen. The yield of gases and the ratio of methane increased with increasing water density. The gasification of the isomers of propylphenols was also examined with the Ru/γ-alumina catalyst. The reactivities of o- and p-propylphenols were relatively higher than those of m-propylphenols.

Gas sensor element

Abstract: A gas sensor element has a solid electrolyte body of oxygen ionic conductivity, a target gas electrode and a reference gas electrode formed on both surfaces of the solid electrolyte body, respectively, a porous diffusion resistance layer, and a catalyst support trap layer. The porous diffusion resistance layer covers the target gas electrode and through which target gases to be measured are passing. The catalyst support trap layer is formed on the outer surface of the porous diffusion resistance layer and supports noble metal catalyst. In the gas sensor element, the noble metal catalyst is made of platinum, rhodium, palladium supported in the catalyst support trap layer. In particular, an addition amount of palladium in the total amount of the noble metal catalyst is within a range of 2 to 65 wt %.