Noble metal

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

Noble metal–metal oxide nanohybrids with tailored nanostructures for efficient solar energy conversion, photocatalysis and environmental remediation

Abstract: The controlled synthesis of nanohybrids composed of noble metals (Au, Ag, Pt and Pd, as well as AuAg alloy) and metal oxides (ZnO, TiO2, Cu2O and CeO2) have received considerable attention for applications in photocatalysis, solar cells, drug delivery, surface enhanced Raman spectroscopy and many other important areas. The overall architecture of nanocomposites is one of the most important factors dictating the physical properties of nanohybrids. Noble metals can be coupled to metal oxides to yield diversified nanostructures, including noble metal decorated-metal oxide nanoparticles (NPs), nanoarrays, noble metal/metal oxide core/shell, noble metal/metal oxide yolk/shell and Janus noble metal–metal oxide nanostructures. In this review, we focus on the significant advances in tailored nanostructures of noble metal–metal oxide nanohybrids. The improvement in performance in the representative solar energy conversion applications including photocatalytic degradation of organic pollutants, photocatalytic hydrogen generation, photocatalytic CO2 reduction, dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are discussed. Finally, we conclude with a perspective on the future direction and prospects of these controllable nanohybrid materials.

Au@ZIF-8: CO Oxidation over Gold Nanoparticles Deposited to Metal−Organic Framework

Abstract: Gold nanoparticles (NPs) were deposited to a zeolite-type metal-organic framework (MOF) by a simple solid grinding method. A catalyst, Au@ZIF-8, represents the first example of an active catalyst in CO oxidation by using a MOF as a novel support for noble metal NPs. The catalytic activity for CO oxidation is improved along with increasing Au loadings, and the highest catalytic activity is obtained for 5.0 wt % Au@ZIF-8, which presents half conversion of CO at approximately 170 degrees C. Gold NPs are close to being monodisperse and have no aggregation during catalytic reaction, and the catalytic activity is reproducible.

Catalytic oxidation of volatile organic compounds on supported noble metals

Abstract: Volatile organic compounds (VOCs) are toxic and mainly contribute to the formation of photochemical smog with a consequent remarkable impact to the air quality. A few techniques are available to reduce VOC emission, among them catalytic oxidation is suitable especially for highly diluted VOCs. The development of noble metals and transition metal oxides as catalysts for VOCs oxidation has been widely reported in the literature and the research field continues to be very active. Selection of catalytic materials for the abatement of organic pollutants is not easy because the activity depends on the specific molecule, on the reactions conditions and many parameters can affect the catalyst activity and resistance. The present review focus on the most used noble metals catalysts for oxidation of not halogenated VOC. The effects of metal salt precursor, chlorine poisoning, water inhibition, particle size dependence, nature of the support are discussed. The calculated reaction order with respect to VOC and oxygen as well as the proposed reaction mechanisms are addressed. Examples of the most recent catalytic systems reported in literature are also included.

Ni–Mo Nanopowders for Efficient Electrochemical Hydrogen Evolution

Abstract: Earth-abundant metals are attractive alternatives to the noble metal composite catalysts that are used in water electrolyzers based on proton-exchange membrane technology. Ni–Mo alloys have been previously developed for the hydrogen evolution reaction (HER), but synthesis methods to date have been limited to formation of catalyst coatings directly on a substrate. We report a method for generating unsupported nanopowders of Ni–Mo, which can be suspended in common solvents and cast onto arbitrary substrates. The mass-specific catalytic activity under alkaline conditions approaches that of the most active reported non-noble HER catalysts, and the coatings display good stability under alkaline conditions. We have also estimated turnover frequencies per surface atom at various overpotentials and conclude that the activity enhancement for Ni–Mo relative to pure Ni is due to a combination of increased surface area and increased fundamental catalytic activity.

Production of hydrogen for fuel cells by steam reforming of ethanol over supported noble metal catalysts

Abstract: The catalytic performance of supported noble metal catalysts for the steam reforming (SR) of ethanol has been investigated in the temperature range of 600–850 °C with respect to the nature of the active metallic phase (Rh, Ru, Pt, Pd), the nature of the support (Al2O3, MgO, TiO2) and the metal loading (0–5 wt.%). It is found that for low-loaded catalysts, Rh is significantly more active and selective toward hydrogen formation compared to Ru, Pt and Pd, which show a similar behavior. The catalytic performance of Rh and, particularly, Ru is significantly improved with increasing metal loading, leading to higher ethanol conversions and hydrogen selectivities at given reaction temperatures. The catalytic activity and selectivity of high-loaded Ru catalysts is comparable to that of Rh and, therefore, ruthenium was further investigated as a less costly alternative. It was found that, under certain reaction conditions, the 5% Ru/Al2O3 catalyst is able to completely convert ethanol with selectivities toward hydrogen above 95%, the only byproduct being methane. Long-term tests conducted under severe conditions showed that the catalyst is acceptably stable and could be a good candidate for the production of hydrogen by steam reforming of ethanol for fuel cell applications.