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Showing papers on "Noble metal published in 2011"



Journal ArticleDOI
TL;DR: It is demonstrated that Au particles in the size range 3-30 nm on TiO₂ are very active in hydrogen production from ethanol, and the high hydrogen yield observed makes these catalysts promising materials for solar conversion.
Abstract: Catalytic hydrogen production from renewables is a promising method for providing energy carriers in the near future. Photocatalysts capable of promoting this reaction are often composed of noble metal nanoparticles deposited on a semiconductor. The most promising semiconductor at present is TiO₂. The successful design of these catalysts relies on a thorough understanding of the role of the noble metal particle size and the TiO₂ polymorph. Here we demonstrate that Au particles in the size range 3-30 nm on TiO₂ are very active in hydrogen production from ethanol. It was found that Au particles of similar size on anatase nanoparticles delivered a rate two orders of magnitude higher than that recorded for Au on rutile nanoparticles. Surprisingly, it was also found that Au particle size does not affect the photoreaction rate over the 3-12 nm range. The high hydrogen yield observed makes these catalysts promising materials for solar conversion.

1,053 citations


Journal ArticleDOI
TL;DR: A mechanism is proposed involving the direct attack of an iron trans-dihydride on carbon dioxide, followed by ligand exchange and dihydrogen coordination, which achieves activities similar to some of the best noble metal catalysts.
Abstract: A highly active iron catalyst for the hydrogenation of carbon dioxide and bicarbonates works under remarkably low pressures and achieves activities similar to some of the best noble metal catalysts. A mechanism is proposed involving the direct attack of an iron trans-dihydride on carbon dioxide, followed by ligand exchange and dihydrogen coordination.

448 citations


Journal ArticleDOI
TL;DR: In this article, a hierarchical N-doped carbon nanotube-graphene hybrid nanostructure (NCNT-GHN) was designed to efficiently support noble metal (e.g., PtRu) nanoparticles.
Abstract: A hierarchical N-doped carbon nanotube-graphene hybrid nanostructure (NCNT-GHN), in which the graphene layers are distributed inside the CNT inner cavities, was designed to efficiently support noble metal (e.g., PtRu) nanoparticles. Well-dispersed PtRu nanoparticles with diameters of 2–4 nm were immobilized onto these NCNT-GHN supports by a low-temperature chemical reduction method without any pretreatment. Compared to conventional CNTs and commercial catalysts. a much better catalytic performance was achieved by a synergistic effect of the hierarchical structure (graphene-CNT hybrid) and electronic modulation (N-doping) during the methanol electrooxidation reaction. Improved single-cell performances with long-term stability are also demonstrated using NCNT-GHN as catalyst support.

352 citations


Journal ArticleDOI
TL;DR: In this paper, the authors review the recent advances in the synthesis of noble metal nanoparticles/carbon nanotubes nanohybrids and their applications in heterogeneous catalysis, fuel cells, and chemo/biosensors.

350 citations


Journal ArticleDOI
TL;DR: In this article, the role of the pH and the nature of the reducing agent to the size and the oxidation state of metal clusters was investigated in the presence of noble metal nanoclusters.
Abstract: Fluorescent noble metal (Au, Ag) nanoclusters have been biolabeled to bovine serum albumin (BSA) by wet chemistry. Spectroscopic and fluorescence investigations relate the role of the pH and the nature of the reducing agent to the size and the oxidation state of metal clusters. Blue-emitting (λ = 450 nm) small gold nanoclusters (eight atoms) prepared at pH 8 weakly bonded to BSA grow at higher pH to form red-emitting (λ = 690 nm) bigger clusters (25 atoms) covalently bonded to BSA via the sulfur group. X-ray photoelectron spectroscopy (XPS) measurements indicate the presence of Au(I) only for the big clusters. Small silver nanoclusters labeled to the protein with a fluorescence emission in the red region are synthesized in the presence of a strong reducing agent and present only Ag(0). Steady-state and lifetime measurements confirm the crucial impact of the size and the oxidation state of Au(I) on the stabilization of the metal core inside the protein and on the presence of a long lifetime component (τ > ...

342 citations


Journal ArticleDOI
TL;DR: In this paper, a Cd1−xZnxS solid solution with nano-twin structures is synthesized and exhibits superior photocatalytic activities for H2 evolution from water under visible light irradiation (λ ≥ 430 nm) without noble metal co-catalysts.
Abstract: Cd1−xZnxS solid solution with nano-twin structures are synthesized and exhibit superior photocatalytic activities for H2 evolution from water under visible light irradiation (λ ≥ 430 nm) without noble metal co-catalysts. Such Cd0.5Zn0.5S nanocrystals show the highest activity for hydrogen evolution with an extremely high apparent quantum yield (AQY = 43%) at 425 nm, achieving a hydrogen evolution rate of 1.79 mmol h−1 without noble metals. The hydrogen evolution rate of 1.70 mmol h−1 was achieved under simulated sunlight conditions (without infrared light). The “back to back” potential formed by parallel nano-twins in the Cd1−xZnxS crystals can significantly improve the separation of the photo-generated electrons/holes (preventing their recombination) thus enhancing the photocatalytic activity. Photodeposition experiments of noble metals strongly support such a mechanism. It is found that noble metals were selectively photo-deposited at central regions between the twin boundaries. The concentration of free electrons at the central region of twins was markedly higher and the twins can effectively separate the H2 evolution sites (electrons) from oxidation reaction sites (holes).

316 citations


Journal ArticleDOI
TL;DR: Noble-metal-free nickel-iron alloy nanoparticles exhibit excellent catalytic performance for the complete decomposition of hydrous hydrazine, for which the NiFe nanocatalyst shows 100% hydrogen selectivity in basic solution.
Abstract: Noble-metal-free nickel–iron alloy nanoparticles exhibit excellent catalytic performance for the complete decomposition of hydrous hydrazine, for which the NiFe nanocatalyst, with equimolar compositions of Ni and Fe, shows 100% hydrogen selectivity in basic solution (0.5 M NaOH) at 343 K. The development of low-cost and high-performance catalysts may encourage the effective application of hydrous hydrazine as a promising hydrogen storage material.

298 citations


Journal ArticleDOI
TL;DR: The development of the discovery that nickel(0), in the form of nanoparticles, can replace the more expensive noble metals in both transfer hydrogenation and hydrogen autotransfer reactions is described.
Abstract: The transfer hydrogenation of organic compounds is a much safer and more environmentally benign process than reduction reactions involving molecular hydrogen, metal hydrides, or dissolving metals. In transfer hydrogenation, 2-propanol is often preferred as the source of hydrogen because it is cheap, easy to remove, and environmentally friendly. This class of transformation has been mostly pursued through the use of expensive noble metals, such as Ru, Pd, and so forth; research involving cheaper catalytically active metals has been relatively neglected.On the other hand, alcohols have recently emerged as desirable alkylating agents, a useful alternative to organic halides, in reactions of hydrogen autotransfer, also known as the “borrowing of hydrogen” methodology. For instance, the α-alkylation of ketones with alcohols is an atom-efficient process that produces water as the only byproduct in the presence of a noble metal catalyst. Hydrogen autotransfer is also successful in the synthesis of amines through...

286 citations


Journal ArticleDOI
TL;DR: In this paper, the additive effects of noble metals on the catalytic performances are summarized in terms of activity, suppression of Ni oxidation, carbon formation, self-activation, and sustainability in the daily startup and shutdown operations.
Abstract: Nickel is an effective component for the steam reforming of methane in terms of the catalytic activity and the catalyst cost. When Ni catalysts are applied to dry reforming, oxidative reforming, and catalytic partial oxidation, it is necessary to add the properties of high resistance to oxidation, hot spot formation, and coke deposition, to the Ni catalysts. An efficient method for giving these properties while considering the catalyst cost is the modification of Ni metal particles with small amounts of noble metals. An important point is that preparation methods can affect the structure of noble metal–Ni bimetallic particles, which is connected to the catalytic performances. The additive effects of noble metals on the catalytic performances are summarized in terms of activity, suppression of Ni oxidation, carbon formation, self-activation, and sustainability in the daily startup and shutdown operations.

281 citations


Journal ArticleDOI
TL;DR: The discovery of a highly active Ni-Co alloy electrocatalyst for the oxidation of hydrazine (N(2)H(4)) is reported and evidence for competing electrochemical (faradaic) and chemical (nonfarADAic) reaction pathways is provided.
Abstract: We report the discovery of a highly active Ni−Co alloy electrocatalyst for the oxidation of hydrazine (N2H4) and provide evidence for competing electrochemical (faradaic) and chemical (nonfaradaic) reaction pathways. The electrochemical conversion of hydrazine on catalytic surfaces in fuel cells is of great scientific and technological interest, because it offers multiple redox states, complex reaction pathways, and significantly more favorable energy and power densities compared to hydrogen fuel. Structure−reactivity relations of a Ni60Co40 alloy electrocatalyst are presented with a 6-fold increase in catalytic N2H4 oxidation activity over today’s benchmark catalysts. We further study the mechanistic pathways of the catalytic N2H4 conversion as function of the applied electrode potential using differentially pumped electrochemical mass spectrometry (DEMS). At positive overpotentials, N2H4 is electrooxidized into nitrogen consuming hydroxide ions, which is the fuel cell-relevant faradaic reaction pathway....

Journal ArticleDOI
TL;DR: In this paper, Ru, Pt and Pd noble metal was used for selective hydrogenation of biomass derived levulinic acid (LA) to γ-valerolactone (GVL) in a continuous down flow fixed-bed reactor system.

Journal ArticleDOI
TL;DR: In this paper, a series of Ni-CexZr1-xO2 catalysts were used for carbon dioxide methanation and their performance was evaluated by means of XRD,TPR, BET, H-2-TPD and SEM-EDX.
Abstract: Carbon dioxide methanation was carried out over a series of Ni-CexZr1-xO2 catalysts prepared by a pseudo sol-gel method. The influence of CeO2/ZrO2 mass ratio and noble metal addition was investigated. The catalysts were subsequently characterized by means of XRD,TPR, BET, H-2-TPD and SEM-EDX. The modification of structural and redox properties of these materials was evaluated in relation with their catalytic performances. All catalysts gave impressive CO2 conversion and extremely high selectivity to methane (superior to 98%). Ni2+ incorporation into the CZ structure was proved to enhance catalysts specific activity. The global performance of the studied systems depended not only on the surface of available metallic nickel but also on the composition of the support and on its modification by Ni2+ doping. As a result of these two phenomena, the Ni-based mixed oxide having a CeO2/ZrO2 = 60/40 exhibited the highest catalytic activity, owing to an optimal Ni2+/Ni-0 ratio. Noble metal addition led to higher Ni dispersion, resulting in a raise of both activity and catalyst life-time. It did not modify the support intrinsic activity. The deactivation was shown not to be due to carbon deposits but rather to nickel particles sintering. The investigated parameters thus allowed an improvement of the previously studied 5 wt% Ni-Ce0.72Zr0.28O2 system. (C) 2010 Elsevier B.V. All rights reserved.

Journal ArticleDOI
TL;DR: Several nanocrystalline Co3O4 catalysts were investigated for their activity and selectivity during the oxidation of 1,2-dichloroethane, which was selected as a model chlorinated volatile organic compound.

Journal ArticleDOI
TL;DR: The present approach exemplifies a totally green synthesis using the plant derived natural product (gum kondagogu) for the production of noble metal nanoparticles and the process can also be extended to the synthesis of other metal oxide nanoparticles.

Journal ArticleDOI
TL;DR: In this paper, the results revealed that the Rh and Ru catalysts showed the highest activity in combined reforming and both the dry reforming and partial oxidation of methane, while the H 2 /CO ratio was around 2 and 0.7 over different catalysts for catalytic partial oxidation and dry reforming.

Journal ArticleDOI
TL;DR: In this paper, the state of the art in the field of polyoxometalates containing noble metal atoms (ruthenium, rhodium, palladium, silver, osmium, iridium, platinum and gold) is described.


Journal ArticleDOI
TL;DR: In this article, the interaction of a range of divalent dopants with CeO2 using density functional theory was examined, and it was found that the dopant preferentially adopts the coordination of its own oxide, instead of the cubic coordination of Ce(IV) in ceria.
Abstract: The doping of ceria (CeO2) with divalent noble metal ions has been shown to improve the reducibility and enhance the oxygen storage capacity (OSC), although the reasons for this are not well understood. We have examined the interaction of a range of divalent dopants with CeO2 using density functional theory, and found that the dopant preferentially adopts the coordination of its own oxide, instead of the cubic coordination of Ce(IV) in ceria. Depending on the electronic structure of the dopants, the different coordinations can create weakly- or under-coordinated oxygen ions that are more easily removed than in pure CeO2. We have used these insights to identify dopants which will increase the reducability of CeO2, while being economically more viable than the presently used noble metals, and we outline guidelines for the design of improved oxide catalysts.

Journal ArticleDOI
Lirong Kong1, Xiaofeng Lu1, Xiujie Bian1, Wanjin Zhang1, Ce Wang1 
TL;DR: A carbon layer was coated onto Fe₃O₄ microspheres by hydrothermal treatment and exhibited a higher catalytic activity toward the reduction of methyl orange than commercially used Pd/C catalyst.
Abstract: Fe₃O₄ microsphere is a good candidate as support for catalyst because of its unique magnetic property and large surface area. Coating Fe₃O₄ microspheres with other materials can protect them from being dissolved in acid solution or add functional groups on their surface to adsorb catalyst. In this paper, a carbon layer was coated onto Fe₃O₄ microspheres by hydrothermal treatment using polyethylene glycol as the connecting agents between glucose and Fe₃O₄ spheres. Through tuning the added amounts of reactants, the thickness of the carbon layer could be well-controlled. Because of the abundant reductive groups on the surface of carbon layer, noble metal ions could be easily adsorbed and in situ reduced to nanoparticles (6-12 nm). The prepared catalyst not only had unique antiacid and magnetic properties, but also exhibited a higher catalytic activity toward the reduction of methyl orange than commercially used Pd/C catalyst.

Journal ArticleDOI
TL;DR: The electrochemical oxidation of ammonia has been studied in the most detail in alkaline solution at platinized platinum as discussed by the authors, in which elemental nitrogen is formed at mildly positive potentials with near quantitative current efficiency through dimerization of partly dehydrogenated ammonia molecules NH x (ads).

Journal ArticleDOI
TL;DR: In this paper, a 3D-ordered macroporous (3DOM) La1−xKxCoO3 (x = 0-0.3) perovskite-type oxide catalysts with large pore sizes and interconnected macroporic frameworks were successfully synthesized by a novel method of carboxy-modified colloidal crystal templates (CMCCT).

Journal ArticleDOI
TL;DR: In this paper, a review discusses the synthesis and the possible applications of nitrogen-doped carbon nanotubes as supports for metal nanoparticles in heterogeneous catalysis, and discusses the applications of carbon-based supports for noble metal catalysts.
Abstract: The science and technology of catalysis is of fundamental importance to a national economy. Today about 90% of all technical chemicals are manufactured by the use of catalysts. Nanoparticles of noble metals are extremely important materials in the catalysis industry due to cost issues and properties that are not found in their bulk state. An efficient way to produce and stabilise noble metal nanoparticles is by dispersion on a suitable support. Carbon-based supports, such as carbon nanotubes, carbon spheres, carbon fibres, etc., have been found to be good supports for metal nanoparticles. However, to be used effectively, the carbon surface must be modified either by functionalisation or doping. This review discusses the synthesis and the possible applications of nitrogen-doped carbon nanotubes as supports for metal nanoparticles in heterogeneous catalysis.

Journal ArticleDOI
TL;DR: In this article, a density functional theory (DFT+U) investigation into methane oxidation over Pd/ceria and quantify the activity of the PdxCe1−xO2(1.1) mixed oxide surface in comparison with the PdO(1−0-0) and Pd(1 1-1) surfaces.

Journal ArticleDOI
TL;DR: In this article, the photocatalytic reforming of methanol was investigated kinetically under steady conditions as a function of the methanoline-to-water partial pressure ratio in the gas mixture fed to the photoreactor.

Journal ArticleDOI
TL;DR: In this paper, catalytic hydrotreatment reactions with mono-and bi-metallic metal catalysts based on Rh, Pt, Pd on a zirconia support were performed in a batch set-up.
Abstract: Fast pyrolysis oil (PO), the liquid product of fast pyrolysis of lignocellulosic biomass, requires upgrading to extent its application range and for instance to allow for co-feeding in an existing oil-refinery. Catalytic hydrotreatment reactions (350 °C, 20 MPa total pressure, and 4 h reaction time) with mono- and bi-metallic metal catalysts based on Rh, Pt, Pd on a zirconia support were performed in a batch set-up. Pd/ZrO2 showed the highest activity, followed by Rh/ZrO2. Upgraded oils with the best product properties were obtained with Rh/ZrO2. For this catalyst, the TGA residue, which is a measure for coking tendency, was 13.4 wt% and the Mw of the upgraded oil (748 g/mol) was lowest. All noble metal catalysts showed higher activities per gram of metal than the benchmark catalyst CoMo/Al2O3. Hydrotreatment reactions at variable batch times were performed to gain insights in reaction pathways and showed the involvement of competitive hydrogenation/hydrocracking and polymerisation pathways. Temperature programmed oxidation (TPO) measurements of spent catalysts showed the presence of carbonaceous deposits on the catalyst (2–6 wt%). These deposits may be removed by oxidation at temperatures lower than 600 °C without changing the morphology of the catalyst.

Journal ArticleDOI
24 May 2011-ACS Nano
TL;DR: In the hydrogen generation tests, the N-doped samples were clearly outperforming their undoped counterparts, showing remarkable efficiency not only under UV-B but also with UV-A illumination.
Abstract: We report the synthesis of N-doped TiO2 nanofibers and high photocatalytic efficiency in generating hydrogen from ethanol–water mixtures under UV-A and UV-B irradiation. Titanate nanofibers synthesized by hydrothermal method are annealed in air and/or ammonia to achieve N-doped anatase fibers. Depending on the synthesis route, either interstitial N atoms or new N–Ti bonds appear in the lattice, resulting in slight lattice expansion as shown by XPS and HR-TEM analysis, respectively. These nanofibers were then used as support for Pd and Pt nanoparticles deposited with wet impregnation followed by calcination and reduction. In the hydrogen generation tests, the N-doped samples were clearly outperforming their undoped counterparts, showing remarkable efficiency not only under UV-B but also with UV-A illumination. When 100 mg of catalyst (N-doped TiO2 nanofiber decorated with Pt nanoparticles) was applied to 1 L of water–ethanol mixture, the H2 evolution rates were as high as 700 μmol/h (UV-A) and 2250 μmol/h ...

Journal ArticleDOI
Zhenghua Wang1, Suping Zhao1, Shiyu Zhu1, Yanling Sun1, Mei Fang1 
TL;DR: In this article, the photocatalytic properties of the prepared M/Cu2O heterogeneous nanocrystals were studied, showing that visible light is more favorable for the deposition of Ag nanoparticles onto the surfaces of Cu2O octahedral nanocrystal, and a solution temperature of more than 30 °C can prevent the erosion of Cu 2O.
Abstract: M/Cu2O (M = Ag, Au) heterogeneous nanocrystals are successfully prepared by depositing noble metal nanoparticles onto the surfaces of Cu2O octahedral nanocrystals through a simple photocatalytic process. The samples are characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). The influence of the light source and solution temperature on the deposition of noble metal (taking Ag as an example) nanoparticles has been studied. The experimental results show that visible light is more favorable for the deposition of Ag nanoparticles onto Cu2O nanocrystals, and a solution temperature of more than 30 °C can prevent the erosion of Cu2O. The photocatalytic properties of the prepared M/Cu2O heterogeneous nanocrystals are studied, showing enhanced photocatalytic activities.

Journal ArticleDOI
Xianghong Liu1, Jun Zhang1, Xianzhi Guo1, Shihua Wu1, Shurong Wang1 
TL;DR: In this article, a novel sensing material of Ni-doped SnO2 hollow spheres was prepared and characterized by X-ray diffraction, Xray photoelectron spectroscopy, inductively coupled plasma-optical emission spectrograms and transmission electron microscopy.
Abstract: A novel sensing material of Ni-doped SnO2 hollow spheres was prepared and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma-optical emission spectroscopy and transmission electron microscopy. Gas sensing properties of the sensor fabricated from the as-prepared Ni-doped SnO2 hollow spheres were systematically investigated and compared with those of pristine SnO2 hollow spheres. Results showed that the Ni-doped sensor had a good selectivity to higher alcohols such as n-butanol with much higher response, while the undoped sensor exhibited poor response to all the tested gases with poor selectivity. The enhanced sensor performances are probably attributed to the formation of p–n heterojunctions between p-type NiO and n-type SnO2. It also suggests that the Ni-dopant is a promising substitute for noble metal additives to fabricate sensor materials with a low cost.

Journal ArticleDOI
TL;DR: In this paper, a 7%CuO/Ce0.7Mn0.3O2 catalyst was used for the removal of benzene in low concentrations at low temperature.
Abstract: Ce1−xMnxO2 (x = 0.1–0.6) mixed oxides were used as supports for preparing 7%CuO/Ce1−xMnxO2 catalysts by impregnation, for use in the total oxidation of benzene. At x = 0.1 and 0.2, most of manganese was fixed in the fluorite structure of CeO2 to form a solid solution. When x exceeds 0.3, some of the manganese appeared as well dispersed MnOx. The redox interaction between CuO and Ce0.7Mn0.3O2 facilitated the activation of surface oxygen for the oxidation of benzene. The defective sites of oxygen on the dispersed MnOx also enhanced the adsorption and oxidation of benzene. 7%CuO/Ce0.7Mn0.3O2 catalyst was a good candidate for replacing noble metal catalysts for the removal of benzene in low concentrations at low temperature.