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Showing papers on "Noble metal published in 2001"


Journal ArticleDOI
TL;DR: In this paper, a tetraoctylammonium bromide (TOAB)-capped metal nanoparticles on TiO2 films improved the photocurrent generation and induced a shift in the apparent flat band potential.
Abstract: Noble metal particles of Au, Pt, and Ir were deposited on nanostructured TiO2 film using an electrophoretic approach. The nanocomposite films were characterized by UV-absorption and atomic force microscopy (AFM). The deposition of tetraoctylammonium bromide (TOAB)-capped metal nanoparticles on TiO2 films improved the photocurrent generation and induced a shift in the apparent flat band potential. The TiO2 films modified with TOAB-capped metal nanoparticles were less prone to the electron scavenging by the oxygen in solution. Improved photoelectrochemical performance of semiconductor−metal composite film is attributed to the shift in quasi-Fermi level of the composite to more negative potentials. Continuous irradiation of the composite films over a long period causes photocurrent to decrease as the semiconductor−metal interface undergoes chemical changes. The role of semiconductor−metal composite films in improving the rate of photocatalytic degradation of an azo dye is also discussed.

897 citations


Journal ArticleDOI
TL;DR: In this paper, a new metal deposition method is demonstrated by deposition of a submonolayer of Pt, a monolayers of Pd and a bilayer of Ag on Au(1.1/1) surfaces by using a Cu adlayer as a template.

557 citations


Journal ArticleDOI
TL;DR: In this article, the authors discuss two different membrane reactor concepts which both rely on supported palladium, on the one hand as a permselective membrane material, and on the other hand as base component of a membrane-type hydrogenation catalyst.
Abstract: Membrane reactors applied to catalytic reactions are currently being studied in many places world-wide. Significant developments in membrane science and the vision of process intensification by multifunctional reactors have stimulated a lot of academic and industrial research, which is impressively demonstrated by more than 100 scientific papers on catalytic membrane reactors being published per year. Palladium as a noble metal with exceptional hydrogen permeation properties and, at the same time, broad applicability as a catalyst, first of all for hydrogenation, is part of many of these developments. This paper discusses two different membrane reactor concepts which both rely on supported palladium, on the one hand as a permselective membrane material, and on the other hand as base component of a membrane-type hydrogenation catalyst. Dense palladium composite membranes can be used for hydrogen separation from packed-bed catalysts in gas-phase hydrocarbon dehydrogenation reactions. Mesoporous membranes containing dispersed bimetallic Pd/X-clusters can be employed as so-called catalytic diffusers for liquid-phase hydrogenation, e.g. of nitrate and nitrite in water. The principles of both concepts are introduced, recently obtained experimental data are evaluated in connection with literature results, and the perspectives for further development are highlighted.

467 citations


Journal ArticleDOI
07 Sep 2001-Science
TL;DR: The electrochemical/catalytic properties of defined atomic ensembles in atomically flat PdAu(111) electrodes with variable surface stoichiometry that were prepared by controlled electrodeposition on Au(111), derived from infrared spectroscopic and voltammetric data obtained for electrode surfaces.
Abstract: Bimetallic electrodes are used in a number of electrochemical processes, but the role of particular arrangements of surface metal atoms (ensembles) has not been studied directly. We have evaluated the electrochemical/catalytic properties of defined atomic ensembles in atomically flat PdAu(111) electrodes with variable surface stoichiometry that were prepared by controlled electrodeposition on Au(111). These properties are derived from infrared spectroscopic and voltammetric data obtained for electrode surfaces for which the concentration and distribution of the respective metal atoms are determined in situ by atomic resolution scanning tunneling microscopy with chemical contrast. Palladium monomers are identified as the smallest ensemble ("critical ensemble") for carbon monoxide adsorption and oxidation, whereas hydrogen adsorption requires at least palladium dimers.

422 citations


Journal ArticleDOI
TL;DR: In this paper, the authors studied the activity for ammonia oxidation and the intermediates formed during the reaction and found that the metal electrodissolution is enhanced by ammonia under these conditions.

300 citations


Journal ArticleDOI
TL;DR: In this paper, the adsorption of l-cysteine on gold electrodes was studied by electrochemical reductive desorption in 0.5 M KOH, and the interaction of l−CSTEine with copper ions was investigated by cyclic voltammetry, chronoamperometry and X-ray photoelectron spectroscopy.

254 citations


Journal ArticleDOI
Abhijit Manna1, Toyoko Imae1, Keigo Aoi1, Masahiko Okada1, Toshinobu Yogo1 
TL;DR: In this article, the synthesis of silver and gold metal nanospherical particles stabilized by the fourth-generation poly(amido amine) (G4 PAMAM) dendrimer is reported.
Abstract: The synthesis of silver and gold metal nanospherical particles stabilized by the fourth-generation poly(amido amine) (G4 PAMAM) dendrimer is reported. The reduction of silver nitrate and sodium tetrachloroaurate in the presence of the PAMAM dendrimer having terminal amine groups results in the formation of stable, water-soluble nanoparticles. The formation and size of the particles have been determined from the UV−vis plasmon absorption band and transmission electron microscopic (TEM) analyses. The average particle sizes are (6.2 ± 1.7)−(12.2 ± 2.9) nm for silver and are (3.2 ± 0.7)−(7.3 ± 1.5) nm for gold, depending on the metal ion-to-dendrimer terminal amine ratio (M:D) used. Thus, dendrimer-protected silver particles are substantially larger than the gold particles synthesized in similar systems. Nanoparticles prepared at 0.25:1 and lower M:D ratios are stable for a long period of time. A TEM study of the morphology also shows a short-ranged hexagonal arrangement of particles in a monolayer onto the c...

224 citations


Journal ArticleDOI
TL;DR: In this article, the current efficiencies for the formation of CO2 during methanol oxidation at smooth polycrystalline platinum electrodes were determined by differential electrochemical mass spectrometry in a thin layer flow through cell.
Abstract: Current efficiencies for the formation of CO2 during methanol oxidation at smooth polycrystalline platinum electrodes were determined by differential electrochemical mass spectrometry in a thin layer flow through cell In all cases, the current efficiencies are below 60%; in particular, values as low as 16% were found in 01 M methanol solution at 06 V, which shows that a large amount of soluble intermediates (formaldehyde and/or formic acid) are formed The extent to which these soluble intermediates are further oxidized to CO2 depends on the diffusion conditions For methanol oxidation a parallel oxidation path via COad is also active The influence of the surface crystal structure and, in particular, of steps was also studied Step decoration by foreign metals allowed examination of the effect of cocatalytic metals on well defined model surfaces

203 citations


Journal ArticleDOI
TL;DR: In this paper, the current efficiency of CO 2 during methanol oxidation was determined by differential electrochemical mass spectrometry (DEMS) using a stochastic geometry of the Pt electrode.

198 citations


Journal ArticleDOI
TL;DR: In this article, the authors present results on the growth of ultrathin films of gold on TiO2(110), as well as the morphology, interface formation, epitaxy, structure and electronic properties of Au on single crystal and planar films.
Abstract: We survey recent studies and present new data on the growth, interactions, structure and chemistry of gold deposited on TiO2(110) surfaces. The noble metal Au on TiO2(110) is a model system for weak interaction of a metal with an oxide substrate; it is also of interest because Au on TiO2 has unusually high activity as a catalyst for CO oxidation at room temperature. In this review, we present results on the growth of ultrathin films of Au on TiO2(110), as well as the morphology, interface formation, epitaxy, structure and electronic properties of Au on TiO2 single crystal and planar films. The results are compared to studies of Au on high-surface-area TiO2 catalysts in an attempt to bridge the gap between surface science experiments and the high pressure conditions of catalyst operation.

161 citations


Journal ArticleDOI
TL;DR: In this paper, the mean diameters of noble metal nanoclusters were characterized and examined by a common method for application to the catalysis for hydrogenation of olefins in homogeneous and heterogeneous systems in the liquid phase.
Abstract: Ligand-stabilized noble metal nanoclusters, prepared by various chemical methods by different research groups in Japan and Germany, were characterized and examined by a common method for application to the catalysis for hydrogenation of olefins in homogeneous and heterogeneous systems in the liquid phase. The mean diameters of palladium, platinum, rhodium and Pd/Pt nanoclusters stabilized by various ligands range from 1.3 to 3.2 nm if prepared by a single reaction, and from 2.2 to 4.0 nm if prepared by a stepwise growth method. The Stokes radii of metal nanoclusters stabilized by surfactants range from 1.7 to 2.1 nm, suggesting a thickness of the protective layer from 1.1 to 1.4 nm, whereas those stabilized by polymers give much larger values, suggesting the formation of aggregates. The catalytic activities of the metal nanoclusters, evaluated by hydrogenation of 1,3-cyclooctadiene and methyl acrylate, depend mainly upon the particle size, i.e. the smaller the size, the higher the activity. However, a strongly interacting ligand like tetraoctylammonium halide and 1,10-phenanthroline can disturb the hydrogenation. In contrast, the activities of heterogeneous catalysts supported on charcoal depend strongly on the covering strength of the stabilizer. Copyright © 2001 John Wiley & Sons, Ltd.

Journal ArticleDOI
TL;DR: In this article, a modified Bonnemann method was used to synthesize carbon-supported Pt-Ru-WO catalysts for the oxidation of H2/CO mixtures and CH3OH.
Abstract: Carbon-supported Pt–Ru–WO x /C catalysts for application in PEMFC anodes were synthesized by a modified Bonnemann method. Their electrocatalytic activity for the oxidation of H2/CO mixtures and CH3OH was measured by E/i-curves in PEM single cell arrangements under working conditions. Information about composition, microstructure and nanomorphology was obtained by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence analysis (XFA) and transmission electron microscopy (TEM). X-ray diffraction data at room temperature show only one single Pt f.c.c. phase; no evidence of Ru, W and their oxides, respectively, is found. Hence, the presence of W and Ru as amorphous oxide species seems likely. Surface-sensitive XPS measurements detect Pt0, platinum oxide and hydroxide species, metallic Ru, ruthenium oxide, hydrous ruthenium oxide and WO3. For the crystalline platinum phase particle sizes of less than 2 nm were determined by TEM images and XRD patterns via solving the Scherrer equation. Temperature-dependent XRD measurements were performed to show the influence of ageing on the catalyst structure.

Journal ArticleDOI
TL;DR: In this article, a series of palladium catalysts supported on ceria and ceria-zirconia/alumina in the calcined state and under a reactive CO+O2 atmosphere has been characterized by a combination of electron transmission microscopy, infrared and electron paramagnetic resonance spectroscopies, and the results obtained used to interpret the catalytic behavior displayed by the samples in the CO oxidation reaction.
Abstract: The state of a series of palladium catalysts supported on ceria–zirconia and ceria–zirconia/alumina in the calcined state and under a reactive CO+O2 atmosphere has been characterized by a combination of electron transmission microscopy, infrared and electron paramagnetic resonance spectroscopies, and the results obtained used to interpret the catalytic behavior displayed by the samples in the CO oxidation reaction. The Ce/Zr promoter enhances the catalytic properties of the noble metal by favoring the formation of the metallic state and through creation of anionic vacancies in the Ce–Zr component even from room temperature. The optimum promoting effect in the CO oxidation is observed for palladium particles in contact with three-dimensional-like Ce–Zr particles due to the appropriate nature and high number of the anion vacancies present at their surface. Compared with classical ceria-based systems, CO oxidation is here maximized for Pd-supported on the bulk material and not on mixed ceria-containing/alumina catalysts. These differences are discussed on the basis of the effect of the ceria and ceria–zirconia promoter particle size on the nature and number of active sites.

Journal ArticleDOI
Luca Giorgi1, Alfonso Pozio1, C. Bracchini1, Rossella Giorgi1, S. Turtu1 
TL;DR: In this paper, the oxidation kinetics of H2 and H2 + 100 ppm CO were investigated on Pt, Ru and Pt-Ru electrocatalysts supported on a high-surface area carbon powder.
Abstract: The oxidation kinetics of H2 and H2 + 100 ppm CO were investigated on Pt, Ru and Pt–Ru electrocatalysts supported on a high-surface area carbon powder The atomic ratios of Pt to Ru were 3, 1 and 033 XRD, TEM, EDS and XPS were used to characterize the electrocatalysts When alloyed with ruthenium, a decrease in mean particle size and a modification of the platinum electronic structure were identified Impedance measurements in H2SO4, at open circuit potential, indicated different mechanisms for hydrogen oxidation on Pt/C (Tafel–Volmer path) and Pt–Ru/C (Heyrowsky–Volmer path) These mechanisms also occur in the presence of CO Best performances, both in H2 and H2 + CO, were achieved by the catalyst with the ratio Pt/Ru = 1 This is due to a compromise between the number of free sites and the presence of adsorbed water on the catalyst For CO tolerance, an intrinsic mechanism not involving CO electroxidation was proposed This mechanism derives from changes in the electronic structure of platinum when alloyed with ruthenium

Journal ArticleDOI
TL;DR: In this paper, the role of the oxygen-containing species generated and adsorbed during surface surface oxidation was investigated and a dual path mechanism was proposed for the alcohols studied.

Journal ArticleDOI
TL;DR: In this paper, the effect of chlorine, added either as a part of the platinum precursor salt or after the noble metal impregnation, on the catalytic activity of Pt/Al2O3 for complete oxidation of toluene was discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the actual cyclic performance of the SERP (Sorption Enhanced Reaction Process) concept for hydrogen production using a pilot-scale apparatus with a proprietary SMR (steam-methane reforming) catalysts and a proprietary CO 2 chemisorbent (pelletized potassium carbonate promoted hydrotalcite).
Abstract: The purpose of this article is to describe the actual cyclic performance of the SERP (Sorption Enhanced Reaction Process) concept for hydrogen production using a pilot-scale apparatus with a proprietary SMR (steam-methane reforming) catalysts (noble metal on alumina) and a proprietary CO 2 chemisorbent (pelletized potassium carbonate promoted hydrotalcite), which has been described earlier (Hufton et al., 1999).

Journal ArticleDOI
TL;DR: In this paper, the results were further improved such that adsorption could be predicted a priori to a very reasonable degree without adjustable parameters, and a comprehensive simulation of uptake as a function of initial platinum concentration, initial solution pH and the surface loading (amount of oxide surface per solution volume) was performed.

Journal ArticleDOI
TL;DR: Chrzanowski et al. as discussed by the authors used ex situ scanning tunneling microscopy (STM) to image the deposition characteristics of ruthenium and osmium islands on Pt(111) single crystal surfaces.

Journal ArticleDOI
TL;DR: In this article, the effect of surface oxidation of the carbon support of Pt catalysts with nitric acid has been investigated and it is speculated that hydrophilic carboxylic acid groups produced by surface oxidation enhance wetting of the catalyst layer.

Journal ArticleDOI
TL;DR: In this article, the performance of noble metal catalysts was compared with that of traditional manganese catalysts for aqueous p-chlorophenol (p-CP) solution at 453 K and 2.6 MPa in a slurry reactor.
Abstract: Heterogeneous catalytic wet oxidation of aqueous p-chlorophenol (p-CP) solution was investigated at 453 K and 2.6 MPa in a slurry reactor. The performance of noble metal catalysts was compared with that of traditional manganese catalysts. Activated carbon supported catalysts showed significant higher activities for total organic carbon (TOC) reduction than those supported on alumina or cerium oxide. Pt was found to be the most active metal for p-chlorophenol oxidation. The activities of noble metal catalysts were found to correlate with heat of formation of metal oxides. CO2 is the predominant oxidation product with formation of minor p-benzoquinone and acetic acid as intermediate compounds. Possible reaction pathway was also discussed.

Journal ArticleDOI
TL;DR: In this paper, a gold-coated iron core-shell structure nanoparticles (Fe/Au) synthesized using reverse micelles were characterized by transmission electron microscopy (TEM).
Abstract: Pure metal iron nanoparticles are unstable in the air. By a coating iron on nanoparticle surface with a stable noble metal, these air-stable nanoparticles are protected from the oxidation and retain most of the favorable magnetic properties, which possess the potential application in high density memory device by forming self-assembling nanoarrays. Gold-coated iron core-shell structure nanoparticles (Fe/Au) synthesized using reverse micelles were characterized by transmission electron microscopy (TEM). The average nanoparticle size of the core-shell structure is about 8 nm, with about 6 nm diameter core and 1∼2 nm shell. Since the gold shell is not epitaxial growth related to the iron core, the morie pattern can be seen from the overlapping of iron core and gold shell. However, the gold shell lattice can be seen by changing the defocus of TEM. An energy dispersive X-ray spectrum (EDS) also shows the nanoparticles are air-stable. The magnetic measurement of the nanoparticles also proved successful synthesis of gold coated iron core-shell structure. The nanoparticles were then assembled under 0.5 T magnetic field and formed parallel nanobands with about 10 μm long. Assembling two dimensional ordered nanoarrays are still under going.

Patent
08 Jun 2001
TL;DR: In this article, a process for preparing metal nanoparticles, comprising reacting suitable metal salts and anionic surfactant containing an anionic group of carboxylic group (COO−), sulfate group (SO4 2−) or sulfonate group(SO3 2−), was described.
Abstract: A process for preparing metal nanoparticles, comprising reacting suitable metal salts and anionic surfactant containing an anionic group of carboxylic group (COO−), sulfate group (SO4 2−) or sulfonate group (SO3 2−) as reducing agent in water under reflux at a temperature of 50-140° C., such that under the reducing power of said anionic surfactant itself, the metal salts can be effectively reduced into metal nanoparticles having a uniform particle size and that the reaction will be not too fast, no large microparticle will be formed, the yield will not be lowered, and the nanoparticle thus prepared can be dispersed stably in polar and non-polar solvent.

Journal ArticleDOI
TL;DR: The importance of the gas composition during NOx release, including the λ-value, humidity, O2, and CO2 concentration, was studied in flow reactor experiments performed with a commercial, noble metal BaO type catalyst.
Abstract: Automotive lean-NOx has become one of the major issues in catalysis research, due to increased environmental concerns. In the present study the NOx storage/release concept has been investigated with respect to the NOx release kinetics. The importance of the gas composition during NOx release, including the λ-value, humidity, O2, and CO2 concentration, was studied in flow reactor experiments performed with a commercial, noble metal BaO type catalyst. The main conclusions are that CO2 has a promoting and O2 a blocking effect on the NOx release.


Journal ArticleDOI
TL;DR: In this article, a dynamic reaction cell (DRC) based solution to the problem is introduced, which works in complete contrast to conventional ICP-MS analysis where the formation of oxides is undesirable and operating conditions are optimised to limit their production.
Abstract: Noble metals are subject to a number of significant oxide-based interferences in ICP-MS analysis. Quantification of these interferences has been largely overlooked despite evidence which suggests that they may, in some cases, represent a significant source of analytical error. Their removal would therefore constitute a significant improvement in analytical accuracy. In this study the oxides that interfere with noble metal analysis have been quantified relative to CeO+/Ce+ ratios. A dynamic reaction cell (DRC) based solution to the problem is introduced, which works in complete contrast to conventional ICP-MS analysis where the formation of oxides is undesirable and operating conditions are optimised to limit their production. Oxygen reaction gas is utilised actively to promote oxidation of interfering species to higher oxides, with a resulting separation of analyte from interfering oxide. Results are presented for Hf, Ta, Nb, and Zr where the single oxide interferes with a noble metal analyte mass. Various higher oxides are formed, leaving the mass free from interference. The reaction mechanism has been determined in each case by monitoring of new multiple-oxide species and scans of the entire mass range to identify new product species. Results confirm the success of an in-cell separation of analyte from metal oxide, facilitating improved detection limits and isotope-ratio precision. The suitability of this method for general environmental use is demonstrated by analysis of a certified soil reference material and isotope-ratio analyses.

Journal ArticleDOI
TL;DR: The mechanism of rhodium adlayer formation on the (100) face of a gold single crystal and on a polycrystalline gold electrode has been studied using cyclic voltammetry and chronoamperometry.

Journal ArticleDOI
TL;DR: In this paper, the existence of two unexpected very sharp peaks in the hydrogen region that were observed by cyclic voltammetry was reported, and the films produced were characterised by X-ray diffraction and transmission electron microscopy.

Journal ArticleDOI
TL;DR: In this article, the chemisorbates formed from ammonia-containing alkaline electrolyte on gold and palladium electrodes have been identified using surface-enhanced Raman spectroscopy (SERS).

Journal ArticleDOI
TL;DR: In this paper, the optical hydrogen sensitivity of composite films composed of noble metals such as Pd, Pt and Au and tungsten oxide (WO3) for optical gas sensing was investigated.
Abstract: Composite films composed of noble metals such as Pd, Pt and Au and tungsten oxide (WO3) for optical gas sensing were prepared by simultaneous rf and dc sputtering deposition, and the optical hydrogen sensitivities of these Pd–WO3, Pt–WO3 and Au–WO3 composite films were investigated together with the WO3 film without containing noble metals. At temperatures of 200–250°C, no change in the visible–near IR absorption of the WO3 film without noble metals could be detected by the presence of 1 vol.% H2 in air. The combination of Pd with WO3 film enhanced the detection of H2 in air through an increasing change of absorbance in the whole visible–near IR wavelength region centered at around λ=1000 nm. This increase of absorbance by H2 can be explained by the formation of tungsten bronze (HxWO3), which is enhanced by the dissociation of H2 on Pd. On the other hand, the combination of Pt with WO3 did not make the film sensitive to H2. In the case of the Au–WO3 composite film, the combination of Au made the film sensitive mainly at the plasmon absorption region around visible wavelengths, in addition to the small sensitivity due to the formation of tungsten bronze around near IR wavelengths. The change of absorbance by H2 in the plasmon absorption region, which include both an increasing change at wavelengths around 550 nm and a decreasing change of absorbance at wavelengths around 700 nm, might be because the absorbance by small Au particles in plasmon band was influenced by the change in the dielectric constant of tungsten oxide which surrounded small Au particles.