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Showing papers on "Noble metal published in 1995"


Journal ArticleDOI
20 Jul 1995-Nature
TL;DR: In this paper, a simple surface reaction, the dissociation of H2 on the surface of gold and of three other metals (copper, nickel and platinum) that lie close to it in the periodic table, was studied.
Abstract: THE unique role that gold plays in society is to a large extent related to the fact that it is the most noble of all metals: it is the least reactive metal towards atoms or molecules at the interface with a gas or a liquid. The inertness of gold does not reflect a general inability to form chemical bonds, however—gold forms very stable alloys with many other metals. To understand the nobleness of gold, we have studied a simple surface reaction, the dissociation of H2 on the surface of gold and of three other metals (copper, nickel and platinum) that lie close to it in the periodic table. We present self-consistent density-functional calculations of the activation barriers and chemisorption energies which clearly illustrate that nobleness is related to two factors: the degree of filling of the antibonding states on adsorption, and the degree of orbital overlap with the adsorbate. These two factors, which determine both the strength of the adsorbate-metal interaction and the energy barrier for dissociation, operate together to the maxima] detriment of adsorbate binding and subsequent reactivity on gold.

2,721 citations


Journal ArticleDOI
B.E. Conway1
TL;DR: In this article, the formation of the oxide films can be examined in detail by recording the distinguishable stages in the film's electrochemical reduction in linear-sweep voltammetry which is sensitive down to OH O fractional coverages as low as 0.5% and over time-scales down to 50μs in experiments on time-evolution and transformation of oxide films.

548 citations


Journal ArticleDOI
TL;DR: Palladium-based catalysts have been found to be the most efficient catalysts for the catalytic oxidation of methane to carbon dioxide and water as discussed by the authors, and the reaction rate is dependent on methane concentration, generally to the first order or less.

361 citations



Journal ArticleDOI
TL;DR: In this article, a series of Bi-Pt/alumina catalysts were used for the partial oxidation of cinnamyl alcohol to cinnamonaldehyde with air in an aqueous solution.

133 citations


Patent
03 Feb 1995
TL;DR: In this article, a support for purifying carbon monoxide, hydrocarbons and nitrogen oxides in exhaust gases at the stoichiometric point or in oxygen-rich atmospheres is presented.
Abstract: A catalyst for purifying carbon monoxide, hydrocarbons and nitrogen oxides in exhaust gases at the stoichiometric point or in oxygen-rich atmospheres, is disclosed, and it includes a support in which at least one element selected from the group consisting of alkali metals, alkaline-earth metals and rare-earth elements including La is dissolved in titania to form a solid solution, and a noble metal catalyst ingredient loaded on the support. A process for purifying, by bringing the exhaust gases into contact with the catalyst, is also disclosed.

115 citations



Journal ArticleDOI
TL;DR: Iridium (2 µg) was deposited on a carbide-coated platform, pre-treated with about 12−13 µmol of Zr or W, and was evaluated as a permanent modifier in electrothermal atomic absorption spectrometry.
Abstract: Iridium (2 µg) was deposited on a carbide-coated platform, pre-treated with about 12–13 µmol of Zr or W, and was evaluated as a permanent modifier in electrothermal atomic absorption spectrometry The noble metal is not vaporized from the integrated platform of the transverse-heated graphite atomizer, provided that the atomization and clean-out temperatures do not exceed 2050–2100 and 2100–2200 °C, respectively Under comparable conditions, Pd exhibits much worse thermal behaviour, being volatilized above 1300 and 1500 °C from Zr- and W-treated platforms, respectively Pyrolysis–atomization curves were plotted for numerous hydride-forming and volatile analytes: Sb, As, Bi, Cd, Pb, Te, Tl, Sn and Se The best characteristic masses for integrated absorbance measurements with the Ir–Zr-treated platforms are 92, 30, 176, 24, 35, 50, 65, 71 and 45 pg, respectively Vaporization temperatures are generally above 1000 °C, except for Cd The effect of atomization temperature on sensitivity in peak height and integrated absorbance measurements is discussed Double peaks were observed for Bi and Te with Ir–W-treated platforms

102 citations


31 Dec 1995
TL;DR: In this article, the possibility of using noble metal catalysts for low-temperature hydrotreating reaction in the presence of sulfur-containing compounds, and the model reaction of naphthalene hydrogenation was used.
Abstract: The hydrogenation of aromatic and polyaromatic compounds are typically exothermic; therefore, a lower reaction temperature is thermodynamically favorable. However, in considering the hydrotreating process of heavy liquids where polycyclic aromatic compounds are abundant, a reaction temperature above 623K is typical which consequently requires a high concentration of hydrogen to offset the limitation of thermodynamic equilibrium conversion. Noble metal catalysts are active for the hydrogenation of aromatics even at a temperature below 473K, but they were not used for hydrotreating purpose owing to the cost and their susceptibility to the poisoning by sulfur-containing compounds. However, recent studies showed that noble metal catalysts may not be as sensitive to sulfur as what has been recognized. This study is therefore attempted to probe the possibility of using noble metal catalysts for low-temperature hydrotreating reaction in the presence of sulfur-containing compounds, and the model reaction of naphthalene hydrogenation in the presence of benzothiophene was used.

92 citations


Journal ArticleDOI
TL;DR: In this paper, thin film composite membranes on PVDF supports with and without catalysts were prepared and their permselectivity data were reported and their catalytic activity was shown by hydrogen sorption.

80 citations


Journal ArticleDOI
TL;DR: In this article, the effect of aging on the oxygen storage/release and activity in a commercial automotive catalyst containing Pt, Rh, Ni, and Ce was studied. And the results indicated that aging the catalyst causes a loss of oxygen storage capacity due to sintering of the ceria particles.
Abstract: We have studied the effect of hydrothermal aging on the oxygen storage/release and activity in a commercial automotive catalyst containing Pt, Rh, Ni, and Ce. X-ray photoelectron spectroscopy (XPS) was used to measure changes in the oxidation state of the Ce and Ni present in the washcoat of the catalyst after various oxidation and reduction treatments and rate measurements of the carbon monoxide oxidation reaction were used to determine the reaction kinetics and activity. The catalyst was tested fresh and after hydrothermal aging at 1000°C under cyclic redox conditions. To determine which Ce species were present on the surface, we fit the XPS Ce(3d) data with combinations of spectra from standard materials (CeO2 and Ce2O3). Based on our measurements we conclude that aging the catalyst causes a loss of oxygen storage capacity due to sintering of the ceria particles which reduces the ceria/noble metal interaction and does not allow the Ce to cycle between oxidation states. In addition, hydrothermal aging causes the loss of oxygen storage of the Ni due to the irreversible formation of NiAl2O4. For the fresh catalyst, the observed kinetics for the uncycled carbon monoxide oxidation reaction show all of the signatures attributable to a catalyst with a high degree of ceria/noble metal interaction (complete suppression of the carbon monoxide inhibition effect, decreased sensitivity of the reaction rate to gas-phase oxygen concentration, and decreased apparent activation energy). Changes in the kinetics upon aging are consistent with a loss of ceria/noble metal contact area due to sintering of the ceria particles.

Patent
17 Feb 1995
TL;DR: In this article, a catalytic component for purification of diesel engine exhaust gas is described, which consists of two elements of iron and manganese and a refractory inorganic oxide and optionally an alkaline earth element and/or rare earth element.
Abstract: A catalyst for purification of diesel engine exhaust gas is disclosed which comprises having (A) a catalytic component comprising the two elements of iron and manganese and a refractory inorganic oxide and optionally an alkaline earth element and/or a rare earth element and (B) a catalytic component comprising at least one noble metal selected from the group consisting of palladium, platinum, and rhodium and a refractory inorganic oxide and optionally copper deposited in the form of a single layer on a refractory three-dimensional structure. This catalyst is capable of removing such harmful components as carbonaceous particulates, unburned hydrocarbons, and carbon monoxide from the diesel engine exhaust gas and, moreover, suppress the formation of sulfates from sulfur dioxide.

Journal ArticleDOI
TL;DR: In this article, solid sols of rhodium, palladium, platinum, silver, and gold in poly(methyl methacrylate) (PMMA) were prepared by the solidification (polymerization) of solutions of starting noble metal compounds in methyl methacarylate monomer and post-heating of the resulting solid solutions of the compounds in PMMA.

Journal ArticleDOI
TL;DR: In this paper, the authors studied CO2-reforming reactions in a plug-flow reactor with catalysts containing less than a monolayer of Rh, Ru, or Ir deposited from tetrametallic dodecacarbonyl clusters onto low surface area polycrystalline α-Al2O3, MgO, CeO2, La2O 3, and TiO2.

Journal ArticleDOI
TL;DR: In this paper, temperature-programmed decomposition and dynamic XRD measurements over Pt-MFI revealed that metallic platinum particles were formed through the decomposition of tetraammineplatinum ion during the pre-treatment around 673 K in helium atmosphere.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the energy of the elementary reactions involved in the direct synthesis of methanol from methane over noble metal catalysts using the bond order conservation Morse potential approach (BOC-MP).

Patent
08 Dec 1995
TL;DR: In this paper, the authors describe a catalyst for purifying exhaust gases, which consists of a porous support; a cerium oxide or a solid solution; and a noble metal element loaded on the porous support.
Abstract: A catalyst for purifying exhaust gases includes a porous support; a cerium oxide or a solid solution of a cerium oxide and a zirconium oxide in a state of mutual solid solution, loaded on the porous support; and a noble metal element loaded on the porous support. The cerium oxide or the solid solution has an average particle diameter of from 5 to 100 nm. The cerium oxide is present in the solid solution in an amount of from 0.2 to 4.0 by molar ratio with respect to the zirconium oxide therein. The catalyst can be prepared by: coating and calcinating on a support substrate a slurry of a cerium oxide sol, a cerium oxide sol and a zirconium oxide sol, on a solid solution powder of a cerium oxide and a zirconium oxide in a state of mutual solid solution; and loading a noble metal element thereon. The cerium oxide or its solid solution has a surface area large enough to effect an oxygen storage function, and has an average particle diameter large enough to prevent the same from entering deeply into fine pores of a porous support, thereby providing a catalyst fully exhibiting both of the oxygen storage capability and the catalytic activity.

Patent
29 Mar 1995
TL;DR: In this paper, the authors proposed a new method for directly oxidizing propylene with oxygen and hydrogen in the presence of a titanosilicate catalyst supporting a noble metal at a specific temperature.
Abstract: PURPOSE: To produce the subject compound in high selectivity without being influenced with a raw material gas composition in oxidizing reaction or preparing conditions of a catalyst according to a new method for directly oxidizing propylene with oxygen and hydrogen in the presence of a titanosilicate catalyst supporting a noble metal at a specific temperature. CONSTITUTION: Propylene is directly oxidized with oxygen and hydrogen in the presence of a catalyst supporting a group VIII noble metal of the periodic table (preferably Pd or platinum) on a titanosilicate at 0-40 deg.C, preferably 10-35 deg.C. A titanosilicate is preferably a synthetic zeolitic substance of the formula nSiO2 . (1-n)TiO2 [(n) is 0.8-0.999] capable of manifesting an X-ray diffraction pattern of a pentasil type structure. The titanosilicate is preferably obtained by hydrolyzing a tetraalkyl orthosilicate and a tetraalkyl orthotitanate with an aqueous solution of a tetraalkylammonium hydroxide and then carrying out the hydrothermal synthesis. The catalyst is preferably prepared by supporting a noble metallic compound on the titanosilicate according to an impregnating method and then conducting the reducing treatment of the noble metallic compound.

Journal ArticleDOI
TL;DR: In this article, it was shown that the reaction on calcined Ni/MgO (6), Ni/CaO (7), and Ni/rare earth oxide catalysts is found to start at much lower temperatures because of their ease of reduction during the initial reaction period.

Journal Article
TL;DR: In this article, the authors define electroless plating as a nonelectrolytic method of deposition from solution, and the minimum necessary components of an electroless plate solution are a metal salt and an appropriate reducing agent.
Abstract: Electroless, or autocatalytic, metal plating is a nonelectrolytic method of deposition from solution. The minimum necessary components of an electroless plating solution are a metal salt and an appropriate reducing agent. An additional requirement is that the solution, although thermodynamically unstable, is stable in practice until a suitable catalyzed surface is introduced. Plating is then initiated upon the catalyzed surface, and the plating reaction is sustained by the catalytic nature of the plated metal surface itself. This definition of electroless plating eliminates both those solutions that spontaneously plate on all surfaces («homogeneous chemical reduction»), such as silver mirroring solutions; also «immersion» plating solutions, which deposit by displacement a very thin film of a relatively noble metal onto the surface of a sacrificial, less noble metal

Journal ArticleDOI
TL;DR: In this paper, the effect of two types of surface additives (Pd and Pt) on the response of reactively sputtered thin films of SnO x gas sensors has been studied, in mixtures of zero grade air and carbon monoxide.
Abstract: The effect of two types of surface additives (Pd and Pt) on the response of reactively sputtered thin films of SnO x gas sensors has been studied, in mixtures of zero grade air and carbon monoxide. The experimental results obtained with surface additives show an abrupt conductance increase around 500 K when carbon monoxide in the ppm range is present, a behaviour which has not been observed with plain SnO x films. A semi-empirical model that explains this behaviour is presented, that is based on the well-established theory for the conductivity of ultrathin discontinuous metal films, i.e. activated charge carrier creation and tunnelling through potential barriers. The proposed model takes into account the dependence of film conductivity both on the thickness of the noble metal deposited on it and on the working temperature. The results of the theoretical analysis are in excellent qualitative agreement with the experimental ones.

Journal ArticleDOI
TL;DR: In this article, surface species formed as a function of the temperature during the preparation of RuO 2 /TiO 2 mixed oxide films were identified by emission FT-IR and FT-Raman spectroscopy.

Book ChapterDOI
TL;DR: In this paper, the main interest is devoted to noble metal complexes of porphyrins, but complexes of hydroporphyrin, porphrin analogs, homologs and phthalocyanines are also mentioned where appropriate.
Abstract: The noble metals ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, and gold form a variety of complexes M(P) LL′ with tetrapyrrole ligands which are studied in many laboratories because their coordination chemistry and catalytic power is similar to that of the corresponding iron and cobalt tetrapyrroles forming the prosthetic groups in heme proteins and vitamin B12. Apart from the corrins and corroles which are treated in the second article of this volume, the main interest is devoted to noble metal complexes of porphyrins, but complexes of hydroporphyrins, porphyrin analogs, homologs, porphyrinoids, and phthalocyanines are also mentioned where appropriate.

Patent
28 Sep 1995
TL;DR: In this paper, a method for improving the performance and longevity of coatings of metal deposited from aqueous solutions of inorganic, organic or oraganometallic metal compounds was proposed.
Abstract: A method for improving the performance and longevity of coatings of metal deposited from aqueous solutions of inorganic, organic or oraganometallic metal compounds. The method involves co-deposition of noble metal or corrosion-inhibiting non-noble metal during growth of oxide film on a component made of alloy, e.g., stainless steels and nickel-based alloys. The result is a metal-doped oxide film having a relatively longer life in the reactor operating environment. In particular, incorporation of palladium into the film provides greatly increased catalytic life as compared to palladium coatings which lie on the oxide surface.

Patent
06 Oct 1995
TL;DR: In this article, an anode electrocatalyst for a fuel cell comprising an alloy essentially consisting of at least one of tin, germanium and molybdenum, and one or more noble metals selected from platinum, palladium and ruthenium is described.
Abstract: Disclosed is an anode electrocatalyst for a fuel cell comprising an alloy essentially consisting of at least one of tin, germanium and molybdenum, and one or more noble metals selected from platinum, palladium and ruthenium. The tin, germanium and/or molybdenum gas the ability of depressing the poisioning of the noble metal with carbon monoxide so that fuel containing a relatively high content of the carbon monoxide may be supplied to a fuel cell equipped with anode in accordance with the present invention which is otherwise liable to be poisioned.

Journal ArticleDOI
TL;DR: In this article, it was shown that the Ag(MNN) electron energies for multilayer silver xanthate were significantly different from those for silver and silver sulfide.

Book ChapterDOI
TL;DR: In this paper, carbon fibrils are used as supports for noble metal particles in liquid phase catalytic processes, and a homogeneous deposition-precipitation procedure is used to obtain carbon fibil-supported palladium catalysts.
Abstract: Carbon fibrils can be produced smoothly by exposing finely dispersed iron or nickel particles to reducing carbon containing gas flows. Alumina-supported iron particles were used to grow carbon fibrils with cylindrical graphite layers parallel to the fibril axis. The carbon fibrils interweave during growth, resulting in the formation of tangled skeins. Owing to the size of the skeins (about 3 μm), the pore volume, the pore size distribution, the surface area, the filterability and the mechanical strength, the skeins are very appropriate as supports for, e.g., noble metal particles, in liquid phase catalytic processes. Therefore, we examined the properties of the bare carbon fibrils, as, well as the properties of catalysts supported on carbon fibrils. To obtain carbon fibril-supported palladium catalysts, a homogeneous deposition-precipitation procedure was utilized. Varying preparation conditions, such as, the atmosphere during drying and the pretreatment of the carbon fibrils, affect the activity in the liquid-phase hydrogenation of nitrobenzene significantly.

Patent
08 Nov 1995
TL;DR: In this paper, a reaction comprising the oxidation of carbon monoxide to carbon dioxide, eg in vehicle exhausts, employs a catalyst composed of metal oxide, eg. ceria, particles among which are uniformly incorporated noble metal particles.
Abstract: A reaction comprising the oxidation of carbon monoxide to carbon dioxide, eg in vehicle exhausts, employs a catalyst composed of metal oxide, eg. ceria, particles among which are uniformly incorporated noble metal particles, the particles having such a high interaction that, without hydrogen reduction pre-treatment, the catalyst exhibits the formation of anionic vacancies on the metal oxide surface at a temperature lower than does the corresponding catalyst prepared by impregnation. The catalyst employed is preferably prepared by co-precipitation.

Patent
26 Apr 1995
TL;DR: In this article, an integrated circuit capacitor (20) includes a bottom electrode structure (24) having an adhesion metal portion (34), a noble metal portion(36), and a second noble metal layer (40).
Abstract: An integrated circuit capacitor (20) includes a bottom electrode structure (24) having an adhesion metal portion (34), a noble metal portion (36), and a second noble metal layer (40). A process of manufacture includes annealing the adhesion metal portion (34) and the noble metal portion (36) prior to the deposition of second noble metal layer (40) for purposes of forming barrier region (38). The electrode (24) preferably contacts metal oxide layer (26), which is made of a perovskite or perovskite-like layered superlattice material. A temporary capping layer (59) is formed and removed in manufacture, which serves to increase polarization potential from the device by at least 40%.

Patent
17 Feb 1995
TL;DR: In this paper, the authors proposed a method for mitigating crack growth on the surface of stainless steel or other metal components in a water-cooled nuclear reactor by injecting a noble metal, e.g., palladium, into the water of the reactor in the form of a solution or suspension.
Abstract: A method for mitigating crack growth on the surface of stainless steel or other metal components in a water-cooled nuclear reactor. A compound containing a noble metal, e.g., palladium, is injected into the water of the reactor in the form of a solution or suspension. This compound has the property that it decomposes under reactor thermal conditions to release ions/atoms of the noble metal which incorporate in or deposit on the interior surfaces of the crack. The compound may be organic, organometallic (e.g., palladium acetylacetonate) or inorganic in nature. The palladium deposited inside a crack should exhibit catalytic behavior even if the bulk surface palladium is depleted under high fluid flow conditions. As a result, the electrochemical potential inside the crack is decreased to a level below the critical potential to protect against intergranular stress corrosion cracking.