Showing papers on "Noble metal published in 1994"

Preparation and Catalysis of Novel Colloidal Dispersions of Copper/Noble Metal Bimetallic Clusters

Abstract: Colloidal dispersions of polymer-protected Cu/Pt alloy clusters have been prepared for the first time by reduction of the corresponding metal hydroxide with a cold alloying process. The Cu/Pt (mole ratio=1/1) colloid with an average diameter of 19 A and Cu/Pt (3/1) with an average diameter of 23 A have the alloy structure of CuPt and Cu 3 Pt, respectively. Colloidal dispersions of polymer-protected Cu/Pd bimetallic alloy clusters have also been prepared by the same method at various Cu/Pd ratios. These bimetallic clusters exhibit excellent properties as the active and selective catalyst for the hydration of acrylonitrile to acrylamide as well as the hydrogenation of 1,3-cyclooctadiene to cyclooctene

Oxygen availability in mixed cerium/praseodymium oxides and the effect of noble metals

Abstract: Oxyreduction studies of mixed Ce/Pr oxides have been carried out. Temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), and temperature-programmed oxidation (TPO) were used to study the uptake and release of the oxygen. Large amounts of oxygen, exceeding those in ceria, are accessible in the mixed metal oxides at moderate temperatures. The addition of small amounts of noble metals to the mixed oxides shifts the accessibility of the “stored” oxygen to still lower temperatures with the effect of Pd being more pronounced than that of Pt. In a sample containing 45 mol % ceria and 55 mol % praseodymia, a small addition of Pd (0.24 mol %) was found to lower the reduction temperature by more than 100 °C. The addition of Pt had a lesser effect. Similarly, in pure praseodymia (Pr6O11) Pd influences the reduction much more strongly than Pt. In the mixed samples, whether doped with a noble metal or not, the whole oxyreduction effect can be accounted for by the change in oxidation state of the praseodymium ions solely. This notwithstanding, the reduction of the mixed oxides, without noble metals or doped by Pt, is more facile than that of praseodymia. Only the incorporation of Pd makes the reduction of praseodymia proceed at a temperature below that registered for a mixed ceriapraseodymia sample.

Aspects of CO2-reforming of Methane

Abstract: The paper analyses present knowledge on the CO 2 -reforming reaction and discusses process options. CO 2 -reforming resembles conventional reforming. Different reaction rates can probably be related to kinetics. CO 2 -reforming involves higher thermody-namic potential for carbon formation. Three solutions are discussed: the use of noble metal catalysts, sulphur-passivated nickel catalysts, and CO 2 -addition to autotherrnal reforming.

Catalyst for purifying exhaust gas

Abstract: PURPOSE:To obtain the subject catalyst excellent in exhaust gas purifying capacity and durability and enabling the effective use of a noble metal by specifying the optimum arranging position of the noble metal in a catalyst bed and the proper supporting ratio of the noble metal. CONSTITUTION:In a catalyst for purifying exhaust gas wherein a monolithic carrier is coated with a catalyst layer reducing carbon monoxide, hydrocarbon and nitrogen oxide discharged from an internal combustion engine, the catalyst layer contains catalyst particles composed of a noble metal selected from either one of Pt, Pd and Rh or a plurality of noble metals supported on heat-resistant inorg. oxide and contains three kinds of noble metals of Pt, Pd and Rh as the whole of catalyst layer. Further, the catalyst layer contains catalyst particles having Pd supported thereon in an amt. of 2-10% by wt. based on heat-resistant inorg. oxide at the position within the thickness range of 1/2 from the surface of the catalyst layer and catalyst particles having at least Rh supported thereon is exposed to the surface of the catalyst layer.

Solid polymer type fuel cell and method for manufacturing the same

Abstract: The invention provides a solid polymer electrolyte having high performances in which the reaction area of electrode is increased by uniformly dispersing and bonding a solid polymer electrolyte and a catalyst and the ability of gas feeding to the reaction site is improved by adding a fluoropolymer so that the catalyst is not excessively coated A method for making the fuel cell is also provided The electrode provided on at least one side of a solid polymer electrolyte membrane is formed by coating on one side of a gas-diffusible layer a mixed dispersion of a noble metal catalyst, a carbon fine powder and a colloidal dispersion of a solid polymer electrolyte, the colloidal dispersion being prepared using an organic solvent having a polar group other than hydroxyl group in the molecule and having a carbon chain of 1-8 carbon atoms which bonds to the polar group or having a dielectric constant of 3-10

Reaction pathways during the oxidation of ethyl acetate on a platinum/alumina catalyst

Abstract: The control of airborne emissions of volatile organic compounds (VOCs) can often be achieved through catalytic oxidation over noble metals (e.g., platinum) supported on alumina. For many classes of materials, high levels of conversion to innocuous materials (CO[sub 2] and water) can be obtained at low temperature, without the appearance of any reaction intermediates. However, other classes of compounds, such as oxygenated species, do produce significant quantities of partial oxidation products, which can greatly limit the utility of catalytic oxidation for VOC destruction. Within this paper, the authors describe their efforts to understand the reaction pathways leading to the formation of partial oxidation products. Oxidation of ethyl acetate over a platinum catalyst dispersed on [gamma]-alumina and supported on a cordierite monolith has been found to produce partial oxidation products including ethanol, acetic acid, and diethyl ether. The reaction pathways leading to the formation of these partial oxidation products have been developed by examining the reaction over the alumina support without any noble metal present. Platinum is seen to produce complete oxidation products, almost exclusively. The total product spectrum can be obtained by assuming no interaction between alumina and platinum; in other words, simple combination of the results observed from reactionmore » over alumina with the complete oxidation pathway catalyzed by platinum.« less

Catalysts for the purification of exhaust gas

Abstract: A catalyst for the purification of exhaust gas comprises a first coating layer of activated alumina containing at least one of Pt, Pd and Rh, a second coating layer of activated alumina containing no noble metal and a third coating layer of zeolite ion-exchanged with Cu or Co and develops excellent purification performance in lean-burn atmosphere after engine aging treatment.

Decomposition of NO2 on metal surfaces: Oxidation of Ag, Zn, and Cu films

Abstract: The dissociation probability of O2 on Cu(111), Ag(111), and Zn(001) surfaces is quite low (<10−2). The oxidation process using molecular oxygen is not practical for work under ultrahigh vacuum conditions. We have found that NO2 is a very good oxygen source for the oxidation of Ag, Zn, and Cu surfaces. At elevated temperatures (300–500 K), the dissociation probability of NO2 on thick Ag, Zn, and Cu films supported on Ru(001) is close to one. The decomposition of NO2 produces a large amount of adsorbed oxygen and gaseous NO and N2. The thermal stability and electronic properties of the O/Ag, ZnOx, and CuOx films were examined using temperature desorption spectroscopy, x‐ray photoelectron spectroscopy (XPS), and x‐ray Auger electron spectroscopy. Large amounts of oxygen can be adsorbed and dissolved in Ag films without oxidation of the noble metal. The zinc oxide films displayed the typical O 1s XPS and Zn L3M4,5M4,5 Auger spectra of polycrystalline ZnO. In addition, the high‐resolution electron energy‐loss spectroscopy spectra of these films exhibited the characteristic phonon losses of bulk ZnO. In the case of Cu films the NO2‐oxidation leads to the formation of a mixture of CuO and Cu2O. The CuO species is relatively unstable and can be reduced to Cu2O by annealing at 700 K (2 CuO→Cu2O+1/2O2) or by direct reaction with metallic Cu at 300 K (CuO+Cu→Cu2O).

New catalyst, and processes for dehydrogenating dehydrogenatable hydrocarbons

Abstract: A new catalyst, especially for the dehydrogenation of dehydrogenatable C2-30 hydrocarbons. The catalyst comprises a carrier consisting essentially of a mixed oxide of magnesium and alumina Mg(Al)O, and also comprises a Group VIII noble metal, a Group IVA metal and optionally a Group IA alkali metal. The catalyst may be subjected to a pretreatment comprising a reduction, a subsequent oxidation and finally a second reduction. The catalyst is particularly suitable for the dehydrogenation of C2-5 paraffins to olefins, with and without simultaneous oxidation of hydrogen.

Effects of rhodium addition on methane oxidation behavior of alumina-supported noble metal catalysts

Abstract: Laboratory methane oxidation experiments were conducted using a series of catalyst samples prepared by impregnating Rh-free noble metal catalysts (i.e., Pt/Pd, Pt or Pd) with various amounts of rhodium (0.0035, 0.005, and 0.014 wt.-% Rh). The addition of these small amounts of rhodium did not significantly change the temperature required for the onset of the methane oxidation. However, variable-composition experiments conducted at a temperature characteristic of warmed-up catalytic converters (ca. 550°C) reveal that the rhodium addition tends to shift the optimum feedstream stoichiometry (at which a maximum methane conversion occurs) toward more reducing conditions. These Rh-induced effects on methane conversion behavior appear to be independent of how the rhodium is incorporated in the catalyst.

Catalyst for purification of exhaust gases

Abstract: A catalyst for purification of exhaust gases, comprising a monolithic carrier and a catalyst layer formed thereon for reduction of the carbon monoxide, hydrocarbons and nitrogen oxides emitted from internal combustion engines, wherein (1) the catalyst layer contains catalyst particles each comprising a heat-resistant inorganic oxide and at least one noble metal selected from Pt, Pd and Rh, loaded thereon, (2) the catalyst layer contains, as a whole, three noble metals of Pt, Pd and Rh, (3) the catalyst layer contains, at any position ranging from the outer surface to the midpoint of the thickness, catalyst particles comprising a heat-resistant inorganic oxide and 2-10% by weight, based on the inorganic oxide, of Pd loaded thereon, and (4) the catalyst layer has, at the outer surface, exposed catalyst particles comprising an heat-resistant inorganic oxide and at least Rh loaded thereon.

Noble metal catalysts highly-dispersed on Sm-doped ceria for the application to internal reforming solid oxide fuel cells operated at medium temperature

Abstract: Steam reforming of CH4 on microcrystalline metal catalysts dispersed on Sm-doped ceria (SDC) was investigated with the intention of the application to an anode for internal reforming-type solid oxide fuel cells to be operated at medium temperature. Ru- or Ir-dispersed SDC exhibited high catalytic activities and low activation energies; these are potential candidates for that application. The high dispersion of microcrystalline noble metal catalysts results in such a high catalytic activity even with a significantly small amount of noble metal.

Method for removal of nitrogen oxides from exhaust gas

Abstract: The removal of nitrogen oxides from an exhaust gas is accomplished by a method which comprises causing the exhaust gas in an oxidizing atmosphere to contact a catalyst comprising a refractory inorganic oxide and catalytically active components, the components comprising 0.1 to 30 g per liter of the catalyst of at least one noble metal selected from the group consisting of Pt, Pd, Rh, and Ru or a compound of the noble metal and 1 to 80 g per liter of the catalyst of at least one metal selected from the group consisting of Li, K, Na, Rb, Ce, Be, Mg, Ca, St, and Ba or a compound of the metal, thereby inducing the catalyst to adsorb thereon the nitrogen oxides in the exhaust gas and, subsequently introducing a reducing substance intermittently into the exhaust gas thereby purifying the exhaust gas by reducing the nitrogen oxides adsorbed on the catalyst.

Hydrogen consuming anodes for energy saving in sodium sulphate electrolysis

Abstract: Gas diffusion electrodes, made of PTFE-bonded carbon with precious metal catalysts, were investigated as hydrogen consuming anodes in sodium sulphate electrolysis. The catalysts used were platinum and palladium and mixtures of both metals, prepared by two different methods. Various metal meshes were used as current collector. The electrodes performed well in pure sulphuric acid (5–15 wt-%) and in mixtures with sodium sulphate (10 wt-%) at temperatures of 30 to 70°C and current densities up to 5 kA/m2. In long-term experiments, at a current density of 2.6 kA/m2, the electrodes were stable over three months. The electrodes were characterised by stationary current density/potential curves and by galvanostatic current interruption measurements.

Interaction of Sulfur with Bimetallic Surfaces: Coadsorption of Sulfur and Noble Metals on Ru(001)

Abstract: The coadsorption of S with Cu or Ag on Ru(001) has been investigated using TDS, XPS, XAES, and CO chemisorption. At 300 K, copper and silver atoms in contact with Ru(001) react with S[sub 2] to form noble-metal sulfides. The Cu-S and Ag-S bonds in these surface compounds break at high temperatures (> 800 K) producing sulfur and noble-metal adatoms that compete for the ruthenium electrons. This competition leads to a weakening of 5-6 kcal/mol in the strength of the Ru-Cu and Ru-Ag bonds. A sulfur adatom produces long-range perturbations on the surface, diminishing the ability for bimetallic bonding of several (5-10) adjacent ruthenium atoms. At [theta][sub s] = 0.2 ML (ML = monolayer), all the ruthenium sites show a strong weakening in their bonding interactions with copper or silver adatoms. Photoemission experiments examining the interaction of S[sub 2] with copper and silver multilayers at 300 K show the formation of thick films of Cu[sub 2]S and Ag[sub 2]S at a fast rate. The decomposition pathways for these films are similar: evolution of S[sub 2] into gas phase, with the noble metal remaining solid. For Ag[sub 2]S films the decomposition process starts around 800 K, whereas Cu[sub 2]S films aremore » stable up to 950 K. 55 refs., 13 figs.« less

Comparison of shear bond strengths of two resin luting systems for a base and a high noble metal alloy bonded to enamel

Abstract: Researchers are investigating the use of noble metals for the fabrication of resin-bonded prostheses because of concerns about health hazards of nickel and beryllium in base metal alloys. Tin-plating has been advocated to improve the bond of resin luting agents to noble metal alloys. Some manufacturers have suggested that tin-plating is unnecessary to bond noble metal alloys to etched enamel with their products. In this study, Rexillium base metal and Olympia noble metal alloy specimens were bonded to extracted human teeth with the use of two resin luting agents (F21 and Panavia OP). One third of the noble metal specimens were tin-plated, one third were oxidized, and one third were oxidized and sandblasted. Each of the bonded specimens were thermocycled and subjected to a shear force until bond failure. The base metal specimens bonded with Panavia OP luting agent exhibited the greatest mean shear bond strengths. The tin-plating surface treatment significantly increased the mean shear bond strengths of Olympia noble metal specimens.

The oxidation of carbon monoxide by oxygen over platinum, palladium and rhodium catalysts from 10−10 to 1 bar

Abstract: The noble metal catalysed oxidation of CO by O2 has been studied on polycrystalline foils, ribbons and wires of Pt, Pd and Rh as well as on a variety of supported Pt catalysts. At temperatures from 180 to 600 °C, the partial pressure ratio was changed over the range 0.01 ⩽ pCO/pO2 ⩽ 50 at partial pressures varying over the range 10−6 ⩽ pi (mbar) ⩽ 40. In the total pressure region below 1 mbar, the results agree very well with model experiments conducted under ultra-high vacuum. The rate values measured at total pressures exceeding 1 mbar correspond to the highest activities ever observed on noble metal catalysts. Even at low temperatures and high gas velocities up to 14 m s−1, such values were mass transfer limited since the reaction was not inhibited by CO. Neither the structure nor the support influence the reaction in the case of supported Pt catalysts. The well-defined geometry of the experimental set up allowed an estimation of the appropriate mass-transfer coefficients and the calculation of the intrinsic reaction rate. The results clearly indicate that in the region where the reaction is first order with respect to the limiting component the intrinsic first-order rate constant has the same value as under high vacuum conditions within the precision of the approach. Thus the apparent gap between the rates of CO oxidation observed in model experiments and under ambient pressure must be attributed to the influence of mass-transfer limitations.

Metal oxide films on metal

Abstract: A structure including a thin film of a conductive alkaline earth metal oxide selected from the group consisting of strontium ruthenium trioxide, calcium ruthenium trioxide, barium ruthenium trioxide, lanthanum-strontium cobalt oxide or mixed alkaline earth ruthenium trioxides thereof upon a thin film of a noble metal such as platinum is provided.

Catalyst-adsorbent for purifying exhaust gas and exhaust gas purifying method

Abstract: PURPOSE:To obtain a catalyst for effectively purifying a harmful material in an exhaust gas, particularly hydrocarbons at the time of cold starting by consisting it essentially of a particle obtained by carrying a noble metal on a heat resistant inorganic oxide as a catalytic material, specifying Pb content, and using a particle consisting essentially of zeolite as an adsorbent. CONSTITUTION:A catalyst-adsorbent covered body composed of the catalytic material for decreasing carbon monoxide, hydrocarbons or the like and the adsorbent for decreasing hydrocarbons at the time of cold starting is carried on a monolith carrier. The catalytic material consists essentially of a catalytic particle formed by carrying one noble metal among Pt, Pd and Pd on the heat resistant inorganic oxide and, in this case, Pd of 2-30wt.% per the heat resistant inorganic oxide is contained. The adsorbent is composed of an adsorbing particle consisting essentially of zeolite.