Showing papers on "Noble metal published in 1990"

Platinum group metal alloy catalysts for hydrogenation of carboxylic acids and their anhydrides to alcohols and/or esters

Abstract: Catalyst composition comprising an alloy of at least one noble metal of group VIII of the Periodic Table and at least one metal capable of alloying with the group VIII noble metal, admixed with a component comprising at least one of the metals rhenium, tungsten or molybdenum, used for producing an alcohol and/or a carboxylic acid ester by reacting hydrogen with a carboxylic acid or anhydride thereof.

Catalyst for the production of alcohols by hydrogenation of carboxylic acids and process for the preparation of the catalyst

Abstract: An improved catalyst comprising a Group VIII noble metal, such as palladium, and rhenium is supported on a high surface area graphitized carbon. In an embodiment the Group VIII metal, e.g., palladium, has an average crystallite size in the range from 30 to 150 Angstroms. A process for making a catalyst is provided in which a support is impregnated with a solution of a Group VIII metal compound, the solvent is removed and the Group VIII metal impregnated support is impregnated with a solution of a rhenium compound using a solvent in which the Group VIII metal compound is insoluble, and thereafter the solvent is removed.

Catalytic destruction of organohalogen compounds

Abstract: This application relates to a catalyst and a process using this catalyst to convert or destroy organic compounds including organohalogen compounds. A preferred catalyst contains as catalytic components titania, vanadium oxide, tungsten oxide, tin oxide and at least one noble metal selected from the group consisting of platinum, palladium and rhodium, characterized in that the vanadium oxide, tungsten oxide and noble metals are uniformly dispersed on the titania. The process of this invention comprises contacting the gas stream, which contains organohalogen compounds and other organic compounds, at a temperature of about 200° to about 500° C. with the catalyst described above in the presence of an oxidizing agent and water. The oxidizing agent can be oxygen or air.

Catalyst for purification of exhaust gases

Abstract: A catalyst for the purification of exhaust gases contains a catalyst carrier with a first coat layer formed on a surface of the catalyst carrier and with a second coat layer formed on a surface of the first coat layer. The first coat layer contains an active alumina and a catalyst component comprised of a noble metal such as platinum and rhodium and at least one of zirconium oxide, lanthanum oxide and barium oxide is immobilized on particles of the active alumina, and the second coat layer contains an active alumina, cerium oxide and a catalyst component comprised of another noble metal such as palladium. The oxides of zirconium, lanthanum and/or barium can prevent the alumina particles from aggregating together due to heat, thereby improving heat resistance of the catalyst.

“Development of Advanced Noble Metal‐Alloy Electrocatalysts for Phosphoric Acid Fuel Cells (PAFC)”

Abstract: In the preparation of highly dispersed noble metal electrocatalysts, the technology is such that crystallites now can be routinely prepared with small dimensions so that 50% of the atom content resides at the particle surface. The crystallite diameters are of the order of 12 Angstrom (1.2 nanometers). Operation of these materials, when applied to phosphoric acid fuel cells as electrocatalysts is, of course, critical. What is important is the realization that due to the high surface energies of these crystallites, they have properties that are unlike the properties of the bulk metals. Although this manufacturing achievement is very great, more recently there has been increased emphasis on preparing alloys of metals with platinum in order to increase the kinetic rate of reaction for the oxygen reduction.—For oxygen reduction, binary alloys of platinum with refractory metals such as vanadium showed higher activity, but the vanadium was rapidly leached out. Alloys with chromium and subsequently with the addition of cobalt to form ternary alloys have now exhibited greater resistance to degradation. These alloys are hard and resistant to sintering, until the alloying element is leached out, then crystallite growth is obtained.—More recently, process modifications to produce ordered alloys have shown stability for over 9000 hours in the hot phosphoric acid fuel cell environment, as have alloys of platinum with cobalt and/or chromium containing gallium additions. It is one theory that there is no catalytic enhancement for oxygen reduction due to these alloying elements, but the increased reactivity is due solely to leaching out of the alloying elements from the alloy surface to produce a microroughness in the platinum crystallite.—In the case of hydrogen oxidation, especially in the presence of electrocatalyst poisons such as carbon monoxide and hydrogen sulphide, alloys of platinum with palladium show greater tolerance to poisoning and greater stability against crystallite growth. Other alloys are now under development to lower the catalyst cost and increase the electrocatalyst performance. This work is coupled with developments of advanced theoretical models that are amenable to computer solution for the operation of gas-diffusion electrodes to maximize both the catalyst utilization within the electrode structure, and within the cell stack.

Method of making a support containing an alumina-ceria washcoat for a noble metal catalyst

Abstract: A high surface area ceria-alumina washcoat is disclosed in which the ceria is prepared from cerium acetate.

Surface modification of biomaterials through noble metal ion implantation.

Abstract: Studies are described involving effects of noble-metal ion implantation on corrosion inhibition and charge-injection capabilities of surgical Ti-6Al-4V alloy. A major factor linked to excellent long-term biological performance is resistance to metal-ion release to tissues. The elements most resistant to corrosion in aqueous solutions are the noble metals. Disadvantages include expense and general inadequacy of mechanical properties. However, if small quantities can be used to surface-modify a surgical device in the last stage of manufacture, that device could possess an optimum combination of environmental integrity, biological response, mechanical properties, and charge-injection capability at miniumum expense. Results for ion-implanted Ir are presented. Iridium has been described as the most corrosion-resistant element known, and its activated oxide as having the highest charge-injection capability of any material known. Ti-6Al-4V samples, ion implanted with 2.5 and 5.0 atomic % peak-maximum concentrations of Ir, were subjected to corrosion treatments to enrich the surface with Ir. Corrosion potential and cyclic voltammetry measurements indicated enrichment in H2SO4, and continued enrichment in isotonic saline, with corrosion potentials approaching that of pure Ir, and charge densities in isotonic saline exceeding that of pure Ir for the 5.0% peak-max Ir implanted material. X-ray photoelectron spectroscopy confirmed the high levels of Ir surface enrichment.

Chromic acid free etching of polymers for electroless plating

Abstract: The process of electroless plating of polymers containing units derived from at least one member of the group consisting of acrylonitrile, butadiene and styrene, is carried out in an environment free of chromium ions, by the sequential steps of roughening and activating the surface of the polymer by contacting the same with an aqueous solution of a concentrated sulfur acid, of concentrated nitric acid or of concentrated phosphoric acid, in the presence of noble metal ion and an oxidant selected from the group consisting of nitric acid, hydrogen peroxide and persulfates. This is followed by an aqueous suspension of Pd 0 and then by the conventional chemical metallization.

Electrolytic capacitor with codeposited noble metal/base metal cathode element and method for making

Abstract: Codeposited noble metal/base metal cathode elements provide electrolytic capacitors with high volumetric efficiencies. The requisite codeposition is obtained by electrodeposition of the metals onto the interior surface of capacitor cases from solutions of the metal salts.

Hydrotreating process using novel multimetallic sulfide catalysts

Abstract: The present invention relates to a process for removing hetero-atoms from a hydrocarbonaceous feedstock using novel catalysts comprised of highly dispersed molybdenum sulfide promoted with a noble metal such that the noble metal is in an oxidation state greater than 0 and coordinated to S. The noble metal is selected from Pt, Pd, Rh, and Ir. It is preferred that the catalysts of be prepared from a precursor composition selected from platinum ethoxyethyl xanthate or platinum dithiocarbamate. Additionally, the catalyst may include a promotor sulfide such as nickel sulfide, cobalt sulfide or iron sulfide, etc. or mixtures thereof.

Contributions of surface analysis to corrosion science: Selective dissolution and oxidation phenomena in alloy corrosion

Abstract: The role for corrosion kinetics of corrosion-induced surface composition changes on alloys is discussed and illutrated with surface analytical (AES, XPS, SIMS) and electrochemical (polarization behaviour) results from the author's laboratory. In situ oxidation of FeCrMo alloys, anodic dissolution in the active state of binary noble metal alloys (AgPd) and anodic dissolution in the passive state are compared

Incipient Hydrous Oxide Species as Inhibitors of Reduction Processes at Noble Metal Electrode

Abstract: Evidence is presented to illustrate the important role of hydrous oxide in noble metal electrocatalysis. It was demonstrated, for instance, that in the case of gold in acid the onset/termination potential, under potential sweep conditions, for hydrazine oxidation and persulfate or iodate reduction occurred at the end of the hydrous oxide reduction peak (recorded for a thick film growth grown by potential multicycling); there was also a maximum in the faradaic ac response for gold in acid in the same region. Both gold and platinum were investigated in acid and base electrolytes. In some cases a range of potential, rather than a discrete value, was found to be involved, different species react with (or are inhibited by) different types (or coverages) of these submonolayer species. In some, possibly electrocatalytically nondemanding, reduction reactions the hydrous oxide seemed to have little effect.

7. distribution of gold, palladium, platinum, rhodium, ruthenium, and iridium in leg 115 hotspot basalts: implications for magmatic processes1

Abstract: A comparison of 50 basalts recovered at Sites 706, 707, 713, and 715 along the Reunion hotspot trace during Ocean Drilling Program Leg 115 in the Indian Ocean shows that seafloor alteration had little effect on noble metal concentrations (Au, Pd, Pt, Rh, Ru, and Ir), determined by inductively coupled plasma-mass spectrometry (ICP-MS), which generally tend to decrease with magma evolution. Their compatible-element behavior may be related to the precipitation of Ir-Os-based alloys, chromite, sulfides, and/or olivine and clinopyroxene in some combination. The simplest explanation indicates silicate control of concentrations during differentiation. Basalts from the different sites show varying degrees of alkalinity. Noble metal abundances tend to increase with decreasing basalt alkalinity (i.e., with increasing percentages of mantle melting), indicating that the metals behave as compatible elements during mantle melting. The retention of low-melting-point Au, Pd, and Rh in mantle sulfides, which mostly dissolve before significant proportions of Ir-Os-based alloys melt, explains increasing Pd/Ir ratios with decreasing alkalinity (increasing melting percentages) in oceanic basalts. High noble metal concentrations in Indian Ocean basalts (weighted averages of Au, Pd, Rh, Pt, Ru, and Ir in Leg 115 basalts are 3.2, 8.1, 0.31, 7.3, 0.22, and 0.11 ppb, respectively), compared with basalts from some other ocean basins, may reflect fundamental primary variations in upper-mantle noble metal abundances.

Reduction and cluster growth of palladium in zeolite Y containing transition metal ions. X-ray absorption studies

Abstract: The effect of a second transition metal on the reducibility and agglomeration behavior of palladium in zeolite Y is studied by EXAFS spectroscopy. Special attention is given to the potential bonding interactions between both metal constituents that could result in chemical anchoring of the noble metal to the support via the unreduced cocation. Zeolite Y was coexchanged with Fe{sup 2+} or Co{sup 3+} and Pd{sup 2+} and with each ion alone. Dehydration in oxygen atmosphere and reduction with hydrogen was performed at different temperatures up to 623 K. The structure of the samples during various stages of pretreatment and reduction was studied with EXAFS on both absorption edges. Palladium is partially reduced to Pd{sup 0} at room temperature and forms small metal clusters at higher temperatures. Iron is oxydized under oxygen atmosphere and is partially present in the form of iron oxide particles, which are redispersed under reducing conditions. A small enhancement of the reducibility of palladium is observed if iron is present in the zeolite, but neither a chemical anchoring nor an effect on the final agglomeration process of palladium is detected by the presence of iron cations. In contrast, coexchange with cobalt results in a substantially higher dispersionmore » of the Pd(0) phase after high-temperature reduction. Apparently, the change in cation distribution induced by the Co ions influences the reduction process of palladium. When palladium ions are diffused into the zeolite containing aqueous Fe(II) ions, a Pd(0) phase consisting of larger crystallites is formed at room temperature by a redox reaction with Fe(II).« less

Titania-supported iron–ruthenium and iron–iridium catalysts. An in situ iron-57 Mössbauer spectroscopic study of the effects of pretreatment in hydrogen

Abstract: The changes induced in some titania-supported iron–ruthenium and iron–iridium catalysts following pretreatment in hydrogen have been examined in situ by 57Fe Mossbauer spectroscopy. Fe3+, which is formed in the supported metallic phase by initial treatment in air, undergoes partial reduction when treated in hydrogen at low temperatures. Further treatment in hydrogen at moderate temperatures results in some of the Fe2+ being oxidised to Fe3+ which, on further exposure to hydrogen at elevated temperatures, is predominantly reduced to Fe0 in an iron-containing alloy. The extent of the initial reduction in hydrogen and subsequent oxidation processes, together with the nature of the reduced materials formed at elevated temperatures, is dependent on the nature of the noble metal, the ratio of iron to noble metal, the conditions under which the catalyst is initially dried in air and the surface area of the titania support. The extent of the anaerobic oxidation is optimised in materials with an iron : noble metal mole ratio of ca. 1 : 2.5 when supported on high-surface-area titania by a preparation involving slow initial drying of the catalyst in air at low temperatures and subsequent treatment in hydrogen at ca. 400 °C. The results are associated with the influence of the metallic composition, the surface area of the support and the thermal treatment on the initial dispersion of the metallic phase, the hydrogen adsorption capacities of the supported metals and the influence of these properties on metal–metal and metal–support interactions.

Method for regenerating a Group VIII noble metal deactivated catalyst

Abstract: A method for regenerating a Group VIII noble metal catalyst which has been contaminated with coke during a reforming process. The method comprises (a) burning off the coke from the catalyst, (b) redispersing the noble metal on the surface of the catalyst support by contacting the catalyst with halogen gas and carbon dioxide, and (c) chemically reducing the catalyst. The presence of carbon dioxide in the redispersing step improves the activity of the regenerated catalyst.

Plastic composition for molding noble metal

Abstract: PURPOSE: To eliminate stickness of powder to a mold and to prevent the development of crack in a sintered product by blending the specific quantities of cellulose series water soluble binder, interface active agent and oils and fats to noble metal powder. CONSTITUTION: Plastic composition for molding noble metal is constituted of composition composed of 50-90wt.% noble metal powder, 0.8-8% cellulose series water soluble binder, 0.03-3% interface active agent, 0.1-3% oils and fats and the balance of water with inevitable impurities. The noble metal powder is desirable to be ≤200μm average particle diameter. This composition is not stuck to hands even if this is molded with the hands, and the hardening velocity is fast. Even if the molding material is sintered without natural-drying, crazing and lowering of gloss are not developed. Therefore, an art object, ornament, etc., can be manufactured in a short time. COPYRIGHT: (C)1992,JPO&Japio

Selective Hydrogenation of 9-Aminoacridine over Supported Noble Metal Catalysts

Abstract: The selective hydrogenation of 9-aminoacridine(1) into 1,2,3,4-tetrahydro-derivative(2) was searched using noble metal catalysts(Pd, Rh, Pt, and Ru) at around 80 °C and 60 °C atm of H2. The Pd/Al2O3 catalyst was found most selective to produce 2 in a higher yield of 60% at a conversion of 97%. The hydrogenation pathway of 1 is discussed in comparison with that of acridine.