Showing papers on "Noble metal published in 1996"

Selective catalytic reduction of nitric oxide by hydrocarbons

Abstract: There are several problems related to the application of currently available NO x control technologies (i.e. three-way catalysts and the selective catalytic reduction of NO by NH 3 ) to lean burn diesel engines, and thus a very significant market potential exists for an improved technology in this area. As a result, the selective catalytic reduction of NO by hydrocarbons derived from on board fuel has received a lot of attention in the past five years. Different forms of base and noble metal exchanged zeolites, as well as supported noble metals appear to be the most active catalysts for this family of reactions. The available literature in this area is summarized in this review, with emphasis placed on the performance of different zeolite and supported noble metal catalysts, the effect of the various exhaust gas components and the mechanistic implications.

Silver nanocrystals in silica by sol-gel processing

Abstract: Silver nanocrystal doped silica films were prepared by the sol-gel process. The sol was prepared from 1:0.12:12:0.2:6:7 molar ratios of Si(OC2H5)4:AgNO3:H2O:HNO3:C3nH7OH:C4iH9OH. The glassy, highly transparent film with high dopant concentration (silver/silicon atomic ratio = 0.12) was successfully prepared by the dip-coating method. After drying in air at 60°C for 30 min, samples were heat-treated, in air, at 300, 350, 400, 450, 500 and 550°C using 30–100 min soaking periods for each step in a cumulative heating procedure. Measurements on the films were made by ultraviolet-visible and infrared spectroscopy, X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry and transmission electron microscopy. Mechanisms of silver colloid formation in the densified silica matrix with respect to the thermal treatment are discussed. To understand the formation of silver nanocrystals from the silver silicate network, the corresponding doped bulk gel samples were analyzed by X-ray diffraction and differential scanning calorimetry.

Photocatalytic reduction of dinitrogen to ammonia over noble-metal-loaded TiO2

Abstract: The photocatalytic reduction of dinitrogen to ammonia is influenced by the nature and amount of metal loading on TiO2. The optimum metal content varies depending on the nature of the metal. A correlation between the ammonia yield and the intermediary MH bond strength is established (low bond strength gives rise to low ammonia yield).

Identification of physical and chemical interaction mechanisms for the metals gold, silver, copper, palladium, chromium, and potassium with polyimide surfaces

Abstract: In this article we briefly review the literature for the evaporated metals gold, silver, copper, palladium, chromium, and potassium on polyimide surfaces and compare these previous results to newer experiments using Fourier transform infrared reflection absorption spectroscopy (FT-IRAS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The polyimide films were prepared by vapor phase deposition. Metal coverages range from submonolayer to several monolayers, but special emphasis in this work is put on the interaction of metals with a polyimide surface at very low metal coverages. Before our new results are presented, we discuss the various chemical and nonchemical effects, which can contribute to the change in IR absorption of polymers. For all of the metals except potassium only attenuation of polymer IR bands is observed. For the metal deposits of Au, Cu, Ag, and Pd the attenuation of the IR bands can be explained by a purely physical interaction mechanism, i.e., dynamical dipole scree...

Low-temperature generation of basic carbon surfaces by hydrogen spillover

Abstract: It is demonstrated that stable basic carbons, which will not adsorb oxygen in ambient laboratory conditions, can be created via a relatively low-temperature process. These highly basic carbons are created by treating mixtures of carbons and platinum (in the form of particles supported on a high surface area material) in hydrogen at 500 °C, or even at lower temperatures in some cases. In the absence of platinum, creation of highly basic and stable surfaces with the same starting material requires hydrogen treatments at far higher temperatures (ca. 900 °C). Evidence is presented to support the hypothesis that the role played by platinum (or any noble metal) is to produce atomic hydrogen, which spills over onto the carbon surface. This atomic hydrogen hydrogasifies the most reactive, unsaturated carbon atoms at far lower temperatures than molecular hydrogen, thus leading to surface stabilization at relatively low temperatures.

Supported catalyst and process for catalytic oxidation of volatile organic compounds

Abstract: A catalyst for effective oxidation of volatile organic compounds (VOCs) includes 0.010-2 wt. % of a noble metal such as platinum in combination with 0.5-15 wt. % of a transition metal oxide such as chromium oxide (Cr2 O3), with at least the noble metal being deposited as a thin outer layer or shell not exceeding 0.10 mm thickness on a porous inert support such as alumina or silica having surface area of 10-400 m2 /g. The catalyst is made by adding the transition metal oxide such as chromium oxide (Cr2 O3) to the support material particles, and then subsequently mixing a solution of ammonium platinum nitrate with a suitable carrier liquid so as to form a "cluster" structure on the support material and which limits penetration of the active noble metal into the porous support, then drying, reducing, and calcining the metals-loaded support material. This catalyst composition and structure is highly effective for the oxidative destruction of VOCs in vapor form at concentrations of 1 ppm--5 vol. % and at reaction temperatures of 50°-500° C., 0-600 psig pressure, and space velocity of 1000-200,000 hr-1 to produce essentially only carbon dioxide and water products.

Noble metal promoted Ni0.03Mg0.97O solid solution catalysts for the reforming of CH4 with CO2

Abstract: Reforming of CH4 with CO2 to produce syngas was studied over Ni0.03Mg0.97O solid solution catalyst and its bimetallic derivative catalysts which contained small amounts of Pt, Pd or Rh (the atomic ratio M/(Ni + Mg) was about 2 × 10−4, M = Pt, Pd or Rh). It was found that although the Ni0.03Mg{0.97}O catalyst showed an excellent stability and activity at the reaction temperature of 1123 K, it lost its activity completely within 51 h when the reaction temperature was as low as 773 K. However, both the activity and the stability at 773 K were improved significantly by adding Rh, Pt, or Pd. This synergistic effect is rationally explained by the promoted reducibility of Ni. On all these catalysts, the amount of deposited carbon during the reaction was very low, suggesting that carbon deposition was not the main cause of the deactivation. Also, the catalytic activity of bimetallic catalysts increased gradually with the noble metal loading, but after passing through a maximum, it decreased with superfluous addition. The maximum was found to be located at around the atomic ratio of M/(Ni + Mg) ≈ 0.02% (M = Pt, Pd and Rh). This phenomenon could most probably be attributed to the different composition of Pt-Ni alloy particles formed after the reduction.

A new dinuclear rhodium(III) ‘sandwich’ polyoxometalate, [(WZnRHIII2)(ZnW9O34)2]10−. Synthesis, characterization and catalytic activity

Abstract: The rhodium containing polyoxometalate, [(WZnRhIII2)(ZnW9O34)2]10− was prepared by reaction of [(WZn3)(ZnW9O34)2]12− with RhCl3. The X-ray diffraction showed this compound to be isostructural to other compounds of this series. This was confirmed by the IR spectra. The elementary analysis and cyclic voltammetry measurements indicated that the polyoxometalate was of high purity. Epoxidation of alkenes with 30% aqueous H2O2 in 1,2-dichloroethane/water biphasic systems using [(WZnRhIII2)(ZnW9O34)2]10− as catalyst showed high overall activity as compared to other noble metal substituted polyoxometalates of this series. The reactions were highly selective to epoxidation of cyclohexene and similar to previously reported [(WZnMnII2)(ZnW9O34)2]12−, except that hydrogen peroxide yields were measurably higher in the rhodium case. The [(WZnRhIII2)(ZnW9O34)2]10− catalyst appears to be stable under turnovers conditions. Using IR spectroscopy as a probe to compare active polyoxometalates (Rh and Mn) versus an inactive one (Zn), showed that in the former case peroxo-tungstate intermediates could be identified whereas for the inactive compound no such intermediate was observed. A possible mechanism taking into account reactivity, steric constraints and IR spectra assuming structural integrity under catalytic turnover conditions was put forth.

Catalyst, method of its production and its use for the production of vinyl acetate monomer

Abstract: A catalyst and method of its production for use in making vinyl acetate monomer. The carrier is impregnated with a basic solution and a solution containing gold salts and palladium salts and finally impregnated with alkali acetate. The activity and selectivity of the catalyst, its mechanical strength, the noble-metal adhesion and the dispersion of noble metal on the carrier can be improved if the carrier is impregnated in a pretreatment with salts containing as cation elements of groups IA, IIA, IIIA and IVB of the periodic table and as anions elements of group VIIA or complex anions such as nitrate, sulfate or anions of organic acids such as acetate and lactate and is subsequently dried and calcined at temperatures of at least 160° C.

Low-Temperature Complete Combustion of Methane over Mn-, Co-, and Fe-Stabilized ZrO2

Abstract: Activity comparable to that of noble metal catalysts is shown by the Mn-, Co-, or Fe-stabilized ZrO2 catalysts for the low-temperature combustion of methane. The incorporation of the transition metal into the ZrO2 bulk structure not only stabilizes the cubic (fluorite) modification, but also increases the reactivity of the lattice oxygen atoms drastically.

Deposition and growth of noble metal clusters on graphite

Abstract: The growth of silver and gold clusters following atomic vapour deposition on highly oriented pyrolytic graphite has been studied using scanning electron microscopy and scanning tunnelling microscopy (STM) Three-dimensional clusters were grown on the terraces and quasi-one-dimensional chains of clusters along the surface steps An STM study was made on the effect of the step height on cluster nucleation Charge-density modulations on the substrate surface around the silver clusters were analysed A preliminary study of the deposition of mass-selected silver clusters from a beam onto the graphite surface has been made The effect of the impact energy of silver clusters on the deposition process is explored

Facile rearrangements of alkynylamino heterocycles with noble metal cations

Abstract: A number of 2-(alkynylamino)-substituted heterocycles have been synthesized. These heterocycles rearrange in the presence of silver(I) and gold(I) salts to give novel 2H-pyrimido[2,1-b]benzoxazoles, 2H-pyrimido[2,1-b]benzothiazoles, and a 2H-pyrimido[2,1-b]benzoselenazole. Two of the the 2H-pyrimido[2,1-b]benzoxazoles were isolated in good yield. The kinetics of the silver tetrafluoroborate-catalyzed rearrangements of selected (alkynylamino)benzoxazoles and benzothiazoles have been examined by 1H NMR in CD3CN. Factors affecting the electron densities of the triple bond and of the nitrogen atom in the heterocycle are important in influencing the rate of rearrangement.

Catalytic wet air oxidation of polyethylene glycol

Abstract: The catalytic oxidation of aqueous solutions of polyethylene glycol of molecular weight 10000, a synthetic polymer used in a wide range of applications, has been investigated using various metal oxide and noble metal heterogeneous catalysts. Catalysts were in slurry or in pellets, at temperatures from 383 K to 463 K and an oxygen partial pressure of 3 MPa. Additional uncatalysed experiments have been performed, and the results are compared to those of the catalysed runs. Reaction intermediates have been determined using HPLC and gel permeation chromatography as the main analytical techniques, and reaction mechanisms have been proposed. Noble metal catalysts were found to be more effective than metal oxide catalysts for oxidising polyethylene glycol, while with both noble metal and metal oxide catalysts the rate of total oxidation was significantly higher than that of the uncatalysed reaction. However, the use of heterogeneous catalysts was found to be responsible for prolonged induction periods, a phenomenon which did not occur significantly during the uncatalysed runs. A palladium supported on alumina catalyst was further studied with respect to its stability and deactivation.

Lead frame, method for partial noble plating of said lead frame and semiconductor device having said lead frame

Abstract: A lead frame for a semiconductor device, made of a copper alloy, capable of preventing the creation of delamination between encapsuling resin and attributable to a lead frame without sacrificing the wire bondability and, a process for producing the lead frame and a semiconductor device using the lead frame. According to the present invention, (1) there is provided a lead frame for a plastic molded type semiconductor device, made of a copper alloy material partially plated with at least one noble metal, for wire bonding or die bonding purposes, selected from silver, gold, and palladium, wherein the whole area or a predetermined area of the surface of the copper at least on its side to be contacted with a encapsuling resin has a thin noble metal plating of at least one member selected from silver, gold, platinum, and palladium. (2) A copper strike plating is provided as a primer plating for the partial noble plating, a copper plating is provided on the thin noble metal plating, and the partial noble metal plating is provided on the copper plating in its predetermined area. (3) A die pad for mounting a semiconductor chip is provided, a partial silver plating is provided, and a zinc flash plating and a copper strike plating are provided in that order at least one on the surface of copper in the back surface of the die pad remote from the surface on which the semiconductor chip is mounted.

CO2 reforming and partial oxidation of methane

Abstract: CO2 reforming and partial oxidation of CH4 were investigated on different supported noble metal and Ni catalysts. A detailed thermodynamic analysis was performed for both reactions. The observed reaction behaviour can be predicted by thermodynamics. Product selectivity is catalyst independent, the role of the catalyst is to bring the reactants to approach equilibrium. The partial oxidation is a two-stage process, total oxidation of CH4 is followed by CO2 and H2O reforming of the remaining CH4. A staged addition of O2 to the reactor is tested and recommended. TPSR show that the catalyst surface for CO2 reforming was highly covered with carbonaceous species of four different types; two were identified as reactive intermediates.

Effect of support oxide and noble metal precursor on the activity of automotive diesel catalysts

Abstract: This paper reports on the investigation of the effect of noble metal precursor and support oxide on their catalytic activity for the conversion of diesel exhaust gas components. The noble metal precursors used in this investigation were hexachloroplatinic acid, platinum nitrate, and tetraammine platinum(II) hydroxide. As support metal oxides zirconia, a base metal doped alumina, alumina, and titania were used. Catalysts were prepared from all combinations of precursors and supports and were tested in an integral model gas test reactor both in the fresh and in the aged state. The catalysts were also characterized by various techniques including BET surface area, CO chemisorption, XRD, and TEM. The results indicate that the catalyst prepared from the tetraammine platinum(II) hydroxide precursor on the base metal doped alumina support shows the highest activity for the conversion of the gaseous exhaust components.

Alumina, ceria, zirconia, nickel oxide, alkaline earth oxide, and noble metal catalyst, and method for preparing

Abstract: A catalyst for cleaning exhaust gas comprises a carrier and a coated layer applied onto the surface of the carrier which comprises an aluminum oxide, a cerium oxide, a zirconium oxide, a nickel oxide, an alkaline earth metal oxide and a noble metal catalytic component. The catalyst can be prepared according to a method which comprises the steps of coating the surface of a carrier with a slurry which comprises active alumina, a cerium compound, a zirconium compound and a nickel compound, drying the coated carrier and then calcining it to complete the carrier, then impregnating the carrier with a solution comprising a catalyst component of a noble metal, drying, then immersing it in a solution of an alkaline earth metal compound, drying the immersed carrier and then calcining the carrier. The catalyst for exhaust gas-cleanup is highly sensitive to HC and CO around the theoretical mixing ratio and within the rich-region and is excellent in durability.

Organic-metallic composite coating for copper surface protection

Abstract: Copper-containing surfaces of substrates such as laminated electronic circuit boards are protected by organometallic coatings comprising organic compounds selected from the group consisting of benzimidazoles, alkylimidazoles, benzotriazozles and alkyltriazoles, substituted or unsubstituted, and metal particles of solder-wettable metals or metal solders. The metal particles can be thermally formed in situ from metallic compounds such as noble metal acetates, acetylacetonates and carbonates.

Catalyst comprising a modified solid oxide

Abstract: There is provided a catalyst comprising a hydrogenation/dehydrogenation component, such as a noble metal, and an acidic solid component comprising a Group IVB metal oxide modified with an oxyanion of a Group VIB metal. An example of this catalyst is zirconia, modified with tungstate and platinum. There is also provided a method for preparing this catalyst. This catalyst may be used, for example, to isomerize C4 to C8 paraffins. The feed to this paraffin isomerization reaction may, optionally, include cyclic hydrocarbons, such as benzene or cyclohexane, which may undergo ring opening reactions during the course of the isomerization reaction.