Showing papers on "Bimetallic strip 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

Bimetallic reactivity. Investigation of metal-metal interaction in complexes of a chiral macrocyclic binucleating ligand bearing 6- and 4-coordinate sites

Abstract: The cooperative physical properties of a chiral macrocyclic binucleating ligand, S,S-cypim, containing 6-coordinate (closed-site) and four coordinate (open-site) compartments bridged by phenolic oxygen atoms have been examined. The chiral (1S,2S)-trans- 1,2-bis(aminomethyl)cyclopentane moiety of the S,S-cypim ligand forces the monometallic and symmetrical bimetallic complexes to adopt one diastereomer. Solution magnetic moments of the bimetallic complexes containing two paramagnetic metals indicate spin-spin coupling at 20 o C. All of the metals in these complexes, except for Co(III), are spin-free

Structural analysis of polymer-protected platinum/rhodium bimetallic clusters using extended x-ray absorption fine structure spectroscopy. Importance of microclusters for the formation of bimetallic clusters

Abstract: The colloidal dispersions of polymer-protected platinum/rhodium bimetallic cluster particles are easily prepared by refluxing solutions of hexachloroplatinic(IV) acid and rhodium(III) chloride in ethanol/water (1/1 v/v) in the presence of poly(N-vinyl-2-pyrrolidone). These colloidal dispersions of the Pt/Rh bimetallic cluster particles are very stable and have a size distribution from 2 to 7 nm in diameter. The electronic spectra and the transmission electron micrographs suggest that the colloidal dispersions are not a mixture of monometallic Rh and monometallic Pt particles but are mostly composed of Pt/Rh alloy particles

1,3-Butadiene selective hydrogenation over Pd/alumina and CuPd/alumina catalysts

Abstract: The selective hydrogenation of 1, 3-butadiene was studied in the presence of a 10:1 excess of 1-butene over supported bimetallic catalysts containing palladium in a vapour phase atmospheric plug flow reactor in the temperature range 288–313 K. Addition of copper to alumina-supported Pd increases its selectivity for converting butadiene to n-butenes without saturating or isomerizing the n-butenes. For example, with atomic ratio Cu/Pd = 2, the bimetallic catalyst selectively converts > 99% of the diene to n-butenes while isomerizing or saturating less than 1% of the starting 1-butene. Under similar conditions, Pd alone maintains high n-butene selectivity to only about 50% conversion of the diene. Over both catalysts the kinetics of 1, 3-butadiene hydrogenation are first order in hydrogen and zero order in butadiene. Hydrogen sorption experiments showed that Cu addition decreases both the surface adsorption and the bulk absorption, the former suggesting surface decoration of Pd by Cu and the latter indicating significant bulk Cu-Pd interaction in the supported bimetallic samples.

Surface characterization of palladium-copper bimetallic catalysts by ftir spectroscopy and test reactions

Abstract: Different bi-metallic palladium-copper catalysts have been prepared according to different sequences of impregnation of a commercial alumina. CO adsorption followed by FTIR spectroscopy was performed in order to identify the nature of the superficial sites. Two test reactions were also used to characterize the nature of the active surface site: gas phase toluene hydrogenation was selected in order to show the hydrogenating activity of metallic palladium, whereas the reaction of decomposition of ethanol, which exhibits 100% selectivity in the formation of ethanal on pure copper catalysts, was also studied on this series of catalysts. The results obtained by both methods are complementary. By comparison with the behaviour of pure palladium or copper based catalysts, they allow to propose hypotheses on the surface composition: separated phases, alloys or a phase covered by the other one.

Improved alkene selectivity in carbon monoxide hydrogenation over silica supported cobalt-molybdenum catalyst

Abstract: The Fischer-Tropsch synthesis performance of a Co-Mo bimetallic catalyst containing 6Co:lMo:4K:100SiO 2 has been studied and compared with a similar monometallic cobalt catalyst. The bimetallic system showed nearly 100% improvement in alkene-alkane ratio at the experimental conditions of 101 kPa and 280°C (553 K) and CO-H 2 ratio of 1:19 to 19:1. Ethylene-to-methane ratio (EMR) over the Co-Mo catalyst was about 70-100% better than the cobalt catalyst over the wide composition range studied. The kinetics over the Co-Mo catalyst also followed conventional Anderson-Schulz-Flory (ASF) polymerisation kinetics suggesting that there is no fundamental change in the reaction mechanism. The increase in chain growth probability and alkene content was attributed to substantial methane suppression caused by the introduction of molybdenum to the catalyst. Activation energy values for the light hydrocarbons over the bimetallic catalyst were in the range 85–120kJ/mol and about 10-15% lower than the corresponding estimates over the monometallic system.

Preparation of platinum-gold bimetallic catalysts by redox reactions

Abstract: Bimetallic Pt-Au/SiO2 catalysts were prepared by reduction of AuC1−4 using hydrogen preadsorbed on a parent monometallic Pt/SiO2 catalyst. In fact during that preparation a direct redox reaction can occur between the reduced platinum and AuCl−4. At low gold coverage the additive is deposited statistically on the whole surface of platinum particles (the reducer is H preadsorbed on Pt). At high gold coverage the additive is preferentially deposited on the high index planes of platinum particles (by direct redox reaction). During the formation of Pt-Au bimetallic entities sintering of platinum can occur as a result of simultaneous oxidation and reduction of platinum.

Dispersion, support, and bimetallic effects in Fischer-Tropsch synthesis on cobalt catalysts

Abstract: Fischer-Tropsch (FT) synthesis site-time yields and intrinsic chain growth kinetics depend only weakly on Co dispersion and on the oxide support (SiO 2 , Al 2 O 3 , TiO 2 ). Dispersion and support effects on C 5 + selectivity arise from changes in the extent of a-olefin readsorption as changes in site density and support structure modify the rate of intrapellet olefin removal. Ru (Ru/Co 5 + selectivity on C0/TiO 2 and allows its regeneration with H2 at synthesis temperatures. Reaction kinetics are not affected by Ru, suggesting that its presence leads to higher Co site densities during catalysis, apparently by inhibiting deactivation processes. Indeed, hydrogenolysis, carbon deposition, and Co oxide reduction rates differ significantly on Co and Co-Ru catalysts. This bimetallic synergy requires intimate contact between Co and Ru components, a state induced by calcination of Co-Ru precursors at high temperatures (>573 K) and confirmed experimentally by several characterization techniques.

Dual bias weld for continuous coiled tubing

Abstract: A dual weld for joining strips to be formed into coiled tubing. Tubing is formed from a first strip (15a) and a second strip (15b), the first and second strips of the same width. A planar end surface (Pa) is formed on an end of the frist strip. Similarly, a planar end surface (Pb) is formed on an end of the second strip. A composite strip is formed by welding the planar end surface of the first strip to the planar end surface of the second strip to form a dual bias weld. Excess-weldment is then removed from top, bottom and edge surfaces of the composite strip such that the width of th weld is identical to the width of the first and second strips. Coiled metal tubing is then formed from the composite strip.

Colloidal copper in aqueous solutions: radiation-chemical reduction, mechanism of formation, and properties

Abstract: Colloidal copper has been obtained by γ-irradiation of aqueous solutions of copper (II) perchlorate in the presence of alcohol and polyethyleneimine (PEI). The sols are spherical particles about 4 nm in diameter, which are quickly oxidized by oxygen or other oxidants. When CuII is not entirely incorporated into the complex with PEI, disproportionation of CuI aqua complexes formed affords the metal, along with Cu2O. Reduction of the PEI complex of CuI by hydrated electrons gives only colloidal copper. The copper ions can be reduced on the surface of silver sols. Optical parameters of the resulting bimetallic particles have been studied. The presence of copper ions leads to broadening of the absorption band associated with the silver sols and shifts it to the UV region, which is due to the transfer of electrons from copper to silver. Three copper monolayers are enough to cause plasmon absorption of colloidal copper.

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

Production and Characterization of Highly Dispersed Catalytic Active Platinum and Palladium Powders by Excimer Laser Photolysis

Abstract: Highly dispersed Pt, Pd, and bimetallic Pt/Pd powders were produced by excimer laser photolysis of their bis(1,1,1,5,5,5-hexafluoro)acetylacetonates in the gas phase under various reaction conditions. Powders were analyzed by XPS, HRTEM, XRD, and CO adsorption. XPS spectra were recorded in order to determine elementary composition of the powders and chemical states of the metals. The produced powders are contaminated with carbon and exhibit unusual electronic structures. The amount of carbon depends on the reaction conditions during powder production. From TEM and XRD analysis particle sizes and size distributions of metal clusters were obtained. The mean size ranged from 1.8 to 2.9 nm. HRTEM of bimetallic powders revealed the existence of bimetallic Pt/Pd clusters supported on carbon particles

Effect of the preparation procedure on the properties of three-way automotive platinum—rhodium/ alumina—ceria catalysts

Abstract: The properties of three-way automotive PtRh/Al 2 O 3 CeO 2 catalysts prepared either by coimpregnation of the two noble metals (CI catalysts) or by a newly devised technique of successive impregnations with an intermediate reducing treatment (SI catalysts) were investigated for the oxidation of a propane—propene mixture under lean conditions and for the CO + NO reaction. After high-temperature aging, bimetallic CI catalysts are far less active than SI catalysts for propane oxidation. On the other hand, they show comparable activities for propene oxidation and reaction CO + NO. The characterization of bimetallic catalysts by TPR and FT-IR experiments suggests that the coimpregnation leads to an intimate interaction between platinum and rhodium while rhodium added by successive impregnations with a reduction step after platinum impregnation would be selectively deposited onto cerium oxide surface in the vicinity of platinum particles, avoiding the formation of Pt/Rh alloy.

Adsorption kinetics on chemically modified or bimetallic surfaces

Abstract: Surface adatom modifiers that act as promoters or poisons on transition metal catalysts can have a large influence on adsorption kinetics along with their influence on adsorption energetics. Accounting for this effect requires recognition of the role of a new kind of intrinsic precursor — the modifier precursor state. A mathematical description of the adsorption kinetics of molecules on chemically modified or bimetallic surfaces incorporating this state has been derived based on Kisliuk’s statistical model [P. Kisliuk, J. Phys. Chem. Solids 3, 95 (1957)]. The resulting equation can be used to explain satisfactorily data on CO adsorption kinetics on chemically modified (Cl‐, P‐, S‐, H‐, O‐, and K‐precovered) Pt(111) surfaces. This concept should have broad implications for many systems in heterogeneous catalysis, such as bimetallic and alloy surfaces and coadsorbed layers, and for the multicomponent surfaces that are involved in materials growth and processing.