Showing papers on "Bimetallic strip published in 1993"
TL;DR: In this article, Ru atoms at the surface of Co crystallites increase the rate of removal of carbon and oxygen species during reaction and during regeneration of deactivated Co catalysts, leading to higher Co site density and enhanced readsorption of α-olefins.
398 citations
TL;DR: In this paper, a bimetallic cluster with a mole ratio of Pd : Pt = 4 : 1 was found to be the most active catalyst, twice as active as a typical colloidal palladium catalyst for diene hydrogenation.
Abstract: Refluxing mixed solutions of palladium(II) chloride and hexachloroplatinic(IV) acid in ethanol–water (1 : 1, v/v) in the presence of poly(N-vinyl-2-pyrrolidone) results in well dispersed and stable colloidal dispersions of polymer-protected palladium/platinum bimetallic clusters. The UV–VIS absorption spectra and transmission electron micrographs indicate that these bimetallic cluster particles are homogeneous in size, each particle containing both palladium and platinum atoms. Dispersions of these bimetallic clusters were used as catalysts for the selective hydrogenation of cycloocta-1,3-diene to cyclooctene at 30 °C under hydrogen gas at atmospheric pressure. The catalytic activity for the partial hydrogenation was found to depend on the metal composition of the particles. A bimetallic cluster with a mole ratio of Pd : Pt = 4 : 1 was the most active catalyst, twice as active as a typical colloidal palladium catalyst, for the diene hydrogenation. The dependence of the activity and the selectivity on the surface structure of the cluster particle strongly indicates that the cluster particle with the highest catalytic activity had a ‘Pd-surrounded Pt core’ structure.
280 citations
TL;DR: The racemic and meso diastereomers of an electron-rich binucleating tetraphosphine ligand have been used to prepare homobimetallic rhodium norbornadiene complexes, giving both a high rate of reaction and high regioselectivity for linear aldehydes.
Abstract: The racemic and meso diastereomers of an electron-rich binucleating tetraphosphine ligand have been used to prepare homobimetallic rhodium norbornadiene complexes. The racemic bimetallic Rh complex is an excellent hydroformylation catalyst for 1-alkenes, giving both a high rate of reaction and high regioselectivity for linear aldehydes, whereas the meso complex is considerably slower and less selective. A mechanism involving bimetallic cooperativity between the two rhodium centers in the form of an intramolecular hydride transfer is proposed. Mono- and bimetallic model complexes in which the possibility for bimetallic cooperativity has been reduced or eliminated are very poor catalysts.
272 citations
TL;DR: In this paper, a mixture of palladium acetate and copper acetate were refluxed in 2-ethoxyethanol in the presence of poly(vinylpyrrolidone) to give 40-angstrom alloy nanoclusters.
Abstract: Bimetallic clusters have been the subject of many studies of the surface chemistry and catalytic properties of metal crystallites on solid supports. Mixtures of palladium acetate and copper acetate were refluxed in 2-ethoxyethanol in the presence of poly(vinylpyrrolidone) to give 40-[angstrom] alloy nanoclusters. TEM and EDAX analysis showed that the particles were homogeneously bimetallic and crystalline, with a composition determined by the ratio of the metal acetates used. Carbon monoxide adsorbed on the colloidal particles binds reversibly to both metals. 9 refs., 3 figs.
139 citations
TL;DR: The gold/platinum bimetallic systems stabilized by polymer and micelle were obtained by alcohol-and photo-reduction of the corresponding metal ions in the presence of water-soluble polymers and non-ionic surfactant-micelles, respectively as mentioned in this paper.
129 citations
96 citations
TL;DR: In this paper, a formal rate equation is suggested (r = ƒ · θorg · �OH) which explains the optimum in promoter/platinum ratio, which is explained by their hydrogen and oxygen sorption characteristics and by the surface geometry of the bimetallic catalysts.
85 citations
TL;DR: In this article, a reversible deactivation phenomenon is observed when copper-nickel particles are reacted in ethylene at temperatures in excess of 700[degrees]C. This deactivation process involves not only the reactions occurring at the gas/catalyst interface but also modifications in the particle chemistry arising from dissolved carbon and hydrogen species, and also the influence of the deposited graphite in the form of a filament at the rear of the particle.
82 citations
TL;DR: A series of iron-platinum bimetallic and pure platinum catalysts supported on carbon were prepared and characterized by means of H 2 O 2 titration, X-ray diffraction, TEM, XPS and cyclic voltammetry as mentioned in this paper.
69 citations
TL;DR: In this paper, a polymer-protected Cu/Pd bimetallic colloid with different atomic ratio of Cu to Pd was successfully prepared by refluxing a glycol solution of hydroxide of copper and palladium in the presence of poly(N-vinyl-2-pyrrolidone).
Abstract: Polymer-protected Cu/Pd bimetallic colloids with different atomic ratio of Cu to Pd were successfully prepared by refluxing a glycol solution of hydroxide of copper and palladium in the presence of poly(N-vinyl-2-pyrrolidone). The TEM, XRD, AAS and UV-vis spectrum measurements indicate the formation of bimetallic alloy phase in the bimetallic colloids. High catalytic activity and selectivity for the hydration of acrylonitrile to acrylamide was achieved by using the Cu/Pd(Cu/Pd = 2) bimetallic colloid as a catalyst.
62 citations
TL;DR: In this paper, the authors used infrared spectroscopy to study carbon monoxide adsorption over an extended pressure range on both silica-supported gold and a gold/platinum bimetallic catalyst.
TL;DR: The effect of the support in constraining the formation and defining the structure of bimetallic particles has been considered in this article, where Alumina and NaY zeolite supported platinum and cobalt bimetal catalysts are illustrated to rationalize this effect.
TL;DR: In this article, Niobla Pd-Cu supported bimetallic catalysts have been studied in the 1,3-butadlene hydrogenation, and the results are ascribed to a structure sensitive reaction.
TL;DR: In this article, the performance of Pt-Sn-containing electrodes for methanol oxidation is discussed. But the Teflon-bonded electrodes are found to be poor electrocatalysts.
Abstract: Carbon-supported platinum oxide–tin oxide samples have been studied as electrocatalysts for methanol oxidation. The Teflon-bonded electrodes are found to be poor electrocatalysts. X-Ray photoelectron and Mossbauer spectroscopy, together with electron microscopy, have been used to determine the nature of the bimetallic crystallites. Differences in the activity of various Pt–Sn-containing electrodes for methanol oxidation are discussed.
TL;DR: In this paper, the formation of (bi-) metallic particles during temperature-programmed reduction of silica-supported mixtures of Pt and Ni chlorides was followed by X-ray absorption spectroscopy.
Abstract: The formation of (bi-) metallic particles during temperature-programmed reduction of silica-supported mixtures of Pt and Ni chlorides was followed by X-ray absorption spectroscopy. The concentration and composition of the metal particles in the final catalysts were derived from the results of the EXAFS analysis. The reduction kinetics followed by XANES were related to the formation of ordered metallic phases. During temperature-programmed reduction, most of the bimetallic phase was formed simultaneously with the reduction of the catalyst precursor. The bimetallic catalysts consisted of at least one bimetallic phase and of the pure phase of the metal in excess. For catalysts containing more than 50 atom % Ni, the authors concluded that there was either an enrichment of the bimetallic phase in Ni or the formation of a second bimetallic phase (Ni[sub 3]Pt). For catalysts containing 50 atom % Ni or less the authors concluded that the stoichiometric NiPt phase was the only bimetallic phase. 19 refs., 8 figs., 6 tabs.
TL;DR: In this paper, a density functional theory has been applied to the study of the interaction of the formate and acetate species with pure rhodium and bimetallic RnSn-tin model clusters.
TL;DR: The effect of the support in constraining the formation and defining the structure of bimetallic particles has been considered in this paper, where Alumina and NaY zeolite supported platinum and cobalt bimetal catalysts are illustrated to rationalize this effect.
Patent•
19 Nov 1993TL;DR: Bimetallic oxynitrides and nitrides which have catalytic properties comprise two transition metals selected from Groups IIIB to VIII of the Periodic Table of the Elements as discussed by the authors.
Abstract: Bimetallic oxynitrides and nitrides which have catalytic properties comprise two transition metals selected from Groups IIIB to VIII of the Periodic Table of the Elements. Preferably, one metal is either molybdenum or tungsten. The other can be tungsten or molybdenum, respectively, or another transition metal, such as vanadium, niobium, chromium, manganese, cobalt, or nickel. They have a face centered cubic (fcc) arrangement of the metal atoms and have a surface area of no less than about 40 m2/gm.
TL;DR: In this paper, the authors used an egg shell type Pd/Al2O3 catalyst as the starting material, which contained Pd only in the outer layers of the pellet.
Abstract: Preparation of supported Pd-Au and Pd-Ag bimetallic catalysts was tried using an egg shell type Pd/Al2O3 catalyst as the starting material, which contain Pd only in the outer layers of the pellet. By means of liquid phase reduction of metal salts, it was possible to deposit Au and Ag preferentially on the surface of Pd particles. By EPMA analysis of the cross section of the catalyst pellet, distribution of Au and Ag was found to coincide with that of Pd, suggesting the formation of egg shell type bimetallic catalysts. These catalysts had high selectivity in the partial hydrogenation of 1,3-butadiene to 1-butene.
TL;DR: The surface area of the supports used ranged from 25 to 500 m 2 /g and the Cu/Ru atomic ratio was varied between 0 and 4 as discussed by the authors, with the largest variations observed on the support with larger surface area.
TL;DR: In this paper, two series of supported bimetallic catalysts containing 1 wt% platinum as the primary group VIII metal and varying contents of either gold or tin were prepared and characterized.
Abstract: Two series of supported bimetallic catalysts containing 1 wt% platinum as the primary group VIII metal and varying contents of either gold or tin were prepared and characterized. The objective was to correlate the microstructure with the activity and selectivity trends in reactions of hydrogen with either n-hexane or neopentane. In a multifaceted characterization protocol, special emphasis was placed on temperature programmed reduction, chemisorption of H 2 , O 2 and CO, infrared spectroscopy of adsorbed CO, and analytical and high resolution electron microscopy. A major objective was to determine the state of the second metal and to assess the extent of solid solution or alloy formation in individual metal particles. The presence of gold manifested itself predominantly in terms of a geometric effect, breaking up larger ensembles of platinum. The behavior of the Pt-Sn catalysts was more complicated. Most of the tin was in a valence state of either Sn(II) or Sn(IV), according to XPS results, and most likely complexed with the alumina support. Tin was always located within close proximity to platinum particles. In a few instances, a few platinum-tin alloy particles were observed. However, they did not appear to play a significant role in controlling the catalytic behavior. Most of the platinum was present in monometallic form, with some particles in intimate contact with patches of ionic tin.
TL;DR: Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to study the structural evolution of monometallic and bimetallic catalysts with metal loadings representative of those used industrially under conditions close to those seen during preparation (calcination and reduction), during catalysis (under a hydrogen-hydrocarbon mixture), and during regeneration (simulated by cycles of reduction and oxidation) as mentioned in this paper.
Abstract: Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to study the structural evolution of monometallic (Pt/Al2O3) and bimetallic (Pt-Re/Al2O3) catalysts with metal loadings representative of those used industrially under conditions close to those seen during preparation (calcination and reduction), during catalysis (under a hydrogen-hydrocarbon mixture), and during regeneration (simulated by cycles of reduction and oxidation). During the catalytic reforming ofn-heptane, the formation of bonds to carbon species is observed directly by EXAFS. Despite the fact that only platinum-carbon bonds are observed, bimetallic systems show significant differences compared with monometallic systems with, in the case of Pt-Re, a reduction in the temperature range over which carbon bonding is observed, and structural modifications of the metallic particles. Under the same conditions, no carbon bonding is observed for the Pt-Sn system. In the case of Pt-Sn/Al2O3, the EXAFS results, confirmed by transmission electron microscopy, demonstrate the high resistance to sintering of this bimetallic system compared to the monometallic system.
TL;DR: In this paper, it was shown for Fe/Rh that the different surfaces have completely different selectivities for cinnamaldehyde hydrogenation and that the catalytic behavior of the alloy is not a simple linear combination of the behaviors observed for the parent metals, indicating that alloys may prove to have unique properties for low temperature selective hydrogenations.
TL;DR: In this paper, the structural evolution of Pt/Al2O3 and Pt-Re/Al 2O3 catalysts has been studied in situ by extended X-ray absorption fine structure (EXAFS) spectroscopy during the catalytic reforming of n-heptane at high pressures and temperatures.
Abstract: The structural evolution of Pt/Al2O3 and Pt–Re/Al2O3 catalysts has been studied in situ by extended X-ray absorption fine structure (EXAFS) spectroscopy during the catalytic reforming of n-heptane at high pressures and temperatures. The results obtained for the monometallic catalyst show the formation of a platinum–carbon bond during the catalytic reaction at 733 K, without marked changes in the size of platinum particles. In contrast, in the case of Pt–Re/Al2O3, this new Pt–C bond is formed only at lower temperatures, and is accompanied by important changes in the structure of the metallic particles. These results show very clearly that the properties of platinum are modified by the presence of rhenium, and explain the higher stability of the bimetallic reforming catalysts in terms of the formation of a bimetallic phase, more resistant to deposition of well structured carbonaceous residues than the monometallic one.In addition, the results obtained at the Re LIII edge show the presence of long Re–O distances (2.20 A) in the reduced Pt–Re/Al2O3 catalyst, compatible with the existence of a rhenium phase incorporated into the alumina support. This phase is partially segregated to the surface and reduced after contact of the catalyst with an H2–hydrocarbon mixture.