Showing papers on "Palladium published in 1993"
TL;DR: In this article, the photocatalytic activity of TiO[sub 2] toward the degradation of organic compounds in aqueous solutions at low concentrations is discussed, and the increase in the catalytic activity when certain metals such as silver, gold, and palladium are deposited on the surface is also discussed.
Abstract: This paper reviews the photocatalytic activity of TiO[sub 2] toward the degradation of organic compounds in aqueous solutions at low concentrations. The photocatalytic activity of both polycrystalline samples and thin films can be related to the method of preparation of the catalyst. The increase in the catalytic activity of TiO[sub 2] when certain metals such as silver, gold, and palladium are deposited on the surface is also discussed. These catalysts have potential use in removing harmful carcinogens from water as well as possible application in reducing the harmful effects of oil spills. 45 refs., 2 figs.
585 citations
TL;DR: Chiral phosphinoaryl-and phosphinoalkyloxazolines, a new class of chelate ligands, were prepared via convenient routes as mentioned in this paper, and Palladium complexes of the new ligands have proved to be highly effective catalysts for allylic substitution reactions.
473 citations
TL;DR: In this paper, a series of phosphorus-containing oxazoline ligands has been developed for asymmetric palladium catalysed allylic substitution of 1,3-diphenylprop-2-enyl-1-acetate 12 with the sodium salt of dimethylmalonate.
377 citations
TL;DR: In the presence of tetrakis(triphenylphosphine)palladium, vinyl and aryl halides or triflates react very rapidly in piperidine or pyrrolidine with terminal alkynes to give conjugated enynes as mentioned in this paper.
306 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: Composite palladium-ceramic membranes with palladium films ranging from 11.4 to 20 [mu]m were made by depositing palladium on the inside surface of asymmetric tubular ceramic membranes.
Abstract: Composite palladium--ceramic membranes with palladium films ranging from 11.4 to 20 [mu]m were made by depositing palladium on the inside surface of asymmetric tubular ceramic membranes. Electroless plating was used to deposit the palladium film. Membranes were characterized by conducting permeability experiments with hydrogen, nitrogen, and helium at temperatures from 723 to 913 K and feed pressures from 160 to 2,445 kPa. The membranes had both a high hydrogen permeability and selectivity. The hydrogen permeability for a composite membrane with an 11.4-[mu]m palladium film was 3.23 [times] 10[sup [minus]9] mol [center dot] m/(m[sup 2] [center dot] s [center dot] Pa[sup 0.602]) at 823 K. Hydrogen/nitrogen selectivity for this membrane sealing should further increase the hydrogen selectivity. Results of this study demonstrate the potential for using composite metal-ceramic membranes in membrane reactors including applications that require operation at relatively high temperatures and transmembrane pressure differences. Some of the many potential applications include steam reforming of methane, water gas shift, and dehydrogenation of various hydrocarbons including cyclohexane, ethylbenzene, ethane, propane, and butane. Another promising application is the decomposition of hydrogen sulfide and ammonia impurities in synthesis gas produced at coal gasification plants.
259 citations
TL;DR: A number of 2,3-disubstituted 1-indenones have been prepared in fair to good yields by treating o-iodo- or o-bromobenzaldehyde with various internal alkynes in the presence of a palladium catalyst.
Abstract: A number of 2,3-disubstituted 1-indenones have been prepared in fair to good yields by treating o-iodo- or o-bromobenzaldehyde with various internal alkynes in the presence of a palladium catalyst. Synthetically, the methodology provides an especially convenient route to stable hindered indenones containing aryl, silyl, and tert-alkyl groups. The reaction is believed to proceed through a palladium-(IV) intermediate, and the regiochemistry of the reaction is controlled sterically
256 citations
TL;DR: In this paper, the performances of platinum-group metals, platinum, iridium, palladium, rhodium and ruthenium supported on γ-alumina, as catalysts for the selective reduction of nitrogen oxides by hydrocarbons were investigated.
Abstract: The performances of platinum-group metals, platinum, iridium, palladium, rhodium and ruthenium supported on γ-alumina, as catalysts for the selective reduction of nitrogen oxides by hydrocarbons were investigated. Platinum and rhodium had high nitric oxide conversion activities both in model mixtures and in real diesel exhaust gases, especially at relatively low temperatures between 200 and 350°C. It was confirmed that the platinum-rhodium and platinum catalysts have higher activity and durability than a catalyst composed of copper supported on ZSM-5 under real diesel exhaust conditions. The platinum-containing catalysts, however, produced more nitrous oxide than nitrogen. It is expected that platinum-group metal catalysts will be able to be used for practical purposes if once their selectivity toward nitrogen is improved.
253 citations
233 citations
TL;DR: In this paper, the effect of ligands and lithium chloride on the rates of the palladium catalyzed coupling between organic triflates and arylstannanes was studied.
Abstract: The effect of ligands and lithium chloride on the rates of the palladium catalyzed coupling between organic triflates and arylstannanes was studied. The dependence of the rate on the ligand is similar to the one previously reported for the coupling of vinylstannanes, but in the present case triphenylarsine is shown to be superior to both triphenylphosphine and tri(2-furyl)phosphine. The effect of added chloride is compler and varies depending on solvent and ligand used. Ortho-substituted arylstannanes tend to transfer alkyl moieties to a substantial extent, and therefore rates and efficiencies of aryl vs alkyl transfer were quantitated
233 citations
TL;DR: In this article, a homogeneous palladium catalysts for the selective production of methyl methacrylate by methoxycarbonylation of propyne was developed. But the performance of these catalysts was limited by the fact that the 2-pyridylphosphine ligand plays an essential role both as a chelating PN ligand and as a monocoordinated ligand in the rate-determining step.
TL;DR: In this article, the mechanism of the oxidative addition of aryl halides to low-ligated zerovalent palladium species obtained by reduction of their divalent precursor complexes, Pd II Cl 2 (PR 3 ) 2, was investigated on the basis of 31 P NMR and electrochemistry.
Abstract: The mechanism of oxidative addition of aryl halides to low-ligated zerovalent palladium species obtained by reduction of their divalent precursor complexes, Pd II Cl 2 (PR 3 ) 2 , was investigated on the basis of 31 P NMR and electrochemistry. In strong contrast to usual expectations, it is shown that the reaction proceeds via a complex sequence of steps: (i) fast addition of the aryl halide to a halide ligated zerovalent palladiumcenter, so as to afford a pentacoordinated anionic arylpalladium(II) center; (ii) a fast but reversible uphill elimination from the pentacoordinated anionic arylpalladium(II) center of a halide ion ligand, possibly through its substitution by a solvent ligand; (iii) rearrangement of this second short-lived intermediate into the thermodynamically stable trans-arylpalladium(II) product of the reaction
TL;DR: The present results demonstrate that the entire volume of nanocrystalline samples was observed to transform to [beta]-PdH upon exposure to hydrogen, indicating that the entropy and/or enthalpy of mixing for the palladium-hydrogen system differs in nanocrystaline and coarse-grained materials.
Abstract: In situ x-ray-diffraction studies of the hydriding behavior of coarse-grained and nanocrystalline palladium samples at ambient temperature are descibed. A previously observed narrowing of the miscibility gap in nanocrystalline palladium was reproduced. The present results, however, demonstrate that this change in the palladium-hydrogen phase diagram for nanocrystalline material is not related to an inability to form the hydride phase in highly disordered grain boundary regions as previously proposed. Instead, the entire volume of nanocrystalline samples was observed to transform to [beta]-PdH upon exposure to hydrogen. This behavior indicates that the entropy and/or enthalpy of mixing for the palladium-hydrogen system differs in nanocrystalline and coarse-grained materials. Because of these changes in thermodynamic quantities, the phase boundary of the palladium-hydrogen miscibility gap is predicted to be shifted to lower temperatures for nanocrystalline samples.
TL;DR: In this article, the codeposition behavior of palladium and silver on porous stainless steel by means of electroless plating was investigated and a combination of XRD and EDX analyses revealed that codeposited Pd and Ag are in separate phases and that small amounts of an amorphous palladium rich phase are also present in the deposited material.
TL;DR: In this paper, the conversion of difluorodichloromethane has been studied in the gas phase between 433 and 523 K at atmospheric pressure aver Pd black and Pd supported on alumina, graphite, or AlF3.
TL;DR: Experiments were reported for hydrogen transport in palladium-coated membranes of niobium, tantalum, and vanadium as discussed by the authors, where hydrogen was extracted at 100% purity.
TL;DR: Acyclic and cyclic, aliphatic or aromatic, 4- or 5-alkenoic acids cyclize in high yield to 5- or 6-membered unsaturated lactones using 5 mol % Pd(OAc) 2, 2 equiv of NaOAc, and 1 atm of O 2 as discussed by the authors.
Abstract: Acyclic and cyclic, aliphatic or aromatic, 4- or 5-alkenoic acids cyclize in high yield to 5- or 6-membered unsaturated lactones using 5 mol % Pd(OAc) 2 , 2 equiv of NaOAc, and 1 atm of O 2
TL;DR: In this article, the effect of surface oxygen groups on the properties of carbon-supported palladium catalysts for liquid-phase hydrogenation of dinitrotoluene has been investigated.
TL;DR: In this paper, the cross-coupling reaction between arylboronic acids, carbon monoxide (1 atm), and aryls iodides in the presence of palladium catalyst and base provided unsymmetrical biaryl ketones in high yields.
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.
TL;DR: In this paper, the influence of stabilized, underpotential deposited (upd) lead on the oxidation of formic acid and its strongly absorbed species on a platinum electrode in HClO[sub 4] has been investigated by measuring simultaneously the rate of CO[sub 2] production from both bulk and adsorbed formic acids.
Abstract: The oxidation of formic acid on noble metals such as platinum or palladium has been studied extensively in the last decades due to its significance in electrocatalysis of fuel-cell reactions. The influence of stabilized, underpotential deposited (upd) lead on the oxidation of formic acid and its strongly absorbed species on a platinum electrode in HClO[sub 4] has been investigated by measuring simultaneously the rate of CO[sub 2] production from both bulk and adsorbed formic acid. The use of on-line mass spectrometry (MS) technique (DEMS) allows a discrimination of the products (CO[sub 2]) between adsorbed and bulk species with the help of isotope-labeled [sup 13]C formic acid as a probe. The pronounced catalytic effect of upd lead adatoms on the bulk formic acid oxidation strongly depends on the coverage degree of adatoms. In addition, upd Pb facilitates the oxidation of formic acid adsorbates. However, the oxidation of formic acid cannot take place on a Pt surface covered up to 100% with upd lead adatoms and CO adsorbates. The results prove once more that a third-body effect cannot account for the observed catalytic effects. An electronic interaction between the upd Pb and the Pt substrate is more likely. This result in anmore » increase in rate of HCOOH electrosorption on the modified free-platinum surface.« less
TL;DR: In this paper, the authors investigated the catalytic CO Oxidation on model silica-supported palladium catalysts with in situ infrared reflection-absorption spectroscopy (IRAS), temperature-programmed desorption/reaction, and kinetic measurements in the pressure range of 10 -9 -15 Torr and the temperature range of 350-1000 K.
Abstract: The catalytic CO Oxidation on model silica-supported palladium catalysts has been investigated with in situ infrared reflection-absorption spectroscopy (IRAS), temperature-programmed desorption/reaction, and kinetic measurements in the pressure range of 10 -9 -15 Torr and the temperature range of 350-1000 K. The model catalysts were prepared by evaporating palladium onto a silica thin film supported on a Mo(110) substrate, an arrangement that facilitates the use of electron spectroscopies and IRAS. The CO oxidation reaction was studied in three pressure ranges: (1) coadsorption and reaction of CO and O under UHV conditions, (2) CO oxidation between 10 -8 and 10 -6 Torr (350-1000 K), and (3) at 15 Torr (500-650 K)