Effect of Dissolving Temperature on the Amount of Palladium Dissolved in Borosilicate Glass

To clarify the dissolving behavior of palladium, the effect of temperature on the amount of palladium dissolved in borosilicate glass was investigated. Glass and palladium oxide, selected as a starter material, were mixed and heated at prescribed temperature. The amount of dissolved palladium became higher with temperature increasing up to 850 °C, and lower above 850 °C. Above 850 °C, the reduction of palladium oxide was accelerated. For palladium dissolution in borosilicate glass, not only the viscosity and basicity of the glass but also the decomposition temperature of the initial palladium species seemed to affect the amount of palladium dissolved in glass.     

Role of palladium in the redox electrochemistry of ferrocene monocarboxylic acid encapsulated within ORMOSIL networks

We report herein the effect of palladium on the redox electrochemistry of ferrocene monocarboxylic acid encapsulated within an organically modified sol-gel glass network (ORMOSIL). It has been found that amount of palladium and its geometrical distribution significantly alter the redox electrochemistry of FcMCA. The geometrical distribution of palladium has been controlled by two methods: (i) palladium is allowed to link within nanostructured network of the ORMOSIL which was subsequently availed from the reactivity of palladium chloride and trimethoxysilane; (ii) palladium powder is encapsulated together FcMCA thus allowing the presence of palladium within the nanoporous domain. The content of palladium is varied by controlling the reaction dynamics of palladium chloride and trimethoxysilane interaction. For this we initially allowed to trigger hydrolysis, condensation and poly-condensation of trimethoxysilane and dimethyldiethoxysilane in acidic medium and subsequently partially dried ORMOSIL film was allowed to interact with palladium chloride. Even with partially dried ORMOSIL derived from trimethoxysilane and dimethyldiethoxysilane undergoes rapid interaction with palladium chloride and the transparent color of ORMOSIL changed to a black colour due to the formation of palladium silicon linkage. The palladium-silicon linkage has been identified by NMR, UV-VIS and transmission electron spectroscopy. The electrochemistry of FcMCA encapsulated within such an ORMOSIL matrix has been studied. Excellent redox electrochemistry of ferrocene monocarboxylic acid having peak potential separation tending to 0 for a multilayered electrode was investigated. The palladium content has been found to affect the redox electrochemistry of ferrocene as well as electrocatalytic efficiency of new ORMOSIL material. The electroanalysis of NADH is reported. The modified electrode is very sensitive to NADH with lowest detection limit of < 1 microM.     

Mechanism of modification by palladium in graphite furnace atomic absorption spectrometry

The effects of palladium and mixtures containing palladium on the absorbance characteristics of lead, thallium, cadmium, selenium, manganese and cobalt are described. These data, together with results of scanning electron microscopy showing the distribution of palladium on the graphite surface, indicate that palladium has a physical mechanism of analyte modification. During furnace heating, the analyte dissolves in molten palladium and may combine with it chemically. However, the rate limiting step leading to atomization appears to be diffusion of the analyte from palladium. The addition of magnesium, molybdenum or powdered carbon increases the speed of diffusion by causing palladium to form smaller droplets, and hence produces sharper absorbance peaks. Palladium becomes less effective as the atomization temperature increases, because the rate of diffusion is higher. This accounts for palladium having only a small stabilizing effect on less volatile elements such as manganese and cobalt. The addition of ascorbic acid to palladium has no significant effect on its modifying properties in a dilute nitric acid matrix. Results of kinetic studies on the atomization of gold are consistent with analyte diffusion out of palladium as the rate-limiting step leading to atomization.     

Stabilization of Palladium Atoms in Nitrogen-Doped Porphyrin-Like Fragments of Carbon Nanofibers

The paper considers the system of nitrogen-doped carbon nanofibers (N-CNFs) with palladium atoms deposited on their surfaces. The concentration of deposited palladium varied in the interval of 0.05-0.6 wt.%. The state of palladium was studied with the methods of quantum chemistry, electron microscopy, CO adsorption, and EXAFS. Carbon structures that contain porphyrin-like defects with four nitrogen atoms in the graphene layer interact strongly with palladium atoms and therefore can be stabilization centers of atomic palladium.     

The Effect of Support Nature and the Temperature of Preliminary Calcination on the Atomic Catalytic Activity of Supported Palladium Catalysts for the Complete Oxidation of Hydrocarbons

It is shown that for palladium catalysts supported on various supports, there is no effect of thermal activation consisting of an increase in the turnover number (TON) of palladium with an increase in the temperature of sample calcination from 500 to 700°C, as was observed in the case of similar supported platinum catalysts; for two palladium–alumina catalysts calcined at 500°C and differing in the concentration of palladium and dispersity, the TON of low-dispersity palladium is substantially higher than the TON of high-dispersity palladium; all other conditions being the same, the TON of supported palladium is determined by the support nature.     

Preparation of thin films comprising palladium nanoparticles by a solid-liquid interface reaction technique

A new approach to the formation of palladium nanoparticulate films with diameter between 6 and 50 nm by the solid-liquid interface reaction technique (SLIRT) has been presented. A solid film of palladium nitrate was formed by the modified spin coating method. This film is subsequently immersed in a reducing solution to initiate a reaction at the interface and ultimately transforms it to a palladium metal film. The kinetics of palladium reduction has been studied by UV-visible spectroscopy. The characterization of the palladium film has been performed by various physicochemical techniques such as XRD, ED, XPS, SEM, EDX, TEM, and UV-visible spectroscopy. The texture and morphology of the materials has been investigated by atomic force microscopy (AFM). At a constant palladium nitrate concentration, the average diameter of palladium nanoparticles decreases with an increase of hydrazine concentration. The effect of concentration of hydrazine on the particle size has been discussed. The palladium film formation mechanism has been proposed for the SLIRT.     

Controlled immobilization of palladium nanoparticles in two different fluorinated polymeric aggregate cores and their application in catalysis

Fluoroalkyl end-capped betaine-type cooligomeric nanocomposites-immobilized palladium nanoparticles were prepared by the reactions of palladium chloride with sodium acetate in the presence of sodium chloride and the corresponding fluorinated cooligomers. Outer blocks of poly(2,3,4,5,6-pentafluorostyrene)-containing ABA-triblock copolymeric nanocomposites-immobilized palladium nanoparticles were prepared by the use of the corresponding block copolymers under similar conditions. TEM images showed that palladium nanoparticles can be immobilized outside the fluorinated cooligomeric nanocomposite cores; in contrast, palladium nanoparticles can be effectively immobilized inside these fluorinated ABA-triblock copolymeric nanocomposite cores. Thus, these two different fluorinated copolymers enabled the controlled immobilization of palladium nanoparticles in the fluorinated nanocomposite cores. These fluorinated nanocomposites-immobilized palladium nanoparticles were also applied to the catalysts for Suzuki-Miyaura cross-coupling reaction, and the different reactivity between these nanocomposites was observed.     

氢氧化钠沉淀分离铜、钯的动力学研究及分析应用

进行了氢氧化钠沉淀分离铜钯的动力学研究,计算了用该法分离铜钯对测定引起的误差,将该法用于测定乙醛催化剂中的钯含量,获得满意结果。     

Living Carbocationic Polymerization. VII. Living Polymerization of Isobutylene by Tertiary Alkyl (or Aryl) Methyl Ether/Boron Trichloride Complexes

Abstract

Colloidal palladium supported on a chelate resin containing iminodiacetic acid groups was prepared by refluxing the palladium chelate resin in methanol-water. Using the resin-supported colloidal palladium as a catalyst, cyclopentadiene was hydrogenated to cyclopentene in 97.1% selectivity at 100% conversion of cyclopentadiene under 1 atm of hydrogen in methanol at 30°C. Finely dispersed metal particles ranging from 10 to 60 Å in diameter were observed in the resin by electron microscopy. Both x-ray microanalysis for palladium and elution analysis of palladium ion with an aqueous solution of ethylenediaminetetraacetic acid disodium salt demonstrated the existence of large amounts of palladium ion complexes in the resin. The amount of palladium metal in the resin was estimated to be about 5% of the total palladium. Since the resin, after removal of most of the ionic palladium, exhibited almost the same catalytic activity as before, it was concluded that the finely dispersed metal particles are the active species in the catalyst.     

Regularities of formic acid oxidation in the presence of porous silicon nanocomposites with palladium

Nanocomposites demonstrating high catalytic activity in the oxidation of formic acid were obtained by depositing palladium on porous silicon support. The palladium samples on porous silicon are superior to commercial samples on carbon black in many characteristics. A decrease in the size of palladium nanoparticles favors an increase in the catalytic activity of the palladium/porous silicon nanocomposites.     

An investigation of the diethyldithio-carbamates of palladium, including the determination of their stability constants

The reaction of palladium with copper diethyldithio-carbamate has been studied and two complexes isolated: palladium diethyldithiocarbamate and palladium chloride diethyldithiocarbamate. The spectra of both complexes have been examined. The extraction constants and partition coefficients between chloroform and water have been determined, the former by the use of other strong complexing reagents as masking agents for palladium. The stability constants and the exchange constant for the two complexes have been calculated.     

Interaction of CO with palladium supported on oxidized tungsten

A model catalyst system, palladium on tungsten oxide, has been examined by temperature-programmed desorption and photoemission spectroscopy. The samples were prepared by evaporation of palladium onto an oxidized tungsten foil under ultrahigh vacuum conditions. Mostly three-dimensional (3-D) palladium (Pd) clusters were found to be present on oxidized tungsten (WOx) surfaces at room temperature. Upon annealing to 670 K, the palladium clusters are redispersed and decorated by the WOx surface layer. The nature of the WOx phase on top of the palladium clusters is dependent on the mode of oxidation of the tungsten foil prior to palladium deposition. Mainly W(2+) species decorate palladium deposits on tungsten oxidized at room temperature, while mainly W(4+) species are on top of palladium deposits on the surface oxidized at 1300 K. The appearance of a Pd(n+)-O-W(4+) mixed oxide phase with n < 2 was observed on the oxidized tungsten surface. The substantial reduction (relative to nonannealed samples) of molecular CO coverage induced by annealing is discussed in terms of the changes in chemical composition and morphology of the outermost surface.     

Autoclave Processing of Concentrates Containing Stable Form of Palladium Oxide

Stable modification of palladium oxide and a material modeling the palladium-containing platinum–palladium concentrate poorly soluble in acids were synthesized. It was found that silica is dissolved in alkaline solutions of sodium formate, and palladium oxide is quantitatively reduced under autoclave conditions, which improves the parameters of the subsequent hydrochlorination of the concentrate. Raising the temperature results in that the separation of the palladium phase from alkaline solution is improved and enables separation via decantation.     

One- and Two-Photon-Induced Photochemistry of Modified Palladium Porphyrazines Involving Molecular Oxygen

Abstract— Octaphenyltetraanthraporphyrazinato palladium undergoes a self-sensitized photoreaction in the presence of oxygen to form a substituted palladium phthalocyanine with four endoperoxide bridges. This compound exhibits photophysical behavior similiar to palladium tetra-tert- butyl-phthalocyanine. The phthalocyanine-palladium complex with four endoperoxide bridges ejects molecular oxygen when excited by consecutive two-photon absorption in the Q-band region at 662 nm. This photocyclo-reversion, which produces palladium porphyrazines bearing a diminished number of endoperoxide bridges, can occur up to four times per initial molecule. Irradiation of these photoproducts in the presence of oxygen produces substituted palladium phthalocyanine containing four endoperoxide groups.     

Substoichiometric determination of traces of palladium by radioactive isotope-dilution analysis

A radioactive isotope-dilution method for the determination of traces of palladium has been developed. It is based on the solvent extraction of palladium dithizonate from acid solution by means of a substoichiometric amount of dithizone in carbon tetrachloride. The separation has been applied to the determination of traces of palladium in platinum, the rocks W-1 and PCC-1 and a biological material (kale). Amounts of palladium down to 3 ng have been determined.     

Calorimetric study of methane interaction with supported Pd catalysts

As supported palladium oxide catalysts present the best performances in methane combustion in lean conditions, microcalorimetric studies of the interaction between methane and palladium oxide or metallic palladium supported on Al₂O₃, ZrO₂ and BN have been performed at 673 K. At this temperature methane reduced the palladium oxide, and the heat of reduction of palladium oxide was shown to depend on the dispersion and on the support. The lowest heats of reduction corresponded to the highest rates of methane combustion. Moreover methane reforming occurred on metallic palladium, producing hydrogen, and again methane decomposition was shown to depend on the support. This revised version was published online in July 2006 with corrections to the Cover Date.     

Separation of traces of silver from palladium by a surface replacement reaction

An effective method has been developed for the enrichment of silver traces in palladium and of carrier-free¹¹¹Ag formed in it by thermal neutron capture and subsequent β-decay. A replacement reaction occurring between hydrogen atoms absorbed in metallic palladium and cations in aqueous solution has been observed. A new device is proposed for the measurement of hydrogen absorbed by finely divided palladium without the necessity of removing it from the metal. Both palladium and silver ions were quantitatively and selectively deposited in the presence of other cations from hydrochloric acid solutions, whereas the deposition proved to be selective and quantitative for silver from ammoniacal solutions. About 0.4 ppm silver in specpure palladium can be removed by this method. A practical example of a more than 500-fold enrichment of silver traces in palladium is described.     

Extraction of palladium(II) from hydrochloric acid solutions with triacylated ethyleneamines

Extraction of palladium(II) from hydrochloric acid solutions with novel efficient extractants, triacylated ethyleneamines, was studied. The most effective extraction of palladium(II) was observed from 0.5–1 M HCl solutions. Extraction of palladium(II) from 1 M HCl solutions was found to occur through mixed (coordination and anion-exchange) mechanism. In the field of dominance of the anion-exchange mechanism of the extraction of palladium(II) with triacylated pentaethylenehexamine the concentration constant of palladium(II) extraction was calculated, and thermodynamic parameters of extraction were evaluated.     

Catalytic Oxidation of Iron(II) Aqua Complex by Oxygen in the Presence of Palladium(II) Tetraaqua Complex

The catalytic oxidation of iron(II) with oxygen occurs along with an autocatalytic reaction between palladium(II) tetraaqua complex and iron(II) aqua complex in an oxygen atmosphere. The reaction is catalyzed by a compound of palladium in an intermediate oxidation state, presumably by a small palladium cluster formed in the course of the reduction of palladium(II) tetraaqua complex with iron(II) aqua complex.     

Substoichiometric determination of traces of palladium by neutron-activation analysis

A highly selective, rapid one-step radiochemical separation procedure for palladium has been developed. It is based on the solvent extraction of palladium diethyldithiocarbamate from a 5M hydrochloric acid solution with a substoichiometric amount of copper diethyldithiocarbamate in chloroform. The separation has been applied to the determination of traces of palladium by neutron-activation analysis, in platinum, the rocks W-1 and PCC-1 and a biological material (kale). Amounts of palladium down to 10(-8) g have been determined.