Pure Palladium Research Articles

X-ray diffraction and scanning electron microscopic characterization of electrolytically hydrogenated nickel and palladium

The effects of hydrogen insertion by electrolytic charging in H 2SO 4 solution in pure nickel and palladium were investigated. The hydrogenated phases of Ni and Pd and their stability during aging were determined by X-ray diffraction. The NiH 0,68 hydride and the α-Ni phase were distinguished by scanning electron microscopy (SEM) operating in the backscattered electrons mode. Interesting features about the intergranular cracks developed during and after charging are discussed.

A 1,1’-ferrocenylene-bridged analogue of BIPNOR

At 170 °C, 1,1’-bis(3,4-dimethylphospholyl)ferrocene ( 7) isomerises through the corresponding 2 H-phospholes that are trapped by diphenylacetylene to give the 1,1’-ferrocenylene-bridged bis–1-phosphanorbornadiene ( 6). After resolution with an optically pure palladium complex, ( R, R)- and ( S, S)-( 6) are tested in the asymmetric hydrogenation of a dehydroaminoacid, hydroformylation of styrene, and allylation of sodium malonate.

The existence of more than one jump process of hydrogen in palladium–silver alloys — an NMR study

The hydrogen dynamics in the α-phase of Pd 1− x Ag x H y has been studied by proton nuclear magnetic resonance (NMR) measurements. Jump frequencies of the hydrogen atoms in the metal lattice have been deduced from the dipolar spin-lattice relaxation rates Γ 1d by applying the BPP model. In PdH y , the temperature dependence of Γ 1d is well described by a single jump process for all hydrogen atoms. In contrast, in the palladium–silver alloys Pd 1− x Ag x H y , the Γ 1d data indicate more than one jump process with different activation energies. Two and three processes could be separated for x=0.1 and x=0.3, respectively. In both alloys, the diffusion process with the lowest activation energy ( E a=226 meV) is comparable to that in pure palladium. The jump processes with higher activation energies occur more frequently in Pd 0.7Ag 0.3 than in Pd 0.9Ag 0.1. This indicates higher energy-barriers for jumps between O-sites in silver-rich environments. Direct measurements of the long-range diffusion coefficients D were performed by pulsed-field-gradient (PFG)-NMR at temperatures up to 450 K. For both Pd 1− x Ag x H y samples, D( T) is well represented by a single Arrhenius law with the diffusion parameters D 0=3.0×10 −7 m 2 s −1 and E a=230 meV for x=0.1 and D 0=2.1×10 −7 m 2 s −1 and E a=260 meV for x=0.3. The diffusivities calculated from the jump frequencies of the hydrogen atoms are in good agreement with these PFG results and also with measurements using the time-lag technique.

Synthesis of palladium nanoparticles in water-in-oil microemulsions

Palladium nanoparticles have been synthesized by the reduction of Pd(NH 3) 4Cl 2 with hydrazine in the cationic water-in-oil (w/o) microemulsions of water/cetyl-trimethyl-amonium bromide (CTAB), n-butanol/isooctane at 25°C. By the analyses of electron diffraction pattern and X-ray diffraction, the resultant particles were characterized to be the pure palladium crystalline with a face-centered cubic (fcc) structure. The investigation on the microemulsion compositions indicated that the average diameter of palladium nanoparticles was affected mainly by the interfacial property, not the size of microemulsion droplets. At a higher ratio of CTAB to n-butanol, smaller particles could be obtained. When Pd(NH 3) 4Cl 2 concentration was fixed, the average diameter of palladium nanoparticles decreased with the increase in hydrazine concentration and then approached to a constant value when the concentration ratio of hydrazine to Pd(NH 3) 4Cl 2 was above 7. At a sufficiently high hydrazine concentration, the average diameter of palladium nanoparticles was independent of Pd(NH 3) 4Cl 2 concentration. In addition, it was surprisingly found that the magnetic susceptibility of the resultant palladium nanoparticles was significantly higher than that of bulk palladium.

Catalytic CO oxidation over pumice supported Pd–Ag catalysts

Results on the catalytic oxidation of CO at 523 K over bimetallic Pd–Ag catalysts supported on pumice are reported and compared with those obtained from the monometallic Pd and Ag catalysts. The catalysts were prepared by organometallic precursors and were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) after different treatments with air and with hydrogen. The activity of the catalysts decreases with increasing Ag/Pd atomic ratio, the monometallic palladium exhibiting the highest activity. Furthermore, the treatment with air and with hydrogen always results in a better catalytic performance. On the basis of the structural characterization by XRD and the surface atomic composition obtained from XPS measurements, Ag has tendency to segregate at the surface of the catalysts, except in air environment at 623 K. In this case, an inward diffusion of silver atoms occurs. By hydrogen treatment at high temperature, silver reappears at the surface with further increase of the catalytic activity. The results are explained in terms of rearrangement of the bimetallic particles with the most active situation represented by clean particles of pure palladium next to dispersed silver particles.

Alloying Effects on N−O Stretching Frequency: A Density Functional Theory Study of the Adsorption of NO on Pd3Mn (100) and (111) Surfaces

We present total energy and N−O stretching frequency calculations for the low-coverage adsorption of NO on palladium−manganese Pd3Mn (100) and (111) surfaces, on the basis of density-functional theory periodic calculations. A complete description of all the different adsorption sites and corresponding N−O vibrations is given and a theoretical interpretation of the experimental IR spectra is proposed. On both Pd3Mn (100) and (111) surfaces, the highly coordinated vertical adsorption sites are always energetically favored. The atop adsorption on the surface manganese atom is also a stable site. On Pd3Mn (100), a new horizontal dibridge site is reported. The adsorption on these palladium−manganese alloy surfaces is weaker than the adsorption on the pure corresponding palladium surfaces. The anharmonic N−O stretching frequencies on the Pd3Mn surfaces are shifted by 60−100 cm-1 toward the lower frequencies by comparison with the pure palladium surfaces. The weakening of the adsorption strength and the global shift for the N−O frequencies has been correlated with the presence of the surface manganese atoms, which play a predominant role for the electronic interactions between the magnetic NO molecule and the alloy periodic surface. An interpretation of the alloying effect on the strength of the N−O bond and the NO adsorption is proposed on the basis of a qualitative Mulliken population analysis. The empty states on the surface manganese atoms are responsible for an increased electron-transfer toward NO, and hence of the smaller vibrational frequency on the alloy compared to pure Pd. Indeed these empty states interact with the π*NO and push it below the Fermi level, resulting in a transfer from the “surface electron reservoir” toward the π*NO molecular orbital.

Deuteron Interaction Within a Microcrack in a Lattice at Room Temperature

The aim of this research was to analyze the reaction of deuteron fusion, catalyzed by the plasmons in lattices with a cubic structure, to varying the temperature. The probability of fusion in pure and impure palladium metal is calculated using a hypothesis that suggests a kind of chain reaction within the crystalline lattice. As a consequence of the enhanced tunneling effect due to increasing the temperature and the concentration of impurities, this chain reaction would be favored by microcracks formed in the structure as a result of lattice deformation. This paper interprets the results obtained, considering the trend of the potential that describes the effective interaction between deuterons within the metal. In effect, the coupling of plasmons and deuterons, in the presence of impurities, can not only reduce the thickness but also lower the height of the Coulomb barrier K.

Extraction of palladium metal from aqueous solution of palladium chloride by laser-induced photochemistry

Laser-induced photoredox reaction of palladium chloride was investigated for the selective extraction of palladium metal in an aqueous solution. The third harmonic of Nd:YAG laser system, 355 nm, which corresponds to the absorption wavelength of the palladium chloride solution was adopted for the photolysis of palladium chloride in solution phase. Since the selection of reducing agents and acidic solvents affect dominantly the reaction efficiency, various solvents (HNO 3, HClO 4, HCl) as well as reducing agents (oxalic acid, formic acid and ethanol) were adopted to determine an optimal condition for the reaction. The optimal condition for the reaction of palladium solution was found to be the combination of oxalic acid as a reducing agent and nitric acid as a solvent. The reaction product was not dissolved back to solution so that the filtration of the solution was enough to collect reaction product. The X-ray diffraction (XRD) study on the precipitation revealed that the precipitation was pure palladium metal. The selective extraction of palladium metal from the mixed solution of palladium and dysprosium was also demonstrated.

Palladium and Rhodium Complexes with Planar-Chiral Carborane Ligands

Base degradation of the prochiral 1-diphenylphosphanyl-2-phenyl-1,2-dicarba-closo-dodecaborane (1) affords the planar-chiral 7-diphenylphosphanyl-8-phenyl-7,8-dicarba-nido-undecaborate anion (2). Resolution of the racemic anion carried out using a well-established procedure, gave the internally diastereomeric palladium complexes 3R-R and 3R-S. These complexes were separated by fractional crystallization. A single-crystal X-ray analysis of 3R-R established the exo-nido bonding of the carborane ligand via the phosphorus atom and the adjacent BH group, and the (R) configuration of the carborane ligand. The enantiomerically pure anions of 2 were liberated from the diastereomerically pure palladium complexes 3R-R and 3R-S, respectively, by subsequent addition of HCl and NaCN. The exo-nido-rhodium−carborane complexes 4−8 were prepared by heating 2eR or 2eS with [Rh(COD)Cl]2 and/or a chiral chelating phosphane, such as DIOP and BINAP, under reflux. The chiral complexes were tested under enantioselective catalysis conditions such as hydrogenation of acetamidocinnamic acid, hydrogenation of ketopantolactone, and hydrosilylation of acetophenone.

ＭＡの応用 単体パラディウムのＢＭＡとその水素吸蔵特性

Nano-structured functional materials are expected to have superior properties to the coarse-grained, bulk materials. In the present paper, pure palladium is refined to nano-sized state to investigate the hydrogen absorption and desorption behavior. Using the bulk mechanical alloying, the palladium platelets can be successfully refined to nano-sized grains with the order of 10nm. In comparison of pressure composition isotherms between nano-sized and bulk palladium, the phase boundary of the Pd-H miscibility gap is significantly narrower for nano-Pd. While the hydrogen solubility at α (α+β) phase boundary is much increased, that at β/(α+β) phase boundary is drastically reduced by nano-structuring. This might be because of the broadening of the site energy distribution, induced by the intrinsic strains constraining the nano-grains. The broadening mechanism of site energy distribution has direct influence on the hydrogen absorption and desorption processes. The Curie temperature for hydrogen absorption and desorption is drastically reduced by 135K through the nanostructuring. The above precise discussion helps us to make nano-structured material design in the hydrogen storage alloys and compounds.

The surface chemistry of acetic acid on Pd{111}

XPS, temperature-programmed reaction and HREELS have been used to study the adsorption and reactions of acetic acid on Pd{111}. At 170 K the adsorbed monolayer contains intact and dissociated acetic acid molecules, the latter consisting of a mixture of bidentate acetate and another species tentatively identified as monodentate acetate. The monodentate acetate appears to resemble closely the acetate species observed under reaction conditions at the surface of a pure palladium vinyl acetate synthesis catalyst. Thermal decomposition of the adsorbate yields CO2, H2O, CO, H2 and carbon. The associated processes may be rationalised in terms of two reaction channels, one due to the monodentate and the other due to the bidentate acetate.

Behavior of Silver and Palladium Mixtures during Heating

The behavior of mixtures of silver and palladium during heating in both air and an inert atmosphere was studied using X‐ray diffractometry (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dilatometry, and scanning electron microscopy (SEM). In situ high‐temperature XRD studies on a commercial 20% palladium material with submicrometer‐sized particles indicated that an intermetallic phase, most likely Ag3Pd, formed in air between 300° and 400°C, the same temperature range where a 13% linear expansion was measured by dilatometry. The DSC data indicated an exothermic peak at 340°C, a temperature where the TGA results indicated that the material had picked up only 0.2% oxygen, compared with the maximum of 1.4% at 525°C. No PdO was detected by XRD at 400°C, which suggests that oxygen was being incorporated in the intermetallic. Microstructural examination using SEM indicated that larger particles, with internal pores, had formed after heating in air to 375°C. When the material was heated in argon for 1 h at 400°C, no intermetallic phase or alloy formed, and minimal expansion occurred. When mixtures of larger silver particles (5–30 μm) with palladium particles (1–3 μm) were heated in air, the maximum amount of expansion that occurred increased from 0% for pure palladium up to a maximum of 18% at 75% silver. This result supports the conclusion that expansion is a result of formation of this new phase, in the presence of oxygen, not of the oxidation of the palladium.

TEST AND QUALIFICATION OF A VARIABLE TEMPERATURE VIBRATING SAMPLE MAGNETOMETER SYSTEM FOR THE MEASUREMENT OF MAGNETIZATION CYCLES UP TO +/-12T IN THE 4.2K-300K TEMPERATURE RANGE

A complete characterisation of an Oxford Instruments Vibrating Sample Magnetometer (VSM) has been made in order to check the limits and the reproducibility of the system as well as the measurement accuracy. Several measurement cycles have then been carried out to check the extent of the difference between the actual sample temperature and the sensor reading, and the weight of this difference on the magnetization data as a function of the temperature. Moreover an unexpected lowering of a reference signal has been observed at low temperatures, most probably due to shielding currents in the structure; this effect influences the sample signals, and has to be taken into account during data analysis. Being the magnetization a relative measurement, a great attention must be paid to the calibration procedure. Calibrations with 99.999% pure Nickel and Palladium, which have magnetization signals two order of magnitude apart, give comparable calibration constants. We observed that in order to have high accuracy measurements, the calibration has to be performed on samples geometrically identical to the test ones, and periodically repeated. The repeatability of the measurements has been found to be ±1%; once corrected the image current effect, the accuracy of the measurements, at 4.2 K, is ±3%. This value was also confirmed by the direct comparison of our results with those obtained at National Institute of Standards and Technology (NIST) on the same Nb 3 Sn samples

Manufacturing, structure and high temperature corrosion of palladium-modified aluminide coatings on nickel-base superalloy M38

Three palladium-modified aluminide coatings were prepared by conventional pack-cementation aluminizing process on the nickel-based superalloy M38, which was previously electroplated with pure palladium, Pd–20 wt.% Ni alloy, or Pd+Ni composite plating. The structure of all coatings was thoroughly analyzed. A major difference between Pt- and Pd-modified aluminide coatings resided in the fact that the Pd zone was single-phased and the constitutive phase was β-(Pd x ,Ni 1− x )Al. The isothermal oxidation resistance of the Pd–20 wt.% Ni alloy modified coatings was better than that of the other two palladium-containing and conventional aluminide coatings in air at 1000°C. The hot corrosion performance of Pd–Ni–Al coatings was also tested in Na 2SO 4 melt at 900°C. As regards their hot corrosion resistance, they behaved at least as well as commercial Pt–Al coatings under the same testing conditions and remarkably better than conventional aluminide coatings. The behavior of cyclic oxidation of Pd–Ni–Al coating was inspected at 1050°C and its corrosion mechanism was also preliminary discussed.

Novel method for preparing palladium membranes by photocatalytic deposition

AbstractAn ultrathin palladium film on a porous TiO2 ceramic membrane was successfully synthesized by a novel photocatalytic deposition (PCD) method. The mechanism was interpreted by the photocatalytic reaction between the surface of the TiO2 semiconductor and the Pd(II) solution. Energy dispersive (EDS) analysis and argon permeability of the membrane were used to characterize the deposited Pd. During the PCD process, photoreaction took place with higher efficiency when the pH value of the solution was controlled at the 3—3.5 range. A short irradiation time of 18 min was enough for PCD at a normal reaction temperature. A methanol additive in the solution of about 40 vol. % was optimum for the deposition of Pd. XRD and SEM results on the Pd‐based membrane prepared by PCD indicated that the metal existed in the form of a pure palladium element, with a layer thickness of about 0.1 μm. The gas permeation experiment was conducted in a high‐temperature permeator from 623 to 723 K. The results indicated that there were contributions to the hydrogen flux attributable to both dense and microholes parts of the resulting Pd/TiO2 membrane.

The adsorption of precious metals and base metals on a quaternary ammonium group ion exchange resin

Adsorption tests were conducted with a quaternary ammonium group ion exchange resin to determine the equilibrium adsorption of precious- and base metals. The resin used is a macroreticular polystyrene type 1 strong base anion exchange resin. The adsorption was determined for synthetic single metal solutions as well as for multi-component solutions. The effect of the Cl − concentration on the equilibrium adsorption was determined for three different HCl concentrations, i. e. 6, 8 and 10%. The effect of chloride strength in the solution was also determined for mixed and base metal solutions. Pure metals, i.e. platinum, palladium and gold, were dissolved in aqua-regia and diluted to 2000 ppm (as metal) in 4M HCl. Ruthenium, rhodium and iridium were dissolved from pure salts in HCl. A 2000 ppm base-metal solution was prepared by dissolving all the required components, including precious metals, to match an in-plant industrial base-metals solution composition. For each precious metal the equilibrium adsorption was determined for typically two solution concentrations. Data points were established by varying the amount of resin added to the solution. The equilibrium concentrations were determined by ICP analysis after 24 hours exposure using the bottle-roll technique.

70%Ag 30%Pd Coated BaTiO3 Powder for Internal Electrode Applications

Recent trends in the electronic passive component manufacturing industry have been to eliminate or reduce reliance of pure Pd and high palladium contained Ag/Pd electrodes by substituting nickel or significantly lowers palladium content in Ag/Pd alloys. The conversion to base metal technology represents a substantial capital expense; the resistance to replace traditional air‐fired kilns to nitrogen or reducing atmosphere kilns has created the need for new low cost air fired electrode technology. This paper presents a new electrode technology incorporating a uniform, continually coated AgPd over engineered dielectric particles. The resulting powder greatly reduces the consumption of precious metal, and provides superior thermal mechanical properties. This is achieved by matching the core ceramic structure of the powder to the manufacturer′s dielectric, thereby controlling shrinkage while maintaining desired electrical properties.

Copper electroless deposition on NiTi shape memory alloy: an XPS study of Sn–Pd–Cu growth

XPS analysis of electroless deposition of successive Sn, Pd and Cu films on NiTi(O) surface has been done in order to explain their nucleation and growth. Chemical interaction of Sn sensitisation element with NiTi(O) surface is shown to be associated with the growth of Sn(O) interfacial oxide which can be formed after the reaction of Sn atoms with Ni 2O 3 nickel oxide. The dissociation of this non-stable oxide leads to the formation of Sn oxide film and to the migration of free metallic nickel atoms at the free surface of the electroless Sn(O) film Pd chemisorption on Sn(O) surface is associated with the formation of strong Sn–O–Pd interfacial bonds. Further on, 2D and 3D growth of pure metallic palladium occurs, leading to the formation of nanometric Pd clusters. The interaction of copper atoms with that palladium surface leads to the formation of interfacial Pd–Cu intermetallic and consequently to strong interfacial adhesion.

ChemInform Abstract: Asymmetric Cyclization/Hydrosilylation of Functionalized 1,6‐Dienes Catalyzed by Enantiomerically Pure Palladium Pyridine—Oxazoline Complexes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Raman Spectroscopic Identification of Synthetic “Braggite” (Pt, Pd, Ni)S Samples in Comparison with Synthetic “Cooperite”

Raman spectra of synthetic “braggite” (Pt, Pd, Ni)S with variable Pt/Pd ratios (atomic ratios between 0.31 and 1.37) and saturated in Ni (up to 1.99 atomic %) have been recorded and compared with the Raman spectra of synthetic “cooperite” and the pure palladium and platinum sulfides. In order to obtain more information on the significant differences in the spectra of these synthetic samples, factor group analyses of “braggite” and “cooperite” have been performed.