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.     

Zinc coverage dependent structure of PdZn surface alloy

Catalytic performances of alloy and surface alloy are sensitive to the surface structures and composition. In this paper we present an overall survey of the surface structure of Pd(111) covered with different amount of Zn using Monte Carlo simulations. We demonstrate that the composition of PdZn surface alloy is Zn coverage dependent: the surface concentration of Zn increases with the increase of the deposited Zn. At one or multi-layer of zinc deposited Pd(111), a multilayer 1?:?1 PdZn surface alloy will be formed. Surface alloy islands dominated by palladium are formed at submonolayer Zn coverage. At very low zinc coverage, small palladium ensembles of 3 to 5 Pd atoms exist preferentially on the Pd(111) surface. Our simulated results which are consistent with the pertinent experiments indicate that the unusual high-temperature desorption peak of formaldehyde observed experimentally has likely originated from the small surface ensembles induced by deposited Zn.     

NiPd/Si界面常温扩散及硅化物形成的XPS证据

Nickel-palladium film on p-Si prepared by potential -controlled electrodeposition has much better adherence than that deposited by other methods .To reveal the reasons of this effect, X-ray photoelectron spectroscopy (XPS) combined with Ar+ sputtering was used to investigate the interface of NiPd /Si. The results showed that dramatic interdiffusion of Ni, Pd and Si had occurred at atmospheric temperature. On the XPS spectra of nickel and palladium , there are two kinds of binding energy , contributed by pure metals and metal silicide respectively. NiSi, PdSi and Pd2Si were formed at the interface. Both of the electric field on the surface and the H atoms in the metal lattice have the possibility to promote reactions between nickel or palladium and silicon .     

钯团簇碰撞沉积钯/银基板的分子动力学模拟

运用分子动力学模拟方法研究了常温下较大的钯团簇以不同初始速度撞击不同硬度基板的微观过程,着重分析了沉积形貌的变化、团簇的嵌入深度和原子的扩散程度、基板碰撞接触区域的温度演变以及碰撞过程中团簇与基板间的能量转化,获得了沉积过程中变形形貌、结构特征及能量转化随团簇尺寸、初始速度及基板材质的变化规律.并进一步探究了第二颗团簇以不同时刻沉积时前一团簇的变形形貌及基板接触区域温度变化的特点,发现短时间间隔下第二颗团簇的沉积更有利于团簇与基板的结合.     

Synthesis and molecular and crystal structure of the octanuclear palladium cluster Pd8(μ3-CO)2(μ2-CO)6(PMe3)7

Treatment of bis(dibenzylideneacetone)palladium with trimethylphosphine under a carbon monoxide atmosphere gives the title complex in good yield. X-ray crystallography has shown the structure of the complex to consist of an octahedron of palladium atoms which is bicapped by two further palladium atoms in an asymmetric fashion. Seven of the eight palladium centres carry terminal trimethylphosphine ligands. Two face-bridging and six edge-bridging CO molecules complete the ligand shell.     

Self-Consistent-Field potential-energy surfaces for hydrogen atom pairs within small palladium clusters

An ab initio electronic structure study is presented of hydrogen–hydrogen interactions in an electronic environment perturbed by the presence of palladium atom clusters. In particular, we investigated changes in the interatomic potential when the atomic centers are trapped inside an fcc palladium octahedral hole and when they are separated from each other by a (111) plane of palladium atoms. The (111) plane was modeled with a cluster of three palladium atoms. Self-consistent field (SCF ) level calculations were performed, and palladium atom pseudopotentials were employed to make the systems studied computationally tractable. For pairs of atoms placed within the octahedral hole, various lines of approach were considered [along the (100), (110), and (111) directions]. Lattice deformations and electronic excitations were examined for their effect on the interatomic potential.     

Effect of plating bath hydrodynamic on the morphology of palladium layer electrolessly deposited on porous ceramic support

The present work was focused on the preliminary stage of palladium composite membrane preparation through electroless plating and the effects of bath hydrodynamic properties on the deposited layer morphology. Eight samples of palladium composite membrane were prepared which were different in terms of plating time, solution stirring rate and bath agitating mode. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used for characterization of deposited layer. In comparison with the support rotating mode, the support fixing and the magnet rotating mode, which are caused running the solution toward the support, were led to a deposited layer with better quality, larger grains of deposited layer, more compacted plating and higher plating efficiency.     

Synthesis and structure of a distorted octahedral palladium(II) complex coordinated with a tetrathioether ligand tethered with bulky substituents

A new type of an o-phenylene-bridged tetrathioether ligand tethered with extremely bulky substituents, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt) groups, at its terminal sulfur atoms, TbtS[(o-phenylene)S]3Tbt (1), was synthesized by taking advantage of the coupling reaction of thiols with iodobenzenes using Cu2O in 2,4,6-trimethylpyridine. Complexation of 1 with Na2PdCl4 gave the corresponding dichloropalladium(II) complex, [PdCl2(1)] (7). The X-ray structural analysis of 7 indicated that the central palladium metal is in a distorted octahedral environment, where the two inner sulfur atoms of 1 and the two chlorine atoms form a square planar arrangement around the palladium metal and the two terminal sulfur atoms of 1 weakly coordinate to the palladium center at the axial positions. In addition, a phenyl analogue of 1, PhS[(o-phenylene)S]3Ph (2), was synthesized by a method similar to that for 1. Reaction of 2 with Na2PdCl4 gave the corresponding dichloropalladium(II) complex, [PdCl2(2)] (8). X-ray crystallography of 8 showed a type of the structure different from the distorted octahedral structure in 7, i.e., a square planar arrangement around the central palladium atom with the one terminal sulfur atom of 2, its neighboring sulfur atom, and the two chlorine atoms. The results of the NMR studies on 8 in a CDCl3 solution were not consistent with the results of the X-ray crystallography and suggested the coordination of the two inner sulfur atoms of 2 to the palladium metal, although a possibility of the existence of the rapid interconversion among isomers could not be excluded.     

Ion- and atom-leaching mechanisms from palladium nanoparticles in cross-coupling reactions

Leaching of palladium species from Pd nanoparticles under C--C coupling conditions was observed for both Heck and Suzuki reactions by using a special membrane reactor. The membrane allows the passage of palladium atoms and ions, but not of species larger than 5 nm. Three possible mechanistic scenarios for palladium leaching were investigated with the aim of identifying the true catalytic species. Firstly, we examined whether or not palladium(0) atoms could leach from clusters under non-oxidising conditions. By using our membrane reactor, we proved that this indeed happens. We then investigated whether or not small palladium(0) clusters could in fact be the active catalytic species by analysing the reaction composition and the palladium species that diffused through the membrane. Neither TEM nor ICP analysis supported this scenario. Finally, we tested whether or not palladium(II) ions could be leached in the presence of PhI by oxidative addition and the formation of [Pd(II)ArI] complexes. Using mass spectrometry, UV-visible spectroscopy and 13C NMR spectroscopy, we observed and monitored the formation and diffusion of these complexes, which showed that the first and the third mechanistic scenarios were both possible, and were likely to occur simultaneously. Based on these findings, we maintain that palladium nanoparticles are not the true catalysts in C--C coupling reactions. Instead, catalysis is carried out by either palladium(0) atoms or palladium(II) ions that leach into solution.     

The Coordination Polyhedra PdX n (X = Cl,Br, I) in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analysis of 106 compounds containing palladium atoms surrounded by halogen atoms. Depending on the oxidation number (2 or 4), Pd atoms can bind 4 to 6 X atoms (X = Cl, Br, I) and form PdX _n coordination polyhedra shaped like octahedra or square pyramids (n = 6), square pyramids (n = 5), or squares (n = 4). A lone electron pair on Pd(II) was found on the basis of X-ray diffraction data. The influence of the palladium valence state on the key stereochemical features of palladium halide complexes is considered in terms of the 18-electron rule. The tendency of palladium atoms to Pd···H aghostic interactions was noted.     

Dissolution of Palladium Deposited onto a Fibrous Carbon Cathode in Nitric Acid Solution through Operation of a Short-Circuited Electrochemical System

Dissolution in 3.5 M NHO₃ of palladium deposited onto a fibrous carbon electrode from hydrochloric and nitric acid solutions was studied. The factors influencing the dissolution of palladium in contact with the electrode were revealed using a model of short-circuited electrochemical system.     

Experimental indications for the existence of different states of palladium(0) at the surface of carbon paste electrodes

The deposition and dissolution of palladium(0) at non-modified carbon paste electrode (CPE) is studied in aqueous chloride solution. During the dissolution one or two Pd oxidation peaks are observed at + 0.1 V and about + 0.45 V vs. SCE, indicating the existence of different states of Pd⁰ at the CPE. In accordance with the experimental results it is assumed that a palladium monolayer is formed when low amounts of Pd are deposited and that multilayers are formed in the case of larger amounts of deposited palladium. The formation of a metal monolayers at CPE is described for the first time.     

Formation of palladium hydride complexes upon the reduction of Pd(II) by hydrogen

Conclusions The reduction of palladium(II) acetate by hydrogen in the presence of 1,10-phenanthroline or 2,2-dipyridyl gives palladium hydride clusters containing a massive metal-like nucleus with interstitial hydrogen atoms. The ligands are found to be peripheral palladium atoms, while the acetate groups are found in the external sphere.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2381–2384, October, 1985.The authors express their gratitude to S. G. Ellert for measuring the magnetic susceptibility and to A. L. Chuvilin for the electron microscopic data.     

Atomic Absorption Spectrophotometric Investigation and Determination of Palladium

This work aims to achieve a determinate characterization of compound formation and to find out the resolution to overcome chemical interferences in atomic absorption spectrophotometric (AAS) determination of palladium. The effect of flame composition in producing a neutral palladium atoms was investigated. A new analytical procedure has been elaborated for the determination of palladium.     

Synthesis and characterization of a new Tiara Pd(II) thiolate complex, [Pd(SC12H25)2]6, and its solution-phase thermolysis to prepare nearly monodisperse palladium sulfide nanoparticles

A new tiara Pd(II) thiolate complex, [Pd(SC12H25)2]6, has been synthesized and fully characterized by X-ray single crystal analysis, elemental analysis, MALDI, 1H NMR, powder XRD, IR, Raman, and UV/vis. It was found that, in each complex cluster, the six palladium atoms form a nearly planar hexagonal ring and the adjacent palladium atoms are bridged by sulfur atoms from both sides. Then the complex was further used as a single-source precursor to prepare nearly monodisperse palladium sulfide (PdS) nanoparticles through the high-temperature-induced decomposition in diphenyl ether. The obtained nanoparticles are 2.87 +/- 0.51 nm in diameter and protected by a layer of thiolate species on the surface.     

Palladium catalysts on porous nickel substrates for alcohol fuel cells

Parameters characterizing the active surface of catalytic palladium layers formed from mixed glycinate-chloride and ammonia complexes of palladium(II) were determined. Cyclic voltammetry on a rotating disc electrode was used to study the catalytic activity of nickel substrates and palladium layers in the reaction of methanol and ethanol oxidation in an alkaline medium. It was shown that electrodes with palladium deposited from mixed glycinate-chloride solutions have a higher catalytic activity that those formed from ammonia palladium(II) complexes.     

有机金属钯硅碳烷树状分子液晶配合物研究

树状分子具有规整结构,其分子体积、形状和功能基团可在分子水平上控制,金属有机树状分子及其超分子化学倍受关注［１］．含锌、铁、钴、镍、铂、钌或铑的金属有机树状配合物的研究已有报道［２,３］,但有机金属钯树状配合物则未见报道．传统的液晶分子为刚性棒状,按...     

Hydrogen diffusion transfer through an asymmetric three-layer vanadium membrane

Hydrogen diffusion transfer through a three-layer membrane has been studied within the framework of the lattice model under the Bragg?Williams approximation. A set of equations describing hydrogen transfer through a vanadium membrane coated with thin palladium layers has been derived taking into account the interactions of hydrogen atoms in the membrane layers. The obtained equations have been solved using the Mathcad-14 software package. It has been shown that the interaction between hydrogen atoms has a significant influence on hydrogen permeability at near-atmospheric pressures. It has been found that the permeability of the vanadium membrane is markedly higher than that of a palladium one at the same thickness. The effect of asymmetric vanadium membrane embrittlement has been shown to depend on the location of palladium layers with different thicknesses. The embrittlement of the vanadium membrane begins at higher pressures, when a thicker palladium layer is located at the inlet. It has been revealed that, for asymmetric membranes, the value of the diffusion flux of hydrogen atoms may depend on the transfer direction. At the same membrane thickness, the permeability of the asymmetric membrane is actually equal to that of a symmetrical membrane, provided that a thicker palladium layer is located at the inlet. At the opposite orientation, of the permeability of the asymmetric membrane is lower than that of the symmetric one.     

Smectic bimetallomesogens: synthesis, characterization and mesomorphic properties and the crystal structure of bis[N-(3-hydroxypropyl)-4-octanoylsalicylaldiminato]copper(II) complex

The synthesis, characterization and mesomorphic properties of copper(II), palladium(II), vanadyl(IV) and iron(III) chloride complexes derived from salicylaldimine structures are reported. The copper and palladium complexes exhibited smectic A phases, however vanadyl and iron chloride complexes showed crystalline phase. The palladium complexes have lower melting and clearing points, and a wider temperature range of mesophase. This lowering in clearing points between M = Pd and M = Cu analogues was attributed to the weaker core-core interaction between palladium centres within layers in the mesophase. The crystal and molecular structures of bis[N-(3-hydroxypropyl)-4-octanoylsalicylaldiminato]copper(II) were determined by means of X-ray analysis. This complex crystallizes in the monoclinic space group p21/c, with a = 5.4908(23) A, b = 19.847(5) A, c = 16.636(4) A, beta = 96.87(3) degree, and Z = 2. The intramolecular separation of Cu-Cu atoms is 3.022(3)A. The structure shows that the molecular shape is nearly flat with two copper atoms lying 0.067(4)A above and below the plane of N1, O1a, O1 and O2 atoms.     

Dynamic processes in silyl palladium complexes: evidence for intermediate Si-H and Si-Si sigma-complexes

The silyl palladium complexes (dcpe)PdH(SiHtBu2) and (dcpe)Pd(SiHMe2)2 display NMR spectra that vary with temperature. The dynamic NMR behavior is consistent with long-lived sigma-complexes as intermediates. In the case of (dcpe)PdH(SiHtBu2), the intermediate is believed to be a symmetric complex with doubly bridged hydrogen atoms between the silicon and palladium. Dynamic interchange of the two silicon atoms in (dcpe)Pd(SiHMe2)2 is consistent with an intermediate Si-Si sigma-complex.