Palladium Content Research Articles

Aqueous co-precipitation of Pd-doped cerium oxide nanoparticles: chemistry, structure, and particle growth

Nanoparticles of palladium-doped cerium oxide (Pd–CeO2) have been prepared by aqueous co-precipitation resulting in a single phase cubic structure after calcination according to X-ray diffraction (XRD). Inhomogeneous strain, calculated using the Williamson–Hall method, was found to increase with palladium content, and the lattice contracts slightly, relative to nano-cerium oxide, as palladium content is increased. Moreover, high resolution transmission electron microscopy reveals some instances of defective microstructure. These factors combined imply that palladium is in solid solution with CeO2 in these nanoparticles, but palladium (II) oxide (PdO) peaks in the Raman spectra indicate that solid solution formation is partial and that highly dispersed PdO is present as well as the solid solution. Nevertheless, the addition of palladium to the CeO2 lattice inhibits the growth of the 6% Pd–CeO2 particles compared to pure CeO2 between 600 and 850 °C. Activation energies for grain growth of 54 ± 7 and 79 ± 8 kJ/mol were determined for 6% Pd–CeO2 and pure CeO2, respectively, along with pre-exponential Arrhenius factors of 10 for the doped sample and 600 for pure cerium oxide.

Separation, Preconcentration, and Recovery of Pd(II) Ions using Newly Modified Silica Gel with Bis(3-Aminopropyl)Amine

Bis(3-aminopropyl)amine bonded silica gel (BAPA-SG) was synthesized and characterized by elemental analysis and FT-IR spectroscopy, and tested for adsorption, preconcentration, and recovery of Pd(II) ions. The effective parameters on the preconcentration of Pd(II) ions such as pH, volume, and flow rate of the Pd(II) solution, and the type and volume of eluent solution, and also matrix ions such as alkaline and heavy metals were investigated. Flame atomic absorption spectrometry was used for the determination of Pd(II) concentration. The modified silica gel could adsorb Pd(II) ions quantitatively from the solutions up to 400 mL at pH 1.0 by the flow rate of 5 mL/min. The retained Pd(II) ions could be easily eluted by using 5 mL of 1% (m/v) thiourea in 1.0 M HCl solution. The recovery of Pd(II) ions was 95 ± 2% at 95% confidence level. The analytical detection limit of Pd was found to be 0.36 µg L−1 at the preconcentration factor of 80. Selective adsorption of Pd(II) ions over some base metal ions was also investigated. The developed method was applied to spent auto catalyst for palladium recovery, and a certified ore sample for the determination of palladium content.

PALLDIUM SUPPORTED MCM-41 MESOPOROUS MOLECULAR SIEVES: SYNTHESIS, CHARACTERIZATION AND CATALYTIC TEST FOR THE REDUCTION OF NO BY CO

Palladium supported MCM-41 molecular sieves with Si/Pd (molar) ratios of 400, 200, 100 and 50 were synthesized by hydrothermal method. All catalysts characterized by various analytical and spectroscopic techniques, viz, XRD, N2 sorption, TEM, DRUV-VIS, Raman. XRD at low angle and high angle studies suggest that the substitution of palladium and presence of palladium oxide phase in the silicate tetrahedral framework structure of MCM-41. TEM investigations confirm the highly ordered cubic structure with irregular distribution of palladium nanoparticles on surface PdMCM-41 . DRUV-VIS and Raman spectra studies indicate the presence of palladium oxide moieties in all PdMCM-41 catalysts. The effect of Si/Pd molar ratio, particle size and reusability with respect to reactor temperature on the catalytic activity of PdMCM-41 catalyst was examined. Comparative study of all these palladium substituted catalysts shows that PdMCM-41(50) catalyst having higher palladium contents shows higher activity at lower temperatures as compared with other PdMCM-41 ( Si/Pd = 100, 200, 400) catalysts.

Rapid Synthesis of Porous Honeycomb Cu/Pd through a Hydrogen‐Bubble Templating Method

A rapid electrochemical method based on using a clean hydrogen-bubble template to form a bimetallic porous honeycomb Cu/Pd structure has been investigated. The addition of palladium salt to a copper-plating bath under conditions of vigorous hydrogen evolution was found to influence the pore size and bulk concentration of copper and palladium in the honeycomb bimetallic structure. The surface was characterised by X-ray photoelectron spectroscopy, which revealed that the surface of honeycomb Cu/Pd was found to be rich with a Cu/Pd alloy. The inclusion of palladium in the bimetallic structure not only influenced the pore size, but also modified the dendritic nature of the internal wall structure of the parent copper material into small nanometre-sized crystallites. The chemical composition of the bimetallic structure and substantial morphology changes were found to significantly influence the surface-enhanced Raman spectroscopic response for immobilised rhodamine B and the hydrogen-evolution reaction. The ability to create free-standing films of this honeycomb material may also have many advantages in the areas of gas- and liquid-phase heterogeneous catalysis.

Thermoelectric power factor of In2O3:Pd nanocomposite films

A nanocomposite exhibiting large thermoelectric powers and capable of operating at temperatures as high as 1100 °C in air was fabricated by embedding palladium nanoparticles into an indium oxide matrix via co-sputtering from metal and ceramic targets. Combinatorial chemistry techniques were used to systematically investigate the effect of palladium content in these nanocomposite films on thermoelectric response. Based on these rapid screening experiments, the thermoelectric properties of the most promising nanocomposites were evaluated as a function of post-deposition heat treatment at high temperatures. An n-type nanocomposite film was developed exhibiting a power factor of 4.5 × 10−4 W/m·K2 at 1000 °C in air.

Pd–Fe nanoparticles stabilized by chitosan derivatives for perchloroethene dechlorination

A series of chitosan-stabilized Pd-NZVI (nano-zero-valent-iron) catalysts for dechlorination with variation in their composition and in the nature of the polymer has been prepared. The synthesis proceduresand palladium and chitosan contents were optimized. It was demonstrated by the XPS method that Fe and Pd in Fe–Pd/chitosan samples exist in the metallic state. The positive shift of the binding energy as compared with the bulk metal shows that the iron metal in the surface layers exists as very small nanoparticles. The prepared materials were characterized also by the XAS method. The presence of O and N atoms in the first coordination shell of the central Fe atom in the Fe–Pd/chitosan samples certifies the binding of the Fe metal particles with the chitosan surface via OH and NH 2 groups. The samples are characterized by the high stability of the nanoparticles as compared to unstabilized Pd-NZVI. The materials were tested to evaluate their catalytic activity in the perchloroethene (PCE) dechlorination reaction. Some samples of chitosan-stabilized Pd-NZVI revealed a good performance in PCE degradation as compared to unstabilized Pd-NZVI.

Formation, structure, and magnetic changes at annealing of films deposited by laser sputtering of Ni and Pd

The electron microscopy investigations of Pd, Ni, and Ni-Pd alloy films are carried out. The films were produced by laser sputtering of one- and two-element targets. It is shown that, in the case of alternate deposition of nickel and palladium, polycrystalline films with a metastable hcp lattice are formed. The hcp lattice parameters increase monotonically with increasing palladium content in the film. As a result of the annealing, Ni and Ni-Pd alloy films acquire an equilibrium fcc structure. A positive deviation from Vegard’s law occurs for the dependence of the lattice parameter of the solid solution on the Pd concentration. The as-prepared Ni and Ni-Pd alloy films with the hcp structure are characterized by the absence of a magnetic moment. The transition into the ferromagnetic state occurs after annealing, and hysteresis is observed upon magnetization reversal.

The Detection of Palladium Particles in Proton Exchange Membrane Fuel-Cell Water by Laser-Induced Breakdown Spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) using conditional data analysis was applied to aqueous suspensions of palladium particles in the reformate water of palladium-based proton exchange membrane fuel cells. A significant amount of palladium was found in the water, indicating degradation of the fuel-cell cathode catalytic layers. The palladium particle-size detection limit was found to be about 400 nm. Calibration procedures to quantify the palladium concentration are discussed.

Structure and magnetic state of the films deposited by laser ablation of composite nickel and palladium targets

Transmission electron microscopy, electron diffraction, and vibrating-sample magnetometry are used to show that a metastable hcp structure can form in both nickel and Ni-Pd alloy films during alternating sputtering of the Ni and Pd components of composite targets. The hcp lattice parameters increase monotonically when the palladium content in a sputtered target increases in the range 0–75%. The ratio of the hcp lattice parameters c/a is close to the ideal ratio for the hcp lattice (1.63) within the limits of experimental error. In the as-deposited state, nickel and Ni-Pd alloy films with an hcp structure have no magnetic moment. Upon annealing, the films transform into a ferromagnetic state with an fcc structure. The concentration dependence of the lattice parameter of the fcc solid solution a 0 is found to exhibit a positive deviation from Vegard’s law, which is characteristic of alloys with a concave liquidus line.

Synthesis, characterization, thermal studies, and DFT calculations on Pd(II) complexes containing N-methylbenzylamine

This work describes the synthesis, characterization, and the thermal behavior investigation of four palladium(II) complexes with general formulae [PdX2(mba)2], in which mba = N-methylbenzylamine and X = OAc− (1), Cl− (2), Br− (3) or I− (4). The complexes were characterized by elemental analysis, infrared vibrational spectroscopy, and 1H nuclear magnetic resonance. The stoichiometry of the complexes was established by means of elemental analysis and thermogravimetry (TG). TG/DTA curves showed that the thermodecomposition of the four complexes occurred in 3–4 steps, leading to metallic palladium as final residue. The palladium content found in all curves was in agreement with the mass percentages calculated for the complexes. The following thermal stability sequence was found: 3 > 2 > 4 > 1. The geometry optimization of 1, 2, 3, and 4, calculated using the DFT/B3LYP method, yielded a slightly distorted square planar environment around the Pd(II) ion made by two anionic groups and two nitrogen atoms from the mba ligand (N1 and N2), in a trans-relationship.

Highly Dispersed Palladium–Polypyrrole Nanocomposites: In‐Water Synthesis and Application for Catalytic Arylation of Heteroaromatics by Direct C–H Bond Activation

AbstractPd@PPy hybrid catalytic materials are synthesized in water via redox polymerization reaction of pyrrole with [Pd(NH3)4Cl2]. The nanocomposites formed are composed of highly dispersed palladium particles which are either zerovalent or easily reducible, and are embedded in spherical polypyrrole globules. A unique combination of high palladium dispersion (NP size: 2.4 nm) and elevated palladium content (35 wt%) is obtained. The components of these novel nanocomposites are characterized by means of FTIR, XPS, XRD, SEM, and TEM microscopy techniques. The process of formation in solution is also monitored using UV‐visible and DLS techniques. The application of these novel hybrid nanomaterials in the palladium‐catalyzed direct arylation of heteroaromatics is reported. High efficiency in C–C bond formation is obtained using these materials. Furans and thiophenes are arylated by using bromoarenes. Pd@PPy nanocomposites can efficiently couple n‐butyl furan and n‐butyl thiophene with bromobenzene and bromoquinoline, as well as with activated or deactivated electron‐poor and electron‐rich functionalized bromoarenes. Thus, a clean reaction process is developed that combines the absence of organic ligand in catalytic reactions and easy recovery of Pd@PPy nanocomposite via simple filtration. Preliminary kinetic and post‐catalysis studies suggest a molecular or colloidal soluble active species. These very active species are efficiently delivered by the nanocomposites and susceptible to a surprisingly uniform back redeposition within the polypyrrole support.

Topography and nanomechanical properties of Pd-C films

Abstract Atomic force microscopy (AFM) topographical studies and results of nanoindentation experiment for several palladium-carbon films (Pd-C film) deposited on various substrates and with varying palladium content are presented. Pd-C films were prepared by a physical vapor decomposition (PVD) process and next were modified by a chemical vapor decomposition (CVD) method to obtain carbonaceous porous structure with dispersed palladium nanograins and a variation in roughness. The dependence of film topography on the kind of substrate such as Al2O3, Mo polycrystalline foil and fused silica was studied by AFM. Nanomechanical properties such as hardness and the reduced indentation modulus were determined by nanoindentation. A comparison of these values for films with different Pd content deposited on various substrates is presented.

Effect of the chemical nature and concentration of palladium (II) precursors on the palladium deposition by atomic hydrogen electrochemically assisted

Pd deposits are obtained by applying −1.92 mA cm −2 during 180 min, employing 0.06 M PdCl 2 + 1 M HCl and 0.06 M PdCl 2 + 28% NH 3 solutions. Some features on Pd depositions using x M PdCl 2 + 1 M HCl ( x = 0.130, 0.060, 0.030, 0.025, 0.020 and 0.010) solutions are detailed. Based on roughness factor ( S) and deposition efficiency ( ɛ Pd) values, Pd deposition is more efficient using PdCl 2 + 1 M HCl than PdCl 2 + 28% NH 3 ( ɛ Pd = 99%, S = 6 in 1 M HCl vs. ɛ Pd = 17%, S = 3 in 28% NH 3). A highly rough Pd deposit ( S = 357) is obtained, by applying −1.92 mA cm −2 during 180 min, using a 0.020 M PdCl 2 + 1 M HCl solution.

The effect of quadrupole ICPMS interface and ion lens design on argide formation. Implications for LA-ICPMS analysis of PGE's in geological samples

The argide levels in laser ablation ICPMS were found to vary 30 times between commonly used quadrupole ICPMS, while other polyatomic interferences like oxides vary less than 3 times. Investigating important parameters revealed that the pressure between skimmer and extraction lenses is key to a low argide rate. The Agilent 7700x with a relatively high pressure due to the restricted gas flow and a small volume between skimmer and ion lenses has the lowest argide levels. The relatively high pressure allows more collisions and breaking apart of weakly bound argide ions. Apparent light PGE (ruthenium, rhodium and palladium) concentration from cobalt, nickel, copper and zinc argides was estimated to be up to 0.00025 times the metal concentration.

Impact of palladium substitution for copper in Bi2CuO4synthesized via sol-gel method

An extensive new solid solution was synthesized by substitution of Pd+2 for Cu+2 in Bi2CuO4 compound [J.-C. Boivin et al., C.R. Hebd. Seances Acad. Sci., Ser. C 276, 1105 (1973)]. Polycrystalline ceramic powder with formula Bi2CuPdxO4 were prepared by sol-gel method using (Bi, Cu, Pd) nitrates and pure citric acid. X-ray patterns show a single phase with tetragonal symmetry and space group P4/ncc (No. 130). In cases, the tetragonal cell c parameter and therefore the metal-metal distance (dM-M = c/2) increases linearly with increasing palladium concentration. Electrical conductivity measurements show that the resistivity decreases regularly with pd2+ substitution. It is possible to obtain materials with an ambient temperature conductivity ranging from 10-6 to 10-3 S cm-1.

Determination of platinum and palladium in dead catalysts using inductively coupled plasma atomic emission spectrometry after sample digestion by high-temperature fusion

A technique for the determination of platinum and palladium in dead catalysts using ICP-AES after sample digestion by high-temperature fusion with potassium pyrosulfate is described. The technique is universal; it offers the possibility to analyze various brands of catalysts and their mixtures at a content of platinum and palladium of 0.1% to whole units of percent in a short time. The accuracy of results of determination of platinum and palladium is confirmed by comparison with the data of interlaboratory control. The relative standard deviation in the developed technique is 4–2.5% for the content of platinum and palladium of 0.1 to 0.5% and 2–1% for higher concentrations of these elements.

XPS study of palladium sensitized nano porous silicon thin film

Nano porous silicon (PS) was formed on p-type monocrystalline silicon of 2–5 Ω cm resistivity and (100) orientation by electrochemical anodization method using HF and ethanol as the electrolytes. High density of surface states, arising due to its nano structure, is responsible for the uncontrolled oxidation in air and for the deterioration of the PS surface with time. To stabilize the material PS surface was modified by a simple and low cost chemical method using PdCl2 solution at room temperature. X-ray photoelectron spectroscopy (XPS) was performed to reveal the chemical composition and the relative concentration of palladium on the nanoporous silicon thin films. An increase of SiO2 formation was observed after PdCl2 treatment and presence of palladium was also detected on the modified surface. I–V characteristics of Al/PS junction were studied using two lateral Al contacts and a linear relationship was obtained for Pd modified PS surface. Stability of the contact was studied for a time period of around 30 days and no significant ageing effect could be observed.

Synthesis and characterization of recyclable and recoverable MMT-clay exchanged ammonium tagged carbapalladacycle catalyst for Mizoroki–Heck and Sonogashira reactions in ionic liquid media

An efficient synthesis of an ammonium tagged carbapalladacycle 5, in modest yield, has been achieved. Further, the clay-nanocomposite 6 was prepared by ion exchange of 5 into clay interlayers as a new organic–inorganic hybrid catalytic system. The ionic tag of the ammonium supported carbapalladacycle 5 assists in the pillaring process and enhances the organophilicity of catalyst 6 in the interlayers of clay. The catalytic activity in ammonium based ionic liquid [TMBA] NTf2 of both the homogeneous and heterogeneous recyclable catalysts 5 and 6 respectively in micromolar concentration of palladium has been tested for Mizoroki–Heck and Sonogashira reactions in good yields with high TON/TOF and negligible metal leaching. Effect of solvent and temperature on the catalytic activity has also been examined.

Investigation of modification of hydrogenation and structural properties of LaNi 5 intermetallic compound induced by substitution of Ni by Pd

The hydrogenation properties of the LaNi 5 (CaCu 5 type, hP6, P6/ mmm) and Pd substituted derivatives LaNi 5 −x Pd x compounds have been studied in the whole homogeneity range of the solid solution (0.25≤ x≤1.5). The pressure versus hydrogen content isotherms show several plateaus and an increase of the plateau pressure as a function of palladium concentration. The volume increase of the Pd substituted alloys should have resulted in a lowering, and not an increase, of the plateau pressure, according to the conventional models based on the size effect. In order to elucidate the origin of this anomalous behavior, both an experimental and a theoretical ab initio electronic structure investigation have been carried out. Experimentally, the nature and the structural properties of the hydrides have been studied by both in situ and ex situ neutron diffraction. The crystal structures of the three hydride phases are reported (LaNi 3.5Pd 1.5D 1.96, filled-up CaCu 5 type, P6/ mmm; LaNi 4PdD 2.72, LaNi 2(Ni 0.75Pt 0.25) 3H 2.61 type, oI128, Ibam; LaNi 4.75Pd 0.25D 5.67, partly ordered CaCu 5 type, P6 mm). In addition, the phase diagram of LaNi 5− x Pd x -H system has been investigated. The electronic and thermodynamic properties of both intermetallic compounds and the hydrides have been studied by ab initio electronic structure calculations. The theoretical results are in good agreement with our experimental data, and show that electronic interactions play a major role in the hydrogenation behavior of these Pd substituted intermetallic compounds, and that these effects cannot be accounted for by a simplistic model based on the size effect alone.

Direct room-temperature synthesis of a highly dispersed Pd nanoparticle catalyst and its electrical properties in a fuel cell

Highly dispersed palladium nanoparticles supported on bacterial cells were successfully prepared by a microbial method using the metal ion-reducing bacterium Shewanella oneidensis. Resting cells of S. oneidensis reduced soluble palladium(II) to insoluble palladium(0) at room temperature and neutral pH within 60 min when formate was provided as the electron donor. Transmission electron microscopy analysis of a thin section of S. oneidensis cells after exposure to a PdCl 2 solution revealed that palladium particles approximately 5–10 nm in size were deposited on the bacterial surface and in the periplasmic space. The initial concentrations of soluble palladium(II) and formate in the precursor solution strongly influenced the rate of palladium(II) reduction and the dispersity of biomass-supported palladium particles. The dried biomass-supported palladium was tested as an anode catalyst in a polymer electric membrane fuel cell for power production. The maximum power generation of the highly dispersed biomass-supported palladium particles was comparable to that of a commercial palladium catalyst.