Formation and structural characteristics of Pd–Ag/SiO2 and Pd–Cu/SiO2 catalysts synthesized by cogelation

Pd–Ag/SiO₂ and Pd–Cu/SiO₂ xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of either Pd and Ag or Pd and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). After an extensive study of the influences of synthesis operating variables over structural characteristics of gels, highly dispersed bimetallic Pd–Ag/SiO₂ and Pd–Cu/SiO₂ xerogel catalysts were obtained. These samples are then composed of completely accessible Pd–Ag and Pd–Cu alloy crystallites with sizes of 2–3.5 nm located inside silica particles exhibiting a monodisperse microporous distribution. It appears also that the metal complex acts as a nucleation agent in the formation of silica particles.     

Preparation and optical properties of silicate glasses containing Pd nanoparticles

We report the space selective precipitation of Pd nanoparticles in Pd²⁺-doped silicate glass by ultrashort laser pulses irradiation and further annealing. Absorption spectra, transmission electron microscopy, refractive index measurement and Z-scan technique demonstrated that metallic Pd nanoparticles were precipitated in the glass sample after irradiation by an 800-nm femtosecond laser and subsequent annealing at 600 °C. We discuss a refractive index change and nonlinear absorption that combines the precipitation of Pd nanoparticles.     

Bias sputter deposition of PdAuSi and PdSi: Composition and thermal behavior

Amorphous films of PdAuSi and PdSi were prepared by bias sputter deposition. Variation of the substrate bias voltage used in rf sputter deposition of PdAuSi films produced changes in chemical composition and thermal behavior as observed by differetial scanning calorimetry. The amount of Ar incorporated during sputtering initially increases with increasing bias voltage, then decreases to a minimum at approximately ?200 V and increases rapidly thereafter. Amorphous films of the binary alloy PdSi were prepared by both rf and dc sputter deposition at a single substrate bias voltage of ?200 V. The heats of crystallization of the ternary sputter deposited films were within 10–20% of those of melt-quenched alloys with similar compositions.     

Effects of metal precursor in the sol–gel synthesis on the physicochemical properties of Pd/Al2O3–CeO2 catalyst: CO oxidation

The object of this research was to investigate the effects of various precursors and different fabricating procedures of Pd/Al₂O₃–CeO₂ catalysts by the sol–gel method. The physicochemical properties and structures of catalyst were characterized with BET surface area, X-ray powder diffraction (XRPD), and scanning electron microscopy (SEM). The performance of the Pd/Al₂O₃–CeO₂ catalyst was also evaluated by CO oxidation tests with a continuous quartz reactor. The results indicated that the catalyst prepared with inorganometallic precursors showed a high dispersion of Pd, large surface area and pore volume, and a high activity in CO oxidation. The higher redox interaction between Pd and Ce of the support starting with inorganometallic precursors, as determined from X-ray powder diffraction, is suggested as being responsible for such a catalytic behavior.     

Effect of temperature on the extraction of Pd by liquid tin from molten borosilicate glass containing simulated radwaste

Separation of Pd from borosilicate glass-melt containing simulated high level radioactive waste (Pd, Mo, Cs, Sr, Zr, Nd, Ni, Fe) using Sn as the solvent metal was studied on lab scale. The separation of Pd was studied using varying amounts of Sn, and the percentage of extraction of Pd and other elements was investigated by varying the process temperature and the starting material for Pd. The process temperature was observed to have a profound influence on the separation of Pd from the glass melt to the metallic tin phase. The % extraction of Pd was found to be less for the batches heat-treated at temperatures below 900 °C. The decrease in the % extraction was due to the entrainment of Pd in the glass phase for the samples heat-treated at low temperatures. The entrainment of Pd leads to the formation of Pd-rose like structures in the glass phase as observed by SEM and EDAX. Similarly, Mo, Fe and Na also formed separate phases inside glass matrix when the samples were heated below 900 °C. However, entrainment was not seen when the samples were heat-treated above 1050 °C in Ar. At 1200 °C, a recovery of about 99% of Pd was obtained. The formation of a PdSn₄ type intermetallic phase was noticed in tin metallic phase. The extraction behavior of Pd in borosilicate glass melt was also studied by using Pd(NO₃)₂ instead of Pd powder as staring material, and the results showed that the process temperature is the key determinant of the extraction behavior of Pd.     

Chemical Deposited Pd on GaAs

The chemical deposition of palladium on n and p‐GaAs from an aqueous solution of PdCl₂, in strong acid medium can be an alternative technique for contacts on GaAs. This paper presents the variations of palladium films thickness (measured by an interferometric method) as a function of solution concentration, reaction time and substrate conductivity. There are presented data concerning the adhesion of palladium films (measured by a mechanical method) related to the film thickness. From a comparative study concerning the adhesion of evaporated films such as: Au/n‐GaAs, Ag/n‐GaAs, AuGe/n‐GaAs and Pd/n‐GaAs, it results the conclusion that the adhesion of palladium films are of the same order of magnitude as the metallic films evaporated without an annealing procedure.     

Palladium (II) compounds with diaminocarboxylic acids: Crystal structures of [Pd(H2Cdta)] · H2O, [Pd(H3Edtp)Cl] · 2H2O, and (H6Edtp)[PdCl4] · 4H2O

The crystal structures of three Pd(II) compounds with diamine tetracarboxylates in different protonation states are determined, namely, [Pd(H₂ Cdta)] · H₂O (I), [Pd(H₃ EdtpCl] · 2H₂O (II), and (H₆ Edtp)[PdCl₄] · 4H₂O (III) (R ₁ = 0.0230, 0.0313, and 0.0277 for 3040, 3377, and 3809 reflections with I > 2σ(I) for I–III, respectively). Crystals I and II are built of neutral complexes [Pd(H₂ Cdta)] and [Pd(H₃ Edtp)Cl], respectively, and crystallization water molecules. Crystal III consists of [PdCl₄]²⁻ anionic complexes, H₆ Edtp ²⁺ cations, and water molecules. In I, one of the protonated acetate groups of the H₂ Cdta ²⁻ ligand forms a very weak additional Pd-O bond [2.968(2) Å] over the 2N + 2O coordination square. In II and III, the protonated propionate groups of the H₃ Edtp ⁻ ligand and the H₆ Edtp ²⁺ cation are not involved in Pd coordination and the coordination squares consist of the 2N + O + Cl and 4Cl atoms, respectively. __________ Translated from Kristallografiya, Vol. 48, No. 2, 2003, pp. 278–282. Original Russian Text Copyright ? 2003 by Polyakova, Poznyak, Sergienko.     

Growth of (Perylene)2 [Pd(mnt)2] crystals

The conditions for the growth of (Perylene)₂ [Pd(mnt)₂] crystals either by chemical oxidation and electrochemical routes are described. The electrocrystallisation is limited by close proximity of the oxidation potentials of the perylene donor and [Pd(mnt)₂]^? anion, and depending on the experimental conditions different morphologies can be obtained. (Per)₂ [Pd(mnt)₂] crystals obtained by elecrocrystallisation were found to be mainly of the β-polymorph with properties comparable to the Cu, Ni and Pt analogues previously described at variance with those obtained by chemical oxidation which are mainly of the α-polymorph .     

Influence of minor addition of Pd, Ag or Au on the microstructural evolution of mechanically alloyed Zr-Ni alloys

In this work, the influence of minor addition of Pd, Ag or Au (1 at.%) on the microstructural evolution of Zr-Ni alloys during mechanical alloying has been investigated using X-ray diffraction and differential scanning calorimetry. The experimental results show that the minor addition of Pd, Ag or Au has no significant influence on the amorphization process and glass forming ability of Zr-Ni amorphous alloys. In comparison with Ag and Pd, the minor addition of Au can enhance the mechanical and thermal stability of the mechanically alloyed Zr-Ni alloy. Discussion has been made based upon the evolution of the nearest-neighbor distance of atoms with increasing milling time.     

Phenylacetylene half-hydrogenation with Pd supported on vitreous materials having different chemical compositions

Pd metal has been supported on vitreous materials prepared by the gel route. Three supports with different chemical compositions of the SiO₂, Al₂O₃ and Na₂O systems were prepared; the corresponding catalysts, performed with very similar degrees of metal dispersion and Pd loading, have been used in the half-hydrogenation of phenylacetylene at different H₂ pressures. The results display an analogous behaviour with modest changes of the catalytic properties on changing the chemical composition of the support. The relatively better catalytic activity of the catalyst with smaller alkaline content is discussed in terms of the possible electronic shift from the metal to the support.     

The growth of Pd thin films on a 6H-SiC(0 0 0 1) substrate

Pd thin films, grown on Si-rich 6H-SiC(0 0 0 1) substrates, were studied by atomic force microscopy, electron diffraction and high-resolution transmission electron microscopy. It is concluded that the growth is successful only when all the growth process takes place at room temperature. Under these conditions a very good epitaxial growth of Pd is achieved, despite the large misfit (about 8.6%) between Pd and the substrate and the existence of a semi-amorphous layer between the thin film and the substrate. A large number of twins appear in these films.     

Spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated bis(acetylacetonato)palladium(II)

This paper reports on a theoretical analysis of spin‐Hamiltonian parameters and local lattice structure for Pd(I) center in γ‐irradiated Pd(II)(acac)₂. Through the crystal‐ and ligand‐field theory, the microscopic spin‐Hamiltonian parameters and local molecular structure for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system have been studied by using the high‐order perturbation formulas and Newman's superposition model. Based on these calculations, it was found that the distance of the metal‐ligand bonds in the square planar complex for Pd(I) center in the γ‐irradiated Pd(II)(acac)₂ system increases by 0.1Å. To understand the detailed physical and chemical properties of the [Pd(I)(acac)₂]^2– complex, the contributions of the spin‐orbit coupling of ligand to spin‐Hamiltonian parameters for Pd(I) ion are considered. The theoretical results are in reasonable agreement with the experimental values. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

XPS study of glassy Pd80Ge20

An X-ray photoemission and Auger electron spectroscopy study of the electronic structure of Pd₈₀Ge₂₀ alloy in its glassy and crystalline states is reported. The glassy state shows some modifications in the valence band structure, symmetry of the Pd $\text{3}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{?3}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ spin-orbit doublet and a shift in M₄₅-V-V Auger transition of Pd. Analysis of the chemical shifts in the core-level binding energies of the constituents indicates negligible charge transfer from the metalloid atom (Ge) to d-band of the Pd.     

Transparent oxide semiconductors based on TiO2 doped with V,Co and Pd elements

In this work, investigations of electrical and optical properties of as-deposited thin films of TiO₂ doped with Pd, Co and V elements prepared by the low-pressure hot-target reactive magnetron sputtering have been outlined. Results allowed to find out how selected properties of TiO₂ had changed from oxide non-conductor to oxide-semiconductor with desired p- or n-type electrical conduction due to the incorporation of the metal components, mentioned above.     

A single-crystal X-ray diffraction study of an Al70.5Pd21Mn8.5 icosahedral quasicrystal

X-ray diffraction data were measured on a single grain of a stable Al_70.5Pd₂₁Mn_8.5 perfect quasicrystal, in order to complement the neutron diffraction data obtained previously. The F-type lattice structure of the six-dimensional periodic arrangement was confirmed along with the very strong chemical order, due basically to an uneven distribution of the Pd atoms among the lattice sites. This distribution might be the origin of the high stability of the icosahedral structure in this system.     

Physical properties of the liquid Pd–18 at.% Si alloy

The temperature dependence of the density, the viscosity, the ultrasound velocity and attenuation and the magnetic susceptibility of the Pd–18 at.% Si alloy in liquid state have been measured. A difference during heating and subsequent cooling with a branching temperature at 1380–1430 K was observed for all measured quantities. An abnormally high attenuation of ultrasound was furthermore observed during several hours after that the sample was melted. The results are interpreted in terms of metastable inhomogeneities existing in the melt.     

Grain refinement in the solidification of undercooled Ni–Pd alloys

Two bulk Ni–Pd alloys Ni₇₅Pd₂₅ and Ni_54.8Pd_45.2 have been undercooled beyond their hypercooling limits. As undercooling increases, two grain refinements, occurring at low and high undercooling, respectively, were observed in the solidification of both alloys, even though the equilibrium crystallization temperature range of the latter is only 5 K. Reaching of the hypercooling limit did not change the microstructural morphology abruptly, and dendritic substructure could still be found in the refined grains. Such experimental results cannot be interpreted satisfactorily by the theory that the break-up of dendrites during solidification is dominated by capillary force. It is proposed that the grain refinement at low undercooling results from the remelting associated with chemical superheating, but that at high undercooling is due to the post-solidification recrystallization.     

Crystallization of metastable phases in the Pd83Si17 amorphous alloy

The crystallization of the Pd₈₃Si₁₇ amorphous alloy started by formation of small crystallites. By comparisons of selected area electron diffraction patterns from the crystallites and patterns calculated from generated models we found that the first observed structures coincide with long range vacancy ordered structures derived from CsCl-type structure, known as τ-structures. The Pd atoms are in the corners and the Si atoms or vacancies are in the centers of basic cubic cell, respectively. It is possible to interpret the formation of these transition structures as consequence of occurrence of small areas with different chemical composition present in original amorphous structure as a result of rapid quenching. After ageing the τ-structures transform by diffusion to the stable Pd₉Si₂ structure.     

On the anomalies in density,Young's modulus and glass temperature of PdSi glasses

The densities, Young's moduli and glass transition temperatures have been measured for binary PdSi glassy alloys. These glassy alloys exhibit a negative deviation from Vegard's law an enhancement in Young's modulus and a tendency to lower the glass transition temperature in the region of the eutectic composition. The observed nonlinearity in these physical properties is shown to be better agreement with an alloy mixing effect rather than the structural ordering model.     

Photoacoustic Spectroscopical Studies on L-Tyrosine and Pd(Tyr)2Cl · H2O Complex Crystal

The complex crystal of Pd(Tyr)₂Cl · H₂O was synthesized and its PA spectra (with L-tyrosine) were determined and explained. A method used to resolve the PA amplitude spectrum was suggested. With the phase spectrum of the complex, the PA absorption peaks were resolved by this method, and the non-radiative relaxation time of all absorption bands were calculated.