Au Pd System Research Articles

Structural Construction of Au–Pd Nanocomposite for Alkali-Free Oxidation of Benzyl Alcohol

A bimetallic Au-Pd system is an alternative candidate to catalyze primary alcohol oxidation and is of crucial importance for the sustainable chemical industry. However, understanding the bimetallic system in terms of the nanostructure is still challenging. Herein, we adopt the in situ colloid immobilization to obtain a series of bimetallic AuxPdy/CNT samples supported by carbon nanotubes (CNTs). Elaborate characterizations confirmed the bimetallic structure of AuPd alloy particles with randomly dispersed Pd2+ on the surface, forming the AuPd@PdO structure on CNTs. Unlike the monometallic samples, bimetallic ones, particularly Au1Pd1/CNT, efficiently transformed benzyl alcohol in an alkali-free mild condition. The DFT simulation confirmed the electron-rich gold atoms as a steric and electronic regulator to confine the electron-deficient Pd atoms in alloy particles. The interacted metal sites in the alloy system activated the alcohol with optimized adsorption configuration. Surface Pd2+ transported active oxygen to capture the abstracted H on alcohol. The collaboration between metal sites facilitated the transformation of benzyl alcohol to benzaldehyde with the selectivity of 91.8% by a fast TOF of 1274 h-1 at only 80 °C.

Development of a ReaxFF potential for Au–Pd

The bimetallic alloys often outperform their single-component counterparts due to synergistic effects. Being widely known, the Au–Pd alloy is a promising candidate for the novel heterogeneous nanocatalysts. Rational design of such systems requires theoretical simulations under ambient conditions. Ab initio quantum-mechanical calculations employ the density functional theory (DFT) and are limited to the systems with few tens of atoms and short timescales. The alternative solution implies development of reliable atomistic potentials. Among different approaches ReaxFF combines chemical accuracy and low computational costs. However, the development of a new potential is a problem without unique solution and thus requires accurate validation criteria. In this work we construct ReaxFF potential for the Au–Pd system based on ab initio DFT calculations for bulk structures, slabs and nanoparticles with different stoichiometry. The validation was performed with molecular dynamics and Monte-Carlo calculations. We present several optimal parametrizations that describe experimental bulk mechanical and thermal properties, atomic order-disorder phase transition temperatures and the resulting ordered crystal structures.

Interface mechanical behavior of gold alloy wire bonding

The connection between the internal chip and external pins of the semiconductor package and the connection between the chip play an important role in establishing the electrical connection between the chip and the outside and ensuring the input/output between the chip and the outside. It is the key to the entire subsequent packaging process. Wire bonding has a dominant position in connection methods due to its simple process, low cost, and application of a variety of packaging forms. In high-reliability fields such as military and aerospace applications, bonding wires are usually used as chip interconnect materials. The bonding wires have good electrical conductivity, thermal conductivity, and oxidation resistance, but there are some reliability problems in bonding due to the production of Au-Al compounds. In this paper, Al element is used to modify the bonding alloy wire innovatively, the mechanical properties of Au-Al and Au-Pd system bonding points and the growth and evolution of IMC are studied, and the influence of Al and Pd elements on the reliability of bonding points is evaluated.

Combinatorial study of thermal stability in ternary nanocrystalline alloys

Nanocrystalline alloys can be stabilized through selective grain boundary segregation of specific solute element additions. Increasing attention is being paid to ternary and higher order systems, where complex interactions govern segregation. To efficiently study the large composition spaces of such systems, we apply a high-throughput combinatorial technique revealing nanocrystalline stability through composition-grain-size maps. We compare two systems with distinct binary and ternary alloy interactions: In Pt–AuAg both binaries are expected to be stable, whereas in Pt–AuPd the Pt–Pd binary is unstable and Au-induced co-segregation of Pd was previously reported. For ternary Pt–AuAg we find excellent thermal stability throughout. The Pt–AuPd system, by contrast, divides into an unstable regime, where Pd solute dominates and precipitates, and a stable regime, where Au solute dominates and retains Pd in the grain boundary. Overall, by combining current theory and the introduced combinatorial approach, stable multicomponent nanocrystalline composition spaces can be rapidly determined.

Thermodynamic Properties of Components in the Ag–Au–Pd System

The absence of consistent thermodynamic data on the systems Au–Pd, Ag–Pd, and Ag–Au–Pd prevents from interpreting the properties of alloys of these types. An approach was proposed to create models for calculating the characteristics of a ternary solid solution and binary solid solutions using a single computational apparatus. Data on the thermodynamic properties of alloys in the systems Au–Pd and Ag–Pd at certain temperatures from various experimental works and calculation models were generalized. The Redlich–Kister formalism was used to estimate the excess partial Gibbs energies and activities of components of a ternary solid solution in the Ag–Au–Pd system in the temperature range 400–1300 K. An algorithm was prepared to create calculation modules in programs for modeling natural mineral formation in systems containing Au, Ag, and Pd.

Optical Property–Composition Correlation in Noble Metal Alloy Nanoparticles Studied with EELS

Noble metals are currently the most common building blocks in plasmonics and thus define the available range of optical properties. Their alloying provides a viable strategy to engineer new materials with a tunable range of optical responses. Despite this attractive prospect, the link between composition and optical properties of many noble metal alloys is still not well understood. Here, electron energy-loss spectroscopy is employed to systematically study AuAg and AuPd nanoparticles of varying compositions. The localized surface plasmons, the bulk plasmons, and the permittivity functions of these two sets of alloys are investigated as functions of their composition. In the case of the more widely studied AuAg alloy system, good agreement is found with previous experimental and theoretical studies. The results on the less scrutinized AuPd system provide highly valuable experimental data that complements other experimental investigations and supports the development of theoretical models.

Order-disorder or phase-separation transition: Analysis of the Au-Pd system by the effective site energy model

Using a many-body interatomic potential for the Au-Pd system, we determine a bulk phase diagram which presents unexpected characteristics for a system with ordering tendency. Indeed, this system displays a miscibility gap between pure Pd and ${\mathrm{Au}}_{c}{\mathrm{Pd}}_{1\ensuremath{-}c}$ (with $c\ensuremath{\approx}0.2$) beyond the order/disorder critical temperature of the ${\mathrm{AuPd}}_{3}$ compound. Enthalpic and entropic contributions of the permutation free energy are determined via Monte Carlo simulations, in particular the vibrational entropy, which is in good agreement with direct calculation. Finally, the effective site energy model, recently developed to describe the thermodynamical forces driving the bulk phase diagram, is used to demonstrate that the miscibility gap in the Au-Pd system comes from competition between elastic and chemical effects.

Thermodynamic properties of Ag–Au–Pd alloys measured by a solid-state EMF method

Although the Ag–Au–Pd system is crucial for several industrial applications and for the research on fundamental physics, no thermodynamic data on this ternary system at low temperatures have been reported in the literature. In the present study, activities of silver are directly measured by employing a solid-state EMF method, by using AgI as the solid electrolyte. The EMF was determined using a galvanic cell $$ \left( - \right){\text{Pt}}\left| {\text{C}} \right.\left| {\text{Ag}} \right|{\text{AgI}}\left| {{\text{Ag-Au-Pd alloy}}} \right|{\text{C}}\left| {{\text{Pt}}\left( + \right)} \right. $$ , which produced novel experimental data on the thermodynamic properties of Ag–Au–Pd alloys. Darken method was used to calculate integral excess thermodynamic properties from the data. New thermodynamic characteristics, such as integral excess mixing Gibbs energy, entropy and enthalpy of the Ag–Au–Pd alloys, have been generated in a temperature range of 475 and 675 K. Isoactivity lines of silver in the system have been drawn throughout the Gibbs triangle. Thermodynamic properties of the binary Au–Pd alloys have been compared with the previous investigations.

Application of a parallel genetic algorithm to the global optimization of medium-sized Au\u2013Pd sub-nanometre clusters

To contribute to the discussion of the high activity and reactivity of Au–Pd system, we have adopted the BPGA-DFT approach to study the structural and energetic properties of medium-sized Au–Pd sub-nanometre clusters with 11–18 atoms. We have examined the structural behaviour and stability as a function of cluster size and composition. The study suggests 2D–3D crossover points for pure Au clusters at 14 and 16 atoms, whereas pure Pd clusters are all found to be 3D. For Au–Pd nanoalloys, the role of cluster size and the influence of doping were found to be extensive and non-monotonic in altering cluster structures. Various stability criteria (e.g. binding energies, second differences in energy, and mixing energies) are used to evaluate the energetics, structures, and tendency of segregation in sub-nanometre Au–Pd clusters. HOMO–LUMO gaps were calculated to give additional information on cluster stability and a systematic homotop search was used to evaluate the energies of the generated global minima of mono-substituted clusters and the preferred doping sites, as well as confirming the validity of the BPGA-DFT approach.

Seed-mediated co-reduction in a large lattice mismatch system: synthesis of Pd-Cu nanostructures.

Metal nanoparticles (NPs) are of interest for applications in catalysis, electronics, chemical sensing, and more. Their utility is dictated by their composition and physical parameters such as particle size, particle shape, and overall architecture (e.g., hollow vs. solid). Interestingly, the addition of a second metal to create bimetallic NPs adds multifunctionality, with new emergent properties common. However, synthesizing structurally defined bimetallic NPs remains a great challenge. One synthetic pathway to architecturally controlled bimetallic NPs is seed-mediated co-reduction (SMCR) in which two metal precursors are simultaneously co-reduced to deposit metal onto shape-controlled metal seeds, which direct the overgrowth. Previously demonstrated in a Au-Pd system, here SMCR is applied to a system with a larger lattice mismatch between the depositing metals: Pd and Cu (7% mismatch for Pd-Cu vs. 4% for Au-Pd). Through manipulation of precursor reduction kinetics, the morphology and bimetallic distribution of the resultant NPs can be tuned to achieve eight-branched Pd-Cu heterostructures with Cu localized at the tips of the Pd nanocubes as well as branched Pd-Cu alloyed nanostructures and polyhedra. Significantly, the symmetry of the seeds can be transferred to the final nanostructures. This study expands our understanding of SMCR as a route to structurally defined bimetallic nanostructures and the synthesis of multicomponent nanomaterials more generally.

Palladium modified gold nanoparticles as electrocatalysts for ethanol electrooxidation

Resemblin, g core-shell electrocatalysts consisting of a Au core and Pd shell (Au@Pd) are synthesized via a Cu underpotential deposition (UPD)-Pd-displacement method. The Pd shell is non-uniform consisting of tiny Pd clusters with a coverage of 0.5–0.6. The ethanol oxidation reaction (EOR) activity of this kind of structure is much higher than Pd/C in an alkaline solution. The forward peak current density of Au@Pd is 5.4 times higher than that of Pd/C. Furthermore, the onset potential for EOR of the former is ∼100 mV more negative. An interesting particle size dependent EOR activity is also observed. With increasing the Au particle size (2.9, 5.8 and 6.5 nm), the EOR activity increases. The strain and ligand effects from the Au core, together with the bifunctional reaction mechanism in the Au–Pd system may be reasons for the enhanced activity in Au@Pd catalysts.

Preparation of an Aurylated Alkylthiophene Monomer via C-H Activation for Use in Pd-PEPPSI-iPr Catalyzed-Controlled Chain Growth Polymerization.

In the search for new synthetic routes toward greener and more facile syntheses of conjugated polymers, C-H functionalization provides a promising solution by minimizing the production and processing of aryl halide monomer precursors used in traditional organometallic coupling reactions. In this paper, we investigate the use of Au(I) and its ability to directly C-H activate 2-bromo-3-hexylthiophene to form a reactive monomer species, bypassing the typical Grignard monomer formation from a dihalogenated thiophene. Addition of Pd-PEPPSI-iPr as a palladium catalyst source in the presence of the resultant aurylated thiophene monomer yielded poly(3-hexylthiophene) as observed by both NMR and GPC. Studies on the growth of these polymers show linear dependence between Mn and monomer conversion, low dispersities, as well as Mn predicted by catalyst loading, which is supportive of a living-type chain growth mechanism. This Au-Pd system represents a novel methodology for incorporating C-H activation into the synthesis of P3HT with control over Mn.

Seeding a New Kind of Garden: Synthesis of Architecturally Defined Multimetallic Nanostructures by Seed-Mediated Co-Reduction

Bimetallic nanoparticles display unique optical and catalytic properties that depend on crystallite size and shape, composition, and overall architecture. They may serve as multifunctional platforms as well. Unfortunately, many routes toward shape and architecturally controlled bimetallic nanocrystals yield polydisperse samples on account of the challenges associated with homogeneously nucleating a defined bimetallic phase by co-reduction methods. Developed by the Skrabalak laboratory, seed-mediated co-reduction (SMCR) involves the simultaneous co-reduction of two metal precursors to deposit metal onto shape-controlled metal nanocrystalline seeds. The central premise is that seeds will serve as preferential and structurally defined platforms for bimetallic deposition, where the shape of the seeds can be transferred to the shells. With Au-Pd as a model system, a set of design principles has been established for the bottom-up synthesis of shape-controlled bimetallic nanocrystals by SMCR. This strategy is successful at synthesizing symmetrically stellated Au-Pd nanocrystals with a variety of symmetries and core@shell Au@Au-Pd nanocrystals. Achieving nanocrystals with high morphological control via SMCR is governed by the following parameters: seed size, shape, and composition as well as the kinetics of seeded growth (through manipulation of synthetic parameters such as pH and metal precursor ratios). For example, larger seeds yield larger nanocrystals as does increasing the amount of metal deposited relative to the number of seeds. This increase in nanocrystal size leads to red-shifts in their localized surface plasmon resonance. Additionally, seed shape directs the overgrowth process during SMCR so the resultant nanocrystals adopt related symmetries. The ability to tune structure is important due to the size-, shape- and composition-dependent optical properties of bimetallic nanocrystals. Using this toolkit, the light scattering and absorption properties of Au-Pd octopods, 8-branched nanocrystals, could be tuned and were shown to be highly sensitive to changes in refractive index. The refractive index sensitivity displayed a linear correlation to the localized surface plasmon resonance initial position, where the sensitivity is greater than that of monometallic Au structures. Due to their bimetallic composition and unique architecture enabled by SMCR, Au-Pd octopods are promising refractive index based sensors. This Account summarizes the underlying principles for synthesis of bimetallic nanocrystals by SMCR, which have been established by systematic manipulation of synthetic parameters in a model Au-Pd system. These principles are anticipated to be general to other bimetallic systems, allowing for the design and synthesis of new nanocrystals with fascinating optical and catalytic properties.

Nucleation and growth of Au and Au–Pd nanoparticles at the beginning of electrochemical deposition

Gold and gold–palladium nanodeposits were obtained by pulse electrolysis in dimethylformamide with 4×10−3M HAuCl4 and in dimethyl sulfoxide solution with a mixture of 4×10−3M HAuCl4 and 4×10−3M PdCl2, respectively. Isolated gold nanoparticles of about 15nm in diameter were found by SEM observation after 6ms of electrochemical deposition. Three pulse and pause periods with duration of 6ms and 300ms respectively led to an increase in the particle size approximately two times. In case of gold-palladium deposition, no particles were detected after 10 electrochemical cycles while after 50 cycles 10–35nm nanoparticles were found. Detailed SEM analysis of electrode surface suggested that at the beginning of electrochemical deposition the growth of gold/nucleation of gold–palladium NPs is a preference for mono-Au/bimetallic Au–Pd system.

Surface segregation in AuPd alloys: Ab initio analysis of the driving forces

In order to determine the energetic driving forces for surface segregation in AuPd alloys, we use a combined approach coupling ab initio calculations and an analysis via an effective Ising model. Previously, this approach has been used successfully in the framework of N-body interatomic potentials to study the surface segregation in both semi-infinite alloys and nanoparticles, allowing one to determine the relative contributions of the different elementary driving forces. Here, we go beyond the use of N-body interatomic potentials by using ab initio calculations to evaluate the segregation enthalpy and the effective pair interactions, the contribution due to the size difference between the constituants being still obtained by N-body interatomic potentials. We show that the decomposition of the segregation enthalpy into its different elementary contributions is still valid at this level of description. This allows us to analyze the segregation driving forces in the two infinite dilute limits of the Au–Pd system, for both (100) and (111) surfaces. Finally, between the two infinite dilute limits, we find that our results are consistent with existing experimental data.

Chiral Ligand-Protected Bimetallic Nanoclusters: How does the Metal Core Configuration Influence the Nanocluster’s Chiroptical Responses?

ABSTRACTWe here present electronic structures and chiroptical responses of gold-based bimetallic nanoclusters protected by chiral thiolate ligand, glutathione (GSH), and compare them with those of monometallic counterparts. The nanoclusters examined are AuPd and AuAg bimetallic systems. The effect of Pd or Ag doping on the chiroptical responses of optically active Au nanoclusters as well as the importance of the bimetallic core configurations are discussed. Briefly, we find that GS-protected AuPd or AuAg nanoclusters exhibit quite different Cotton effects from those of the monometallic nanoclusters in metal-based electronic transition regions. In the AuPd system, all bimetallic nanoclusters exhibit featureless absorption profiles, but their circular dichroism (CD) signals are structured, offering a greater advantage in detecting a foreign atom doping in the nanocluster system. In the AuAg system, the nanocluster compounds exhibit relatively weaker CD responses than those of the corresponding Au compounds. This CD decrease can be explained in terms of the increased geometrical isomers that are formed by statistical distribution of Ag heteroatoms in the nanocluster, since an increased number of possible configurations gives an average in the CD response with positive and negative bands of different optical isomers.

Effects of Zr, Mo and Y-Doping on Microstructure and Mechanical, Electrical Properties of Au-Pd Binary Alloy

Abstract Au-Pd alloys doped with Zr, Mo and Y, respectively, were prepared in a vacuum high frequency melting furnace. The effects of rare metal doping on Microstructure and mechanical, electrical properties of the binary alloy was investigated. X-ray diffractometer and metallographic microscopy were employed to detect the microstructures. Electric bridge and eddy current conductive instrument were employed to test the electrical resistivity and the mechanical properties of alloys were tested by AG-X100KN type tensile testing machine. The results show that adding rare metal elements into Au-Pd system could refine microstructure effectively, increase the melting point, density and electrical resistivity of the alloy, and improve mechanical properties, but the processing property of the alloy is decreased.

Seed-Mediated Co-reduction: A Versatile Route to Architecturally Controlled Bimetallic Nanostructures

Gold-palladium octopods and new concave and shape-controlled alloy nanostructures are synthesized by seed-mediated co-reduction, wherein two metal precursors are reduced in the presence of seeds that serve as preferential sites for the growth of the larger nanostructures. Here, the first comprehensive study of this technique is presented in a model Au-Pd system and provides insight into the mechanism of formation for these architecturally distinct nanocrystals. A systematic evaluation of synthesis conditions decoupled the roles of (i) Au:Pd precursor ratio, (ii) reaction pH, and (iii) capping agent concentration in morphology development. These factors provide control of growth kinetics and ultimately the morphology and composition of the final nanostructures. Significantly, elucidating the overgrowth processes during seed-mediated co-reduction will lead to the synthesis of other architecturally controlled bimetallic nanocrystals.

Formation of Bimetallic Au–Pd and Au–Pt Nanoparticles under Hydrothermal Conditions and Microwave Irradiation

The reduction of chlorocomplexes of gold(III) from muriatic solutions by nanocrystal powders of palladium and platinum at 110 and 130 °C under hydrothermal conditions and the action of microwave irradiation has been investigated. The structure and composition of the solid phase have been characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and chemical methods. Bimetallic particles with a core-shell structure have been revealed. The obtained particles are established to have a core of the metal reductant covered with a substitutional solid (Au, Pd) solution in case of palladium, and isolated by a gold layer in the case of platinum. The main reason for such a difference is the ratio between the rates of aggregation and reduction. It has been shown by the example of the Au-Pd system that the use of microwave irradiation allows us not only to accelerate the synthesis of particles but also to obtain more homogeneous materials in comparison with conventional heating.

Characterization of Bimetallic Systems with UPS and PAX: Gold on Platinum and Palladium Surfaces

In the present study the thermal behavior of ultrathin Au films deposited on different noble metal single crystal surfaces was studied by means of ultraviolet photoelectron spectroscopy and photoemission of adsorbed xenon. The primary goal of this work was to demonstrate the power of photoemission of adsorbed xenon as an easy to handle and very surface sensitive technique for the characterization of multi-component systems. All investigated systems, Au–Pt(111), Au–Pd(111) and Au–Pd(110) show a particular dependence of their electronic and structural properties on the annealing temperature. Au multilayer films with a thickness of 3 monolayer prepared at 150 K undergo in all cases a smoothening by annealing up to room temperature. While on Pd this effect is mainly detectable on the topmost atomic layer the ordering process on Pt is also affecting the deeper layers. Further annealing of the Au–Pd system to 450 K and the Au–Pt system to 750 K, respectively, results in the onset of the alloying process at the interface between metal film and substrate. After annealing to 650 and 950 K, respectively, the alloying finally extends to the very surface. The complete loss of Au from the surface can be detected at 1050 K on Pd and at 1150 K on Pt. The orientation of the substrate has only a weak influence, showing up e.g. in additional electronic states of the not alloyed Au–Pd(111) and Au–Pd(111) systems. Adsorption of CO as a probe molecule illustrates the formation of different adsorption sites on the bimetallic systems during the Au diffusion process.