Pd Core Shell Nanoparticles Research Articles

Theoretical study of Cu–Pd core–shell nanoparticles: structure, stability and electronic

Theoretical study of Cu–Pd core–shell nanoparticles: structure, stability and electronic

Electronic structure and catalytic activity of exsolved Ni on Pd core-shell nanoparticles.

This study reports first principles calculations performed to study the electronic structure and catalytic activity of exsolved Ni on Pd core-shell catalysts reported in recent experimental literature. The modification in the electronic and geometric properties of the Ni/Pd bimetallic system as successive layers of Ni are added on top of Pd is systematically investigated using the d-band model as well as the adsorption of O and CO on the surface of these core-shell structures. The results show that the adsorption of O and CO is more favourable on Ni/Pd core-shell catalysts compared to the pure Ni surface. As the dissociation of the O2 molecule into atomic oxygen and CO oxidation are key steps in metal-catalysed oxidation reactions, we have examined the energetics of O2 dissociation and CO oxidation reaction over the (111) faces of Ni as well as Ni/Pd structures. Our results suggest that both adsorption and dissociation are easier on Ni/Pd surfaces compared to a simple Ni surface. Unlike O2 dissociation, we find that CO oxidation is unfavourable on Ni/Pd in comparison to Ni. The energetics of both reactions follow Brønsted-Evans-Polanyi relationships where the activation energy is linearly related to the reaction energy for all surfaces studied here. We found that a single monolayer of Ni on Pd, due to the synergistic effect of geometric and electronic factors, is the most active among the surfaces studied here towards the adsorption and dissociation of O2. Both adsorption and dissociation become less favourable with an increase in the thickness of the Ni shell in these core-shell catalysts. A close analysis of the results indicates that both strain and ligand effects are active in the improved catalytic activity seen in Ni on Pd catalysts. Quite understandably, the ligand effect is only seen for the single monolayer of Ni on Pd and fades off as we go to two monolayers of Ni. The results reported here help us understand the connections between the electronic structure and catalytic activity of Ni/Pd core-shell nanoparticles, and these insights are expected to be useful in the development of core-shell catalysts.

Bimetallic Au-Pd nanoparticles supported on silica with a tunable core@shell structure: enhanced catalytic activity of Pd(core)-Au(shell) over Au(core)-Pd(shell).

A facile ligand-assisted approach of synthesizing bimetallic Au–Pd nanoparticles supported on silica with a tunable core@shell structure is presented. Maneuvering the addition sequence of metal salts, both Aucore–Pdshell (Au@Pd–SiO2) and Pdcore–Aushell (Pd@Au–SiO2) nanoparticles were synthesized. The structures and compositions of the core–shell materials were confirmed by probe-corrected HRTEM, TEM-EDX mapping, EDS line scanning, XPS, PXRD, BET, FE-SEM-EDX and ICP analysis. The synergistic potentials of the core–shell materials were evaluated for two important reactions viz. hydrogenation of nitroarenes to anilines and hydration of nitriles to amides. In fact, in both the reactions, the Au–Pd materials exhibited superior performance over monometallic Au or Pd counterparts. Notably, among the two bimetallic materials, the one with Pdcore–Aushell structure displayed superior activity over the Aucore–Pdshell structure which could be attributed to the higher stability and uniform Au–Pd bimetallic interfaces in the former compared to the latter. Apart from enhanced synergism, high chemoselectivity in hydrogenation, wide functional group tolerance, high recyclability, etc. are other advantages of our system. A kinetic study has also been performed for the nitrile hydration reaction which demonstrates first order kinetics. Evaluation of rate constants along with a brief investigation on the Hammett parameters has also been presented.

Au–Pd core–shell nanoparticle film for optical detection of hydrogen gas

Hydrogen use, as a clean and almost infinite energy source, has an economic impact in many industries. The problem is that this gas cannot be used like any gas because of its explosiveness at 4% in the air, hence the need to know its concentration any time for security reasons. The permanent detection of hydrogen leaks is essential to monitor and to control the hydrogen concentration to prevent any possible risk. In our current research, we have developed hydrogen ultrasensitive sensors by depositing a thin film of Au–Pd core–shell nanoparticles (NPs) on a transparent glass substrate in order to detect hydrogen in its gaseous form. The colloidal Au–Pd core–shell NPs were synthesized according to a multi-reduction step method. The structural characterizations, the nature, and the density of Au–Pd core–shell NPs have been characterized by scanning electron microscopy and transmission electron microscopy. The morphology, size, and structure of Au–Pd core–shell NPs can be controlled under synthesis conditions. The size of the core–shell studied in this work is 13 nm for gold NP diameter and 0 nm–2.3 nm for palladium thicknesses. The physical properties of NPs, such as the optical absorbance response under hydrogen, strongly depend on the nature of the shell and the ratio between the core and the shell. At different hydrogen concentrations ranging from 1% to 4%, the optical response changes in the position of the surface plasmon resonance peak on the absorbance spectrum after the first loading/unloading hydrogen cycle.

Transformation of Au–Pd alloy nanoparticles to core-shell nanoparticles by electron irradiation

Abstract Present work reports on the electron irradiation induced modification in Au–Pd alloy based spherical shaped nanoparticles in scanning electron microscope (SEM). The Au–Pd alloy thin films were synthesized by DC sputtering of an Au–Pd alloy target and subsequent annealing at 800 °C. The composition and thickness of the as-deposited film was measured by Rutherford Backscattering Spectrometry (RBS). SEM confirmed the formation of spherical shaped Au–Pd alloy nanoparticles in annealed film. In-situ study on the transformation of Au–Pd alloy based spherical shaped nanoparticles to the Au@Au–Pd core-shell nanoparticles during electron irradiation in the SEM was performed. Structural characterizations were carried out by grazing incidence X-ray diffraction (GIXRD) and morphological changes were investigated qualitatively by grazing incidence small angle X-ray scattering (GISAXS) of the annealed film before and after electron irradiation. Theoretical calculations of electron energy loss indicate neither knock-on displacements nor temperature rise are responsible for structural transition observed in present case. It is suggested that electronic-excitations induced atomic displacements may cause spherical to core-shell phase transition.

Improving biosynthesis of Au[sbnd]Pd core-shell nanoparticles through Escherichia coli with the assistance of phytochelatin for catalytic enhanced chemiluminescence and benzyl alcohol oxidation

In this work, AuPd core-shell nanoparticles (NPs) biosynthesized through Arabidopsis thaliana phytochelatin synthase-modified Escherichia coli (Au-Pd/AtPCS1-E. coli) with catalytic enhanced chemiluminescence (CL) and benzyl alcohol oxidation (BAO) was investigated. Such biosynthesis of AuPd core-shell NPs was obviously enhanced due to insertion of the gene sequence of Arabidopsis thaliana phytochelatin synthase (AtPCS1) to a plasmid vector (pET-28b) of Escherichia coli (E. coli). The obtained Arabidopsis thaliana phytochelatin synthase-modified Escherichia coli (AtPCS1-E. coli) could generate phytochelatins (PCs, (γ-Glu-Cys)n-Gly, n > 1) for efficient capture and enrichment of Au3+. The component and morphology of AuPd core-shell NPs were checked through X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS). Catalytic CL (in H2O2-luminol system) and BAO (in H2O2-benzyl alcohol system) effect with different experimental conditions were examined, respectively. These results revealed that multifunctional PCs could effectively facilitate biosynthetic process of AuPd core-shell NPs with better distribution, higher yield and lower cost while stronger CL intensity and higher conversion could be obtained for further quantitative analysis and application.

Composition-dependent CO2 electrochemical reduction activity and selectivity on Au–Pd core–shell nanoparticles

Au–Pd core–shell nanoparticles can convert CO2 into CO with a high selectivity and mass activity due to the more balanced *COOH/*CO adsorption.

Carbon black supported Au–Pd core-shell nanoparticles within a dihexadecylphosphate film for the development of hydrazine electrochemical sensor

An amperometric method for the determination of hydrazine (HDZ) using a glassy carbon (GC) electrode modified with carbon black supported Au–Pd core–shell structured nanoparticles (Au@Pd/CB) within dihexadecylphosphate (DHP) film (Au@Pd/CB-DHP/GCE) is proposed. Au@Pd nanoparticles were synthesized by chemical reduction of AuCl3 and PdCl2 using ethylene glycol as a reducing agent, and the nanoparticles supported on CB were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The proposed Au@Pd/CB-DHP/GCE and CB-DHP/GCE (without Au@Pd) electrodes were used to investigate the electrochemical behavior of HDZ using cyclic voltammetry. When the Au@Pd/CB-DHP/GCE was used, an electrocatalytic effect was observed, the analytical signal was substantially increased (87%) and the oxidation potential decreased, i.e. in 728mV. Additionally, the apparently heterogeneous electron-transfer rate constant (k0) obtained for the Au@Pd/CB-DHP/GCE (0.15cms−1) was about two orders of magnitude greater than that obtained using the CB-DHP/GCE (0.068cms−1). Under the optimized conditions for the amperometric technique, a linear analytical curve for HDZ was obtained in the range of 2.50–88.0μmolL−1, with a limit of detection of 0.23μmolL−1 (0.0074ppm). The proposed method was satisfactorily applied to determine the concentration of HDZ in natural lake and tap water samples.

Stability of Au–Pd Core–Shell Nanoparticles

The stability of Au–Pd alloys with sizes close to 3 nm and icosahedral, decahedral, and truncated octahedral geometries with AucorePdshell and PdcoreAushell elemental distributions have been studied using canonical molecular dynamics simulations. The analysis of excess energy show that the PdcoreAushell ordering is more stable than the AucorePdshell for particles of this size, while the analysis of the order parameter Q6 revealed that some of the particles with AucorePdshell ordering exhibited geometric and structural changes previous to melting of the particles. Analysis of the local density of the species revealed that these changes are due to diffusion of Pd atoms into the inner core of the particles. The geometry and structure of all of the particles with PdcoreAushell were preserved until just before the solid–liquid transition, as well as showing a lower melting temperature than the AucorePdshell particles.

Strain Effects on the Oxidation of CO and HCOOH on Au–Pd Core–Shell Nanoparticles

The mechanism of CO and HCOOH electrooxidation in an acidic solution on carbon-supported Au–Pd core–shell nanoparticles was investigated by differential electrochemical mass spectrometry and in situ Fourier transform infrared (FTIR) spectroscopy. Analysis performed in nanostructures with 1.3 ± 0.1 nm (CS1) and 9.9 ± 1.1 nm (CS10) Pd shells provides compelling evidence that the mechanism of adsorbed CO (COads) oxidation is affected by structural and electronic effects introduced by the Au cores. In the case of CS10, a band associated with adsorbed OH species (OHads) is observed in the potential range of CO oxidation. This feature is not detected in the case of CS1, suggesting that the reaction follows an alternative mechanism involving COOHads species. The faradaic charge associated with COads oxidation as well as the Stark slope measured from FTIR indicates that the overall affinity and orbital coupling of CO to Pd are weaker for CS1 shells. FTIR spectroscopy also revealed the presence of HCOOads intermed...

Ni–Pd core–shell nanoparticles with Pt-like oxygen reduction electrocatalytic performance in both acidic and alkaline electrolytes

The prepared monodisperse Ni@Pd3 core–shell nanoparticles with a Pd-enriched surface exhibited a Pt-like ORR electrocatalytic activity and long durability under both acidic and alkaline conditions.

Carbon supported Au–Pd core–shell nanoparticles for hydrogen production by alcohol electroreforming

Monodisperse faceted icosahedral Au–Pd core–shell nanocrystals of small size (<12 nm) supported on Vulcan XC-72 (Au–Pd/C) are employed in electroreforming for the cogeneration of hydrogen and valuable chemicals.

Ni2P-Graphite Nanoplatelets Supported Au–Pd Core–Shell Nanoparticles with Superior Electrochemical Properties

Nanoparticles of Au–Pd with core–shell structure were synthesized through the coreduction of HAuCl4 and Na2PdCl4 in aqueous media by using cetyltrimethylammonium chloride as a reducing agent. The morphology and structure of the core–shell NPs were confirmed by transmission electron microscopy, X-ray diffraction, and UV–vis spectroscopy. We further demonstrate that the core–shell structure is formed as a synergistic result of low interfacial energy and small lattice mismatch between Au and Pd, different redox potentials of PdCl42–/Pd and AuCl4–/Au, and low reduction rates of HAuCl4 and Na2PdCl4. The catalyst of Au–Pd core–shell nanoparticles supported on Ni2P–graphite nanoplatelets (Au@Pd/Ni2P-GNPs) exhibits a noticeably higher activity than Pd and Pt catalysts in electrochemical ethanol oxidation. Moreover, we show that the activity and stability of Au–Pd core–shell for ethanol oxidation can be significantly enhanced using Ni2P nanoparticles as a cocatalyst. The prepared Au@Pd/Ni2P-GNPs catalyst exhibits ...

Synthesis of Zirconia–Palladium Core–Shell Nanoparticles as Three-Way Catalysts

Zirconia–palladium (ZrO2–Pd) core–shell nanoparticles were synthesized by two different methods, namely, hydrothermal and common precipitation method. A non-ionic surfactant polyvinylpyrrolidone was used as dispersant while ammonia solution as precipitator to fabricate the zirconia core particles, on which the palladium shell was subsequently forming by reducing palladium nitrate with an eco-friendly reductant–ascorbic acid. A mechanical blending method was applied to fabricate the three-way catalysts (TWCs). The physicochemical properties of ZrO2–Pd nanoparticles and catalytic performance of each catalyst were systematically studied and compared. The scanning electron microscopy, transmission electron microscopy-energy diffraction X-ray, BET, X-ray diffraction of the ZrO2 or the ZrO2–Pd nanoparticles results clarified that ZrO2–Pd core–shell nanoparticles with high dispersion and surface area were successfully prepared through hydrothermal method. A higher content of Pd was obtained in catalysts fabricated by hydrothermal method according to the inductively coupled plasma atomic emission spectrometry results. The CO pulse adsorption, H2-temperature-programmed reduction results and catalytic tests indicated that the aged catalysts (calcined at 1000 °C) possessed the higher active component dispersion, lower reduction temperature and performed the higher catalytic activity than the fresh catalysts (calcined at 550 °C), especially for that with ZrO2–Pd core–shell nanoparticles synthesized through hydrothermal method. Thus, the ZrO2–Pd core–shell structure can significantly enhance the thermal stability of TWCs.

One step preparation of ‘ready to use’ Au@Pd nanoparticle modified surface using deep eutectic solvents and a study of its electrocatalytic properties in methanol oxidation reaction

A facile one pot synthesis andin situelectrodeposition of Au–Pd core–shell nanoparticles (Au@Pd NPs) could be achieved in a deep eutectic solvent. The fabricated Au@Pd NPs modified graphite showed superior electrocatalytic properties for methanol oxidation at low activation energies.

Atomic Structure Characterization of Au–Pd Bimetallic Nanoparticles by Aberration-Corrected Scanning Transmission Electron Microscopy

Au–Pd core–shell nanoparticles were structurally characterized using spherical aberration (Cs) corrected scanning transmission electron microscopy (STEM). The microscope is equipped with a detector of high-angle annular dark field (HAADF)-STEM, in addition with an energy-dispersive X-ray spectrometer (EDS). The high-resolution elemental line-scan was carried out using the combination of STEM-EDS which allowed us to obtain an elemental analysis at atomic level. The effect of the Pd in the formation of Au–Pd core–shell has been studied by HAADF-STEM images and molecular dynamics studies. The obtained results predict that the growth of Pd on the Au core is through the formation of islands, suggesting a preferential growth of the Volmer–Weber type model.

Methanol and ethanol oxidation on carbon supported nanostructured Cu core Pt–Pd shell electrocatalysts synthesized via redox displacement

Abstract Six different carbon-supported Cu core Pt–Pd shell (Cu@Pt–Pd) catalysts have been successfully synthesized by the galvanic replacement of Cu atoms by Pt4+ and Pd2+ ions at room temperature and their electrocatalytic activity for methanol and ethanol oxidation have been evaluated in acid media. Cu@Pt–Pd core shell nanoparticles with a narrow size distribution and an average diameter in the range of 3.1–3.5 nm were generated onto the carbon support. The compositional and the structural analysis of the as-prepared materials pointed out that the nanoparticles are formed by a Cu rich core covered by a Pt–Pd rich shell due to the interdiffusion of the metals after the galvanic replacement reaction. The electrocatalytic properties of the Cu@Pt–Pd electrodes in the electro-oxidation of methanol and ethanol was found to be dependent on the electrochemical surface area, lattice strain of the surface, composition and thickness of the Pt–Pd shell surrounding the Cu core. The optimum catalyst composition to obtain the best performance for methanol and ethanol electro-oxidation was determined to be Pt0.59Pd0.324Cu0.167/C (6.2 wt.% Pt, 2.2 wt.% Pd and 0.7 wt.% Cu). This catalyst has a greatly enhanced mass activity, lower onset potential and poisoning rate, and higher turnover number in the MOR and EOR reactions compared to a commercial Pt0.51Ru0.49/C (20 wt.% Pt and 10 wt.% Ru). Consequently, this simple preparation method is a viable approach to making a highly active catalyst with low platinum content for application in direct alcohol fuel cells (DAFCs).

Au–Pd Core–Shell Nanoparticles as Alcohol Oxidation Catalysts: Effect of Shape and Composition

The right combination: Shape and composition are two important factors governing the catalytic properties of bimetallic nanocatalysts. Combining gold and palladium in a Au-core–Pd-shell structure coupled with an icosahedral morphology is shown to maximize catalytic performance for the selective oxidation of the biorenewable sources glycerol and 1,2-propanediol to glyceric and lactic acids, respectively.

In Situ X-ray Absorption Spectroscopic Analysis of Gold–Palladium Bimetallic Nanoparticle Catalysts

Gold–palladium core–shell nanoparticles have been previously shown to be extremely effective catalysts for a number of oxidation reactions including the aerobic oxidation of alcohols. However, the novel activity and durability of such catalysts are still poorly understood, and there are several putative mechanisms by which oxidation reactions can proceed. Previously we showed that Pd(II) salts in the presence of Au nanoparticles were also effective catalysts for the room temperature oxidation of crotyl alcohol. Herein we show an in situ X-ray absorption spectroscopy (XAS) study at both the Pd–K and Pd-LIII edges of Au nanoparticle/Pd(II) salt solutions in the presence of crotyl alcohol. Liquid cells with X-ray permeable windows were used to obtain quick-scan XAS data during the oxidation of crotyl alcohol, allowing for time-resolved Pd speciation information and information about the reaction mechanism and kinetics. XAS measurements definitively show that the first step of this reaction involves Pd reduction onto the Au nanoparticles; in addition, further studies of the stability of the resulting Au–Pd core–shell nanoparticles toward oxygen gas suggests that the role of Au in such catalysts is to prevent the reoxidation of the catalytically active surface Pd atoms. Catalytic crotyl alcohol oxidation measurements were done which validated that the in situ reduction of Pd(II) in the presence of Au nanoparticles did indeed result in catalytically active AuPd bimetallic catalysts.

Origin and shape evolution of core–shell nanoparticles in Au–Pd: from few atoms to high Miller index facets

Au–Pd core–shell nanocubes and triangular nanoparticles were systematically synthesized from a few Pd layers up to fully grown morphologies by a modified seed-mediated growth method. The shape evolution of Au–Pd core–shell nanoparticles from single crystal and singly twinned seed to final concave nanocube and triangular plates are presented at atomic level by Cs-corrected scanning transmission electron microscopy (STEM). The growth mechanism of both morphologies was studied throughout different sizes. It was found that the concave nanocubes grew from octahedral Au seeds due to fast growth along 〈111〉 directions; while the triangular nanoparticles grew from singly twinned Au seeds, growing twice as fast in 〈110〉 directions along the twin boundary; compared to the 〈111〉 direction perpendicular to the twin boundary. Both the concave nanocubes and triangular nanoparticles presented high index facet (HIF) surfaces that will increase the catalytic activity of different reactions.