Au-Pd Alloy Research Articles

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.

Au–pd bimetallic alloy nanoparticle-decorated BiPO4 nanorods for enhanced photocatalytic oxidation of trichloroethylene

Photocatalytic oxidation reactions are regarded as promising green synthesis methods for the photodegradation of volatile organic compounds such as trichloroethylene. However, low photocatalytic efficiency and selectivity limit practical application of the technique. We report the synthesis of novel hexagonal BiPO4/Au-Pd nanorods with diameters of 500nm that display excellent performance in degrading trichloroethylene under visible-light irradiation. With co-catalytic Au–Pd bimetallic alloy nanoparticles deposited on the nanorod surfaces, the photocatalytic activity is enhanced approximately 25 times compared to that of the BiPO4 nanorods. The dramatic enhancement of activity is attributed to the Au–Pd alloy nanoparticles effectively separating the oxidation and reduction sites, thereby promoting charge-separation efficiency and providing abundant catalytically active sites to enhance the reactivity of BiPO4. The excellent photocatalytic performance is also attributed to the moderated conduction band position and an optimum Au–Pd weight percentage. This material provides a promising strategy for degradation of volatile organic compounds.

Surfactant dependent evolution of Au-Pd alloy nanocrystals from trisoctahedron to excavated rhombic dodecahedron and multipod: a matter of crystal growth kinetics

In wet chemical syntheses of noble metal nanocrystals, surfactants play crucial roles in regulating their morphology. To date, more attention has been paid to the effect of the surfactant on the surface energy of crystal facets, while less attention has been paid to its effect on the growth kinetics. In this paper, using the growth of Au-Pd alloy nanocrystals as an example, we demonstrate that different concentration of surfactant hexadecyltrimethyl ammonium chloride (CTAC) may cause the different packing density of CTA+ bilayers on different sites (face, edge or vertex) of crystallite surface, which would change the crystal growth kinetics and result in preferential crystal growth along the edge or vertex of crystallites. The unique shape evolution from trisoctahedron to excavated rhombic dodecahedron and multipod structure for Au-Pd alloy nanocrystals was successfully achieved by simply adjusting the concentration of CTAC. These results help to understand the effect of surfactants on the shape evolution of nanocrystals and open up avenues to the rational synthesis of nanocrystals with the thermodynamically unfavorable morphologies.

Basic anion-exchange resin (AER)-supported Au-Pd alloy nanoparticles for the oxidation of 5-hydroxymethyl-2-furfural (HMF) into 2,5-furan dicarboxylic acid (FDCA)

Au-Pd alloy nanoparticles supported on basic anion-exchange resin (AER) have exceptional catalytic activity for the oxidation of 5-hydroxymethyl-2-furfural (HMF) into 2,5-furan dicarboxylic acid (FDCA) with an equimolar amount of base. SEM-EDX and TEM analyses show that 5–20nm Au-Pd alloy nanoparticles are well dispersed both on the resin surface and inside resin spheres by a simple procedure without any assistance of additives. XPS analysis reveals that Au- and Pd metals exist in an alloy form on the AER support, which is confirmed by a comparison study with a mixture of AER-supported monometallic nanoparticles (AER-supported Au and AER-supported Pd). In the presence of a 1:1 ratio of Au-Pd alloy nanoparticles over Amberlite IRA-743 resin with O2 (10bar) at 373K in an equimolar Na2CO3 aqueous solution, HMF is oxidized to FDCA with a 93.2% yield. On the other hand, mixture of AER-supported Au and AER-supported Pd affords only a 52% FDCA yield under identical conditions. This catalyst can be used 6 times without any significant loss of activity. FDCA is also obtained from HMF with an 82.9% yield in air (40bar).

Synthesis of Au-Pd Bimetallic Nanoflowers for Catalytic Reduction of 4-Nitrophenol.

Due to the great potential to improve catalytic performance, gold (Au) and palladium (Pd) bimetallic catalysts have prompted structure-controlled synthesis of Au-Pd nanoalloys bounded by high-index facets. In this work, we prepared Au-Pd bimetallic nanoflowers (NFs) with a uniform size, well-defined dendritic morphology, and homogeneous alloy structure in an aqueous solution by seed-mediated synthesis. The prepared bimetallic NFs were fully characterized using a combination of transmission electron microscopy, Ultraviolet-Visible (UV-vis) spectroscopy, inductively coupled plasma optical emission spectroscopy, and cyclic voltammetry measurements. The catalytic activities of the prepared Au-Pd nanoparticles for 4-nitrophenol reduction were also investigated, and the activities are in the order of Au@Pd NFs > Au-Pd NFs (Au1Pd1 core) > Au-Pd NFs (Au core), which could be related to the content and exposed different reactive surfaces of Pd in alloys. This result clearly demonstrates that the superior activities of Au-Pd alloy nanodendrites could be attributed to the synergy between Au and Pd in catalysts.

DFT study reveals geometric and electronic synergisms of palladium-mercury alloy catalyst used for hydrogen peroxide formation

One of the main obstacles confronting the direct synthesis of hydrogen peroxide (H2O2) is how to maintain the unbroken OO bonding of the intermediate species on the catalytic surface. To address this challenge Pd-Hg alloys have been used with initial reports suggesting their performance offers advantages when compared to monometallic Pd and Pd-Au alloys; however, the interactions of O2 with Pd-Hg alloys are not well characterised. In this study, density functional theory (DFT) calculations, employed to investigate O2 adsorption on the Pd and Pd-Hg alloy surfaces, suggested O2 adsorption can occur via either a superoxo or a peroxo pathway and that when Hg is alloyed to Pd there are more surface adsorbed superoxo groups compared to adsorption on a monometallic Pd surface. The Hg in Pd6Hg3/Pd(111) results in an electronic surface structure different to that of Pd(111) and a reduced O2 adsorption energy. The stronger O2 surface interactions, when combined with weaker OO bonding (of the adsorbed O2), which result from the presence of Hg on the Pd-Hg surface leads to synergistic geometric and electronic effects that result in an increased selectivity during of the synthesis of H2O2.

Sub 1 nm aggregation-free AuPd nanocatalysts confined inside amino-functionalized organosilica nanotubes for visible-light-driven hydrogen evolution from formaldehyde

Novel amino-functionalized organosilica nanotubes (AM-NT) were facilely synthesized by the hydrolysis and co-condensation of 3-aminopropyltrimethoxysilane (APTMS) with 1,4-bis(triethoxysilyl)benzene (BTEB) using a simple micelle-templating approach. Through adjusting the ratios of organosilane precursors, the very short AM-NT with ∼60nm in length and ∼6nm in pore diameter could be controllably obtained. By using the unique AM-NT as the supports, a series of AuPd alloy nanoparticles with the average size of sub 1nm could be synthesized after the liquid phase reduction of HAuCl4 and H2PdCl4 in water, which were mostly confined inside the short organosilica nanotubes and further applied for the hydrogen evolution from formaldehyde aqueous solution. These bimetallic AuPd nanocatalysts in the organic-modified nanotubes exhibited remarkably improved catalytic activity under visible light irradiation and the highest initial TOF value of 241.7h−1 could be achieved at the room temperature. Furthermore, these ultrasmall nanocatalysts exhibited high reaction stability and no aggregation of metal nanoparticles was observed even after 5 recycles. The superior catalytic activity was mainly attributed to the uniform and ultrafine AuPd nanostructure, benefiting from the synergetic stabilizing effects of amino and benzene groups in the nanotube frameworks. The fast electron transfer from much smaller Au with localized surface plasmon resonance (LSPR) to active Pd sites could efficiently occur, resulting in the excellent photocatalytic activity.

Alloying of AuNPs with palladium: A promising tool for tuning of selectivity for epoxide in oxidation of styrene using molecular oxygen

• Epoxidation of styrene on gold and Au-Pd alloy nanoparticles using molecular oxygen . • Lowest catalyst quantity 0.038 mmol%. • 98% conversion with 75% selectivity for epoxide. • A green protocol with general applicability. Present investigation, deals with synthesis of gold and gold palladium alloy nanoparticles and their application to epoxidation of styrene using molecular oxygen. Synthesized AuNPs@ Resin and bimetallic Au-Pd NPs@ Resin of average size <5 nm were analyzed by various techniques such as X-ray diffraction (XRD), SEM-EDX, TEM-EDS, inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS). Results showed that alloying of Au with Pd enhanced selectivity of the catalyst towards epoxidation. Au/Pd molar ratio (1/1) provided 98% conversion of styrene with 75% selectivity towards styrene oxide with a TOF of 0.181 (s −1 ) in terms of gold present in catalyst. The catalyst is promising candidate for industrial application as it showed remarkable stability, reusability and general applicability.

3DOM LaMnAl11O19-supported AuPd alloy nanoparticles: Highly active catalysts for methane combustion in a continuous-flow microreactor

Three-dimensionally ordered macroporous (3DOM) LaMnAl11O19 and xAuPdy/3DOM LaMnAl11O19 (x=0.44−1.91wt%; y=1.80−1.86) were prepared via the polymethyl methacrylate (PMMA)-templating and gas bubble-assisted polyvinyl alcohol (PVA)-protected reduction routes, respectively. Physicochemical properties of the samples were characterized by a number of analytical techniques. Catalytic activities of the samples were measured for methane combustion in a continuous-flow microreactor. It is shown that the LaMnAl11O19 in each of the samples was hexagonal in crystal structure, and all of the samples possessed a good-quality 3DOM architecture with a surface area of 24.4−28.2m2/g. The Au–Pd nanoparticles (NPs) with an average size of 2.8nm were uniformly dispersed on the macropore walls of 3DOM LaMnAl11O19. The 1.91AuPd1.80/3DOM LaMnAl11O19 sample performed the best for methane combustion (T50%=342°C and T90%=402°C at a space velocity of 20,000mL/(gh)). The deactivation of the 1.91AuPd1.80/3DOM LaMnAl11O19 catalyst induced by water vapor introduction was reversible, whereas that induced by SO2 addition was irreversible. It is concluded that the good catalytic activity of 1.91AuPd1.80/3DOM LaMnAl11O19 was related to its good-quality 3DOM structure, highly dispersed Au–Pd NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Au–Pd alloy NPs and 3DOM LaMnAl11O19.

DFT study of hydrogen production from formic acid decomposition on Pd-Au alloy nanoclusters

Recently, it has been reported that the hydrogen production rate of formic acid decomposition can be significantly increased using Pd-Au binary alloy nano-catalysts [Wang et al. J. Mater. Chem. A 1 (2013) 12721–12725]. To explain the reaction mechanism of this alloy catalysis method, formic acid decomposition reactions on pure Pd and Pd-Au alloy nanoclusters are studied via density functional theory simulations. The simulation results indicate that the addition of inert element Au would not influence formic acid decomposition on Pd surface sites of Pd-Au alloy nanoclusters. On the other hand, the existence of Au surface sites brings relative weak hydrogen atom adsorption. On Pd-Au alloy nanoclusters, the dissociated hydrogen atoms from formic acid are easier to combine as hydrogen molecules than that on pure Pd clusters. Via the synergetic effect between Pd and Au, both formic acid decomposition and hydrogen production are events with large probability, which eventually results in high hydrogen production rate.

Polyethyleneimine modified AuPd@PdAu alloy nanocrystals as advanced electrocatalysts towards the oxygen reduction reaction

Designing the low cost, active, durable, and alcohol-tolerant cathode catalysts towards the oxygen reduction reaction (ORR) is significant for the large-scale commercialization of direct alcohol fuel cells. Recently, Pd-based nanocrystals have attracted attention as Pt-alternative cathode catalysts towards the ORR in the alkaline electrolyte. Unfortunately, the pristine Pd-based nanocrystals lack the selectivity towards the ORR due to their inherent activity for the alcohol molecule oxidation reaction in the alkaline electrolyte. In this work, polyethyleneimine (PEI) modified AuPd alloy nanocrystals with Au-rich AuPd alloy cores and Pd-rich PdAu alloy shells (AuPd@PdAu-PEI) are successfully synthesized using a traditional chemical reduction method in presence of PEI. The rotating disk electrode (RDE) technique is applied to evaluate the ORR performance of AuPd@PdAu-PEI nanocrystals. Compared with commercial Pd black, AuPd@PdAu-PEI nanocrystals show significantly enhanced activity and durability towards the ORR, and simultaneously exhibit particular alcohol tolerance towards the ORR in the alkaline electrolyte.

Surface evolution of a Pt–Pd–Au electrocatalyst for stable oxygen reduction

Core–shell nanocatalysts have demonstrated potential as highly active low-Pt fuel cell cathodes for the oxygen reduction reaction (ORR); however, challenges remain in optimizing their surface and interfacial structures, which often exhibit undesirable structural degradation and poor durability. Here, we construct an unsupported nanoporous catalyst with a Pt–Pd shell of sub-nanometre thickness on Au, which demonstrates an initial ORR activity of 1.140 A mgPt−1 at 0.9 V. The activity increases to 1.471 A mgPt−1 after 30,000 potential cycles and is stable over a further 70,000 cycles. Using aberration-corrected scanning transmission electron microscopy and atomically resolved elemental mapping, the origin of the activity change is revealed to be an atomic-scale evolution of the shell from an initial Pt–Pd alloy into a bilayer structure with a Pt-rich trimetallic surface, and finally into a uniform and stable Pt–Pd–Au alloy. This Pt–Pd–Au alloy possesses a suitable configuration for ORR, giving a relatively low free energy change for the final water formation from adsorbed OH intermediate during the reaction. Metal alloys possessing core–shell structures have potential as low-Pt catalysts for the oxygen reduction reaction in fuel cells, but can suffer from poor stability. Using high-resolution microscopy, Li et al. find that a Pt–Pd–Au catalyst undergoes surface atomic rearrangement and becomes more active on electrochemical cycling.

Concurrent catalytic removal of typical volatile organic compound mixtures over Au-Pd/α-MnO2 nanotubes

α-MnO2 nanotubes and their supported Au-Pd alloy nanocatalysts were prepared using hydrothermal and polyvinyl alcohol-protected reduction methods, respectively. Their catalytic activity for the oxidation of toluene/m-xylene, acetone/ethyl acetate, acetone/m-xylene and ethyl acetate/m-xylene mixtures was evaluated. It was found that the interaction between Au-Pd alloy nanoparticles and α-MnO2 nanotubes significantly improved the reactivity of lattice oxygen, and the 0.91wt.% Au0.48Pd/α-MnO2 nanotube catalyst outperformed the α-MnO2 nanotube catalyst in the oxidation of toluene, m-xylene, ethyl acetate and acetone. Over the 0.91wt.% Au0.48Pd/α-MnO2 nanotube catalyst, (i) toluene oxidation was greatly inhibited in the toluene/m-xylene mixture, while m-xylene oxidation was not influenced; (ii) acetone and ethyl acetate oxidation suffered a minor impact in the acetone/ethyl acetate mixture; and (iii) m-xylene oxidation was enhanced whereas the oxidation of the oxygenated VOCs (volatile organic compounds) was suppressed in the acetone/m-xylene or ethyl acetate/m-xylene mixtures. The competitive adsorption of these typical VOCs on the catalyst surface induced an inhibitive effect on their oxidation, and increasing the temperature favored the oxidation of the VOCs. The mixed VOCs could be completely oxidized into CO2 and H2O below 320°C at a space velocity of 40,000mL/(g·hr). The 0.91wt.% Au0.48Pd/α-MnO2 nanotube catalyst exhibited high catalytic stability as well as good tolerance to water vapor and CO2 in the oxidation of the VOC mixtures. Thus, the α-MnO2 nanotube-supported noble metal alloy catalysts hold promise for the efficient elimination of VOC mixtures.

Study of Two-Body Wear Performance of Dental Materials

IntroductionThe purpose of this study was to evaluate the two-body wear resistances of natural enamel and four dental materials in vitro. MethodsThe testing machine was modified to form a type of pin-on-disk wear test apparatus. Four dental material specimens (Au-Pd alloy, Ag-Pd alloy, FiltekTMP60 and FiltekTMZ350 composite resins) and enamel were used as the pins, and a steatite ceramic grinding wheel was used as the abrasive counter face. The wear volume loss and the rigidity value was measured. The worn surface and the element analysis of the debris were analyzed. ResultThe wear volume loss of Au-Pd alloy and its steatite antagonists were the nearest to those of the dental enamel. SEM microphotographs showed that, the main wear mechanism of the dental materials was abrasive and adhesive wear. ConclusionsAu-Pd alloy had good wear resistance and was more suitable for dental applications than other three dental materials.

Facile fabrication of polystyrene microsphere supported gold-palladium alloy nanoparticles with superior catalytic performance for the reduction of 4-nitrophenol in water

Herein a simple method is reported for depositing gold-palladium alloy nanoparticles (NPs) with various chemical compositions on the surface of polystyrene microspheres (abbreviated as PS/Au-Pd composite particles) based on a thermodynamic effect. Noticeably, surface pretreatments of PS microspheres and Au-Pd alloy NPs are not required at all for achieving the self-assembly of preformed heterogeneous particles. The Au-Pd alloy NPs act as steric stabilizer and attach spontaneously onto the surface of the PS microspheres to reduce the Gibbs free energy of the colloidal system. Afterwards, we investigate the catalytic properties of PS/Au-Pd composite particles for the reduction of 4-nitrophenol, which is of industrial significance for converting 4-nitrophenol (a water pollutant with high toxicity) into 4-aminophenol (an important intermediate of various industries). We have found that the catalytic activity of PS/Au-Pd composite particles is remarkably affected by the chemical composition of supported Au-Pd alloy NPs. The maximum activity is achieved in the case of supported alloy NPs having the Au/Pd molar ratio of 54:46, which is much higher than that of pure Au NPs and Pd NPs supported on the PS microspheres. Furthermore, these PS/Au-Pd composite particles can be easily recovered owing to the large size of PS microspheres and reused three times without significant loss of catalytic activity.

Peptide‐FlgA3‐Based Gold Palladium Bimetallic Nanoparticles That Catalyze the Oxygen Reduction Reaction in Alkaline Solution

AbstractGiven the synergetic properties of different metal species, bimetallic nanoparticles are of immense scientific interest and technological importance in the field of catalysis. A peptide‐based method represents a new avenue to fabricate bimetallic nanocatalysts with a controllable size, shape, composition, and subtle surface microstructure. However, the electrocatalytic abilities of these peptide‐based bimetallic nanoparticles remain largely unexplored. Herein, we employed the peptide sequence FlgA3 to fabricate a series of AuPd alloys that were used as catalysts for the oxygen reduction reaction (ORR). Among the samples tested, Au33Pd67 exhibited the best activity, evidenced by the most positive onset potential and the largest diffusion‐limited current. Notably, the ORR activity of Au33Pd67 was comparable with that of commercial Pt/C, and the long‐term durability was significantly superior to that of Pt/C. A peptide‐enabled approach might pave the way for the fabrication of bimetallic nanomaterials with enhanced electrocatalytic properties under mild conditions.

Ultrasonic-assisted synthesis of N-doped graphene-supported binary PdAu nanoflowers for enhanced electro-oxidation of ethylene glycol and glycerol

The design of cost-efficient catalysts for the electrooxidation of small organic molecules are highly desirable for the commercial application of direct fuel cells. Shape-controlled PdAu alloys with N-doped graphene support are highly efficient electrocatalysts for the electrooxidation of ethylene glycol and glycerol in the alkaline media. Impressively, the newly generated Pd1Au1-NF/NG catalysts prepared by a facile ultrasonic-assisted synthetic method in this work exhibit the unprecedentedly high mass activities with 12.8 and 8.7Amg −1 towards ethylene glycol and glycerol oxidation, which are 10.07- and 12.25-fold enhancements than that of commercial Pd/C catalyst (1.27 and 0.71Amg −1), respectively. This work may open a new way in enlarging the surface area and ultimately maximizing the electrocatalytic activities by tuning the morphology of metallic alloy and introducing the appropriate catalyst supports.

Electrochemically shape-controlled formation of concave AuPd alloy nanoparticles on ITO substrate

Shape-control of AuPd alloy nanoparticles (AuPd NPs) substrated on indium-tin oxide (ITO) was successfully achieved, for the first time, by using electrochemical square-wave-potential (SWP) method. Concave trisoctahedral AuPd alloy NPs (TOH AuPd NPs) and concave hexoctahedral AuPd alloy NPs (HOH AuPd NPs) were prepared under SWP conditions with lower potential of 0.3 V while different upper potentials of 0.64 and 0.70 V, respectively. Different techniques including SEM, EDX and electrochemical cyclic voltammetry were employed to characterize the morphology and composition of AuPd alloy NPs. The results demonstrated that the as-prepared TOH AuPd NPs and HOH AuPd NPs are uniform in shape of correspondingly concave TOH and concave HOH, and are well dispersed on the ITO substrate. The composition in terms of and Au:Pd atomic ratio of both TOH and HOH AuPd alloy NPs is determined by EDX around 3:1. However, a surface enrichment of Au on the AuPd NPs was observed, and is ascribed to the lower surface energy of Au in comparison with that of Pd. It has been found that, starting from the as-synthesized TOH AuPd NPs, shape transformation from TOH to HOH can be accomplished by applying a treatment of square wave with lower potential of 0.3 V and upper potential of 0.7 V. Prolonging the treatment time results in increasing the size of AuPd NPs, while the HOH shape is preserved.

Tunability of the Adsorbate Binding on Bimetallic Alloy Nanoparticles for the Optimization of Catalytic Hydrogenation.

In this paper, we show that PtAu and PdAu random alloy dendrimer-encapsulated nanoparticles with an average size of ∼1.6 nm have different catalytic activity trends for allyl alcohol hydrogenation. Specifically, PtAu nanoparticles exhibit a linear increase in activity with increasing Pt content, whereas PdAu dendrimer-encapsulated nanoparticles show a maximum activity at a Pd content of ∼60%. Both experimental and theoretical results suggest that this contrasting behavior is caused by differences in the strength of H binding on the PtAu and PdAu alloy surfaces. The results have significant implications for predicting the catalytic performance of bimetallic nanoparticles on the basis of density functional theory calculations.

PdAu Alloy Nanoparticle Catalysts: Effective Candidates for Nitrite Reduction in Water

Well-defined palladium–gold nanoparticles (PdAuNPs) with randomly alloyed structures and broadly tunable compositions were studied in catalytic nitrite (NO2–) reduction. The catalysts were synthesized using a microwave-assisted polyol coreduction method. PdxAu100–xNPs with systematically varied compositions (x = 18–83) were supported on amorphous silica (SiO2) and studied as model catalysts for aqueous NO2– reduction in a batch reactor, using H2 as the electron donor. The reactions followed pseudo-first-order kinetics for ≥80% NO2– conversion. The PdxAu100–xNP-SiO2 catalysts showed a volcano-like correlation between NO2– reduction activity and x; the highest activity was observed for Pd53Au47, with an associated first-order rate constant of 5.12 L min–1 gmetal–1. Alloy NPs with greater proportions of Au were found to reduce the loss in catalytic activity due to sulfide fouling. Density functional theory calculations indicate that this is because Au weakens sulfur binding at PdAuNP surfaces due to atomic e...