Preparation of onion-like Pd–Bi–Au/C trimetallic catalyst and their application

This paper describes the preparation of dispersed onion-like Pd–Bi–Au/C catalyst with average diameter of 13 nm obtained by consecutive chemical reduction of precursor gold, bismuth and palladium salts in aqueous solution and immobilization on active carbon. High-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy experiments were performed to analyze the structure and to characterize the Pd–Bi–Au/C catalyst. The onion-like morphology is composed of high content of gold inner core, a Bi-rich intermediate layer and a Pd-rich external layer. The catalytic activity of the catalyst was subsequently investigated and they were found to be efficient catalysts for the aerobic liquid phase oxidation. The results showed that the catalytic activity of Pd–Bi–Au/C was higher than that of Pd–Au/C bimetallic catalyst, indicating that bismuth plays an important role in synergistic effect between gold and palladium.     

Carbon-Supported Palladium–Gold Bimetallic Disperse Systems Formed in Aqueous Solutions at 110°С

Various palladium–carbon composites have been manufactured by autoclaving at 170°С to be used as precursors for manufacturing bimetallic particles. The morphology of the manufactured items was comprehensively studied by scanning electron microscopy; the ultrafine metal palladium was found to have particles sizes lying in the range 30–120 nm. The specifics of hydrothermal reduction of gold(III) chloro complexes by palladium–carbon composites at 110°С have been studied. An appreciable increase in gold(III) reduction rate was observed with the use of a palladium–carbon composite relative to the rate observed for ultrafine metallic palladium. Gold is reduced on a palladium–carbon composite to an individual metallic phase.     

Preparation of PdCo Bimetallic Hollow Nanospheres and its Electrocatalytic Activity for Oxidation of Formic Acid

The performance of the direct formic acid fuel cell (DFAFC) is considerably higher than the direct methanol fuel cell (DMFC) because of some characteristics of formic acid1. For example, formic acid is non-toxic. Formic acid has two orders of magnitude smaller crossover flux through a Nafion membrane than methanol2. In DFAFC, the concentration of formic acid can be as high as 20 mol/L, while the best concentration of methanol in DMFC is only about 2 mol/L3. Thus, the power density of …     

Bismuth modified Pd/C as catalysts for hydrogen related reactions

The electrocatalytic activity of bimetallic BiPd catalysts supported on Sibunit carbon towards hydrogen oxidation/evolution reactions (HOR/HER) was studied in a gas diffusion electrode (GDE) setup. Catalysts were synthesized by deposition of Pd on the carbon support, followed by impregnation of Pd/C precursor with Bi(NO₃)₃ solution and reduction in hydrogen. Transmission electron microscopy and local EDX elemental analysis revealed that BiPd/C catalysts contain bimetallic particles with narrow size distribution with maxima at 3.2–4.1 nm. X-ray diffraction evidenced that bimetallic particles are constituted by Pd–Bi solid solution. It was shown that modification of Pd/C by bismuth increases the specific activity of palladium towards HOR/HER by a factor of 3.     

Polyamidoamine dendrimers-assisted electrodeposition of gold-platinum bimetallic nanoflowers

Novel Au-Pt bimetallic flower nanostructures fabricated on a polyamidoamine dendrimers-modified surface by electrodeposition are reported. These polyamidoamine dendrimers were stable, and they assisted the formation of Au-Pt bimetallic nanoflowers during the electrodeposition process. These nanoflowers were characterized by field-emitted scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and electrochemical methods. FE-SEM images showed that the bimetallic nanoflower included two parts: the "light" and the "pale" part. The two parts consisted of many small bimetallic nanoparticles, which was attributed to the progressive nucleation process. Moreover, the "light" part contained more bimetallic nanoparticles. The morphologies of bimetallic nanoflowers depended on the electrodeposition time and potential and the layer number of assembled dendrimers. The average size of nanoflowers increased with the increase in electrodeposition time. The layer number of assembled dendrimers obviously affected the size and morphologies of the "pale" parts of deposited nanoflowers. EDS and XPS indicated that the content of Au element was higher than that of Pt element in the nanoflowers. The bimetallic nanoflowers-modified electrode had electrochemical properties similar to those of bare gold and platinum electrodes. It also exhibited significant electrocatalytic activities toward oxygen reduction.     

Bimetallic palladium-platinum dendrimer-encapsulated catalysts

We report the synthesis, characterization, and catalytic activity of bimetallic palladium-platinum dendrimer-encapsulated catalysts (DECs). These materials are prepared by co-complexation of different ratios of palladium and platinum salts to the interior tertiary amines of fourth-generation, hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers. Chemical reduction of these composites yields stable, fairly monodisperse, water-soluble bimetallic DECs having sizes on the order of 1.9 +/- 0.4 nm. Evidence that these nanoparticles are bimetallic comes from single-particle X-ray energy dispersive spectroscopy (EDS) and catalysis experiments. The latter indicate that the hydrogenation rate of allyl alcohol is enhanced in the presence of the bimetallic nanoparticles compared to DECs containing only platinum or only palladium nanoparticles. EDS results indicate that the percentage composition of the bimetallics is reflected by the percentage of metal salts initially complexed with the dendrimer.     

Synthesis of gold nanoparticles from an organometallic compound in supercritical carbon dioxide

This article presents the synthesis of gold nanoparticles in a single-phase supercritical fluid carbon dioxide solvent. The gold nanoparticles were formed by the reduction of triphenylphosphine gold(I) perfluorooctanoate with dimethylamineborane. Transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis spectroscopy reveal the formation of gold nanoparticles of 1 nm in diameter. A high dispersion stability of the gold nanoparticles in supercritical carbon dioxide can be obtained by binding both triphenylphosphine and fluorocarbon ligands on the surface of the gold nanoparticles.     

Elaboration by high-energy ball milling of copper/palladium composite materials – characterization and electrocatalytic activity for the reduction of nitrate in alkaline medium

In this study, an original approach was explored to decorate copper particles with palladium and well-defined bimetallic copper/palladium powders were elaborated through a two-step ball milling procedure. First, copper powder was milled with previously determined optimal conditions (ball-to-powder mass ratio of 2, milling duration of 6 h under argon) in order to obtain spherical nanocrystalline copper particles with an average diameter of 800 μm. Then, an additional milling in presence of 1 at.% of palladium powder was performed, leading to the formation of Cu–Pd composite materials. Palladium surface concentrations from 3 to 62 at.% were obtained by varying both the ball-to-powder mass ratio (2:1 or 10:1) and the milling duration (from 5 to 30 min). Scanning electron microscopy, optical microscopy, X-ray photoelectron spectroscopy and X-ray diffraction analyses confirmed that the more intense the milling is, the easier the palladium diffuses into the copper matrix and smaller the palladium concentration on copper particles is. Cyclic voltammetry and electrolysis experiments showed that palladium inclusions on copper improve greatly the electrocatalytic activity for nitrate reduction in alkaline media. The key role of Pd in the Pd–Cu composite electrodes is to accelerate the reduction of nitrite, formed by the electrochemical reduction of nitrate on Cu sites. Also different nitrate electroreduction behaviors were observed at copper and copper–palladium electrodes leading to the preferential formation of nitrite or ammonia depending on the applied potential and the Pd surface concentration.     

Ultrafine palladium particles immobilized on polymer microspheres

Ultrafine palladium particles immobilized on submicrometer copolymer microspheres were prepared by reduction of palladium ions in the presence of the copolymer microspheres. Copolymer microspheres with surface carboxylic or cyano functionality were used. Transmission electron microscopy observation and X-ray diffraction analysis indicated that ultrafine palladium particles of nanometer size were formed and were attached on the surface of the copolymer microspheres. The interaction between palladium particles and surface functionality of the copolymer microspheres was studied by IR spectroscopy and X-ray photoelectron spectroscopy. Received: 9 February 2000 Accepted: 17 August 2000     

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.     

Synthesis of bimetallic powders of alloys of platinum with tin

Technique of obtaining nanosized bimetallic powders of alloys of platinum metals with tin by reduction of complexes of metals with tin halide ligands using zinc from aqueous HCl solutions was developed. These powders were studied by X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy.     

Preparation of Nanosized Metallic Particles in Polyaniline

The preparation of nanosized gold and palladium particles in polyaniline has been carried out via the reduction of AuCl(3) or Pd(NO(3))(2) by polyaniline in either aqueous media or N-methylpyrrolidinone (NMP). When the reduction of AuCl(3) was carried out in NMP solutions of polyaniline, the Au particles were on the order of 20 nm. The reduction of AuCl(3) or Pd(NO(3))(2) by polyaniline in the powder form in aqueous media resulted in the accumulation of the elemental Au or Pd on the surface of the polyaniline particles. Subsequent dissolution of the polyaniline in NMP resulted in metal particles of about 50 to 200 nm being dispersed in the NMP solution of polyaniline. The rate of metal salt reduction and the size of the metal particles were found to be strongly dependent on the medium used, the initial ratio of metal ions to polyaniline, and the reaction time. The polyaniline-metal particle systems were characterized using X-ray photoelectron spectroscopy, UV-visible absorption spectroscopy, and FTIR spectroscopy. Scanning and transmission electron microscopy and laser light scattering were used to determine the size of the metal particles in polyaniline. Copyright 2001 Academic Press.     

Synthesis of hafnium oxide-gold core-shell nanoparticles

Developing cheap composite nanoparticle systems that combines a high dielectric constant with good conductivity is important for the future of the electronic industry. In this study, two different sizes, 7.3 ± 2.2 and 5.6 ± 1.9 nm, of HfO(2)@Au core-shell nanoparticles are prepared by using a high-temperature reduction method. The core-shell nanoparticles are characterized by powder X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray analysis (EDX), and UV-visible absorption spectroscopy. HfO(2) exhibits no absorption in the visible region, but the HfO(2)@Au core-shell nanoparticles show a plasmon absorption band at 555 nm that is 25 nm red-shifted as compared to pure gold nanoparticles. According to transmission electron microscopy and energy dispersive X-ray analysis, the HfO(2) particles are coated with approximately three atomic layers of gold.     

Synthesis and characterization of N,N-dimethyldodecylamine-capped Aucore-Pdshell nanoparticles in toluene

In this paper a convenient route for synthesizing Au(core)-Pd(shell) bimetallic nanoparticles in toluene has been reported as a result of co-reduction of gold(III) and palladium(II) precursors in toluene. N,N-Dimethyldodecylamine was used as a capping agent for the core-shell particles, which not only imparts stability to the organosol but also controls morphology of the evolved particles. The particles were characterized using UV-visible, transmission electron microscopy, and X-ray diffraction measurements. All results substantiate the formation of core-shell structure of the synthesized particles.     

Platinum-catalyzed synthesis of water-soluble gold-platinum nanoparticles

The ability to control composition and size in the synthesis of bimetallic nanoparticles is important for the exploitation of the bimetallic catalytic properties. This paper reports findings of an investigation of a new approach to the synthesis of gold-platinum (AuPt) bimetallic nanoparticles in aqueous solution via one-phase reduction of AuCl(4-) and PtCl(4)(2-) using a combination of reducing and capping agents. Hydrogen served as a reducing agent for the reduction of Pt(II), whereas acrylate was used as a reducing agent for the reduction of Au(III). The latter reaction was found to be catalyzed by the formation of Pt as a result of the reduction of Pt(II). Acrylate also functioned as capping agent on the resulting nanocrystals. By controlling the feed ratios of AuCl(4-) and PtCl(4)(2-) and the relative concentrations of acrylate, an effective route for the preparation of AuPt nanoparticles with bimetallic compositions ranging from approximately 4 to 90% Au and particle sizes ranging from 2 to 8 nm has been demonstrated. The composition, size, and shell properties were characterized using transmission electron microscopy, direct current plasma-atomic emission spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. Implications of the results to the exploration of bifunctional catalysts are also briefly discussed.     

Rapid green synthesis of gold nanoparticles using Rosa hybrida petal extract at room temperature

This study reports a green method for the synthesis of gold nanoparticles using the aqueous extract of rose petals. The effects of gold salt concentration, extract concentration and extract quantity were investigated on nanoparticles synthesis. Gold nanoparticles were characterized with different techniques such as UV-vis spectroscopy, FT-IR spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, dynamic light scattering and transmission electron microscopy. Transmission electron microscopy experiments showed that these nanoparticles are formed with various shapes. FT-IR spectroscopy revealed that gold nanoparticles were functionalized with biomolecules that have primary amine group (-NH2), carbonyl group, -OH groups and other stabilizing functional groups. X-ray diffraction pattern showed high purity and face centered cubic structure of gold nanoparticles. Dynamic light scattering technique was used for particle size measurement, and it was found to be about 10nm. The rate of the reaction was high and it was completed within 5 min.     

聚多巴胺功能化硅胶沉积单分散Pd纳米粒子的简易原位合成及用作醇需氧氧化反应的多相可循环使用的纳米催化剂（英文）

本文报道了一种不使用任何稳定剂或还原剂,原位合成硅胶/聚多巴胺复合物(SiO_2/PDA)负载的Pd纳米颗粒(Pd NPs)的简易方法.该方法先将PDA涂覆的SiO_2颗粒浸在Pd镀液中,然后利用PDA中含N基团的还原能力将Pd物种原位还原为纳米簇合物.并采用高分辨透射电镜、前场扫描电镜、能量散射谱、X射线衍射、X射线光电子能谱、诱导耦合等离子体和红外光谱等手段对所得纳米复合物的结构、形貌和物化性质进行了表征.被PDA基团锚合的Pd NPs具有显著的小颗粒(30–40 nm)特性.作为一个可循环使用的纳米催化剂,SiO_2/PDA/Pd NPs在醇的需氧氧化反应中表现出高活性.另外,催化剂经回收和多次重复使用时未出现明显的失活.     

The properties of Pd/Au bimetallic colloidal catalysts stabilized by chitosan and prepared by simultaneous and stepwise chemical reduction of the precursor ions

Bimetallic Pd/Au nanoparticle catalysts were prepared with chitosan as a stabilizer. The preparation procedure included mixing or stepwise adding palladium and gold ions in various molar ratios followed by simultaneous or stepwise reduction using either methanol or sodium borohydride (nb) as reducing agents. TEM and UV-Vis characterization showed that the particle size of bimetallic Chi-Pd/Au prepared by simultaneous reduction was smaller than that of the samples prepared by stepwise reduction methods. The particle size varied in the 1 to 24 nm range at all Pd/Au molar ratios of bimetallic compositions. Sodium borohydride was the most effective reducing agent for the preparation of bimetallic Chi-Pd_coreA_ushell by the stepwise reduction. The catalytic activities of Chi-Pd/Au prepared by either simultaneous or stepwise reductions were generally higher than those of the respective monometallic systems whereas the most active catalysts were prepared by the simultaneous reduction. Shielding the palladium metal colloid with gold sol led to the decrease in catalytic activity. The turnover frequencies (TOFs) for Chi-Pd/Au-me in catalytic hydrogenation of 1-octene were as high as 20.855 and 89.336 for monometallic and bimetallic catalysts respectively. TOFs for Chi-Pd/Au-nb were in the region between 2.978 and 87.429. The core-shell and alloy formation of the bimetallic Chi-Pd/Au were inferred from the particle size measurements and evaluation of catalytic activity.     

Biogenic synthesis of palladium nanoparticles using Boswellia sarrata and their applications in cross-coupling reactions

A facile and green route for biogenic synthesis of palladium nanoparticles (PdNPs) using aqueous extract of nontoxic and renewable Boswellia sarrata leaves is reported. The as-synthesized PdNPs were systematically characterized by using ultraviolet (UV)–visible spectroscopy, X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The PdNPs were crystalline and cubic in nature with average particle size of ~6 nm and successfully employed as heterogeneous catalyst in the Suzuki–Miyaura and Mizoroki–Heck cross-coupling reactions. The PdNPs could be recycled up to five times with modest change in the catalytic activity.     

Synthesis and electrochemical characteristics of polymeric bimetallic Pt—Pd nanocatalysts

A method for the formation of catalytically active functional electrode nanocomposites with bimetallic platinum—palladium nanoparticles supported on a polymer matrix is described. The phase composition of nanocomposites was examined by X-ray powder diffraction, scanning electron microscopy and cyclic voltammetry were also applied in the study.