Monodisperse Palladium Nanoparticles Research Articles

Green and effective route for the synthesis of monodispersed palladium nanoparticles using herbal tea extract (Stachys lavandulifolia) as reductant, stabilizer and capping agent, and their application as homogeneous and reusable catalyst in Suzuki coupling reactions in water

A simple and eco‐friendly procedure has been devised for the green synthesis of palladium nanoparticles, using the aqueous extract of herbal tea (Stachys lavandulifolia), a renewable and nontoxic natural phyto‐exudate. The water‐soluble components of the extract act as reducing agent and stabilizer. This green route does not require a surfactant or capping agent for the growth of palladium nanoparticles. The generated nanoparticles were analysed using UV–visible spectroscopy, transmission electron microscopy, X‐ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X‐ray analysis and inductively coupled plasma. The palladium nanoparticles having spherical shape and dimensions of between 5 and 7 nm were employed as a homogeneous catalyst for Suzuki coupling reactions conducted in water under mild conditions. Good yields of products, a facile work‐up, no evidence of leached palladium from the catalyst surface and smooth recovery of the catalysis by adding ethyl acetate, which could be reused at least eight times, confirm the very good efficiency of the catalytic reaction. Copyright © 2014 John Wiley & Sons, Ltd.

Schottky diode performance of an Au/Pd/GaAs device fabricated by deposition of monodisperse palladium nanoparticles over a p-type GaAs substrate

Au/Pd/p-GaAs Schottky diodes were fabricated by simple assembly of monodisperse Pd nanoparticles on a p-type GaAs semiconductor. Monodisperse 5-nm Pd nanoparticles were synthesized via reduction of palladium(II) acetylacetonate in oleylamine using a borane tert-butylamine complex. The Au/Pd/p-GaAs Schottky diodes provided a barrier height of 0.68eV, which is higher than room-temperature values reported in the literature. A double distribution was observed for the barrier height for the Schottky diodes from I–V–T measurements. A decrease in temperature lowered the zero-bias barrier height and increased the ideality factor. These observations were ascribed to barrier height inhomogeneities at the interface that altered the barrier height distribution. Values of the series resistance obtained by the Norde method decreased with increasing temperature. Understanding the temperature dependence of the current–voltage characteristics of Au/Pd/p-GaAs devices might be helpful in improving the quality of Pd deposited on GaAs for future device technologies.

One-Pot Synthesis of Graphene-Supported Monodisperse Pd Nanoparticles as Catalyst for Formic Acid Electro-oxidation

To synthesize monodisperse palladium nanoparticles dispersed on reduced graphene oxide (RGO) sheets, we have developed an easy and scalable solvothermal reduction method from an organic solution system. The RGO-supported palladium nanoparticles with a diameter of 3.8 nm are synthesized in N-methyl-2-pyrrolidone (NMP) and in the presence of oleylamine and trioctylphosphine, which facilitates simultaneous reduction of graphene oxide and formation of Pd nanocrystals. So-produced Pd/RGO was tested for potential use as electrocatalyst for the electro-oxidation of formic acid. Pd/RGO catalyzes formic acid oxidation very well compared to Pd/Vulcan XC-72 catalyst. This synthesis method is a new way to prepare excellent electrocatalysts, which is of great significance in energy-related catalysis.

Controllable synthesis of palladium nanoparticles and their catalytic abilities in Heck and Suzuki reactions

The monodisperse palladium nanoparticles with the size of about 5.0nm were prepared by the thermal decomposition of palladium acetylacetonate in the presence of oleylamine and borane tributylamine complex. The palladium nanoparticles were loaded on the active carbon black by the sonication followed by the acetic acid cleaning, and then they are used as the nanocatalysts for carbon coupling reactions, such as Heck reactions and Suzuki reactions. The nanocatalysts can promote Heck reactions and Suzuki reactions efficiently with the high catalytic activity and stability. The nanocatalysts can be recycled for at least six times and their morphologies almost have no great changes. In addition, the catalytic performances of nanocatalysts would decrease with the repeated usages due to the increasing sizes of the palladium nanoparticles.

Size-Dependent Hydrogenation of p-Nitrophenol with Pd Nanoparticles Synthesized with Poly(amido)amine Dendrimer Templates

Monodisperse palladium nanoparticles consisting of 10–200 atoms were prepared using poly(amido)amine (PAMAM) dendrimer templates and were evaluated as catalysts using the model reduction of para-nitrophenol. The use of dendrimer templates allows for fine control of the average number of atoms per nanoparticle and systematic investigation of the effect of size on the catalytic activity of nanoparticles less than 2 nm in diameter. The palladium dendrimer-encapsulated nanoparticles (DENs) were found to be highly active for the hydrogenation of para-nitrophenol to para-aminophenol, with surface area-normalized rate constants ranging from 0.87 to 1.65 L s–1 m–2 (which is greater than any previously reported system). A near linear dependence of the observed rate constant on the synthetic Pd2+:dendrimer ratio was observed, suggesting that, within the size regime studied, most of the atoms lie on the surface of the nanoparticle and contribute to the catalytic activity. Interestingly, for Pd clusters containing be...

Chronoamperometric-based detection of hydrogen peroxide using palladium nanoparticles

Monodisperse palladium nanoparticles were used to develop a chronoamperometric–based sensor for the detection of hydrogen peroxide (H2O2). Thioether stabilised palladium nanoparticles with diameters of 1.8 nm, 2.0 nm and 3.0 nm were synthesised using a pyrolysis method. The palladium nanoparticles were immobilised on gold electrode surfaces using an organic linker. The effect of particle size on sensor performance was evaluated. The sensor was effective in detecting H2O2 in a Phosphate–Buffered Saline (PBS) solution and in milk samples. Detection limits of 45 µM and 75 µM, respectively, were obtained. The sensitivity of the sensor allowed detection of H2O2 at levels below the maximum admissible concentration.

HIGHLY CATALYTICALLY ACTIVE PALLADIUM NANOPARTICLES INCORPORATED INSIDE METAL-ORGANIC FRAMEWORK PORES BY DOUBLE SOLVENTS METHOD

Highly monodispersed palladium (Pd) nanoparticles have been successfully incorporated inside the mesopores of a metal–organic framework (MOF), MIL-101, without deposition of Pd nanoparticles on the external surfaces of framework by using the "double solvents" method, in which cyclohexane is used as a hydrophobic solvent to disperse the mesoporous MOF and an aqueous solution of Pd precursor is used as a hydrophilic solvent to fill the mesopores. The resulting Pd @MIL-101 composite is highly catalytically active for the reduction of 4-nitrophenol (4-NPh) by sodium borohydride ( NaBH4 ). The observed excellent catalytic performances are attributed to the small Pd nanoparticles within the pores of MIL-101.

Synthesis of monodispersed palladium nanoparticles using tannic acid and its optical non-linearity

Palladium nanoparticles with average size 11.3nm have been synthesized via a one-step reduction and capping method. This colloidal route using tannic acid does not require any other surfactant or capping agent to direct the growth of palladium nanoparticles. The effect of temperature on the conversion of Pd2+ ion to Pd0 is investigated. The growth process of nanoparticles is monitored using UV–visible spectra. The morphology and phase transformation have been confirmed by transmission electron microscopy and X-ray diffraction. An attempt to reveal the capping mechanism of tannic acid is done through FTIR analysis. The optical non-linearity of the samples was studied using open aperture Z-scan technique. The significance of this protocol for the generation of environmentally benign palladium nanoparticles lies mainly in its simplicity and cost effectiveness.

Back Cover: Mechanism of Formation of Palladium Nanoparticles: Lewis Base Assisted, Low-Temperature Preparation of Monodisperse Nanoparticles (Angew. Chem. Int. Ed. 45/2012)

Monodisperse palladium nanoparticles can be produced at lower temperature in the presence of a Lewis base via Pd amido and hydride intermediates. In their Communication on page 11350 ff., M. O. Wolf et al. use NMR studies to elucidate the mechanism of formation of amine-capped Pd nanoparticles from [Pd(acac)2]. Lewis bases increase the nucleophilicity of the amine to enhance the formation of a ketamine by-product, thus resulting in more facile formation of reactive intermediates and nanoparticles.

Hydrolytic dehydrogenation of ammonia borane catalyzed by reduced graphene oxide supported monodisperse palladium nanoparticles: High activity and detailed reaction kinetics

A highly active and stable catalyst for the hydrolytic dehydrogenation of ammonia borane (AB) was prepared by supporting monodisperse palladium nanoparticles (Pd NPs) on reduced graphene oxide (RGO) via a facile method. RGO was prepared via modified chemical route and used as support matrices for monodisperse Pd NPs that were formed by the reduction of palladium(II) acetylacetonate by borane tert-butylamine complex in the presence of oleylamine. RGO supported Pd NPs (RGO@Pd) show high activity and stability in the hydrolytic dehydrogenation of AB. The RGO@Pd catalysts provide the turnover frequency of 26.3min−1—the best among the all Pd-based catalysts and even comparable to Pt-based catalysts tested in the hydrolysis of AB. They are also very stable catalysts providing 11,600 total turnovers in 46h. The detailed reaction kinetics of catalytic hydrogen generation from the hydrolysis of AB revealed that the reaction proceeds first order with respect to the Pd concentration and zeroth order with respect to the AB concentration. The apparent activation parameters of the catalytic hydrolysis reaction were also calculated; apparent activation energy (Eaapp)=40±2 kJ mol−1, activation enthalpy (ΔH#,app)=38±1kJmol−1 and activation entropy (ΔS#,app)=−134±1JK−1mol−1.

Size Control and Catalytic Activity of Highly Dispersed Pd Nanoparticles Supported on Porous Glass Beads

This paper presents a novel in situ method to prepare monodispersed palladium nanoparticles supported on porous glass beads with an egg-shell structure at room temperature. This method integrates two processes of ion exchange and reduction in one step just by changing the solvent from water to alcohol. The monodispersed Pd nanoparticles around 3.75 nm in diameter with a face-centered cubic structure have been successfully prepared. The adsorption capacity for palladium reached 55.00 ± 0.55 mg/g in ethanol, which was 26 times larger than that in water. These Pd nanoparticles supported on porous glass beads showed an excellent catalytic performance through the hydrogenation of cyclohexene. In addition, this in situ method was also successfully applied to prepare monodispersed silver and gold nanoparticles supported on porous glass beads. Overall, this facile method provided an alternative for preparing a supported nanoparticle catalyst in a green way.

In Situ Reduction, Oxygen Etching, and Reduction Using Formic Acid: An Effective Strategy for Controllable Growth of Monodisperse Palladium Nanoparticles on Graphene

AbstractGraphene‐supported, monodisperse palladium nanoparticles (Pd NPs) are fabricated successfully by an effective strategy combining in situ reduction, O2 etching, and reduction using formic acid without the use of surfactants. By utilizing the reductive ability of graphene prepared previously by an in situ, self‐generating template route, Pd2+ ions are first absorbed and partly in situ reduced to give Pd NPs on graphene (denoted as Pd/GN‐SR). The Pd NPs in Pd/GN‐SR exhibit poor monodispersion, large particle size, and low loading on graphene. Some unreduced Pd2+ ions still exist in the solution. Second, formic acid as the secondary reducing reagent is introduced into the same solution after the in situ reduction. Some Pd NPs on graphene are gradually etched to Pd2+ ions by oxygen dissolved in the solution, and therefore become smaller NPs. Meanwhile, with the formic acid further reduction, these Pd2+ ions and unreduced Pd2+ ions are together reduced as small‐sized Pd NPs on graphene (denoted as Pd/GN‐FA). X‐ray powder diffraction, X‐ray photoelectron spectroscopy, and transmission electron microscopy measurements show that the Pd NPs in Pd/GN‐FA have smaller particle size and higher monodispersion on graphene compared with that in Pd/GN‐SR. Furthermore, the electrooxidation of formic acid on the Pd/GN‐FA catalyst has been investigated by cyclic voltammetry. The Pd/GN‐FA catalyst exhibits enhanced electrocatalytic activity and stability towards formic acid oxidation owing to the small size, the high monodispersion of Pd NPs, and the stabilizing effect of graphene. The results presented herein indicate that the Pd/GN‐FA might be a promising anode electrocatalyst in direct formic acid fuel cells.

New monodispersed palladium nanoparticles stabilized by poly-(N-vinyl-2-pyrrolidone): Preparation, structural study and catalytic properties

Mesitylene/1-hexene solvated palladium nanoparticles, obtained by metal vapour synthesis (MVS) technique, were stabilized in solution at room temperature with poly-(N-vinyl-2-pyrrolidone) (PVP) and isolated by precipitation with a diethyl ether or THF as brown powder. HRTEM and FT-IR analyses on samples with different Pd/PVP ratio (1%, 5%, 10%, 15%, 20 w/w%) showed palladium nanoparticles with mean diameters limited in the range 1.5–2.5 nm and the presence of competitive intermolecular interactions between C O groups and palladium atoms on nanoparticle surface. The Pd–PVP systems, dissolved in EtOH solvent, showed excellent catalytic activity and selectivity in the hydrogenation of aliphatic alkynes (1-hexyne, 2-hexyne, 3-hexyne, 3-hexyne-1-ol) to the corresponding (Z)-alkenes. The catalytic activity of Pd–PVP samples, dissolved in 1-methyl-2-pyrrolidinone (NMP), has been also evaluated in the Mizoroki–Heck C–C coupling reaction of iodobenzene and bromo-arenes with butyl acrylate showing high efficiency. Moreover, the catalyst can be quantitatively recovered at the end of the reaction by precipitation with diethyl ether and reused without significant loss of catalytic activity.

Synthesis of nearly monodisperse palladium (Pd) nanoparticles by using oleylamine and trioctylphosphine mixed ligands

In this paper, we report a facile method to prepare nearly monodisperse Pd nanoparticles by heating Pd(II) ions in 4- tert-butyltoluene solvent, in the presence of oleylamine and trioctylphosphine (TOP) ligands. It has been found the concentration of TOP ligand was highly pivotal for the formation of Pd nanoparticles. Without TOP, only aggregated Pd particles were obtained due to the reduction of Pd(II) by oleylamine. When the molar ratio of TOP to Pd(II) was less than two, well-protected Pd nanoparticles were obtained. However, when the molar ratio reached to two, only Pd(II)–TOP coordination complexes were obtained as the final product. Also, the addition of excess oleylamine as a supplementary protecting ligand has proven to be very important. By controlling the experimental conditions, Pd nanoparticles were obtained by this simple synthetic process, and the average size controllable in the range of 9.5–14.9 nm, with standard deviation in the range of 8–13%.

Electrodeposition of a palladium nanocatalyst by ion confinement in polyelectrolyte multilayers

A highly efficient and selective material for electrocatalytic hydrogenation has been prepared by depositing monodisperse palladium nanoparticles of size (6+/-1) nm by electrochemical reduction of PdCl(4)(2-) confined in a polyelectrolyte multilayer film.

Monodisperse Thioether-Stabilized Palladium Nanoparticles: Synthesis, Characterization, and Reactivity

Size control of monodisperse palladium nanoparticles with sizes ranging from 1.7 to 3.5 nm was accomplished using thioethers as stabilizing ligands, in a one-step procedure. Modulation of the reaction temperature, reaction time, solvent, and carbon chain length of the thioether provided control over the nanoparticle size and size distribution. The resulting Pd nanoparticles were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD). 1H NMR spectroscopy provided insight into the thioether−Pd nanoparticle surface interaction. To demonstrate the catalytic activity of the thioether-stabilized Pd nanoparticles, hydrogenation reactions were carried out using the as-synthesized Pd nanoparticles. We observed a trend in the reactivity of the nanoparticles with respect to their size, however, recovery of the nanoparticles following subsequent reactions was rather challenging. Immobilization of the Pd nanoparticles onto commerci...

Synthesis of monodispersed palladium nanoparticles to study structure sensitivity of solvent-free selective hydrogenation of 2-methyl-3-butyn-2-ol

A novel method for isolation of monodispersed Pd nanoparticles from a reverse microemulsion was developed using hydrocarbon evaporation and methanol-assisted particle purification from a surfactant. Fcc Pd nanoparticles of 6, 8, 11, and 13 nm in diameter were isolated from water/AOT/isooctane mixture and used to study a size effect during solvent-free hydrogenation of 2-methyl-3-butyn-2-ol to 2-methyl-3-buten-2-ol. The initial TOF calculated per mole of surface palladium atoms was duplicated when particle size was increased from 6 to 13 nm but remained constant when accounted per number of specific Pd atoms on Pd(111) facets. Selectivity to olefinic alcohol was not size-dependent, but an increase in particle size decreased the byproduct ratio of dimers to saturated alcohol. Acetylenic alcohol hydrogenation is shown to be a structure-sensitive but size-independent reaction for Pd particles with size of 6–13 nm. The work shows also that the Pd size controlled the reaction rate and the byproduct distribution.

Applications of pore-expanded mesoporous silica 6. Novel synthesis of monodispersed supported palladium nanoparticles and their catalytic activity for Suzuki reaction

MCM-41 silica, whose pores have been expanded by post-synthesis treatment with N , N -dimethyldecylamine, was used as an inexpensive high-surface area, large-pore support for rapid preparation of monodispersed palladium nanoparticles. The nanoparticles, initially prepared at room temperature, showed remarkable thermal stability as their size increased from 2.8 ± 0.8 to only 3.4 ± 0.8 nm after calcination at 500 °C in air followed by reduction in H 2 at the same temperature. These materials were found to be highly active and stable catalysts for the Suzuki coupling reaction with virtually no leaching.

A simple route to water-soluble size-tunable monodispersed Pd nanoparticles from light decomposition of Pd(PPh 3) 4

Water-soluble monodispersed palladium nanoparticles of diameters 2.5, 5 and 10 nm controlled by varying the concentration of CTAB (hexadecyltrimethylammonium bromide) micelles have been prepared from light decomposition of Pd(PPh 3) 4. The size and structure of these single crystalline particles have been confirmed using UV–vis spectroscopy, high resolution transmission electron microscope, energy dispersive X-ray analysis and powder X-ray diffraction methods.

Synthesis and characterization of lower size, laurylamine protected palladium nanoparticles

A procedure to synthesize lower size mono dispersed palladium nanoparticles is described. The nanoparticles are stabilized by lauryl amine and are isolable as dispersible solids. The particles are characterized by UV–Vis, FT-IR, XRD, STM and TEM techniques.