PdAg2 nanoparticles in aqueous solution: Preparation, characterization, and catalytic properties

The reduction of a heterobimetallic complex, Pd(OOCMe)₄Ag₂(HOOCMe)₄, with hydrogen or sodium borohydride in an aqueous solution produces PdAg₂ nanoparticles of an alloy or intermetallic type. It is shown that the catalytic activity of the particles in the reduction of methyl viologen with hydrogen is lower than that of palladium nanoparticles of the same size. Therewith, ??borohydride?? nanoparticles manifest a higher catalytic activity than do ??hydrogen?? ones. Unlike silver nanoparticles, PdAg₂ nanoparticles do not catalyze the decomposition of hydrazine.     

Synthesis and properties of Cu–Pd hydrosol: Hydrogen reduction of Cu<Superscript>2+</Superscript> ions catalyzed by palladium nanoparticles

A method has been developed for obtaining Cu–Pd hydrosols via catalytic reduction of copper ions by hydrogen on seed palladium nanoparticles 2.5 ± 0.3 nm in size. It has been found that reduction of Cu²⁺ to metal proceeds stage-by-stage through the formation of an intermediate Cu⁺ ion. Cu–Pd hydrosol remains stable with respect to sedimentation and aggregation for several weeks. The hydrodynamic size of Cu–Pd nanoparticles increases proportionally to the copper content in particles. It has been shown that this is due to an acidification of the solution as a result of H⁺ ions formation via the reaction of reduction of Cu²⁺ ions by hydrogen.     

Catalytic activity of palladium supported on single wall carbon nanotubes compared to palladium supported on activated carbon Study of the Heck and Suzuki couplings, aerobic alcohol oxidation and selective hydrogenation

Nanoparticles (2–10 nm) of palladium have been deposited on single wall carbon nanotubes (SWNT) by spontaneous reduction from Pd(OAc)₂ or from oxime carbapalladacycle. These catalysts exhibit higher catalytic activity than palladium over activated carbon (Pd/C) for the Heck reaction of styrene and iodobenzene and for the Suzuki coupling of phenylboronic and iodobenzene. This fact has been attributed as reflecting the dramatic influence of the size particle on the activity of the palladium catalyst for CC bond forming reactions as compared to other reaction types less demanding from the point of view of the particle size. Thus, in contrast to the Heck and Suzuki reactions, Pd/C is more active than palladium nanoparticles deposited on SWNT for the catalytic oxidation by molecular oxygen of cinnamyl alcohol to cinnamaldehyde and for the hydrogenation of cinnamaldehyde to 3-phenylpropionaldehyde.     

Palladium nanoparticles supported on mesoporous natural phosphate: An efficient recyclable catalyst for nitroarene reduction

We report the preparation of palladium nanoparticles supported on mesoporous natural phosphate (Pd@NP) using a wetness impregnation method. The prepared catalyst was characterized using various techniques. Furthermore, the reduction and preparation of the palladium nanoparticles was followed using UV–visible spectra. Based on the Scherrer equation, the crystallite size of the as‐synthesized palladium nanoparticles was 10.88 nm. The performance of the synthesized catalyst was investigated in the reduction of 4‐nitrophenol as a model substrate to 4‐aminophenol using NaBH₄ as a hydrogen source. Moreover, catalytic reduction of various nitroarenes was studied and monitored using UV–visible spectroscopy and gas chromatography. The Pd@NP catalyst showed a high activity for the selected reaction and could be recycled.     

Nano-scale effects in electrochemistry

We report combined scanning tunneling microscopy and electrochemical reactivity measurements on individual palladium nanoparticles supported on a gold surface. It is shown that the catalytic activity towards electrochemical proton reduction is enhanced by more than two orders of magnitude as the diameter of the palladium particles parallel to the support surface decreases from 200 to 6 nm. Density functional theory (DFT) calculations combined with molecular dynamics (MD) simulations have been used to investigate the origin of the effect. It is concluded that the size effect is given by the thickness-variation of the support-induced strain at the surface of the palladium nanoparticles.     

Properties of palladium catalysts on carbon supports prepared from chemically modified and activated anthracites

The influence of chemical modification and thermal activation on the porous structure of Donbass anthracites (Ukraine) and on the state and catalytic properties of supported palladium has been studied. The most regular distribution of supported palladium particles with an average size of about 2 nm was observed for the supports prepared from the chemically modified anthracites. The activity of supported palladium in the liquid-phase hydrogenation of cyclohexene varies more than 10-fold depending on the preparation method of the anthracite support. The catalysts with the palladium nanoparticles located in micropores of the carbon support exhibit a lower catalytic activity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Immobilized palladium nanoparticles on silica functionalized N-propylpiperazine sodium N-propionate (SBPPSP): catalytic activity evaluation in copper-free Sonogashira reaction

An efficient heterogeneous palladium catalyst system has been developed based on immobilization of Pd nanoparticles on silica-bonded N-propylpiperazine sodium N-propionate (SBPPSP) substrate. SBPPSP substrate can stabilize the Pd nanoparticles effectively so that it can improve their stability against aggregation. In addition, grafted piperazine species on to the silica backbone prevent the removing of Pd nanoparticles from the substrate surface. Transmission electron microscopy (TEM) of catalyst is shown the size of Pd nanoparticles, also it confirmed by particle size analyzer which shown the average size of 21 nm for Pd. The catalytic activity of these catalysts was investigated in the Sonogashira reaction. The catalyst could be recycled several times without appreciable loss in catalytic activity.     

Structure and catalytic properties of nanosized alumina supported platinum and palladium particles synthesized by reaction in microemulsion

Mixtures of nanosized platinum and palladium particles have been prepared by reduction of salt-containing microemulsion droplets using hydrazine as the reducing agent. To avoid possible negative effects of the presence of sulfur compounds during the preparation the microemulsion was made using the sulfur-free nonionic polyoxyethylene 4 lauryl ether surfactant. Transmission electron microscopy showed that the as-prepared mixtures contained crystalline platinum particles of fairly homogeneous size (20 to 40 nm) with adsorbed amorphous palladium particles 2 to 5 nm in size. Catalyst samples were prepared by depositing the nanoparticles on a gamma-Al(2)O(3) support followed by heating in air at 600 degrees C. Alloyed particles of platinum and palladium with sizes ranging from 5 to 80 nm were obtained during the heating. The majority of the particles had the fcc structure and their compositional range was dependent upon the Pt:Pd molar ratio of the microemulsion. A catalyst prepared from a microemulsion with a 20:80 Pt:Pd molar ratio showed the highest catalytic activity for CO oxidation, while pure platinum and palladium catalysts showed higher sulfur resistance. These results differ from the performance of conventional wet-impregnated catalysts, where a 50:50 Pt:Pd molar ratio resulted in the highest catalytic activity as well as the highest sulfur resistance.     

Size-Controlled Synthesis of Palladium Nanoparticles

Palladium nanoparticles protected by PVP were obtained first by reducing PdCl₂ with NaBH₄ solution. Then different size palladium nanoparticles with a large size range (1.49 nm ～ 23.26 nm) were prepared by the multi-step reduction of PdCl₂ by hydrogen adsorbed on the surface of palladium nanoparticles. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) were used to characterize the nanoparticles. The increasing value of average diameter from the first to the eighth reduction reaction is about 0.58 nm, from the ninth to the fifteenth reduction reaction the value is about 2.44 nm.     

Composition Control Synthesis and Catalytic Properties in the Suzuki Reaction of Bimetallic PdSn Nanoparticles

We have successfully prepared 6.5 nm palladium tin (PdSn) alloy nanoparticles (NPs) with tunable compositions by high‐temperature reduction of tin acetate and palladium bromide in the presence of oleylamine and trioctylphosphine. The catalytic activities of PdSn NPs with different compositions were evaluated through Suzuki reactions. The PdSn nanocatalysts show better catalytic activity on Suzuki reactions than an equal amount of pure Pd NPs, and their catalytic activities are highly composition dependent. Among these NPs, Pd₆₃Sn₃₇/C NPs exhibited the highest catalytic performance with higher reaction activity, lower Pd leaching properties, and higher stability even after eight recycle reactions.     

Novel palladium nanoparticles supported on mesoporous natural phosphate: Catalytic ability for the preparation of aromatic hydrocarbons from natural terpenes

Various ratios of palladium nanoparticles supported on mesoporous natural phosphate (Pd@NP) were prepared using the wetness impregnation method. The prepared catalysts were characterized by IR, XRD, CV, SEM, EDX, XRF, TEM and BET analysis. The reduction and preparation of the palladium nanoparticles afford a crystallite size of 10.88 nm. The performance of the synthesized catalyst was investigated in the solvent-free dehydroaromatization of α-, β- and γ-himachalene mixture from Cedrus atlantica oil as a model substrate. In order to achieve an efficient and selective catalysis, the catalytic dehydroaromatization of various terpenes such as limonene, limonaketone, carvone, carveol and perillyl alcohol was studied. The Pd@NP catalyst performed a high catalytic activity, selectivity and recyclability in the terpenes dehydroaromatization reaction.     

Activity of palladium nanoparticles on graphene oxide in the Suzuki—Miyaura reaction

A convenient express method for obtaining palladium nanoparticles on the graphene oxide support was developed. The data of transmission electron microscopy and X-ray diffraction analysis indicated the formation of palladium nanoparticles with an average size of 2 nm. The obtained nanocomposite material showed high catalytic activity in the cross-coupling reaction of bromobenzene with phenylboronic acid. The efficiency of the catalyst increases when using a mixture of organic solvents with water.     

Sustainable Catalysis: Rational Pd Loading on MIL‐101Cr‐NH2 for More Efficient and Recyclable Suzuki–Miyaura Reactions

Palladium nanoparticles have been immobilized into an amino‐functionalized metal–organic framework (MOF), MIL‐101Cr‐NH₂, to form Pd@MIL‐101Cr‐NH₂. Four materials with different loadings of palladium have been prepared (denoted as 4‐, 8‐, 12‐, and 16 wt %Pd@MIL‐101Cr‐NH₂). The effects of catalyst loading and the size and distribution of the Pd nanoparticles on the catalytic performance have been studied. The catalysts were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier‐transform infrared (FTIR) spectroscopy, powder X‐ray diffraction (PXRD), N₂‐sorption isotherms, elemental analysis, and thermogravimetric analysis (TGA). To better characterize the palladium nanoparticles and their distribution in MIL‐101Cr‐NH₂, electron tomography was employed to reconstruct the 3D volume of 8 wt %Pd@MIL‐101Cr‐NH₂ particles. The pair distribution functions (PDFs) of the samples were extracted from total scattering experiments using high‐energy X‐rays (60 keV). The catalytic activity of the four MOF materials with different loadings of palladium nanoparticles was studied in the Suzuki–Miyaura cross‐coupling reaction. The best catalytic performance was obtained with the MOF that contained 8 wt % palladium nanoparticles. The metallic palladium nanoparticles were homogeneously distributed, with an average size of 2.6 nm. Excellent yields were obtained for a wide scope of substrates under remarkably mild conditions (water, aerobic conditions, room temperature, catalyst loading as low as 0.15 mol %). The material can be recycled at least 10 times without alteration of its catalytic properties.     

纳米铂颗粒的控制生长

Different size platinum nanoparticles, ranging in size from 1.8-14.1 nm, were prepared by multi-step reduction of H2PtCl6 by hydrogen adsorbed on platinum atoms. Transmission electronic microscopy and X-ray diffraction were used to characterize the nanoparticles. After thirty-two iterations of the reaction, the diameter of platinum nanoparticles increased from 1.8 nm to 14.1 nm. The average iterative increase was approximately 0.4 nm. The size distribution of the nanoparticles was narrow. Synthesis procedures which allow for control of platinum nanoparticle size offer the possibility for the further research into how the sizes of nano-catalysts effect catalytic activity.     

Size-controlled synthesis and characterization of polyvinyl alcohol coated palladium nanoparticles

In order to synthesize stable, catalytically active palladium nanoparticles with low polydispersity, a one-pot synthesis by the facile reduction of palladium chloride with citric acid in an aqueous solution of steric stabilizer polyvinyl alcohol (PVA) has been developed. The resulting nanoparticles are highly water-dispersible, excellent electro-catalysts, and have long shelf life. The palladium nanoparticles have been characterized by physico-chemical, spectroscopic, microscopic, and CV studies. The average size of the nanoparticles can be readily tuned from 8.1 to 53 nm by controlling the extent of reflux for mixtures containing suitable concentrations of metal ion, reducing agent and capping polymer, which also influence the size. Despite the surface-protecting action of PVA, the palladium nanoparticles are electro-catalytically active and exhibit size-dependent electro-catalytic behavior.     

Noble metallic nanoparticles from waste Nypa fruticans fruit husk: Biosynthesis,characterization, antibacterial activity and recyclable catalysis

Biogenic synthesis of noble metal nanoparticles is particularly interested due to the effective applications for plasmonic catalysis and bioactivity. In this work, aqueous extract of waste Nypa fruticans (NF) fruit husk was utilized to synthesize silver nanoparticles (NF-AgNPs) and gold nanoparticles (NF-AuNPs). The effected parameters on the green reduction of metallic nanoparticles (MNPs) were investigated. Under optimum conditions of concentration, temperature and time, the biosynthesized NF-AgNPs and NF-AuNPs showed spherical nanoparticles with average size of 10–15 nm and 15–20 nm, respectively. The presence of AgCl in NF-AgNPs has been demonstrated by X-ray diffraction analysis. The elemental components of all samples confirmed the presence of anions and cations come from the aqueous extract. The biosynthesized nanoparticles were evaluated bacterial activity against three bacterial strains. NF-AgNPs exhibited selective antibacterial activity against Bacillus cereus but no activity against Staphylococcus aureus and Salmonella typhimurium at all tested concentrations. The recyclable catalysis activity of the biosynthesized nanoparticles was evaluated for the reduction of nitrophenols in the presence of sodium borohydride which possessed good catalytic performance in six running numbers. Additionally, AgCl played role as a source supplying AgNPs has been demonstrated in catalytic reduction of p-nitrophenol. For study of catalytic kinetic, NF-AgNPs possessed higher rate constant in comparison with NF-AuNPs whereas TOF values of NF-AuNPs was determined to be higher than those of NF-AgNPs.     

Oxygen reduction at platinum monolayer islands deposited on Au(111)

Atomic monolayer islands of Pt, namely, two-dimensional Pt nanoparticles, on a Au(111) electrode have been studied for the first time, focusing on their electrocatalytic activities for oxygen reduction in acid solutions. The Pt islands' electrodes were prepared using the self-assembled technique of thiols together with the replacement of Pt with a Cu monolayer. The states of adsorbed OH and the catalytic activities of oxygen reduction were sensitive to the Pt island size. As island size decreased, a delay in the reduction of surface oxide was observed. However, negligible influence of adsorbed OH on activity for oxygen reduction was observed. Pt islands of sizes ranging from 5 to 10 nm showed higher specific catalytic activities for oxygen reduction. Specific catalytic activities decreased by a factor of 10 with a decrease in island sizes from 5.5 to 3.1 nm. Size effects observed in Pt monolayer islands were discussed in comparison with three-dimensional nanoparticles, to obtain information concerning the size effects of metal nanoparticles.     

Formation of palladium hydride nanoparticles in Pd/C catalyst as evidenced by <Emphasis Type="Italic">in situ</Emphasis> XAS data

X-ray absorption spectroscopy was used to investigate the formation of palladium hydride upon treatment of metallic Pd nanoparticles 0.9–2 nm in size supported on carbon-carbonaceous material SIB UNIT? with hydrogen. Nanoparticles with the size as small as 0.9 nm can still form hydride PdH. Changes in the chemical composition of gaseous medium cause a reversible transformation of metallic palladium nanoparticles to palladium hydride nanoparticles with tentative stoichiometry PdH_0.6.     

胶原纤维接枝多酚负载纳米钯的制备及其对硝基苯加氢的催化特性

以胶原纤维(CF)接枝表棓儿茶素棓酸脂(EGCG)为载体,制备了新型非均相钯(Pd)纳米催化剂(CF-EGCG-Pd).EGCG作为"桥分子"不仅对Pd纳米颗粒具有锚定作用,而且能控制Pd纳米颗粒的大小及分布.通过SEM、TEM、XRD、XPS对该催化剂的形貌和物理特性能进行了表征,发现该催化剂具有规整的纤维结构,在胶原纤维的外表面形成了高分散的平均粒径在3.8 nm的Pd纳米颗粒.将该催化剂用于硝基苯液相催化加氢反应,结果表明在308 K和1.0 MPa氢压下,硝基苯转化速率(TOF)达到34.13 mol·mol-1·min-1,苯胺选择性为100%,催化剂重复使用3次其催化活性基本不变.     

Hydrogenation catalysts based on platinum- and palladium-containing nanodiamonds

Platinum and palladium nanoparticles of 4–5 nm size applied at nanodiamonds have been shown to efficiently catalyze liquid-phase hydrogenation of different organic compounds (nitrocompounds, azomethines, and unsaturated hydrocarbons and alcohols) under mild conditions (T = 318 K, hydrogen pressure of 0.1 MPa, solution in ethanol). Using of palladium on nanodiamond containing 3 wt % of metal has been most efficient.