Reduction Of Palladium Research Articles

Ligand-controlled fabrication of core-shell PdNi bimetallic nanoparticles as a highly efficient hydrogenation catalyst

A series of PdNi/SiO2 bimetallic nanoparticles were synthesized using polyvinylpyrrolidone (PVP) and 2,6-bis(5,6-dimethyl-1,2,4-triazine-3-yl) pyridine (BTP) as ligands through sol-gel method. BTP was proved to be an effective ligand that can delay the reduction of palladium (II), which helps the formation of palladium-rich shell bimetallic nanoparticles. Pd3Ni7-BTP/SiO2 exhibited the best catalytic performance (TOF=180h−1) among all the catalysts for hydrogenation of nitrobenzene under ambient conditions and was successfully reused for at least five times without loss in activity. The excellent catalytic performance could be ascribed to the small nanoparticle size (2.14nm) and the palladium-rich shell structure it bears.

The Effect of Graphene on Catalytic Performance of Palladium Nanoparticles Decorated with Fe3O4, Co3O4, and Ni (OH)2: Potential Efficient Catalysts Used for Suzuki Cross—Coupling

In this research, we report a scientific investigation of an efficient method used for the synthesis of highly active Palladium Nanoparticles decorated with Fe3O4, Co3O4, and Ni (OH)2 Supported on Graphene as Potential Efficient Catalysts for Suzuki Cross—Coupling. Pd/Fe3O4 nanoparticles supported on graphene nanosheets (Pd/Fe3O4/G) showed an excellent catalytic activity for Suzuki coupling reactions and recycled for up to four times without loss of catalytic activity. An efficient magnetic catalyst has been successfully synthesized using a simple, reproducible fast and reliable method using microwave irradiation conditions. The prepared catalysts are magnetic as in case of iron and cobalt oxides which is an advantage in the separation process of catalyst from the reaction medium via applying a strong external magnetic field. The synthesis approach is based on the Microwave (MW)-assisted simultaneous reduction of palladium and ferric nitrates in the presence of graphene oxide (GO) nanosheets using hydrazine hydrate as the reducing agent. The results provide a fundamental understanding of the system variables by comparing the catalytic activity and recyclability of different catalysts with different properties. The most active and recyclable catalyst was Pd–Fe3O4—supported on graphene which offers several added advantages including recyclability of up to seven times, mild reaction conditions, and short reaction times in an environmentally benign solvent system. Furthermore, the magnetic properties imparted by the Fe3O4 component of the catalyst enables the catalyst to be easily isolated and recycled, thus greatly simplifying the ability to purify the reaction products and increasing the economic value of the catalyst. The utility of these magnetic catalysts towards Suzuki cross coupling reaction was also demonstrated. The high activity and recyclability of these catalysts are attributed to a strong catalyst-support interaction where the defect sites in the reduced GO nanosheets act as nucleation centers for anchoring the Pd and Fe3O4 nanoparticles thus minimizing the potential of their agglomeration and the subsequent decrease in the catalytic activity.

Platinum Inhibits Low-Temperature Dry Lean Methane Combustion through Palladium Reduction in Pd-Pt/Al2 O3 : An In Situ X-ray Absorption Study.

Palladium-platinum bimetallic catalysts supported on alumina with palladium/platinum molar ratios ranging from 0.25 to 4 are studied in dry lean methane combustion in the temperature range of 200 to 500 °C. Platinum addition decreases the catalyst activity, which cannot be explained by the decrease in dispersion or the structure sensitivity of the reaction. In situ X-ray absorption near-edge structure and extended X-ray absorption fine structure spectroscopy measurements have been conducted for monometallic Pd, Pt, and 2:1 Pd-Pt catalysts. Monometallic palladium is fully oxidized in the full temperature range, whereas platinum addition promotes palladium reduction, even in a reactive oxidizing environment. The Pd/PdO weight ratio in bimetallic Pd-Pt 2:1 catalysts decreases from 98/2 to 10/90 in the 200-500 °C temperature range under the reaction conditions. Thus, platinum promotes the formation of the reduced palladium phase with a significantly lower activity than that of oxidized palladium. The study sheds light on the effect of platinum on the state of the active palladium surface under low-temperature dry lean methane combustion conditions, which is important for methane-emission control devices.

Decoupling and elucidation of surface-driven processes during inorganic mineralization on virus templates

There is a lack of fundamental information about the molecular processes governing biomineralization of inorganic materials to produce nanostructures on biological templates. This information is essential for the directed synthesis of high quality nanomaterials via biotemplating. We characterized palladium (Pd) mineralization via the individual adsorption, reduction, and nanocrystal growth processes, which simultaneously occur during the hydrothermal synthesis on the Tobacco mosaic virus (TMV). The adsorption of precursor and reduction of palladium were decoupled through UV–vis Spectroscopy and in situ X-ray absorption spectroscopy studies. The role of additional cysteine (Cys) residues, ionic strength, and coating density on the fundamental parameters describing these processes were quantitatively evaluated. Primary nanocrystal growth and structural orientation of Pd nanoparticles was characterized using in situ small angle X-ray scattering. The adsorption, reduction of Pd species, and nanocrystal sizes were significantly changed on addition of Cys residues to the amino terminus of the TMV coat protein. Reduction of Pd on an already coated virion was dependent on the Pd surface area, and was hindered by the presence of residual salt. Furthermore, trends in Pd adsorption intensity and capacity suggested that chloride ions affected the adsorption equilibrium. Application of this fundamental approach with further optimization of parameters dictating biomineralization would facilitate directed synthesis and scale up of bioinorganic systems.

Pd 나노 촉매가 도입된 나피온 막의 기계적 강도 및 고분자 전해질막 연료전지 (PEMFC) 성능

>> A simple solid state incorporation method was employed in order to incorporate Pd nanocatalyst into a Nafion film for polymer electrolyte membrane fuel cell (PEMFC) via the reduction of palladium (II) bis (acetylacetonate), Pd(acac)2. It was sublimed, penetrated into Nafion film and then reduced to Pd nanoparticles simultaneously in a glass reactor of N2 atmosphere at 180 o C for 1, 3 and 5 min. This reaction was took place without any reducing agent and any solvent. The morphology of the Pd nanoparticles was observed by transmission electron microscopy (TEM), and Pd distribution was analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). And 23% modification of tensile strength of Pd/Nafion composite film was measured by universal testing machine and I–V curve was estimated by using a unit cell with 5×5 cm 2 active area.

Stereoselective synthesis of tricyclic compounds by intramolecular palladium-catalyzed addition of aryl iodides to carbonyl groups.

Starting from γ-ketoesters with an o-iodobenzyl group we studied a palladium-catalyzed cyclization process that stereoselectively led to bi- and tricyclic compounds in moderate to excellent yields. Four X-ray crystal structure analyses unequivocally defined the structure of crucial cyclization products. The relative configuration of the precursor compounds is essentially transferred to that of the products and the formed hydroxy group in the newly generated cyclohexane ring is consistently in trans-arrangement with respect to the methoxycarbonyl group. A transition-state model is proposed to explain the observed stereochemical outcome. This palladium-catalyzed Barbier-type reaction requires a reduction of palladium(II) back to palladium(0) which is apparently achieved by the present triethylamine.

Polymer and Membrane Design for Low Temperature Catalytic Reactions.

Catalytically active asymmetric membranes have been developed with high loadings of palladium nanoparticles located solely in the membrane's ultrathin skin layer. The manufacturing of these membranes requires polymers with functional groups, which can form insoluble complexes with palladium ions. Three polymers have been synthesized for this purpose and a complexation/nonsolvent induced phase separation followed by a palladium reduction step is carried out to prepare such membranes. Parameters to optimize the skin layer thickness and porosity, the palladium loading in this layer, and the palladium nanoparticles size are determined. The catalytic activity of the membranes is verified with the reduction of a nitro-compound and with a liquid phase Suzuki-Miyaura coupling reaction. Very low reaction times are observed.

CERIUM(III) CARBONATE HYDROXIDE NANOPARTICLES ENCRUSTED BY METALLIC PALLADIUM. SYNTHESIS AND INVESTIGATION

Cerium(III) nitrate and urea solution mixture were treated by hydrothermal and microwavehydrothermal methods, as a result cerium(III) carbonate hydroxide nanoparticles (22-37 nm) were obtained. Cerium(III) carbonate hydroxide nanoparticles, encrusted by palladium were obtained using palladium reduction process from cerium(III) carbonate hydroxide solution. It is shown, that palladium occurrence disturbs hard hydrogen bond system, leading to carbonate hydroxide nanoparticles structure disorder and also increases efficiency of catalytic reactivity process.

Highly active carbon supported Pd cathode catalysts for direct formic acid fuel cells

One of the drawbacks of low-temperature fuel cells is high price of platinum-based catalysts used for the electroreduction of oxygen at the cathode of the fuel cell. The aim of this work is to develop the palladium catalyst that will replace commonly used platinum cathode catalysts. A series of palladium catalysts for oxygen reduction reaction (ORR) were prepared and tested on the cathode of Direct Formic Acid Fuel Cell (DFAFC). Palladium nanoparticles were deposited on the carbon black (Vulcan) and on multiwall carbon nanotubes (MWCNTs) surface by reduction of palladium(II) acetate dissolved in ethanol. Hydrazine was used as a reducing agent. The effect of functionalization of the carbon supports on the catalysts physicochemical properties and the ORR catalytic activity on the cathode of DFAFC was studied. The supports were functionalized by treatment in nitric acid for 4h at 80°C. The structure of the prepared catalysts has been characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscope (TEM) and cyclic voltammetry (CV). Hydrophilicity of the catalytic layers was determined by measuring contact angles of water droplets. The performance of the prepared catalysts has been compared with that of the commercial 20wt.% Pt/C (Premetek) catalyst. The maximum power density obtained for the best palladium catalyst, deposited on the surface of functionalized carbon black, is the same as that for the commercial Pt/C (Premetek). Palladium is cheaper than platinum, therefore the developed cathode catalyst is promising for future applications.

Ni@Pd core-shell nanoparticles supported on a metal-organic framework as highly efficient catalysts for nitroarenes reduction

Ni@Pd core-shell nanoparticles with a mean particle size of 8–9 nm were prepared by solvothermal reduction of bivalent nickel and palladium in oleylamine and trioctylphosphine. Subsequently, the first-ever deposition of Ni@Pd core-shell nanoparticles having different compositions on a metal-organic framework (MIL-101) was accomplished by wet impregnation in n-hexane. The Ni@Pd/MIL-101 materials were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy and also investigated as catalysts for the hydrogenation of nitrobenzene under mild reaction conditions. At 30 °C and 0.1 MPa of H2 pressure, the Ni@Pd/MIL-101 gives a TOF as high as 375 h−1 for the hydrogenation of nitrobenzene and is applicable to a wide range of substituted nitroarenes. The exceptional performance of this catalyst is believed to result from the significant Ni-Pd interaction in the core-shell structure, together with promotion of the conversions of aromatics by uncoordinated Lewis acidic Cr sites on the MIL-101 support.

Supercritical CO2 mediated synthesis and catalytic activity of graphene/Pd nanocomposites

Graphene sheets were decorated with palladium nanoparticles using a facile and efficient method in supercritical CO2. The nanoparticles were formed on the graphene sheets by the simple hydrogen reduction of palladium(II) hexafluoroacetylacetonate precursor in supercritical CO2. The product was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Highly dispersed nanoparticles with various sizes and shapes adhered well to the graphene sheets. The composites showed high catalytic activities for the Suzuki reaction under aqueous and aerobic conditions within 5min. The effects of the different Pd precursor loadings on the catalytic activities of the composites were also examined.

DETERMINATION OF PALLADIUM IN HYDROGENATION CATALYSTS BY HR-CS FAAS METHOD

Present paper deals with analytical control of hydrogenation supported catalysts (Pd/AC) composition using high-resolution continuum source atomic absorption spectrometry with flame atomization (HR-CS FAAS). Catalysts were prepared with expected 3 wt. % Pd content by the simple technique of deposition – reduction of palladium in a basic environment. Formaldehyde was applied as the reduction agent. The working conditions (gas flow and burner height) for determination of the catalytically active component in the prepared Pd/AC catalysts were found. Prior to the analysis by HR-CS FAAS method Pd/AC was subjected to microwave (MW) assisted digestion in the environment of strong oxidizing acids. Appropriate digestion time of 15 min and temperature of 200 °C had been also experimentally obtained.

Microwave-assisted synthesis graphite-supported Pd nanoparticles for detection of nitrite

The graphite-supported palladium (Pd/Grp) nanocomposite modified glassy carbon (GC) electrode was fabricated and their catalytic properties towards nitrite were studied. Pd/Grp was synthesized by microwave-assisted hydrogen reduction of palladium (II) acetate with graphite power. TEM displayed a high density of slightly aggregated Pd nanoparticles loading on the surface of graphite power with a diameter of 5–15nm. The electrode exhibits enhanced electro-catalytic behavior to the oxidation of nitrite compared to the activated carbon-supported palladium and SiO2-supported palladium modified GC electrode. Under the optimal conditions, the Pd/Grp modified GC electrode can be used to determine nitrite concentration in a wide linear range and a limit of detection of 0.071μM at a signal-to-noise ratio=3 (S/N=3). The sensitivity of the electrode was 0.29μAμM−1cm−2.

Role of PdAg interface in Pd-Ag/SiO2 bimetallic catalysts in low-temperature oxidation of carbon monoxide

An approach to the development of bimetallic nanoparticles with the separated but interacting phases of silver and palladium was proposed to effectively separate the active sites of silver, which possess high activity in activation of molecular oxygen, and the sites of palladium-containing phases, which are responsible for CO adsorption. The structure of PdAg particles was determined using X-ray diffraction analysis, electronic diffuse reflectance spectroscopy, and temperature-programmed reduction. It was found that the introduction of silver led to easier reduction of palladium from oxidized states in an atmosphere of CO. The activity of the bimetallic PdAg catalysts in the oxidation of CO increased, as compared with that of the Pd/SiO2 catalyst. The oxidized bimetallic catalyst, in which palladium occurred in an oxide state, was even more effective in the oxidation of CO; this can be related to the better cooperation of the active sites of silver and palladium oxide, which are responsible for the activation and conversion of CO and oxygen at the Ag-PdO interfacial boundary.

Reduction of palladium onto pyrogallol-derived nano-resin and its mechanism

In this study, we designed and synthesized a pyrogallol containing resol nano resin (PGNR) which has the ability to reduce palladium(II) ions to metallic form has been designed and synthesized. The main possible application area of PGNR particles is recycling comparatively dilute e-wastes. According to thermal gravimetric analysis, weight loss of the PGNR particles increased to 87% with changing temperature from 570K to 712K. Synthesized polymer was utilized as an adsorbent for recovery of palladium(II) ions from chloride-containing solutions. Then, the effects of pH, chlorine concentration, and temperature on adsorption were investigated and optimized by batch adsorption experiments. As a result, we estimated the palladium particle size as 16nm. The formation of PGNR and Pd-adsorbed PGNR were characterized by FE-SEM, EDAX, XRD, and FTIR instrumentations. Adsorption of the positively charged and neutral chloropalladium(II) species mostly takes place via redox reduction reaction to Pd(0). The ease of synthesis, having low cost, coupled with the highly efficient and rapid reduction of Pd(II) ions onto surface, make PGNR polymer an attractive adsorbent.

Mechanistic study of the hydrothermal reduction of palladium on the Tobacco mosaic virus

The fundamental mechanisms governing reduction and growth of palladium on the genetically engineered Tobacco mosaic virus in the absence of an external reducer have been elucidated via in situ X-ray absorption spectroscopy. In recent years, many virus-inorganic materials have been synthesized as a means to produce high quality nanomaterials. However, the underlying mechanisms involved in virus coating have not been sufficiently studied to allow for directed synthesis. We combined XAS, via XANES and EXAFS analysis, with TEM to confirm an autocatalytic reduction mechanism mediated by the TMV1Cys surface. This reduction interestingly proceeds via two first order regimes which result in two linear growth regimes as spherical palladium nanoparticles are formed. By combining this result with particle growth data, it was discovered that the first regime describes growth of palladium nanoparticles on the virion while the second regime describes a second layer of larger particles which grew sporadically on the first palladium nanoparticle layer. Subsequent aggregation of free solution based spherical particles and metallized nanorods characterize a third and final regime. At the end of the second reduction regime, the average particle diameter of particles tethered to the TMV1Cys surface are approximately 4.5nm. The use of XAS to simultaneously monitor the kinetics of biotemplated reactions along with growth of metal nanoparticles will provide insight into the pertinent reduction and growth mechanisms so that nanorod properties can be controlled through their populating nanoparticles.

Nitrate uptake using mesoporous silica embedded with zero-valent palladium nanoparticles

In situ reduction of palladium(ii) acetylacetonate during the synthesis of SBA-15 mesoporous silica affords material impregnated with palladium nanoparticles, with the material being effective for nitrate-nitrogen removal.

Monodisperse palladium nanoparticles supported on chemically derived graphene: highly active and reusable nanocatalysts for Suzuki--Miyaura cross-coupling reactions

Addressed herein is the catalysis of monodisperse palladium nanoparticles (NPs) supported on chemically derived graphene (CDG) for the Suzuki--Miyaura cross-coupling of phenylboronic acid and various aryl halides. Monodisperse Pd NPs were synthesized by the solution phase reduction of palladium(II) acetylacetonate with morpholine borane complex in oleylamine and deposited on CDG via the liquid phase self-assembly method. Colloidal Pd NPs and CDG-Pd catalyst were characterized by TEM, XRD, SEM, and ICP-MS analyses. The CDG-Pd catalyst showed high activity in the Suzuki--Miyaura cross-couplings of different aryl halides including iodides, bromides, and even chlorides with phenylboronic acid under mild conditions. More importantly, the reusability experiments revealed that CDG-Pd catalyst was highly durable by almost maintaining its inherent activity after the 15th catalytic cycle.

Highly efficient and magnetically recyclable graphene-supported Pd/Fe3O4 nanoparticle catalysts for Suzuki and Heck cross-coupling reactions

Herein, we report a facile and efficient one-step method for the synthesis of highly active, Pd/Fe3O4 nanoparticles supported on graphene nanosheets (Pd/Fe3O4/G) that exhibit excellent catalytic activity for Suzuki and Heck coupling reactions and that can be magnetically separated from the reaction mixture and recycled multiple times without loss of catalytic activity. The synthesis approach is based on the Microwave (MW)-assisted reduction of palladium and ferric nitrates in the presence of graphene oxide (GO) nanosheets using hydrazine hydrate as the reducing agent. The results provide a fundamental understanding of the system variables by comparing the catalytic activity and recyclability of four different catalysts with different properties. The most active and recyclable catalyst contains 7.6wt% Pd nanoparticles with 4-6nm diameters in Pd(0) oxidation state well-dispersed with 30wt% Fe3O4 nanoparticles with 12–16nm diameters on highly reduced GO containing a C/O ratio of 8.1. These combined properties produce remarkable catalytic activity for Suzuki cross coupling reactions under MW reaction conditions with an extremely high turnover number (TON) of 9250 and turn over frequency (TOF) of 111,000h−1 at 80°C. The magnetic properties imparted by the Fe3O4 component of the catalyst enables the catalyst to be easily isolated and recycled, thus greatly simplifying the ability to purify the reaction products and increasing the economic value of the catalyst. The utility of these magnetic catalysts towards Suzuki and Heck cross coupling reactions with a variety of functionalized substrates was also demonstrated.

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.