Nano-sized Palladium Research Articles

An unusual Microdomain Factor Controls Interaction of Organic Halides with the Palladium Phase and Influences Catalytic Activity in the Mizoroki-Heck Reaction.

In this work, using a combination of scanning and transmission electron microscopy (SEM and TEM), the transformations of palladium-containing species in imidazolium ionic liquids in reaction mixtures of the Mizoroki-Heck reaction and in related organic media are studied to understand a challenging question of the relative reactivity of organic halides as key substrates in modern catalytic technologies. The microscopy technique detects the formation of a stable nanosized palladium phase under the action of an aryl (Ar) halide capable of forming microcompartments in an ionic liquid. For the first time, the correlation between the reactivity of the aryl halide and the microdomain structure is observed: Ar-I (well-developed microdomains) > Ar-Br (microphase present) > Ar-Cl (minor amount of microphase). Previously, it is assumed that molecular level factors, namely, carbon-halogen bond strength and the ease of bond breakage, are the sole factors determining the reactivity of aryl halides in catalytic transformations. The present work reports a new factor connected with the nature of the organic substrates used and their ability to form a microdomain structure and concentrate metallic species, highlighting the importance of considering both the molecular and microscale properties of the reaction mixtures.

Nonisothermal melt crystallization kinetics of laser-irradiated Pd/PVA nanocomposite

In the present work, we used the ex situ casting technique to synthesize a nanocomposite (NC) of polyvinyl alcohol (PVA) and nanosize palladium (Pd). The Pd has a particle size in the range from 2 to 22 nm with 10 nm on average. Samples from the synthesized NC have been irradiated with different fluences ranging from 2 to 20 J/cm2 from GaAs infrared pulsed laser (5-watt power, 904 nm wavelength, 200 ns pulse duration, 1200 Hz frequency and 0.28 cm2 spot area). Nonisothermal crystallization kinetics of the synthesized NC was investigated using differential scanning calorimetry (DSC) with different cooling rates. The Jeziorny and Mo approaches were applied to describe the nonisothermal analysis. Several nonisothermal kinetic parameters, such as the crystallization peak temperature (Tc ), the enthalpy of crystallization (ΔHc ), the degree of crystallinity (Xc ), the crystallization halftime (t 1/2), the Avrami exponent (n) and the activation of crystallization (Ea ) were evaluated and interpreted as a function of laser fluences. The results indicated that the incorporation Pd nanoparticles into the PVA matrix accelerate the crystallization process, while the laser radiation causes chain crosslinking that reduces the crystallinity.

Electrochemical sensing of indole in plasma using Pd nanoparticles modified metal-organic framework Cr-MIL-101/ionic liquid sensor

Herein, an electrochemical sensor for detection of indole was fabricated based on Pd nanoparticles modified Metal-Organic Framework Cr-MIL-101 (Pd@Cr-MOF) and ionic liquid (IL). The electrochemical behavior of indole was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at the surface of the modified electrode. The sensor was developed by incorporating of ultra-small nano-sized palladium particles stabilized on metal–organic framework Cr-MIL-101 and 1-hexyl-3-methylimidazolium chloride in the carbon paste electrode (CPE). The synthesized Pd nanoparticles modified Metal-Organic Framework Cr-MIL-101 (Pd@Cr-MOF) was characterized using Brunauer-Emmett-Teller (BET), EDS, XRD, SEM and TEM techniques. The Pd@Cr-MOF/IL/CPE exhibited the good sensitivity towards indole compared to the unmodified electrode. The linear range for determination of indole by this sensor was found to be 1 to 1100 nM with a detection limit of 0. 3 nM. Also, the proposed sensor was successfully applied for monitoring of indole in human serum sample and satisfactory results were obtained. Ultimately, high performance liquid chromatography (HPLC) method was applied for the validation of the electrochemical method for the determination of indole in human serum sample.

In vivo evaluation of Nano-palladium toxicity on larval stages and adult of zebrafish (Danio rerio)

The existence and usage of nano-sized palladium (nano-Pd) as catalytic promoters among industries and researchers have been laid a way to explore the release of nano-Pd particles into the aquatic environment, bio-accumulating in living organisms. However, the data on fate and toxicity in response to nano-Pd on aquatic organisms are very limited. Herein, we report the concentration-specific toxicity of nano-Pd in zebrafish (Danio rerio). Nano-Pd was synthesized and characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Dynamic Light Scattering (DLS) and Zeta potential. To determine the in vivo toxicity of nano-Pd, the 96 hpf larvae and the adult zebrafish were treated with two (22 and 0.4 ng/L) environmental relevant concentrations. High doses of nano-Pd influenced the hatching rate, embryo survival, heartbeat and teratological anomalies in the 96 hpf larvae. Reactive oxygen species (ROS) and apoptosis were also influenced by nano-Pd exposure while the acetylcholinesterase (AChE) activity was declined in a dose dependent manner. In long-term exposure (42 days), the adult fish showed erratic movements in swimming pattern inhibiting the AChE activity in both the concentrations of brain and liver. The antioxidant enzyme activity such as superoxide dismutase (SOD), catalase (CAT), glutathione-S-transferase (GST), glutathione reductase (GR) and lipid peroxidation (LPO), showed a significant change (P < 0.05) indicating that oxidative stress was induced by nano-Pd. Similarly, nano-Pd also induced histopathological lesions in gill, liver and brain providing an insight of fate and toxicity of nano-Pd in the aquatic environment. Our study contributes a significant mechanism to understand the toxicity concern of nano-Pd in the aquatic environment.

FORMATION OF NANO-AND ULTRAFINE PALLADIUM POWDERS IN THE PRESENCE OF «RED-OX»SYSTEM«TITANIUM (III) - TITANIUM (IV)»

The results of studies on the processes of obtaining ultra - and nanodispersed palladium powders from sulphate solutions by a combined chemical and electrochemical method in the presence of a "red-ox" system of titanium (III) - titanium (IV) are presented. It has been shown that when a titanium trivalent sulphate solution is added to a solution containing palladium (II) ions, palladium ions are immediately reduced to elemental state to form a nanodispersed powder. The completeness of the above-mentioned oxidizing-reducing reactions is established on the basis of calculating the equilibrium constant (K), which is 1034 and indicates that trivalent titanium ions completely reduce palladium ions to elemental state. Effect of initial concentration of palladium ions on amount of formed palladium powder with addition of equivalent amount of trivalent titanium ions is investigated. According to the authors, upon reduction of palladium ions, elemental palladium is formed in the atomic state, and over time, the atoms begin to combine with each other. Subsequently, atomic particles are combined into colloidal particles. It has been found that in the absence of coagulants, the colloidal palladium solution is stable for 2-3 hours, and in the presence of gelatin, the stability increases and remains for 36 hours. It was shown that in all experiments powders with spherical particles are formed, the average sizes of which range from 0.116-0.240 microns. Based on the results of the presented studies, a new technology for producing ultra - and nano-sized palladium powders is proposed.

Use of Palladium-Modified Polyaniline Electrode as a Sensitive Element of Fire Sensor

Results of the development of a method for immobilizing nanosized palladium into an electrochemically synthesized polyaniline (PAn) electrically conductive porous matrix to create a sensitive element of an ignition sensor are presented. Two methods of manufacturing a sensitive element in the form of an electrode are investigated. The first method consists in the co-precipitation of polyaniline and palladium on a graphitized butyl rubber substrate in a mode of cycling of potential. It was shown that this method can be used to obtain a volume-porous electrode in which palladium nanoparticles are embedded in a polyaniline matrix. The second method involves the deposition of palladium on a polyaniline film formed on graphitized butyl rubber. It was shown that micron-sized island palladium conglomerates on the surface of a polyaniline film can be obtained by this method. The conclusions made are confirmed by physical research methods and the results of scanning electron microscopy. Investigations of the electrocatalytic properties of the electrode in the sensor model showed that with a change in the H2 concentration formed upon ignition, occurs change in the hydrogen concentration on the surface of metal-catalyst (Pd) and a linear change in the current of electrochemical reaction. Comparison of a composite volume-porous polyaniline electrode with embedded palladium showed its superior efficiency compared to a compact palladium electrode and an electrode in which palladium is deposited on the surface of a polyaniline film. The possibility of using an electrochemical detector based on polyaniline with immobilized palladium nanoparticles for a gas amperometric sensor of low hydrogen concentrations and a fire hazard detector is shown.

Nanosized palladium loaded on porous ceria: A three-dimensional boosted electrocatalyst for electrooxidation of C1 compounds

The solution combustion synthesis was used for preparation of porous CeO2 with two different fuels; glucose and citric acid, for combustion. The samples of porous CeO2 are labeled as PCOGlu and PCOCit. The surface area of PCOCit and PCOGlu were estimated as 44.50 ± 0.12, and 47.72 ± 0.16 m2 g−1, respectively. The cavities acidity, OH groups on surface, and its bond strength to the active cerium sites are compared by measuring the pH of zero charges; that it was 11.95 ± 0.02, and 11.90 ± 0.03 for PCOCit and PCOGlu, respectively. The nanosized palladium (NPd) was loaded on PCOGlu and PCOCitvia wetness incorporation. As-prepared nano-microstructure electrocatalysts are utilized in the electrooxidation of C1 compounds, including methanol, formaldehyde, and formic acid. The NPd-PCOGlu presents higher electrocatalytic activity, stability and CO-tolerance ability for the electrooxidation of C1 compounds as compared to the NPd-PCOCit and NPd as non-supported palladium; So that, the performance of the modified electrodes increase in the order of NPd < NPd-PCOCit < NPd-PCOGlu. The PCO with porous structural network affected on the electrochemical surface area, dispersion, and durability of NPd. It is effective the capability of removing the poisoning species of the electrooxidation of C1 compounds on NPd through the lattice oxygen, and the activation of an oxidation−reduction cycle between the high and low chemical valences of cerium, leading to improve the electrocatalytic efficiency of NPd. Lastly, the conversion of methanol to formaldehyde, and then to formic acid during electrooxidation is confirmed by using cyclic voltammetry.

Structural, thermal and optical characteristics of laser-exposed Pd/PVA nanocomposite

Nanocomposite of polyvinyl alcohol (PVA) and nanosize palladium (Pd) were fabricated by ex situ casting technique. The fabricated Pd/PVA nanocomposite film has been exposed to infrared pulsated laser with fluences in the range 2–20 J/cm2. The effect of the laser radiation on the structural, thermal and optical properties of Pd/PVA has been investigated using XRD, TGA and UV–Vis spectroscopy. Exposure of IR laser radiation raises the refractive index from 1.84 to 3.38 at 700 nm which confirms the predominance of crosslinking process in the Pd/PVA nanocomposite. Furthermore, the reduction in the optical energy gap from 1.87 to 1.72 eV could be attributed to the increase in the structural disorder resulting from the coordination reaction between OH of PVA and Pd nanoparticles. The attained results reveal that the IR laser radiation enhances the dispersion of Pd nanoparticles in the PVA matrix resulting in more compact structure of Pd/PVA nanocomposite. Consequently, the onset temperature of decomposition increased upon laser irradiation. Commission Internationale de E’Claire (CIE units x, y and z) methodology was employed to describe the color of the studied samples. The color difference between the exposed nanocomposite films and the non-exposed one was raised from 5.63 to 12.01 as the laser fluence increases up to 20 J/cm2. Thus, the present study suggests that the IR laser radiation affects the microstructure of the Pd/PVA nanocomposite which in turn assists in tailoring the thermal and optical properties of such nanocomposite for usage in optoelectronics applications.

One-step green synthesis of palladium nanoparticles using neem gum (Azadirachta Indica): characterization, reduction of Rhodamine 6G dye and free radical scavenging activity

Nano-sized Palladium particles, synthesized by microwave irradiation method using neem gum, is a novel, single step and cost-effective with high yield. Water-soluble neem gum has been employed as stabilizing and reducing agent without any harmful chemicals for obtaining the PdNPs. The prepared PdNPs were characterized by UV–Vis, XRD, FTIR and TEM techniques. Average particle size was about 4 nm. FTIR confirmed that hydroxyl and carboxylic groups are involved in reduction and stabilizing process. The PdNPs catalytic activity was examined spectrophotometrically through the reduction of Rhodamine 6G dye by NaBH4. The PdNPs stabilized by neem gum exhibited excellent catalytic activity towards reduction of Rhodamine 6G. The reaction showed pseudo-first order kinetics and the rate constant obtained was 0.1875 min−1. The antioxidant activity of PdNPs by DPPH was studied by UV–Visible spectrophotometry and PdNPs were found to have significant free radicle scavenging activity.

Formation and stabilization of colloidal ultra-small palladium nanoparticles on diamine-modified Cr-MIL-101: Synergic boost to hydrogen production from formic acid

Ultra-small nano-sized palladium particles were successfully stabilized within the pores of diamine groups grafted open metal site metal-organic frameworks of Cr-MIL-101; coordinated diamine groups of ethylene diamine (ED) and propyl diamine (PD) on the active site of chromium units of Cr-MIL-101. The physiochemical properties of the Pd@Cr-MOFs were investigated using FTIR, XRD, SEM/EDX mapping, TEM, BET, and AAS. The Cr-MIL-101 stabilized ultra-small Pd nanoparticles, Pd@(ethylene diamine)/Cr-MIL-101, and Pd@(propyl diamine)/Cr-MIL-101, displayed catalytic activity for clean dehydrogenation of formic acid and generation of hydrogen at room temperature. The resultant Pd@ED/Cr-MIL-101 catalyst indicates high catalytic activity with turnover frequency (TOF) of 583 h−1 at 328 K, which is superior to most of the reported catalysts, including Pd@PD/Cr-MIL-101 with TOF 532 h−1. Our studies open up a new method to the design of an ultra-small metal nanoparticle for the catalytic dehydrogenation of HCOOH.

Gamma-induced changes in the optical and structural properties of palladium/polycarbonate nanocomposite membrane

Makrofol Polycarbonate (PC) is a polymeric solid-state nuclear track detector (SSNTD) by which various applications can be used in several dosimetric and industrial fields. In this work, nano-sized palladium Pd was prepared and mixed with PC (5 wt.%) to produce nanocomposite films. Samples from the Pd/PC nanocomposite films have been irradiated with gamma doses 20–300 kGy. The modification induced in the optical properties and structure of the Pd/PC nanocomposite samples due to gamma irradiation has been investigated. The increase of Urbach energy, accompanied by a decrease in energy band gap, with the gamma dose indicated that the gamma irradiation up to 300 Gy increases the intermolecular interaction of PC chains and Pd leading to an increase in the disorder in the naocomposite samples. It is well known that the nano-palladium is effective in stabilizing the PC, resulting in the enhancement in both refractive index and intrinsic viscosity with the gamma dose. This leads to a more compact structure of PC due to crosslinking. Additionally, the color sensitivity for the non-irradiated Pd/PC nanocomposite sample showed a significant behavior toward gamma radiation. The color intensity ΔE is the difference in the color between non-irradiated samples and the samples irradiated with various gamma doses. ΔE is increased by increasing the dose till 300 kGy, accompanied by an increase in the yellow color component. Finally, FTIR spectroscopy was performed on the non-irradiated and irradiated samples to correlate the induced changes in Pd/PC nanocomposite with the changes in the function groups.

Preparation of Palladium Nanoparticles Decorated Polyethyleneimine/Polycaprolactone Composite Fibers Constructed by Electrospinning with Highly Efficient and Recyclable Catalytic Performances

Nano-sized palladium nanoparticles showed high catalytic activity with severe limitations in catalytic field due to the tendency to aggregate. A solid substrate with large specific surface area is an ideal carrier for palladium nanoparticles. In present work, polyethyleneimine/polycaprolactone/Pd nanoparticles (PEI/PCL@PdNPs) composite catalysts were successfully designed and prepared by electrospinning and reduction methods using PEI/PCL elexctrospun fiber as carrier. The added PEI component effectively regulated the microscopic morphology of the PEI/PCL fibers, following a large number of pit structures which increased the specific surface area of the electrospun fibers and provided active sites for loading of the palladium particles. The obtained PEI/PCL@PdNPs catalysts for reductions of 4-nitrophenol (4-NP) and 2-nitroaniline (2-NA) exhibited extremely efficient, stable, and reusable catalytic performance. It was worth mentioning that the reaction rate constant of catalytic reduction of 4-NP was as high as 0.16597 s−1. Therefore, we have developed a highly efficient catalyst with potential applications in the field of catalysis and water treatment.

Novel Processing of Cathodes for Solid Oxide Fuel Cells

Solid-oxide fuel cells (SOFCs) are electrochemical devices that efficiently convert chemical energy of fuels into electricity.[1] However, they typically operate at high temperature (800–1000 °C) causing substantial challenges in cost and material compatibility. SOFC that can work at intermediate temperature (IT) (500–750 °C) is thus more attractive.[2] SOFC is generally composed of anode, electrolyte and cathode. A practical cathode for SOFCs should possess sufficiently high thermo-mechanical stability, good thermal and chemical compatibility with the electrolyte, high chemical stability against the surrounding atmosphere, good electro-catalytic activity for oxygen reduction reaction (ORR), as well as high electrical conductivity.[1] However, the current widely used cathode, lanthanum strontium manganite (LSM), rapidly loses activity below 800 °C.[3] According to numerical calculations, the efforts to optimize the oxygen surface exchange reaction are required while very high ionic conductivities are not necessary in order to achieve the goal of a highly active cathode.[4] Nano-sized palladium (Pd) and platinum (Pt) show very high activity towards oxygen activation, which can substantially increase the cathode electrochemical performance by improving the surface properties. However, precious metals are expensive and undergo sintering. Silver is a good alternative for its relatively low price and high electrocatalytic activity for oxygen activation, however more easily sintered than Pt and Pd resulting in the electrode deactivation.[5] As the electrodes and the dense electrolyte are sintered together in SOFC, the deactivated electrodes are normally neither regenerable nor replaceable, what brings the end of the SOFC. On the other hand, the Ag-doped perovskites have promoted catalytic oxidation of CO, CH4, n-hexane, and NO,[6] which was significantly improved by the partial substitution of Ag into the A-site of perovskite together with the additional formation of the oxygen vacancy and the metallic Ag on the surface of the perovskite forming composite materials. [7, 8] Among several ways to process the composites, infiltration has shown promising results bringing the possibility to tailor electronic, ionic and mixed ionic electronic conductivities in a porous backbone of proton conducting oxides. [9, 10] The exsolution of nickel, ruthenium, silver or other metal nanoparticles has been investigated in reducing conditions for the design of the electrodes for SOFC. [11-13] The development of highly electrochemically active cathodes for SOFCs requires the optimization of materials composition together with micro- and nanostructures in order to form stable and catalytically active composite electrodes. Here we report on the novel heterostructured silver nanoparticle-decorated perovskite composites La0.95-xSrxMn1-y-z(Fe,Ni,Zn,Mg)zNbyO3-δ – 0.05Ag (exLSAMN) as highly active and durable cathodes for SOFCs, derived from single phase La0.95-xSrxAg0.05Mn1-y-z(Fe,Ni,Zn,Mg)zNbyO3-δ (LSAMN) perovskite precursors through an exsolution process. We report LSAMN as a novel precursor which can develop into high-performance nanosized silver modified LSM-based electrode under cathodic polarization or reducing atmosphere with improved stability and in situ electrochemical regeneration capability. The LSAMN materials were synthesized by solid state reaction and wet chemical synthesis method in order to compare the activity. The electrochemical intercalation/de-intercalation of metal catalysts is a conceptually attractive approach that is also applicable for the development of other metal-modified oxide electrodes. The composite formation and properties were tailored by changing the synthesis route and thermal treatment. A thorough description of the synthesis methods is presented as well as a careful characterization of the microstructure and phase composition of the resulting composite electrodes. The performance of the new composite cathodes with gadolinia-doped ceria (CGO) electrolyte is demonstrated. The exLSAMN electrode showed fairly high electrochemical activity and low area specific resistance (ASR). These unique features make the new materials highly promising cathodes for SOFCs at intermediate temperatures. References A. B. Stambouli, E. Traversa, Renew. Sust. Ener. Rev., 6 (2002) 433.J. A. Kilner, M. Burriel, Ann. Rev. Materi. Res., 44 (2014) 365.S. P. Jiang, J. Mater. Sci., 43 (2008) 6799.J. Fleig, J. Pow. Sour., 105 (2002) 228.T. Z. Sholklapper et al. J. Pow. Sour., 175 (2008) 206.D. Y. Yoon et al. J. Catal., 319 (2014) 182.K. Wang et al. Catalysis Today, 158 (2010) 423.G. Pecchi et al. App. Catalysis A: General, 371 (2009) 78.C. Duan et al. Science, 349 (2015) 1321.C. Duan et al. Energy Environ. Sci., 10 (2017) 176.Y. Zhu et al. Nano Lett., 16 (2016) 512.J. T. S. Irvine et al. Nature Energy, 1 (2016) 15014.G. Tsekouras, D. Neagu, J. T. S. Irvine, Energy Environ. Sci., 6 (2013) 256.

Long-term atomistic simulation of hydrogen absorption in palladium nanocubes using a diffusive molecular dynamics method

Understanding the transport of hydrogen within metallic nanomaterials is crucial for the advancement of energy storage and the mitigation of hydrogen embrittlement. Using nanosized palladium particles as a model, recent experimental studies have revealed several interesting phenomena that occur over long time periods. The time scale of these phenomena is beyond the capability of established atomistic models such as molecular dynamics. In this work, we present the application of a new approach, referred to as diffusive molecular dynamics (DMD), to the simulation of long-term diffusive mass transport at the atomic scale. Specifically, we simulate the absorption of hydrogen by palladium nanocubes with edge lengths in the range of 4 nm and 16 nm. We find that the absorption process is dominated by the initiation and propagation of an atomistically sharp α/β Pd-H phase boundary, with thickness in the range of 0.2 to 1.0 nm, which separates an α phase core from a β phase shell. The evolution of phase boundary and the resulting local lattice deformation are described in this paper in detail. The effects of size on both equilibrium and kinetic properties are also assessed.

Efficient direct formic acid fuel cell (DFAFC) anode of nano-sized palladium complex: High durability and activity origin

The low stability of Pd-based catalysts extremely obstructs their applied application in the direct formic acid fuel cells (DFAFCs). Herein, a novel nano-sized palladium-complex (nano-Pdcomplex) with outstanding performance (activity and durability) for DFAFCs anodic reaction (Formic acid oxidation; FAO) compared to the commercial Pd-based catalysts is introduced. Morphologically, nano-sized Pd-complex shows an intersected nano-rod like structure with an average particle size ca. 17nm. Electrochemically, nano-Pdcomplex modified GC electrode (Nano-Pdcomplex/GC) has 12 times higher electrocatalytic activity, 8.0 times higher electrochemical active surface area, 3.0 times higher catalyst utilization, and ca., 16 times higher stability after 5.0h than that of traditional Pd nanoparticles modified GC electrode (PdNPs/GC) with the same Pd loading. This significant enhancement in both activity and stability is attributed to nano-Pdcomplex bulky structure hindering the agglomeration of the Pd active sites and inhibiting the adsorption of poisoning CO-like intermediate species. DFT studies shows that nano-Pdcomplex has two different geometries: (a) cis-structure which has a square planar geometry and it is inactive for FAO, and (b) trans-structure with a tetrahedral geometry and it is highly active for FAO. This study introduces a new promising category of Pd-based catalyst with high activity, catalyst utilization and durability for DFAFCs applications.

Subchronic exposure to palladium nanoparticles affects serum levels of cytokines in female Wistar rats.

Recently, palladium nanoparticles (PdNPs) have been increasingly used in many industrial sectors, and this has led to a significant release of nano-sized palladium particles into the environment. However, despite the increase in occupational and general population exposure, information on the potential adverse effects of these PdNPs is still limited and their impact on the immune system constitutes a major health concern. Therefore, the aim of this study was to investigate the potential adverse effects induced by subchronic intravenous administration of PdNPs on the immune system of female Wistar rats by evaluating alterations in Interleukin (IL)-1α, IL-2, IL-4, IL-6, IL-10, IL-12, granulocyte-macrophage colony-stimulating factor (GM-CSF), Interferon (INF)-γ, and Tumor Necrosis Factor (TNF)-α serum levels. Exposed and control animals were randomly divided into five groups (0, 0.012, 0.12, 1.2, and 12 μg PdNPs per kg body weight) which were treated with repeated intravenous injections of vehicle or PdNPs (on day 1, 30, and 60). Subchronic exposure to PdNPs induced a decreasing trend in serum levels in most of the cytokines investigated, with the highest concentration (12 μg/kg) determining significant inhibitory effects. Overall, these results showed that PdNPs are able to alter cytokine serum levels in subchronically treated Wistar rats, suggesting a possible impact of these xenobiotics on the immune system after long-term exposures.

A novel nano-palladium complex anode for formic acid electro-oxidation

This study introduces a novel nano-sized palladium complex with high electrocatalytic activity and stability as a catalyst for the anodic reaction of direct Formic acid fuel cell (DFAFC). Morphologically, as prepared Pd-complex has intersected nano-rod like structure with an average particle size of 7nm. Nano-Pd-complex modified GC electrode showed 10 times higher electrocatalytic activity and 16 times higher stability compared with the traditional Pd nanoparticles modified GC electrode with the same Pd weight. This significant improvement may be attributed to its small size and bulky structure that hinders the sintering of the active Pd atoms (i.e., obstructs the growth of Pd particle size) and impedes the adsorption of poisoning intermediate species (e.g., CO) and/or formation reversible surface hydride as evidenced by the DFT calculations. This study introduces a new promising category of Pd-based catalyst with high activity, catalyst utilization and durability for DFAFCs applications.

Palladium Nanoparticles: Is There a Risk for Aquatic Ecosystems?

Nano-sized palladium (nano-Pd) is used in catalytic converters of automobiles, where it can be released into the environment by abrasion. Although these particles may subsequently be transported into surface water bodies, no data estimating their fate and toxicity in aquatic systems exists. This study characterized the particle size development of nano-Pd (advertised size ~12nm; hydrodynamic size ~70nm) in media with variable ionic strength (IS). Additionally, the particles' acute toxicity for daphnids and chironomids was assessed. While nano-Pd agglomerated more quickly with increasing IS, it caused only marginal effects in both test species after 96h of exposure. After 144h of exposure, however, an EC50 value of 1.23mg nano-Pd/L for daphnids was determined indicating effects over the long run. When considering the relatively low environmental concentration of elemental Pd in surface waters (usually ng/L), though, this study suggests only a low aquatic risk in response to nano-Pd.

Efforts for long-term protection of palladium hydrodechlorination catalysts

Nano-sized palladium (Pd) catalysts are known for their high intrinsic hydrodechlorination (HDC) activity towards many chlorinated water pollutants, converting them into non-harmful compounds. Optimization of catalyst protection by embedding various types of Pd catalysts (Pd on oxidic supports and in-situ generated Pd clusters) into poly(dimethylsiloxane) (PDMS) layers was studied together with their use in HDC reactions. The catalyst performance in standard batch and long-term experimental set-ups was used to better understand and optimize the Pd-PDMS system. The phenomenon of polymer deterioration by entrapped HDC-generated HCl is studied for various systems and found to be the main reason for limited life times of Pd-PDMS systems.Pd-PDMS composites were found to provide long-term protection from ionic catalyst poisons. This gain in prolonged catalyst protection goes along with an inevitable decrease in specific catalyst activity which is unhesitantly accepted for the benefit of a longer-lasting catalytic activity. However, when comparing the relative loss of the specific Pd activity due to embedding, it is found to be much lower for initially less active catalyst particles (e.g. a factor of 2 for Pd/Al2O3) compared to about two orders of magnitude for the highly active nanoscale Pd particles. It could be shown that embedded catalysts in continuously operated long-term set-ups have enhanced resistance and longevity compared to those tested in repeated batch-type reaction cycles. PDMS-embedded Pd/Al2O3 maintains its full initial activity up to turnover numbers of >750 (for trichloroethene as probe substance), whereas the catalyst system loses more than 50% of its initial activity for a comparable catalyst utilization (TON≈750) operated in batch cycles.

Direct synthesis of supported palladium catalysts for methane combustion by stagnation swirl flame

The titania supported palladium nano catalysts (Pd/TiO2) are synthesized in one-step using a premixed stagnation swirl flame (SSF) with ultra-fine spray system. This novel SSF method, with features of short residence time and fast quenching, produces nanosized (<2.5nm) palladium particles being well dispersed on the 7–8nm TiO2 particle surface, with an overall specific surface area of 210–220m2/g. The X-ray photoelectron spectroscopy (XPS) results indicate that the collected palladium particles are a mixture of both Pd and PdO, whereas the TiO2 support is mainly in anatase phase by X-ray diffraction (XRD). A revised population balance model (PBM) by incorporating coagulation, sintering and scavenging of the binary system (Pd and TiO2) is developed to explain the in situ doping mechanism of Pd/TiO2 composites in the flame domain. Then, we use the synthesized nano catalyst to conduct the catalytic combustion of methane under 5–15% Pd loadings. It exhibits more excellent activity than those in the literature under identical temperatures. The T20, as 20% methane conversion temperature, can reduce to as low as 293°C at 15% Pd loading. It is because that the Pd/TiO2 catalysts made from the stagnation flame show a good dispersion of size-controlled palladium on TiO2 which may not be accessible by wet-chemistry and even other flame synthesis routes.