Palladium Content Research Articles

Surface characterization of silver and palladium modified glassy carbon

In this work, the influence of silver and palladium on the surface of undoped, boron doped and phosphorus doped glassy carbon has been studied. The silver and palladium concentrations in solution, after metal deposition, were measured by atomic absorption spectrophotometer. The morphology of metal coatings was characterized by scanning electron microscopy. In order to investigate the nature and thermal stability of surface oxygen groups, temperature-programmed desorption method combined with mass spectrometric analyses, was performed. The results obtained have shown that silver and palladium spontaneously deposit from their salt solutions at the surface of glassy carbon samples. Silver deposits have dendrite structure, whilst palladium forms separate clusters. The highest amount of both silver and palladium deposits at the surface of sample containing the highest quantity of surface oxide complexes. It has been concluded that carboxyl groups and structure defects are responsible for metal reduction. Calculated desorption energies have shown that the surface modification by metal deposition leads to the formation of more stable surface of undoped and doped glassy carbon samples.

Enhanced Visible‐Light Photocatalytic Degradation of Humic Acid by Palladium‐Modified Nitrogen‐Doped Titanium Oxide

Palladium‐modified nitrogen‐doped titanium oxide (TiON/PdO) nanoparticles were synthesized by a sol–gel process, for visible‐light‐induced photocatalysis using humic acid (HA) as a target. Our work shows that palladium modification has strong effects on the optical and photocatalytic properties of nitrogen‐doped titanium oxide (TiON) photocatalysts. TiON/PdO nanoparticles demonstrated an enhanced photocatalytic activity over TiON within a narrow range of palladium concentration. Beyond this range, the adverse effect of palladium modification was observed in the visible‐light‐induced degradation of HA. The effects of palladium modification are discussed in terms of its role in controlling electron–hole recombination.

Preparation, Characterization and Catalytic Activity of Palladium Nanoparticles Encapsulated in SBA-15

A simple adsorption method was studied for the preparation of SBA-15-encapsulated palladium nanoparticles. This method employed the SBA-15 with organic template removed by ethanol extraction for the adsorption of cationic Pd precursors in alkaline solution followed by calcination and H2 reduction. The pH of the solution was found to be a critical factor in determining the palladium content and the ordered mesoporous structure. Our characterizations revealed that the Pd nanoparticles prepared by this method were located inside the mesoporous channels and were quite uniform in size (mostly 3–4 nm). The SBA-15-encapsulated uniform Pd nanoparticles were efficient catalysts for solvent-free aerobic oxidation of alcohols.

The hydrolysis and precipitation of Pd(II) in 0.6 mol kg −1 NaCl: A potentiometric, spectrophotometric, and EXAFS study

The soluble and insoluble hydrolysis products of palladium were investigated in aqueous solutions of 0.6 mol kg −1 NaCl at 298.2 K. Potentiometric titrations of millimolal palladium(II) solutions were used to monitor hydrolysis reactions of the mononuclear PdCl 3OH 2− and PdCl 2 OH 2 2 - species. Spectrophotometric titrations were also used to corroborate the speciation change and to extract the correlative molar absorption coefficients for the PdCl 3OH 2− species in the 210–320 nm range. Longer-term potentiometric titrations systematically yielded precipitates which matured over a period of 6 weeks and resulted in a more extensive release of protons to the solution. Precipitation experiments in the 3–11 pH range showed the dominant precipitating phase to be Pd(OH) 1.72Cl 0.28. EXAFS measurements yielded an average of 3.50 O and 0.50 Cl atoms per Pd atom with a Pd–O distance of 2.012 Å and a Pd–Cl distance of 2.185 Å. Speciation modeling of proton and palladium mass balance data of experiments for palladium concentrations ranging from 0.047 to 10.0 mmol kg −1 required the presence of polynuclear complexes containing 3–9 palladium atoms. The existence of such complexes is moreover supported by previous investigations of palladium hydroxide chains of the type [Pd(OH) 1.72Cl 0.28] n , that are coiled and/or aggregated into nanometer-sized (15–40 Å) spheroids.

Sulphur poisoning of palladium catalysts used for methane combustion: Effect of the support

Four different supported palladium catalysts (using alumina, silica, zirconia and titania as supports), prepared by incipient wetness impregnation, were tested as catalysts for methane oxidation in presence of sulphur dioxide. The catalyst supported on zirconia showed the best performance, whereas the silica-supported one showed the fastest deactivation. Temperature-programmed desorption experiments of the poisoned catalysts suggest that SO 2 adsorption capacity of the support plays a key role in the catalyst poisoning. In order to study the effect of promoters, expected to improve the thermal stability and thioresistance of the catalyst, commercial zirconia modified by yttrium and lantane was tested as supports. It was found that the presence of these promoters does not improve the performance of the zirconia-supported catalyst. A deactivation model – considering two different active sites (fresh and poisoning), pseudo-first order dependence on methane concentration and poisoning rate depending on sulphur concentration and fraction of non-poisoned palladium – was used for modelling the deactivation behaviour.

Electroless gold plating from tetrachloroaurate solutions containing hexacyanoferrate(II) ions

A hexacyanoferrate–tetrachloroaurate electroless gold plating solution has been developed for production on Ni–P, Ni–B, Ni–Pd and Cu substrates, giving gold coatings up to 0·25–0·38 μm in thickness. The rate of gold deposition depends on the nature of the substrates and decreases in the series Ni–P>Ni–B>Ni–Pd>Cu. The rate of gold plating on Ni–Pd decreases with the growth of palladium content in the alloy. Gold deposition occurs by mechanisms of cementation (immersion replacement) and gold reduction with hydrazine hydrochloride. The fraction of cementation does not exceed 30–40% with deposition on Ni–P and Ni–B substrates, 10% on copper and diminishes slightly with gold film deposition.

Linear and nonlinear optical behavior of palladium nanoparticle reinforced fluoropolymer composites

The linear and nonlinear optical properties of palladium nanoparticle reinforced fluorinated ethylene polymer matrix nanocomposite were investigated in this work. Synthesized through decomposition of a palladium organometallic chemical species in the bulk of fluorinated polymer films, the composites consisted of discrete, palladium nanoparticles distributed throughout the polymer matrix. The low-intensity reflectivities were measured as a function of palladium content and compared to behavior predicted using the Tourquato–Kreibig–Fresnel (TKF) theory. Optical limiting experiments using 8 ns duration laser pulses at 1064 nm yielded a 90% reduction in transmissivity with pulse fluences of nearly 1.3 × 10 4 mJ/cm 2.

Nanoscale Pd/Fe bimetallic particles: Catalytic effects of palladium on hydrodechlorination

Reported herein is a study on the catalytic properties of palladium for hydrodechlorination using nanoscale zero-valent iron particles. Temperature-dependent experiments and X-ray diffraction (XRD) are conducted to characterize reactions of chlorinated ethylenes with nanoscale Fe and Pd/Fe particles. XRD results suggest bimetallic structures are created as a result of Pd(II) reduction by zero-valent iron and the degree of surface palladium loading is proportional to the initial amount of palladium applied. The optimal content of palladium in the bimetallic particles for dechlorination is in the range of 1–5% by weight. XRD analyses further suggest that oxidation of iron produces mainly iron oxides. No oxidized species of palladium (e.g., PdO) is found before or after the reactions. Activation energies of the dechlorination reactions with the nanoscale Pd/Fe and Fe particles are estimated to be 31.1 and 44.9kJ/mol, respectively. A conceptual model for the catalytic hydrodechlorination by the nanoscale Pd/Fe particles is presented.

Sulfide saturation mechanisms in gabbroic intrusions in the Nipigon Embayment

The Seagull and Kitto intrusions in the Nipigon Embayment of northwestern Ontario were studied to gain an understanding of the processes involved in sulfur saturation of the mafic to ultramafic magmas leading to the formation of platinum group element (PGE) concentrations. Profiles of sulfur, copper, nickel, gold, palladium, and platinum concentrations as a function of depth revealed that sulfur saturation occurred at the base of the Seagull intrusion. A higher grade horizon occurs well above the base of the intrusion, suggesting that a reef-type of process was significant here and possibly in the Kitto intrusion, as well. Olivine compositions indicate that, in both cases, the parental magmas were undersaturated with respect to sulfur. Sulfur, neodymium–samarium, and rubidium–strontium isotopic data suggest that assimilation of country rock and sulfide played a role, especially in the formation of basal concentrations of PGEs.

Platinum and palladium variations through the urban environment: Evidence from 11 sample types from Sheffield, UK

Platinum (Pt) and Palladium (Pd) concentrations have been analysed in 194 samples from within the city of Sheffield in the UK. The samples were taken from road dust, gully pots (also known as drains), soils, a motorway drainage pipe, rivers, lakes, sewage sludge, incinerator ash, incinerator ash in landfill, street cleansers and gully cleansers. The introduction of Pt- and Pd-bearing automobile catalysts, has been cited as the cause of a rise in the concentration of urban Pt and Pd accumulations. Geochemical analyses for the different sample types are used here to show how the Pt and Pd accumulate in different urban environments as they are transported from their catalytic source. Initially Pt and Pd collect in road dust and gully pots at values of up to 450 ppb although most analyses for both elements are around 100 ppb. The four roadside soils analysed, have a great range in values, the highest with a value of over 600 ppb Pt and 1000 ppb Pd. Then the fate of the Pt and Pd is either to be removed by gully flushers and road sweepers (which contain around half the concentration of that in road dust) or to be washed from the roads, through the gully pots, into either the river or urban drainage systems. Due to the addition of terrestrial sediments, river samples contain much reduced values of Pt and Pd, at approximately an order of magnitude lower than in road dust. Similarly, sewage sludge contains Pt and Pd values which are lower than road dust. However, the Pt and Pd analyses are much higher in incinerated sewage (with many samples over 150 ppb for both metals), probably due to the loss of the mass of other material during the incineration process. Weathered incinerator ash in landfill has lower values of Pt and Pd than fresh ash from the incinerator. Although the range in values of Pt and Pd is similar for road dust and gully pot sediments their modal values tell a different story. The mode for Pt is very similar for both road dust and gully pot sediments, at around 100 ppb, whereas there is a drop of 50 ppb in the mode for Pd in the gully pots (from 80 ppb to around 40 ppb). Given that gully pot sediment is derived from road dust, it is suggested that in gully pots, Pd is preferentially mobilized over Pt. Furthermore, a comparison of the modal values of Pt and Pd in river sediments suggests that this process continues into the natural drainage system of the city.

Grain size partitioning of platinum-group elements in road-deposited sediments: Implications for anthropogenic flux estimates from autocatalysts

Twelve road-deposited sediment samples were analyzed for platinum-group elements (PGEs) and Pb in the <63 μm fraction of an urban watershed in Hawaii. Three samples were further fractionated into five size classes, from 63–125 μm to 1000–2000 μm, and these were analyzed for PGEs and Pb. Concentrations in the <63 μm fraction reached 174 μg/kg (Pt), 101 μg/kg (Pd), 16 μg/kg (Rh), and 1.3 μg/kg (Ir). Enrichment ratios followed the sequence Rh > Pt = Pd > Ir. Iridium was geogenic in origin, while the remaining PGEs indicated significant anthropogenic contamination. Palladium, Pt and Rh concentrations and enrichment signals were consistent with PGE bivariate ratios and PGE partitioning in three-way catalysts. Size partitioning indicated that the <63 μm fraction had the lowest PGE concentrations and mass loading percentages. These data suggest that autocatalyst PGE flux estimates into the environment will be significantly underestimated if only a fine grain size fraction is analyzed.

Sorption of palladium on carbon adsorbents from nitric acid solutions

Sorption recovery of palladium from nitric acid solutions on carbon adsorbents BAU, LKAU-7, ABG and UC has been investigated using model solutions with concentrations 8 × 10−4–8 × 10−3 mol/l for palladium and 1, 2 and 5 mol/l for nitric acid. The recovery degrees of Pd(II) depend on the concentration of palladium in contacting solutions as well as on the type of sorbent used. On average, they reach 60%–100% with the maximum in 1 M HNO3 The palladium desorption by 10% thiocarbamide solution in 1M H2SO4 proceeds completely for the sorbent LKAU-7. The use of thiocarbamide solutions in 0.1 M NaOH increases the desorption of palladium from the sorbents BAU and UC up to 80%–85%

Two-Component Films of Fullerene and Palladium as Materials for Electrochemical Capacitors

The redox-active films, , formed by electrochemical reduction of solutions containing palladium(II) acetate and fullerene have been studied as active components for electrochemical capacitors. The capacitance properties of these materials have been investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The structure and electrochemical properties of films deposited on an electrode surface depend on the composition of the solution from which they are grown. Films formed in a solution with a low concentration of palladium(II) acetate exhibit conductivity in the potential range of the film reduction. The faradaic process of reduction gives rise to pseudocapacitance. The capacitance of this polymer depends on the solvent and the size of the cations in the supporting electrolyte. For an acetonitrile solution containing only tetra(methyl)ammonium perchlorate, the film displays a high specific capacitance, close to . Films formed in a solution with a high concentration of palladium(II) acetate also contain metallic palladium nanoparticles. Such systems exhibit conductivity at potentials less negative than the potentials for film reduction, and these films can be considered as double-layer capacitors. The specific capacitance of these films is much smaller (about ) but a large potential window (from ) is available for the performance of these capacitors.

Oxygen kinetics and mechanism at electrocatalysts on the base of palladium–iron system

Binary nanodispersed carbon XC72 supported PdFe catalysts with different atomic palladium-to-iron ratios are synthesized and studied in oxygen reduction reaction in acid solution at 60 °C. The Pd:Fe ratio was well controlled by the initial concentrations of Pd and Fe in the precursor solutions. The nanoparticles were characterized by transmission electron microscopy, X-ray diffractometry and X-ray photoelectron spectroscopy. The optimum Pd:Fe ratio for this reaction was determined to be 3:1. The comparison of activities of the catalysts with component ratios equaled 3:1 and 10:1 is shown that the activities are differed from each other by 10–15 times in advantage of catalyst with lesser content of palladium. This phenomenon can be related to the different particle size of both catalysts and different distribution of particles by size discovered by TEM method. The achievement of maximum activity near the ratio of Pd:Fe = 3:1 is due to as effect of alloy-forming and the influence of binary system component ratio and synthesis conditions on dispersity degree of metallic phase nanoparticles. Under optimal conditions of precursor mixture high-temperature pyrolysis, iron produces the stabilizing effect palladium. It gives rise to obtaining the uniform and finely divided (7–8 nm) metallic particles.

Changes in Palladium, Platinum, and Rhodium Concentrations, and Their Spatial Distribution in Soils Along a Major Highway in Germany from 1994 to 2004

Soil samples were collected along the highway A5 from the major junctions Frankfurter Kreuz to Darmstäder Kreuz from July to September, 2004 and analyzed for palladium (Pd), platinum (Pt), and rhodium (Rh). The results were compared to analyses of platinum group elements (PGE) in soils collected along this same stretch of highway in 1994. The goal of this study is to detect any changes that may have occurred in the concentration and environmental distribution patterns of these metals over this 10 year period. The concentrations of Pd in soils along the highway were found to be about 15 times higher on average than those measured in 1994. Pt and Rh concentrations increased 2 and 1.6 times, respectively, during this time period. The significant rise in Pd concentrations in soils observed for the time period of analysis is likely due to its use in automobile catalytic converters in Germany since 1993. The results also show a strong positive relationship between PGE emissions and traffic density and speed. The results indicate that increases in the concentrations of Pd, Pt, and Rh in soils along the highway are not limited to the soil surface. Pt was measured as deep as 12 cm. Pd was determined at even greater depths of 12-16 cm. The presence of Pd at lower depths compared to Pt suggests that this element has a higher solubility. Pd, Pt, and Rh concentrations display a strong inverse relationship with distance from the road, with decreasing levels with increasing distance from the highway. Nonetheless, Pd and Pt were detected in a meadow as far as 50 m from the highway, a much greater distance compared to that measured for these metals in 1994. Pt concentrations were also found to significantly correlate with levels of Rh and Pd. The ratios between the PGE analyzed (Pt/Rh and Pd/Rh) display a shift toward Pt and Pd. The results clearly show that PGE concentrations have increased over time. Observed increases in Pd concentrations are particularly a cause of concern.

The adsorption of ethylene on Au/Pd(1 1 1) alloy surfaces

The adsorption of ethylene on gold–palladium alloys formed on a Pd(1 1 1) surface is investigated using a combination of temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). Various alloy compositions are obtained by depositing four monolayers of gold on a clean Pd(1 1 1) surface and annealing to various temperatures. For gold coverages greater than ∼0.7, ethylene adsorbs primarily on gold sites, desorbing with an activation energy of less than 55 kJ/mol. At gold coverages between ∼0.5 and ∼0.7, ethylene is detected on palladium sites in a π-bonded configuration (with a σ–π parameter of ∼0.1) desorbing with an activation energy of between ∼57 and 62 kJ/mol. Further reducing the gold coverage leads to an almost linear increase in the desorption activation energy of ethylene with increasing palladium content until it eventually reaches a value of ∼76 kJ/mol found for ethylene on clean Pd(1 1 1). A corresponding increase in the σ–π parameter is also found as the gold coverage decreases reaching a value of ∼0.8, assigned to di-σ-bonded ethylene as found on clean Pd(1 1 1).

Graphite fluoride intercalation compounds for manufacturing composites with metal nanoparticles

The feasibility of using graphite fluoride intercalation compounds (GFICs) containing metal compounds for manufacturing metal nanoparticles in a graphite or graphite fluoride matrix is shown using the hydrogen reduction of a dicarbon fluoride matrix intercalated with a chloroform solution of palladium acetylacetonate Pd(AA)2. The composite manufactured with a GFIC containing about 10.5 wt % Pd(AA)2 at 80°C is Pd-fluorographite; at 450°C, Pd-graphite is manufactured. The palladium particle size in the composites is about 20–30 nm; the palladium concentration is about 5 and 9 wt %, respectively.

Microwave-enhanced electro-deposition and stripping of palladium at boron-doped diamond electrodes

In situ microwave activation has been applied to the electro-deposition and stripping of palladium metal (which is widely used as a catalyst) at cavitation resistant boron-doped diamond electrodes. Focused microwave radiation leading to heating, boiling, and cavitation is explored as an option to improve the speed and sensitivity of the analytical detection procedure. The deposition and anodic stripping of palladium by linear sweep voltammetry in 0.1M KCl (pH 2) solution and at boron-doped diamond electrodes is shown to be strongly enhanced by microwave activation due to both (i) the increase in mass transport and (ii) the increase in the kinetic rate of deposition and stripping. The temperature at the electrode surface is calibrated with the reversible redox couple Fe(CN)(6)(4-)/Fe(CN)(6)(3-) and found to be reach 380K. In the presence of microwave radiation, the potential of onset of the deposition of palladium is strongly shifted positive from -0.4 to +0.1V versus SCE. The optimum potential for deposition in the presence of microwaves is -0.4V versus SCE and the anodic stripping peak current is shown to increase linearly with deposition time. Under these conditions, the stripping peak current varies linearly with the palladium concentration down to ca. 2muM. At concentration lower than this a logarithmic variation of the stripping peak current with concentration is observed down to ca. 0.1muM (for 5min pre-concentration in presence of microwave radiation).

Application of thiophene-2-carbaldehyde-modified mesoporous silica as a new sorbent for separation and preconcentration of palladium prior to inductively coupled plasma atomic emission spectrometric determination

A new and efficient method was described for an easy synthesis of functionalized mesoporous silica (MCM-41) using thiophene-2-carbaldehyde. This new chemically bonded analytical reagent was used as an effective sorbent for the solid phase extraction of palladium(II) ion from aqueous solutions. Conditions for effective adsorption of trace levels of palladium concentration were optimized with respect to different experimental parameters in batch process. Thiourea solution could efficiently elute adsorbed palladium(II) ion from the surface of the sorbent which then was determined by inductively coupled plasma atomic emission spectrometer (ICP-AES). Common coexisting ions did not interfere with the separation and determination. The preconcentration factor was 100 (1 ml elution volume) for a 100 ml sample volume. The limit of detection of the proposed method is 0.2 ng ml −1. The maximum sorption capacity of sorbent under optimum conditions has been found to be 5 mg of palladium per gram of sorbent. The relative standard deviation under optimum conditions was 3.2% ( n = 10). Accuracy and application of the method was estimated by using test samples of natural and synthetic water spiked with different amounts of palladium(II) ion.

The effect of palladium additions on the solidus/liquidus temperatures and wetting properties of Ag–CuO based air brazes

As a means of increasing the use temperature of ceramic–ceramic and ceramic–metal air brazes, palladium was investigated as possible ternary addition to the currently employed silver–copper oxide system. The silver component was directly substituted with palladium to form the following series of alloys: (100 − y)[(100 − z)Pd − ( z)Ag] − ( y)CuO x where y = 0–34 mol% CuO x and z = 50–100 mol% silver and where x = 0, 0.5, or 1, respectively, denotes copper metal, Cu 2O, or CuO. From differential thermal analysis, it was determined that the addition of palladium causes an increase in the solidus and liquidus temperatures of the resulting Pd–Ag–CuO brazes. In general, the liquidus was found to increase by approximately 220 °C for the (100 − y)(25Pd − 75Ag) − ( z)CuO x filler metal compositions relative to comparable Ag–CuO x alloys. Likewise, the solidus was found to increase for these alloys, respectively, by 185 and 60 °C, respectively, for CuO x contents of y = 0–1 mol% and 4–10 mol%. For the (100 − y)(50Pd − 50Ag) − ( y)CuO x alloys, the solidus increased between 280 and 390 °C over a copper oxide compositional range of x = 0–8 mol%. It was determined from sessile drop experiments conducted on alumina substrates that in all cases the palladium causes an increase in the wetting angle relative to the corresponding binary braze. Alloy compositions of (100 − y)(25Pd − 75Ag) − ( y)CuO x displayed increased wetting angles of 5–20° relative to comparable binary compositions. (100 − y)(50Pd − 50Ag) − ( y)CuO x alloys exhibited an increase in contact angle of 10–60° and compositions containing less than 10 mol% CuO x were not able to wet the substrate. Metallographic analysis indicated that the microstructure of the braze consists of discrete CuO x precipitates in an alloyed silver–palladium matrix. In both the binary and ternary filler metal formulations, a reaction layer consisting of CuAlO 2 was observed along the interface with the alumina substrate. This reaction product appears to be beneficial in promoting wetting by the remaining braze filler metal. However the formation of this layer is hindered as the concentration of palladium in the filler metal is increased, which appears to be the primary cause of poor wettability in these compositions, as indicated by the substantial amount of porosity found along the braze/substrate interface.