Mixture Of Palladium Research Articles

Hydrodehalogenation of aryl halides by the mixture of palladium(II) and a newly synthesized chiral macrocyclic bis(N-heterocyclic carbene) ligand

A novel macrocyclic bis(N-heterocyclic carbene) precursor was designed and prepared, which manifested high catalytic efficiency when combining Pd(OAc)2 in hydrodehalogenation of aryl halides. The generation of a little amount of the intermediate product chlorobenzene is closely related with the synergistic effect of two imidazoline protons lying on the two opposite sides of the macrocycle.

Development of Titanium Dioxide-Supported Pd Catalysts for Ligand-Free Suzuki–Miyaura Coupling of Aryl Chlorides

The catalyst activities of various heterogeneous palladium catalysts supported by anatase-, rutile- and brookite-type titanium oxide for ligand-free Suzuki–Miyaura cross-coupling reactions of aryl chlorides were evaluated. Palladium acetate [Pd(OAc)2], supported on anatase-type titanium oxide (TiO2) via acetonitrile solution impregnation process without reduction [Pd/TiO2 (anatase-type)], demonstrated the highest catalyst activity in comparison to those of other titanium oxide (rutile- or brookite-type) supported Pd(OAc)2 without reduction and reduced Pd/TiO2 (anatase-type) [Pd(red)/TiO2 (anatase-type)]. Various aryl chloride and bromide derivatives were smoothly coupled with arylboronic acids including heteroarylboronic acids in the presence of 5–10 mol% Pd/TiO2 (anatase-type) without the addition of any ligands. Although the fresh Pd/TiO2 (anatase-type) catalyst was surprisingly comprised of ca. 1:2 mixture of palladium(II) and palladium(0) species according to X-ray photoelectron spectroscopy (XPS), in spite of no reduction process, significant further increment of palladium(0) species was observed during the Suzuki–Miyaura coupling reaction, and Pd/TiO2 (anatase-type) was converted into a catalyst, which contained palladium(0) species as the main component [ca. 1:5 mixture of palladium(II) and palladium(0) species]. Therefore, the reduction via the electron donation process to the palladium(II) species may have occurred during the reaction on anatase-type titanium oxide.

Arsenic speciation in artificial saliva extract of smokeless tobacco products by extraction methodologies coupled with electrothermal atomic absorption spectrometry

Simple and rapid preconcentration methods viz. cloud point extraction (CPE) and solid phase extraction (SPE) were applied for the determination of As3+ and total inorganic arsenic (iAs) in artificial saliva extract (ASE) of smokeless tobacco (SLT) product (mawa). The iAs species were separated from organic As by adsorbing on titanium dioxide (TiO2), whereas the organic As was eluted out. The retained iAs species was eluted by 1.0mL of 0.5M NaOH solution. The CPE method has been used for the preconcentration of As3+, using ammonium pyrrolidinedithiocarbamate (APDC) as complexing reagent. The resulting solutions of each method were determined by electrothermal atomic absorption spectrometry with a mixture of palladium and magnesium nitrates as modifier. The % recovery of As3+ and iAs were found to be >98%. The adsorption capacity of TiO2 for iAs was calculated to be 11.5mgg−1. The accuracy of methods was tested by simultaneously analyzing certified reference material, Virginia tobacco leaves and spike recovery test. Under the optimized experimental conditions, the detection limits for As3+ and iAs were 28 and 20ngmL−1 for CPE and SPE, respectively. The enrichment factor for SPE and CPE were obtained as 25 and 20, respectively. The concentration of As+3 and As5+ were found in the range of 26–45 and 50–98ngg−1, respectively in studied SLT product. The artificial saliva extractable arsenic (As) corresponds to 19%–25%, of total As in SLT product.

Investigation of chemical modifiers for sulfur determination in diesel fuel samples by high-resolution continuum source graphite furnace molecular absorption spectrometry using direct analysis

High-resolution continuum source graphite furnace molecular absorption spectrometry has been applied for sulfur determination in diesel fuel. The sharp rotational lines of the carbon monosulfide molecule (formed during the vaporization step) were used to measure the absorbance. The analytical line at 258.056nm was monitored using the sum of three pixels. Different chemical modifiers were investigated and the mixture of palladium and magnesium was used as chemical modifier in combination with iridium as permanent modifier. l-Cysteine was chosen as sulfur standard and the calibration was done against aqueous standard solutions. The proposed method was applied for the analyses of four diesel samples: two S10 samples and two S500 samples. The trueness of the method was checked with a certified reference material (CRM) of sulfur in diesel fuel (NIST 2724b). Accurate results, for samples and CRM, were achieved after a dilution with propan-1-ol. The following figures of merit were obtained: characteristic mass of 17±3ng, limit of detection and limit of quantification of 1.4mgkg−1 and 4.7mgkg−1, respectively.

Method development for the determination of bromine in coal using high-resolution continuum source graphite furnace molecular absorption spectrometry and direct solid sample analysis

This work reports a simple approach for Br determination in coal using direct solid sample analysis in a graphite tube furnace and high-resolution continuum source molecular absorption spectrometry. The molecular absorbance of the calcium mono-bromide (CaBr) molecule has been measured using the rotational line at 625.315nm. Different chemical modifiers (zirconium, ruthenium, palladium and a mixture of palladium and magnesium nitrates) have been evaluated in order to increase the sensitivity of the CaBr absorption, and Zr showed the best overall performance. The pyrolysis and vaporization temperatures were 800°C and 2200°C, respectively. Accuracy and precision of the method have been evaluated using certified coal reference materials (BCR 181, BCR 182, NIST 1630a, and NIST 1632b) with good agreement (between 98 and 103%) with the informed values for Br. The detection limit was around 4ng Br, which corresponds to about 1.5μgg−1 Br in coal, based on a sample mass of 3mg. In addition, the results were in agreement with those obtained using electrothermal vaporization inductively coupled plasma mass spectrometry, based on a Student t-test at a 95% confidence level. A mechanism for the formation of the CaBr molecule is proposed, which might be considered for other diatomic molecules as well.

Direct Determination of Arsenic in Beet Sugar Molasses Using Nickel as Chemical Modifier by Electrothermal Atomic Absorption Spectrommetry

AbstractA simple electrothermal atomic absorption spectrometric (ETAAS) method is described for direct determination of arsenic in sugar beet molasses samples. Pyrolytic graphite tubes were used as atomizers. The compression between modifiers such as nickel nitrate, palladium nitrate and the mixture of palladium and magnesium nitrate were performed and nickel nitrate selected as the best chemical modifier. The effects of pyrolysis and atomization temperature were also studied and the pyrolysis temperature of 900 °C and atomization temperature of 2300 °C have been chosen for temperature program. The detection limit of the method was 1 ng/mL As in sugar beet molasses samples. The relative standard deviation for ten determination of a spiked sample with concentration of 50 ng/mL As was 2.4%. The accuracy of the method was confirmed by the analysis of spiked samples. The linear rang of calibration is in the range of 1‐100 ng/mL of arsenic.

Application of hydrogen vacuum treatment of palladium powders for production of efficient metal alloy cathodes of self-heated magnetron

A method to improve emission homogeneity of pressed palladium-barium cathodes applied in magnetrons with self-heating initiation is proposed. The initial palladium powder is annealed at 950°C for 60 min and then calcined in vacuum under pressure of residual gases P ≤ 1 × 10−4 Pa. It is demonstrated that cathodes produced by pressing and subsequent sintering of a powdered mixture of palladium and intermetallic compound Pd5Ba in vacuum are characterized by a high distribution homogeneity of components. Within testing of magnetrons produced with such cathodes, the yield of good items is increased by a factor of 1.5.

Role of a Binary Metallic Modifier in the Determination of Cadmium in Graphite Furnace Atomic Absorption Spectrometry

In order to discuss the matrix modifier effect of palladium, iron, and a mixture of palladium and iron for the determination of cadmium in graphite-furnace atomic absorption spectrometry (GF-AAS), we measured the absorption profiles of a cadmium line at various compositions of these elements. Variations in the gas temperature were also estimated with the progress of atomization, by using a two-line method under the assumption of a Boltzmann distribution. The atomic absorption of cadmium appeared on the way of heating from the charring temperature to the atomizing temperature while the gas temperature was still low; it was thus considered that cadmium was atomized through direct conductive heating from the wall of the graphite furnace. Therefore, the effectiveness of modifiers for cadmium would be determined through any reactions on the furnace wall at the programmed charring and atomizing temperatures. The addition of iron, palladium, and an iron-palladium mixture all enhanced the absorption signal of cadmium compared to a pure cadmium sample; however, their effects were different from one another. Each addition of iron or palladium to the sample solution led to an enhancement of the cadmium absorbance, indicating that iron or palladium individually became an effective matrix modifier for the determination of cadmium. However, the addition of palladium was ineffective for the matrix modification in the coexistence of large amounts of iron. Although these phenomena are very complicated, and thus cannot be understood completely, any metallurgical reaction between the constituent elements during heating of the furnace wall, such as the formation of solid solutions and intermetallic compounds, would cause the effect of a matrix modifier in GF-AAS.

CURBING DIESEL ENGINES’ COST

AN IMPROVEMENT to catalysts found in fuel-efficient diesel engines could make this clean technology less expensive. Wei Li, a project manager at General Motors Global Research & Development, in Warren, Mich., and his colleagues replaced platinum in catalysts used to clean the exhaust gas from diesel engines with a mixture of palladium, which is four to five times cheaper than platinum, and perovskite oxides ( Science 2010, 327, 1624). “Platinum is a lot more expensive than everything else in the converter,” Wei says. He adds that his team is hoping to validate the new catalysts over the next few years, but “there is still a long way to go before the technology is put into new vehicles.” James E. Parks II, a group leader at Oak Ridge National Laboratory specializing in emissions and catalysis, says in a commentary about the work that the perovskite catalysts being developed by Wei and colleagues are “encouraging.” Even ...

Biaryl-Like CATPHOS Diphosphines via Double Diels–Alder Cycloaddition between 1,4-Bis(diphenylphosphinoyl)buta-1,3-diyne and Anthracenes: Efficient Ligands for the Palladium-Catalyzed Amination of Aromatic Bromides and α-Arylation of Ketones

A mixture of palladium(0) and CATPHOS, the 1,3-butadiene-bridged diphosphine generated via double Diels–Alder cycloaddition between bis(diphenylphosphinoyl)buta-1,3-diyne and anthracene, catalyzes the amination of a range of aromatic bromides as well as the α-arylation of ketones, giving conversions that either rival or exceed those obtained with BINAP.

Simultaneous spectrophotometric determination of mercury and palladium with Thio-Michler's Ketone using partial least squares regression and orthogonal signal correction

A simple, novel and sensitive spectrophotometric method was described for simultaneous determination of mercury and palladium. The method is based on the complex formation of mercury and palladium with Thio-Michler's Ketone (TMK) at pH 3.5. All factors affecting on the sensitivity were optimized and the linear dynamic range for determination of mercury and palladium found. The simultaneous determination of mercury and palladium mixtures by using spectrophotometric method is a difficult problem, due to spectral interferences. By multivariate calibration methods such as partial least squares (PLS), it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. Orthogonal signal correction (OSC) is a preprocessing technique used for removing the information unrelated to the target variables based on constrained principal component analysis. OSC is a suitable preprocessing method for PLS calibration of mixtures without loss of prediction capacity using spectrophotometric method. In this study, the calibration model is based on absorption spectra in the 360–660 nm range for 25 different mixtures of mercury and palladium. Calibration matrices were containing 0.025–1.60 and 0.05–0.50 μg mL −1 of mercury and palladium, respectively. The RMSEP for mercury and palladium with OSC and without OSC were 0.013, 0.006 and 0.048, 0.030, respectively. This procedure allows the simultaneous determination of mercury and palladium in synthetic and real matrix samples good reliability of the determination.

Interference-free determination of thallium in aqua regia leaches from rocks, soils and sediments by D 2-ETAAS method using mixed palladium–citric acid–lithium chemical modifier

The mixture of palladium (chloride) with citric acid and lithium is proposed as a new chemical modifier for the elimination of interference occurred during the determination of Tl in aqua regia extracts from rocks, soils and sediments by electrothermal atomic absorption spectrometry using instrumentation with deuterium-lamp background correction (D 2-ETAAS). Palladium was preferred to rhodium and platinum as to analyte stabilization, citric acid served as an effective reducing agent facilitating formation of Pd–Tl stable covalent bonds playing an important role in the analyte stabilization. Citric acid in addition helps to remove most of interfering chloride at low temperature. The further addition of Li increased significantly the robustness of chemical modifier against strongly interfering ZnCl 2 matrix by binding free chlorine into a more stable LiCl molecule. In the presence of the proposed chemical modifier the temperature for the final step of pyrolysis was adjustable up to 1000 °C, without any noticeable loss of volatile Tl species and the interference of the rest chloride matrix was significantly reduced. The application of the modifier to direct determination of Tl in aqua regia extracts from rocks, soils and sediments has ensured the characteristic mass and LOD value for the original sample 13 pg and 0.043 μg g −1, respectively (10-μL aliquots of sample) and has enabled the use of matrix-free standard solutions for attaining accurate analysis. The accuracy was verified by the analysis of certified reference samples and by the comparison of results with those found by an inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometer (ICP-oa-TOFMS) method.

Behaviour of chemical modifiers in the determination of arsenic by electrothermal atomic absorption spectrometry in petroleum products

Most comparative studies on the efficiency of chemical modifiers have been conducted in aqueous media. In the present work, we proposed a detailed study of the use of different chemical modifiers for direct determination of arsenic in complex organic matrices by electrothermal atomic absorption spectrometry (ETAAS). Palladium, rhodium, tungsten, silver, lanthanum and a mixture of palladium and magnesium were tested. The figures of merit used for evaluation and comparison were acquired in the optimal conditions for each modifier, established by multivariate optimization of the main variables based on Doehlert designs. Singular features were observed for the chemical behaviour of some modifiers in organic matrices compared to aqueous media, such as the worse performance of Pd + Mg modifier and no notice of severe tube corrosion from La application. Lanthanum was chosen as the best chemical modifier for the present application, according to predefined criteria. Lanthanum showed the minimum limit of detection, characteristic concentration and blank signal among all tested species and no effect of the concomitants usually present in petrochemical feedstocks. Using a 200 mg L −1 lanthanum solution as a chemical modifier, the average relative standard deviations of 7 and 16% (at 3–15 μg L −1 level) and characteristic concentrations of 0.47 and 0.77 μg L −1 for naphtha and petroleum condensates, respectively, were observed.

Palladium-catalysed Synthesis of Pyrimidines

Satisfactory yields of 4-substituted pyrimidines and bicyclic pyrimidines are produced from α-methyl or α-methylene ketones when reacted with formamide and tetrakis(triphenylphosphine)palladium(0) or a 1:2 mixture of palladium(II) acetate and triphenylphosphine as catalysts. Under the same reaction conditions pyridines or imidazole are formed from 1,3- or 1,2-diketones.

Sodium nitrate and tungsten as matrix modifiers for the determination of arsenic in shotgun pellets by electrothermal atomic absorption spectrometry

A method for the determination of arsenic in a complicated sample matrix by Zeeman effect electrothermal atomic absorption spectrometry using tungsten and sodium nitrate as matrix modifiers was developed. The determination of arsenic in SRM C2416 (Bullet Lead) and SRM 2710 (Montana Soil) by ETAAS using a mixture of palladium and magnesium nitrate as a matrix modifier failed to obtain the certified concentrations at the 95% level of confidence using the t-test. Both tungsten and sodium nitrate as matrix modifiers stabilized arsenic so that the certified concentrations of the SRMs were determined with high accuracy and precision (RSD < 4%). The high values of the regression correlation coefficients (r > 0.999), with low detection and quantification limits, were obtained in the calibration range 20–100 µg L−1. Sample matrix interferences can be eliminated by increasing the pyrolysis temperature to 1400 °C with tungsten and to 1500 °C with sodium nitrate matrix modification. The standard additions method was also carried out in the case of SRM C2416 in order to check the linear relationship between integrated absorbance and concentration for the calibration range used. The new method was utilized for the analysis of shotgun pellets.

Behavior of Silver and Palladium Mixtures during Heating

The behavior of mixtures of silver and palladium during heating in both air and an inert atmosphere was studied using X‐ray diffractometry (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dilatometry, and scanning electron microscopy (SEM). In situ high‐temperature XRD studies on a commercial 20% palladium material with submicrometer‐sized particles indicated that an intermetallic phase, most likely Ag3Pd, formed in air between 300° and 400°C, the same temperature range where a 13% linear expansion was measured by dilatometry. The DSC data indicated an exothermic peak at 340°C, a temperature where the TGA results indicated that the material had picked up only 0.2% oxygen, compared with the maximum of 1.4% at 525°C. No PdO was detected by XRD at 400°C, which suggests that oxygen was being incorporated in the intermetallic. Microstructural examination using SEM indicated that larger particles, with internal pores, had formed after heating in air to 375°C. When the material was heated in argon for 1 h at 400°C, no intermetallic phase or alloy formed, and minimal expansion occurred. When mixtures of larger silver particles (5–30 μm) with palladium particles (1–3 μm) were heated in air, the maximum amount of expansion that occurred increased from 0% for pure palladium up to a maximum of 18% at 75% silver. This result supports the conclusion that expansion is a result of formation of this new phase, in the presence of oxygen, not of the oxidation of the palladium.

Reversible Hydriding of LaNi5 − x Al x ― Pd Composites in the Presence of Carbon Monoxide

Carbon monoxide is one of the most dangerous impurities in gas mixtures involved in the hydriding of intermetallic compounds, and up to the present time the concentration limit 0.03 vol.% CO has not been surmounted. The objective of the present work was to investigate the possibility of reversibly hydriding LaNi5 − xAlx ― Pd composites in gas mixtures containing up to 5 vol.% CO. The experimental specimens were mixtures of palladium black and LaNi5, LaNi4.7Al0.3, LaNi4.5Al0.5, LaNi4.2Al0.8, and LaNi4Al powders cold pressed at 300 MPa. The intermetallics were preliminarily dispersed by hydriding and mechanical grinding. The concentration of palladium black in the powder mixtures was varied from 0 to 1.5 mass%. It was shown that it is possible to reversibly hydride LaNi5 − xAlx ― Pd composites in mixtures of hydrogen and carbon monoxide containing up to 5 vol.% CO at the temperatures 423 and 473 K. It was established that alloying LaNi5 with aluminum in amounts which raised the stoichiometric concentration above 0.5 stabilized the absorption properties of LaNi5 − xAlx ― Pd in the presence of CO. The composition LaNi4Al was optimal. Palladium additions to LaNi5 − xAlx ― Pd composites also increased the stability of hydrogen absorption by the intermetallic. It is noted that the effect of palladium was more positive than that of aluminum.

Determination of trace metals (As, Cd, Hg, Pb and Sn) in marine sediment slurry samples by electrothermal atomic absorption spectrometry using palladium as a chemical modifier

Methods for the determination of As, Cd, Pb, Hg and Sn by electrothermal atomic absorption spectrometry in marine sediment slurry samples were developed. Triton X-100 was used as surfactant to stabilize the marine sediment slurry. Palladium or a mixture of palladium and magnesium nitrates was used as a chemical modifier. With the use of these modifiers it was possible to stabilize As, Cd, Pb, Hg and Sn to temperatures of 1200, 700, 900, 200 and 1300°C respectively, and the optimum atomization temperatures were 2300, 2500, 2500, 1450 and 1900°C. Precision and accuracy of the method were investigated using the marine sediment reference material PACS-1 (National Research Council Canada). The detection limits were 44, 0.08, 60, 70 and 57 μg kg −1 for As, Cd, Pb, Hg and Sn respectively.

Determination of Sb, Ni and V in slurry from airborne particulate material collected on filter by graphite furnace atomic absorption spectrometry

A microdigestion procedure performed directly in the autosampler cup is proposed. Small quartz filter pieces loaded with the particulate material are transferred to the cup. The sample is digested by a mixture of nitric, sulfuric and hydrofluoric acid (1:1:1) under sonication. After the addition of a boric acid solution the elements are determined by graphite furnace atomic absorption spectrometry using the autosampler to deliver the slurry into the furnace. A mixture of palladium and magnesium nitrates was used as a modifier for Sb. Spiking studies showed recoveries close to 100% using aqueous analytical curves for Ni and Sb. For V, an analytical curve in the blank slurry, obtained by submitting an unloaded filter to the same procedure, was used. The method was applied to two standard reference materials, Coal Fly Ash (NIST 1633a) and Urban Particulate (NIST 1648) and the concentrations showed good agreement with the certified or recommended values using aqueous analytical solutions.

Determination of Ultratrace Amounts of Copper and Cadmium in Seawater by Graphite Furnace Atomic Absorption Spectrometry with Flow-Injection Semi On-line Preconcentration

Methods are described for the determination of ultratrace amounts of copper and cadmium in seawater by graphite furnace atomic absorption spectrometry with flow-injection, microcolumn preconcentration. A new type of C 18 column loaded with sodium diethyldithiocarbamate (sodium-DDC) was used to extract copper and cadmium from seawater as the DDC chelates. The analytical effects of the pH of the mixture of the sample and sodium-DDC solutions and the concentration of the chelating reagent were studied. Sodium-DDC-loaded columns and unloaded C 18 columns with different shapes and volumes were compared. To determine copper in seawater, a simple aqueous calibration was made with a mixture of palladium and magnesium nitrate as a matrix modifier, while for cadmium no matrix modifier was necessary. This method required only small seawater volumes, 600 and 400 μl for the determination of copper and cadmium respectively, with preconcentration factors of 15-fold for copper and 10-fold for cadmium. Detection limits for the preconcentration of aqueous solutions of copper and cadmium were 0.024 and 0.004 μg liter −1 (3σ), respectively. Results for determinations of copper and cadmium in National Research Council of Canada, CASS-2, Nearshore Seawater Reference Material showed no significant differences between the certified values and the measured values, based on Student′s t test at the 95% confidence level. The relative standard deviations of the various measurements varied between 2 and 8%.