Small Amount Of Pd Research Articles

Palladium Supported on Fluorite Structured Redox CeZrO4-δfor Heterogeneous Suzuki Coupling in Water: A Green Protocol

Pd on redox CeZrO4-δ catalysts was prepared, characterized and their activity was evaluated for Suzuki coupling reaction in water under reflux condition. Fresh and reduced form of 5 % Pd (R−Pd5) on CeZrO4-δ catalyst exhibited 100 % conversion in 2.5 and 1 h, respectively. R−Pd5 shows significant activity for wide range of substrate compatibility and for less reactive aryl bromides too. The mechanistic investigations proved the important role of redox CeZrO4-δ support on the catalytic activity. It was observed that the presence of oxygen vacancy along with Ce3+ enhances the activity. 1 wt % Pd photodeposited on pre-reduced CeZrO4-δ support requires a mere 20 min. for 100 % conversion of Suzuki coupling. Effect of metal dispersion and particle size on catalytic activity is also discussed. High Pd dispersion with small particle size (4±1 nm), particle size preservation after reaction, strong metal-support interaction and no leaching fully suggest the heterogeneous mechanism is operative for Suzuki coupling on 1 wt % Pd photodeposited on reduced CeZrO4-δ support. Present work hints the possibility of achieving high conversion for Suzuki reaction with very small amount of Pd through better dispersion by taking advantage of redox support and in water.

ChemInform Abstract: Highly Active Palladium‐Based Catalyst System for the Aerobic Oxidative Direct Coupling of Benzene to Biphenyl.

A highly efficient Pd-containing catalytic system for the intermolecular direct C−H homocoupling of benzene to biphenyl has been developed. The catalytic system was composed of Pd(OAc)2 with trifluoromethanesulfonic acid (TfOH) as an additive and O2 as the sole oxygen source in the absence of any metal-containing cocatalyst. An excellent efficiency of PdII with the acidic additive was attained in the aerobic oxidation of benzene to biphenyl. A high yield (25.3 %) and selectivity (98 %) were achieved by using a small amount of Pd(OAc)2 (0.07 mol %) and TfOH, which gave a high turnover number (180) for Pd species. Theoretical calculation by DFT and UV/Vis absorption spectra illustrated that the formation of electropositive PdII species in the presence of TfOH contributed to the high efficiency of the catalytic system.

New strategy by a two-component heterogeneous catalytic system composed of Pd–PVP–Fe and heteropoly acid as co-catalyst for Suzuki coupling reaction

We have developed a simple and efficient catalytic protocol composed of hollow palladium-poly(N-vinylpyrrolidone)-nano zero valent iron and H5PMo10V2O40 (Mo10V2) supported on Fe2O3@SiO2 core–shell nano particles, as reusable catalytic system for Suzuki coupling reaction under ligand- and base-free conditions. These reusable solid catalysts exhibited excellent activity and the methodology is applicable to diverse substrates providing good-to-excellent yields of desired products. This method has advantages of high yields, low reaction times, elimination of ligand and base, heterogeneous catalysts, and simple methodology. In order to study the role of Fe@Si–Mo10V2 in the Suzuki coupling reaction, electron transfer property of Fe@Si–Mo10V2 and Pd–PVP–Fe by means of cyclic voltammetry measurements were investigated. Moreover, this catalytic system could be recovered in a facile manner from the reaction mixture and recycled several times without any significant loss in activity. In this study, the heterogeneity of both component of our catalytic system was investigated and the content of palladium (Pd) and Mo10V2 into filtrates was evaluated quantitatively by inductively coupled plasma atomic emission spectroscopy (ICP-AES). According to the obtained results from the ICP-AES measurements, the small amount of Pd and Mo10V2 leach have been obtained.

Oxidation of palladium on Au(111) and ZnO(0001) supports.

The oxidation behavior of supported Pd-deposits on Au(111) and ZnO(0001) single crystals has been studied by x-ray photoemission spectroscopy (XPS). Oxidation has been carried out ex situ in a high-pressure cell and subsequent vacuum-transfer and characterization by ultra-high vacuum XPS, as well as in situ characterization by synchrotron based near ambient pressure XPS. On Au(111) alloying of Pd with the substrate competes with oxidation and only for sufficiently thick Pd films oxidation is obtained. For Pd deposits on ZnO the oxidation condition depends on the amount of deposited Pd. Thicker Pd-deposits behave similar to bulk Pd-samples, while for thinner films the oxidation temperatures may be lowered. Interestingly, for very small amounts of Pd, in situ XPS shows full oxidation at room temperature and at less than 0.6 mbar O2 pressure. This indicates lowering of the kinetic barriers for oxidation of very small supported Pd-clusters. The formed oxide is, however, not stable in ultra high vacuum and a slow reduction is observed. The instability of this oxide in UHV indicates that the formed Pd-oxide at the interface to ZnO may have different chemical properties compared to bulk PdO or surface oxides on Pd.

ChemInform Abstract: A NiPdB‐PEG(800) Amorphous Alloy Catalyst for the Chemoselective Hydrogenation of Electron‐Deficient Aromatic Substrates.

A new Pd and polyethylene glycol 800 [PEG(800)]-modified NiB [NiPdB-PEG(800)] amorphous alloy catalyst was prepared, which demonstrated excellent activities, similar to those of noble metal catalysts, in the chemoselective hydrogenation of a series of electron-deficient aromatic substrates in water. The addition of small amounts of Pd to NiB markedly improved its activity. The Pd not only benefits the dispersion of active species but also contributes to the activity of the catalyst. The accompanying agglomeration can be inhibited with the further addition of PEG(800), which results in the largest surface area, the smallest particle size, and the greatest number of active species, resulting in optimum H2-chemisorption and accounting for its highest activity. The key factors determining the main reaction products depend not only on the structures of the substrates but also on the character of the solvents. Water is found to be the most effective solvent for most of the substrates.

Selective hydrogenation of ethyl benzoate over Ni–B amorphous alloys supported on γ-Al2O3

A series of Ni–B amorphous alloys supported on γ-Al2O3 was prepared by an impregnation chemical reduction method and tested in the selective hydrogenation of ethyl benzoate to ethyl cyclohexane carboxylate. The effect of different metal additives on the activity of the supported Ni–B amorphous alloys was investigated. It was found that the addition of small amounts of Pd to Ni–B amorphous alloy supported on γ-Al2O3 could markedly improve its activity and the yield of ethyl cyclohexane carboxylate can reach 88.1 % under the optimal reaction conditions. Furthermore, this catalyst could be recycled eight times without appreciable loss of its initial activity, much better than the unsupported one. The Ni–Pd–B amorphous alloy was proven to be highly dispersed on the surface and in the pores of γ-Al2O3, resulting in its larger BET area, more active Ni species, better stability, and hence accounting for its good catalytic performance.

High sensitive gas sensor based on Pd-loaded WO3 nanolamellae

An impregnation method has been proposed to prepare Pd-loaded WO3 nanolamellae for the gas sensing application. WO3 nanolamellae were synthesized via an acidification method and impregnated with H2Pd2Cl4 solution followed by an ammonia washing treatment. The microstructure and H2 sensing characteristics of the Pd-loaded WO3 nanolamellae were investigated. Electron microscopy studies revealed that PdO particles have been deposited on the surfaces of WO3 with a diameter ranging from 3 to 15nm. With quite a small amount of Pd, the sensor resistivity was greatly enhanced and it demonstrated an extremely large response to the reduced gas. It was found that sensing response at low temperature increased dramatically with a rise in the gas concentration for Pd-loaded sensors. However, the sensor response at high temperature quickly saturated with increasing the H2 concentration for larger amount of Pd loading. An enhanced combustion effect of Pd and chemical adsorbed water could be responsible for such a saturation of sensing response at high temperatures.

Nanoarchitectures Based on Layered Titanosilicates Supported on Glass Fibers: Application to Hydrogen Storage

This work reports on the synthesis of nanosheets of layered titanosilicate JDF-L1 supported on commercial E-type glass fibers with the aim of developing novel nanoarchitectures useful as robust and easy to handle hydrogen adsorbents. The preparation of those materials is carried out by hydrothermal reaction from the corresponding gel precursor in the presence of the glass support. Because of the basic character of the synthesis media, silica from the silicate-based glass fibers can be involved in the reaction, cementing its associated titanosilicate and giving rise to strong linkages on the support with the result of very stable heterostructures. The nanoarchitectures built up by this approach promote the growth and disposition of the titanosilicate nanosheets as a house-of-cards radially distributed around the fiber axis. Such an open arrangement represents suitable geometry for potential uses in adsorption and catalytic applications where the active surface has to be available. The content of the titanosilicate crystalline phase in the system represents about 12 wt %, and this percentage of the adsorbent fraction can achieve, at 298 K and 20 MPa, 0.14 wt % hydrogen adsorption with respect to the total mass of the system. Following postsynthesis treatments, small amounts of Pd (<0.1 wt %) have been incorporated into the resulting nanoarchitectures in order to improve their hydrogen adsorption capacity. In this way, Pd-layered titanosilicate supported on glass fibers has been tested as a hydrogen adsorbent at diverse pressures and temperatures, giving rise to values around 0.46 wt % at 298 K and 20 MPa. A mechanism of hydrogen spillover involving the titanosilicate framework and the Pd nanoparticules has been proposed to explain the high increase in the hydrogen uptake capacity after the incorporation of Pd into the nanoarchitecture.

Liquid Phase Hydrogenation of &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;-Chloronitrobenzene on Au-Pd/TiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Catalysts: Effects of Reduction Methods

The effects of palladium addition and the reduction methods on Au/TiO2 were investigated. Pd was loaded on TiO2 firstly by incipient-wetness impregnation, Au was then loaded by deposition-precipitation method. The nominal loadings of Au and Pd were 1 wt% and 0.01 wt%. The bimetallic catalysts were reduced by heating at 453 K, by flowing H2 at 423 K, or by NaBH4 at 298 K. The catalysts were characterized by ICP, XRD, TEM, HRTEM, TPR and XPS. Hydrogenation of p-chloronitrobenzene was carried out at 1.2 MPa H2 pressure and 353 K. The results showed that even adding very small amount of Pd could enhance activity and selectivity of p-chloroaniline significantly. Pd and Au formed alloy and Pd could donate partial electron to Au. Pd metal on the surface of alloy could adsorb hydrogen and enhanced the activity. The pretreatment methods did not change particle size significantly, all were below 4 nm. The sample reduced by NaBH4 could have higher concentration of Au0 and sustain small Au particle size, resulting in high activity.

Effect of groundwater geochemistry on pentachlorophenol remediation by smectite-templated nanosized Pd0/Fe0

Zero-valent iron holds great promise in treating groundwater, and its reactivity and efficacy depend on many surrounding factors. In the present work, the effects of solution chemistry such as pH, humic acid (HA), and inorganic ions on pentachlorophenol (PCP) dechlorination by smectite-templated Pd(0)/Fe(0) were systematically studied. Smectite-templated Pd(0)/Fe(0) was prepared by saturating the negatively charged sites of smectite clay with Fe(III) and a small amount of Pd(II), followed by borohydride reduction to convert Fe(III) and Pd(II) into zero-valent metal clusters. Batch experiments were conducted to investigate the effects of water chemistry on PCP remediation. The PCP dechlorination rate critically depends on the reaction pH over the range 6.0~10.0; the rate constant (k (obs)) increases with decreasing the reaction pH value. Also, the PCP remediation is inhibited by HA, which can be attributed to the electron competition of HA with H(+). In addition, the reduction of PCP can be accelerated by various anions, following the order: Cl(-) > HCO (3) (-) > SO (4) (2-) ~no anion. In the case of cations, Ca(2+) and Mg(2+) (10 mM) decrease the dechlorination rate to 0.7959 and 0.7798 from 1.315 h(-1), respectively. After introducing HA into the reaction systems with cations or/and anions, the dechlorination rates are similar to that containing HA alone. This study reveals that low pH and the presence of some anions such as Cl(-) facilitate the PCP dechlorination and induce the rapid consumption of nanosized zero-valent iron simultaneously. However, the dechlorination rate is no longer correlated to the inhibitory or accelerating effects by cations and anions in the presence of 10 mg/L HA.

Effect of Pd on CH&lt;sub&gt;4&lt;/sub&gt; Reforming with CO&lt;sub&gt;2&lt;/sub&gt; Catalyzed by Ni over Mixed Titian –Alumina Support

The catalytic reforming of methane with carbon dioxide using Pd promoter on 1% Ni/20%TiO2-P25+80%α-Al2O3 was investigated. An experimental study was carried out using the catalyst prepared by impregnation method. The catalysts were dried at 120°C and calcined at 900°C. The reforming reactions were carried out using CO2/CH4/N2 feed ratio of 5/5/1, F/W=44 ml/min.gcat and reaction temperature of 700°C. The effect of nominal load of Pd ranging from 0.0 to 0.48 was studied by evaluating catalyst activity, stability, coke and (H2/CO) ratio. The prepared catalysts were tested in micro reactor at atmospheric pressure. The effluents were analyzed using an online gas chromatography equipped with a thermal conductivity detector. EDS and TGA for the fresh and spent catalysts were evaluated. Results indicate that the addition of small amounts of Pd is preferable in terms of activity and carbon deposition than higher Pd loading. For instance, 0.01%Pd gives a conversion of 78.4 for CH4 and 4.9% deactivation factor. While, 0.48%Pd gives a conversion of 75.6 for CH4 and 29.9% deactivation factor. Thus higher loading of Pd causes the catalyst to show poor performance with lower conversion and higher carbon formations. It can be concluded that Pd promoter has an optimal concentration with respect to the active metal of the catalyst beyond which the performance deteriorates.

Construction of multilayers of bare and Pd modified gold nanoclusters and their electrocatalytic properties for oxygen reduction

Multilayers of gold nanoclusters (GNCs) coated with a thin Pd layer were constructed using GNCs modified with self-assembled monolayers (SAMs) of mercaptoundecanoic acid and a polyallylamine hydrochloride (PAH) multilayer assembly, which has been reported to act as a three-dimensional electrode. SAMs were removed from GNCs by electrochemical anodic decomposition and then a small amount of Pd was electrochemically deposited on the GNCs. The kinetics of the oxygen reduction reaction (ORR) on the Pd modified GNC/PAH multilayer assembly was studied using a rotating disk electrode, and a significant increase in the ORR rate was observed after Pd deposition. Electrocatalytic activities in alkaline and acidic solutions were compared both for the GNC multilayer electrode and Pd modified GNC electrode.

Oxygen non-stoichiometry in perovskitic catalysts: Impact on activity for the flameless combustion of methane

Perovskite-like LaBO 3 catalysts (B = Co, Mn, Fe), prepared by flame pyrolysis, and doped with Ce, Sr or with small amounts of Pd or Pt were used for the flameless combustion of methane. The effect of the dopants on the reducibility of the B metal ion has been analysed comparatively, trying to correlate this parameter with catalytic activity. The higher the B 3+ ion reducibility, the lower was the light off temperature of the reaction. However, the correlation with the temperature of half conversion revealed that a too high reducibility of the catalyst depressed the second step of the Mars–van Krevelen reaction mechanism, i.e. the reoxidation of active site. The quantitative elaboration of the TPR pattern allowed to determine oxygen non-stoichiometry, at least for the LaCoO 3 based samples. Furthermore, the available oxygen amount was correlated to catalytic activity.

Catalytic characterization of hollow silver/palladium nanoparticles synthesized by a displacement reaction

Hollow Ag/Pd nanoparticles have been successfully prepared by a galvanic displacement reaction, in which a small amount of Pd(NO 3) 2 is allowed to react with previously synthesized Ag nanoparticles that act as templates. The resulting hollow Ag/Pd (Ag/Pd hollow) nanoparticles are found to be icosahedral and decahedral in structure. The kinetics of electroless copper deposition (ECD) catalyzed by these bimetallic (Ag/Pd hollow) nanoparticles are analyzed using an electrochemical quartz crystal microbalance (EQCM). The results reveal that these Ag/Pd hollow nanoparticles have better catalytic activities than monometallic Ag and Pd nanoparticles. Furthermore, the catalytic activities of these hollow nanoparticles in the ECD bath can be controlled by tuning their alloy ratios in a suitable manner.

Distribution and Elimination of Palladium in Male Wistar Rats Following 14-Day Oral Exposure in Drinking Water

The Pd tissue distribution and elimination in rats following oral exposure in drinking water of dipotassium hexachloropalladate at doses of 100 or 250 ng/ml for 14 d were determined. The sector field inductively coupled plasma mass spectrometry used for Pd quantification showed the adequate sensitivity (10 ng/l) and accuracy (96–105%), and all the more in consideration of the very low levels of Pd accumulated. Tissues were taken and analyzed after 14 d. The tissue containing the highest Pd concentration was the kidney (4 ng/g dry weight in controls and 75 ng/g dry weight at the maximum dose), with left and right kidneys showing a comparable accumulation. The Pd kidney levels rose, but not significantly, with the administered dose. None of the other organs (liver, lung, spleen, adrenal glands, and bones) appeared to accumulate Pd, even at the highest dose. At the 250-ng/ml dose, small amounts of Pd were found in serum (0.27 ng/ml vs. 0.19 ng/ml in controls), while they were higher in urine (1.2 ng/ml vs. 0.16 ng/ml in controls) and in feces (3,231 ng/g dry weight vs. 69 ng/g dry weight in controls). Feces were the main excretion route for Pd, with a significant linear correlation with exposed dose, which is likely due to low intestinal absorption of Pd.

Oxidative steam reforming of methane over Ni/α-Al2O3 modified with trace Pd

Ni catalysts supported on α-Al2O3 modified with small amounts of Pd were prepared by different impregnation methods to investigate catalytic performance and catalyst bed temperature profile in oxidative steam reforming of methane. The Pd + Ni bimetallic catalysts prepared by the co-impregnation method showed higher resistance to hot-spot formation than monometallic Ni and bimetallic Pd/Ni catalysts prepared by two sequential impregnations, in particular, Pt + Ni catalysts prepared by the co-impregnation method. The additive effect of Pd on the Pd/Ni catalysts was discussed on the bases of metal particle size and structural analysis by Pd K-edge extended X-ray absorption fine structure (EXAFS).

Metallization of a Thiol-Terminated Organic Surface Using Chemical Vapor Deposition

The deposition and the subsequent decomposition of an organometallic precursor, (eta (3)-allyl)(eta (5)-cyclopentadienyl)palladium [Cp(allyl)Pd], on an organic surface exposed by self-assembled monolayers (SAM) was studied using X-ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS). The interfacial chemical reactions of the vapor-deposited metal precursor with the pendant thiol group of the SAMs made from oligophenyldithiols, which are either prepared directly (terphenyldimethyldithiol, TPDMT) or by a deprotection route from SAMs formed by a monoacylated derivative of biphenyldimethyldithiol (dep. BPDMAc-1) have been studied in detail. When the TPDMT-SAMs were exposed to Cp(allyl)Pd vapor, a Pd (2+)/allyl-terminated SAM surface was obtained (to a lower extent this was also the case for dep. BPDMAc-1 SAMs), which was stable against exposure to H 2 gas. Reduction to Pd (0) by H 2 was only observed when small amounts of Pd (0) were already present, for example, after prolonged exposure to the precursor. The catalytic activity of the small Pd (0) particles also caused a decomposition of the SAMs upon exposure to air.

Mesoporous Co 3O 4–CeO 2 and Pd/Co 3O 4–CeO 2 catalysts: Synthesis, characterization and mechanistic study of their catalytic properties for low-temperature CO oxidation

Several nanosized catalysts Co 3O 4–CeO 2 with varying compositions were synthesized by a surfactant-template method and further promoted by a small amount of Pd (0.5 wt%). These catalysts exhibit uniform mesoporous structure and high surface area (>100 m 2 g −1). The Co 3O 4 crystallites in these catalysts are encapsulated by nanosized CeO 2 with only a small fraction of Co ions exposing on the surface and strongly interacting with CeO 2. Such structure maximizes the interaction between Co 3O 4 and CeO 2 in three dimensions, resulting in unique redox properties. The introduction of Pd prominently enhances both the reduction and oxidation performance of the catalysts, due to hydrogen or oxygen spillover. These catalysts prepared by surfactant-template method exhibit excellent oxidation performance, especially the ones promoted with Pd, which show markedly enhanced CO oxidation activity even at room temperature. Based upon the results of structural properties, redox behaviors and in situ DRIFTS study, two different reaction pathways over Co 3O 4–CeO 2 and Pd/Co 3O 4–CeO 2 are proposed.

Reaction oftrans-Pd(styryl)Br(PMePh2)2with Styryl Bromide Affording 1,4-Diphenylbutadiene. An Unexpected Homocoupling Process Induced by P−C Reductive Elimination

Reaction of (Z)-styryl bromide (1) with PhB(OH)2 in toluene at 80 °C for 1 h in the presence of Pd(PPh3)4 (1.5 mol %) and an aqueous solution of K2CO3 (3 equiv) affords (Z)-stilbene as the cross-coupling product in 99% yield. On the other hand, the same reaction of the (E)-isomer of 1 forms considerable amounts of homocoupling products (1,4-diphenylbutadiene (2, 22%) and biphenyl (27%)) in addition to the cross-coupling product ((E)-stilbene, 73%). The formation of 2 was examined by kinetic experiments using trans-Pd(CH═CHPh)Br(PMePh2)2 (3) as a model of the presumed intermediate. Complex 3 reacts with 1 at 50 °C for 5 h, giving 2 (91%) and trans-PdBr2(PMePh2)2 (4, 92%), together with a small amount of Pd(η2-PhCH═CHPMePh2)Br(PMePh2) (5, 8%). The reaction rate shows first-order dependence on the concentration of 3 and 5, respectively, but is independent of the concentration of 1. A novel homocoupling process induced by P−C reductive elimination from 3 giving 5 is proposed.

Effect of palladium on sulfur resistance in Pt–Pd bimetallic catalysts

The interactions of H 2 and H 2S molecules with Pt–Pd bimetallic catalysts were investigated at the molecular level using a DFT (density functional theory) approach to better understand the structures and properties of active sites, and the relations between structural changes and sulfur resistance. It was found that when alloying the Pt catalyst with a small amount of Pd at a particular surface atomic ratio range, both H 2 and H 2S showed different adsorption properties compared to those on monometallic Pt or Pd catalyst. The adsorptions of both H 2 and H 2S were enhanced, but the adsorption energy of H 2 increased more than that of H 2S, indicating that the adsorption of H 2S became less favorable compared with H 2 on the bimetallic Pt–Pd catalyst surface. The desorption energy of hydrogen from monometallic Pt or Pd, as well as bimetallic Pt–Pd supported on zeolite, were calculated by temperature-programmed desorption (TPD), the values were compared against the DFT results to explain experimentally and theoretically why the bimetallic Pt–Pd catalyst has better sulfur resistance than monometallic Pt catalyst.