Colloidal Palladium Research Articles

Investigation of interference mechanisms of nickel chloride on copper determination and of colloidal palladium as modifier in electrothermal atomic absorption spectrometry using a dual cavity platform

The interference of nickel chloride on the determination of copper by electrothermal atomic absorption spectrometry was investigated using a specially designed dual cavity platform (DCP), which allows the analyte and interferent to vaporize from separate cavities, so that gas and condensed phase interferences can be distinguished to some extent. It was found that, when low pyrolysis temperatures were used, the interference of nickel chloride on copper originated from the formation of copper chloride in the condensed phase, which is not efficiently dissociated in the atomization stage. Alternately, when analyte and interferent were in separate cavities of the DCP, a gas-phase reaction between copper and chlorine in the atomization stage resulted in a similar signal depression. When higher pyrolysis temperatures were used, interference could be attributed to losses of volatile copper chloride in the pyrolysis stage. These losses were more pronounced when analyte and interferent were in separate cavities of the DCP, indicating again a gas-phase reaction between copper and chlorine, as well as a protective action of nickel oxide, when analyte and interferent were mixed. Colloidal palladium used as modifier removed the chloride interference independent of the pyrolysis temperature applied, when copper and nickel chloride were mixed. Colloidal palladium also increased the integrated absorbance for copper by 40–50%, even when analyte and modifier were in separate cavities of the DCP, indicating a strong gas-phase interaction between copper atoms and the modifier through adsorption/desorption processes.

Remarkably Facile Heck and Suzuki Reactions in Water Using a Simple Cationic Surfactant and Ligand‐Free Palladium Catalysts.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Carbon-supported spherical palladium nanoparticles as potential recyclable catalysts for the Suzuki reaction

Carbon-supported PVP–Pd nanoparticles prepared by adsorption of colloidal PVP–Pd nanoparticles onto activated carbon are used as catalysts for the Suzuki reaction between phenylboronic acid and iodobenzene to form biphenyl. These carbon-supported nanoparticles result in a lower biphenyl yield during the first cycle than the colloidal Pd nanoparticles that we studied previously. The carbon-supported Pd nanoparticles retain 69% of its activity upon recycling (second cycle), which is almost double the recycling potential observed in colloidal Pd nanoparticles (37% retention of activity). In addition, the carbon-supported Pd nanoparticles retain 73 ± 3 % of their catalytic activity during the second through fifth cycles of the Suzuki reaction, while the catalytic activity of the colloidal Pd nanoparticles greatly decreases during that time frame. The carbon support that the palladium nanoparticles are adsorbed onto helps to preserve its catalytic activity for longer time periods. The effect of catalysis and recycling on the nanoparticle size is also investigated. The average size of the carbon-supported palladium nanoparticles is 1.9 ± 0.1 nm initially, 2.6 ± 0.1 nm after the first cycle, and 3.1 ± 0.1 nm after the second cycle. The continued growth of the supported nanoparticles suggests that the carbon support protects the palladium nanoparticles during the harsh Suzuki reaction and prevents aggregation and precipitation unlike the colloidal palladium nanoparticles. In addition, a narrow size distribution during the growth process (Ostwald ripening) is observed for the carbon-supported nanoparticles. This could be due to the adsorption method for preparing carbon-supported Pd nanoparticles because excess unaggregated palladium atoms will not be adsorbed onto the carbon support.

Effect of Direct-Current Magnetic Field on the Rate of Catalytic Hydrogenation and Oxidation in the Presence of Colloidal Palladium in situ

Preliminary exposure of a perchlorate solution of palladium(II) tetraaqua complex to a dc magnetic field (0.1–0.95 T) affects the rate of a series of hydrogenation and oxidation reactions catalyzed by this species.

Preparation of a Well-Defined Amino-Terminated Self-Assembled Monolayer and Copper Microlines on a Polyimide Substrate Covered with an Oxide Nanoskin

A well-ordered, uniform amino (NH(2))-terminated organosilane self-assembled monolayer (SAM) was prepared on a polyimide (PI) substrate, the surface of which had silica-like reactivity. First, through chemical vapor deposition of 1,3,5,7-tetramethylcyclotetrasiloxane and subsequent photooxidation using 172 nm vacuum ultraviolet light, an extremely thin silicon dioxide (SiO(2)) layer about 1 nm thick, which we call an "oxide nanoskin" (ONS), was prepared on a PI substrate. Due to the presence of this ONS layer, the PI surface's properties became almost identical with those of Si covered with native oxide (SiO(2)/Si) without any marked change in surface morphology, as evidenced by zeta-potential measurements, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Next, this ONS-covered PI (ONS/PI) surface was exposed to vapor of a 12.5 vol % solution of N-(6-aminohexyl)(3-aminopropyl)trimethoxysilane (AHAPS) molecules diluted with absolute toluene. On the basis of contact angle analysis, the surface energy of this AHAPS/ONS/PI sample was mostly consistent with that of a SiO(2)/Si substrate covered with an AHAPS-SAM (AHAPS/SiO(2)/Si). On the other hand, the surface energy of an AHAPS-treated PI (AHAPS/PI) substrate was much smaller than that of the AHAPS/ONS/PI substrate due to insufficient surface coverage by the AHAPS molecules. This was also confirmed by lateral force microscopy using photolithographically micropatterned samples. Fabricated micropatterns composed of AHAPS- and SiO(2)-covered regions were clearly imaged on the AHAPS/ONS/PI substrate through their difference in friction, while the friction contrast of the micropatterned AHAPS/PI substrate was unclear. This marked difference in packing density of the AHAPS molecules had a direct influence on the adsorption behavior of palladium colloids and subsequent electroless plating of copper (Cu). As confirmed by AFM and XPS, metallization proceeded only on the AHAPS-covered regions, while the SiO(2)-covered regions remained free of deposits, resulting in the formation of 10-mum-wide Cu microlines on both samples. However, the plating rate achieved on the AHAPS/ONS/PI substrate was about 4.5 times faster than that on the AHAPS/PI substrate and the pattern resolution was considerably fine.

Remarkably facile Heck and Suzuki reactions in water using a simple cationic surfactant and ligand-free palladium catalysts

A facile surfactant mediated Heck and Suzuki coupling procedure in water has been developed using ligand-free Pd-catalysts. The procedure which involves nanometric palladium colloids, is operationally simple, environmentally benign and synthetically as efficient as conventional procedures using organic solvents.

New and efficient heterogeneous catalytic system for Heck reaction: palladium colloid layer in situ reduced in the channel of mesoporous silica materials

The synthesis and characterization of palladium colloid layer grafted mesoporous SBA-15 material, designated as Pd-SBA, are described. In the preparation of this new catalyst, the Si H functional groups were introduced into the channel of SBA-15 mesoporous materials resulting in highly dispersed metal colloid layer on the pore walls of the supporting material. The material is investigated for Heck coupling reactions with activated and non-activated aryl substrates. The ultrahigh specific area, large pore opening, and highly dispersed catalyst species in Pd-SBA material create one of the most active heterogeneous catalysts for Heck coupling reactions.

A Highly Efficient Heterogeneous Catalytic System for Heck Reactions with a Palladium Colloid Layer Reduced in situ in the Channel of Mesoporous Silica Materials.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Fabrication of Electrical Circuit Using Palladium Colloid

A precise electrically conductive circuit was fabricated on a plastic film substrate with an electroless Cu-plating layer that was formed on a metal colloid printed pattern. The printed pattern was formed with the inks that contain the mixture of silver colloid and palladium colloid. The degree of catalytic activity of the printed pattern upon the electroless Cu-plating was enhanced by the addition of an extremely small amount of palladium colloid into the metal colloid ink; plating speed was increased by the three times on the metal colloid pattern that was formed with the inks containing only 1 wt% of mixed metal colloids. The Electronic circuit formation and its practical performance were confirmed for the circuit fabricated by both PIJ (Cu-plating on ink jet pattern) and PFS (Cu-plating on filled and squeezed pattern) processes.

Role of catalyst deactivation and regeneration in the heck reaction involving unactivated aryl bromides

Excess aryl halide and a reducing agent admixture extend the lifetime of a catalyst in the Heck reaction. In the presence of a simple catalytic system without any ligands, the reaction between an unactivated aryl bromide and styrene in dimethyl formamide yields a stoichiometric amount of the product when the starting mixture contains 0.04–1.6 mol % PdCl2 , 18% HCOONa, 112% AcONa, and a sixfold excess of the aryl bromide (with respect to the initial amount of styrene). It is possible to raise the turnover number of the catalyst by conducting the reaction in several successive runs without regenerating or separating the catalyst. The data obtained confirm the earlier hypothesis that colloidal palladium particles formed during the reaction serve as a main “reservoir” accumulating catalytically active, homogeneous Pd(0) complexes.

Role of catalyst deactivation and regeneration in the heck reaction involving unactivated aryl bromides

Excess aryl halide and a reducing agent admixture extend the lifetime of a catalyst in the Heck reaction. In the presence of a simple catalytic system without any ligands, the reaction between an unactivated aryl bromide and styrene in dimethyl formamide yields a stoichiometric amount of the product when the starting mixture contains 0.04–1.6 mol % PdCl 2 , 18% HCOONa, 112% AcONa, and a sixfold excess of the aryl bromide (with respect to the initial amount of styrene). It is possible to raise the turnover number of the catalyst by conducting the reaction in several successive runs without regenerating or separating the catalyst. The data obtained confirm the earlier hypothesis that colloidal palladium particles formed during the reaction serve as a main “reservoir” accumulating catalytically active, homogeneous Pd(0) complexes.

A catalytic and mechanistic investigation of a PCP pincer palladium complex in the Stille reaction

In an improved procedure, the complex {2,6-bis[(diphenylphosphino)methyl]benzene}chloropalladium(II) (1) was synthesised as its THF adduct and the structure was determined by X-ray crystallography. The catalytic properties of the derivative {2,6-bis[(diphenylphosphino)methyl]benzene}(trifluoroacetato)palladium(II) (2) was investigated in the Stille reaction. Complex 2 proves to be an excellent catalyst for the C-C cross-coupling between trimethyl phenyl stannane and aryl bromides using a very low catalyst loading (0.1-0.0001%), giving high turnover numbers (TONs) up to 6.9 x 10(5). A kinetic investigation of the catalytic reaction suggests a heterogeneous colloidal palladium catalyst formed from the PCP Pd(II) pre-catalyst.

Investigation of interference mechanism of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry

The interferences of cobalt chloride on the determination of bismuth by electrothermal atomic absorption spectrometry (ETAAS) were examined using a dual cavity platform (DCP), which allows the gas-phase and condensed phase interferences to be distinguished. Effects of pyrolysis temperature, pyrolysis time, atomization temperature, heating rate in the atomization step, gas-flow rate in the pyrolysis and atomization steps, interferent mass and atomization from wall on sensitivity as well as atomization signals were studied to explain the interference mechanisms. The mechanism proposed for each experiment was verified with other subsequent sets of experiments. Finally, modifiers pipetted on the thermally treated sample+interferent mixture and pyrolyzed at different temperatures provided very useful information for the existence of volatilization losses of analyte before the atomization step. All experiments confirmed that when low pyrolysis temperatures are applied, the main interference mechanisms are the gas-phase reaction between bismuth and decomposition products of cobalt chloride in the atomization step. On the other hand, at elevated temperatures, the removal of a volatile compound formed between analyte and matrix constituents is responsible for some temperature-dependent interferences, although gas-phase interferences still continue. The experiments performed with colloidal palladium and nickel nitrate showed that the modifier behaves as both a matrix modifier and analyte modifier, possibly delaying the vaporization of either analyte or modifier or both of them.

A mechanistic study of H 2O 2 and H 2O formation from H 2 and O 2 catalyzed by palladium in an aqueous medium

The simultaneous determination of H 2 conversion, selectivity for H 2O 2, and concentration of H 2O 2 has provided insight into the pathways for the reactions of H 2 and O 2 over colloidal palladium in an aqueous medium. Reactions typically were carried out at an O 2/H 2 ratio of 4 and at 10 °C by introducing the gases at 1 atm into a solution that was 0.1 N in HCl and 0.01 M in Br − ions. Palladium was added to the system as the metal supported on microspheroidal silica. Concentrations of H 2O 2 approaching 2 wt% have been achieved with selectivities, based on H 2 reacted, in excess of 90%. Water is formed both by a parallel reaction between H 2 and O 2 and by a secondary reduction of H 2O 2 by H 2. The parallel reaction is inhibited by the presence of bromine. Hydronium ions can serve as the source of hydrogen and may be involved in a catalytic cycle that includes their reaction with peroxide species to form H 2O 2.

Palladium nanoparticles from solvated atoms—stability and HRTEM characterization

Palladium particles of nanometric dimensions were synthesized by the chemical liquid deposition method in which the Pd atoms were co-deposited at 77 K with 2-propanol, acetone, and tetrahydrofurane vapor to obtain colloidal dispersions. The colloidal dispersions were characterized by UV–visible spectrophotometry, transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The palladium colloids synthesized by use of these solvents are very stable. A strong absorption band in the UV region suggests that quantum confinement occurs in the nanoparticles obtained by this procedure. Studies of TEM micrographs reveal average size distributions between 1 and 5 nm for all Pd colloids. Whereas particle sizes in Pd–2-propanol colloids are not very sensitive to concentration change, the particle-size average in Pd–acetone and Pd–THF increases by 0.5 nm when the concentration increases from 10−3 to 10−2 mol l−1. The HRTEM results show the high crystallinity of Pd nanoparticles and three low-energy structure shapes were found: cuboctahedron, tetrakaidecahedron, and icosahedron.

Formation of Heat Stable Circuit Pattern on Organopolysilane-Coated Films.

Palladium colloid reduced from the salt by polysilane is a good catalyst for electroless metalization. Self-assembled monolayer of alkanethiol was formed at the palladium colloid on a polysilane-coated polyimide film. Metal lines with 1.5μm pitched scale were formed on the film. UV-irradiation and heat aging improved adhesion between the metal and the film.

A highly efficient heterogeneous catalytic system for Heck reactions with a palladium colloid layer reduced in situ in the channel of mesoporous silica materials.

A new catalyst, Pd-SBA, was prepared by the introduction of an Si-H function into the channel of SBA-15 mesoporous materials resulting in a highly dispersed metal colloid layer on the pore walls of the support material, creating one of the most active heterogeneous catalysts for Heck coupling reactions.

Hydrogention and Oxidation of Allyl Alcohol in the Presence of Colloid Palladium In Situ

Kinetic regularities of hydrogenation, oxidation with oxygen, and condensation of allyl alcohol in the presence of colloid palladium in situ were revealed. A mechanism of the reactions was proposed.

Kinetics of Reaction between Oxygen and Hydrogen in Water in the Presence of Pd(0)-containing Compounds

Kinetic features of the reaction of oxygen with hydrogen in water in the presence of colloidal palladium in situ, palladium black, and the giant Pd cluster Pd5 6 1Phen6 0(OAc)1 8 0 are studied, and the reaction mechanism is proposed.

Polymer-protected palladium nanoparticles. Morphologies and catalytic selectivities

Colloidal palladium nanocatalysts prepared by in situ reductions of palladium chloride were immobilized and protected by either of two water-soluble polymers. The particle sizes and size distributions of the palladium colloids were determined by transmission electron microscopy. Their selectivities as catalysts were determined by comparing the extents of hydrogenation of carefully chosen pairs of small-molecule olefins. There was found to be high hydrogenation selectivity with regard to cyclic vs. noncyclic olefins. Selectivity was relatively low, however, among olefins that differed only in size (such as hexene vs. octene), or olefins differing only with regard to the positions of the double bonds (such as 1-octene vs. 3-octene). Selectivity could be improved by careful choice of the immobilizing polymer, and by its use at relatively high concentrations.