Colloidal Palladium Research Articles

MICROFLUIDIC CHANNELS MODIFIED WITH COLLOIDAL PALLADIUM AS AN EFFICIENT CATALYST FOR HIGH THROUGHPUT SUZUKI COUPLING REACTIONS

International Journal of Computational Engineering ScienceVol. 04, No. 03, pp. 683-686 (2003) Poster PapersNo AccessMICROFLUIDIC CHANNELS MODIFIED WITH COLLOIDAL PALLADIUM AS AN EFFICIENT CATALYST FOR HIGH THROUGHPUT SUZUKI COUPLING REACTIONSAIPING FANG, HIAN KEE LEE, and SURESH VALIYAVEETILAIPING FANGDepartment of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore Search for more papers by this author , HIAN KEE LEEDepartment of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore Search for more papers by this author , and SURESH VALIYAVEETILDepartment of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, SingaporeTo whom correspondence should be addressed. Search for more papers by this author https://doi.org/10.1142/S1465876303002040Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractIt is highly desirable to develop a phosphine-free recyclable heterogenous catalytic system without the use of expensive and air-sensitive basic phosphines for palladium-catalysed coupling reactions. Nano-palladium catalysts for example, in various stabilised forms have been extensively explored as potential alternatives to achieve a higher catalytic activity. In line with the great interest directed towards the development of microfabricated chemical systems for a variety of chemical and biological applications, we demonstrate here a microreactor based on microfluidic channels on glass chips for the continous flow organic synthesis using immobilised nano-palladium. The palladium colliods were immobilised on the inner-walls of the microchannels via an intermediate organosilane monolayer. The covalent attachment of colloidal palladium provides minimum leaching of the catalyst. The Suzuki coupling of an aryl halide and an organoboron has been used a model system to investigate the performance characteristics. The reaction affords an excellent yield, a higher turnover rate and the ease of catalyst recycling. Similarly, the approach can be applied to other palladium-catalysed syntheses, such as Heck-, Sonogashira-, and Stilles-type coupling reactions.Keywords:MicroreactorPalladium colloidsSuzuki couplingHeterogenous catalysis References A. Manzet al., Advances in Chromatography 33, 1 (1993). Google ScholarA. Manzet al., Analusis 22, M25 (1994). Google ScholarA. T. Woolleyet al., Analytical Chemistry 68, 4081 (1996). Crossref, Google ScholarS. C. Jacobson and J. M. Ramsey, Analytical Chemistry 68, 720 (1996). Crossref, Google ScholarD. C. Duffyet al., Analytical Chemistry 70, 4974 (1998). Crossref, Google Scholar Book of Abstracts, Proceedings of the IMRET 3 Conference, 1999 . Google ScholarG. M. Greenwayet al., Sensors and Actuators B 63, 153 (2000). Crossref, Google ScholarN. Miyaura and A. Suzuki, Chemical Reviews 95, 2457 (1995). Crossref, Google ScholarB. I. Aloet al., Journal of Organic Chemistry 56, 3763 (1991). Crossref, Google ScholarJ. D. Aiken and R. G. Finke, Journal of Molecular Catalysis A: Chemical 145, 1 (1999). Crossref, Google ScholarP. C. Hidberet al., Langmuir 12, 1357 (1996). Google Scholar FiguresReferencesRelatedDetails Recommended Vol. 04, No. 03 Metrics History KeywordsMicroreactorPalladium colloidsSuzuki couplingHeterogenous catalysisPDF download

Sodium Ascorbate Method for the Synthesis of Colloidal Palladium Particles of Different Sizes

Journal Article Sodium Ascorbate Method for the Synthesis of Colloidal Palladium Particles of Different Sizes Get access D.A. Meyer, D.A. Meyer Department of Animal Sciences, University of Wisconsin, Madison, WI 53706 Search for other works by this author on: Oxford Academic Google Scholar R.M. Albrecht R.M. Albrecht Department of Animal Sciences, University of Wisconsin, Madison, WI 53706 Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 9, Issue S02, 1 August 2003, Pages 1190–1191, https://doi.org/10.1017/S1431927603445959 Published: 06 August 2003

Amphiphilic Poly(organosiloxane) Nanospheres as Nanoreactors for the Synthesis of Topologically Trapped Gold, Silver, and Palladium Colloids

Amphiphilic poly(organosiloxane) nanospheres with different core−shell architectures are employed as passive nanoreactors for the synthesis of noble metal colloids. The amphiphilic poly(organosiloxane) nanospheres, which have diameters between 15 and 40 nm, possess a hydrophilic interior and a hydrophobic shell. Dispersed in organic solvents such as toluene, it has been achieved to transfer hydrophilic noble metal salts through the solvent into the nanospheres by either liquid−liquid or solid−liquid phase transfer. Subsequently, reduction of the noble metal salt with lithium triethylborohydride led to the formation of 2−5 nm sized noble metal colloids. If the network density of the shell of the poly(organosiloxane) nanospheres is small enough, the colloids are topologically trapped inside the nanospheres and stabilized against aggregation. By employing hydrogen tetrachloroaurate(III), silver nitrate, or palladium(II) chloride, it was possible to synthesize topologically trapped gold, silver, or palladium ...

Preparation of Au–Ag–Pd trimetallic nanoparticles and their application as catalystsElectronic supplementary information (ESI) available: UV-vis spectra and EDX analysis of Au–Ag–Pd colloidal suspensions. See http://www.rsc.org/suppdata/jm/b3/b300952a/

Dispersed alloy-like Au–Ag–Pd nanoparticles with average diameters of 4.4 ± 1.5 nm have been prepared by laser irradiation of a mixture containing gold, silver, and palladium colloids. The catalytic activity of the nanoparticles was subsequently investigated and they were found to be efficient catalysts for the Heck reaction.

Synthesis of polysiloxane stabilized palladium colloids and evidence of their participation in silaesterification reactions.

The role of "Pd" colloids in Pd(OAc)2 -catalyzed silaesterification reactions was investigated. The first example of the generation and utilizations of recyclable polysiloxane network stabilized palladium nanoparticles is described. We also provide the evidence that the silicon polymers play the role of stabilizing agents, preventing the generation of bulk palladium without compromising the activity of the catalyst.

The direct formation of H 2O 2 from H 2 and O 2 over colloidal palladium

Additional evidence is presented for the catalytic role of aqueous colloidal palladium in the direct conversion of H 2 and O 2 to H 2O 2. Reactions typically were carried out at an O 2/H 2 ratio of 2, and 25 °C, by introducing the gases at 1 atm through a frit into the aqueous slurry. The source of palladium was either PdCl 2 or reduced palladium supported on silica gel. During the course of the reaction the palladium is distributed among PdCl 4 2−, colloidal palladium, palladium deposited on the frit, and Pd/SiO 2 when SiO 2 is present. Although the amount of colloidal palladium differs, depending on its source and the time on stream, the rate of H 2O 2 formation is proportional to the amount of colloid present at a particular time. Maximum rates were observed for colloids prepared from Pd/SiO 2; however, the largest H 2O 2 concentration of 0.7 wt% was attained when PdCl 2 was the source of colloidal palladium. The ultimate steady-state concentration of H 2O 2 is, in part, affected by the rate of H 2O 2 decomposition, which is relatively large over the Pd/SiO 2 sample that was tested. The rate of decomposition also is determined by the H + concentration. Results obtained with a mixture of 16O 2/ 18O 2 confirm that oxygen remains undissociated during the formation of H 2O 2, which may explain why palladium is uniquely suited as a catalyst for this reaction.

Palladium colloids from an organometallic route: redox reaction between [VCp2] and [(Pd(η3-allyl)2Cl]2. Catalytic application to the hydrogenation of aromatic nitro compounds

[Pd(η3-C3H5)2Cl]2 reacts in THF in the presence of poly(vinylpyrrolidone) (PVP), with the 15-electron complex vanadocene [V(C5H5)2], to give PVP-protected palladium particles. High resolution electron microscopy (HREM) and wide angle X-ray scattering (WAXS) experiments were carried out on the PVP-protected palladium particles as obtained when exposed to H2 and O2 and after hydrogenation catalysis. In each case, the particles display the fcc lattice of bulk palladium and a narrow size distribution centred near 2–3 nm. Catalytic hydrogenation reactions of nitrotoluene and 2,4-dinitrotoluene into their corresponding aniline and 2,4-diaminotoluene were performed in CH2Cl2 and in H2O/CH2Cl2 biphasic conditions. The catalytic reactions were found to be zero order with respect to the substrate and first order with respect to dihydrogen and catalyst.

Pd-coated Ni nanoparticles by the polyol method: an efficient hydrogenation catalyst

Pd-coated Ni nanoparticles of 50 ± 15 nm size are prepared by the polyol method and characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and thermogravimetry analysis. Surface coverage of Pd on Ni particles is less than a monolayer for 0.5 and 1 at% Pd-coated Ni. Quantitative conversion of nitrobenzene to aniline is observed over these Pd-coated Ni particles at 27 °C under one atmospheric pressure of hydrogen. 0.5 and 1 at% Pd-coated Ni exhibits 10 times greater activity than that of typical colloidal palladium and platinum catalysts and 2.5 times higher activity than commercial 5 wt% Pd/C.

Evidence for the Role of Colloidal Palladium in the Catalytic Formation of H2O2 from H2 and O2

The direct production of H2O2 from H2 and O2 (O2/H2=2) at 25°C and 760 Torr occurs in an aqueous phase over colloidal palladium that may be introduced either via PdCl2 or via Pd supported on silica gel (Pd/SiO2). In the latter case, aqueous HCl facilitates the dissolution of the supported Pd. The presence of colloidal palladium was confirmed by electron microscopy. When the solution was either 0.1 M or 1.0 M in HCl, removal of the silica, along with any remaining supported Pd, did not affect the rate of H2O2 formation because the amount of active colloidal Pd remained unchanged. The specific activity of the supported Pd is only 3% of that for colloidal Pd, probably because of transport limitations within the pores of the silica.

Kinetics of Hydrogenation and Oxidation of Benzyl Alcohol in the Presence of Colloid Palladium in situ

The kinetics of hydrogenation and oxidation with molecular oxygen of benzyl alcohol in the presence of colloid palladium in situ were studied. Mechanisms of the reactions studied were proposed.

Application of colloidal palladium modifier for the determination of As, Sb and Pb in a spiked sea water sample by electrothermal atomic absorption spectrometry

Colloidal palladium was used as a chemical modifier for analysis of complex samples by electrothermal atomic absorption spectrometry. In order to demonstrate high potential of the modifier, optimization of the time–temperature program of the atomizer was limited with only pyrolysis and atomization temperatures. Fixed palladium modifier masses were applied (6 μg for pure analyte solutions and 15 μg for matrix-containing solutions). It was shown that in the presence of colloidal palladium, interference-free determinations of As, Sb and Pb are possible up to at least 450 μg of chloride ion, or 40 μg of sulfate ion (as their sodium salts) in the atomizer. Colloidal palladium was used for the direct determination of As, Sb and Pb in a spiked sea water sample (from Bosphorus channel near Istanbul) by means of the calibration graphs prepared with pure analyte solutions. The detection limits for As, Sb and Pb in a sea water matrix calculated according to 2σ criteria are 5.4, 3.6 and 1.1 ng ml−1, respectively (for sample volume 10 μl). In unspiked sea water, the contents of As, Sb and Pb were found to be below the detection limits. Recoveries of spiked analytes (25 and 50 ng ml−1) were in the region of 98–112% depending on the nature of analyte and the concentration of spike.

Fluorous Phase Soluble Palladium Nanoparticles as Recoverable Catalysts for Suzuki Cross-Coupling and Heck Reactions

1,5-Bis(4,4‘-bis(perfluorooctyl)phenyl)-1,4-pentadien-3-one stabilizes palladium(0) nanoparticles (transmission electron microscopy) formed in the reduction of palladium dichloride with methanol. These palladium colloids are soluble in perfluorinated solvents, and they are efficient recoverable catalysts for Suzuki cross-couplings and Heck reactions under fluorous biphasic conditions.

In situ PHIP NMR — a new tool to investigate hydrogenation mediated by colloidal catalysts

It is known that some colloidal catalysts show “homogeneous”-like behavior, but it is unclear which parameters define the borderline between heterogeneous, i.e. surface reactions, and homogeneous-type catalysis of colloidal systems. The reaction of ethynylbenzene (phenylacetylene) with parahydrogen using the colloidal palladium catalyst Pd x [(N(octyl) 4Cl] y leads to nuclear spin polarization in the hydrogenation products. Accordingly, the in situ NMR method parahydrogen induced polarization (PHIP) is an appropriate tool to investigate hydrogenation mediated by colloidal catalysts.

Palladium metal catalysts in Heck CC coupling reactions

This review is devoted to the application of palladium metal catalysts to the Heck reaction (arylation or vinylation of alkenes with aryl or vinyl halides and pseudohalides). The number of relevant articles published in recent years shows steadily increasing interest in this field. A brief outline of the historical development of heterogeneous catalysis as applied to the Heck reaction is given ( Section 2). Both supported metal catalysts ( Section 3) and stabilized colloidal palladium catalysts ( Section 4) are included. Heterogeneous catalysts supported over different kinds of supports (carbon, inorganic oxides, molecular sieves, polymeric materials, etc.) are reviewed under separate headings. Particular attention is paid to the metal leaching and the nature of catalysis, two tightly connected problems which appear to be still controversial ( Section 5). Some perspectives are shortly discussed in the final section ( Section 6).

Size-selective electrochemical preparation of surfactant-stabilized Pd-, Ni- and Pt/Pd colloids.

A detailed study concerning the size-selective electrochemical preparation of R4N+Br- -stabilized palladium colloids is presented. Such colloids are readily accessible using a simple electrolysis cell in which the sacrificial anode is a commercially available Pd sheet, the surfactant serving as the electrolyte and stabilizer. It is shown that such parameters as solvent polarity, current density, charge flow, distance between electrodes and temperature can be used to control the size of the Pd nanoparticles in the range 1.2-5 nm. Characterization of the Pd colloids has been performed using transmission electron microscopy (TEM), small angle X-ray scattering (SAXS) and X-ray powder diffractometry (XRD) evaluated by Debye-function-analysis (DFA). Possible mechanisms of particle growth are discussed. Experiments directed towards the size-selective electrochemical fabrication of (n-C6H13)4N+Br- -stabilized nickel colloids are likewise described. Finally, a new strategy for preparing bimetallic colloids (e.g., Pt/Pd nanoparticles) electrochemically is presented, based on the use of a preformed colloid (e.g., (n-C8H17)4N+Br- -stabilized Pt particles) and a sacrificial anode (e.g., Pd sheet).

A Novel Ultraviolet Irradiation Technique for Fabrication of Polyacrylamide–metal (M = Au, Pd) Nanocomposites at Room Temperature

Polyacrylamide (PAM)–metal (M = gold, palladium) nanocomposites with metal nanoparticles homogeneously dispersed in the polymer matrix have been prepared via a novel ultraviolet irradiation technique at room temperature, which is based on the simultaneous occurrence of photo-reduction formation of the colloidal metal particles and photo-polymerization of the acrylamide (AM) monomer. The UV–vis absorption spectra and TEM were employed to characterize the M-PAM nanocomposites by different irradiation times. The average sizes of the colloidal gold and palladium particles dispersed in the nanocomposites were calculated by XRD patterns and TEM images. The present method may be extended to prepare other metal–polymer hybrid nanocomposite materials.

Optical spectra of Pd-561 nanoclusters in aqueous solutions

Optical absorption spectra of aqueous solutions of the giant cluster Pd561Phen60(OAc)180 (1) were studied in air and after treatment with H2. The results obtained were compared with the corresponding data for 2—4-nm nanoparticles of colloidal palladium prepared by the radiochemical and chemical reduction of the PdII complexes in aqueous solutions. The optical spectra of cluster 1 and nanoparticles of colloidal palladium are of the same nature and are caused by the light absorption by free electrons in the metal.

Functionalised microgels: novel stabilisers for catalytically active metal colloids

Microgel stabilised palladium colloids have been prepared by a novel strategy based on the synthesis of microgels upon radical solution copolymerisation of suitable functional monomers containing sulfonic acid groups. These microgels can be conveniently loaded with Pd 2+ ions which are subsequently reduced. The resulting metal colloids (10–20 nm diameter) can be precipitated from the reaction mixture and redispersed in suitable solvents. Preliminary tests indicate that microgel stabilised palladium colloids are active catalysts for the vinylation of aryl iodides and bromides (Heck reaction).

Synthesis and study of palladium colloids and related catalysts

Colloidal palladium particles were prepared by reduction with hydrogen of H 2PdCl 4 in a mixture of H 2O, trioctylamine (TOA), and cyclohexane. According to 14N NMR, 35Cl NMR and EXAFS data, the reduction of Pd was found to proceed under an auto-catalyzed regime via (HTOA) 2 [PdCl 4] complex formation. After complete reduction of Pd(II) (1 mol H 2 consumed per 1 Pd atom), H 2 consumption abruptly changed to 0.7 H 2 mol per 1 Pd atom. Unusually large amounts of H 2 adsorbed per Pd-atom could be due to the formation of palladium hydride by highly dispersed and defected Pd particles. TEM shows that Pd particles in catalysts obtained by metal particles deposition on carbon material Sibunit look like “hedgehogs” with needles 100 Å long and 20–40 Å in diameter.

Cryo-Imaging of Palladium Colloids

Cryo-Imaging of Palladium Colloids