Formation and Catalytic Functionality of Synthetic Polymer-Noble Metal Colloid

Colloidal dispersions of noble metals in synthetic polymers are prepared by reduction with alcohol. Reflux of a solution of rhodium(III) chloride and poly(vinyl alcohol) (PVA) in a methanol-water mixed solvent under argon or air for 4 hr gives a homogeneous solution of colloidal dispersion of rhodium (Rh-PVA-MeOH/H₂O). The particle size of metallic rhodium is distributed n a narrow range of 30-70 Å, and the average diameter is 40 A. The formation of colloidal rhodium proceeds through three steps: coordination of poly(vinyl alcohol) to rhodium(III) ion, reduction with methanol to form small particles (8 Å in diameter), and growth of the small particle to large particle (40 Å in diameter). Polyvinylpyrrolidone (PVP) and poly(methyl vinyl ether) (PMVE) can be used in place of poly(vinyl alcohol) and result in colloidal dispersions, respectively, similar to Rh-PVA-MeOH/H₂O. Colloidal dispersions in nonaqueous solvent can be prepared by using ethanol instead of methanol-water (Rh-PVP-EtOH) and by using methanol instead of methanol-water, with addition of small amount of methanol solution of sodium hydroxide (Rh-PVP-MeOH/NaOH). The average diameters of rhodium particles in Rh-PVP-EtOH and Rh-PVP-MeOH/NaOH are 22 and 9 Å, respectively. The colloidal dispersions of palladium, silver, osmium, iridium, platinum, and gold in aqueous or nonaqueous solvent are prepared by using polyvinylpyrrolidone. The colloidal dispersions are very stable even under air for 20 days. Those of rhodium, palladium, and platinum are effective catalysts for hydrogenation of olefins at 30°C under an atmospheric hydrogen pressure. The colloidal dispersion of palladium catalyzes highly selective hydrogenation of diene and dienoate to monoene and monoenoate, respectively.     

Preparation of Colloidal Rhodium in Poly(vinyl Alcohol) by Reduction with Methanol

Refluxing of a solution of poly(vinyl alcohol) and rhodium(III) chloride in methanol-water gives a colloidal dispersion of rhodium which is an effective catalyst for hydrogenation of cyclohexene in methanol at 30°C under atmospheric hydrogen pressure. Formaldehyde is produced quantitatively with the reduction of rhodium(III) chloride to metallic rhodium. The rhodium particles in the colloidal dispersion are found to consist of two kinds of particles, about 8 and 40 Å in diameter by electron microscopy. The sizes of the small (8 Å) and large (40 Å) particles are almost constant during the course of refluxing. The number of small particles, which is the great majority of particles at the early stage of refluxing, gradually decreases; concurrently the number of large particle increases on prolonged refluxing. An absorption peak appears at 260 nm at the early stage of refluxing. The presence of the 260 nm peak, which indicates the coordination of poly(vinyl alcohol) to rhodium(III) ion, is indispensable for the formation of a homogeneous colloidal dispersion of rhodium. The addition of ethylenediamine inhibits the formation of colloidal rhodium in refluxing. The catalytic activity of colloidal dispersion of rhodium is dependent upon the concentration of rhodium(III) chloride charged and is independent of that of poly(vinyl alcohol). The formation mechanism of colloidal rhodium is discussed.     

Spectrophotometric determination of noble metals with tin(II) in bromide solutions

In presence of tin(II) bromide, noble metals give coloured products which are suitable for spcctrophotometric determinations. The colours are red (platinum), yellow-orange (rhodium), yellow-brown (palladium), yellow (iridium) and violet (gold) They are extracted, except for gold, with isoamyl alcohol Platinum, rhodium and palladium can be separated from irdium, and rhodium and platinum from palladium. Rhodium and platinum can be determined simultaneously.     

Polyoxometalates containing late transition and noble metal atoms

This review describes the state of the art in the field of polyoxometalates containing noble metal atoms (ruthenium, rhodium, palladium, silver, osmium, iridium, platinum and gold). The structures of the various species are listed together with their applications (mainly in catalysis).     

Cation-exchange behaviour of the platinum group and some other rare elements in hydrobromic acid-thiourea-acetone media

Ion-exchange distribution coefficients and elution curves are presented for copper(I), silver, gold(I), palladium, platinum(II), rhodium(III), iridium(III), ruthenium(III), osmium(III), mercury(II), thallium(I), tellurium(II), lead and bismuth in mixtures of thiourea, hydrobromic acid, acetone and water, with the cation-exchange resin AGW50W-X4. The system affords excellent separations of rhodium, mercury, silver (or copper), tellurium, gold, and palladium (or platinum) from each other.     

The group VIII platinum-group metals and the Periodic Table

The six platinum group metals (pgms: ruthenium, rhodium, palladium, osmium, iridium and platinum) posed a number of problems for 19th-century chemists, including Mendeleev, for their Periodic classification. This account discusses the discovery of the pgms, the determination of their atomic weights and their classification.     

Countercurrent extraction separation of some platinum group metals

Distribution coefficients were determined for the partitioning of the chloro-complexes of platinum, palladium, rhodium, and iridium between tributyl phosphate and various concentrations of hydrochloriic acid. Theoretical calculations based on the experimentally determined distribution coefficients indicated that a seventeen stage countercurrent extraction apparatus would resolve mixtures of platinum and palladium, platinum and rhodium, and rhodium and iridium.Mixtures of platinum and palladium, and platinum and rhodium were resolved in a fashion predicted by theory. Mixtures of rhodium and iridium were not completely resolved.     

含有不同脂肪环胺侧基的聚丙烯酰胺保护的贵金属胶体制备的研究

<正> 近年来高分子保护金属胶体的研究在金属催化剂领域中受到人们的突出关注。自Hirai等人对聚乙烯吡咯烷酮保护的铂族金属胶体的系统研究工作发表之后,一项重要的研究进展是双金属胶体的制备成功。当前制备窄分布乃至单分散胶体的努力成为众多研究的集中目标,具有重要的理论意义和实际应用价值。Bradley等报道用金属蒸汽冷凝至含有高分子稳定剂的有机溶剂中制备得到2.0—5.0nm直径的金属胶体,Schmid等报道用水溶性三苯膦磺酸钠小分子配位体作为稳定剂制备得到直径为18.6±0.1nm的金胶体。Esumi等用在有机溶剂中热解乙酸钯的方法制备得到不同粒径的均一球形的钯金属胶体。     

Furan derivatives of group VIII elements (review)

Methods for the synthesis of the furan derivatives of iron, cobalt, nickel, rhodium, palladium, osmium, iridium, and platinum and their physicochemical and chemical properties are reviewed.Latvian Institute of Organic Synthesis, Riga. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 154–179, February, 1997.     

A new solvent extraction scheme for the separation of platinum,palladium, rhodium and iridium

A new scheme is proposed for the separation of platinum, palladium, rhodium and iridium in hydrochloric acid solutions, by solvent extraction. Platinum and palladium are complexed with 2-mercaptobenzothiazole and potassium iodide and simultaneously extracted into chloroform, thus separating them from rhodium and iridium. Palladium is separated from platinum by extracting its dimethylglyoxime complex into chloroform, while rhodium is separated from iridium by extracting its 2-mercaptobenzothiazole complex into chloroform after reduction with tin(II) chloride.     

Cytotoxicity of metal 8-quinolinethiolates

High cytotoxicity has been established for the 8-quinolinethiolates of copper, cadmium, indium, antimony, bismuth, ruthenium, rhodium, palladium, osmium, iridium, and platinum on HT-1080 (human fibrosarcoma), MG-22A (mouse hepatoma), and B-16 (mouse melanoma) tumor cells. The greatest activity against HT-1080 was possessed by the iridium complex, and against MG-22A by the osmium complex. All the investigated metal 8-quinolinethiolates were highly toxic in relation to NIH 3T3 normal mouse embryo fibroblasts. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 870–873, June, 2006.     

Neutron activation analysis of noble metals in vegetation

Detection limits are presented for the platinum metals in vegetation for different neutron activation analysis conditions, namely, short irradiation, cyclic and long irradiations both thermally and epithermally. These detection limits for instrumental neutron activation analysis are compared with those using preconcentration technique—dry ashing and fire assay and post irradiation separation of the platinum metals using Srafion NMRR in exchange resin. The results are evaluated for plant material and it is concluded that dry ashing followed by cyclic, epithermal irradiation for rhodium and palladium and long, thermal irradiations for osmium, platinum, iridium and ruthenium enable these elements to be detected in plants at background levels.     

Synthesis of colloidal dispersions of rhodium nanoparticles under high temperatures and high pressures

Colloidal dispersions of rhodium (Rh) nanoparticles have been synthesized by the reduction of Rh ions (III) in high-temperature and high-pressure water, ethanol, or water-ethanol mixture under the existence of the protective polymer of poly(N-vinyl-2-pyrrolidone). The possibility of the regulation of the particle size and size distribution has been tested under several solvents at various temperatures and pressures. At 473 K and 25 MPa, particularly, concentrated colloidal dispersions of Rh particles of 2.5+/-0.5 nm were synthesized from the ionic solution of ethanol ([Rh]=15 mM) within a few seconds. Dilute colloidal dispersions of Rh particles were also synthesized from the dilute ionic solution ([Rh]=1.5 mM) with a diameter of 2.0+/-0.4 nm. From the water solution, Rh particles tended to form aggregates, especially for the lower concentration solution. In the case of solutions in water and ethanol mixture, the average diameter of Rh particles tended to be larger than in ethanol solution, and their distribution became broad.     

pH- and thermosensitive polyaniline colloidal particles prepared by enzymatic polymerization

Polyaniline colloids were prepared by enzymatic polymerization using chitosan and poly(N-isopropylacrylamide) as steric stabilizers. The resulting nanoparticles undergo flocculation by changing the pH or temperature of the aqueous dispersions. The environmentally responsive behavior of these colloids contrasts with that of polyaniline colloids synthesized using poly(vinyl alcohol) as the steric stabilizer. The colloid size was a function of the steric stabilizers and ranged from approximately 50 nm for polyaniline particles prepared in the presence of chitosan and partially hydrolyzed poly(vinyl alcohol) up to 350 nm for the particles synthesized using poly(N-isopropylacrylamide). UV-visible and Fourier transform infrared spectroscopic studies indicate that polyaniline colloids are spectroscopically similar to those obtained by traditional dispersion polymerization of aniline by chemical oxidation. These polyaniline colloids have potential applications in thermochromic windows and smart fluids.     

Electroreduction of carbon dioxide: Part III. Adsorption and reduction of CO2 on platinum

The main properties of reductional adsorption of CO₂ on the platinum metals are studied. Chemisorbed particles are found to be produced only on platinum and rhodium. Electroreduction of CO₂ on these metals proceeds as a result of the interaction of CO₂ molecules activated in the course of adsorption on the metal surface with chemisorbed hydrogen. As a result, strongly chemisorbed particles are obtained on the surface which are the products of more profound reduction of CO₂ than to formic acid. The further reduction of these chemisorbed particles, accompanied by their desorption into the solution, is very slow due to very strong coupling of sorbed particles with the surface and to very fast backward adsorption of the reduction products. Neither reductional chemisorption of CO₂ nor interactions of CO₂ with adsorbed hydrogen were observed for iridium, palladium, osmium or ruthenium.     

Sterically stabilized polypyrrole–palladium nanocomposite particles synthesized by aqueous chemical oxidative dispersion polymerization

Aqueous chemical oxidative dispersion polymerizations of pyrrole using PdCl₂ oxidant were conducted using water-soluble polymeric colloidal stabilizers in order to synthesize polypyrrole–palladium (PPy–Pd) nanocomposite particles in one step. PPy–Pd nanocomposite particles with number average diameters of approximately 30 nm were successfully obtained as colloidally stable aqueous dispersions, which were stable at least for 7 months, using poly(4-lithium styrene sulfonic acid) colloidal stabilizer. The resulting nanocomposite particles were extensively characterized with respect to particle size, size distribution, colloidal stability, nanomorphology, surface/bulk chemical compositions, and conductivity. X-ray photoelectron spectroscopy indicated the existence of poly(styrene sulfonic acid) colloidal stabilizer on the surface of the nanocomposite particles. Transmission electron microscopy studies confirmed that nanometer-sized Pd nanoparticles were distributed in the PPy matrix.     

Spectrographic determination of gold and platinum metals in geological and other materials by fire-assay preconcentration

A method is described for the determination of gold, platinum, palladium, rhodium and iridium at microgram levels in geological and other materials by a combination of fire-assay preconcentration and emission spectrography. The noble metals are collected into 4-mg silver or platinum prills by a normal fire-assay technique. These prills are arced between graphite electrodes at 12 A d.c. No buffer is required to prevent ejection of the prill. Gold, platinum and palladium are determined in the silver prills and gold, palladium, rhodium and iridium in the platinum prills. Low, but reproducible, results are found for iridium. At the 0.08 ppm level an overall coefficient of variation of 11% is found. This technique is simple and rapid for the determination of the precious metals.     

Determination of microgram amounts of the six platinum-group metals in iron and stony meteorites

Microgram amounts of the 6 platinum-group metals in 5 stony and 3 iron meteorites were determined spectrophotometrically after perchloric acid decomposition and ion-exchange separation. The accuracy of the determinations of osmium, ruthenium and platinum was improved by the use of more sensitive procedures; arsenazo III was used for the determination of palladium in presence of platinum, rhodium and iridium. The data for platinum-group metals thus obtained are compared with published data obtained by neutron activation and spectrographic methods for the same meteorites or for other meteorites of the same class. With a few exceptions, the agreement between the new data and published data is satisfactory.     

Formation of CuI Colloidal Particles in Aqueous Solution

Morphology, structure, and optical properties of ultradisperse CuI particles synthesized in the presence of water-soluble polymers [poly(vinyl alcohol) and gelatin] are studied. It is shown that forming CuI particles are roundish with the sizes varying from 5 to 20 nm. The particles form the aggregates whose shapes and sizes are governed by the nature of stabilizing agent. It is established that, in the presence of gelatin, CuI nanoparticles of hexagonal and cubic modifications are formed, while in the presence of poly(vinyl alcohol), particles only of cubic modification. The studied CuI colloidal solutions are stable with respect to aggregation over long time; however, during their aging at room temperature, morphological and structural properties of CuI nanoparticles are changed.