Templating of electrodeposited platinum group metals as a tool to control catalytic activity

The present study is focused on the synthesis and investigation of Pt and Pt-Ru nanostructures templated by anodic aluminum oxide films. Samples of this sort may be considered in future as model electrode materials of high roughness and specific controllable nanostructural features. Nanostructure and morphology of electrodeposited materials are characterized using scanning electron microscopy and scanning tunneling microscopy techniques. A possibility to control catalytic activity of electrodeposits by means of templating is discussed as well. Higher catalytic activity of nanostructured Pt-Ru as compared to usual electrodeposit is very promising for further clarification of structural effects in electrocatalysis. In particular, newly proposed materials combine high roughness and the increased number of grain boundaries known to provide high catalytic activity of platinum group metals in certain processes. Future prospects of obtaining materials with even higher roughness factors are discussed.     

Potentials of zero total and zero free charge of platinum group metals

Some fundamental definitions and relations of the thermodynamic theory of the platinum electrode are considered. The notions of the potential of zero total charge (pztc) of the first and second kind are discussed. It is shown that in the presence of excess of surface-inactive ions, the potential of zero total charge of the second kind can be regarded as the potential of zero free charge (pzfc). The pzfc is an analogue of the pzc of metals not adsorbing hydrogen and oxygen. The methods of determination of the pztc and the pzfc of platinum metals, of their dependence on solution pH and salt concentration are considered, as well as the dependence of the pzfc on surface coverage with adsorbed hydrogen. Tables listing the pztc and the pzfc of platinum metals are given. The conditional nature of the notions pzfc and the charge of the double layer in the presence of strong chemisorption of ions is demonstrated and the difference between the formal and the true coefficients of charge transfer is emphasized. The notion of the charging curves and electrocapillary curves of the first and second kind is introduced and the methods of their finding are discussed. The electrocapillary curves of the first and second kind are given for platinum in solutions of different composition.     

Fabrication of sorption-active polyamide fibres for sorption of platinum group metals

Moscow State Textile Academy. Translated from Khimicheskie Volokna, No. 2, pp. 47–50, March–April, 1994.     

金属载体失效汽车尾气催化剂铂族金属回收工艺研究

失效汽车尾气催化剂已成为铂族金属重要的二次资源,其中以堇青石为载体的失效汽车尾气催化剂回收工艺的研究较多,而以金属载体的失效汽车尾气催化剂回收的研究较少。因为金属载体用湿法和火法回收比较困难,副产物多且污染较大。研究了一种新工艺来处理回收金属载体失效汽车尾气催化剂,该工艺流程简短,污染低,铂族金属综合回收率可达90%以上。     

Electrochemical dissolution of metals of the platinum group by alternating current

The electrochemical dissolution of metals of the platinum group in acid solutions using an alternating current is investigated. It is shown that this is an efficient and promising method for the production of pure noble metal salts, and for the analysis and extraction of small amounts of noble metals from waste and poor ores. The production of pure bromides and chlorides of gold and rhodium is particularly efficient because their rates of dissolution are high. The mechanism of the influence of the alternating current on the metal/electrolyte interface is also discussed.     

Adsorption of palladium, platinum, and gold chloride complexes by carbon fibers with various structures

Data are given characterizing the effects of the porous structures in activated carbon fibers (ACF) and the amounts of oxidized carbon forms on the extent and rate of adsorption for various chloride complexes of the platinum metals and gold. The adsorption mechanisms on ACF are considered for these metal chloride complexes. The practical significance of the research is considered. Translated from Khimicheskie Volokna, No. 4, pp. 61–69, July–August, 2008.     

失效汽车尾气净化催化剂中铂族金属回收技术

主要对失效汽车尾气净化催化剂中的铂族金属回收技术做了综述。失效催化剂的回收技术包括催化剂预处理、铂族金属的富集、铂族金属的精炼、回收铂族金属后废渣的回收应用等多个环节。铂族金属的富集主要有火法与湿法两大工艺。火法工艺包括等离子熔炼法、金属捕集法、干式氯化法等技术;湿法工艺有载体溶解法、活性组分溶解法、全溶法及加压氰化法等技术。铂族金属的精炼主要有还原沉淀法、离子交换法、溶剂萃取法等。其中在富集工艺中火法有着处理量大、铂族金属回收率稳定、不需要处理大量废液等技术优势。     

失效汽车尾气净化催化剂中铂族金属回收技术

主要对失效汽车尾气净化催化剂中的铂族金属回收技术做了综述。失效催化剂的回收技术包括催化剂预处理、铂族金属的富集、铂族金属的精炼、回收铂族金属后废渣的回收应用等多个环节。铂族金属的富集主要有火法与湿法两大工艺。火法工艺包括等离子熔炼法、金属捕集法、干式氯化法等技术;湿法工艺有载体溶解法、活性组分溶解法、全溶法及加压氰化法等技术。铂族金属的精炼主要有还原沉淀法、离子交换法、溶剂萃取法等。其中在富集工艺中火法有着处理量大、铂族金属回收率稳定、不需要处理大量废液等技术优势。     

An X-ray photoelectron spectroscopic study of electrocatalytic activity of platinum group metals for chlorine evolution

A correlation of the catalytic activity for anodic chlorine evolution of platinum group metals to the nature of the surface film formed during chlorine evolution in a sodium chloride solution was studied by X-ray photoelectron spectroscopy. The change in the surface film with increasing potential was found on platinum, including an increase in the cationic valence. This seemed responsible for the decrease in the activity for chlorine evolution on platinum in the high potential region. Increasing potential did not result in the appreciable increase in the cationic valence in the surface film on the other platinum group metals. Replacement of hydroxyl ions in the surface film by chloride ions became easier in the order of rhodium, iridium and palladium, and the activity for anodic chlorine evolution increased in this order due possibly to an increase in the amount of chloride ions in the film which seemed to be one of the reactants in the rate determining electrochemical desorption of adsorbed chlorine atom. Chlorine molecules adsorbed on the surface film were also found. It was assumed that the activity for anodic chlorine evolution might be low when the metal surface was covered by a large amount of molecular chlorine which was the reaction product.     

Recovery of platinum group metals from secondary materials. I. Palladium dissolution in iodide solutions

Thermodynamic predictions are reported for platinum and palladium in aqueous ammonia and iodide solutions, to define less aggressive conditions than used hitherto for leaching palladium and platinum from secondary materials. Cyclic voltammetry and amperometry of thin films of palladium, electrodeposited onto rotating vitreous carbon disc electrodes, indicated that partially oxidised adsorbed species passivated dissolution in aqueous ammonium sulfate. By contrast, dissolution rates in aqueous potassium iodide solutions were a significant fraction of that corresponding to the mass transport controlled rate of reduction of tri-iodide, which was demonstrated to be a suitable oxidant for the envisaged metal recovery process. However, iodide concentrations > 1 m were required to achieve adequate solubility of the oxidation products, assumed to be PdI₄²⁻ ions, thereby avoiding inhibition by PdI₂. The reduction of tri-iodide on palladium was very facile, with large exchange current densities and Tafel coefficients; two alternative mechanisms are proposed that fitted experimental results well. In addition, a kinetic model to predict dissolution rates of Pd in tri-iodide solutions gave good agreement with experimental data, provided an equilibrium constant of 10^−4.5 was used for the PdI₂/PdI₄²⁻ reaction, rather than the value of 10^−2.8 derived from thermodynamic data.     

Fabrication of gold and platinum single crystal ultramicroelectrodes

Recent work in this laboratory involving the fabrication of single crystal ultramicroelectrodes (SCUMES) of gold and platinum is summarized in this paper. The method for growing the gold and platinum single crystals of micron dimensions is discussed in detail and the technique for incorporating these crystals into ultramicroelectrodes is described. The electrochemical response of these ultramicroelectrodes is shown with cyclic voltammograms recorded in selected electrolytes. The atomic force microscopy (AFM) images of the platinum and gold crystals, which were used to make the ultramicroelectrodes, are also presented.     

Supported gold and gold palladium catalysts for selective chemical synthesis

Catalysts based on gold are now well established as very active and selective for broad ranges of redox reactions. Although primarily known for selective and preferential oxidation reactions, gold catalysts are also highly effective for selective hydrogenation. Hydrogenation reactions provide the focus for this perspective paper that is based on a François Gault lecture given at the Sabatier Conference in 2007. In particular, two reactions will be discussed; namely, the use of supported gold catalysts for selective hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols, and the use of supported gold palladium alloys for the direct hydrogenation of molecular oxygen to form hydrogen peroxide in preference to water.     

The effects of residual chlorine on the behaviour of platinum group metals for oxidation of different hydrocarbons

The oxidation of a mixture of four hydrocarbons and carbon monoxide has been studied over alumina-supported palladium, platinum and rhodium catalysts made using chloride precursor salts. The order of the light-off temperatures for the hydrocarbons is the same for each metal (1-hexene, toluene, benzene and finally iso-octane) but the separation between each and their occurrence relative to carbon monoxide varies. The absolute values, especially for iso-octane, are strongly dependent on the pretreatment procedure. Exposure to H₂/H₂O in the place of O₂ gives much higher activity. Activation can also be achieved by repeated runs with the reactant mixture. Chlorobenzene is produced in small amounts during experiments using partially activated catalysts especially with rhodium. Other reasons for believing that the development of activity is at least partly associated with the removal of chlorine are discussed.     

Synthetic fibres which are flammable to a limited extent

Conclusions As a result of examining the literature data, one can draw the conclusion that the new synthetic fibers which belong to the class of thermally resistant fibers are very resistant with respect to a flame.Certain forms of heat-resistant fibers do not maintain combustion even in a oxygen-enriched atmosphere, up to 40–75% by wt.Translated from Khimicheskie Volokna, No. 4, pp. 6–9, July–August, 1983.     

Electrocatalytic oxidation of mono- and polyhydric alcohols on gold and platinum

A survey of representative studies on the oxidation of mono- and polyhydric alcohols on gold and platinum electrodes is given, with a special attention to the reaction mechanisms and the effect of the molecular structure of these compounds on their electrocatalytic reactivity.     

高碱玻璃纤维性能缺陷难克服

1牢记历史的教训 我国玻璃纤维工业发展初期的品种之一是用铂坩埚拉制的高碱玻璃纤维(含R2O≥15%)即用平板玻璃的玻璃成分,制成玻璃球,再拉制成纤维,织造成纱和布等产品.经过几年的运行,在20世纪60年代初出现了严重的问题,高碱玻璃纤维产品变脆,尤其在南方,经黄梅雨高湿度季节后,该现象尤其严重,用手指就可在布上戳出个洞,用户纷纷退货,年轻的玻璃纤维工业严重受挫,几近夭折.     

Effect of platinum particle size and catalyst support on the platinum catalyzed selective oxidation of carbohydrates

The effect of the platinum particle diameter and the catalyst support was investigated for the aqueous phase selective oxidation of methyl α-D-glucopyranoside, octyl α-D-glucopyranoside and α-cyclodextrin with molecular oxygen. No platinum particle size effect was observed in the platinum particle diameter range of 1.4 to 3.0 nm. The structure-insensitivity is attributed to the high degree of surface coverage by oxygen. The rate of deactivation due to over-oxidation of the catalyst increases to a small extent with decreasing platinum particle diameter. The effect of the catalyst support is much larger than the platinum particle size effect. The turnover frequency for platinum on activated carbon and carbon fibrils supported catalyst is 3-7 times higher than for graphite as the catalyst support. The support effect is attributed to the hydrophilic character of the support. This revised version was published online in July 2006 with corrections to the Cover Date.