Of platinum metal

Figure Bl.25.3. Pt 4f XPS spectra of platinum metal (top) and of the two organoplatinmn compounds (a) and (b), middle and bottom respectively, shown in figure B 1.25.2, illustrating that the Pt 4f bmding energy reflects the oxidation state of platinum (from [9]).

Osmium occurs in iridosule and in platinum-bearing river sands of the Urals, North America, and South America. It is also found in the nickel-bearing ores of Sudbury, Ontario region along with other platinum metals. While the quantity of platinum metals in these ores is very small, the large tonnages of nickel ores processed make commercial recovery possible. 

EXAFS spectra of platinum metal, having a face-centred cubic crystal stmcture, have been obtained at 300 K and 673 K. Explain what qualitative differences you might expect. How many nearest-neighbour atoms are there in this stmcture Illustrate your answer with a diagram. 

E. Savitsky and co-workers. Physical Metallurgy of Platinum Metals MIR Publishers, Moscow, CIS, 1978. 

Significant distinction in rate constants of MDASA and TPASA oxidation reactions by periodate ions at the presence of individual catalysts allow to use them for differential determination of platinum metals in complex mixtures. The range of concentration rations iridium (IV) rhodium (III) is determined where sinergetic effect of concentration of one catalyst on the rate of oxidation MDASA and TPASA by periodate ions at the presence of another is not observed. Optimal conditions of iridium (IV) and rhodium (III) determination are established at theirs simultaneous presence. Indicative oxidation reactions of MDASA and TPASA are applied to differential determination of iridium (IV) and rhodium (III) in artificial mixtures and a complex industrial sample by the method of the proportional equations. 

In the table are submitted speetrophotometrie eharaeteristies of eolor reaetions of platinum metals with a 3,5-diBr- PADAPH... 

Stratifying water systems for selective extraction of thiocyanate complexes of platinum metals have been proposed. The extraction degree of mthenium(III) by ethyl and isopropyl alcohols, acetone, polyethylene glycol in optimum conditions amounts to 95-100%. By the help of electronic methods, IR-spectroscopy, equilibrium shift the extractive mechanism has been proposed and stmctures of extractable compounds, which contain single anddouble-chai-ged acidocomplexes [Rh(SCN)J-, [Ru(SCN)J, [Ru(SCN)J -have been determined. Constants of extraction for associates investigated have been calculated. 

Ninety-eight per cent of the world s supply of platinum metals comes from three countries — the former Soviet Union (49%), the Republic of South Africa (43%), and Canada (6%). Because of the different proportions of Pt and Pd in their deposits, the Republic of South Africa is the major source of Pt and the former USSR of Pd. Only in the RSA (where the Bushveld complex contains over 70% of the world s reserves of the platinum metals at concentrations of 8-9 grams per tonne) are the... 

Perhaps the most familiar example of heterogeneous catalysis is the series of reactions that occur in the catalytic converter of an automobile (Figure 11.12). Typically this device contains 1 to 3 g of platinum metal mixed with rhodium. The platinum catalyzes the oxidation of carbon monoxide and unburned hydrocarbons such as benzene, C6H6 ... 

The reaction with CO to afford C02 and N20 is particularly interesting in view of the use of platinum metal compounds in automobile cataytic converters. 

Figure 8.29. NEMCA-generated volcano plots obtained by increasing the catalyst work function above its open-circuit value during CO oxidation on Pt pCo=0.2 kPa, Po2=t 1 kPa, , T=560°C, r0= 1.5x1 O 9 mol O/s O, T=538°C ro=0.9xl0 9 mol O/s.36 Reprinted by permission of Platinum Metals Review.

Table 2. Crystal Structures and Boron Coordination of Platinum Metal Borides WITH Isolated B Atoms (Owing to Defect Boron Sublattice)...

For oxygen reduction, one can use electrodes made of carbon materials, and when the solutions are alkaline, one can also use electrodes of silver and nickel, apart from those made of platinum metals. 

Sometimes anodic protection is used, in which case the metal s potential is made more positive. The rate of spontaneous dissolution will strongly decrease, rather than increase, when the metal s passivation potential is attained under these conditions. To make the potential more positive, one must only accelerate a coupled cathodic reaction, which can be done by adding to the solution oxidizing agents readily undergoing cathodic reduction (e.g., chromate ions). The rate of cathodic hydrogen evolution can also be accelerated when minute amounts of platinum metals, which have a stroug catalytic effect, are iucorporated iuto the metaf s surface fayer (Tomashov, 1955). 

Oxides of Platinum Metals Anodes of platinum (and more rarely of other platinum metals) are used in the laboratory for studies of oxygen and chlorine evolution and in industry for the synthesis of peroxo compounds (such as persulfuric acid, H2S2O8) and organic additive dimerization products (such as sebacic acid see Section 15.6). The selectivity of the catalyst is important for all these reactions. It governs the fraction of the current consumed for chlorine evolution relative to that consumed in oxygen evolution as a possible parallel reaction it also governs the current yields and chemical yields in synthetic electrochemical reactions. 

Much of the Pt Mossbauer work performed so far has been devoted to studies of platinum metal and alloys in regard to nuclear properties (magnetic moments and lifetimes) of the excited Mossbauer states of Pt, lattice dynamics, electron density, and internal magnetic field at the nuclei of Pt atoms placed in various magnetic hosts. The observed changes in the latter two quantities, li/ (o)P and within a series of platinum alloys are particularly informative about the conduction electron delocalization and polarization. 

Vest, P. Schuster, M. Koenig, K. H. Solvent extraction of platinum metals with N-mono- and N,N-disubstituted benzoylthioureas. Fresenius Z. Anal. Chem. 1989, 335, 759-763. 

Schuster, M. Selective complexing agents for the trace enrichment of platinum metals. Fresenius J. Anal. Chem. 1992, 342, 791-794. 

A review is concerned with carboxylate complexes of platinum metals and their versatility as catalysts their moderate stability and high lability (the monodentate, bidentate character of the carboxylate ligand, and its ready removal by acid) render them particularly promising (157). 

Nonsymmetrical ligand substitution reactions also play an important role in a number of biological processes. One of these concerns the antitumor activity of platinum metal complexes, for which substitution processes involving DNA moieties are generally accepted to... 

The oxidation behavior of platinum metals is of importance for their applications at high temperatures. These metals form solid oxides and also volatilize as oxides at higher temperature in an oxidizing atmosphere. Most of the gaseous oxides are stable only at high temperatures and usually contain the metal in its highest oxidation states. Palladium is an exception since it dissolves oxygen in the solid state and only forms the solid oxide PdO which dissociates at temperatures above 800 °C. 

Anodic corrosion in case of platinum metals mostly is insignificant or at least small for most anolyte compositions and conditions. But it may be an economic problem for industrial applications. Furthermore, as aforementioned, it can be the reason of cathode poisoning. The corrosion rate of gold, and especially of the less noble metals, is very dependent on the pH value of the anolyte. 

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