Metals of the platinum family

2 Metals of the platinum family. These metals pertain to the 2nd and 3rd transition rows. They represent, together with silver and gold, the metals also known with the common name of noble metals. 

Ruthenium (Ru, [Kr]4 /75.v ), name and symbol from the Latin word Ruthenia (Russia). Discovered (1844) by the Russian chemist Karl K. Klaus. 

Bluish silvery, solid, hard, brittle metal. 

Osmium (Os, [Xe + 4/ l4]5 /66.v2), name from the Greek oop/ij (osme, smell). Powdered Os slowly gives off 0s04 toxic and with a strong smell. Discovered with 

Rhodium (Rh, [Kr]4t/x5v1), name from the Greek po ov (rhodon rose). Discovered (1803) by the English chemist William Hyde Wollaston. 

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Iridium, a metal of the platinum family, is white, similar to platinum, but with a slight yellowish cast. Because iridium is very hard and brittle, it is hard to machine, form, or work. 

Iridium — (L. iris, rainbow), Ir at. wt. 192.217(3) at. no. 77 m.p. 2446°C b.p. 4428°C sp. gr. 22.562 (20°C) valence 3 or 4. Discovered in 1803 by Tennant in the residue left when crude platinum is dissolved by aqua regia. The name iridium is appropriate, for its salts are highly colored. Iridium, a metal of the platinum family, is white, similar to platinum, but with a slight yellowish cast. It is very hard and brittle, making it very hard to machine, form, or work. It is the most corrosion-resistant metal known, and was used in making the standard meter... 

Metals in the platinum family are recognized for their ability to promote combustion at lowtemperatures. Other catalysts include various oxides of copper, chromium, vanadium, nickel, and cobalt. These catalysts are subject to poisoning, particularly from halogens, halogen and sulfur compounds, zinc, arsenic, lead, mercury, and particulates. It is therefore important that catalyst surfaces be clean and active to ensure optimum performance. 

The most successful class of active ingredient for both oxidation and reduction is that of the noble metals silver, gold, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Platinum and palladium readily oxidize carbon monoxide, all the hydrocarbons except methane, and the partially oxygenated organic compounds such as aldehydes and alcohols. Under reducing conditions, platinum can convert NO to N2 and to NH3. Platinum and palladium are used in small quantities as promoters for less active base metal oxide catalysts. Platinum is also a candidate for simultaneous oxidation and reduction when the oxidant/re-ductant ratio is within 1% of stoichiometry. The other four elements of the platinum family are in short supply. Ruthenium produces the least NH3 concentration in NO reduction in comparison with other catalysts, but it forms volatile toxic oxides. 

Iridium is in Group 9 (VIIIB) of the periodic table. The periodic table is a chart that shows how elements are related to one another. Iridium is a transition metal that is also part of the platinum family. 

An interesting, peculiar laboratory preparative reaction may finally be mentioned. This is based on the very high stability of the intermetallic compounds of actinides (and lanthanides) with the platinum family metals. The combined reduction capability of Pt with H2 (coupled reduction, see 6.7.2 fi) can be used to obtain, from its oxide, the platinide of the actinide metal. The An-Pt intermetallic compound can then be decomposed by heating in vacuum and the actinide can be obtained by distillation. 

Platinum family metals preparation. The platinum metals (with gold and silver) are commonly found together, and a number of schemes are in current use for their separation. Platinum metals not only are extracted from ores but, due to their high value, are also recovered from a wide range of industrial residues such as Pt, Rh gauze catalysts, defective components from glass industries, etc. 

Platinum family metals and alloys. The platinum family (platinum group) metals (Ru, Os, Rh, Ir, Pd, Pt) belong (together with Au and possibly Ag and Re) to the class of precious metals. This characteristic together with their inertness to the environment (with regard to corrosion and oxidation) is the basis for a number of uses such as in the following. 

The powder and dust of rhodium metal are flammable in air. Some of the compounds may cause skin irritations. It is best to use approved laboratory procedures when handling any of the six elements in the platinum family of metals. 

One of palladiums unique characteristics is its abihty to absorb 900 times its own volume of hydrogen gas. When the surface of the pure metal is exposed to hydrogen gas (H ), the gas molecules break into atomic hydrogen. These hydrogen atoms then seep into the holes in the crystal structure of the metal. The result is a metallic hydride (PdH that changes palladium from an electrical conductor to a semiconductor. The compound palladium dichloride (PdCl ) also has the ability to absorb large quantities of carbon monoxide (CO). These characteristics are useful for many commercial applications. Palladium is the most reactive of all the platinum family of elements (Ru, Rh, Pd, Os, Is, and Pt.)... 

What oxidation states are exhibited by the platinum metals— analogues of the iron family elements In what are they similar to iron, cobalt, and nickel ... 

Platinum is one member of a family of six elements, called the platinum metals, which almost always occur together, Before the discovery of the sister elements, the term platinum was applied to an alloy with Pt as the dominant metal, a practice that persists to some degree even today. The major properties of the platinum metals are given in Table 1 See also Iridium Osmium Palladium Rhodium and Ruthenium. 

This section deals only with solvents whose reduction products are insoluble in the presence of lithium ions. The list includes open chain ethers such as diethyl ether, dimethoxy ethane, and other polyethers of the glyme family cyclic ethers such as THF, 2Me-THF, and 1,4-dioxane cyclic ketals such as 1,3-dioxolane and 1,3-dioxane, esters such as y-butyrolactone and methyl formate and alkyl carbonates such as PC, EC, DMC, and ethylmethyl carbonate. This list excludes the esters, ethyl and methyl acetates, and diethyl carbonate, whose reduction products are soluble in them (in spite of the presence of Li ions). Solutions of solvents such as acetonitrile and dimethyl formamide are also not included in this section for the same reasons. Figure 6 presents typical steady state voltammo-grams obtained with gold, platinum, and silver electrodes in Li salt solutions in which solvent reduction products are formed and precipitate at potentials above that of lithium metal deposition. These voltammograms are typical of the above-mentioned solvent groups and are characterized by the following features ... 

The linear CO stretching frequency for the carbonylated platinum colloid while lower than that found for surface bound CO, is in the range reported for the platinum carbonyl clusters [Pt 3 (CO) 6 ] n / sind we find that the carbonylated colloid is easily transformed into the molecular cluster [Pt 12 (CO) 24 ] (10) reaction with water. The cluster was isolated in 50 yield based on platinum content of the precipitate by extraction with tetraethylammonium bromide in methanol from the aluminum hydroxide precipitated when water is added to the aluminoxane solution. The isolation of the platinum carbonyl cluster reveals nothing about the size or structure of the colloidal platinum particles, but merely emphasizes the high reactivity of metals in this highly dispersed state. The cluster isolated is presumably more a reflection of the stability of the [Pt3(CO)6]n family of clusters than a clue to the nuclearity of the colloidal metal particles - in a similar series of experiments with colloidal cobalt with a mean particle size of 20A carbonylation results in the direct formation of Co2(CO)8. 

The driving force for tlie development of non-platinum exliaust emission catalysts is the price, strategic importance and low availability of the platinum group metals. Our studies have shown that catalysts based on tin(IV) oxide (Sn02) promoted with chromium and/or copper (Cr-Sn02 and Cu-Cr-Sn02 catalysts) which exhibit excellent three-way catalytic activity - activity which is comparable to that shown by noble metals dispersed on ahunina. This family of materials offers tremendous promise as cheap and efficient catalyst systems for the catalytic conversion of noxious emissions from a variety of sources. In tliis paper we describe tliree aspects of this family of environmental catalysts (1) the synthesis, (2) tlieir characterisation, and (3) their catalytic activity. 

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