Platinum family metals palladium

Ruthenium is most often combined with platinum or palladium in alloys. Electrical contacts, devices for measuring very high and very low temperatures, and medical instruments are often made from ruthenium alloys. Ruthenium is also used in alloys with other platinum family metals to make jewelry and art objects. This use is limited, however, because of the high cost of ruthenium metal. 

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. 

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.)... 

The lower selectivity of PtHFAU catalysts is due to the very rapid formation of Ce cyclic hydrocarbons (family 1). The same trend has been found in the case of acetone transformation [3]. This can be explained by the lower activity of the palladium relatively to the platinum to hydrogenate the C=0 bond. This lower activity which has been found in the case of cyclohexanone hydrogenation on platinum group metals was explained by a weaker adsorption of the ketone on Pd in comparison with Pt and Ru [9]. 

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. 

In Group VIII, each position instead of being filled by a single element is occupied by a group of three elements. Thus there appear in triads iron, cobalt, and nickel ruthenium, rhodium, and palladium and osmium, iridium, and platinum. In this group there is no subdivision into families, but all the members are heavy metals. 

Most modern hydrocracking processes are catalytic, and the catalyst employed is usually dual functional with both a hydrogenation component and an acidic component. Typical acidic components include amorphous silica-alumina, alumina, and a large family of zeolites. Typical hydrogenation components are noble metals such as palladium and platinum and nonnoble metals such as nickel, cobalt, tungsten, and molybdenum. The latter metals are usually in sulfided form. 

The second family of compounds has a larger transition metal and/or indium content. In all of these compounds T-ln bonding is much more important than in the / -rich compounds. The transition metal atoms have broadly varying indium coordination. In compounds like Ce8Pd24ln (Gordon et al., 1996), only one indium atom is bonded to palladium. Such small fragments also occur in the rare earth metal rich compoimds. Normally, the lowest coordination number for a transition metal by indium is three. In fig. 94 we present the various Rhln c, Pdln, and Ptln monomeric units in the ternary indides with rhodium, palladium, and platinum as transition metal component. With the other late transition metals similar... 

Another chapter examines recent work in the area of metal-organic complexes derived from palladium(II) and platinum(II) diimine-dithiolate complexes. Pilato (Qiap. S), who is a leader in the development of new luminescent complexes of this family, has pioneered their application to sensing oiganophosphates and oxygen. His chapter describes the synthesis of these complexes, provides a comprehensive overview of their photophysical properties, and gives some examples of their application to the development of solid-state sensors. 

The examples presented in this subchapter represent only a selected portion of the vast amount of literature publications highlighting the ability of cycloisomerization reactions to built structural diversity within the class of sesquiterpenoids. As the reaction mechanisms are refined and more things are currently known not only from palladium cycloisomerization chemistry but also from other unique pi-metals like gold and platinum, more impressive cascades are expected to flourish the chemical literature. Although cycloisomerization reaction is counting more than four decades from its concept discovery, we are convinced that it will stiU remain one of the best atom-economical methods for the construction of structurally comphcated natural products as those contained in the unlimited sesquiterpene family. 

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