Platinum or Palladium

Iron-Platinum or Palladium. - The nature of supported bimetallic catalysts can be probed by determining the chemical state of one metallic component, 

Engels, Tran Kim Thanh, and M. Wilde, Chem. Tech. (Leipzig), 1975, 27, 459. 

Charcosset. R. Frety, G. Leclercq, B. Moraweek, L. Tournayan, and J. Varloud, React. Kinet. Catal Lett, 1979, 10, 301. 

Silica was chosen to support Pt-Fe on the basis of negligible influence on 

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The above catalysts contain about 30 per cent, of metal catalyst with 10 per cent, of metal may be readily prepared by reducing the quantity of platinum or palladium chloride used. 

Dispersed Metals. Bifimctional zeoHte catalysts, principally zeoHte Y, are used in commercial processes such as hydrocracking. These are acidic zeoHtes containing dispersed metals such as platinum or palladium. The metals are introduced by cation exchange of the ammine complexes, foUowed by a reductive decomposition (21) ... 

PGM catalyst technology can also be appHed to the control of emissions from stationary internal combustion engines and gas turbines. Catalysts have been designed to treat carbon monoxide, unbumed hydrocarbons, and nitrogen oxides in the exhaust, which arise as a result of incomplete combustion. To reduce or prevent the formation of NO in the first place, catalytic combustion technology based on platinum or palladium has been developed, which is particularly suitable for appHcation in gas turbines. Environmental legislation enacted in many parts of the world has promoted, and is expected to continue to promote, the use of PGMs in these appHcations. 

In past years, metals in dilute sulfuric acid were used to produce the nascent hydrogen reductant (42). Today, the reducing agent is hydrogen in the presence of a catalyst. Nickel, preferably Raney nickel (34), chromium or molybdenum promoted nickel (43), or supported precious metals such as platinum or palladium (35,44) on activated carbon, or the oxides of these metals (36,45), are used as catalysts. Other catalysts have been suggested such as molybdenum and platinum sulfide (46,47), or a platinum—nithenium mixture (48). 

Reactive halogens in various series have been removed by catalytic hydrogenation with either platinum or palladium catalysts, and other nucleophiles which have been used in chloride displacements include hydroxide ion, alkoxides, hydrosulflde, hydrazine and toluene-p-sulfonylhydrazine, and trimethyl phosphite. 

Dihydromorphinone, Cj,Hjg03N, and derivatives. Dihydromorphinone (LIII MeO HO) is formed when morphine in solution is treated with relatively large quantities of platinum or palladium catalyst under various conditions.It melts at 262-3° and yields an oxime, m.p. > 234°. The hydrochloride is the drug known as dilaudid. On 0-methyla-tion dihydromorphinone yields dihydrocodeinone (see above), and when dissolved in ether and treated with methyllithium the corresponding tertiary alcohol, 6-methyldihydromorphine, CigHggOgN, m.p. 209-211°, Wd ° 14i7° (EtOH), is formed. This on methylation with diazomethane gives 6-methyldihydrocodeine as described above (Small and Rapoport... 

The 5a-isomer is obtained from hydrogenation of A -7-keto steroids over platinum or palladium. In the latter case the addition of pyridine to the reaction mixture greatly increases the amount of 5a- product formedd a Attack also takes place on hydrogenation (deuteration or tritiation )... 

The catalyst exerts some influence on the bonds broken in hydrogenolysis of saturated cyclopropanes (775), but in vinyl and alkylidene cyclopropanes the effect is pronounced. Platinum or palladium are used frequently. In one case, Nishimura s [124a) catalyst, rhodium-platinum oxide (7 3), worked well where platinum oxide failed (.75). An impressive example of the marked influence of catalyst is the hydrogenation of the spirooctane 42, which,... 

Hardacre et al. have developed a procedure for the synthesis of deuterated imidazoles and imidazolium salts [65]. The procedure involves the platinum- or palladium-catalyzed deuterium exchange of 1-methyl-d -imidazole with D2O to give 1-methylimidazole-d , followed by treatment with a deuterated alkyl halide. 

The deliberate raising of the electrical potential of titanium, either by the attachment of discrete particles of a noble metal, such as platinum or palladium, at the surface, or by the application of positive direct current to force the formation of a protective film, is dealt with at a later point. The electrochemical aspect of the corrosion of titanium is comprehensively treated in a number of papers ... 

Bursting discs may be fabricated of gold, silver, platinum or palladium. The recommended maximum temperatures for continuous use are 80 C for gold, 150 C for silver, 300 C for palladium and 450 C for platinum. Figure 6.6 gives bursting pressure/disc thickness data for these metals and for aluminium and nickel. 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

Hydrogen usually adds to benzo-annulated oxepins in the presence of noble-metal catalysts such as platinum or palladium with saturation of the nonbenzenoid C-C double bonds to give 6152,154 and 7.17-89-93... 

Since the reaction between hydrogen and oxygen is very slow at room temperature, catalysts are incorporated in the carbon electrodes. At the anode, suitable catalysts are finely divided into platinum or palladium at the cathode, cobaltous oxide, or silver. The two halfreactions shown above yield the overall result as ... 

The NOxTrap can be assimilated to a three-way catalyst7 complemented by a NOz storage function. This system contains two types of precious metals the first one, dedicated to NO, HC and CO oxidation in lean operating mode, will generally consist of platinum or palladium. The second one, dedicated to NOx reduction in rich operating mode, is typically rhodium. Rhodium price spectacularly increases, with a multiplication by three of its value in 2006 (see Figure 7.13)8. 

The reaction of these platinum or palladium clusters with transition metal compounds has also been studied and many cluster derivatives have been prepared for this method, which included reactions with gold,3 02-3306 silver, 302,33 3,3307-3310 copper 3302,3303,3309-3311 Qr mercury com ... 

Catalytic converters are basically smog control devices on newer automobiles. Catalytic converters have an oxidation catalyst that oxidizes CO and hydrocarbons to CO2 and H2O. It may also have a reduction catalyst that reduces NO to N2. The catalysts involved with these processes are generally platinum or palladium metal operating at relatively high temperature. 

With slight modifications in procedure, one basic synthesis of leucovorin and the subsequent isolation of its salts have remained unchanged for nearly thirty years. The method involves hydrogenation of folic acid (pteroylglu-tamic acid) in the presence of a platinum or palladium catalyst, as first described by O Dell et al.15 This... 

More recently Hartog and Zwietering (103) used a bromometric technique to measure the small concentrations of olefins formed in the hydrogenation of aromatic hydrocarbons on several catalysts in the liquid phase. The maximum concentration of olefin is a function of both the catalyst and the substrate for example, at 25° o-xylene yields 0.04, 1.4, and 3.4 mole % of 1,2-dimethylcyclohexene on Raney nickel, 5% rhodium on carbon, and 5% ruthenium on carbon, respectively, and benzene yields 0.2 mole % of cyclohexene on ruthenium black. Although the cyclohexene derivatives could not be detected by this method in reactions catalyzed by platinum or palladium, a sensitive gas chromatographic technique permitted Siegel et al. (104) to observe 1,4-dimethyl-cyclohexene (0.002 mole %) from p-xylene and the same concentrations of 1,3- and 2,4-dimethylcyclohexene from wi-xylene in reductions catalyzed by reduced platinum oxide. 

With the addition of Sn as a second metal the composition was closer to that predicted for pure Cg cyclization. Rhenium had the opposite effect (107). Suppression of the acidity of the alumina support (of platinum or palladium) by incorporation of sodium nitrate (126) decreases first the C5 - Cg ring enlargement activity of the catalyst (124, 127). Potassium ions (94-94b) or iec-butylamine (70) have a similar effect. 

The secret that makes this process work is no surprise, the catalyst. Those that work include some of the noble metals, specifically, platinum or palladium, a rare earth metal like cerium or neodynium (are they rare or what ) on alumina, or a non-noble metal like chromium on a silica-aluminum support. 

Alkynes may also be hydrogenated, initially to alkenes, and then further to alkanes. By suitable modification of the catalyst, it has proved possible to stop the reaction at the intermediate alkene. Typically, platinum or palladium catalysts partially deactivated (poisoned) with lead salts are fonnd to be suitable for reduction of alkynes to alkenes. Again, syn addition is observed. 

Hydrogenation over rhodium (5% on alumina) in acetic acid at room temperature and 3-4 atm of hydrogen was successfully used for reduction of benzene rings in compounds containing functions which would be hydrogen-olyzed over platinum or palladium catalyst [390], Palladium at low temperature usually does not reduce benzene rings and is therefore suited for hydro-genolysis of benzyl derivatives (pp. 150, 151). 

Cathodic surfaces of finely divided platinum, palladium and nickel have a low hydrogen overvoltage and the dominant electrochemical reaction is the generation of a layer of hydrogen atoms. The electrocatalytic hydrogenation of aldehydes and ketones can be achieved at these surfaces. Cathodes of platinum or palladium black operate in both acid solution [203] and in methanol containing sodium methoxide [204], The carbonyl compound is converted to the alcohol. Reduction of 4-tert-butylcyclohexanone is not stereoselective, however, 1,2-diphenylpropan-l-one is converted to the / reo-alcohol. 

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