Catalyst in hydrogenations

Palladous oxide,3/ PdO, may be prepared by the fusion of palladous chloride with sodium nitrate, and is an effective catalyst in hydrogenation, the most active form being produced when the fusion temperature is 600°,... 

Comyns et al.516 first observed the rate enhancement by Lewis acid catalysts in hydrogen exchange in the tritiation of toluene by tritium chloride. Second-order rate coefficients were given approximately by... 

Case - Use of Carbon Nanotube-Based Catalysts in Hydrogen Production... 

Gryaznov, V.M., M.M. Ermilova, L.S. Morozova, and N.V. Orekhova, Palladium alloys as hydrogen permeable catalysts in hydrogenation and dehydrogenation reactions, ]. Less-Common Metals, 89,529-535,1983. 

Consequently, it is I ICo(CN)s3 that functions as a catalyst in hydrogenation processes. In the first step of the process shown in Figure 22.9, the alkene coordinates to HCo(CN)s3 as one hydrogen atom is added to the molecule so that only one double bond remains. The monoene is bonded to the cobalt in rf fashion. In the second step, another HCo(CN)53- transfers hydrogen to the alkene, which undergoes reductive elimination and leaves, having been converted to 1-butene. 

The occurrence of multinuclear catalysts in hydrogenations catalyzed by rhodium-DIOP systems seems unlikely, although the trans-RhCl(CO)(DIOP) complex 43 is dimeric (276), and in basic methanolic solution the 1 1 diphos complex exists as Rh3(diphos)3(OMe)2 + (138a, Section II, B, 1). 

James and coworkers found that one benzylamine is actually bound to the rhodium in the active catalyst in hydrogenations of PhCH=NRCH2Ph using [Rh(COD)(PPh3)2]PF6 as catalyst precursor. However, the addition of more than two equivalents of benzylamine inhibited the catalysis [63]. 

W(CH3CN)(C0)3(TPPMS)2] was obtained in the reaction of TPPMS and [W(CH3CN)3(C0)3], and was used as catalyst in hydrogenation of benzene in water/heptane biphasic systems [164]. At 100 °C and 70 bar H2 the catalytic activity was found rather low (average TOP 1 h ). The same complex is also active in the hydrogenation of olefins (e.g. 1-hexene, 2,3-dimethyl- 1 -butene). 

Nickel acetylacetonate is used as a catalyst in hydrogenation and other organic reactions. 

Platinum also is used extensively as a catalyst in hydrogenation, dehydrogenation, oxidation, isomerization, carbonylation, and hydrocracking. Also, it is used in organic synthesis and petroleum refining. Like palladium, platinum also exhibits remarkable abdity to absorb hydrogen. An important application of platinum is in the catalytic oxidation of ammonia in Ostwald s process in the manufacture of nitric acid. Platinum is installed in the catalytic converters in automobile engines for pollution control. 

Rhenium is used in tungsten and molybdenum-based alloys. It is used for filaments for ion gages in mass spectrometers. Rhenium-tungsten alloys are used in thermocouples to measure temperatures up to 2,200°C. Rhenium wire is used in flash bulbs for photography. Rhenium compounds also are used as catalysts in hydrogenation and hydrocracking reactions in petroleum refining. 

Fig. 4. Activation of zinc oxide catalysts in hydrogen -I- 2 % deuterium, flow rate 0.119 cc./sec. 215°C. A, X aSl C., O230°C.

The formation of a metal-substrate bond of intermediate stability is of key importance in a successful hydrogenation. If this bond is too strong, the subsequent migratory insertion may be hindered and hydrogenation cannot take place. Strongly chelating dienes, such as 1,5-cyclooctadiene (COD) or cyclopentadiene, form stable complexes that, in turn, are used as catalysts in hydrogenations. 

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