Catalysts hydrogenation, selective

Conditions of hydrogenation also determine the composition of the product. The rate of reaction is increased by increases in temperature, pressure, agitation, and catalyst concentration. Selectivity is increased by increasing temperature and negatively affected by increases in pressure, agitation, and catalyst. Double-bond isomerization is enhanced by a temperature increase but decreased with increasing pressure, agitation, and catalyst. Trans isomers may also be favored by use of reused (deactivated) catalyst or sulfur-poisoned catalyst. 

Homogeneous and heterogenous catalysts which selectively or partially hydrogenate fatty amines have been developed (50). Selective hydrogenation of cis and trans isomers, and partial hydrogenation of polyunsaturated moieties, such as linoleic and linolenic to oleic, is possible. 

A good catalyst is also stable. It must not deactivate at the high temperature levels (1300 to 1400°F) experienced in regenerators. It must also be resistant to contamination. While all catalysts are subject to contamination by certain metals, such as nickel, vanadium, and iron in extremely minute amounts, some are affected much more than others. While metal contaminants deactivate the catalyst slightly, this is not serious. The really important effect of the metals is that they destroy a catalyst s selectivity. The hydrogen and coke yields go up very rapidly, and the gasoline yield goes down. While Zeolite catalysts are not as sensitive to metals as 3A catalysts, they are more sensitive to the carbon level on the catalyst than 3A. Since all commercial catalysts are contaminated to some extent, it has been necessary to set up a measure that will reflect just how badly they are contaminated. 

The available data in Table 6 reveal that palladium complexes are excellent catalysts for selective hydrogenation of C=C in NBR. Recent attempts to recover the catalyst (see Section VII) after hydrogenation and lower the cost of the metal make it an attractive supplement in the industrial production of HNBR. 

Acetone can also he coproduced with allyl alcohol in the reaction of acrolein with isopropanol. The reaction is catalyzed with an MgO and ZnO catalyst comhination at approximately 400°C and one atmosphere. It appears that the hydrogen produced from the dehydrogenation of isopropanol and adsorbed on the catalyst surface selectively hydrogenates the carhonyl group of acrolein ... 

GP 8[ [R 7] Rhodium catalysts generally show no pronoimced activation phase as given for other catalysts in other reactions [3]. In the first 4 h of operation, methane conversion and hydrogen selectivity increases by only a few percent. After this short and non-pronounced formation phase, no significant changes in activity were determined in the experimental runs for more than 200 h. 

At least rune manufacturing technologies are available for the production of caprolactam and, in most, hydroxylamine (hyam) is one of the important raw materials. In particular, in the HPO process the hydroxylamine is made by using a precious metal powdered catalyst to selectively hydrogenate nitric acid. Evonik... 

When the reactant provides more than one kind of hydrogen for insertion, the catalyst can influence selectivity. For example, Rh2(acam)4 gives exclusively insertion at a tertiary position, whereas Rh2(02CC4F9)4 leads to nearly a statistical mixture.217aThe attenuated reactivity of the amidate catalyst enhances selectivity. 

Other poisons (modifiers) used to create such selective Pd catalysts may be metals 23 Zn, Cd, Zr, Ru, Au, Cu, Fe, Hg, Ag, Pb, Sb, and Sn or solvents (organic modifiers) 24 pyridine, quinoline, piperidine, aniline, diethylamine, other amines, chlorobenzene, and sulfur compounds. Hydroxides have also been used to increase the half-hydrogenation selectivity of Pd. 

Bose and coworkers [10] have described hydrogenation using ammonium formate as hydrogen donor and Pd/C as catalyst for selective transformations (Tab. 8.1) of /7-lactams 10, as shown in Scheme 8.6. 

NASA conducted studies on the development of the catalysts for methane decomposition process for space life-support systems [94], A special catalytic reactor with a rotating magnetic field to support Co catalyst at 850°C was designed. In the 1970s, a U.S. Army researcher M. Callahan [95] developed a fuel processor to catalytically convert different hydrocarbon fuels to hydrogen, which was used to feed a 1.5 kW FC. He screened a number of metals for the catalytic activity in the methane decomposition reaction including Ni, Co, Fe, Pt, and Cr. Alumina-supported Ni catalyst was selected as the most suitable for the process. The following rate equation for methane decomposition was reported ... 

Another useful compound is the 1 2 telomer of malonate and butadiene, 137. The first example is the synthesis of pellitorine (138), a naturally occurring pesticide (126). The terminal double bond was hydrogenated selectively with RuCl2(PPh3)3 as a catalyst. Partial hydrolysis afforded the monoester, which was treated with PhSeSePh to displace one of the carboxyl group with phenylselenyl group. Oxidative removal of the phenylselenyl group afforded 2,4-decadienoate (139), which is converted to pellitorine (138) ... 

Progress is being made in the search for catalysts to hydrogenate aromatic systems (see Section VII). This area is likely to become increasingly important if coal, which contains polyaromatic compounds, is utilized more for production of petrochemicals. Stereospecific production of fully m-C6D6H6 from perdeuterobenzene has been reported catalysts for selective hydrogenation of benzene to cyclohexene would be valuable. 

---