Hydrogen cycloalkanes dehydrogenation

Dehydrogenation of cycloalkanes such as cyclohexane, methylcyclohexane and decalin has been used for the storage and transportation of hydrogen fuel at an ambient temperature and pressure [2, 4, 14-20]. The advantages of cycloalkane dehydrogenation systems are as follows ... 

Another area of high research intensity is the catalytic dehydrogenation of alkanes to yield industrially important olefin derivatives by a formally endothermic (ca. 35 kcal mol-1) loss of H2. Recent results have concentrated on pincer iridium complexes, which catalytically dehydrogenate cycloalkanes, in the presence of a hydrogen accepting (sacrificial) olefin, with turnover numbers (TONs) of >1000 (Equation (23)) (see, e.g., Ref 33,... 

Finally, whilst rhenium hydride complexes have not been reported to hydrogenate alkenes, there are several reports of the dehydrogenation of alkanes in the presence of tBuCH=CH2 as an hydrogen acceptor (Scheme 6.14) [136-142]. For example, cycloalkanes are transformed catalytically into the corresponding cyclic alkene, which shows that, in principle, a Re-based catalyst could be designed. 

Benzene, naphthalene, toluene, and the xylenes are naturally occurring compounds obtained from coal tar. Industrial synthetic methods, called catalytic reforming, utilize alkanes and cycloalkanes isolated from petroleum. Thus, cyclohexane is dehydrogenated (aromatization), and n-hexane(cycli> zation) and methylcyclopentane(isomerization) are converted to benzene. Aromatization is the reverse of catalytic hydrogenation and, in the laboratory, the same catalysts—Pt, Pd, and Ni—can be used. The stability of the aromatic ring favors dehydrogenation. 

The platforming catalyst was the first example of a reforming catalyst having two functions.43 44 93 100-103 The functions of this bifunctional catalyst consist of platinum-catalyzed reactions (dehydrogenation of cycloalkanes to aromatics, hydrogenation of olefins, and dehydrocyclization) and acid-catalyzed reactions (isomerization of alkanes and cycloalkanes). Hyrocracking is usually an undesirable reaction since it produces gaseous products. However, it may contribute to octane enhancement. n-Decane, for example, can hydrocrack to C3 and C7 hydrocarbons the latter is further transformed to aromatics. 

Hydrogen is stored efficiently by the exothermic hydrogenation of aromatic compounds, such as benzene, toluene and naphthalene, into the corresponding cycloalkanes at lower temperatures of 100-250 °C and relatively higher pressures of 1-10 bar, while hydrogen is preferably supplied by endothermic dehydrogenation (AHf= -65-68 kJ/mole H2) of cycloalkanes, such as cyclohexane, methylcyclohexane and decalin, by heating them above 250 °C ... 

Another system involving Re and 3,3-dimethyl-l-butene as a hydrogen acceptor is used to dehydrogenate cycloalkanes . 

Dehydration of cyclopentanemethanol over aluminum oxide at 320° tgave an olefin mixture whence hydrogenation afforded a mixture (94%) of [14C]methylcyclopentane with about 34% of [14C]cyclohexane. The mixed cycloalkanes were transformed into [14C]cyclo-hexane by Nenitzescu and Cantuniari s method,154 and dehydrogenation on a platinum-charcoal catalyst at 360° then yielded [14C1]benzene. 

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