Coupled dehydrogenation/hydrogenation

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Coupling of Hydrogenation and Dehydrogenation Reactions Nonporous Pd-based membranes... 

Figure 8.4 Coupling of hydrogenation and dehydrogenation reactions with a catalytic membrane...

I-Butene dehydrogenation coupled with hydrogen oxidation/ dense Pd membrane... 

The mechanism of paraffin hydrocracking over bifunctional catalysts is, essentially, the carbenium ion chemistry of acid cracking coupled with metal-centered dehydrogenation/hydrogenation reactions. The presence of excess hydrogen and the hydrogenation component of the catalyst result in hydrogenated products and inhibition of some of the secondary reactions and coke formation. 

Coupled Dehydrogenation and Hydrogenation Reactions in a Pd/Ag Membrane Reactor... 

Fig. 13 The CH ,-CHy coupling mechanism of FT synthesis (1) CO and H2 dissociation. (2) Hydrogenation/dehydrogenation of Ci species (in quasi-equilibrium) and CH4 desorption. (3) Two pathways of chain growth, the CH3-1-C and CH2-I-CH2 coupling. (4) Hydrogenation or dehydrogenation of C2 species, and CH3CH3 and CH2CH2 desorption. (5) The coupling of RCH2 + C, RCH + CH2, RC-I-CH and RC-I-C. Reprinted from ref. 64 with permission from Elsevier.

Keywords Alcohols Amides Amines Carbon dioxide Catalysis Dehydrogenative coupling Esters Hydrogen Imines Iridium Metal-ligand cooperation O-H activation Pincer complexes PNN PNP Ruthenium... 

Squalane [111-01-3] (fully saturated squalene) is produced synthetically by the coupling of two molecules of geranyl acetone with diacetylene, followed by dehydration and complete hydrogenation (205). Squalane can also be made by dimerization of dehydroneroHdol, followed by dehydrogenation and hydrogenation (206). 

Many other authors studied the catalytic activity of palladium in more complicated hydrogenation reactions because of being coupled with isomerization, hydrogenolysis, and dehydrogenation. In some cases the temperatures at which such reactions were investigated exceeded the critical temperature for coexistence of the (a + /3)-phases in the other case the hydrogen pressure was too low. Thus no hydride formation was possible and consequently no loss of catalytic activity due to this effect was observed. 

A technique used to overcome the unfavorable thermodynamics of one reaction is to couple that reaction with another process that is thermodynamically favored. For instance, the dehydrogenation of cyclohexane to form benzene and hydrogen gas is not spontaneous. Show that, if another molecule such as ethene is present to act as a hydrogen acceptor (that is, the ethene reacts with the hydrogen produced to form ethane), then the process can be made spontaneous. 

Figure 10-2. Coupling of dehydrogenation and hydrogenation reactions by an intermediate carrier.

Kato, Y., and H. Kameyama, 1986. Study of Catalyst-Assisted Chemical Heat Pump with Reaction Couple of Acetone Hydrogenation and 2-Propnanol Dehydrogenation, Proc. of World Congress III of Chemical Engineering, I, Tokyo, pp. 676-679. 

Meng, N., S. Shinoda, and Y. Saito, Improvements on thermal efficiency of chemical heat pump involving the reaction couple of 2-propanol dehydrogenation and acetone hydrogenation. Int. J. Hydrogen Energ., 22, 361-367 (1997). 

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