Alkylaromatic Hydrocarbons Dehydrogenation

Oxides before alkali-metal evaporation were calcined at 1023 K, NaCl at 723 K 

The reaction mechanism for a very strong one-electron donor centre in the dehydrogenation of alkylaromatic hydrocarbons is similar to that proposed by Krause for ethylbenzene dehydrogenation [reactions (5) and (6)]. The mechanism for n-propylbenzene transalkylation and cyclization on the radical pathway has been suggested.  

Hydrogenation of n-AIkenes. - The activity of oxides with alkali metals in the hydrogenation of alkenes is similar to the activity of EDA complexes of alkali metals with organic electron acceptors described by Tamam. Hydrogenation of alkenes occurs at 423-473 K under normal pressure. In Table 5 are given the initial rates of hydrogenation reactions of alkenes in the presence of oxides doped with sodium and potassium vapours. 

The adsorption of TCNE in stoicheiometric amount to the concentration of one-electron donor centres on MgO-Na and MgO-K surfaces causes the 

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Transformations of hydrocarbons promoted by solid metals and their oxides play very important roles in chemical industry [1], Heterogeneous metal-containing catalysts [2] are widely employed for cracking (see, e.g [3]) of oil fractions, oxidation, dehydrogenation, isomerization and many other processes of saturated as well as alkylaromatic hydrocarbons. 

Without going into detail we simply note that oxidation of alkylaromatic hydrocarbons with polymer-immobilized catalysts can be considered as a system of successive-parallel reactions including mononuclearic hydroxylation to phenols, oxidation of phenols, oxidative dehydrogenation of hydroquinones, oxidative decomposition of quinones and thermal and catalytic decomposition of peracids. 

Debras, G., Grootjans, J., and Delorme, L., Process for the Catalytic Dehydrogenation of Alkylaromatic Hydrocarbons , European Patent 0 482 276 Al issued to FINA Research, S. A. (1992). 

Acidic zeolites are known for their excellent catalytic activity in cracking and isomerization of hydrocarbons (75). In the absence of metal, however, these catalysts rapidly deactivate due to the formation of carbonaceous products, usually referred to as coke. The carbonaceous residues are mainly formed via alkylaromatics and polyaromatics, which are the result of dehydrogenation, cyclization, and further alkylation processes. The coke deposits lower the catalytic activity by site poisoning and eventually also by pore blocking, which inhibits access of hydrocarbon molecules to the acid sites (286). 

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