Catalytic activation of reactions

The reactions are activated by catalyses capable of favoring isomerization and cydi zation as well as dehydrogenation. This means that the catalytic systems used are multifunctionai, and that they theoretically possess the following  

An acid function, provided by the support, with or without the addition of a halogenated compound, which favors isomerization and cyclization reactions to varying degrees. The acidity must be controlled to moderate hydrocracking. 

Oxides and sulfides were the hrst to be employed because they were un ected by the sulfur compounds in the feedstock. Due to their low selectivit however, they have been supnseded by noble metal based catalysts. Forcooventionaf systems, these catalysts exhibit the following charactenstics  

New bi and mulrimetalUc catalysts have been marketed more recently  

The role of tbe additives, which may be used in bi- or muitnnetaltic combinations (Re, Ir, Ru, Ag, Au, Ge etc.) is poorly umterstood. They help to enhance the properties of platinum hy keeping it in a suitable state of dispersion, and to modulate the acidic character of the support. They appear to oppose the sintering of metallic crystallites by the formation of alloys or polymetallic dusters. 

The formation of coke is due to the olefin and diolefin compounds whose appearance may be limited by lowering the temperature, raising the pressure, and increasing the hydrogen hydrocarbon ratio in the reactor. 

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