Coking is the deposition of carbon-rich solids. In heterogeneous catalysis, the process is undesirable because the clinker blocks the catalytic sites. Coking is characteristic of high temperature reactions involving hydrocarbons feedstocks. Typically coking is reversed by combustion, provided that the catalyst will tolerate such.
A simplified equation for coking is shown in the case of ethylene:
- 3 C2H4 → 2 C ("coke") + 2 C2H6
A more realistic but complex view involves the alkylation of an aromatic ring of a coke nucleus. Acidic catalysts are thus especially prone to coking because they are effective at generating carbocations (i.e., alkylating agents).
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