Chemistry – Organic chemistry - Alkenes | e-Consult
Organic chemistry - Alkenes (1 questions)
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Reaction Equation:
C4H10 (n-butane) → C2H4 (ethene) + H2 (hydrogen)
Mechanism of Catalyst Action:
The cracking reaction facilitated by a solid acid catalyst like Al2O3 or SiO2 proceeds through a surface reaction. Here's a simplified explanation:
- Adsorption: The n-butane molecule adsorbs onto the surface of the catalyst. The catalyst's acidic sites (e.g., hydroxyl groups on silica) interact with the alkane molecule.
- Bond Weakening: The interaction between the alkane and the catalyst weakens the carbon-hydrogen and carbon-carbon bonds within the n-butane molecule. This is due to the polarized nature of the catalyst surface.
- Bond Breaking: The weakened bonds break, leading to the formation of a carbenium ion (C4H9+). This is a highly reactive intermediate.
- Ethene Formation: The carbenium ion loses a proton (H+) from a neighboring carbon atom to form ethene (C2H4). This proton is abstracted by another catalyst site.
- Hydrogen Formation: The carbenium ion can also lose a proton to form hydrogen (H2).
- Desorption: The ethene and hydrogen molecules desorb from the catalyst surface, freeing up the active sites for further reactions.
The catalyst provides a surface where the reaction can occur more easily than in the gas phase. The acidic sites on the catalyst surface promote the formation of the carbenium ion, which is a crucial step in the cracking mechanism. The catalyst also helps to stabilize the intermediates and products, increasing the overall reaction rate.