Adsorption and cracking of n-alkanes over ZSM-5: Negative activation energy of reaction

✍ Scribed by James Wei

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 229 KB
• Volume: 51
• Category: Article
• ISSN: 0009-2509
• DOI: 10.1016/0009-2509(96)00187-x

✦ Synopsis

The heat of adsorption of normal-p~ on ZSM-5 is a linear function of the number of carbon atoms on the paraffin n, and is approximately half of the latent heat of condensation The rate of cracking of nparaffins over ZSM-5 increases exponentially with n, which is consistent with a linear dependence of A G ° with n. As temperature is increased, the cracking rate increases when n is less than 16, but decreases when n is greater than 16. This phenomenon is contrary to normal expectations, and is a consequence of the competition between two effects: the increase of intrinsic kinetics with temperature, and the decrease of adsorption strength and the concentration of active intermediates with temperature. The heat of adsorption becomes larger than the activation energy of the intrinsic kinetics when n= 16.