Reaction mechanism of isopropylation of Naphthalene on Faujasite Zeolite: A quantum chemical study

Karan Bobuatong, Supawadee Namuangruk

Abstract


The reaction mechanisms of isopropylation of naphthalene by propene on faujasite zeolite (FAU) has been systematically investigated using the density functional theory with the M06-2X functional. The catalytic cycle of the β, β-selectivity towards the 2-isoproplynaphthalene (2-IPN) and 2,6-diisopropylnaphthalene (2,6-DIPN)[S.N.1] [KB2]  is proposed to proceed through the three elementary steps. The reaction is initiated by the protonation of a propene resulting in an isopropoxide species bounded on the FAU framework with the highest activation barrier for overall reaction pathway of 18.1 kcal/mol. The second step is the isopropylation of naphthalene by isopropoxide from the first step leading to the formation of a key intermediate, naphthalynic carbocations, which is subsequently transformed to 2,6-DIPN via the proton back-donation in the final step. It appears that the large 56T cluster including zeolite pore structure  is able to stabilize naphthalynic carbocations as a stable intermediate by the confinement effects. The results of this study demonstrate the importance of using a large zeolite cluster for understanding the relationship between the steric constraints and van der Waals dispersion induced by the pore structure of FAU and its catalytic activity.


Keywords


Isopropylation, Faujasite zeolite, naphthalene, DFT, M06-2X

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