Reaction mechanism of isopropylation of naphthalene on Faujasite Zeolite: A quantum chemical study
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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) 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.
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