DFT Study on the Effect of Aluminum Position in Zn-Exchanged MFI on Methane Activation

The position of aluminum atoms in ion-exchanged zeolites is known to affect the reactivity of active sites. In this work, we used DFT calculations to systematically quantify the effect of Al-atom position within the α-ring of Zn-exchanged MFI (Zn-MFI) on the activation of methane. Our DFT results indicate that the most stable configuration for the Zn-exchanged cluster of the α-ring is obtained when the Al atoms are located at the T11-T2 crystallographic sites. For each Al-atom configuration, we analyzed the reaction pathways for methane activation. Our results suggest that the activation of methane yields the formation of a Bronsted acid site, which can be formed at an oxygen atom within the α-ring or at an oxygen atom that lies outside the α-ring, and that the lowest reaction energy for methane activation is obtained when the Bronsted acid site is formed at the oxygen atom in which the HOMO of the isolated cluster is located. Furthermore, our results indicate that the partial atomic charge of the Zn atom...