Understanding the influence of the Al-array in metal-ion exchanged zeolites is of particular importance to elucidate its effect on the adsorption energies and reactivity of catalytic sites. In this work, we used DFT to systematically evaluate 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-configuration, we analyzed the reaction pathways for methane activation with all the possible oxygen atoms. The activation of methane yields the formation of a Brønsted 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. Our results indicate that the lowest reaction energy for methane activation is obtained when the Brønsted acid site is formed at the oxygen atom in which the HOMO of the isolated cluster is located. Furthermore, our results suggest that the partial atomic charge of the Zn atom within the a-ring of MFI can be correlated to the transition state energy of methane activation, which range from 87 to 136 kJ/mol depending on the Al location. The fundamental studies conducted in this work contribute to the elucidation of essential parameters and correlations, based on electrostatic and electron transfer interactions, for the activation of methane on Zn-MFI zeolites.

DFT study on the effect of the distribution of aluminum atoms in Zn-exchanged MFI on methane activation

2019 Spring National Meeting

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