Theoretical study of olefin protonation reactions confined inside mordenite zeolite by energy decomposition analysis

Abstract

The protonation reactions of ethene, propene and isobutene confined inside 8-MR and 12-MR pore structures of mordenite (MOR) zeolite are theoretically studied in order to reveal the origin of different catalytic activity. It is found that the higher activity of propene in 8-MR pore comes from the better fit of dimensional sizes compared to small ethene and bulky isobutene; while in case of large 12-MR pore, the reactivity is enhanced with the increase of molecular size. The interaction energy for the transition state is further investigated by energy decomposition analysis (EDA) method. Two physical properties are shown to highly contribute to the stability of transition state species: the charge property of adsorbed molecules related to the electrostatic interaction and the orbital overlap between adsorbates and zeolite framework involved in the orbital interaction. By using principal components analysis, the major role of electrostatic and orbital interactions in the apparent activation energies were also observed.