The key role of adsorbate-catalyst interactions into catalytic activity of [CTA+]-Si-MCM-41 from electron density analysis

Abstract

In this work, we analyzed the role of the interactions involved in the reaction mechanism for the transesterification of ethyl acetate and methanol on the pore mouth of [CTA+]-Si-MCM-41 catalyst. The Quantum Theory of Atoms in Molecules (QTAIM) was applied for the analysis of adsorbate-catalyst interactions in order to gain a deeper understanding about the relationship between bonding and catalytic properties along the reaction coordinate and the role of weak interactions in the catalytic activity. Experimental FT-IR spectrum was supported by the theoretical model for the coadsorption of both reagents following a dual-site mechanism. Our results reveal that the key role of the (CTA+)(SiO- ) ion pair is to stabilize the reactant species. During the reaction coordinate, the silica and the head of the surfactant are bonded through several O⋅⋅⋅H(CH3) interactions forming the bifunctional active site on the surface of the solid catalyst. Four interactions are associated with the reaction mechanism. The rest of weak adsorbate-catalysts interactions along the reaction coordinate are related to the additional stabilization of the reactants on the pore mouth of the catalyst.