In this work we studied the host–guest interactions between confined molecules and zeolites and their relationship with the energies involved in the reaction of methylation of benzene by methanol in H-ZSM-5 and H-Beta zeolites employing density functional theory (DFT) methods and the quantum theory of atoms in molecules. Results show that the strength of the interactions related to adsorption and coadsorption processes is higher in the catalyst with the larger cavity; however, the confinement effects are higher in the smaller zeolite, explaining, from an electronic viewpoint, the reason why the stabilization energy is higher in H-ZSM-5 than in H-Beta. The confinement effects of the catalyst on the confined species for methanol adsorption, benzene coadsorption, and the formed intermediates dominate this stabilization. For the transition state (TS), the stability of the TS is achieved due to the stabilizing effect of the surrounding zeolite framework on the formed carbocationic species (CH3 +) which is higher in H-ZSM-5 than in H-Beta. In both TSs the methyl cation is multicoordinated forming the following H2O···CH3 +···CB concerted bonds. It is demonstrated that, through the electron density analysis, the criteria can be defined to discriminate between interactions related to the confinement effects and the reaction itself (adsorption, coadsorption, and bond-breaking and bond-forming processes) and, thus, to discriminate the relative contributions of the degree of confinement to the reaction energies for two zeolite catalysts with different topologies.

In the present work, we studied the protonation reaction of styrene inside the cavity of acidic H-Y zeolite. Density functional theory calculation using M06-2X functional and analysis of quantum theory of atoms in molecules are used to investigate the confinement effects of zeolite framework on species involved on the reaction. A detailed analysis of the topology of the electron density of interactions among reactants, transition state, and intermediate products with the cavity of H-Y zeolite is performed, extracting conclusions about adsorption, catalysis, and confinement effects. Identification and quantification of host−guest interactions between zeolite framework and styryl cation support the larger contribution of weak closed-shell interactions in stabilization of the formed carbenium ion. Our results clearly show that reaction energies for all formed species inside a zeolite with large void structure are also significantly governed by the confinement effects related to weak host−guest interactions. In other words, zeolite confinement effect is a crucial factor that may affect the catalytic activity even on zeolites with large pore size and void structure as H-Y.