Origin of Zeolite Confinement Revisited by Energy Decomposition Analysis

Abstract

Our previous work demonstrated that hydrocarbon species can be stabilized in the confined zeolite in the form of an ion pair, π complex, and alkoxy species. Nevertheless, the interaction mechanism between the different reactants/intermediates and the zeolite framework remains undetermined, and thus, the origin of the zeolite confinement effect has not been thoroughly revealed. In this work, a recently developed energy decomposition analysis (EDA) method was applied to theoretically investigate the energy parameters of a series of hydrocarbon species confined in the zeolitic catalysts with different pore diameters. It is demonstrated that for the carbenium ion intermediates, the electrostatic interaction plays a key role in their stabilization; for the alkoxy species, both orbital and electrostatic interactions are the key factors, while for the neutral hydrocarbons, the dispersion interaction favors their stabilization. In addition, the principal components analysis (PCA) reveals that the dispersion interaction does not play a crucial role in improving the reaction activity due to the same extent of stabilization effect for different reaction species (e.g., reactant, transition state, intermediate, or product), and thus, the dispersion contribution would be counteracted in a specific zeolite catalytic reaction. In contrast, the difference in electrostatic interaction caused by the variations of charge characteristics of the various confined species considerably contributes to the decrease of the activation barrier and the increase of the reaction energy, which in turn largely promotes the catalytic performance of zeolite catalysts.