First principles study on the alkylation of benzene with ethene over different zeolites: Insight into the intrinsic mechanism and structure-reactivity relationship

Abstract

• The concerted pathway is kinetically more favorable over the H-ZSM-5, H-BEA and H-MOR. • The activity variation with different temperatures is mainly contributed from the entropy part. • Zeolite with large tridimensional channels is more active for the alkylation of benzene with ethene. • The possibility to further improve reaction activity by subtly tailoring the zeolite structure was demonstrated theoretically. • Zeolite acts as a charge acceptor firstly and then turns to be a donor along the reaction coordinate. Zeolite has been applied extensively in petrochemistry field, and its structure has a significant effect on the reactivity and mechanism. However, the intrinsic mechanism difference over various zeolites and the structure-reactivity relationship still remain unclear. Herein, the alkylation of benzene with ethene was selected as a model reaction to illustrate these concepts over H-BEA, H-ZSM-5 and H-MOR based on the DFT calculations. Overall, the concerted mechanism is kinetically more favored over all the three zeolites, and temperature has a much more significant effect on the activity than pressure. It is mainly the entropy part that dominates the variation of reaction rates at different temperatures. For the domination of the concerted mechanism, our study provides the possibility to further improve reaction activity by subtly tailoring the zeolite structure. H-BEA exhibits higher activity than H-ZSM-5 and H-MOR under both mechanisms, indicating zeolite with large three-dimensional framework is more active for this reaction. Charge transfer was also conducted revealing that zeolite acts as a charge acceptor firstly and then turns to be a donor along the reaction coordinate, and the stepwise pathway can be regarded as a coupling of two different pathways with or without benzene involved. Additionally, it's revealed that charge transfer between the reactants and zeolite mainly occurs via the acidic proton of zeolite and the charge variation of the transition state referred to its precursor is proportional to the corresponding energy barrier.