Three-Dimensional Kinetic Trends in Zeolites Catalyzed Benzene Ethylation Reaction: A Descriptor-Based DFT Study Coupled with Microkinetic Modeling

In zeolite catalysis, both the Bronsted acidity (e.g., acid strength) and reaction conditions (e.g., temperature) have significant influence on catalytic performance. Because of the intimate coupling between acidity-relevant enthalpies and temperature-relevant entropies, it has been challenging to locate the optimal reactivity zone for a given reaction. Here, periodic DFT calculations combined with microkinetic modeling were employed to investigate the effect of both acid strength and reaction temperature simultaneously on benzene ethylation reaction in MFI-structured zeolites involving both the concerted and stepwise pathways. The acid strength using the adsorption energy of ammonia as a descriptor was tailored by two strategies of the isomorphic substitution of heteroatoms and the introduction of extra-framework cations. Good scaling relations were established between the enthalpies of involved transition states and intermediates and the descriptor of acid strength. We pioneered the revelation a three-dimensional activity plot varying with the acid strength and reaction temperature. Three regions with diverse kinetic trends and two boundaries signifying the maximum activity were theoretically demonstrated in benzene ethylation. Subsequent kinetic analyses rationalized these intriguing properties and indicated that the rate-limiting step actually changes with the acid strength. The results hold broad implications for understanding Bronsted acid catalyzed reactions and developing robust catalysts in the future.