Thermodynamic Insight into Thermal Cracking of n-Hexane in the H-FAU Zeolite

Abstract

To understand catalytic cracking processes of alkanes in the petrochemical industry, the monomolecular cracking mechanism of n-hexane in the H-FAU zeolite has been examined using ab initio molecular dynamics simulations combined with enhanced sampling techniques. It has been found that the adsorption energies of short n-alkanes are linearly correlated with the chain length and contact areas with the zeolite framework, while no such correlation can be applied to the short n-alkenes. High-dimensional free energy landscapes characterizing four cracking modes of n-hexane at three different temperatures have been drawn. The electron transfer in the cracking process was analyzed by quantifying the charge evolution for carbon atoms. The formation of carbonium ions in each cracking mode is found to be the rate-limiting step. At high temperature, free energy differences are nonpositive values, suggesting that the cracking of n-hexane is spontaneous, which is also coincident with the experimental observation. The cracking of the central C–C bond of n-hexane is easier than the cracking of terminal C–C bonds, which is due to the lower free energy barrier. The present work sheds new insights into the cracking process of n-alkanes in the industrially used FAU zeolite catalysts.

Highly Active Palladium-Containing FAU Zeolite Catalyst for Suzuki–Miyaura Reaction

“…Additionally, it has been evidenced that H-type zeolite matrices exhibit greater electrophilicity compared to their Na-type counterparts, influencing the charge distribution on metal species embedded within the framework . Further, the presence of these acidic sites may intensify the interactions between reactant molecules and the zeolite framework, resulting in modulations of catalytic reactivity . This could shed light on the observation that Pd/zeolite catalysts possessing acidic sites exhibit expedited reaction rates compared to their nonacidic counterparts.…”

“…40 Further, the presence of these acidic sites may intensify the interactions between reactant molecules and the zeolite framework, resulting in modulations of catalytic reactivity. 41 This could shed light on the observation that Pd/ zeolite catalysts possessing acidic sites exhibit expedited reaction rates compared to their nonacidic counterparts. However, this accelerated catalysis may prompt a swifter formation of the Pd(0) species.…”

Zeolites synthesized from agro‐industrial residues applied in agriculture: A review and future prospects

“…The high thermal stability of zeolites (from 600 to 1100°C, in the function of the structural and compositional characteristics), physical and chemical stability, and the voids with active sites within the structure enable their application as catalysts. Because of these characteristics, zeolites are used in catalytic cracking in the petrochemical industry (Alaithan, 2022; Liu et al., 2023; Zhang, Bin Samsudin, et al., 2022; Zhang, Li, et al., 2022).…”

Understanding the Hydrocracking of Polycyclic Aromatic Hydrocarbons within FAU Zeolites: Hydrogen Splitting Catalyzed by the Frustrated Lewis Pair

“…Preorganized Lewis donor/acceptor pair interacts with H 2 in a synergistic manner, resulting in the heterolytic H-H bond cleavage. , Recently, the FLP concept was extended into heterogeneous zeolitic catalysis. Due to the coexistence of aluminum and silicon in the framework of zeolites, Brønsted and Lewis acid sites , are separately and/or synergistically concerned with catalytic conversion processes. − The ionic FLP site composed of deprotonated Brønsted acid site (deBAS) and protonated PAHs stabilizing proton and hydride separately was proposed as the catalytic center for alkane activation and the hydrocracking of dihydroanthracenes (DHAs) . While another combination of the FLP, viz., the molecular FLP consisting of the Lewis acid site (LAS) (electron/hydride acceptor) and the neutral aromatic ring (electron donor/proton acceptor), has never been examined for the hydrocracking processes.…”

“…16,17 Recently, the FLP concept was extended into heterogeneous zeolitic catalysis. Due to the coexistence of aluminum and silicon in the framework of zeolites, Brønsted and Lewis acid sites 18,19 are separately and/or synergistically concerned with catalytic conversion processes. 20−22 The ionic FLP site composed of deprotonated Brønsted acid site (deBAS) and protonated PAHs stabilizing proton and hydride separately was proposed as the catalytic center for alkane activation 23 and the hydrocracking of dihydroanthracenes (DHAs).…”