A theoretical investigation into thiophenic derivative cracking mechanism over acidic and cation-exchanged beta zeolites

Mao, Xinfeng; Sun, Yi; Pei, Supeng

doi:10.1016/j.comptc.2015.10.019

Cited by 3 publications

(7 citation statements)

References 55 publications

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“…In our previous study, , we have proposed two reaction mechanisms of HDS process of thiophene molecules over acidic zeolites: unimolecular and bimolecular cracking mechanisms. The corresponding pathways are given in Schemes and .…”

Section: Resultsmentioning

confidence: 99%

“…It is well-known that the bare cluster model cannot explain the influence of the zeolite framework, and the periodic DFT approach is too expensive to treat a large zeolite framework. A recently developed quantum mechanical/molecular mechanical (QM/MM) method as well as the more general ONIOM (Our-own-N-layered Integrated molecular Orbital + molecular Mechanics) scheme have been extensively used to explore the catalytic mechanisms in zeolites. − The scheme combines the advantages of the high accuracy of quantum mechanics calculations and the high efficiency of the molecular mechanics force field. We have investigated successfully several reaction mechanisms on the desulfurization process of thiophene catalyzed by zeolites using the QM/MM method in previous studies as mentioned above. , …”

Section: Introductionmentioning

confidence: 99%

“…They revealed that in the whole loading range, the thiophene adsorption mechanism could be divided into two parts: ideal adsorption and insertion adsorption. 18 In our recently published studies, two-layer ONIOM calculations were performed on C−S bond cracking of a thiophenic derivative over H-Beta 19 and HDS of thiophene over H-FAU zeolite. 20 The calculated results suggested that a bimolecular HDS mechanism is more favorable due to the lower activation barriers.…”

Section: Introductionmentioning

confidence: 99%

“…We have investigated successfully several reaction mechanisms on the desulfurization process of thiophene catalyzed by zeolites using the QM/MM method in previous studies as mentioned above. 19,20 In this work, the HDS reaction mechanism of thiophene in a series of acidic zeolites such as H-Beta, H-FAU, H-MCM-22, and H-ZSM-5 was investigated by a two-layer ONIOM study. These four zeolites are typical catalysts and have wide applications in the petrochemical industry.…”

Section: Introductionmentioning

confidence: 99%

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Understanding the Nature of Transition States in the Confined Nanospace of Different Acidic Zeolites on the Desulfurization Mechanism of Thiophene

et al. 2018

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We have presented a two-layer ONIOM study on the unimolecular and bimolecular hydrodesulfurization (HDS) mechanisms of thiophene catalyzed by H-Beta, H-MCM-22, H-ZSM-5, and H-FAU zeolites. The rate-determining step for HDS is the hydrogenation step. The bimolecular desulfurization mechanism is more favorable to occur due to the lower free energy barriers, which is in good accord with experimental observations. Hammond's postulate was validated by analyzing the thermodynamics and geometrical structures of transition states (TSs). The difference charge density (DCD), reduced density gradient (RDG), localized orbital locator (LOL), and Fukui functions were used to understand the nature of the TSs. For the dimerization step of two thiophene molecules, the DCD analysis indicates a dramatic electron transfer from the thiophene fragment to the hydrothiophene fragment in the TS. High LOL values between two α-C atoms of two thiophene rings indicate a strong interaction and a high degree of covalence between these two C atoms. For the step of H 2 S formation, a DCD analysis suggests a clear electron transfer from the H 2 S fragment to the organic carbon chain in the TS; the plots of RDG and LOL indicate a weak interaction between the C atom of the organic chain and the H 2 S fragment. The confined nanospace in zeolite has important stabilization effects on TSs and intermediates. The calculated results suggest that almost all the reaction steps in the unimolecular and bimolecular mechanisms on four zeolites are entropy-decreased processes. The stabilization effect of the ZSM-5 framework mainly originates from the VDW attractive interactions. The classic electrostatic interactions favor the formation of all the TSs on MCM-22. In the bimolecular mechanism, the behaviors of TSs in Beta are contrary to those in ZSM-5; the electrostatic interactions favor the formation of TSs over FAU, but no clear variation trend of VDW interactions is found.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Understanding the Nature of Transition States in the Confined Nanospace of Different Acidic Zeolites on the Desulfurization Mechanism of Thiophene

et al. 2018

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“…In all geometry optimization calculations, all atoms within the cluster were relaxed, except for the terminal H-atoms that were kept fixed. The methodology that we employed in this work has been previously applied and validated by different authors for the computational study of zeolites, such as MFI, , BEA, , and FAU. , The partial atomic charges were obtained with the natural bond orbital (NBO) population analysis . Vibrational frequencies were calculated for each optimized structure, within the rigid rotor, harmonic oscillator approximation.…”

Section: Methodsmentioning

confidence: 99%

DFT Study on the Effect of Aluminum Position in Zn-Exchanged MFI on Methane Activation

2019

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The position of aluminum atoms in ion-exchanged zeolites is known to affect the reactivity of active sites. In this work, we used density functional theory (DFT) calculations to systematically quantify the effect of the Al-atom position within the α-ring of Zn-exchanged MFI (Zn-MFI) on the activation of methane. Our DFT results indicate that the most stable configuration for the Zn-exchanged cluster of the α-ring is obtained when the Al atoms are located at the T11-T2 crystallographic sites. For each Al-atom configuration, we analyzed the reaction pathways for methane activation. Our results suggest that the activation of methane yields the formation of a Brønsted acid site, which can be formed at an oxygen atom within the α-ring or at an oxygen atom that lies outside the α-ring, and that the lowest reaction energy for methane activation is obtained when the Brønsted acid site is formed at the oxygen atom in which the highest occupied molecular orbital of the isolated cluster is located. Furthermore, our results indicate that the partial atomic charge of the Zn atom within the α-ring of MFI can be correlated with the transition-state energy of methane activation, which ranges from 87 to 131 kJ/mol depending on the location of Al atoms. The fundamental studies conducted in this work contribute to the elucidation of essential parameters and correlations, based on electrostatic and electron density, for the activation of methane on Zn-MFI zeolites.

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A DFT study on catalytic oxidative desulfurization with H2O2 over Ti-MWW zeolite

Wang

Lin

2019

J Mol Model

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A theoretical investigation into thiophenic derivative cracking mechanism over acidic and cation-exchanged beta zeolites

Cited by 3 publications

References 55 publications

Understanding the Nature of Transition States in the Confined Nanospace of Different Acidic Zeolites on the Desulfurization Mechanism of Thiophene

Understanding the Nature of Transition States in the Confined Nanospace of Different Acidic Zeolites on the Desulfurization Mechanism of Thiophene

DFT Study on the Effect of Aluminum Position in Zn-Exchanged MFI on Methane Activation

A DFT study on catalytic oxidative desulfurization with H2O2 over Ti-MWW zeolite

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