DFT—Quantum chemical study of the HZSM-5-cyclohexene interaction pathways

Cuán, A.; Martínez-Magadán, José Manuel; García–Cruz, Isidoro; Galván, Marcelo

doi:10.1016/j.molcata.2005.04.021

Cited by 5 publications

(3 citation statements)

References 36 publications

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“…To evaluate the chemical potential and the hardness as a reactivity global parameter from the equations 4 and 5, the corresponding values are 4.63 eV and 1.68 eV for the neutral azomethine and 8.28 eV and 1.48 eV for the protonated, respectively. The proton affinity calculated for the azomethine is of 231.55 Kcal/mol, so far, the current results for the model representation give a good description of the system, also in line with previous literature reports (16,17). The obtained values for the global reactivity descriptor (η) indicates that the protonated azomethine becomes less hard, i.e., more soft than the neutral species.…”

Section: Resultssupporting

confidence: 90%

Theoretical Study of pH Stability of Azomethine Based on Hardness Calculations

et al. 2009

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The behavior of neutral and protonated azomethine has been investigated by means of quantum-chemical calculations of its structural and electronic properties. The most stable structural configuration has been optimized at the B3LYP/6311G (d,p) level of theory where a dihedrical angle of 24 degrees from the molecule base C-C-N-C has been obtained. The distribution of the HOMO and LUMO isosurface of both neutral and protonated azomethine molecules was also obtained and discussed. Hardness values of the species involved show that protonated azomethine is more reactive than neutral since its softness value is higher than the latter species which indicates protonated species is more susceptible to chemical transformation or self-decomposition. Furthermore, the IR spectra of the species aforementioned were successfully calculated and reproduced in order to compare both chemical systems in detail.

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Section: Resultssupporting

confidence: 90%

Theoretical Study of pH Stability of Azomethine Based on Hardness Calculations

et al. 2009

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“…The proton affinity calculated for the neutral AD to form protonated AD is of 240.96 Kcal/mol. The current results for the model representation give a good description of the system, also in line with previous literature reports (8)(9)(10).…”

Section: Ecs Transactions 29 (1) 421-431 (2010)supporting

confidence: 91%

Quantum Chemical Calculations in Stepwise Adrenaline Deprotonation

et al. 2010

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Theoretical calculations of adrenaline structures formed during the in-vacuo deprotonation were performed using the DFT approach. The electronic properties of these chemical structures such as the atomic charge, the HOMO-LUMO electron distribution and its energy associated are presented and discussed. According to our results, the proton loss is more feasible during the deprotonation process of the amino group followed by cathecol aromatic ring deprotonation and then by the hydrogen loss of the aliphatic hydroxyl group. In fact, the results of the energy values of the latter deprotonation process indicate that it is very unlikely that the aliphatic OH group might loss its proton since it yields unstable chemical species. Under biological pH environment, adrenaline is a fully protonated species which avoids the amino group might be modified by oxidation-reduction reactions. This causes, however, that the cathecol aromatic ring be sensitive to chemical modification by the aforementioned reactions since adrenaline electronic properties are modified by the protonated amino group. This indicates that orbital re-distribution of the molecule might occur due to the proton presence.

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“…Some cyclic cations have been experimentally observed to be important long-lived intermediates in some reactions of hydrocarbons on zeolites. 52 A DFT study of the cyclohexene interaction in H-ZSM-5 53 revealed the formation of carbenium species instead of alkoxides as local energy minima. The bulkiness of cyclic carbenium with respect to non-cyclic ones may indeed be a factor of easier stabilization of cyclic carbenium, preventing the approach to framework oxygen atoms.…”

Section: Introductionmentioning

confidence: 99%

Location of the Active Sites for Ethylcyclohexane Hydroisomerization by Ring Contraction and Expansion in the EUO Zeolitic Framework

et al. 2019

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Identifying the location of the active sites in a zeolite is a current challenge, impeding the design of optimal catalysts. In this work, we identify the location of the most active sites of 1-ethylcyclohexene isomerization in the EUO framework (10 MR channels, 12 MR side pockets), thanks to DFT calculations corroborated by experiments. Skeletal isomerization of cycloalkenes is a crucial industrial reaction for the bifunctional isomerization of ethylbenzene. Ethylcyclohexene is protonated by framework protons into cyclic carbenium ions, which undergo ring contraction-expansion reactions through protonated cyclopropane (PCP) like transition states. Ab initio calculations clearly show that the acid sites located at the intersection between the channel and the pocket stabilize much less the cyclic carbenium ions involved in the reaction than 12 MR pockets and 10 MR channel sites, due to stronger dispersion stabilizing interactions. This computational finding is fully confirmed experimentally by the comparison of the catalytic performances of the H-EU-1 and H-ZSM-50 zeolites in ethylcyclohexane hydroisomerization. Both zeolites possess the EUO structure, but with different location of the acid sites. The ratio in turnover frequencies is quantitatively rendered by the DFT calculated free energy profiles. Diffusion measurements reveal similar ethylcyclohexane diffusion times for the two zeolites, supporting that the difference in activity is primarily driven by the location of the active sites.

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DFT—Quantum chemical study of the HZSM-5-cyclohexene interaction pathways

Cited by 5 publications

References 36 publications

Theoretical Study of pH Stability of Azomethine Based on Hardness Calculations

Theoretical Study of pH Stability of Azomethine Based on Hardness Calculations

Quantum Chemical Calculations in Stepwise Adrenaline Deprotonation

Location of the Active Sites for Ethylcyclohexane Hydroisomerization by Ring Contraction and Expansion in the EUO Zeolitic Framework

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