Dynamics of benzene, cyclohexane and n-hexane in KL zeolite studied by 2H NMR

Sato, Takayuki; Kunimori, Kimio; Hayashi, Shigenobu

doi:10.1039/a903786a

Cited by 35 publications

(43 citation statements)

References 16 publications

(9 reference statements)

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“…After the protonation step, the C1–C2 bond of the aromatic‐based carbenium ion B stretches, and the reaction reaches its isomerization transition‐state structure TS1 in which the methyl group transfers from one carbon atom to the neighboring carbon atom on the benzene ring. It has been experimentally estimated that there is a rotation energy barrier of the protonation species around its C 2 axis 28. 29 The geometrical structure of TS1 is shown in Figure 4 a, which gives an indication of its vibrational mode.…”

Section: Resultsmentioning

confidence: 99%

ONIOM Study of Isomerization Reactions of Aromatic Hydrocarbons in Acidic Mordenite Zeolite

Yang

2009

ChemPhysChem

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Two different mechanisms: Shift 1,2-isomerization and isomerization via the disproportionation reaction are investigated for aromatic hydrocarbons over acidic mordenite zeolite by using our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) scheme. The picture shows a schematic energy profile for the isomerization of toluene catalyzed by acidic mordenite.The geometrical structures and energies of isomerization reactions of aromatic hydrocarbons catalyzed by the 128T cluster model of acidic mordenite zeolite are studied by using our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) scheme. The aromatic hydrocarbons investigated are toluene, xylenes, and trimethylbenzenes. Two proposed intramolecular reaction mechanisms, that is, shift 1,2-isomerization and isomerization via the disproportionation reaction, are studied and discussed in detail. Both of the mechanisms firstly proceed by protonation of aromatic hydrocarbons to form the aromatic-based carbenium ions. Attempts to determine the prevailing reaction mechanism of the isomerization are evaluated. In most cases, the isomerization reactivity sequence is: trimethylbenzenes>xylenes>toluene. The conclusions obtained using the ONIOM scheme agree with the available periodic DFT and experimental results on acidic mordenite zeolite.

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Section: Resultsmentioning

confidence: 99%

ONIOM Study of Isomerization Reactions of Aromatic Hydrocarbons in Acidic Mordenite Zeolite

Yang

2009

ChemPhysChem

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“…It was reported that the apparent activation energy is 28 kJ mol À1 for the jump motion of benzene molecules interacting with K + ions in KL zeolite. 37 KL zeolite has a one-dimensional channel of 12-menbered rings with a channel opening of 0.71 nm in diameter. The activation energy is increased by the more restricted space in ZSM-5/pNA.…”

Section: H Nmr Of Zsm-5/pna-d With Medium Loading Levelmentioning

confidence: 99%

“…[22][23][24][25] Molecular motions of guest molecules such as benzene and p-xylene in inorganic hosts have been studied extensively by means of 2 H NMR. [26][27][28][29][30][31][32][33][34][35][36][37][38] We have studied the motion of pNA guest molecules in the micropores of ZSM-5 zeolite mainly by solid-state NMR and reported preliminarily that pNA molecules were not in a rigid state when the sample contained about four molecules per unit cell. 39 In the present study, we have measured temperature dependences of the NMR spectra in detail and determined the modes and rates of motions successfully.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of p-nitroaniline molecules in siliceous ZSM-5 studied by solid-state NMR

Komori¹,

Hayashi²

2003

Phys. Chem. Chem. Phys.

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Sites and dynamics of p-nitroaniline (pNA) molecules in the micropores of siliceous ZSM-5 zeolite have been investigated by means of solid-state NMR. The adsorbed amounts of pNA studied were about 1.5, 4 and 6 molecules per unit cell of ZSM-5. 2 H NMR and 13 C NMR revealed that the motion of pNA was a 180 flip-flop around the C 2 axis of the molecule when the adsorbed amount was less than four molecules per unit cell. The rate of the motion was about 50 kHz at 297 K, and the apparent activation energy was 57 AE 17 kJ mol À1 . 13 C NMR confirmed the presence of different adsorbed states of pNA when the adsorbed amount was more than four molecules. Furthermore, 2 H NMR revealed that the flip-flop motion of pNA was largely suppressed. These results indicate that the motion of pNA in the micropores of ZSM-5 depended on the adsorbed amount of pNA, and that the interaction between the guest molecules influenced the dynamics of the guest molecules.

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“…2 H NMR has been shown to be a powerful tool to probe the dynamics of molecular species confined in microporous materials. [18][19][20][21][22][23][24] The spectrum line shape and spin relaxation of 2 H nuclei is mainly governed by electric intramolecular quadrupolar interaction, 25,26 which gives the possibility to characterize the molecular dynamics over a broad time scale from 10 -4 -10 -6 s to 10 -8 -10 -10 s, respectively.…”

Section: Introductionmentioning

confidence: 99%

Mobility of n-Butane in ZSM-5 Zeolite Studied by ²H NMR

2010

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The mobility of linear alkane, n-butane, adsorbed in zeolite ZSM-5 was investigated by deuterium solid-state NMR ( 2 H NMR). Analysis of the 2 H NMR spectra line shape and spin-lattice relaxation time permitted characterizing the influence of pore confinement on the dynamics of the molecule over a broad temperature range (123-413 K). It has been found, that at a loading of two molecules per unit cell, n-butane molecules are essentially located in both straight and zigzag channels and not the intersections. The adsorbed molecules are involved in fast intramolecular motions and reorientation as a whole. Intramolecular motions are methyl group rotation and conformational exchange occurring at τ ≈ 4-8 × 10 -11 s (at 300 K) with an activation barrier of E ci ≈ 11-12 kJ mol -1 . The reorientation of the molecule as whole is a complex anisotropic motion, which consists of jump exchange between neighboring channels, occurring at τ D ≈ 3.7 × 10 -10 s (at 300 K) with an activation barrier of E D ≈ 5 kJ mol -1 and of other rotational modes that may correspond to uniaxial rotation and librations of n-butane in the pores. Influence of pore confinement on the dynamics of the adsorbed alkane is manifested by the complete suppression of isotropic reorientation.

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Dynamics of benzene, cyclohexane and n-hexane in KL zeolite studied by 2H NMR

Cited by 35 publications

References 16 publications

ONIOM Study of Isomerization Reactions of Aromatic Hydrocarbons in Acidic Mordenite Zeolite

ONIOM Study of Isomerization Reactions of Aromatic Hydrocarbons in Acidic Mordenite Zeolite

Dynamics of p-nitroaniline molecules in siliceous ZSM-5 studied by solid-state NMR

Mobility of n-Butane in ZSM-5 Zeolite Studied by ²H NMR

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Dynamics of benzene, cyclohexane and n-hexane in KL zeolite studied by 2H NMR

Cited by 35 publications

References 16 publications

ONIOM Study of Isomerization Reactions of Aromatic Hydrocarbons in Acidic Mordenite Zeolite

ONIOM Study of Isomerization Reactions of Aromatic Hydrocarbons in Acidic Mordenite Zeolite

Dynamics of p-nitroaniline molecules in siliceous ZSM-5 studied by solid-state NMR

Mobility of n-Butane in ZSM-5 Zeolite Studied by 2H NMR

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Mobility of n-Butane in ZSM-5 Zeolite Studied by ²H NMR