Effect of pore characteristics on the dynamics of cyclohexane molecules confined in ZSM-5 and MCM-41 molecular sieves: FTIR and QENS study

Sahasrabudhe, A.; Mitra, S.; Tripathi, A. K.; Mukhopadhyay, R.; Gupta, Nandini

doi:10.1039/b303782g

Cited by 24 publications

(30 citation statements)

References 35 publications

(57 reference statements)

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“…The properties of water in organized pores with one-dimensional tubes and two-dimensional nanosheets have been established using experimental and computational techniques. Various experimental techniques, including quasielastic neutron scattering (QENS) 15 , vibrational spectroscopy, and NMR have been used to investigate the properties of fluids in confined spaces 16 – 19 . The translational and rotational dynamics of water are highly sensitive to size and surface charges.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulation of Water Confinement in Disordered Aluminosilicate Subnanopores

Ohkubo

Gin

Collin

et al. 2018

Sci Rep

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The porous structure and mass transport characteristics of disordered silicate porous media were investigated via a geometry based analysis of water confined in the pores. Disordered silicate porous media were constructed to mimic the dissolution behavior of an alkali aluminoborosilicate glass, i.e., soluble Na and B were removed from the bulk glass, and then water molecules and Na were introduced into the pores to provide a complex porous structure filled with water. This modelling approach revealed large surface areas of disordered porous media. In addition, a number of isolated water molecules were observed in the pores, despite accessible porous connectivity. As the fraction of mobile water was approximately 1%, the main water dynamics corresponded to vibrational motion in a confined space. This significantly reduced water mobility was due to strong hydrogen-bonding water-surface interactions resulting from the large surface area. This original approach provides a method for predicting the porous structure and water transport characteristics of disordered silicate porous media.

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Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulation of Water Confinement in Disordered Aluminosilicate Subnanopores

Ohkubo

Gin

Collin

et al. 2018

Sci Rep

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“…However, it is worth noting that the authors gained a great deal of insight from the comparison with structural studies and simulations to show how both the orientation and location of m-and p-xylene isomers lead to this methyl rotation blocking. Cyclohexane rotation in H-ZSM-5 has also been studied [47] and through the fitting of a 3-site jump rotation model it was concluded that cyclohexane was in the chair conformation, the D 3d symmetry of which would allow for such rotations to be observed with a residence time of 8.2 ps at room temperature. We note that this is roughly twice as fast as that found for our methyl groups in dimehylhexane which, given the size of the cyclohexane molecule/circle around which the protons are jumping, may seem strange.…”

Section: (B) 25-dimethylhexane Dynamicsmentioning

confidence: 99%

Octane isomer dynamics in H-ZSM-5 as a function of Si/Al ratio: a quasi-elastic neutron scattering study

O’Malley

Sakai

Dimitratos

et al. 2020

Phil. Trans. R. Soc. A.

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Dynamical behaviour of n- octane and 2,5-dimethylhexane in H-ZSM-5 zeolite catalysts of differing Si/Al ratios (15 and 140) was probed using quasi-elastic neutron scattering, to understand molecular shape and Brønsted acid site density effects on the behaviour of common species in the fluid catalytic cracking (FCC) process, where H-ZSM-5 is an additive catalyst. Between 300 and 400 K, n -octane displayed uniaxial rotation around its long axis. However, the population of mobile molecules was larger in H-ZSM-5(140), suggesting that the lower acid site concentration allows for more molecules to undergo rotation. The rotational diffusion coefficients were higher in H-ZSM-5(140), reflecting this increase in freedom. 2,5-dimethylhexane showed qualitative differences in behaviour to n -octane, with no full molecule rotation, probably due to steric hindrance in the constrictive channels. However, methyl group rotation in the static 2,5-dimethylhexane molecules was observed, with lower mobile fractions in H-ZSM-5(15), suggesting that this rotation is less hindered when fewer Brønsted sites are present. This was further illustrated by the lower activation barrier calculated for methyl rotation in H-ZSM-5(140). We highlight the significant immobilizing effect of isomeric branching in this important industrial catalyst and show how compositional changes of the zeolite can affect a range of dynamical behaviours of common FCC species upon adsorption. This article is part of a discussion meeting issue ‘Science to enable the circular economy’.

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“…To understand the dynamics and binding states of various hydrocarbon molecules adsorbed in different sizes of pores in different zeolites, we have studied benzene, cyclohexane, methanol, propylene etc. in ZSM-5 zeolites [6][7][8] and propane, acetylene, 1,3-butadiene, and propylene molecules in Na-Y zeolite [9][10][11][12][13]. Various combinations of guest and host systems were considered.…”

Section: Hydrocarbons Adsorbed In Zeolitesmentioning

confidence: 99%

Molecular motion in restricted geometries

2008

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Molecular dynamics in restricted geometries is known to exhibit anomalous behaviour. Diffusion, translational or rotational, of molecules is altered significantly on confinement in restricted geometries. Quasielastic neutron scattering (QENS) offers a unique possibility of studying molecular motion in such systems. Both time scales involved in the motion and the geometry of motion can be studied using QENS. Molecular dynamics (MD) simulation not only provides insight into the details of the different types of motion possible but also does not suffer limitations of the experimental set-up. Here we report the effect of confinement on molecular dynamics in various restricted geometries as studied by QENS and MD simulations. An example where the QENS technique provided direct evidence of phase transition associated with change in the dynamical behaviour of the molecules is also discussed.

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Effect of pore characteristics on the dynamics of cyclohexane molecules confined in ZSM-5 and MCM-41 molecular sieves: FTIR and QENS study

Cited by 24 publications

References 35 publications

Molecular Dynamics Simulation of Water Confinement in Disordered Aluminosilicate Subnanopores

Molecular Dynamics Simulation of Water Confinement in Disordered Aluminosilicate Subnanopores

Octane isomer dynamics in H-ZSM-5 as a function of Si/Al ratio: a quasi-elastic neutron scattering study

Molecular motion in restricted geometries

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