Adsorption of Hydrogen in Ca-Exchanged Na-A Zeolites Probed by Inelastic Neutron Scattering Spectroscopy

Eckert, Juergen; Nicol, Jacqueline M.; Howard, Joseph; Trouw, F.

doi:10.1021/jp952982d

Cited by 49 publications

(33 citation statements)

References 22 publications

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“…There have been a number of experimental studies of H 2 and its isotopes within or on the surface of solids such as the rare gases, 7 alkali-metal halides, 8,9 silica, 10 zeolites, [11][12][13][14][15] and carbon nanotubes, 16 along with GaAs 17 and silicon. 18 -20 In some of the former cases, purely vibrational transitions have been detected in IR.…”

Section: H 2 Within or On The Surface Of Solidsmentioning

confidence: 99%

Dynamics of interstitialH2in crystalline silicon

2002

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The dynamics of interstitial H 2 and its isotopes in crystalline silicon have been studied by using a potentialenergy function for the molecule that consists of the superposition of potentials for two separated hydrogen atoms as generated from the quantum-mechanical calculations of Porter, Towler, and Needs. The rotational properties were calculated using the approach of Martin and Fowler and the vibrational properties of the molecules as a whole were obtained. The results of these calculations indicate nearly free rotational motion, consistent with shallow rotational potentials. Confinement of the molecules leads to center-of-mass vibrations of a few hundred wave numbers and dynamical ''off-centeredness'' that breaks tetrahedral symmetry and allows purely vibrational transitions to occur. This approach has also been used to investigate tetrahedral interstitial H 2 adjacent to a bond-centered oxygen atom. The results of these calculations provide a framework for understanding the rovibrational properties of H 2 and O-H 2 and their isotopes, including experiments involving uniaxial stress.

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Section: H 2 Within or On The Surface Of Solidsmentioning

confidence: 99%

Dynamics of interstitialH2in crystalline silicon

2002

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“…6,7,[9][10][11][12][20][21][22][23][24][25][26][27][28] The IR lines identified in these papers have been attributed to intramolecular vibrational motions, centerof-mass ͑CM͒ motions, and rotational motions coupled to intramolecular vibrations. Neutron studies [29][30][31][32][33][34] have revealed information about translational motions, and importantly, about hindered rotational levels inaccessible to IR because the transitions involve the flipping of a nuclear spin.…”

Section: A Adsorbate Locations and Orientationsmentioning

confidence: 99%

“…Consider the INS study of H 2 in Na-Ca-A. 30 A line at approximately 5.6 meV in the H 2 spectrum naturally seemed to correspond to a line at 4 meV in the D 2 spectrum. While the ratio of these energies is in excellent agreement with the CM vibrational isotope effect, the line was determined not to be a CM vibration, but rather a rotation, because it was absent on the energy-loss side of the HD spectrum.…”

Section: A Adsorbate Locations and Orientationsmentioning

confidence: 99%

“…Analysis based on neutron experiment assigns roughly the same simple twofold rotational barrier to H 2 in Na-A as it does to Ca-Na-A: the 6.4 kJ/mol mentioned earlier. 30 We have estimated ⌬E from a sample trajectory in our zeolite model. A trajectory of 500 steps was generated at a temperature of Tϭ77 K with the bond length corresponding to B 0 in Eq.…”

Section: F Comparison With Ir Experimentsmentioning

confidence: 99%

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Computational study of molecular hydrogen in zeolite Na–A. II. Density of rotational states and inelastic neutron scattering spectra

MacKinnon

Eckert

Coker

et al. 2001

The Journal of Chemical Physics

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Articles you may be interested inProbing the hydrogen equilibrium and kinetics in zeolite imidazolate frameworks via molecular dynamics and quasi-elastic neutron scattering experiments J. Chem. Phys. 138, 034706 (2013); 10.1063/1.4774375An inelastic incoherent neutron scattering study of water in small-pored zeolites and other water-bearing minerals Computational study of molecular hydrogen in zeolite Na-A. I. Potential energy surfaces and thermodynamic separation factors for ortho and para hydrogen Part I of this series ͓J. Chem. Phys. 111, 7599 ͑1999͔͒ describes a simulation of H 2 adsorbed within zeolite Na-A in which a block Lanczos procedure is used to generate the first several ͑9͒ rotational eigenstates of H 2 , modeled as a rigid rotor, and equilibrated at a given temperature via Monte Carlo sampling. Here, we show that rotational states are strongly perturbed by the electrostatic fields in the solid. Wave functions and densities of rotational energy states are presented. Simulated neutron spectra are compared with inelastic neutron scattering data. Comparisons are made with IR spectra in which rotational levels may appear due to rovibrational coupling.

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“…In Figure 7 we have assumed an arbitrary amplitude for each contribution to fit the data. The values for the excitation levels shown in Figure 7 are very different from the principal adsorption energies of ~80 K and ~40 K, respectively, for the S1 and S2 bonding sites for hydrogen in zeolite-13X as determined from neutron scattering experiments [29,30]. The S1 sites are at the centers of the six-membered rings adjacent to the eight-sided opening of the α-supercages of the zeolite structure, and the S2 sites are located close to the octagonal openings of the α-supercages.…”

Section: Resultsmentioning

confidence: 96%

Interactions and Diffusion of Methane and Hydrogen in Microporous Structures: Nuclear Magnetic Resonance (NMR) Studies

Sullivan

Tang

et al. 2013

Materials

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Measurements of nuclear spin relaxation times over a wide temperature range have been used to determine the interaction energies and molecular dynamics of light molecular gases trapped in the cages of microporous structures. The experiments are designed so that, in the cases explored, the local excitations and the corresponding heat capacities determine the observed nuclear spin-lattice relaxation times. The results indicate well-defined excitation energies for low densities of methane and hydrogen deuteride in zeolite structures. The values obtained for methane are consistent with Monte Carlo calculations of A.V. Kumar et al. The results also confirm the high mobility and diffusivity of hydrogen deuteride in zeolite structures at low temperatures as observed by neutron scattering.

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Adsorption of Hydrogen in Ca-Exchanged Na-A Zeolites Probed by Inelastic Neutron Scattering Spectroscopy

Cited by 49 publications

References 22 publications

Dynamics of interstitialH2in crystalline silicon

Dynamics of interstitialH2in crystalline silicon

Computational study of molecular hydrogen in zeolite Na–A. II. Density of rotational states and inelastic neutron scattering spectra

Interactions and Diffusion of Methane and Hydrogen in Microporous Structures: Nuclear Magnetic Resonance (NMR) Studies

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