Rates and Mechanisms of Conversion of Ice Nanocrystals to Ether Clathrate Hydrates:  Guest-Molecule Catalytic Effects at ∼120 K

2006 ◽  
Vol 110 (5) ◽  
pp. 1901-1906 ◽  
Author(s):  
Dheeraj B. Gulluru ◽  
J. Paul Devlin
Keyword(s):  
Guest Molecule ◽  
Clathrate Hydrates ◽  
Catalytic Effects

2H and13C NMR study of guest molecule orientation in clathrate hydrates

1984 ◽  
Vol 2 (1-2) ◽  
pp. 239-247 ◽  
Author(s):  
D. W. Davidson ◽  
C. I. Ratcliffe ◽  
J. A. Ripmeester
Keyword(s):  
Guest Molecule ◽  
Clathrate Hydrates ◽  
Nmr Study

scholarly journals Impact of the Confinement on the Intra-Cage Dynamics of Molecular Hydrogen in Clathrate Hydrates

2016 ◽  
Vol 879 ◽  
pp. 1294-1299
Author(s):  
Margarita Russina ◽  
Evout Kemner ◽  
Ferenc Mezei
Keyword(s):  
Time Scale ◽  
Guest Molecule ◽  
Ambient Pressure ◽  
Jump Diffusion ◽  
Clathrate Hydrates ◽  
Dynamic Heterogeneity ◽  
Temperature Dependent ◽  
Neutron Spectrometer ◽  
Hydrogen Molecules ◽  
Host Structure

We have studied the diffusive mobility of hydrogen molecules confined in different size cages in clathrate hydrates. In clathrate hydrate H2 molecules are effectively stored by confinement in two different size cages of the nanoporous host structure with accessible volumes of about 0.50 and 0.67 nm diameters, respectively. For the processes of sorption and desorption of the stored hydrogen the diffusive mobility of the molecules plays a fundamental role. In the present study we have focused on the dynamics of the H2 molecules inside the cages as one aspect of global guest molecule mobility across the crystalline host structure. We have found that for the two cage sizes different in diameter by only 34 % and in volume by about a factor of 2.4, the dimension can modify the diffusive mobility of confined hydrogen in both directions, i.e. reducing and surprisingly enhancing mobility compared to the bulk at the same temperature. In the smaller cages of clathrate hydrates hydrogen molecules are localized in the center of the cages even at temperatures >100 K. Confinement in the large cages leads to the onset already at T=10 K of jump diffusion between sorption sites separated from each other by about 2.9 Å at the 4 corners of a tetrahedron. At this temperature bulk hydrogen is frozen at ambient pressure and shows no molecular mobility on the same time scale. A particular feature of this diffusive mobility is the pronounced dynamic heterogeneity: only a temperature dependent fraction of the H2 molecules was found mobile on the time scale covered by the neutron spectrometer used. The differences in microscopic dynamics inside the cages of two different sizes can help to explain the differences in the parameters of macroscopic mobility: trapping of hydrogen molecules in smaller pores matching the molecule size can to play a role in the higher desorption temperature for the small cages.

Far infrared absorption and rotational vibrations of the guest molecules in structure I clathrate hydrates between 4.3 and 100 K

1977 ◽  
Vol 55 (10) ◽  
pp. 1777-1785 ◽  
Author(s):  
John E. Bertie ◽  
Stephen M. Jacobs
Keyword(s):  
Ethylene Oxide ◽  
Guest Molecule ◽  
Signal To Noise Ratio ◽  
Michelson Interferometer ◽  
Far Infrared ◽  
Force Constants ◽  
Clathrate Hydrates ◽  
High Signal ◽  
Guest Molecules ◽  
Trimethylene Oxide

The infrared spectra between 330 and 15 cm−1 of the structure I clathrate hydrates of ethylene oxide, cyclopropane, and trimethylene oxide, at 4.3 K are presented. The spectra have an unusually high signal-to-noise ratio made possible by a Michelson interferometer and a silicon bolometer detector which operates at 1.2 K. Rotational vibrations of the guest molecules were observed at 65.0 and 35.6 cm−1 for ethylene oxide and at 69 and 50 cm−1 for trimethylene oxide. Inter-guest coupling of rotational vibrations is small and the two frequencies are assigned to vibrations about different inertial axes. The resulting force constants are 487 and 264 ferg rad−2 for ethylene oxide and 1190 and 1130 ferg rad−2 for trimethylene oxide and are discussed in relation to the barriers to reorientation of the guest molecule. The bands due to these vibrations are fairly sharp at 4.3 K, but are broad and poorly defined at 100 K. The guest and water vibrations interact predominantly through their transition dipoles, although the main contribution to the force constants of the rotational vibrations is from steric forces. The absorption by the water vibrations above 100 cm−1 is very similar for ethylene oxide and cyclopropane hydrates but significantly different for trimethylene oxide hydrate. Strong objections exist to the obvious interpretations of this difference which remains unexplained.

Modeling Dissociation Pressure of Semi-Clathrate Hydrate Systems Containing CO2, CH4, N2, and H2S in the Presence of Tetra-n-butyl Ammonium Bromide

2019 ◽  
Vol 44 (1) ◽  
pp. 15-28 ◽  
Author(s):  
Mohammad Mesbah ◽  
Ebrahim Soroush ◽  
Mashallah Rezakazemi
Keyword(s):  
Gas Phase ◽  
Mass Fraction ◽  
Guest Molecule ◽  
Clathrate Hydrate ◽  
Clathrate Hydrates ◽  
Ammonium Bromide ◽  
Guest Molecules ◽  
Dissociation Pressure ◽  
Tuning Parameters ◽  
Langmuir Adsorption

Abstract In this study, the phase equilibria of semi-clathrate hydrates of methane (CH4), carbon dioxide (CO2), nitrogen (N2), and hydrogen sulfide (H2S) in an aqueous solution of tetra-n-butyl ammonium bromide (TBAB) were modeled using a correlation based on a two-stage formation mechanism: a quasi-chemical reaction that forms basic semi-clathrate hydrates and adsorption of guest molecules in the linked cavities of the basic semi-clathrate hydrate. The adsorption of guest molecules was described by the Langmuir adsorption theory and the fugacity of the gas phase was calculated by Peng–Robinson (PR) equation of state (EOS). The water activity in the presence of TBAB was calculated using a correlation, dependent on temperature, the TBAB mass fraction, and the nature of the guest molecule. These equations were coupled together and form a correlation which was linked to a genetic algorithm for optimization of tuning parameters. The results showed an excellent agreement between model results and experimental data. In addition, an outlier diagnostic was performed for finding any possible doubtful data and assessing the applicability of the model. The results showed that more than 97 % of the data were reliable and they were in the applicability domain of the model.

Decomposition of peroxobenzoic acid in benzene catalyzed by transition metal 2,4-pentanedionates

1984 ◽  
Vol 49 (3) ◽  
pp. 673-679 ◽  
Author(s):  
Pavel Lederer ◽  
Eva Mácová ◽  
Josef Vepřek-Šiška
Keyword(s):  
Transition Metal ◽  
Reaction Rate ◽  
Reaction Products ◽  
Acid Decomposition ◽  
Analogous Experiment ◽  
Catalytic Effects

The decomposition of peroxobenzoic acid in benzene was studied, and catalytic effects of Fe(III), Mn(III), Co(II), Co(III), and Cr(III) on the reaction rate and the composition of the reaction mixture were investigated. An analogous experiment carried out in perdeuterobenzene and determination of the distribution of deuterium in the reaction products provided evidence for the participation of the solvent in peroxobenzoic acid decomposition.

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