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Neutron and Raman Spectroscopes of 134 and 134a Hydrofluorocarbons Encaged in Na-X Zeolite

Published online by Cambridge University Press:  22 February 2011

T. J. Udovic ,
J. M. Nicol ,
R. R. Cavanagh ,
J. J. Rush ,
M. K. Crawford ,
C. P. Grey  and
D. R. Corbin
T. J. Udovic
Affiliation:
National Institute of Standards and Technology, Gaithersburg, MD 20899
J. M. Nicol
Affiliation:
National Institute of Standards and Technology, Gaithersburg, MD 20899
R. R. Cavanagh
Affiliation:
National Institute of Standards and Technology, Gaithersburg, MD 20899
J. J. Rush
Affiliation:
National Institute of Standards and Technology, Gaithersburg, MD 20899
M. K. Crawford
Affiliation:
E. I. Du Pont de Nemours and Company, Experimental Station, Wilmington, DE 19880
C. P. Grey
Affiliation:
E. I. Du Pont de Nemours and Company, Experimental Station, Wilmington, DE 19880
D. R. Corbin
Affiliation:
E. I. Du Pont de Nemours and Company, Experimental Station, Wilmington, DE 19880
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Abstract

Inelastic neutron scattering methods were used in conjunction with Raman spectroscopy to probe the vibrational density of states of the hydrofluorocarbons (HFCs) 134 (HF2C-CF2H) and 134a (F3C-CFH2) adsorbed in the cages of dehydrated Na-X zeolite. A comparison of the vibrational spectra of the encaged HFC species with those of their gas-phase analogs indicates that the HFCs adsorb nondissociatively at room temperature and are most likely associated with Na cations in the supercages at the SIII sites. Guest-host interactions are manifested by adsorption-induced perturbations of the gas-phase torsional and C-H stretching vibrations and the presence of additional features presumably due to low-energy whole-molecule vibrations and adsorbate-coupled zeolite framework vibrations. Moreover, although the 134 trans conformer is favored by 5 kJ/mole in the gas phase at 300 K, the gauche conformer seems to be more prevalent in the zeolite at this temperature and below. This suggests that a sizeable fraction of the Na-X adsorption sites provides a stabilizing configuration for the otherwise higher-energy gauche conformation, perhaps due to hydrogen-bonding interactions with the zeolite framework.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 376: Symposium BB – Neutron Scattering in Materials Science , 1994 , 751
Copyright
Copyright © Materials Research Society 1995

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References

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