A Raman Study of Fluorinated Ethanes Adsorbed on Zeolite NaX
Due to the destructive effect of chlorofluorocarbons (CFCs) upon the ozone layer, the major global producers of CFCs have agreed to cease production by 1996. As a result of this agreement there is a need to find replacements for CFCs in a number of applications. Hydrofluorocarbons (HFCs) offer reasonably effective alternatives in uses such as refrigeration and air conditioning. One of the primary replacements for CFCs such as CFC-12 (CF2CI2) for use in automobile air conditioners is HFC 134a (CF3CFH2). HFC 134 (CF2HCF2H), an isomer of 134a, is also a potentially useful HFC. A number of routes in the syntheses of these HFCs involve the use of heterogeneous catalysts to improve the efficiency and specificity of the chemical reaction sequences. Since the HFCs interact with the catalyst surface, it is of general interest to understand the nature of these molecule-surface interactions. For this reason we have undertaken this study of the adsorption of HFCs 134, 134a, and 143 (CF2HCFH2) on the zeolite NaX (Na86Al86Si106O384). Zeolites have found wide application as heterogeneous catalysts and sorbs in many industrial chemical processes, and from our perspective they have the advantages of large surface areas and relatively weak Raman scattering. These features make zeolites ideal hosts for studies of molecule-surface interactions. Furthermore, NaX binds the HFC molecules nondissociatively at room temperature with high enough number densities to produce reasonably intense Raman bands.
KeywordsRaman Band Permanent Dipole Moment Trans Conformer Microwave Spectroscopy Gauche Conformer
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