Adsorption of trichloro- and trifluoromethane in Y-zeolites as studied by IR spectroscopy and multinuclear solid-state NMR


The adsorption of CH(D)Cl3 and CHF3 on a series of alkali-exchanged Y- zeolites was studied by 1H- and 23Na-NMR and by FTIR spectroscopy. Several adsorption structures were detected which involve H-bonding C-H(D)···O(Z) between the acidic C-H(D) group and basic O(Z)-framework atoms and between the exchangeable cations and halogen atoms of the probe molecules. 1H-NMR demonstrated rapid exchange between several adsorption species and IR spectroscopy permitted detection of at least two different species, namely purely H-bonded species I and species II and/or III involving cation-halogen interactions. It is inferred that these species can undergo facile interconversion and that such processes may be involved in the rapid exchange as detected by NMR. Based on 23Na-NMR results it is concluded that adsorption of CHCl3 on NaY modifies the negative charge distribution in the zeolite framework. The adsorption-induced C-H(D)-stretching frequency shift of trichloromethane is considered to be a measure of the base strength of the framework O(Z)-atoms.

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Physical Chemistry Chemical Physics