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

The adsorption of CH(D)Cl(3) and CHF(3) on a series of alkali-exchanged Y-zeolites was studied by (1)H- and (23)Na-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. (1)H-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 (23)Na-NMR results it is concluded that adsorption of CHCl(3) 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.