Spectroscopic study on the adsorption of ammonia in a series of alkali-exchanges Fausjasite zeolites

The basic properties of a series of cationic zeolites have been investigated by means of FTIR and TPD coupled with mass spectrometer techniques using ammonia as probe molecule. Our TPD results demonstrate clearly that the adsorption strength of ammonia on these cationic zeolites is strongly dependent on the Lewis acidity of counter-ions, indicating that the interaction between ammonia and cationic zeolites is dominated by an electrostatic interaction between counter-ions and the lone electron pair an nitrogen atoms. However, the variation of the shift value in wavenumber of vibration bands of ammonia adsorbed on different cationic zeolites revealed by FTIR can not be explained only by this electrostatic interaction. The existence of a supplementary interaction between the negatively charged oxygen atoms of framework with the hydrogen atoms of ammonia is postulated.