Infrared evidence of three types of interaction between methylamine and a series of alkali cation exchanged faujasite zeolites

The acid-base properties of a series of cationic faujasite zeolites have be en studied using methylamine as a probe molecule by means of in situ infrar ed spectroscopy. The results have been correlated with the nature of counte rions and the Si/Al ratio of the studied zeolites. The present work reveals three kinds of interaction between methylamine and cationic zeolites. Meth ylamine can interact not only with alkali cations via the lone electron pai r on nitrogen atoms but also with the negatively charged oxygen atoms of th e framework via the hydrogen atoms of both NH2 and CH3 groups as well. The interaction between the methyl groups and these oxygen atoms is for the fir st time postulated. However, the Lewis acidity of counterions remains the d ominating factor in the interaction between methylamine and cationic zeolit es. A deformation of the zeolite framework due to the adsorption of methyla mine has been observed. This work shows clearly that methylamine can be an efficient probe molecule for the characterization of acid-base properties o f zeolites.