Confirmation of the strongest nitriles–hydroxy groups interaction in the side pockets of mordenite zeolites

The adsorption/desorption of various nitriles on mordenite type zeolites has been studied by FTIR spectroscopy. The two different hydroxy groups present in mordenite give rise to distinct interactions with nitriles as probe molecules. As soon as the adsorbed nitrile is small enough to penetrate the side pockets and react with acid hydroxy groups located inside, a very strong interaction appears leading to a typical high frequency stretching vibration ν(CN)HF. The present paper indicates that there is no proton transfer from the zeolite to the nitrile at room temperature. Such a high ν(CN) frequency is not due to a protonated form of nitrile but to a very strong hydrogen bonding. A stronger interaction of nitriles with hydroxy groups located inside the side pockets than with those located in the main channels could be due to both confinement and solvent effects.