Confinement effect on the interaction of hydroxy groups contained in the side pockets of H-mordenite with nitriles; a FT-IR study

Adsorption of CD3CN and CH2ClCN was studied at room temperature on an H-mordenite (H-MOR) (Si : Al = 10.7) sample by FT-IR spectroscopy. Study of both v(OH) vibrations of the zeolite and nu(C equivalent to N) frequencies of adsorbed species allowed differentiation of the interaction of nitriles with OH groups in the main channels and in the side pockets. Observed nu(C drop N) frequencies were compared to those of nitriles in variable H-0 solutions. It is concluded that protonated species are formed in side pockets while in the main channels only strongly H-bonded species occur. Results were confirmed using a pyridine-pretreated sample and a more bulky nitrile probe, CHCl2CN. They were explained involving confinement effects in the side pockets.