Adsorption sites for benzene in the 12R window zeolites: A molecular recognition effect

Abstract

Publisher Summary The present paper describes the changes in the location of benzene adsorbed in zeolites containing 12R windows upon NH3 adsorption and brings more insights on the dominating factors for benzene adsorption. The samples are NaEMT and KL. The first one has tridirectional network of 12R channels and the second one has parallel non intersecting 12R pores. Adsorption sites of benzene with and without coadsorption of ammonia have been studied by infrared spectroscopy over NaEMT and KL zeolites and compared with other zeolites containing 12R windows, such as NaX, NaY dealuminated NaY (NaYd), HY and NaBeta zeolites. When benzene is present alone, only one kind of adsorption site has been observed in NaEMT and KL zeolites as observed in NaYd and HY zeolites. It has been attributed to the interaction of x electron cloud of benzene with the Na + ions in NaEMT and the K + ions in KL. No significant adsorption of benzene on the 12R windows has been detected. This is in contrast to what has been found in NaX, NaY and NaBeta zeolites. However, upon coadsorption of ammonia, a migration of adsorbed benzene molecules from the cationic sites to the 12R aperture sites has been evidenced in NaEMT as observed previousely in NaX, NaY, NaYd and HY zeolites.