Comparison of acid-base properties of FAU, EMT, LTL and MOR (Na forms) in benzene adsorption and alkylation of aniline with methanol Original Research Article

Five different Na or K forms of 12R window zeolites (X, Y, EMT, LTL and MOR) were studied regarding the adsorption of an aromatic model molecule (benzene) and catalytic reaction involving an aromatic ring (alkylation of aniline with methanol). The benzene adsorption occurs on the cations (Lewis acid sites) on all the zeolites and on the oxygen of the 12R window on FAU and MOR and on EMT in the presence of ammonia. The absence of any interaction with the oxygen in KL, even in the presence of ammonia, and by contrast the high adsorption on these sites in MOR suggest that a molecular recognition effect directs the location of benzene within the large window (chemical and geometric requirements) in a way that is specific for each structure. The alkylation of aniline at 673 K may involve cations to give C-alkylation or basic framework oxygen to catalyze N-alkylation. The activity at short time-on-stream may be ranked NaX > NaY > NaEMT > NaL > NaMOR. A rapid aging is observed for NaX and NaL. The more selective samples are NaL and NaMOR which give a high N-alkylation. The comparison of the various zeolite structures suggests that in addition to the acid-base properties of the zeolites, geometric effect, characteristic of each structure may govern the selectivity.