DEALUMINATED H-Y ZEOLITES - RELATION BETWEEN PHYSICOCHEMICAL PROPERTIES AND CATALYTIC ACTIVITY IN HEPTANE AND DECANE ISOMERIZATION

The acidity of a series of commercial dt aluminated H-Y zeolites was s tudied by means of MAS NMR and XPS spectroscopy. Al-27 MAS NMR has sho wn the presence of three types of Al in the dealuminated samples: fram ework tetrahedral Al, nonframework octahedral Al, and a third type of Al. As inferred from the framework Si/Al ratio obtained by Si-29 MAS N MR spectra and from the evolution of the. unit cell parameter determin ed by XRD, this third type of Al may be localized into the zeolite fra mework. XPS characterization of the samples in their acid form has all owed us to establish the relative concentration of Al at the outer sur face of the particles. Upon adsorption of ammonia on the dealuminated zeolites, three types of acid sites have been evidenced by XPS. The an alysis of the XPS data indicates that the strength of the acid sites a ssociated with tetrahedral framework Al atoms is not influenced by the other types of Al. The catalytic results of heptane and decane hydroi somerization have evidenced that the acid sites of certain dealuminate d H-Y zeolites may be very efficient. The information provided by MAS NMR, combined with the XPS results and literature data, has allowed us to partially elucidate the origin of the high activity of some dealum inated H-Y zeolites.