STUDY OF THE BULK AND SURFACE-ACIDITY OF PROTONATED Y ZEOLITES BY TPDAND XPS

The combined use of temperature programmed desorption (TPD) of nitroge ned bases (ammonia, pyridine) and x-ray photoelectron spectroscopy (XP S) was applied to the study of acidity of HY zeolites with different m olar Si/Al ratios (approximately 2.7, 5.8, 24). N1s binding energies o f probe molecules showed two types of sites (Bronsted and Lewis) whose relative proportions varied with pretreatment and desorption temperat ures, and a dissociative adsorption of NH3 for dehydroxylated zeolites . The TPD curves and the XPS quantitative analyses of probe molecule c oncentration in zeolites allowed the determination of acid sites distr ibution in terms of strength for the real surface of crystals and for a sub-surface partially freed of extra-framework species that cover it . These data showed that the acid sites located in sodalite units are mostly strong and Bronsted type sites.