Specific behavior of beta-zeolites upon the modification of the surface acidity by Cs and Li exchange

A study on the modification of the surface acidity of beta zeolite exchange d with Cs and Li was carried out by means of X-ray diffraction, nitrogen ad sorption (BET), Al-27-MAS-NMR, (Cs-133, Li-6)-MAS-NMR, surface paramagnetic shift (SUPAS) with adsorbed O-2, FTIR of adsorbed pyridine and NH3-TPD. An inverse correlation between the amount of cations exchanged and the number of acid sites was verified, as well as a gradual decrease of the micropore surface area, i.e. a 38% negative variation for the fully exchanged solids Z beta Cs2 and Z beta Li3. The Cs-133 and Li-6 (SUPAS)-MAS-NMR technique s uggested that Cs cations were located in accessible sites, while Li cations were inaccessible and possibly located in cavities within the channels net work. The crystallinity of the original beta zeolite was modified slightly after the ion exchange and no trace of amorphous material was detected by X RD and Al-27-MAS-NMR techniques. By means of NH3-TIPD it was found that at similar cation molar concentrations the number of acid sites was about 4 ti mes higher for Li-exchanged zeolites, therefore Cs showed a stronger neutra lization power of the acid sites.