A new way to obtain acid or bifunctional catalysts. III. Steaming of as-synthesized TPA, MeNH3-[Ga,Al]-ZSM-5 zeolites obtained from alkali-free media Original Research Article

The steaming of as-synthesized alkali-free TPA-MeNH3-[Ga0.99Al1.99]-ZSM-5 zeolite was carried out at temperatures of 530°C (St-530), 550°C (St-550), and 600°C (St-600). Physical characterization of the solids was carried out by XRD, IR, N2 adsorption, and27Al and71Ga MAS-NMR. n-Heptane cracking (T=350°C; PN2/PnC7=4; P=1 atm) was used as a model reaction to characterize the acidity of the catalysts. Propane aromatization (T=530°C; P=1 atm) was used to characterize the acid or the bifunctional behavior of solids. Results show that steaming produces less acid solids due to degalliation and dealumination of the zeolite structure. Because the presence of steam reduces the temperature at which the formation of extra framework gallium species occurs, bifunctional “Ga2O3”/H-[Ga,Al]-ZSM-5 catalysts are formed at lower temperature (T=530°C) in comparison when calcination is carried out under dry air. Catalysts are less selective to BTX as steaming temperature increases because of a strong reduction of Bronsted acid sites.