HZSM-5 Zeolites with Different SiO2/Al2O3 Ratios. Characterization and NH3 Desorption Kinetics

The article reports the influnce of the SiO2/Al2O3 ratio (30, 80, and 280) on HZSM-S zeolite properties XRD patterns show a decrease in the XRD peak intensity at low 2 theta angles for low SiO2/Al2O3 ratio zeolites N-2 adsoption and desorption isotherms display hysterisis with both cmicroores and mesopores likely contributing to the patciles network. The NLDFT cylindrical model confirms the charactersitic. 5.5 angstrom micropores in the zeolite pore framework. Furthermore specific surface area pore volume, and pore size distruped demonstrate that changes in the SiO2/Al2O3 ratio do not influence HZSM-S structural properties. NH3-TPD shown both weak and strong acid sites. Pyridine-FTIR also confirms that, in HZSM-S the wear acidity encompasses Lewis and hydrogen-bonded sites while the strong acidity manly involves the Bronsted and sites. It is proven that the ratio of weak to strong acid sties and measure by NH3 desorption kinetics and numerical regression allow the establishment of energies of activation for both strong and weak acid sites. It is also found that the kinetic desorption rate constants vary in agreement with the changes in weak and strong acid sites as observed with NH3-TPD and Prridine-FTIR.