This
article reports the influence of the SiO2/Al2O3 ratio (30, 80, and 280) on HZSM-5 zeolite properties.
XRD patterns show a decrease in the XRD peak intensity at low 2θ
angles for low SiO2/Al2O3 ratio zeolites.
N2 adsorption and desorption isotherms display hysteresis
with both micropores and mesopores likely contributing to the particles
network. The NLDFT cylindrical model confirms the characteristic 5.5
Å micropores in the zeolite pore framework. Furthermore, specific
surface area, pore volume, and pore size distributions demonstrate
that changes in the SiO2/Al2O3 ratio
do not influence HZSM-5 structural properties. NH3-TPD
shows both weak and strong acid sites. Pyridine-FTIR also confirms
that, in HZSM-5, the weak acidity encompasses Lewis and hydrogen-bonded
sites, while the strong acidity mainly involves the Brönsted
acid sites. It is proven that the ratio of weak to strong acid sites
as measured by NH3-TPD and Pyridine-FTIR displays similar
changes to the SiO2/Al2O3 ratio.
Furthermore, 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 Pyridine-FTIR.
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