*2.2.5 Fourier transform infrared*

**Figure 4** shows the infrared absorption spectra of ZSM-5 zeolites. The band at 820–650 cm<sup>−</sup><sup>1</sup> can be assigned to symmetric stretching vibration mode of


### **Table 1.**

*Physicochemical properties of ZSM-5 zeolites.*

**Figure 4.** *FTIR absorption spectra of ZSM-5 h zeolites.*

T − O (T = Si or Al) and the band at 650–500 cm−1 that can be attributed to the pentasil double-5-ring bending vibration [18]. Absorption bands at 3745, 3605, and 3500 cm<sup>−</sup><sup>1</sup> were observed in the infrared spectra of ZSM-5 zeolites, which are assigned for the stretching vibration of terminal Si-OH, Si-O(H+ )-Al, and Si−OH nests, respectively [19].
