the production of thymoquinone from thymol and carvacrol

7.1.4. FTIR Spectroscopy Analysis
IR spectra of NaY zeolite and metal-exchanged zeolites showed strong zeolite
lattice bands in the range 450-1200 1/cm as shown in Figure 7.3. The strong and broad
band at the region 1000 1/cm could be attributed to the asymmetric stretching vibrations
of (Si/Al)O4 units. The broad bands at the region 1650 and 3500 1/cm were due to
lattice water molecules and surface hydroxylic groups. No shift of zeolite lattice bands
was observed in the spectra of encapsulated complexes given in Figure 7.4, which
further implies that the zeolite framework has remained unchanged upon the
encapsulation of complexes.
Figure 7.3. IR spectra of zeolite NaY, CrNaY, ZnNaY, FeNaY, NiNaY, BiNaY
A partial list of the IR spectra results of ligand (Figure 7.5), encapsulated
complexes and free complexes (Figure 7.4) were given in Table 7.2. The IR spectra of
ligand exhibited a broad band between 2400-2700 1/cm region due to hydrogen bonding
between phenolic hydrogen and azomethine nitrogen atoms. The multiple bands around
2900 1/cm in IR spectrum of ligand were due to the presence of -CH2- group. Absence
of the band was due to hydrogen bonding and coordination of oxygen to the metal after
proton removal. In IR spectra of encapsulated complexes the zeolite bands were
dominant. Only weak bands were observed for zeolite-encapsulated complexes due to
lower complex concentration. The coordination in the pores could be identified from the
43