the production of thymoquinone from thymol and carvacrol

7.1.3. X-ray Diffraction (XRD) Analysis
The XRD patterns of NaY-zeolite, M-NaY (M=Ni(II), Zn(II), Cr(III), Fe(III),
Bi(III)) and their complexes of H2salpn (L) encapsulated in NaY-zeolite were recorded
at 2θ values between 5 and 60º. These observations indicated that zeolite framework
has not undergone any significant structural change during the encapsulation of M-
H2salpn and the crystallinity of NaY-zeolite was preserved, though, only slight change
in the intensity of the bands was observed. Slight change in the intensities of the peaks
suggested that the supercages of the zeolite were able to store these complexes without
any strain (Maurya et al. 2002). The main framework of the zeolite was not damaged.
Moreover, no specific crystalline patterns were seen for the encapsulated complexes;
this might be because of their fine distribution in the lattice (Xavier et al. 2004). All
samples exhibited patterns, which could be indexed to NaY and not to the complex.
This indicated that the crystallinity and morphology of zeolite was preserved during
encapsulation process.
XRD can be used to investigate the distribution inside the zeolite matrix. An
empirically derived relationship exists between the relative peak intensities of the 331,
311, and 220 reflections and the location of small cations in NaY-zeolite (Balkus et al.
1995). Cations were randomly distributed within the lattice if I331>I220>I311. From a
comparison of XRD patterns it was seen that little changes occurred in the relative
intensities of the peaks at 331, 311 and 220 reflections upon encapsulation of metal (Ni,
Fe, Zn, Bi, Cr) complexes of H2salpn (L) in zeolite-Y. Fan et al. (2003) and Joseph et al.
(2002) also observed and used these relative intensities changes for the explanation of
encapsulation.
XRD patterns of NaY, ligand (H2 salpn) and all encapsulated complexes were
shown in Figure 7.2. Figure 7.2 shows that samples have the faujasite topological
structure with high crystallinity. Upon complexing metal ions with salpn ligand and
further soxhlet-extracting, the faujasite structure basically remained unchanged. This
indicated that complexing and extraction processes did not have strong influence on the
structure of the zeolite. Nevertheless, slight modification occurred, as confirmed by the
alteration of the relative intensity of the peaks at 220 and 311 reflections (2θ of about 10
and 12°, respectively). For Cr-NaY, I220 was slightly higher than I311, whereas after
being coordinated to salpn, I220 became lower than I311. In BiNaY and Bi(salpn)-NaY
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