the production of thymoquinone from thymol and carvacrol

Table 7.1. Metal content of encapsulated catalysts.
Catalyst Metal content (wt. %) Color
Cr(salpn)-NaY 1.74 Pale blue-green
Fe(salpn)-NaY 1.36 Pale brown
Bi(salpn)-NaY 1.04 White
Ni(salpn)-NaY 0.15 Off white
Zn(salpn)-NaY 0.51 Off white
The prepared catalysts were further characterized by using SEM, XRD and FTIR
techniques to confirm the encapsulation of metal complexes inside the zeolite
supercage.
7.1.2. Scanning Electron Microscopy (SEM) Analysis
SEM micrograph can be used to observe changes in the morphology of zeolite
after encapsulation of the metal complexes. It was also possible to observe the excess
complexes, if any, located on the external surface of zeolite.
The SEM images of M(salpn)-NaY were similar to those observed for NaY,
indicating that they possessed the same morphology, i.e., the framework around the
guest molecule M(salpn) was faujasite-Y (Figure 7.1). The Si/Al ratio of the catalyst
samples was 2.5±0.1, ascertained by EDS. It was observed that the Si/Al ratio (2.5±0.1)
of the catalyst samples did not change comparing with the Si/Al ratio (2.5±0.1) of NaY
zeolite. This result confirmed that there was no dealumination of the zeolite during
catalyst preparation. SEM micrographs of NaY and Cr(salpn)-NaY Ni(salpn)-NaY,
Fe(salpn)-NaY, Zn(salpn)NaY and Bi(salpn)-NaY were shown in Figure 7.1. In the
SEM of catalyst samples, no surface complexes were seen and the particle boundaries
on the external surface of zeolite were clearly distinguishable. These micrographs
revealed the efficiency of purification with soxhlet-extraction for complete removal of
extraneous complexes, leading to well-defined encapsulation in the cavity only (Skrobot
et al. 2003, Varkey et al. 1998, Xavier et al. 2004, Maurya et al. 2003).
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