the production of thymoquinone from thymol and carvacrol

CHAPTER 4
DESIGN OF INTRAZEOLITE COMPLEXES
In the catalyst synthesis, the encapsulation of metal complexes into the zeolite
cavities is known as a ship in a bottle procedure. These encapsulated catalysts are often
referred to as zeozymes as they behave functionally similar to many enzyme catalysts in
oxidation reactions (Maurya et al. 2002). Encapsulation of metal complexes is occurred
in the super cages of the Y-zeolite. There are three possible approaches to incorporate
metal complexes inside the pores or cavities of a zeolite. Encapsulated complexes are
prepared by general flexible ligand method, ligand synthesis method inside the super
cages of the Y-zeolite and zeolite synthesis method (Sheldon et al. 1998).
4.1. Flexible Ligand (FL) Method
A flexible ligand is able to diffuse freely through the zeolite pores as seen in
Figure 4.1 and make complexes with a previously exchanged metal ion in the flexible
ligand method (Velde et al. 2000). The resulting complex becomes too large and rigid to
escape out of the cages. This approach is well adapted for encapsulation of metal-salen,
salpn complexes, because the salen, salpn ligand offers the desired flexibility. Thus a
large variety of metal salen, salpn complexes were prepared by FL method within the
Y-faujasite (Chandra et al. 1998).
Zeolites Y is having pore opening of 7Å. Inside parts of zeolites have 12-13 Å
supercage. The H2 (salpn) ligand is having molecular dimensions less than 7 Å. It can
easily diffuse inside the zeolite pore. The formed metal complex is too large to diffuse
out (Brunel et al. 1998).
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