the production of thymoquinone from thymol and carvacrol
the production of thymoquinone from thymol and carvacrol
the production of thymoquinone from thymol and carvacrol
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NH4 +2 generates <strong>the</strong> acid sides. Catalytic activity <strong>of</strong> <strong>the</strong> zeolites is attributed to <strong>the</strong><br />
presence <strong>of</strong> <strong>the</strong>se acidic sites.<br />
The most commonly encountered faujasites are zeolites X (higher Al) <strong>and</strong><br />
zeolite Y (lower Al). Zeolite Y is <strong>the</strong> most important catalytic zeolite, <strong>and</strong> is generally<br />
syn<strong>the</strong>sized in <strong>the</strong> Na form (Richardson 1989).<br />
There are 70 known different kinds <strong>of</strong> building arrangements, each resulting in a<br />
distinct structure. Some <strong>of</strong> <strong>the</strong>se occur as natural minerals; some are syn<strong>the</strong>tic.<br />
Catalytically important zeolites are listed in Table 2.1 (Sen et al. 1999, Richardson<br />
1989).<br />
Table 2.1. Catalytic zeolites<br />
(Source: Richardson 1989)<br />
Zeolite Pore type Dimensions(Å)<br />
Faujasite, X, Y<br />
Modernite<br />
Zeolite beta<br />
ZSM –5<br />
Zeolite A<br />
2.4 Properties <strong>of</strong> Zeolite<br />
interconnected<br />
spheres<br />
interconnected<br />
channels<br />
interconnected<br />
channels<br />
interconnected<br />
channels<br />
interconnected<br />
spheres<br />
4.1 Å diameter pore<br />
11.4 Å diameter cavity<br />
6.5x7.0 Å channels<br />
2.6x5.7 Å channels<br />
7.6x6.4 Å channels<br />
5.5x5.5 Å channels<br />
5.3x6 Å channels<br />
5.1x5.5 Å channels<br />
4.1 Å diameter pore<br />
11.4 Å diameter cavity<br />
A large-pore zeolite such as zeolite Y, whose structure consists <strong>of</strong> almost<br />
spherical 13 Å supercages interconnected tetrahedrally through smaller apertures <strong>of</strong> 7.4<br />
Å in diameter. This is limited regarding <strong>the</strong> size <strong>of</strong> guest molecules by <strong>the</strong> space<br />
available in <strong>the</strong>se cavities (Hoelderich et al. 2000).<br />
Zeolite properties can be changed with modification <strong>of</strong> cation exchange,<br />
impregnation. These techniques are used to introduce metal into zeolites. Impregnation<br />
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