Crystal of zeolite omega

The change in morphology of crystals of zeolite omega has been analyzed with respect to the evolution of the concentration of aluminium in the parent liquor. In agreement with the overlapping principle, crystal habit is determined by the faces with the lowest growing rate. 

A better picture of the crystallization phenomena was obtained from the microscope examination of the crystals at different stages of their development. The first crystals of zeolite omega appeared as spheres with diameters around 0.5-1 pm (Fig.2). With the appearance of (001) faces, this form evolved into barrel-shaped particles (Fig.3). At a later stage of the syntheses, the habit evolved to euhedral hexagonal with the development of (100) faces (Fig.4). 

Figure 3. Kaolinite and barrel-shaped ((001) and (hkO) faces exposed) crystals of zeolite omega. (See text). Scale bar ...

The crystallization of zeolite omega was studied on reaction mixtures containing alcohols and water (at 130 °C) [94E1]. The crystallization was favored by the presence of longer-chain alcohols, ethanol, and 1-butan. Zeolite omega produced in the mixed-solvent phase consisted of well-ordered bundles of long acicular crystals as cortqrared to the spherulites formed in the aqueous system. 

Kinetics and Mechanism of Crystal Growth of Zeolite Omega... 

Crystal habit modification. Several crystal habits have been reported in the open and patent literature for zeolite omega. Elongated hexagonal rods (15,16) or fibres (17) have been reported when the zeolite resulted from the recrystallization of another zeolite, Y (15) or S (17), or of clays (16). Moreover the natural counterpart of zeolite omega, mazzite, appears as bundles of needle-shaped particles (18). All these solids have been grown at low supersaturation levels, hence under conditions in which our results show that the growth in the direction <001> prevails on the growth normal to the c-axis (Fig.8). 

Figure 2. Mixture of unreacted kaolinite and of spheroids (high index faces exposed) of zeolite omega obtained in the first stages of the crystallization. Scale bar 5 urn.

Figure 10. Synthesis of zeolite omega at 115°C with external supply of aluminium. Change of the crystal size in the <001> ( ) and (0) directions.

Unlike the usual amorphous, microporous adsorbents, it is possible to calculate the theoretical micropore volume of a dehydrated zeolite from the known crystal structure. We have performed these calculations here for several of the better known zeolites including zeolite A, zeolite X, zeolite L, mordenite (Zeolon), (8) zeolite omega, (4) and the zeolite 0 (offretite... 

Influence of Agitation upon the Formation of Sieve Omega. When the preferred reaction mixture was not stirred throughout the reaction period, mixtures of zeolite to and erionite ( 60/40) were obtained. Thus, at least a mild agitation is necessary when crystallizing pure specimens according to this recipe. 

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