For zeolite ZSM

Figure 3 2D 27Al-29Si RAPT-CP-CPMG HETCOR data for zeolite ZSM-4 recorded at 14.1 T with 10 kHz MAS. The 2D spectrum was acquired in 30 rows of hypercomplex data, with 64K scans per row, h increments of 100 ps, and acquisition time of 38 hours. In the right, ID slices taken through the centers of Ah and Al2 resonances are compared with ID 29Si MAS spectrum.

Figure 5. Calculated powder X-ray diffraction profiles for the FAU (a) and BSS frameworks (b) and the sum of these two components in the ratio BSS FAU = 3.0 (c) which approximates observed profiles for zeolite ZSM-20 materials (lower vertical bars- positions of allowed reflections).

Percentage of crystallinity for zeolites ZSM-48 and function of Na20 content in the gel. 

Once the high crystallization temperature is reached, zeolite crystallization will start after an induction period. During this induction period the dissolution of the gel phase continues, leading to the formation of clusters of polysilicates or aluminosilicates that become stable above a certain critical dimension (e.g. about 10 A for zeolite A and about 20 A for zeolite ZSM-5), and crystallization commences. The course of nucleation and crystallization of zeolites can generally be described by a characteristic S-shaped crystallization curve, in which the amount of crystalline material is plotted against crystallization time. Depending on the... 

A particularly clear structural change is observed for zeolite ZSM-39, which is the silicate analog of the 17 A cubic gas hydrate [59]. Its structure was proposed by Schlenker et al. [60] and refined from single crystal data in the space group Fd3 by Gies et al. [61]. However, x-ray powder patterns of the room temperature form show a few very weak extra reflections, indicating a space... 

Three-letter code of the International Zeolite Association for zeolites ZSM-5/ silicalite-1... 

It is sometimes possible to differentiate between aluminium atoms oeeupying crystallographically distinet T sites in zeolites, but to a mueh smaller degree than is possible for silieon. For zeolite ZSM-4, for example, the two erystallo-graphic sites are readily resolved, but for ZSM-5 the (orthorhombie) aluminosilicate version of silicalite-1, the best separations, even using 2 D MQ MAS NMR, only resolve two groups of peaks, rather than 12 separate peaks. Continued development is needed to increase resolution, to give quantitative information on whether all T-sites are occupied in an ordered way, or whether they are distributed randomly, details that have important implications for catalytic performance. There is evidence, for example, that the type of template used in a synthesis could affect this distribution (see Chapter 5). 

Flg. 2. Typical X-ray powder pattern for zeolite ZSM-58 after calcination in air for 16 hours at 813 K (CuKa-radiation)... 

The template concentration in the gel composition for the synthesis of zeolite ZSM-58 initially derived from the patent literature (vide supra) was relatively high (MTI/SiO2=0.25). Therefore, Ernst and Weitkamp also systematically varied the template content of the gel between 0.30 and zero [19] keeping all other factors constant. These authors found that MTI/S102 can be reduced down to 0.15 (i. e. nearly one half of the initial value) without significantly affecting the quality of the crystalline product. Upon further reduction of the template content, and even in the absence of methyltropiniumiodide and in new autoclaves, pure zeolite ZSM-5 was obtained. Hence, by chance a template-free synthesis for zeolite ZSM-5 was discovered. 

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