Zeolite fluoride route

MFI-type zeolites with Si PARTLY SPBSTITPTKD bv TIII(T-B.Al.Fe.Ga). The fluoride route can be used to prepare MFI-type zeolites with... 

As for all other zeolite crystals prepared with the fluoride route, the crystals of the structure types FER TON and HTT are of very large size in the absence of seeds. The FER-type crystals are aggregates of plates, the size of which can be larger than 200 pm. The other structure types (TON and HTT) show a fibrous aspect, the length being over 100 pm for a diameter below 1 pm (Figure 5). 

From that time, the synthesis of zeolites by the so-called fluoride route has developed to a large extent, with great contributions by Guth et It has been successfully appHed to pure-silica, alumi-... 

Structure-Direction Issues in the Fluoride Route to Pure-Silica Zeolites... 

However, there are at least two additional important structure-direction factors interplaying with that of fluoride in the synthesis of pure-silica zeolites by the fluoride route the OSDA and the degree of dilution of the synthesis gel. Villaescusa and Camblor have shown that the general concepts outlined above regarding structure-direction by OSD As can be successfully used in the search for new pure-silica materials, as shown for instance by the synthesis strategies that finally lead to the three-dimensional large pore zeolite ITQ-7. Nonetheless, we would like to point out at least one peculiarity, in this respect, of the fluoride route small cations may show by this route a rather specific structure-direction effect (like 1,3,5-trimethylimidazolium, which has a (C- -N)/N ratio of 8 but shows a rather large specificity towards zeolite ITQ-12 in fluoride aqueous medium). 

Villaescusa L, Camblor M (2003) The fluoride route to new zeolites. Recent Res Dev Chem 1 93-141 Wagner T, Waitz T, Roggenbuck J, Froba M, Kohl C-D, Tiemann M (2007) Ordered mesoporous ZnO for gas sensing. Thin Solid Films 515 8360-8363... 

Synthesis may also be carried out at a lower pH using fluoride-containing media, wherein F ions are thought to act as structure directors via strong interactions with framework Si atoms. Consequently, the nucleation rate is decreased, which yields larger crystals relative to standard alkaline hydrothermal routes.The fluoride route under neutral/acidic pH conditions is also extremely useful to synthesize zeolite-like materials called zeotypes, which contain elements other than silicon and aluminum (e.g., titanosilicates, zirconosilicates, etc.). Under alkaline conditions, the precursors would be preferentially precipitated as hydroxide species rather than ordered arrays. 

In addition to the materials listed in Table 16.1, several silica-based microporous materials were also synthesized using the fluoride route CJS-3[64] (certainly a clathrasil), ITQ-10 [81] (beta like) and ITQ-14 [81] (BEA-BEC overgrowth), PREFER (a lamellar precursor of ferrierite) [82], SSZ-61 (Standard Oil Synthetic Zeolite-61) [12, 83], Nu-86 [12], ZSM-48 [68, 86], ITQ-28 [85], and SSZ-70 (aborosilicate) [86]. 

Table 16.1 Silica-based ((Si) or (Si,AD) microporous materials prepared via the fluoride route in the alphabetic order of their code assigned by the Structure Commission of the International Zeolite Association (SC-IZA) [25]...

Table 16.2 Phase selectivity for pure silica zeolites prepared under the fluoride route as a function of the water content with three different OSDAs...

Finally, the ionothermal synthesis route developed since 2004 by Morris et al. [187] was not successful for the silica-based materials but the ionic liquids themselves can act as classical OSDAs in aqueous media. Thus, by using the fluoride route, Zones et al. synthesized pure silica zeolites of TON, ITW and MTT topologies using the OSDAs l,3-dimethyl-37/-imidazol-l-ium, l,2,3-trimethyl-3//-imidazol-l-ium and 1,3-diisopro-pyl-3//-imidazol-l-ium, respectively [12]. Then, in 2009, we reported the synthesis of IM-16 (UOS) a germanosilicate prepared with the ionic liquid 3-ethyl-l-methyl-3//-imidazol-l-ium as OSD A in aqueous media. This microporous material possesses a new topology built from d4r and mtw composite building units [165]. The ionothermal synthesis route, up to now, was only successful in the formation of new phosphate-based microporous materials, as mentioned in the next paragraph. 

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