Zeolites type seeds

Y. Liu, W. Zhang, and TJ. Pinnavaia, Steam-stable Aluminosilicate Mesostructures assembled from Zeolite Type Y Seeds. J. Am. Chem. Soc., 2000, 122, 8791-8792. 

The simple two-parametric equation for fitting the crystallization curve of zeolite in the presence of seeds is proposed. The equation is genetically related with Avrami-Erofeev equation and has the following expression, jc = 1- exp[-Axexp( xr)]. Applicability of the proposed equation was verified by examples on ZSM-5 and NaA crystallization with MFl and LTA type seeds, respectively. 

The hydrothermal stability and acidity of aluminosilicate mesostructures can be improved substantially through the surfactant - directed assembly of protozeolitic aluminosilicate nanoclusters that normally nucleate (seed) the formation of microporous zeolites. Our results indicate that zeolite type Y, Beta, and ZSM-5 seeds are particularly effective at forming steam stable aluminosilicate mesostructures, which we generally denoted as MSU-S. 

Itabashi K, Kamimura Y, lyoki K, Shimojima A, Okubo T. A working hypothesis for broadening framework types of zeolites in seed-assisted synthesis without organic structure-directing agent J Am Chem Soc 2012 134 11542-9. 

Most zeolites are synthesized from proportional mixtures of sodium aluminate and sodium silicate and, in some cases, colloidal silica. The procedure is different to that for the preparation of silica alumina catalysts because zeolites form under alkaline conditions as the silica/alumina co-gel crystallizes in the presence of hydroxyl ions. The zeolite type formed depends on the proportion of silicate and aluminate in the solution and the reaction temperature and pressure. The time taken for zeolite crystals to form can range from a few hours to several days. Seeds or templates are often added to induce formation of the appropriate crystalline product. Knowhow is very important, and precise details for a specific preparation are not always published. 

Bronid, J., Subotid, B., and Skreblin, M. (1999) Investigation of the influence of seeding on the crystallization of zeolite A in the membrane-type reactor micropor. Mesopor. Mater., 28, 73-82. 

Another recent modification to the secondary growth method as applied to MFI-type zeolite membranes is to perform the hydrothermal growth on the seeded... 

It is well known that zeolites of type NaP co-crystallize with faujasites (15,16). The typical reaction sequence under the appropriate synthesis condition is (17) amorphous— faujasite — . gismondine type Na-P. However, in some cases, zeolite Na-P appears as the first crystalline phase when freshly prepared gel has been heated at the appropriate temperature (15,18) in these cases, faujasite can be crystallized either by adding the seed crystals into the freshly prepared gel (6,13.18) or by ageing the gel at ambient temperature prior to the crystallization at the... 

Metal incorporation into the zeolite using metal loaded seed materials. The combination of catalyst metal with zeolite catalyst is one of the most intriguing subjects for bifunctional catalysis. The achievement of prominent effect of the seed crystals on the crystallization of ZSM-34 type catalyst induced an idea that the seed material on which a catalyst metal had been supported previously would also be effective for rapid crystallization. 

Even if the problems of poor crystal intergrowth due to local exhaustion of reactants in the autoclave and synthesis of zeolite material in the bulk of the solution were solved, an important problem remains, related to the fact that several batch synthesis cycles (with their associated heating and cooling processes) are often required to achieve a zeolite membrane of good quality. Thus, a synthesis procedure in which reactants are continuously supplied to the synthesis vessel while this is maintained at a constant temperature would clearly be desirable not only for performance but also for the feasibility of the scale-up. This type of approaches has already been tested for inner MFI and NaA zeolite membranes [33-35], and the results obtained indicate that the formation of concomitant phases and the amount of crystals forming in the liquid phase are greatly reduced. Similarly, the continuous seeding of tubular supports by cross-flow filtration of aqueous suspensions [36-37] has been carried out for zeolite NaA membrane preparation. 

Huang AS, Lin YS, and Yang WS. Synthesis and properties of A-type zeolite membranes by secondary growth method with vacuum seeding. J Membr Sci 2004 245 41-51. 

A polycrystalline Y-type zeolite membrane was formed by hydrothermal synthesis on the outer surface of a porous a-alumina support tube, which was polished with a finely powdered X-type zeolite for use as seeds. When an equimolar mixture of CO2 and N2 was fed into the feed side, the CO2 permeance was nearly equal to that for the singlecomponent system, and the N2 permeance for the mixture was greatly decreased, especially at lower permeation temperatures. At 30"C, the permeance of CO2 was higher than 10- mol m-2 s- Pa-, and the permselectivity of CO2 to N2 was 20-100. 

For the FER-type zeolite, y 0.066 and synthesis duration was 14 days at 170°C in a static mode. The TON-type zeolite as obtained for y 0 and heating for 3 days at 170°C under agitation with 5 wt. % seeds (with respect to silica). 

It is north noting that with the diamines, MFI-type zeolite was obtained instead of FER-type zeolite for z = 6 and of TON-type zeolite for z = 7. The influence of the agitation and the presence of seeds adds to the influence of the Si/Al ratio in the reaction mizture in directing the crystallization towards FER- or TON types. These three factors were investigated at 170°C for reaction miztures containing n-butylamine which is able to produce the two structures (Figure 4). 

It can be seen that an agitated medium is markedly favourable to the TON-type zeolite, the FER-type zeolite being less sensitive to this factor. The presence of seeds increases the crystallization rate for both zeolites. FER-type zeolites containing Co2 or Mg2 could be prepared with Co2 or Mg2 - ezchanged aluminosilicate gels (20). In addition to the above-mentioned templates for TON-type zeolites, two other amines, di-n pentylamine and 1,4-diamino n-pen-tane, yield the same structure. 

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). 

The seeding can be performed under vacuum [102] or by electrophoretic deposition in aqueous or non-aqueous medium [103]. The latter method has been applied to the rapid synthesis of A-type zeolite membranes. Two strategies can be used for an electrostatic attachment of the seeds to the support either a fine-tuned surface charge by pH control and measurement of the support zeta-potential or the adsorption of positively charged polymers [104], and immersion in a suspension whose pH is such that the seed particles are negatively... 

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