Silicalite synthesis

The quantification of D5R and other silicates during a silicalite synthesis at 95 °C from clear solution. 

Silicalite Synthesis from Clear Solution. In order to check whether the above findings on the presence of polymeric species in solution and on the fast rate of exchange between the smaller silicates are also applicable in a real zeolite synthesis mixture, we have studied a silicalite synthesis in more detail. Starting from a clear, filtered solution of molar composition 25 Si02 9 TPAOH ... 

NaOH 450 H2O at 95 °C, four identical non-stirred syntheses were carried out these syntheses were terminated after different time intervals. The composition of the solution was quantified at 95 °C by chemical trapping and the solid phase by XRD and elemental analyses (wt % Si, C, H, N). In this way a Si mass balance over the solution and the solid phase during the silicalite synthesis was obtained. The results are summarized in Table I, which also gives the results of a similar procedure for an analogous synthesis in the presence of DMSO. In this latter case, however, we were not able to filter the solution as thoroughly as in the first one, so that at the beginning of the synthesis a minor trace of amorphous material was present. 

The amount of DnR silicates in solution during the silicalite synthesis in the presence of DMSO is, as expected, much higher than without DMSO present (see Table I). Nevertheless, the rate of formation of silicalite in the presence of DMSO seems to be somewhat slower (see Figure 5) thus, if D5R species indeed act as precursor species, they are highly immobilized. Moreover, the products... 

Liquid state Si and P NMR experiments were carried out taking Silicalite synthesis clear solution samples in a leak-proof sealed plastic tube (8 mm i.d., 40 mm length) devoid of any background Si signal. The spectra were obtained on a Bruker MSL-300 FT-NMR spectrometer by co-addition of 8 successive spin-echos, and a magnitude mode of Furrier Transform of the resultant time domain signal as detailed earlier [6]. 

Fig. 3. a Predicted (curve) and experimental (points) values of the nucleations rate vs. time. Theoretical values based the classical homogeneous nucleation model and the population balance model developed in [36]. Data for silicalite synthesis replotted from [32]. b Predicted (curve) and experimental (points) values of the per cent zeolite in the solid phase. Model calculations and data from same sources as a... 

It is possible to formulate a conceptual model of the mechanism for the zeolite crystal growth process, based on the various pieces of information that have been reported in research studies to date for silicalite synthesis in clear solutions. It is speculated that this system is representative of zeolite crystal growth, that the knowledge will be applicable to other systems, and that seemingly different features of other systems stem from differences in degree rather than mechanism. Points which must be kept in mind are ... 

The zeolite nanocrystals have attracted the considerable attention of many researchers [1-5]. The syntheses of several types of zeolites with different nanometer sizes, such as silicalite-1, ZSM-5, A-type and Y-type, have been reported. Recently, micellar solutions or surfactant-containing solutions have been used for the preparation of zeolite nanoerystals [4,5], We have also successMIy prepared silicalite nanoerystals via hydrothermal synthesis using surfactants. In this study, we demonstrate a method for preparing mono-dispersed silicalite nanoerystals in a solution consisting of surfiictants, organic solvents and water. 

Ail these data confirm that a well-defined zeolite silicalite-type crystalline phase has been formed in the presence of the alumina porous tube (which seems indispensable for the zeolite synthesis, as no material is formed in its absence). 

An environmentally friendly synthesis of 1,2-methylenedioxybenzene (MDB) can be efficiently carried out in the gas phase, by feeding pyrocatechol (PYC) and formaldehyde acetals and using a catalyst containing weak acid sites and redox sites. The Ti-silicalite (TS-1) was identified as the most active and selective catalyst, indicating the role of well-dispersed octahedrally-coordinated Ti" ions in comparison with some model catalysts. 

MFI and MTW zeolites with Fe species introduced during zeolite synthesis were investigated. Fe-silicalite and Fe-MTW catalysts were synthesized accordingly to... 

The synthesis of carbon templated mesoporous tin MFI catalysts with different Si/Sn was carried out using microwave and in typical synthesis methodology TEOS, TPAOH, [Sn(C5H70)2]2]Cl2, ethanol and water were employed where the molar composition of the reaction mixture was 0.06 TPAOH 0.67 H20 0.028 TEOS 1.3 g EtOH X mg of tin precursor (X = 85, 63, 42, 21 mg). This synthesis mixture was stirred for 90 min at room temperature and then Black pearl 2000 carbon (10% wt. of TEOS) was added and again stirred for 4 h vigorously. The crystallization of C-meso-Sn-Silicalite was performed in a Teflon cup placed in a microwave oven (MARS-5, CEM, maximum power of 1200 W). 

Recently, based on such an oxidative system, the synthesis of nitrone (12) an inhibitor of 5a-reductase has been carried out (Scheme 2.7) (50). Oxidation of amines with H2O2 can be catalyzed with peroxotungstophosphate (PCWP) (51), Se02 (52-54), and titanium silicalite molecular sieves TS-1 and TS-2 (55, 56). 

The titanium-silicalite composihon, TS-1, has achieved commercializahon in selective oxidation processes and iron-siUcalite in ethylbenzene synthesis. 

A new microporous solid material has been obtained made of Ti02 and Si02 (TS-1) which has a silicalite-1 structure modified by isomorphous substitution of Si(IV) with Ti(IV), Its synthesis takes place in the presence of tetraalkylammonium bases under carefully controlled conditions,... 

Supported Co-Mn Fischer-Tropsch Catalysts. F-T synthesis of lower hydrocarbons on silicalite-1 supported Co and Co-Mn catalysts was reported by Das et C03O4 was found to be the only phase present in Mn-free... 

N2 adsorption-desorption isotherms and pore size distribution of sample II-IV are shown in Fig. 4. Its isotherm in Fig. 4a corresponds to a reversible type IV isotherm which is typical for mesoporous solids. Two definite steps occur at p/po = 0.18, and 0.3, which indicates the filling of the bimodal mesopores. Using the BJH procedure with the desorption isotherm, the pore diameter in Fig. 4a is approximately 1.74, and 2.5 nm. Furthermore, with the increasing of synthesis time, the isotherm in Fig. 4c presents the silicalite-1 material related to a reversible type I isotherm and mesoporous solids related to type IV isotherm, simultaneously. These isotherms reveals the gradual transition from type IV to type I. In addition, with the increase of microwave irradiation time, Fig. 4c shows a hysteresis loop indicating a partial disintegration of the mesopore structure. These results seem to show a gradual transformation... 

Recently, there has been a growing interest into niobium- and tantalum-containing molecular sieves. The introduction of niobium into mesoporous molecular sieves has been studied by Ziolek et al [3,4], while Antonelli and Ying reported the synthesis of mesoporous niobium oxide [5], The synthesis and characterization of niobium- and tantalum-containing silicalite-1 (NbS-1 and TaS-1) was published recently [6,7,8] and some evidence has been presented for isomorphous substitution [6,8] of Nb and Ta into the silicalite-1 framework. The synthesis of NbS-2 (MEL) [9] and a new molecular sieve named NbAM-11 have been reported as well [10],... 

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