Synthesis parameters

Tab. 13.1 Effect of synthesis parameters, aging time, reaction temperature, and concentration of metal ions, upon the particle size of the LDHs.

Type compound CycUzation type Synthesis parameters and results with [m.4.0]-type analogs (327b) References... 

Decomposition of the organics leads then to the separation of all elements into Cu and Y oxides and barium carbonate. This brings the synthesis parameters back to the problems encountered in the conventional solid state approach except that the heterogeneity may be over a submicron scale. Thus, reaction temperature may be slightly lowered (850°C instead of 900°C). 

Generally, metal nitride and oxynitride catalysts have been prepared by the temperature programmed ammonolysis method. This technique was originally applied by Volpe and Boudart to M0O3 precursors to produce y-Mo2N which was pseudomOrphic with the precursor, with surface areas up to 225 m g The resultant surface area of materials is known to be a strong function of the synthesis parameters as demonstrated in Table 1. ... 

Lavigne, J., Lessard, P., Ahad, E., and Dubois, C. (1994) Correlation of propellant mechanical properties and branched gap synthesis parameters. 

The main feature of this synthesis is the possibility to adjust the synthesis parameters in order to obtain dense spherical silica particles with a size range between 1 and 10 pm, as shown on the SEM picture (Fig. 3). Indeed, particle sizing shows that the size distribution of... 

In order to optimize the synthesis parameters, a series of experiments were carried out to study in detail the factors influencing the formation of integrated MCM-41 structure in fluoride medium, such as F7Si molar ratio, pH value, Na+/Si molar ratio, CTMABr/Si molar ratio, temperature as well as Al/Si molar ratio. In these experiments, the crystallization was performed at 100 °C using the molar composition of SiC 0.54 NaOH 0.50 CTMABr 0.34 HF 100 H20. 

Figure 1 shows that the phase transformation, the crystallization rates as well as the length of the induction periods, depends drastically on the kind of template and the alkalinity. One has to take into account that all other synthesis parameters have been kept as constant as possible. 

Phenyl-functionalized silicate mesophases with hexagonal or cubic symmetries influence of synthesis parameters. 

In this paper, we will investigate different synthesis parameters (PTES/TEOS and EtOH/Si ratios) to see how they influence the architecture of the mesophase. 

The mechanical properties of Micelle-Templated Silicas (MTS) are very sensitive items for industrial process applications which might submit catalysts or adsorbents to relevant pressure levels, either in the shaping of the solid or in the working conditions of catalysis or separation vessels. First studies about compression of these highly porous materials have shown a very low stability against pressure. These results concern these specific materials tested. In this study, we show very stable MTS with only a loss of 25% of the pore volume at 3 kbar. The effects of several synthesis parameters on the mechanical strength are discussed. 

The limits for the synthesis parameters are lower temperature limit 1070-1270 K lower pressure limit 4.8 GPa for H20/4.3 GPa for urea/4.6 GPa for boric acid. 

Tab. 10.1 Initial pool of elements and selected synthesis parameters...

For the present case, only wet impregnation of metal salts on supports was considered, to restrict the field of synthesis parameters and also since this process was found to be quite adapted to the step-by-step requirements of the automated synthesis. 

Synthesis procedures to obtain large zeolite crystals are well developed (1,2). In particular much attention has been paid to the synthesis of ZSM-5 crystals (3-6). Elongated prismatic (Fig. la) and cubic-shaped orthorhombic (Fig. lb) ZSM-5 crystals of sizes between 2-50 /tm were reported in the first recipes (7) in the patent literature. Later on, systematic studies have led to excellent synthesis prescriptions for the growth of large crystals of the prismatic (8) as well as of the orthorhombic form (9). The synthesis parameters which are dominant in the crystallization of pure ZSM-5 single crystals, are still under study (10,11). 

Factorial experiments can successfully serve to determine significant synthesis parameters for aluminophosphates and zeolites. Future studies will also focus on the underlying mechanisms of the nucleation and growth of high-silica zeolites out of alkaline-free ammonia containing reaction mixtures. 

The aim of the present paper is double. Firstly, we wish to question more precisely the role of TEA+ ions in competition with the Na+ cations and possibly in close relation with other synthesis parameters such as the silica source, or the alumina content, by comparing a series of other physicochemical characterizations(chemical composition, nature of the occluded organics, void volume...) of zeolites ZSM-20 and Beta. In a second step, we conduct a more in depth investigation of the whole synthesis conditions and their modification in order to propose selective preparation routes for both zeolites and to possibly define further favorable conditions for the formation of other potential open phases. 

ZSM-20 is a highly metastable zeolite. Its preparation necessitates the use of very specific and drastic conditions low synthesis temperatures, adequate nucleation period and a careful selection of the ingredient nature and composition. A severe and simultaneous control of all the synthesis parameters is indispensible to obtain pure ZSM-20 in high yield and reproducible conditions. 

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