Structure directing reagents

Fig. 4.23 Preparation of mesoporous silica materials with chirally twisted rod-like structures by using surfactant with a chiral amino acid moiety as a structure-directing reagent.

Organic block copolymer micelles serve as structure-directing reagents in a sol-gel mixture with inorganic precursors to form mesoporous inorganic structures... 

Although traditional synthetic methods can be used for preparing a variety of porous materials, the development of template synthesis strategies has prompted an explosive-like growth of synthetic methods. Template synthesis roughly involves the use of a structure-directing reagent that facilitates the porous material to adopt the desired structure, followed by the template release. Three main types of templates, soft, hard, and complex, can be used (Zhao, 2006). 

The synthesis and characterization of a mesoporous silicoalumino phosphate are given employing typical structure directing reagent viz. cetyltrimethyl ammonium bromide. The Si MAS NMR showed that silicon is found in coordination with 1, 2, 3 and 4 A1 ions through oxygen bridges. The sorption characteristics of this new mesoporous SAPO material are also presented. Keywords Silico aluminophosphate, Mesoporous, ordered molecular arrays, MAS NMR. 

Here M is the direct reagent which is chemically rebuilt and has the enhanced energy and necessary structural possibilities, including coordination vacancy, to participate in the reaction. A sum of elementary acts b+c, which cannot be easily discriminated, has been called 1st step since in this stage of the reaction the alkane is involved in the interaction for the first time. A sequence of steps a+b+c... 

We have developed an automated parallel synthesis methodology that permits the rapid and detailed Investigation of hydrothermal systems. The general procedure is as follows automatic dispensing of reagents into autoclave blocks followed by synthesis, product isolation and automated structure analysis with X-ray diffractometry. Here we describe the application of this technique to the exploration of the aluminophosphate synthesis field. The effects of template, template concentration, A1 sources as well as mixed template systems are investigated. Emphasis is put on the study of cooperative structure direction effects. 

In most syntheses, a gel is initially prepared that contains framework-building inorganic species, typically aluminates, silicates, phosphates or metal-oxyani-ons, available in a reactive form. There are also syntheses that result in crystallisation from clear solution, and others that proceed under essentially dry gel conditions (without added water). The sources of the reagents can determine the products that form in general more reactive sources are favoured. In addition, for zeolites and related solids, structure directing species must be present in the gel that can stabilise the open framework structures relative to denser phases of the same composition. Hydrated metal cations and/or organic cations perform this function in zeolite preparations. 

---