Quaternary ammonium salt, templating

Furthermore, investigations of template decomposition in zeolites upon calcination of the as-synthesized materials have received much attention by researchers (248-250). However, the decomposition mechanisms of quaternary ammonium salts, which are commonly used as templates for zeolite synthesis, are still not well understood. Thus, MAS NMR investigations of the decomposition of quaternary ammonium ions in zeolites bear the potential of significantly improving the understanding of these processes (243,251). For this purpose, a general method was developed for the synthesis of... 

In the present work, three approaches supercritical drying, templating with surfactants of quaternary ammonium salts and a two-step modification are applied to the sol pillared clay to tailor the pore structure. Mechanisms involved in these processes are discussed in detail. 

Templating with quaternary ammonium salt surfactants... 

Chiral phase transfer catalysts have been exploited in a wide range of reactions which involve anionic intermediates. Remarkably, quaternary ammonium salts of 1 and 2 have been shown to induce asymmetry in many different synthetic reactions, and the cinchona alkaloids appear to be a charmed template for the design of effective phase transfer catalysts [14],... 

The typical A1P0 synthesis gel contains four components an alumina source, a phosphate source, water, and an organic amine or quaternary ammonium salt. The relative concentrations and, of course, the individual characteristics of these reactants are important factors in the preparation of A1P0<, molecular sieves. One factor is particularly evident, namely, without the organic no A1P0<, molecular sieves are formed. The concept of a template in molecular sieve synthesis is not new. A template is a spec-... 

Sayari et al [202,203] extended the LCT technique to the synthesis of mesostructured zirconium oxide. The use of long chain quaternary ammonium salts or primary amines as templates led to the formation of hexagonal and lamellar Zr02 phases, respectively. Zr(S04)2 was used as zirconium source, which provided a highly acidic medium, pH < 1.5. Consistent with the synthesis conditions and EDX analysis data a S X I mechanism where the surfactant-inorganic interaction is mediated by sulfate anions was proposed. Unfortunately, both structures collapsed upon removal of the surfactant either by high temperature calcination or by solvent extraction [203]. However, the hexagonal form was successfully... 

The same types of surface-imprinted polymers were also used to discriminate between the enantiomers of bifunctional amino acids [24]. In this study, the functional host molecule was the quaternary ammonium salt and the templates were the A -protected amino acids shown in Fig. 5. 

Traditionally the synthesis of ordered mesoporous silica materials, with pores in the 2-50 nm range, is templated by surfactants, hi this soft-templating approach, quaternary ammonium salts and non-ionic polyether-based surfactants are the most used templates, leading to pore distributions of 2-6 and 4-30 nm respectively [6,7]. Under specific reaction conditions, a mixture of the silica precursor and the surfactant yields a meso-structured solid, which, after removal of the template, becomes an open mesoporous structure. Many synthetic protocols have been developed by varying the surfactant, silicon source or synthesis conditions, but most preparations occur at low or high pH. Extensive reviews on the synthesis of ordered mesoporous materials are available [8-10]. 

An alumina source (e.g., pseudo-boehmlte or aluminum 1sopropoxlde) Is mixed with dilute orthophosphor 1c acid, then combined with an aqueous solution containing the metal salt. Finally the template, an amine or quaternary ammonium hydroxide, Is added. 

The synthesis of a MeAPO molecular sieve typically uses an aqueous reaction mixture formed by combining a dissolved form of the divalent metal, orthophosphoric acid, a reactive alumina, and an amine or quaternary ammonium templating agent (R). The metal is typically introduced as the acetate or sulfate salt, or as the metal oxide dissolved in dilute phosphoric acid. A synthesis mixture is prepared in one of two ways ... 

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