Organic templates molecular sieve synthesis

Thermal treatments can be applied to modify the properties of a material, for example, dealumination and optimization of crystalHne phases. These techniques do not require oxidants. Oxidative thermal treatments are generally employed to activate molecular sieves, by removing the organic templates employed during synthesis. This is one of the key steps when preparing porous catalysts or adsorbents. In air-atmosphere calcination, the templates are typically combusted between 400... 

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-... 

Niobium and titanium incorporation in a molecular sieve can be achieved either by hydrothermal synthesis (direct synthesis) or by post-synthesis modification (secondary synthesis). The grafting method has shown promise for developing active oxidation catalyst in a simple and convenient way. Recently, the grafting of metallocene complexes onto mesoporous silica has been reported as alternate route to the synthesis of an active epoxidation catalyst [21]. Further the control of active sites, the specific removal of organic material (template or surfactant) occluded within mesoporous molecular sieves during synthesis can also be important and useful to develop an active epoxidation catalyst. Thermal method is quite often used to eliminate organic species from porous materials. However, several techniques such as supercritical fluid extraction (SFE) and plasma [22], ozone treatment [23], ion exchange [24-26] are also reported. 

Similarly, zeotype molecular sieves are synthesized by mixing the basic ingredients with the organic template, e.g. aluminophosphates are prepared from alumina and phosphoric acid. Other main group or transition elements can be incorporated into the framework by adding them to the initial sol-gel. Alternatively, different elements can be introduced by post-synthesis modification (see later), e.g. by dealumination followed by insertion of the new elements into the framework position [31]. 

Organic templates Cp 2 Co+ are usually occluded in the as-synthesized UTD-1. The typical method to remove these organic species from pores is that the samples are heated at 500 °C to decompose Cp 2 Co+ to cobalt oxide, followed by treatment with HC1 to remove cobalt oxide, and then are washed by water and dried in air. The obtained UTD-1 molecular sieve has good thermal stability, and its crystal lattices remain stable upon being heated to 1000 °C. The synthesis of Al-containing high-silicate UTD-1 is very difficult, which needs a two-step synthesis in general. 

The main difference between the synthesis of MCM-41 mesoporous material and traditional synthesis of zeolite or silica molecular sieve is the use of different templates. An individual organic molecule or metal cation is used for the traditional synthesis of silica microporous molecular sieve. For example, the typical template for ZSM-5 synthesis is tetrapropylammonium ion the crystal is formed through the condensation of silicate species around the template molecule, while for the formation of MCM-41, the typical template is the assembly of large molecules containing one hydrophobic chain with more than 10 carbons. 

On the role of organic amine templates in the synthesis of AlPO molecular sieves ... 

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