Zeolites structure-directing agents

Zeolite synthesis around a metal complex was introduced by Balkus [40]. The metal complex is added to the zeolite synthesis mixture and is incorporated into the zeolite structure during the zeolite synthesis. Of course, this procedure is only applicable when the metal complex is soluble in the synthesis mixture and can withstand the hydrothermal synthesis conditions. Another requirement is that the zeolite structure-directing agent added must be removable by a milder... 

Quaternary ammonium compounds as structure directing agents in zeolite synthesis... 

The importance of quats as structure-directing agents in zeolite synthesis was recently underlined (ref. 5) by the synthesis of the new zeolites SSZ-26 and -33, which combine 10- and 12-ring pores. The templates applied are shown in Figure 3. 

Since then, organic amines, quaternary-ammonium bases, metal complexes, and other compounds have been extensively used in zeolite synthesis, acting as space fillers with low specificity, structure-directing agent, or true templates ... 

The same periodic structures can also be formed from alternating AIO4 and PO4 tetrahedra the resulting aluminophosphates are not called zeolites but AlPOs. Zeolites are made by hydrothermal synthesis under pressure in autoclaves, in the presence of template molecules such as tetramethylammonium, which act as structure directing agents. 

Al-containing ITQ-21 zeolite ((Si+Ge)/Al=25, Si/Ge=20) was synthesized using N(16)-methyl-sparteinium cation (MSPT+) as the organic structure-directing agent in combination with fluoride anions and germanium as described in [1], The composition of the final synthesis gel was ... 

Fig. 4 Proposed defect cluster model in as-made zeolites with quaternary ammonium cations as structure directing agents (SDAs) hydrogen bond distances of 1.68 A are determined experimentally from the H NMR chemical shift of 10.2 ppm X and Y are atoms not further specified in the SDA the interaction between the SDA and the SiO- group is assumed based on bond valence arguments (see text)...

Fig. 5 (a) Structure directing agent (SDA) in the synthesis of zeolite ITQ-3 N quaternary nitrogen A-I carbon atoms of SDA, l,3,3,6,6-pentamethyl-6-azonium-bicyclo[3.2.1]octane some 13C line assignments were not unequivocally possible, so these are left open the orientation of the dipole moment was calculated with a semiempirical AM-1 simulation with the origin at the center of gravity of the molecular cation (b) 13C H 27A1 REAPDOR experiment on synthetic zeolite ITQ-3. Adapted from [204]... 

The advent of the addition of a quaternary ammonium cation as template or structure directing agent (SDA) to the alkaline gel by Barter and coworkers, and Mobil Oil coworkers, led to the Si02 enriched zeolite A in the case of Barter and to the high silica zeolites. Beta and ZSM-5, by the Mobil group. The latter synthesis temperature typically is 100-200 °C, higher than Milton s original work. 

In situ crystallization begins with a precursor synthesis sol consisting of Si, Al, Na, H2O and a structure-directing agent (or template) [7]. The composition of the sol is dependent on the type of zeolite being synthesized and the final desired... 

Both piperidine and pyridine serve as structure-directing agents in the commercial production of Ferrierite zeolite. More recently, use of DMAP has allowed preparation of novel metallo-aluminophosphate molecular sieves with both small- <2006W02006037437> and large-pore architecture <2006USA074267>. 

Zeolites having ZSM-48 topology also crystallize from hydrogels containing other linear organic structure directing agents, such as diamines (2) or various (poly)alkylamines ( ). 

Although not by design, Balkus and coworkers have successfully synthesized the ZSM-48 - SSZ-31 - UTD-1 sigma expansion series by incrementally increasing the size of a cobaltocenium-derivatized structure-directing agent. They found that Cp2Co+ directs for ZSM-48, (MeCp)2Co+ directs for SSZ-31 and Cp 2Co+ directs for the 14 MR zeolite, UTD-1 [47]. 

---