Zeolite-template interactions

This procedure and, importantly, the force fields used to describe the zeolite-template interactions in the atom-atom approximation, have been well validated against experiments. Firstly, the locations of a number of templates within zeolites have been determined by single crystal or powder X-ray diffraction. Thus, for example, the templates 1-aminoadamantane and N-methylquinuclidinium cation have been used to crystallize the LEV... 

Role of alkali and NH cations in the crystallization of ZSM-5 Introduced in an aqueous (alumino) silicate gel (sol), the bare alkali cations will behave in various ways firstly, they will interact with water dipoles and increase the (super) saturation of the sol. Secondly, once hydrated, they will interact with the aluminosilicate anions with, as a result, the precipitation of the so formed gel (salting-out effect). Thirdly, if sufficiently small, they also can order the structural subunits precursors to nucleation species of various zeolites (template function-fulfilled by hydrated Na+ in the case of ZSM-5 (11,48)). ... 

Quaternary amines, such as tetraalkylammonium bromides and hydroxides (the alkyl group being Q to C4) are the typical zeolite templates. Quaternary amines fulfill the above-mentioned requirements of stability, specific interaction with the precursor (electrostatic interaction between quaternary amines and silicate), and easy removal (by calcination). 

The diffusion, location and interactions of guests in zeolite frameworks has been studied by in-situ Raman spectroscopy and Raman microscopy. For example, the location and orientation of crown ethers used as templates in the synthesis of faujasite polymorphs has been studied in the framework they helped to form [4.297]. Polarized Raman spectra of p-nitroaniline molecules adsorbed in the channels of AIPO4-5 molecular sieves revealed their physical state and orientation - molecules within the channels formed either a phase of head-to-tail chains similar to that in the solid crystalline substance, with a characteristic 0J3 band at 1282 cm , or a second phase, which is characterized by a similarly strong band around 1295 cm . This second phase consisted of weakly interacting molecules in a pseudo-quinonoid state similar to that of molten p-nitroaniline [4.298]. 

Pr4N+ cations were recognized to form complexes with silica-te (46) or aluminosilicate (23) species and subsequently to cause replication of the so formed framework structure via stereo-specific interactions (template effect). During this process, they are progressively incorporated and stabilized within the zeolite framework (1 1,47,48). Rollmann (37) has shown that initial Pr +/... 

M ions (among which Na+ from NaCl) interact with the aluminosilicate gel (and eventually direct its structure towards a zeolite framework by template effect), more readily than the Na+ which were originally associated with the silicate anions. 

Figure 3.2 Two steps in the synthesis of the ZSM-5 zeolite (a) template-inorganic precursor interaction and (b) periodic repetition of the inorganic template-solid hybrid, source of the crystalline framework.

One cation examined was not effective in converting the Cubic P but was effective in blocking the surface of the Cubic P so that other templates were ineffective. The study opens questions regarding how the polar and the nonpolar ends interact with Cubic P and how they relate to the synthesis of SSZ-13 and other zeolites (including void-filling). 

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