Organic-functionalized molecular sieves (OFMS'S): A new class of materials

Citation

Jones, Christopher W. (1999) Organic-functionalized molecular sieves (OFMS'S): A new class of materials. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6xz1-hh23. https://resolver.caltech.edu/CaltechETD:etd-11152005-152437

Abstract

Throughout the last two decades, there has been a tremendous interest and growth in molecular sieve science. In particular, substantial attention has been paid to the development of new molecular sieves for catalytic applications, as molecular sieves have the unique ability to promote reactions in a shape-selective manner. To increase the variety of reactions that can be catalyzed by molecular sieves, recent efforts have focused on generating new types of active sites in molecular sieves by incorporating transition metals into the silicate framework or by supporting metal-based species within the micropores. Despite this, there are still many chemistries that can not be carried out over molecular sieve catalysts where significant benefit could be gained if the reaction were to be accomplished in a shape-selective manner. To address this problem, I have prepared a new class of molecular sieves that contain intracrystalline organic functionalities [denoted organic-functionalized molecular sieves (OFMS's)]. Previous attempts to synthesize silicate-based molecular sieves with organic functionalities within the micropores have focused on grafting organic groups onto preformed zeolites. However, this is not a viable route to the production of OFMS's that can function as shape-selective catalysts, as the organic groups preferentially functionalize the external crystal surface. Here, the problems with this approach are circumvented by preparing OFMS's by direct synthesis.

Attempts to synthesize OFMS's directly both in the presence and absence of organic structure-directing agents (SDA's) are described. Pure-silica beta zeolites containing a variety of intracrystalline organic groups are synthesized using tetraethyl ammonium fluoride (TEAF) as the SDA. Porosity is generated by removing the occluded TEAF by solvent-extraction techniques. Following extraction, the exposed organic functionalities are further altered by chemical techniques, e.g., amines to imines, phenethyl groups to phenethylsulfonic acid groups. The ability to perform shape-selective acid catalysis (phenethylsulfonic acid) and shape-selective formation of imines from amines indicates that the organic moieties reside largely in the micropores of the molecular sieve. Several preparation variables have an impact on the nature of the resulting OFMS's, the most of important of which are the synthetic method, silicon source, and extraction method. The effects of these synthetic factors on the crystal size and morphology, porosity and hydrophobicity of the products are discussed.

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