Structural investigations of zeolites

Microporous materials (including zeolites) that contain molecular-sized pores and cavities have found wide-spread use in industry as molecular sieves for chemical separations, as ion-exchangers for detergents and as heterogeneous, shape-selective catalysts. Knowledge of the crystal structure of these microporous solids can provide important insights into their properties that can ultimately lead to the design of desirable materials. However, the structure solution of microporous, materials can be challenging because they tend to form as micron or submicron sized crystals that are too small for single crystal X-ray analysis. Thus, the objective of this work is to develop and apply new techniques for solving the structures of microporous materials that tend to form micro- and nanocrystals and to utilize these structural investigations to gain a more thorough understanding of the zeolite/organic structure directing agent (SDA) interactions that lead to the observed zeolite phase selectivity in their synthesis.; In the absence of single crystal data, structure solution and refinement have typically required the use of powder X-ray data. The difficulty in solving crystal structures from powder X-ray data is that the three dimensions of information available in a single crystal data set are collapsed into one dimension (d-spacing) in a powder X-ray data set. Several techniques are applied here for solving microporous crystal structures from powder X-ray data.; Computational techniques for solving the structures of microcrystals from powder X-ray data are continuing to increase in sophistication and capability. The crystal structures of two high-silica molecular sieves, SSZ-44 and SSZ-35, are solved using Fourier recycling and represents the first application of this new computational technique for solving novel high-silica zeolite structures from powder X-ray data.; Electron diffraction data, obtained from a transmission electron microscope (TEM), has inherent advantages over X-ray data for analyzing small crystals due to the stronger interaction between the electron beam and matter compared to X-rays. The development of electron diffraction methods for solving the structure of nanocrystals is described and the application of this technique to solve the structure of a large-pore, high-silica zeolite, SSZ-48, that contains an occluded organic structure directing agent is presented.; Two studies are conducted to probe the relationship between the organic structure directing agent and the zeolite framework that is formed from its use. The first study probes the interaction between the CIT-5 framework and the N(1)-methyl-$a$-isosparteine SDA I that is found to be a more effective structure directing agent for CIT-5 than the diastereomer N(16)-methylsparteinium II originally used to direct this new high-silica zeolite.; Finally, a study into the guest/host interactions between three new zeolite structures, SSZ-35, SSZ-36 and SSZ-39 and the 37 organic structure directing agents that are capable of directing for these zeolites is presented. Computational calculations of the organic/inorganic energy of interactions provided significant insights into the observed zeolite phase selectivity by the organic SDAs. The molecular modeling investigations presented here highlight the potential for developing a rational route to the design of desirable zeolite frameworks. (Abstract shortened by UMI.)...