[CCoE Notice] Dissertation Defense: Controlling Structure and Properties of Zeolites

[Grayson, Audrey A]

PhD DEFENSE STUDENT: Matthew Oleksiak
DATE: Tuesday,May 31, 2016
TIME: 4:00 PM
PLACE: Mechanical Engineering Large Conference Room
DISSERTATION CHAIR: Dr. Jeffrey Rimer
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TITLE:

Controlling Structure and Properties of Zeolites

Prepared in Organic-free Media

Zeolites are used extensively for ion-exchange, gas adsorption, and catalysis due to their unique pore structures of molecular dimensions that arise from the crystal structures. However, the majority of zeolites (>200) require an organic additive, which must be removed post-synthesis, to be formed. Removing this organic increases cost and may be hazardous to both health and the environment. These concerns limit large-scale synthesis of zeolites for practical applications primarily to the ones that are formed in the absence of organic chemicals. To this end we have identified the effects of various synthetic parameters, specifically growth solution composition, crystallization temperature, and heating time on the phase behavior of zeolite crystallization and mapped these results using ternary diagrams. We used these diagrams to characterize intercrystalline transformations and identify synthesis conditions leading to the formation of metastable zeolites.
The crystallization of two commercial zeolite structures, FAU and LTA, was correlated to the heterogeneous nature of common growth solutions under realistic growth conditions. These studies showed that phase separation indeed influences the local environment for nucleation and crystallization and provided evidence that nucleation events occur at the interface between precursor particles and growth solution. Based on these observations we proposed that nucleation within the interior of precursors would be limited due to confinement effects, leading to preferred interfacial (heterogeneous) nucleation.
We were also able to utilize our phase diagrams to define growth conditions that would lead to zeolites of similar topology with subtle structural differences. To this end we showed the ability to control the formation of two distinct polymorphs, P1 and P2, both of which have the GIS framework. Interestingly, while nearly identical in composition and structure, these two polymorphs exhibit different gas adsorption capacities and thermal stabilities.
Furthermore, we established novel synthetic procedures for the LTA and FAU frameworks. Specifically, we designed a protocol for increasing the silica content of LTA two-fold compared to conventional materials via a cost-effective, one-step synthesis procedure. The resulting material, named HOU-2, exhibits improved thermal stability, which increases its potential use as a catalyst. Similarly, we increased the silicon-to-aluminum ratio of FAU to 3.0 (i.e., HOU-3) and demonstrated its improved properties for catalytic cracking, which is its main industrial use.
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