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Altering Framework Topology and Heteroatom Distributions of Molecular Sieves by Designed Organic Structure-Directing Agents


Park, Youngkyu (2024) Altering Framework Topology and Heteroatom Distributions of Molecular Sieves by Designed Organic Structure-Directing Agents. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/d1xj-kn25.


The growing demand for chemical production combined with the urgent need to mitigate the accelerated climate and environmental changes motivates efforts to create highly efficient and selective catalysts and adsorbents. Zeolites and molecular sieves are a key class of materials for addressing these needs because of their high activity and selectivity with catalytic reactions. Additionally, they can show superior adsorption properties because of their structure and surface polarity that can also give shape selectivity with molecules smaller than ca. 1 nanometer. Further advancements in molecular sieve properties will rely on advancements in preparation methods. To this end, the research results presented here explore synthetic approaches for controlling the framework topology and the heteroatom incorporation within silicate-based molecular sieves by means of the strategic design of their organic structure-directing agents (OSDAs).

Part I presents the synthesis of STW-type germanosilicate molecular sieves with high-silica framework compositions and the enrichment of chirality. A chiral OSDA is computationally designed based on the predicted stabilization energy toward the pure-silica STW framework. An improved synthesis route for both enantiomers of the OSDA is developed. The enantiopure OSDA is capable of crystallizing a high-silica STW-type germanosilicate molecular sieve that shows distinct framework compositions from previously reported germanium-rich STW. The enantiomeric enrichment of powdered samples without occluded enantiopure OSDAs is characterized by the dynamical refinement of microcrystal electron diffraction data. The high-silica, enantiomerically enriched STW exhibits the framework stability upon thermal treatment and the enantioselective adsorption of 2-butanol. The results in Part I demonstrate the design strategy of OSDAs for crystallizing stable, enantio-enriched molecular sieves for enantioselective chemical separations and catalysis.

In Part II, the distribution of heteroatoms incorporated within borosilicate molecular sieves is studied with regard to its control by cationic OSDAs. To aid in the characterization of the heteroatom sites within borosilicate molecular sieves, the relationship between the 11B NMR chemical shift and the local geometry of boron within tetrahedrally coordinated silicate frameworks is first investigated. From crystalline borosilicate minerals with highly ordered, tetrahedrally coordinated boron atoms, it is revealed that the chemical shifts from 11B NMR linearly correlate with the local geometric parameters. Further studies on the borosilicate molecular sieves that possess more open space and wider angles suggest that the correlation between the average bond angles and 11B NMR chemical shifts can be employed for the entire class of three-dimensional, crystalline borosilicates. Two structurally similar quaternary ammonium OSDAs with different locations of positive charge are designed and synthesized. MWW-type borosilicate molecular sieves are crystallized by both OSDAs, and the quaternary ammonium moieties in the two OSDAs are found to interact with boron species with significantly different 11B NMR chemical shifts. Using the correlation developed here, the characterization results demonstrate that the heteroatom siting within the molecular sieve framework can be selectively altered by tailoring the OSDA structure in terms of the position of positive charge.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Molecular Sieves; Heterogeneous Catalysis; Adsorbent; Organic Structure-Directing Agents; Enantiomeric Enrichment; Heteroatom Incorporation; Borosilicate; Nuclear Magnetic Resonance
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Thesis Availability:Not set
Research Advisor(s):
  • Davis, Mark E.
Thesis Committee:
  • Flagan, Richard C. (chair)
  • Manthiram, Karthish
  • Stoltz, Brian M.
  • Zones, Stacey I.
  • Davis, Mark E.
Defense Date:13 May 2024
Funding AgencyGrant Number
Chevron Energy and Technology CompanyUNSPECIFIED
Record Number:CaltechTHESIS:04292024-055507772
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for Chapter 5
Park, Youngkyu0000-0001-7328-7565
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:16362
Deposited By: Youngkyu Park
Deposited On:05 Jun 2024 18:46
Last Modified:05 Jun 2024 18:46

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