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A First Principles Approach to Investigation of the Role of Cations in Zeolite Growth and Stability

Freeman, Emily (2021) A First Principles Approach to Investigation of the Role of Cations in Zeolite Growth and Stability. Master's Thesis, University of Pittsburgh. (Unpublished)

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Abstract

Zeolites are porous aluminosilicate materials that find various applications in the chemical industry in separations, catalysis, ion exchange, etc. However, despite their widespread use, the reaction mechanisms occurring during zeolite growth are still unclear. Herein, we use Density Functional Theory calculations to gain insights into the thermodynamics of oligomerization, which constitute the initial steps of zeolite growth. By taking into consideration solvent and temperature effects, our results demonstrate that the growth of aluminosilicate systems is significantly more exothermic than their pure silicate counterparts. Under pH neutral conditions, water prefers to dissociate on the early-growth-stage aluminosilicate complexes rather than desorb, thus generating potential Brønsted acid sites on the oligomers. We take into consideration the role of cations during these first steps of growth as well as their role in the final zeolite product. These (alumino)silicate growth pathways are evaluated in the presence of Na+ cation, as well as the Ca2+ and Zn2+ cations for the pure silicate pathway. The presence of cations increases the exothermicity of growth, with Ca2+ exhibiting the most energetically favorable growth environment for the silicate systems. Importantly, we demonstrate through reaction extent analysis that the presence of cations modulates the speciation of the formed oligomers, with Na+ favoring linear species in addition to the generally preferred cyclic ones. To further understand the energetic preference of cation localization in the final zeolite structure we perform a series of systematic cation substitution calculations as both framework and extraframework atoms. Overall, this work provides a fundamental understanding of the thermodynamics of complex reaction paths that occur during early stages of zeolite growth and unravels thermodynamic preference of cation localization on final zeolite structure.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Freeman, Emilyeef26@pitt.edueef26
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairMpourmpakis, Giannisgmpourmp@pitt.edu
Committee MemberVeser, Goetzgveser@pitt.edu
Committee MemberWilmer, Christopherwilmer@pitt.edu
Date: 13 June 2021
Date Type: Publication
Defense Date: 31 March 2021
Approval Date: 13 June 2021
Submission Date: 4 April 2021
Access Restriction: 2 year -- Restrict access to University of Pittsburgh for a period of 2 years.
Number of Pages: 88
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Chemical Engineering
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Zeolites, Computational Chemistry
Date Deposited: 13 Jun 2021 17:27
Last Modified: 13 Jun 2021 17:27
URI: http://d-scholarship.pitt.edu/id/eprint/40511

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