Exploration of Secondary Structure Directing Agents on the Formation of Hierarchical and 2D Zeolites
Date of Award
12-2023
Degree Type
Thesis
Degree Name
Master of Science in Chemical Engineering
Department
Chemical and Biomedical Engineering
First Advisor
Yang, Shaowei
Second Advisor
Uz, Metin
Third Advisor
Thrash, Marvin
Abstract
Hierarchical and 2D zeolites address the diffusion limitation of conventional zeolites by enhancing diffusion in the mesopores. So far, the surfactant compounds, which successfully produce hierarchical zeolites, have complex molecular structures making the zeolite synthesis expensive and uncompetitive for commercialization, making cost-effective synthesis of hierarchical and 2D zeolite highly desirable. However, the development of effective synthesis protocols relies on a good understanding of the SDA's influence on crystal morphology development, which is largely unknown. Here, we explore inexpensive and readily available compounds via a dual-SDA strategy and use MFI zeolite as the model system for the research. TPAOH served as the primary SDA to promote MFI zeolite formation and several other surfactant molecules served as the secondary SDA to restrict crystal growth along a particular zeolite channel.
First, the synthesis using an in-situ growth method was performed and the concentration of the primary SDA was modulated. Another set of zeolite synthesis conditions, arbitrarily chosen, was used to study the synergistic roles between dual-SDA and synthesis conditions on zeolite crystal morphology development. Moreover, we explored dual-SDA zeolite synthesis in a seed-mediated solution, for which the zeolite seeds promote nucleation and is anticipated to overcome the strong growth restriction of the secondary SDAs. The synthesis conditions had no significant effect on the zeolite formation and the secondary SDA plays a key role in the final crystal morphology, which is attributed to how well the secondary SDA can fit into the zeolite channels and restrict the growth along a particular direction.
We further investigate the same set of SDAs for another type of zeolitic material, i.e., silicoaluminophosphates (SAPO). This involved mixing multiple amino acids in a precursor solution with seed crystals of SAPO-34 zeolite. leading to different zeolite crystal phases. Although they generated similar crystal phases for in situ growth. This indicates strong synergistic effects between secondary SDA and synthesis conditions, such as seeding, on crystal growth. Taken together, our findings provide insight into the effect of multiple SDAs and seed crystals on the synthesis of hierarchical and 2D zeolites. This opens possibilities for exploration into inexpensive and commercially available structure-directing agents.
Recommended Citation
Yahaya, Suleiman, "Exploration of Secondary Structure Directing Agents on the Formation of Hierarchical and 2D Zeolites" (2023). ETD Archive. 1369.
https://engagedscholarship.csuohio.edu/etdarchive/1369
