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Synthesis Structure Relationships in Amine Functionalized Mesoporous Silica Supports for Improved Catalytic Performance

Chen, Jee-Yee
http://orcid.org/0009-0001-9713-4341
http://rave.ohiolink.edu/etdc/view?acc_num=osu1689682657410763

Abstract Details

2023, Doctor of Philosophy, Ohio State University, Chemical Engineering.
Investigating the impact of the structure of heterogeneous catalysts on performance is crucial for designing catalysts with enhanced activity. A significant challenge is creating uniform catalytic materials since current synthetic methods tend to produce materials with a wide distribution of catalytic sites. Indeed, materials that are seemingly simple have been revealed to be staggeringly complex, including materials such as zeolites, alumina, silica, and aminosilane modified materials called amino-silicas. Amino-silica heterogeneous catalysts are widely used in many applications, including pharmaceuticals, carbon dioxide adsorption, and biomass upgrading. Amino-silica materials can be designed with cooperative interactions to enhance catalytic performance in different reactions, such as the aldol reaction and condensation. One common mesoporous support is Santa Barbara Amorphous 15 (SBA-15). SBA-15 has exceptional properties, including thermal stability and high surface area. The porosity of SBA-15 can be tuned through synthesis conditions. In this dissertation, we demonstrate that limiting the micropore volume in SBA-15 can further increase the overall catalytic performance. This result indicates that catalytic sites located within micropores are inactive during catalytic reactions, disproving the previous assumption that all sites have equal contributions. We conduct a poisoning test to quantify the catalytic sites on both regular (REG) and negligible-micropore (NMP) SBA-15. The results of site quantification demonstrate that amine-functionalized SBA-15 has multiple types of catalytic sites with different activities, including high activity, medium activity, low activity, and inactive sites. With our new understanding of different types of sites in aminosilica materials, it was intriguing to re-evaluate previous observations (e.g., surface density) through the lens of whether the difference was associated with the activity of the sites or the fraction of catalytic sites. We further investigate the mechanisms associated with these different activity levels. By controlling the amine surface loading on NMP-SBA-15, it is shown that the low activity sites are lacking amine-silanol cooperative interactions. These materials are also investigated to determine the stability of the different types of sites. Stability studies reveal that the high activity sites are the least stable compared to other types, as they transform into the least active sites after reuse. This transformation primarily occurs during the first round of use of the catalyst and causes significant deactivation. Several characterization methods suggest that the loss of cooperative interactions in the high activity sites is likely because of organic accumulation during recycling. We can remove the organic accumulation by washing the catalyst with a dilute sodium carbonate solution at room temperature for a short period. As a result, the recycled catalyst material is reactivated and exhibits similar catalytic performance to the fresh catalyst. To further understand the sites on our catalysts, we examine the relation between preferential grafting of acid-base attraction with types of site formation. A carbamate group protected neutralized aminosilane is used for grafting, which is able to limit the acid-base interaction during synthesis. To examine the relation between preferential grafting of acid-base attraction with types of site formation, a carbamate group protected neutralized aminosilane is used for grafting. The neutralized aminosilane is able to limit the acid-base interaction during the grafting. The carbamate group can be removed using a thermal treatment to produce the desired aminosilane functional group on the material. Site quantification results show that the carbamate group protected material has a higher active sites ratio than the regular base aminosilane grafted material. Interestingly, it is also shown that the thermal treated material increases the catalytic activity of the material regardless of synthesis method. The results are consistent with the hypothesis that the treatment temperature affects the silanol group distribution and correspondingly the catalyst activity. Last, we expand beyond the aldol reaction and condensation for the aminosilica catalysts. It is shown in literature that the nitroaldol reaction rate can be affected by the pore size of the support. The synthesis-structure relationship is investigated for the NMP SBA-15 to understand the relationship between pore size and site distribution for the nitroaldol reaction while limiting the micropores. We show that the pore size of NMP SBA-15 can be tuned from 5.5 to 12 nm through different aging temperatures, pore-expanding agents, and structure directing surfactants. The catalytic testing for these materials with pore size difference is ongoing work in our group. Overall, this work provides insights into the pore structure of SBA-15 and demonstrates the ability to control and enhance the catalytic performance of amino-silica catalyst materials, thereby extending their lifetime. This work further shows the complexity of NMP SBA-15 with different types of catalytic sites and determines the catalytic performance on a per-site basis.
Nicholas Brunelli (Advisor)
Yiying Wu (Committee Member)
Lisa Hall (Committee Member)
Aravind Asthagiri (Committee Member)
Chemical Engineering
Aldol, SBA-15, biomass upgrading, catalysis, heterogeneous catalyst, amine-silica, structure synthesis

Recommended Citations

Citations

  • Chen, J.-Y. (2023). Synthesis Structure Relationships in Amine Functionalized Mesoporous Silica Supports for Improved Catalytic Performance [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1689682657410763

    APA Style (7th edition)

  • Chen, Jee-Yee. Synthesis Structure Relationships in Amine Functionalized Mesoporous Silica Supports for Improved Catalytic Performance. 2023. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1689682657410763.

    MLA Style (8th edition)

  • Chen, Jee-Yee. "Synthesis Structure Relationships in Amine Functionalized Mesoporous Silica Supports for Improved Catalytic Performance." Doctoral dissertation, Ohio State University, 2023. http://rave.ohiolink.edu/etdc/view?acc_num=osu1689682657410763

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.
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