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<div dir="ltr"><a name="Chapter1" style="font-family: "Times New Roman", serif; font-size: 12pt;"><b><span style="font-size:14.0pt">NAME:</span></b></a><span style="font-family: "Times New Roman", serif; font-size: 12pt;"> Thuy Thanh Le</span><br>
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<p class="MsoNormal" style=""><span style=""><b><span style="font-size:14.0pt; color:#201F1E">ADVISORS:</span></b></span><span style=""><b><span style="color:#201F1E">
</span></b></span><span style=""><span style="color:#201F1E">Dr. Jeffrey Rimer</span></span><span style=""><span style="color:#660033"></span></span></p>
<p class="MsoNormal" style=""><span style=""><b><span style="font-size:14.0pt; color:#201F1E">DATE:</span></b></span><span style=""><span style="color:#201F1E"> </span></span><span style="">Wednesday, October 14, 2020<span style="color:#660033"></span></span></p>
<p class="MsoNormal" style=""><span style=""><b><span style="font-size:14.0pt; color:#201F1E">TIME</span></b></span><span style=""><span style="font-size:14.0pt; color:#201F1E">:</span></span><span style=""><span style="color:#201F1E">
</span></span><span style="">12-3:00 PM<span style="color:#660033"></span></span></p>
<p class="MsoNormal" style=""><span style=""><b><span style="font-size:14.0pt; color:#201F1E">LOCATION:</span></b></span><span style=""><span style="color:#201F1E"> Zoom meeting ID: 947 3670 1166 (Please email for passcode)</span></span></p>
<p class="MsoNormal"><span style=""><b><span style="font-size:14.0pt; color:#201F1E">TITLE:</span></b></span><span style=""><b><span style="color:#201F1E"> </span></b></span></p>
<p class="MsoNormal" align="center" style="text-align:center"><span style=""><b><span style="font-size:14.0pt; color:#201F1E">Modulation of Zeolite Composition and Its Catalytic Effect on Methanol-to-Hydrocarbons Reaction</span></b></span></p>
<p class="MsoNormal"><span style=""><b> </b></span></p>
<p class="MsoNormal" align="center" style="text-align:center"><span style=""><b> </b></span></p>
<p class="MsoNormal" align="center" style="text-align:center"><span style=""><b>ABSTRACT</b></span></p>
<p class="MsoNormal" align="center" style="text-align:center"><span style=""><b> </b></span></p>
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<span style="">Zeolites, with their diverse framework topology and tunable acidity, are highly utilized as commercial catalysts with one of the most popular applications being the production of hydrocarbons from methanol (MTH). Although MTH is a commercial
reaction, there are various mechanistic aspects that are not fully understood, and ongoing efforts are focused on ways to improve catalyst performance and establish fundamental understandings of structure-performance relationships. One of the critical challenges
in this area of research is the inherent complexity of zeolite synthesis, which can result in catalysts with a range of compositions, morphologies, and defects. This dissertation aims to better correlate the physicochemical properties of zeolites with their
catalytic performance through the development of characteristic descriptors and elucidating the effect of compositional (acid site) gradients using MTH as a benchmark reaction.
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<span style="">We first investigated the introduction of defects that occurs during zeolite ZSM-5 crystallization as a result of complex nonclassical crystallization mechanisms using time-resolved dissolution studies coupled with
<i>ex situ</i> electron and scanning probe microscopy. Our findings reveal that ZSM-5 (<b>MFI</b> framework) undergoes multiple stages of growth (both classical and nonclassical), which can lead to catalysts with a high concentration of crystalline defects.
These defects can affect mass transport properties of zeolites and consequentially catalytic performance. To quantitatively assess the impact of mass transport limitations in zeolites, we investigated the use of experimentally obtained diffusional timescales
to account for the effect of diffusional constraints, imposed by crystallite size and defects, on catalytic lifetime in MTH reaction for three zeolites/zeotypes: ZSM-5 (MFI), ZSM-11 (MEL), and SAPO-34 (CHA).
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<span style="">Lastly, using the developed descriptors, we focused on elucidating the impact of mesoscopic compositional gradients within zeolite catalysts on MTH catalyst performance. In recent years, improvements in the design and optimization of zeolite
catalysts have shifted toward modulation of elemental composition, including the characterization and understanding of acid site speciation and distribution within zeolite particles; however, mesoscopic compositional gradients within zeolite catalysts is often
overlooked. Here, we reported a one-pot synthesis of ZSM-5 with compositional gradient (i.e. zoning) and investigated its performance in MTH. We demonstrated that Si-zoned ZSM-5 exhibits improved lifetime in comparison to its homogeneous counterpart due to
the reduction of diffusion limitations and the suppression of external coking as a result of its siliceous (passivated) exterior. We further expanded this study to determine the effect of siliceous shell thickness in core-shell zeolite catalysts (i.e. zoning
analogues), which show similar improvement in lifetime, albeit with different trends in selectivity. Our findings suggest that there are distinct differences at the exterior-interior interface for zoned and core-shell catalysts that can influence mass transport
properties and impact product selectivity. </span><b></b></p>
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