Browsing by Author "Lee, ChoongSze"

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    Supporting data for "Catalysis-in-a-Box: Robotic Screening of Catalytic Materials in the Times of COVID-19 and Beyond"
    (2020-05-29) Kumar, Gaurav; Bossert, Hannah; McDonald, Dan; Chatzidimitriou, Anargyros; Ardagh, Alexander M; Pang, Yutong; Lee, ChoongSze; Tsapatsis, Michael; Abdelrahman, Omar A; Dauenhauer, Paul; hauer@umn.edu; Dauenhauer, Paul, J; Dauenhauer Research Group
    The emergence of a viral pandemic has motivated the transition away from traditional, labor-intensive materials testing techniques to new automated approaches without compromising on data quality and at costs viable for academic laboratories. Reported here is the design and implementation of an autonomous micro-flow reactor for catalyst evaluation condensing conventional laboratory-scale analogues within a single gas chromatograph (GC), enabling the control of relevant parameters including reactor temperature and reactant partial pressures directly from the GC. Inquiries into the hydrodynamic behavior, temperature control, and heat/mass transfer were sought to evaluate the efficacy of the micro-flow reactor for kinetic measurements. As a catalyst material screening example, a combination of four Brønsted acid catalyzed probe reactions, namely the dehydration of ethanol, 2-propanol, 1-butanol, and the dehydra-decyclization of 2-methyltetrahydrofuran on a solid acid HZSM-5 (Si/Al 140), were carried out in the temperature range 403-543 K for the measurement of apparent reaction kinetics. Product selectivities, proton-normalized reaction rates, and apparent activation barriers were in agreement with measurements performed on conventional packed bed flow reactors. Furthermore, the developed micro-flow reactor was demonstrated to be about ten-fold cheaper to fabricate than commercial automated laboratory-scale reactor setups and is intended to be used for kinetic investigations in vapor-phase catalytic chemistries, with the key benefits including automation, low cost, and limited experimental equipment instrumentation.
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    Understanding Length Scales of Diffusion in Hierarchical Materials
    (2022-04) Lee, ChoongSze
    The utility of probe molecules, such as pyridine, benzene, and mesitylene, in infrared (IR) spectroscopy is ubiquitous in the catalysis field to assess the number and type of sites in zeolites. A challenge remains in determining the accessibility and uniformity of these acid sites within the confined voids of zeolite micropores and mesopores. Time-resolved Fourier Transformed Infrared (FTIR) Spectroscopy is a powerful technique to elucidate transient diffusion of organic probe molecules through zeolite pores by assessing the distinct transport properties of seed and finned zeolites, a new class of hierarchical material. In this work, we present an alternative approach to compare internal diffusion properties of zeolites using branched, cyclic amines, where diffusion regimes within the zeolite confinements are discerned. We show that the diffusion time scale for trimethylpyridine and dimethylpyridine through MFI/MEL and FER pores are much slower than for pyridine due to steric hindrance from its methyl groups. This methodology can be further extended to probe diffusion regimes and obtain active site distributions of various zeotype catalysts.