Date of Award
12-2022
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemical and Biomolecular Engineering
Committee Chair/Advisor
Dr Rachel B. Getman
Committee Member
Dr Ming Yang
Committee Member
Dr. Christopher L. Kitchens
Committee Member
Dr. Leah B. Casabianca
Abstract
Advances in extraction of shale oil and gas has increased the production of geographically stranded natural gas (primarily consisting of methane (C1) and ethane (C2)) that is burned on site. A potential utilization strategy for shale gas is to convert it into fuel range hydrocarbons by catalytic dehydrogenation followed by oligomerization by direct efficient catalysts. This work focuses on understanding metal cation catalysts supported on metal-organic framework (MOF) NU-1000 that will actively and selectively do this transformation under mild reaction conditions, while remaining stable to deactivation (via metal agglomeration or sintering). I built computational models validated by experimental methods to elucidate the structure-function relationship of catalysts for reactions of small molecules (ethane in this work) in natural gas. Computational techniques and characterization data from experimental collaborations at Argonne National Lab and Northwestern University were used to build kinetic models to learn about mechanism of ethene hydrogenation on M-NU-1000 catalysts (M = Ni, Cu, Zn, Co, Mn, Fe). Hydrogen adsorption and dissociation barrier is identified as the reason for discrepancy between experimental and computational data. Quantum density functional theory (DFT) simulations and microkinetic modeling on an expanded mechanism with multiple hydrogen adsorption and dissociation steps is performed. The model predicted spin state of metal as an important design variable with high spin and low spin metals following different mechanistic pathways due to different hydrogen adsorption and dissociation energies. This resolved the discrepancies between the model and experiments. The impact of different modeling choices on microkinetic modeling is analyzed by expanding the method to include Molecular Dynamics (MD) simulations and comparing different catalyst models in ethene dimerization reaction on Ni@NU-1000. Adsorption and desorption steps are identified as being more significant for determining rates than the activated steps. In collaboration with Northwestern University and Stonybrook University, polyoxometalate and polysulfidometalate catalysts supported on NU-1000 active for CO oxidation and electrochemical hydrogen evolution reaction are studied. Computationally elucidated structure of these catalysts is validated by experimental methods (XAS, XRD and DRIFTS) and provided the insight that the clusters need to be reduced further to remove the peripheral sulfur atoms to tailor them for more challenging reductive chemistry. Using this information our collaborators synthesized a a catalyst with lower sulfur content that was found to be active for acetylene hydrogenation. Overall, this work furthered our understanding of catalyst structure and mechanisms for reductive chemical transformation for shale gas to liquid conversion with insights that are applicable generally to MOF catalysts.
Recommended Citation
Shabbir, Hafeera, "Elucidation of Active Site and Mechanism of Metal Catalysts Supported in NU-1000" (2022). All Dissertations. 3211.
https://tigerprints.clemson.edu/all_dissertations/3211
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