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Computational modeling of diverse active site environments in heterogeneous catalysis
Nolen, Michelle A.
Nolen, Michelle A.
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2025
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Nolen_mines_0052E_13048.pdf
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2026-05-11
Abstract
The global energy sector is responsible for a significant portion of greenhouse gas emissions, which are directly correlated to rising surface temperatures. Policy efforts to mitigate climate change must include both short- and long-term approaches, such as decarbonizing operational processes and/or reducing their energy demands, and implementing alternatives to fossil-fuel-based feedstocks. Heterogeneous catalysis is critical to many industrial processes today, and will continue to play a pivotal role the global pursuit of emissions reduction via both long- and short-term strategies. For example, a multitude of catalytic materials can facilitate CO2 conversion reactions to produce platform and/or value-added chemicals. Catalysts with high reactivity and targeted selectivity can reduce energy demands by lowering heat requirements and moderating energy-intensive downstream separations. Heterogeneous catalysts are also critical in fuel production technologies that utilize renewable feedstocks as fossil-fuel-based alternatives. Thus, the continued design of catalytic materials with improved reactivity and tunable selectivity remains an imperative area of research.
Catalyst design strategies rely upon a fundamental understanding of structure-function relationships. Towards this goal, this thesis combines density functional theory (DFT) calculations, microkinetic models, and ab-initio thermodynamics to explore the role of distinct active sites on a variety of materials, ranging from transition-metal nanoparticles to zeolites. First, DFT-derived models reveal reaction mechanisms and rate-limiting steps involved in CO2 hydrogenation to C1 products on common transition-metal based catalysts. These mechanistic trends are investigated under a range of CO2 hydrogenation conditions relevant to both the clean-surface limit and moderate surface coverages. Next, a study of the role of confinement effects during toluene alkylation in zeolites reveals the pivotal role of van der Waals interactions in stabilizing key intermediates. Finally, ab-initio thermodynamics and site-titration experiments are combined to develop a methodology for identifying physically relevant active site models. The work presented herein provides an atomic-scale investigation into the intrinsic reactivity and selectivity of active sites relevant to C1 production, industrial aromatic alkylation reactions, and biomass upgrading processes. In doing so, this thesis offers insights into design strategies for the continued development of heterogeneous catalysts and their role in the global energy transition.
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