Computational Analysis and Screening of Nitrogen Conversion Reactions over Metal Oxide Surfaces
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Tian, Nianhan
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Abstract
This thesis uses first-principles modeling to guide the design of catalysts and electrode materials for nitrogen conversion applications, such as decentralized ammonia production and nutrient recovery. Since ammonia from nitrogen fixation is primarily produced through the Haber-Bosch process, we explore catalyst design for less energy-intensive and lower carbon footprint applications, such as photocatalysis and electrolysis of waste activated sludge, that provide alternative nitrogen conversion pathways.
We first present an overview of emerging alternative nitrogen fixation technologies, including electrocatalysis, plasma catalysis, mechanocatalysis, and photocatalysis. We highlight the need for selective and stable catalysts that can operate under ambient conditions using air as the nitrogen source.
In the first technical chapter, DFT simulations show that carbon species derived from methanol can couple with nitrogen on titania. The resulting C–N intermediates lower thermodynamic barriers for reduction, reframing carbon from a hole scavenger to a co-reactant in photocatalysis. This mechanistic study offers a new route to activate molecular nitrogen at the catalyst surface.
Next, a high-throughput DFT screen focused on N2 versus O2 adsorption selectivity identifies a small set of photocatalyst surfaces. Metastable TiO2 and vanadium borates emerge as promising candidates. We address the challenge of photocatalytic nitrogen fixation without pure nitrogen feedstock.
Finally, we develop Pourbaix analysis to assess bulk material stability under electrochemical nutrient recovery conditions. Incorporating ligand effects from NH3, glycine, and CN- shows that common electrode materials like Ni and Au are prone to dissolution, while Ti-based alloys remain thermodynamically stable under EWAS-relevant conditions.
Overall, this work shows how first-principles modeling can guide the design of materials that balance catalytic performance and sustainability. By advancing frameworks for nitrogen fixation and recovery, the thesis contributes new strategies for supporting a circular nitrogen economy at the molecular level.
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Date
2025-08-15
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Dissertation (PhD)