ADVANCING BIOFUEL CATALYSIS: DECIPHERING HOW SURFACE INTERACTIONS AND ELECTRIC FIELDS SHAPE HYDRODEOXYGENATION FROM FIRST PRINCIPLES

Naseeha Afra Cardwell

doi:10.7273/000007333

To optimize hydrodeoxygenation for biofuel production, it is essential to understand the behavior of molecules in the fuel and the catalysts used to develop the fuel. Modeling these systems requires the inclusion of lateral interactions which influence reaction pathways. These are affected by other factors, such as the metal catalyst type, the coverage of adsorbed species, and reaction conditions. This dissertation provides a foundation for modeling biofuel adsorbates and potential catalysts for hydrodeoxygenation under different reaction conditions. The first-principles-based results reveal that the adsorption of aromatics is greatly influenced by the aromatic's complexity and the coverage. The lateral interactions can be parsed out into the surface-mediated and through-space interactions. Surface-mediated interactions, stronger on noble metals like platinum, govern the behavior of closed-shell aromatics, while through-space interactions become more dominant for open-shell and complex aromatics. Using simple descriptors for the mean-field parameters, parity plots are developed to predict the coverage-dependent adsorption energies for all aromatic/metal combinations studied, enabling the inclusion of experimentally-relevant coverages in reaction studies with significantly reduced computational cost. Further work explored the use of electric fields to mitigate iron catalyst oxidation. The findings show that electric fields weaken oxygen adsorption on iron, regardless of coverage or iron facet. Comparison with experimental work highlights the value of combining theory and experiment to understand catalytic systems. The results indicate that the different iron facets have varied responses to changes in reaction conditions, emphasizing the importance of modeling catalytic systems to optimize reactions and enhance catalyst effectiveness. The role of alkali metals on the hydrodeoxygenation of phenol in the presence of water over an iron catalyst is also explored. Alkali metals are found to attract water molecules, reducing interactions between water and iron and potentially extending the catalyst lifespan by preventing oxidation. Cesium is shown to inhibit phenol tautomerization in favor of direct oxygen cleavage. The interactions between the catalyst, phenol, water molecules, and alkali metal alter the reaction pathways, complementing the findings from the other studies. The impact of coverage on phenol and hydroquinone decomposition products is further examined. The study shows that phenol and hydroquinone follow similar thermal decomposition pathways. High coverage is found to introduce complexity in the catalytic systems, likely due to increased through-space interactions, making thermal X-ray photoelectron spectroscopy spectra difficult to deconvolute, but highlighting the importance of lateral interactions in affecting reaction pathways and energetics. The studies in this dissertation emphasize the importance of incorporating lateral interactions for accurately modeling catalytic hydrodeoxygenation systems. High coverage, solvent environments, electric fields, and other adsorbates are shown to alter both adsorption energies and reaction pathways, affecting catalyst performance. By modeling and understanding these systems, we can optimize catalyst properties and reaction conditions, ultimately improving reaction efficiency and extending catalyst lifespans, laying the foundation for optimizing biofuel production.

ADVANCING BIOFUEL CATALYSIS: DECIPHERING HOW SURFACE INTERACTIONS AND ELECTRIC FIELDS SHAPE HYDRODEOXYGENATION FROM FIRST PRINCIPLES

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