TUNING FE-BASED CATALYSTS FOR ENHANCED HYDRODEOXYGENATION: AN ATOMISTIC APPROACH

Isaac Onyango

doi:10.7273/000007073

Bio-oils from biomass are a compelling alternative to fossil-based fuels. Biomass is converted into bio-oil via fast pyrolysis. However, bio-oils derived by pyrolysis need upgrading to increase their usability and hydrodeoxygenation (HDO) is a promising means of upgrading the bio-oils. Fe-based catalysts have been demonstrated to be highly selective HDO catalysts. This dissertation investigates Fe-based catalysts with the aim of gaining fundamental insights into how they can be tailored for the design of long lasting, cost efficient and highly selective HDO catalysts. The work is predominantly from an atomistic perspective using atomistic models based on density functional theory. It is important to account for coverage effects in theoretical modelling as they have a significant impact on thermodynamics and kinetic properties of surface reactions. Chapter 3 covers the various methods used to capture coverage effects in heterogeneous catalysis and Chapter 4 demonstrates of how coverage effects influence spatial arrangements of adsorbates using propylene on Cu(111). Fe-based catalysts are covered in Chapters 5 through 8. In Chapter 5, we quantify the interaction of carbon on Fe(100) and use DFT-parameterized lattice gas cluster expansion (LG CE) to account for coverage effects. This study provides great insight into coke formation, a phenomenon which leads to catalysts deactivation, during HDO. In Chapter 6, we determine the distribution of four precious metals (Pt, Pd, Rh, and Ru) on Fe(100) using LG CEs. These precious metals have been demonstrated to protect Fe-based catalysts from oxidative deactivation and also enhance the activity of the catalysts for the HDO of phenolics. Our results show that the four metals have very distinct distributions and ground states, and thus the reaction environment for the HDO depends on the nature of the precious metal used to promote the Fe- based catalyst. In Chapter 7, we mechanistically study the tautomerization of phenol on an alkali-promoted Fe(110) surface. By comparing tautomerization to the direct C-O bond cleavage mechanism, we gain fundamental insights into the improved selectivity towards arenes during HDO of phenol on alkali-promoted Fe catalysts. In Chapter 8 we determined the impact of electric fields on the oxidation of Fe. Our results show that the initial oxidation kinetics show that strong increases in electric fields facilitate the formation of an oxide, but as one approaches equilibrium, high fields mitigate oxide formation. This study demonstrates that electric fields are a viable knob to use in order to mitigate oxidative deactivation during HDO reactions.

TUNING FE-BASED CATALYSTS FOR ENHANCED HYDRODEOXYGENATION: AN ATOMISTIC APPROACH

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