UC Irvine

This thesis presents an atomic-level investigation into chemical processes occurring on heterogeneous interfaces. Specifically, it delves into the catalytic surface reaction at the gas-solid interface and charge transfer at the liquid-solid interface, using ab initio simulations based on Density Functional Theory (DFT) calculations. The first topic addresses heterogeneous catalysis of ethane hydrogenolysis using Ru and Co catalysts with oxide supports (SiO2, TiO2, ZrO2), for chemical recycling of plastic waste. This study aims to investigate the role of oxide support on the reactivity of metal catalysts. We use DFT combined with Climbing Image Nudged Elastic Band (CI-NEB) and harmonic approximation (HA) methods to obtain the free energy profile of the molecular dissociation of adsorbed *CHCH* to 2CH* – the rate-limiting step of ethane hydrogenolysis – on metal surfaces. Comparing the two metals without the oxide support, we find that Ru(0001) has a lower free energy of the transition state (TS) compared to Co(0001), in agreement with Ru being the most reactive catalyst for ethane hydrogenolysis. However, we find that the free energy of the TS state in Co with SiO2, TiO2, ZrO2 is lower than either Co(0001) or Ru(0001). The results suggest that the reaction barrier using Co can be lowered using oxide supports, making the earth-abundant Co a competitive catalyst for rare-earth metal Ru. The second topic explores the charge stability of boron vacancy in hexagonal boron nitride (hBN) in contact with water with varying thicknesses of hBN for quantum sensing applications in an aqueous environment. Despite previous literature highlighting the existence of negatively charged boron vacancy in hBN as a promising spin qubit, little is known about its stability in water. To address this gap, we carry out ab initio molecular dynamics simulations based on DFT for hBN in contact with water to study the charge transfer to boron vacancy from two types of electron donors: an oxygen dopant in hBN serving as a “static electron donor”, and the hydronium radical in water serving as a “mobile electron donor”. We find that the spin triplet state of boron vacancy is stable in a monolayer hBN in contact with water using either electron donor, suggesting that the charge transfer efficiency from the donor to the vacancy is efficient for monolayer hBN. However, in bulk hBN, the charge transfer efficiency to the boron vacancy appears to be limited using a hydronium radical, and there is a significant fluctuation in the charge state of boron vacancy in bulk hBN. This finding contrasts sharply with spin defects in 3D semiconductors, e.g., nitrogen-vacancy centers in diamonds, where the charge stability decreases as the location of the defect is closer to the surface.