Using Density Functional Theory to Study the Catalytic and Electronic Properties of Metals and Metal Oxides: Focus on H2 Activation and CO2 Desorption



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Catalysis plays an essential role in modern civilization, as it spans the fields of chemical, pharmaceutical, energy and electronic industries. Recent progress in computational infrastructure and experimental techniques is pushing forward the systematical understanding of catalysis. This dissertation aims to study the catalytic and electronic properties of metal and metal oxides with Density Functional Theory (DFT). The widespread adoption of water electrolysis using renewable energy for the sustainable production of H2 is hindered by the scarcity and high price of Pt, the catalyst of choice for HER. The high catalytic activity of Pt has been attributed to its optimal binding strength of hydrogen (ΔG). However, the ΔG descriptor has shortcomings, as thermodynamics dictate ΔG=0 at equilibrium. We have found a new descriptor using the binding energy difference (ΔΔG) between the weaker and stronger binding sites, which linearly correlates with the reaction barrier (Ea). The kinetics are rigorously captured by ΔΔG as alternative descriptor, as it conforms to thermodynamic principles and removes ambiguity in choosing surface coverages. Next, the mechanism for UV and gas detection on ZnO surface is investigated. Known as a good semiconducting and photocatalytic material, the mechanism behind the photocatalytic properties of ZnO is poorly understood. There are two opposite mechanisms showing the desorption of O2 or CO2 changes the conductivity. We have performed careful experiments along with DFT simulations to study the mechanism underlying the photocatalytic properties. Experimental and computational evidence has proved a direct link between CO2 desorption and ZnO conductivity change. Finally, the connection between electronic and catalytic properties is studied. While the adsorption of atoms on metals is well described by the d-band model, a robust theoretical framework for the adsorption of hydrogen on metal oxides is less developed. We have used electronic structure simulations to systematically study hydrogen binding on spinel oxides with the formula MAl2O4. Preliminary results show a positive correlation between the bulk band gap and the hydrogen binding energy. Our detailed investigation of hydrogen interactions with a well-defined library of spinel allows us to derive novel structure-property relationships, which can guide the design of oxide catalysts for selective (de-)hydrogenation reactions.



Catalysis, DFT