A density functional theory study into the mechanism and reactivity in heterogeneous system

Abstract

Heterogeneous catalysis is universally acknowledged as a paramount approach in a wide range of the chemical, biological, and energy industries. Moreover, heterogeneous catalysis has also been applied to solving the problem of many aspects in our daily life, such as environmental enhancement, energy shortage, efficient synthesis. Just as its name implies, heterogeneous catalysis is catalysis where the phase of catalyst differs from the reactants or products. Normally it usually happens at the gas-solid or liquid-solid interface.

This PhD theses mainly addresses two types of heterogeneous reactions: the one happens at the interface between gas and solid (chapter 3 and chapter 4), and the other occurs between liquid and solid (chapter 5 and chapter 6). According to the reaction properties, we tackle these two kinds of reactions with different methods. The gas-solid reactions are solved by traditional Density Functional Theory (DFT) method; while liquid-solid reactions are carried out using ab initio Molecular Dynamics (MD) simulation.

Chapter 1 focuses on the background and theoretical methods applied in the projects. In chapter 2, fundamental theories and techniques in this thesis are introduced in detail, as well as VASP software packages.

Chapter 3 comprehensively introduces the mechanism of Fisher-Tropsch process on stepped Ru(0001) surface. In this part, two most possible mechanisms are both discussed: CO insertion and carbide mechanism. Additionally, the coverage effect is introduced to acquire more realistic results, based on which we reveal the selectivity, activity and ratedetermined step of Fisher-Tropsch process from syngas to C2 compounds.

Chapter 4 presents the distinct catalytic performances on three different types of NiO surface. The methane combustion process is investigated as a probe on these surfaces. In this part, activation of methane is studied under different coordination environment of Ni2+, such as sheet NiO, cubic NiO and octahedral NiO represented by NiO(110), NiO(100) and NiO(111), respectively. The mechanism schemes of the pathway are all simulated to search the most favorable methane oxidation route.

Chapter 5 presents the calculation on Pt(111)/H2O interface to research the preference for CO adsorption in liquid with an advanced Molecular Dynamic (MD) approach, namely umbrella sampling. Both the hollow site and the top site are simulated for CO adsorption and desorption with free energy chemisorption energy obtained.

In chapter 6, the slow-growth (SG) approach and constrained molecular dynamics (CMD) are adopted and combined to address the oxygen evolution reaction (OER) on the interface between water and IrO2(110) surface under electrostatic potential environment. The surface is terminated by adsorbed oxygen atoms on the iridium atoms to account for the electrochemical potential in experiments. The different reaction pathways are discussed to figure out the most possible mechanism. In order to make the reaction environment closer to the realistic condition, a constant potential model is achieved by correcting constant potential charge via workfunction calculations.

Date of Award	Jul 2021
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Chinese Scholarship Council (CSC)
Supervisor	Peijun Hu (Supervisor) & Haresh Manyar (Supervisor)