Carbon plays an important role on Earth. It is integral to the formation of life, the origin and storage of fossil fuel, and the global climate. Therefore, it is necessary to study its distribution, long-term cycle, and evolution. The cycle of carbon from Earth’s surface is of great importance to solve the energy problem and climate change on the geological time scale. Both the energy problem and global warming are severely threatening human development. Because this field of research can help to better understand the structure of the Earth, understanding the behaviour of carbon on Earth is fast becoming an important topic. For example, the Deep Carbon Observatory (DCO) is a global research programme aimed at transforming the understanding of carbon’s role in Earth. This thesis...[ Read more ]

Carbon plays an important role on Earth. It is integral to the formation of life, the origin and storage of fossil fuel, and the global climate. Therefore, it is necessary to study its distribution, long-term cycle, and evolution. The cycle of carbon from Earth’s surface is of great importance to solve the energy problem and climate change on the geological time scale. Both the energy problem and global warming are severely threatening human development. Because this field of research can help to better understand the structure of the Earth, understanding the behaviour of carbon on Earth is fast becoming an important topic. For example, the Deep Carbon Observatory (DCO) is a global research programme aimed at transforming the understanding of carbon’s role in Earth. This thesis mainly focuses on the hydrocarbon reaction in the mantle. During the research, it was noticed that the results of the water-gas shift reaction at high temperatures and pressures, which generate formic acid as the final product, was totally different from the findings of previous studies close to ambient conditions. As such, detailed research was performed on the mechanism and kinetic thermodynamic properties. This thesis contains six chapters. Chapter 1 briefly introduces the hydrocarbon reactions and some of the relevant research from recent years, together with a selection of studies on water-gas shift reactions. It also outlines the objectives of the thesis. Chapter 2 details the techniques that were used to perform the ab initio molecular dynamics (MD) simulations. Chapter 3 focuses on the most important part of the research: the water gas shift reaction. First, a series of ab initio molecular dynamic simulations were conducted on this type of reaction, where it was found that carbon monoxide has relatively high chemical reactibility. It is able to quickly react with water at 1400 K and at pressures greater than 10 GPa. Furthermore, the reaction generates formic acid as a stable final product, while in previous studies, research mainly focused on industrial conditions (200-450 °C and ambient pressure). These studies reached the conclusion that the water-gas shift reaction will produce carbon dioxide and hydrogen from the reactants. It is hoped that this present study will provide further inspiration for future research in this field. Chapter 4 details other types of hydrocarbon reactions among H₂O, CO₂, CO, CH₄, H₂, and sodium acetate (CH3COONa). By conducting similar ab initio MD simulations, some interesting results were found. Hydrocarbon reactions all tend to form heavier molecules when the temperature and pressure are above 2500 K, 15 GPa. To further study the mechanism, the characteristics of the reaction process were analysed. Chapter 5 provides theoretical calculations regarding the free energy and entropy of the water-gas shift reaction. Due to simulation time limits, the formic acid may be at the metastable state. Hence, this study compares the free energy between the two sides of the water gas shift reaction. The results indicate that formic acid is stable under such conditions. Chapter 6 concludes the findings of the study. In addition, an outlook for future study into hydrocarbon reactions in the deep Earth is also discussed.