A DFT study of hydrogen abstraction from light alkanes: Pt alloy dehydrogenation catalysts and TiO2 steam reforming catalysts

Sustainable energy production is one of the biggest challenges of the 21st century. This includes effective utilization of carbon-neutral energy resources as well as clean end-use application that do not emit CO2 and other pollutants. Hydrogen gas can potentially solve the latter problem, as a clean burning fuel with very high thermodynamic energy conversion efficiency in fuel cells. In this work we will be discussing two methods of obtaining hydrogen. The first is as a byproduct of light alkane dehydrogenation where we obtain a high value olefin along with hydrogen gas. The second is in methane steam reforming where hydrogen is the primary product. Chapter 1 begins by introducing the reader to the current state of the energy industry. Afterwards there is an overview of what density functional theory (DFT) is and how this computational technique can elucidate and complement laboratory experiments. It will also contain the general parameters and methodology of the VASP software package that runs the DFT calculations. Chapter 2 will introduce the reader to light alkane dehydrogenation over platinum. Then this chapter goes into detail about the current industry standard alloy, PtSn, and how it dehydrogenates light alkanes. After the dehydrogenation process, the olefin may be further dehydrogenated into coke precursors which are often thought of as atomic carbon. This work looks into this claim by continuing the dehydrogenation down to atomic carbon and testing its thermodynamic and kinetic possibilities. Chapter 3 will follow up with light alkane dehydrogenation over various platinum alloys. This works consists of a comprehensive comparison of alloys of platinum with transition and post-transition metals. Trends in reactivity will be used to predict optimum alloy compositions. Chapter 4 will introduce a common method of removing carbon monoxide while producing hydrogen gas, the water gas shift (WGS) reaction. The various WGS kinetic pathways over TiO2 have been mapped out including all thermodynamic reaction energies. These energies indicate the most probable pathways for WGS over anatase TiO2. The role of water in the elementary reaction steps is of special interest. Chapter 5 expands the scope of TiO2 surface reactions to include methane steam reforming coupled with the WGS reaction. The role of water in methane activation is examined, and the predicted reaction pathways are explored in the presence of adsorbed water molecules. The potential energy surfaces for steam reforming have been investigated along with both binding energies and activation energies.Ph.D.Includes bibliographical referencesby Alexander Hoo