Theoretical study of short chain hydrocarbon conversion

Catalytic conversion of hydrocarbons serve an essential role in generating energy and creating high value chemicals. In some cases, as in propylene combustion, a commercial catalyst does exist, however, the catalyst is expensive and inefficient, which calls for a better catalyst. In other cases, such as converting methane to ethylene, there is not a viable catalyst. In both cases, fundamental understanding and new concepts are needed to develop new catalysts. In this thesis, if a commercial catalyst exists, we attempt to shed light on the fundamentals explaining why the catalyst works and how to further improve the catalytic activity. If no catalyst exists for the process, we attempt to fundamentally understand the challenge in the catalytic process, identify the key properties of the ideal catalyst, and present options for developing that catalyst. We employ density functional theory (DFT) coupled with microkinetic modeling tools to achieve those goals. Experimental data, when available in the literature, are compared to our theoretical predictions to assess their reliability. The conversion of methane into higher value chemicals (i.e. ethane/ethylene) can play a key role in transforming the chemical industry, especially with the recent surge in natural gas production. The catalytic process, however, remains a major challenge due to the difficulty in activating the strong C-H bond in methane without producing the thermodynamically more favorable complete combustion products. The primary objective of Chapters 2 is to fundamentally understand why MgO, one of the rare catalysts that has shown some catalytic activity in the process, works. Chapter 3 attempts to go beyond the limitations of MgO and proposes new catalysts for the process. The conversion of methanol to formaldehyde presents a similar challenge since the desired product, formaldehyde, is more active that the starting material, methanol. Silver is one of the few catalysts that are used commercially for the process. Chapter 4 attempts to shed light on why silver is an effective catalyst for the process. Efficient hydrocarbon combustion remains imperative until new alternative fuels are developed. The computational study of hydrocarbon combustion, however, remains a major challenge in computational catalysis due to the great many possible intermediates. Chapters 5 and 6 present a methodical way of tackling that problem, focusing on methane, ethylene, and propylene as model compounds. The last chapter (Chapter 6) discusses a new approach for calculating the C-C transition state energy based on a few simple calculations. It is an attempt to reduce the computational cost of studying complex hydrocarbon conversion processes by reducing the calculations cost. In summary, the dissertation presents a fundamental approach for studying short chain hydrocarbon conversion and highlights the important factors affecting the catalytic activity. The overall goal is to help in guiding experimentalists to a creative design of new catalysts for those processes.

Keywords: Chemical Engineering.
Advisor: Cargnello Matteo
Noerskov Jens
Tarpeh William