Oxidative coupling of methane (OCM) represents a potentially viable method to convert methane directly into more desirable products such as ethane, and ethylene. In this dissertation, a comprehensive kinetic study of oxidative coupling of methane was performed over La2O3-based catalysts.
An accurate and reliable gas-phase model is critical for the entire mechanism. The gas-phase kinetics was first studied using a jet-stirred reactor without catalyst. Both experiments and simulations were conducted under various operating conditions using different gas-phase models. Quantities of interest and rate of production analyses on hydrocarbon products were also performed to evaluate the models. NUIGMech1.1 was selected as the most comprehensive model to describe the OCM gas-phase kinetics and used for the next study.
Next, microkinetic analysis on La2O3-based catalysts with different dopants was performed. The Ce addition has the greatest boost over the performance. The kinetics at low conversion regimes were analyzed and correlated to the catalysts’ properties. The activation energy for methane hydrogen abstraction was estimated, with the formation rate of primary products, which suggested that the initiation reaction steps were similar for La2O3-based catalyst.
A homogeneous-heterogeneous kinetic model for La2O3/CeO2 catalyst was then constructed. By applying in situ XRD, the doping of CeO2 not only enhanced catalytic performance but also improved catalyst stability from CO2 and H2O. A wide range of operating conditions was investigated experimentally and numerically, where a packed bed reactor model was constructed based on the dimensions of experimental setup and catalyst characterization. The rate of production (ROP) was also performed to identify the important reactions and prove the necessity of surface reactions for the OCM process. Laser-induced fluorescence was implemented to directly observe the presence of formaldehyde.
The last section includes the implementation of in situ laser diagnosis techniques at the near-surface region to solve the existing challenges. Raman scattering was implemented to quantitate the concentration profiles of major stable species near the surface and measure the in situ local temperatures at different heights above the catalyst surface, to study the kinetics transiting from the surface edge to the near-surface gas phase and provide a new perspective in OCM kinetic studies.
|Date of Award
- Physical Sciences and Engineering
|Mani Sarathy (Supervisor)
- Kinetic modeling
- Homogeneous-heterogeneous reaction networks
- oxidative coupling of methane