UBC Theses and Dissertations
Synthesis of nanostructured catalysts for low temperature methane combustion Dai, Yiling
The number of natural gas vehicles (NGVs) is increasing rapidly due to the growing concern for the environmental impact of gasoline and diesel-powered automobiles. However, the main component of natural gas, methane, is a potent greenhouse gas. Thus, removal of unburned methane from the exhaust of NGVs is important and this requires catalysts for methane oxidation at low temperature (less than 500-550 °C). In this thesis, different types of nanostructured catalysts were developed. Noble metal catalysts, like Pd-based catalysts, and non-precious metal catalysts, such as spinel catalysts, were synthesized, characterized and examined for catalytic methane combustion. To enhance the catalytic activity, NiCo₂O₄ catalysts with a unique bowtie-structure were synthesized. The morphology, growth mechanism, catalytic and kinetic performance were explored. These NiCo₂O₄ catalysts exhibited excellent activity for methane oxidation, but were unable to maintain their performance in the presence of water vapor. In addition, active site distribution plays an important role on catalytic activity. Taking this into account, MnO₂ aerogels supporting precious or non-precious metal oxide catalysts were explored. Both types of catalysts showed enhanced catalytic activity. The hydrothermal stability and sulfur tolerance were studied for PdO/MnO₂, and the deactivation mechanism was explored. Besides outstanding activity, commercial catalysts must be stable in practical usage. In order to improve the stability of Pd-based catalysts, nanostructured materials were prepared by embedding Pd into CeO₂ inside the channels of a mesoporous host, SBA-15. It was found that the materials showed excellent catalytic activity and improved activity after hydrothermal treatment. However, their performance in the presence of water vapor still needs to be enhanced. Furthermore, to solve the problem of poor water stability and sulfur tolerance, CoCr₂O₄ composites were selected as catalysts. Nanospheres of CoCr₂O₄ were prepared by a straightforward solvothermal method. These materials achieved 100% methane conversion below 500 °C and they also displayed excellent stability even in the presence of 10% water vapor and 5 ppm SO₂. Furthermore, the CoCr₂O₄ catalysts were scaled up and coated onto cordierite monoliths via a modified wash-coating method. The coated monolith showed excellent activity and stability, and these materials have potential to be applied for NGVs.
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