Supported metal catalysts for water-gas shift conversion
Master Thesis
2014
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University of Cape Town
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The interests in an alternative, sustainable power generation method has greatly increased in the past decade due to increases in greenhouse gases and its impact on global climate change. The use of fuel cells as a form of energy generation is extremely promising as it converts chemical potential energy directly to electrical energy, bypassing the Carnot cycle limitations. Various types of fuel cells have been developed, with the proton exchange membrane fuel cell (PEMFC) being most promising for mobile and small-scale stationary uses under transient conditions. The PEMFC uses hydrogen and oxygen to generate electrical energy. While oxygen can be obtained from air, hydrogen does not exist in its elemental form; hence a process train is required to refine fuels (such as fossil fuels and bio-fuels) into pure hydrogen. This has been successfully achieved by large-scale industrial plants. A typical fuel processing train consists of a steam reforming stage converting the fuel into syngas. This is followed by a water-gas shift (WGS) stage to convert carbon monoxide, which is a poison for the platinum catalysts within fuel cells, into carbon dioxide. If the CO concentration required is extremely low, a methanation or preferential oxidation stage can be used subsequent to the WGS stage. This study focuses on the water-gas shift stage of the fuel processing train. Industrial base metal WGS catalysts are not suitable for a miniaturized fuel processing train due to the catalysts being developed for continuous operations, as miniaturized fuel processing trains are expected to operate at transient conditions. A slow and controlled reduction process is also required prior to operation, as well as the pyrophoricity of industrial catalysts after reduction. These can pose safety issues with non-technical personnel in household applications (e.g. CHP). PGM-based catalysts have shown high activities for the water-gas shift reaction in literature, are not pyrophoric and do not require lengthy and sensitive reduction processes prior to operation. The objective of this study was to investigate and compare two base metal catalysts (high temperature (HT) shift Fe₃O₄/Cr₂O₃ and low temperature (LT) shift CuO/ZnO/Al₂O₃ catalyst) with a PGM based counterpart, as well as to investigate whether the catalysts are able to achieve a required 1 vol% CO via the water-gas shift reaction. For these investigations a synthetic feedstock was used, based on typical exit concentrations of a steam methane reformer.
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Tsui, L. 2014. Supported metal catalysts for water-gas shift conversion. University of Cape Town.