Methane decomposition utilizing a molten metal catalyst : An experimental analysis of methane decomposition utilizing pyrolysis and a NiMo-Bi catalyst in an aluminium oxide reactor

Sammanfattning

The increasing demand for hydrogen in Northern Sweden driven by industrial decarbonization and the transition toward fossil-free steel production calls for scalable and energy-efficient hydrogen production methods. This thesis explores the feasibility of methane pyrolysis using a molten metal catalyst composed of nickel, molybdenum, and bismuth (Ni-MoBi) within an aluminium oxide reactor. Compared to water electrolysis, methane pyrolysis offers significantly lower electricity requirements and avoids CO₂ emissions associated with conventional steam methane reforming. Methane pyrolysis is a thermochemical process in which methane (CH₄) is decomposed at high temperatures into hydrogen gas (H₂) and solid carbon (C), without the formation of carbon dioxide. When paired with a molten metal catalyst, this process can be optimized for high selectivity and energy efficiency, offering a promising route for low-emission hydrogen production. The experimental work involved designing and constructing a high-temperature reactor system, preparing and reducing the catalyst, and performing pyrolysis tests across a temperature range of 800–1100 °C and flowrates from 50 to 300 ml/min. Gas products were analysed using gas chromatography (GC) and FTIR, while catalyst samples were characterized using XRD and SEM. Complementary CFD simulations were performed to investigate gas flow through the molten catalyst and understand bubble formation dynamics. The results show that temperature has a substantially greater effect than flowrate on methane conversion and hydrogen selectivity. Higher temperatures consistently improved performance, even at higher flowrates, demonstrating that elevated temperatures can compensate for reduced residence time. In contrast, increasing flowrate alone at lower temperatures led to diminished yields. Catalyst reduction was also shown to be critical in preventing oxygen-related side reactions. CFD simulations supported experimental trends and offered insights into flow behaviour and gas–liquid interactions. This study highlights the importance of high operational temperatures in maximizing hydrogen yield in molten metal-catalyzed methane pyrolysis and provides a foundation for further scaling and optimization of this promising technology.