Incorporating minimal quantities of oxidants into methane pyrolysis has demonstrated a notable increase in carbon and hydrogen outputs while maintaining catalyst performance, challenging established notions regarding the process. Traditionally, methane pyrolysis entails the decomposition of methane without oxygen, employing a catalyst to reduce the temperature and speed up the reaction, thereby offering a promising low-emission technique for hydrogen generation.
Researchers from Stanford University, including Marco Gigantino and Henry Moise, exhibited in a fluidised bed reactor with an Fe/Al₂O₃ catalyst at 750°C that introducing 5% carbon dioxide into the methane stream resulted in a twofold increase in carbon yield along with enhanced hydrogen production. This method, although generating carbon monoxide as a secondary product, aids in the creation of removable carbon layers, perfect for collecting solid carbon without interrupting the catalyst.
Experiments involving water and oxygen reflected similar advantages. Ideal oxidant-to-methane ratios for both carbon dioxide and water resulted in more than a 30% rise in carbon yield compared to methane alone after 14 minutes. Even with Ni/Al₂O₃ and Co/Al₂O₃ catalysts, carbon dioxide co-feeding surpassed methane-only scenarios.
The research indicated that oxidants speed up the decomposition of cementite (Fe₃C), rejuvenating active sites on catalysts to enhance carbon output. Raman spectroscopy revealed that oxidants encourage the elimination of amorphous carbon, promoting the development of graphitic materials such as carbon nanotubes, thereby extending catalyst durability and improving the quality of carbon byproducts.
Economic evaluations propose that utilizing oxidants may minimize the requirement for methane recycling, thus optimizing operational costs and feasibility of the process, and is less energy-demanding than steam methane reforming. Chester Upham from the University of British Columbia praised the research as a significant contribution to the burgeoning interest in pyrolysis for sustainable hydrogen production.