(117b) Kinetic Modeling and Mechanistic Understandings of Catalytic Methane Pyrolysis to Produce CO2-Free Hydrogen and Carbon Nanotubes

Clean hydrogen has been identified as one possible solution to the growing energy demand while simultaneously reducing CO₂ emissions. Established methods of hydrogen production like steam methane reforming are the most economically feasible, but form CO₂ as a byproduct. Catalytic methane pyrolysis, which sequesters carbon in a solid product rather than release it as CO₂, is one possible large-scale alternative method of hydrogen production. Recent advances in the development of reusable pyrolysis catalysts indicate we can facilitate in-situ separation of the nanotube product from the catalyst and continue methane conversion.

This presentation focuses on fitting a kinetic model to H₂ production and carbon nanotube growth rates on our Co-Mo/MgO catalyst. Previous work on Ni-Mo/MgO indicates different kinetic regimes exist during the carburization and nanotube nucleation phase vs. the deactivation and steady state growth regimes.¹ We incorporate the effect of hydrogen as a co-feed, which even as a reaction product serves to enhance observed rates by cleaning active sites up to approximately 0.3 atm at 800°C. At higher pressures, the benefits are attenuated as the reverse reaction is facilitated and surface carbon chemical potential is reduced. Activation energies in the presence of hydrogen are reduced from artificially high apparent barriers down to 110 kJ/mol with co-fed hydrogen due to increased active site stability over Co. We also quantify the rate of the reverse reaction, showing that Co facilitates carbon methanation much faster than Fe and Ni, illustrating more rapid C surface flux and weaker bound carbon species in the former. We also highlight a 2^nd order rate dependence of hydrogen on the reverse reaction, illustrating the strong binding of carbon species during the process.

1. Gomez, Bavlnka, Nguyen, Alalq, Sabisch, Boscoboinik, Resasco, and Crossley. Evolution of Ni-Mo/MgO during catalytic methane pyrolysis to produce base-growth nanotubes, Cell Reports Physical Science (2025), https://doi.org/10.1016/j.xcrp.2025.102519