(50f) Low-Carbon Hydrogen Production Via Oxidant-Assisted Catalytic Methane Pyrolysis

Current hydrogen manufacture emits 8-12 kg CO₂/kg H₂ through the combination of methane steam or autothermal reforming followed by water-gas shift. On the other hand, methane pyrolysis produces hydrogen by decomposing methane in a non-oxidative environment, while also producing solid carbon that can either find value in the market or be sequestered in a much more manageable way as compared to CO₂. Additionally, compared to an alternative H₂ production method such as decomposition via, methane pyrolysis requires only about 1/4 of its thermodynamic energy input of water electrolysis.

Catalytic approaches applied to methane pyrolysis allow to produce high-quality carbon forms, such as carbon nanotubes (CNTs), but are strongly limited by catalyst deactivation. Herein, we propose a seemingly counterintuitive variant of methane pyrolysis called oxidant-assisted methane pyrolysis that integrates oxidant co-feeds to enhance stability of the catalyst and products yield. Incremental amounts of certain oxidants, namely CO₂, H₂O, and O₂, were co-fed with a constant methane flow into a fluidized bed of catalyst particles composed of Fe supported on Al₂O₃, while tracking the amount of solid carbon produced. Hydrogen and carbon yields increased in the case of CO₂ and H₂O co-feed at certain concentrations of the oxidant. The beneficial role of these two oxidants can be attributed to cyclic formation-decomposition of the Fe₃C phase, which allows for in-situ regeneration of catalytic sites and significant carbon dislodging from the catalyst surface. The addition of oxidants increased the production of carbon without impacting its quality, favoring the formation of carbon shells that encapsulated the catalyst particles. These shells were easily dislodged through the mechanical friction generated under the fluidization regime. Stable operation was demonstrated for the CO₂ and H₂O co-feed that maximized carbon production, resulting in significantly prolonged activity with higher carbon and hydrogen yields as compared to pure methane feed.