Emission-Free Hydrogen and High-Value Carbon Co-Production from Methane Pyrolysis

Methane pyrolysis is a technology that allows to produce greenhouse-gas-free H₂ along with solid carbon using less energy per mole H₂ than water electrolysis (37 vs. 286 kJ/mol H₂). Catalytic approaches applied to methane pyrolysis are strongly limited by catalyst deactivation from carbon coking. In addition, a system that possesses high and stable H₂ yield while producing high-quality carbon has remained elusive. Here, we report on a novel methane pyrolysis process for the co-production of H₂ and high-value carbon, which contains a large fraction of carbon nanotubes. The process consists of repeated pyrolysis steps followed by in-situ (i.e., within the reactor) regeneration steps of an iron-based catalyst, aimed at dislodging the carbon from the catalyst active surface. In such way, the catalyst can be reused while the carbon can be collected in a semi-continuous fashion. We demonstrated the operation for multiple cycles with high CH₄ conversion, high selectivity for H₂, and carbon dislodging in a fluidized-bed reactor system. Besides methane, we also investigated ethane as a feedstock for this process, since it is another main component of natural gas. Overall, this process demonstrates the production of high-quality carbon and hydrogen without carbon emissions.