|LAUTERBACH, JULIA - National Energy Technology Laboratory
|SMITH, MARK - National Energy Technology Laboratory
Submitted to: International Journal of Hydrogen Energy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2023
Publication Date: 11/26/2023
Citation: Ellison, C.R., Lauterbach, J.C., Smith, M.W. 2023. Activated carbon supported Ni, Fe, and bimetallic NiFe catalysts for COx-free H2 production by microwave methane pyrolysis. International Journal of Hydrogen Energy. https://doi.org/10.1016/j.ijhydene.2023.11.150.
Interpretive Summary: Steam methane reforming currently supplies 50% of the world’s hydrogen from methane; however, considerable CO2 emissions are co-produced. Catalytic methane pyrolysis is a method for CO2-free hydrogen production from methane; however, due to the considerable energy inputs required for this high-temperature process, more efficient reactor concepts and catalyst systems need to be further investigated for commercialization. ARS and NETL researchers demonstrated a microwave-assisted catalytic methane pyrolysis process using microwave-specific catalysts to improve the hydrogen yield of methane pyrolysis. Activated carbon supported iron and nickel-based catalysts were considered, and it was found that a catalyst incorporating both metals (bimetallic) may have the best performance by achieving high hydrogen yields while delaying deactivation compared to the individual metal (monometallic) catalysts. The results from this study can be used to further optimize process conditions and catalyst systems for microwave-assisted methane pyrolysis for CO2-free hydrogen production.
Technical Abstract: The goal of this study was to test the effect of metal-impregnated carbon-based catalysts on the conversion of methane to hydrogen gas and solid carbon using microwave reactor technology. Monometallic and bimetallic catalysts on activated carbon supports (Ni/AC, Fe/AC, Ni-Fe/AC) are compared during methane pyrolysis testing. Catalytic methane pyrolysis was carried out in a microwave reactor at reaction temperatures of 600 °C and 800 °C. For comparison, one of the catalysts (Ni-Fe/AC) was tested in a conventionally heated reactor at 800 °C. The prepared catalysts were characterized by X-ray diffraction (XRD), while post-reaction catalysts were characterized by XRD and SEM. During reaction testing, the monometallic Ni/AC catalyst exhibited the best catalytic activity (CH4 conversion: 46.0 and H2 yield: 46.9%) when reacted in the microwave reactor, however, it suffered from rapid deactivation from carbon deposition (carbon yield: 0.39 g C/g catalyst). The bimetallic Ni-Fe/AC catalyst was slightly less active (CH4 conversion: 36.9 and H2 yield: 40.5%) but it was more resistant to carbon formation (carbon yield: 0.27 g C/g catalyst) suggesting it may have greater long-term stability. The Ni-Fe/AC catalyst was also the most energy efficient as it required the least microwave power to maintain the 800 °C reaction temperature compared to the other catalysts tested. Methane conversion of the bimetallic Ni-Fe/AC at 800 °C under microwave irradiation was three times the conversion under conventional heating at the same reaction temperature. This work demonstrates the use of microwave-specific catalysts for catalytic methane pyrolysis in a microwave reactor, and can be used as a foundation for further methane pyrolysis process and catalyst optimization for CO2-free H2 production.