Activated carbon supported Ni, Fe, and bimetallic NiFe catalysts for COx-free H2 production by microwave methane pyrolysis

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, NiFe/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 (NiFe/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 NiFe/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 NiFe/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 NiFe/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 COx-free H2 production.