Structure sensitivity and its effect on methane turnover and carbon co-product selectivity in thermocatalytic decomposition of methane over supported Ni catalysts

Thermocatalytic decomposition of methane (TCD) is a promising approach for producing CO2-free hydrogen and solid carbon co-product. In this study, a series of Al2O3- and MgAl2O4-based Ni catalysts, prepared with varying synthesis and pretreatment methods, were evaluated for methane TCD performance at 650 degrees C and characterized before and after reaction to elucidate activity-structure relationships. We found that methane TCD turnover increases with Ni particle size. Further, large Ni particle sizes (i.e., >20 nm) are selective toward the formation of carbon nanotubes (CNTs), while small Ni particle sizes (i.e., <10 nm) are selective toward the formation of graphitic carbon layers. The formation of graphitic carbon layers block access to Ni active sites, thus rendering the catalyst inactive more quickly than when CNTs are produced. Additionally, the catalyst deactivation observed with time-on-stream is due to the fragmentation of Ni particles into smaller Ni particles followed by their encapsulation with graphitic carbon layers.

Automated summary

The size of Ni particles has an impact on the catalytic performance in methane thermocatalytic decomposition, with larger particles leading to the formation of carbon nanotubes and smaller particles resulting in graphitic carbon layers. The formation of graphitic carbon layers blocks access to active sites, causing faster deactivation of the catalyst.