关键词: 甲烷热解, 多相催化, 镍, 碱金属氧化物掺杂剂, 颗粒尺寸, 碳纳米纤维

Abstract: Methane pyrolysis is a promising route for low-emission H₂ production with valuable nanostructured carbon as coproduct. Tuning catalyst performance through the addition of dopants has transformed many catalytic reactions, yet their role in methane pyrolysis remains largely unexplored. In this study, the role of three alkali oxide dopants (MgO, Na₂O and K₂O) is investigated in Ni-catalysed methane pyrolysis. The dopants greatly affected the lifetime and carbon yield of Ni/C in a thermogravimetric reactor: Mg-doping resulted in a threefold increase in carbon yield and more than double the catalyst lifetime, while K-doping decreased the carbon yield by around 50% at a concentration of 5 at%. This unexpectedly large effect of the dopants was elucidated with high-resolution electron microscopy. We revealed that the dopants remained well-dispersed on the support during catalysis and that they control particle growth at the start of the reaction there. Mg- and Na-doping enhanced Ni particle growth from 5‒6 nm to a more optimal size of 10‒12 nm, whereas K-doping stabilizes smaller Ni particles (7 nm). The final carbon yield was found to be critically dependent on the active Ni particle size, suggesting that the particle growth mediated by the dopants defines for a large part the overall performance of the catalyst in methane pyrolysis.

Key words: Methane pyrolysis, Heterogeneous catalysis, Nickel, Alkali, Particle size, Carbon nanofibers