Mechanism on CMD reaction regulated by supports and promoters of Fe-based catalysts

Methane cracking technology for low-carbon energy conversion to produce hydrogen is a key technical approach in the pursuit of fossil energy decarbonization. Catalytic methane decomposition (CMD) is a process that accomplishes the fundamental removal of carbon from fossil energy without oxygen, producing high-quality carbon-based materials and H2. The functionality of supports and promoters was investigated using inorganic metal oxide support Al2O3, supported active metal Fe, and cocatalyst K. The results show that the Al2O3–Fe catalyst achieves the highest CH4 conversion of 65% at 850 °C, with a gas-phase H2 yield of 1189.72 mmol/gFe within 3 h, and a solid-phase carbon yield of 6.32 g/gFe, significantly higher than at 750 °C. The Al2O3–Fe–K catalyst achieves a methane conversion rate of 66.28% at 850 °C for 1.5 h, exhibiting relatively fast deactivation. The Al2O3–Fe catalyst catalyzes the formation of carbon nanotubes (CNTs) through methane cracking, resulting in mainly 'chain-locked' morphology. The promoter K acts on the surrounding metal clusters to influence the dispersion of active metal. The Al2O3–Fe–K catalyst is more favorable for the production of 'bamboo-shaped' carbon nanotubes, suggesting that K has a more significant impact on shaping the CNTs' products.