Lanthana-Enhanced Iron Catalysts for CO₂-Free Hydrogen and Carbon Nanotubes via Catalytic Methane Decomposition

Catalytic methane decomposition (CMD) offers a promising route for hydrogen production without CO₂ emissions, while simultaneously generating valuable carbon nanostructures. In this study, iron-based catalysts supported on alumina and lanthana-modified alumina were synthesized and evaluated in a fixed-bed reactor at 700 °C under atmospheric pressure. The 20Fe/La─Al catalyst exhibited superior performance, achieving the highest hydrogen production rate (0.44 mmol/g_M/s) and stable methane conversion (from initial conversion of 70.2% to final value of 79.5%) compared to Fe/Al (demonstrating deactivation from initial conversion of 74.3% to final value of 22.7%) and previously reported systems. Characterization using XRD, TPR, SEM, HRTEM, and TGA revealed that lanthana modification significantly improved iron dispersion, reducibility, and metal–support interaction, leading to enhanced catalytic activity and stability. TG/DTG analysis confirmed higher carbon deposition and better graphitization for lanthana-modified catalysts, while HRTEM images verified the formation of high-purity multi-walled carbon nanotubes. These findings highlight the critical role of support modification in optimizing catalyst properties for efficient hydrogen generation and carbon nanotube production via CMD.