Catalytic decomposition of methane (CDM) enables COx-free H2 while co-producing solid carbon. Its viability hinges on catalysts that couple high activity with stable carbon co‑product formation. We evaluate Ni catalysts on FeAl2O4 (hercynite) and identify ~ 40 wt% NiO as the optimum loading that balances activity with carbon yield. Promoter screening (La, Mg, Co; 5 wt%) reveals distinct control of reducibility and metal–support interaction (MSI). La lowers the reduction temperature, refines Ni/NiO crystallites, and increases Ni dispersion, delivering the highest initial CH4 conversion (52.3%) and H2 production rate (90.6 mmol gcat −1 min−1), albeit with deactivation at ~ 150 min due to rapid carbon encapsulation. Mg strengthens the MSI and stabilizes residual NiO through MgO/MgAl2O4, lowering the initial activity. In contrast, Co promotes spinel formation and Ni aggregation, yielding the weakest activity. CDM is highly selective to H2 with carbon as the sole co-product; the carbon forms multi-walled carbon nanotubes (MWCNTs) with ~ 16–24 nm diameters. Operating parameters further tune performance, with 650 °C being most effective. Lowering the space velocity extends the timeon- stream to ~ 450 min, increases the initial conversion to 59.4%, and raises the carbon yield from ~ 970% to ~ 1470%. Comprehensive characterization links promoter-dependent reducibility and metal–support interaction to activity, stability, and MWCNT yield. These results provide practical guidance for co-optimizing composition and operating conditions in CDM. NiO/FeAl2O4 with ~ 40 wt% NiO can serve as a baseline; La addition elevates initial rates, and operating at lower space velocity mitigates carbon-induced deactivation, thereby increasing H2 productivity and improving CNT quality.

Promoter-Driven enhancement of NiO/FeAl2O4 catalysts for efficient carbon nanotube synthesis and COx-Free hydrogen production via methane pyrolysis
    Abstract
    1 Introduction
    2 Experimental
        2.1 Materials
        2.2 Catalysts preparation
        2.3 Catalyst characterization
        2.4 Catalytic testing
    3 Results & discussion
        3.1 Characterization of as-prepared catalysts
        3.2 Catalytic activity and carbon co-product
        3.3 Effects of promoters on the physicochemical properties of catalysts
            3.3.1 Catalytic activity of 40Ni-5M/HN catalysts
    4 Conclusion
    References

• Soo Hong Lee(Chemical Process Research Division, Korea Research Institute of Chemical Technology (KRICT), Daejeon 34114, Republic of Korea) Corresponding author
• Shaikh Shayan Siddiqui(Chemical Process Research Division, Korea Research Institute of Chemical Technology (KRICT), Daejeon 34114, Republic of Korea, Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon 34113, Republic of Korea)
• Nodira Urol Kizi Saidova(Chemical Process Research Division, Korea Research Institute of Chemical Technology (KRICT), Daejeon 34114, Republic of Korea, Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon 34113, Republic of Korea)
• Ji Sun Im(Chemical Process Research Division, Korea Research Institute of Chemical Technology (KRICT), Daejeon 34114, Republic of Korea, Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Daejeon 34113, Republic of Korea)