Thermo-catalytic methane pyrolysis for sustainable carbon production in steelmaking applications: Stainless steel catalysis and CO₂-enhanced catalyst regeneration

This study presents a scalable and eco-friendly thermo-catalytic methane pyrolysis (TCMP) for producing high-value carbon materials with tailored crystallinity and morphology, aiming to provide a sustainable alternative to conventional carbon materials such as furnace-derived morphology-controlled carbon. A key innovation is the use of stainless steel as both the reactor container and catalyst, utilizing the iron and nickel content to enhance methane decomposition efficiency. This dual function not only simplifies the reactor design but also supports large-scale production, solving the previous limitation of reactor clogging. Moreover, the study pioneers use of CO 2 injection as the second novel strategy for in-situ catalyst regeneration. These approaches simplify reactor design, reduce clogging, and improve process sustainability, addressing key limitations in existing TCMP systems. The resulting carbon materials exhibit diverse morphologies, allowing customization for varied industrial applications. Although definitive performance correlations require further study, Sample A displayed a relatively higher graphitization level, while Sample B exhibited more amorphous features, both addressing potential for distinct applications such as conductivity, catalysis, or adsorption depending on specific functionalization and purification. Characterization through Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM) confirms the structural adaptability achieved. While elemental traces of Fe, Cr, and Ni are present, they are consistent with catalytic residues and may be acceptable or beneficial in some industrial uses. This work also investigates the interconnection between hydrogen generation and carbon valorization, proposing that the solid carbon byproduct from methane pyrolysis, particularly the low-porosity, partially graphitized material, may serve as a feedstock in metallurgical processing such as ironmaking, where high-carbon-content reductants are essential. In this way, the dual utility of methane decomposition products enhances the overall sustainability and circularity of the TCMP process. • Stainless steel reactor acts as both methane pyrolysis vessel and catalytic surface. • CO₂ in-situ-injection enables catalyst regeneration and minimizes contamination. • Graphitic and amorphous carbon morphologies tailored via process conditions. • Carbon structures confirmed by SEM, TEM, XRD, and Raman spectroscopy.