Characterization of carbon derived from ferrocene-catalyzed methane decomposition in a floating catalyst tubular reactor

The development of sustainable energy technologies and demand for advanced carbon materials drives innovation in methane pyrolysis, particularly catalytic approaches using ferrocene (Fe(C5H5)2) as a dual catalyst/carbon source. This study investigates methane decomposition in a ferrocene-fed tubular reactor using undiluted CH4 at temperatures of 633 to 1046 °C and flow rates of 0.063–0.25 SLPM, corresponding to gas hourly space velocities of approximately 16–65 h-1. The reactor achieved conversions of 3%–83% at lower temperatures than for an uncatalyzed reactor, and produced agglomerates of ordered graphitic carbon particles (4.34±1.52μm) contrasting to the submicron particles in non-catalytic processes. The particles consisted of approximately 57 wt% graphitic carbon and 4 wt% amorphous carbon, with the remaining weight fraction attributed to metal-containing phases, including α−Fe and iron carbide, as determined by X-ray diffraction coupled with Rietveld analysis. The highly ordered graphitic layers (interplanar spacing: 3.3 Å) were confirmed by transmission electron microscopy (TEM) while Raman spectroscopy demonstrated reduced defects in catalytic runs (ID/IG=0.64±0.01) versus non-catalytic (0.86±0.16). The increased graphitization of the catalytic carbon was also demonstrated by its thermogravimetric analysis in air, which showed a carbon–iron composite profile with combustion peaks at approximately 637 °C and 670 °C. The catalytic carbon has a high surface area (31 m2/g), and high electrical conductivity, i.e., 3.1 S/cm (in-plane) and 6.5 S/cm (through-plane). Microstructural variability was limited; however, increasing temperature and conversion drove phase evolution, manifested predominantly as graphitic carbon accumulation. Ferrocene lowered reaction temperatures and increased the order, graphitization and size of the formed carbon containing particles (i.e, 4.34±1.52 μm). Its usage could result in reactors with reduced energy demand, lower operating temperature (allowing for conventional reactor materials to be used), and increased carbon particle separation efficiency via industrial cyclones, resulting in a more energy efficient process and improved carbon quality. These findings underscore ferrocene-catalyzed pyrolysis as a scalable, sustainable route to high-quality carbon materials for electronic and structural applications.