Thermocatalytic Decomposition of Methane over Ni-Based Catalysts for Hydrogen and Carbon Nanotube Synthesis: an Experimental and Theoretical Study

Abstract The activity of four nickel-based catalysts (60Ni/40SiO2, 60Ni/40Al2O3, 80Ni/10Cu/10SiO2, and 90Ni/10Al2O3) was evaluated in methane pyrolysis experiments. The highest hydrogen molar concentrations were achieved with 60Ni/40SiO2 (12.7% at 550°C) and 80Ni/10Cu/10SiO2 (32.8% at 650°C and 57% at 750°C). The study proposes a novel gas-flow mathematical model for the thermocatalytic decomposition of methane (TCDM), presenting both analytical and numerical solutions. Model verification against experimental data yielded a digital twin of the process with a 10% error margin. Characterization of the carbonaceous products by X-ray phase diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) showed the multiplicity of multiwalled carbon nanotubes (MWCNTs) in all cases. However, the copper-promoted catalyst produced MWCNTs with a broader diameter distribution, poorer wall alignment, and the presence of amorphous carbon, whereas the copper-free catalysts yielded nanotubes with superior uniformity, alignment, and surface purity.