Temperature Programmed CVD: A Novel Technique to Investigate Carbon Nanotube Synthesis on FeMo/MgO Catalysts

In this work, it is demonstrated how a novel technique based on temperature-programmed chemical vapor deposition (TPCVD) can be used to investigate the synthesis of carbon nanotubes (CNTs) from methane on a classic catalyst FeMo _x /MgO (x = 0.07, 0.35 and 1.00). TPCVD monitors carbon deposition by measuring H₂ formed during CH₄ decomposition and affords information on the different catalytic species, deactivation process, reaction kinetics and carbon yields. The obtained results showed for FeMgO catalyst a simple TPCVD peak related to the production of carbon beginning at 760 °C with maximum at 800 °C followed by a rapid deactivation resulting in a low carbon yield. The addition of Mo to Fe/MgO catalyst completely changes the TPCVD profile with the formation of a new catalytic species active at temperatures higher than 900 °C, which is stable and continuously decomposes CH₄ to produce high carbon yields. Raman, TG/DTG, Mössbauer, SEM, TEM, XRD and TPR analyses suggested that this active catalytic phase is likely related to Fe–Mo and Fe–Mo–C phases active to produce single wall and mainly multiwall carbon nanotubes.