Effect of Sn on methane decomposition over Fe supported catalysts to produce carbon

In this work, alumina-supported Sn containing Fe catalysts were investigated in CVD reactions (Chemical Vapor Deposition) using methane for carbon production. The catalysts were prepared with 10 wt.% of Fe (as Fe₂O₃) and 3, 6 and 12 wt.% of Sn (as SnO₂) supported on Al₂O₃ named hereon Fe10Sn3A, Fe5Sn6A and Fe10Sn12A, respectively. These catalysts were characterized by SEM, TPCVD, TPR, TG, Raman, XRD and ⁵⁷Fe and ¹¹⁹Sn Mössbauer spectroscopy. Methane reacts with Fe10A catalyst (without Sn) in the temperature range 680?C900°C to produce mainly Fe⁰, Fe₃C and 20 wt.% of carbon deposition. TPR and TPCVD clearly showed that Sn strongly hinders the CH₄ reaction over Fe catalyst. ⁵⁷Fe Mössbauer suggested that in the presence of Sn the reduction of Fe^?+?3 by methane becomes very difficult. ¹¹⁹Sn Mössbauer showed Sn^?+?4 species strongly interact with metallic iron after CVD, producing iron-tin phases such as Fe₃SnC and FeSn₂. This interaction Sn?CFe increases the CVD temperatures and decreases the carbon yield leading to the production of more organized forms of carbon such as carbon nanotubes, nanofibers and graphite.