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

Abstract

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,XRDand 57Fe and 119Sn Mössbauer spectroscopy.Methane reacts with Fe10A catalyst (without Sn) in the temperature range 680–900◦C to produce mainly Fe0, Fe3 C 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–Fe 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.