Production of carbon nanotubes through combination of catalyst reduction and methane decomposition over Fe–Ni/ZrO2 catalysts prepared by the citrate method

Abstract

Fe–Ni/ZrO2 catalysts (40wt.-%) were prepared by the citrate method and used without pre-reduction in the thermal catalytic decomposition (TCD) of CH4 at 650°C. The reaction was studied by the thermogravimetric method, monitoring the real time mass change of the catalyst due to reduction by CH4 and carbon deposition. The direct activation of the samples in CH4 was affected by the catalyst composition. While the simultaneous occurrence of catalyst reduction and carbon formation was observed for catalysts consisting mostly of NiO, carbon deposition over catalysts with higher Fe contents only started after an extensive reduction of the samples. Formation of Fe–Ni alloys occurred in the bimetallic catalysts during TCD of CH4, which strongly affected both carbon deposition and deactivation rates of the samples. As a result, the carbon yield of the bimetallic catalysts was slightly higher than that of the monometallic catalyst. The structural properties of the deposited carbon were highly dependent on the catalyst composition, going from a highly disordered turbostratic carbon on the Fe–containing catalysts to a well-ordered almost graphitic carbon on the monometallic Ni sample.