Modified carbon nanotubes by KMnO4 supported iron Fischer–Tropsch catalyst for the direct conversion of syngas to lower olefins

Abstract

Manganese and potassium promoters coated carbon nanotubes (i.e., MnK-CNTs) were synthesized by a redox reaction between CNTs and KMnO₄, in which the CNTs act as reducing agent and as substrate for the heterogeneous nucleation of K-doped manganese oxide. The as-synthesized MnK-CNTs were employed to support Fe catalyst (i.e., Fe/MnK-CNTs, the loadings of 7.9 wt% Fe, 15.7 wt% Mn and 1.9 wt% K) for the direct conversion of syngas to lower olefins. It is revealed that Fe/MnK-CNTs catalyst is more active and stable than FeMnK/CNTs catalyst prepared by co-impregnation method using CNTs as a support. Furthermore, under similar CO conversion, the Fe/MnK-CNTs catalyst exhibits higher selectivity of hydrocarbons especially lower olefins. This could be related to the small-sized and uniform nanoparticles, the well-distributed promoters, the weak metal–support interaction and the greater defects on support, which are the consequences of the unique structural transformation of MnK-CNTs as a function of temperature and atmosphere.