A Facile and Efficient Modification of CNTs for Improved Fischer-Tropsch Performance on Iron Catalyst: Alkali Modification

In this paper, a facile and environmentally benign method is used to pretreat carbon nanotubes (CNTs) by alkali modification, which decreases the wall thickness, increases the inner diameter, and improves the graphitization degree of CNTs compared to conventional acid treatment. The iron catalyst supported on alkali modified CNTs shows extraordinary Fischer-Tropsch synthesis (FTS) activity and CO conversion (1.78 and 2.41times, respectively) compared with those supported on either the acid treated or pristine CNTs. Additionally, the diesel (C10-20) selectivity on Fe/CNTs-Na is up to 60%, which is much higher than that calculated from the Anderson-Schulz-Flory distribution (39%). Similar results are also found by using activated carbon (AC) and N-doped multiwall carbon nanotubes (NCNTs) as supports for FTS, proving the universal applicability of alkali modification on carbon material. The positive relationship between the C5+ selectivity and C-2-C-4 olefin/paraffin ratio of iron catalyst can also be achieved irrespective of the support type.