Cobalt nanocrystals on carbon nanotubes in the Fischer-Tropsch synthesis: impact of support oxidation

Abstract The effect of oxidation of a carbon nanotube (CNT) support on the structure and catalytic performance in the Fischer-Tropsch (FT) synthesis of pre-synthesized cobalt nanocrystals (NC) has been investigated. 6 nm CoO-NC were prepared using colloidal techniques and impregnated on pristine and surface-oxidized CNT. The CoO-NC on pristine CNT were reduced completely to Co, while ∼50 % CoO reduction was observed on oxidized CNT (oxCNT), indicating a stronger Co-support interaction on oxCNT. In FT, the turnover frequency (TOF) after 100 h was exceptionally high on pristine CNT (150·10-3 s-1) against 63·10-3 s-1 on oxCNT. In the initial stage of FT, the TOF was 35 % lower on oxCNT than on pristine CNT, which matched with 32 % lower crystallinity of cobalt determined using in situ XRD. Furthermore, deactivation was observed mainly on oxCNT. These results demonstrate the large impact of the support on the structure and performance of nanocrystal-based catalysts.