Effects of Promoters on the Physicochemical Properties of Cobalt-Iron Catalysts Supported on Multiwalled-Carbon Nanotubes

Cobalt-iron bimetallic catalysts promoted with Nb, Ru or Rh and supported on multiwalled-carbon nanotubes (MWCNTs) were synthesized using a reverse-microemulsion method. The synthesized catalysts were characterized by TEM, N 2 -physical adsorption, XPS, XRD, and TPD/R/O methods. XPS analyses showed an increasing trend of the Co 2+ /Co 3+ atomic ratios for the promoted catalysts, compared to that of the un-promoted Co–Fe/CNTs catalyst. The dispersion for the un-promoted Co–Fe /CNTs catalyst was 15.9% and it increased to 23.0, 20.4, and 17.7% in the presence of 0.1 wt.% Nb, Ru, and Rh promoter, respectively. The addition of Nb-promoter also improved the reducibility of the catalyst as exhibited by the H 2 -TPR study. The presence of Nb, Ru, and Rh promoters improved the catalytic performance in a Fischer–Tropsch synthesis where the TOF over the un-promoted catalyst increased from 5.1 to 6.2, 5.7, 5.2 × 10 –1 s −1 upon the addition of Nb, Ru and Rh promoter, respectively. Thus, the Nb promoter was a better promoter than Ru and Rh for the Co–Fe/CNTs catalyst. Graphical Abstract