Effects of manganese and reduction promoters on carbon nanotube supported cobalt catalysts in Fischer–Tropsch synthesis

Carbon nanotube (CNT) supported Co catalysts were promoted with manganese and noble metals (Pt, Ru) and tested in Fischer–Tropsch synthesis at temperatures between 200 and 250 °C and pressures of 1 and 30 bar. A significant decrease in methane selectivity and with that an increase in C5+ selectivity was found due to promotion with manganese. In addition, the activity (syngas conversion) slightly increases and the olefin selectivity drastically increases. The promotion with noble metals (Pt, Ru) resulted in a higher degree of catalyst reduction, yet otherwise only had small effects. The double promotion of Co with Mn and Pt or Ru lead to a higher activity and activation energy in the case of Pt, and in both cases to a lower olefin selectivity compared to the catalyst promoted with manganese only.For a Mn promoted and an unpromoted Co/CNT catalyst, an increase of total pressure from 1 to 30 bar leads to a lower methane selectivity and higher chain growth probability. The rate of syngas consumption was found to be very similar at 30 bar compared to 1 bar.

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► CNT supported promoted cobalt catalysts were tested in Fischer–Tropsch synthesis.
► The methane selectivity is significantly reduced by manganese promotion.
► The short chain olefin selectivity is strongly increased.
► Additional reduction promoters influence the promoter effect of manganese.
► Promoter effects were found to be dependent on total reaction pressure.