Synthesis of higher alcohols by Fischer–Tropsch synthesis over alkali metal-modified cobalt catalysts

• Na-modified Co catalysts produced appreciable amounts of higher alcohols in FT synthesis.
• The addition of Na decreased the size of the Co nanoparticles and increased Co(II) species.
• The addition of Na enhanced the surface basicity for SiO2-supported Co catalysts.
• Na showed superior effects for alcohol formation over Co catalysts compared to other alkali metals.

Alkali metal-modified unsupported and supported cobalt catalysts worked efficiently in the Fischer–Tropsch (FT) synthesis for the production of higher alcohols in a batch slurry-phase reactor. Sodium-modified Co catalysts exhibited the highest catalytic performance in terms of catalytic activity and higher alcohol selectivities compared to other alkali metal-modified Co catalysts: they also gave appreciable amounts of higher alcohols with more than four carbon atoms (C5+ alcohols) as much as 77% of the total alcohol distribution. According to the characterization of the catalysts using XRD, TEM, XPS, XAFS, and CO2-TPD, the effect of Na was suggested as follows: (i) a decrease in the size of Co nanoparticles, (ii) a decrease in the reducibility of Co(II) to Co(0), and (iii) an increase in surface basicity. These factors enable the production of higher alcohols with high selectivities at high CO conversions.

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