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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