Research PaperDirect synthesis of long-chain alcohols from syngas over CoMn catalysts

- Na-promoted CoMn catalyst is able to produce higher alcohols with high C2+ and C6+ fractions.
- Significant structural evolution occurs during reaction with formation of bulk Co2C and MnCO3.
- Na plays a significant role in promotion of Co2C formation.
- Co2C/Co and synergistic effect of certain facets of Co2C are suggested to be active sites for higher alcohol synthesis.

CoMn model catalysts were prepared by co-precipitation and evaluated for higher alcohol synthesis (HAS) via syngas. The selectivity to oxygenates (mainly alcohols and aldehydes) was found to be higher than 20 C% for the Na-promoted CoMn catalyst. Among the oxygenates, C2+ and C6+ fractions accounted for >90 wt% and ∼50 wt%, respectively. Metallic Co0 particles and MnCO3 were found in both Na-promoted and unpromoted CoMn catalysts after the reaction, whereas Co2C nanoparticles could only be observed in the spent Na-promoted catalyst. The addition of Na benefited the carbonization of cobalt and increased the selectivity to oxygenates and CO2. Our studies thus suggested that Co/Co2C were the bifunctional dual-sites for the oxygenates formation over the Na-promoted CoMn catalyst, where Co catalyzed CO dissociation and chain propagation, while Co2C was responsible for CO non-dissociative activation and subsequent insertion. In addition, the sole Co2C nanoparticles with certain exposed facets may also act as another kind of active dual-sites for oxygenates formation.

Na-promoted CoMn catalyst is able to produce higher alcohols via syngas with C2+ and C6+ fractions account for >90 wt% and ∼50 wt%, respectively.122