The impact of Al2O3 promoter on an efficiency of C5+ hydrocarbons formation over Co/SiO2 catalysts via Fischer-Tropsch synthesis

•Al2O3 dopant to Co/SiO2 Fischer-Tropsch catalyst promotes synthesis of C5nH10n+2.•The highest promotion effect was detected at 1 wt.% of Al2O3 loading into Co/SiO2.•Al2O3 addition into Co/SiO2 catalyst alters dispersion of the formed Co° particles.•Co° particles of 8 nm mean size were formed at 1 wt.% of Al2O3 loading.

The influence of doping of Co/SiO2 catalysts with alumina on a performance of Fischer-Tropsch synthesis (FTS) was studied by extended FTS trials in a fixed-bed tubular pilot-scaled reactor. The addition of small amount of Al2O3 causes apparent promotional effect on the catalysts activity and C5+ hydrocarbons selectivity. The largest promotion effect was observed for the catalysts with 1 wt.% of alumina loading. The modification of the catalyst with alumina (1 wt.%) changes molecular weight distribution of the resultant C5+ paraffins with increasing the fraction of C8-C25 and decreasing the fraction of longer chain hydrocarbons. The addition of a proper amount of alumina into Co/SiO2 catalyst alters Co° particle size distribution making it narrower with the maximum at 8 nm and the same mean value for Co° particle size. A volcano-like dependence of CO chemisorption on alumina loadings with a maximum at 1 wt.% was observed. Relatively high CO chemisorption at the proper amount of alumina decreases the ratio of surface hydrogen to carbon monoxide and in such a way promotes formation of C5+ hydrocarbons.

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