Fuel-lean combustion synthesized cobalt catalysts for Fischer-Tropsch reaction

Abstract

The present study investigates synthesis of liquid fuels and higher hydrocarbons via Fischer Tropsch (FT) reaction using combustion synthesis (CS) catalysts. The CS method employed citric acid (C6H8O7) as fuel with lean stoichiometry (ϕ = 0.3, ϕ = 0.6) for the catalyst synthesis. CS reactions at lean conditions can be easily controlled, and holds the structural integrity of the catalyst support, resulting in no loss of active sites. The fuel-lean conditions show decreased formation of cobalt aluminates, resulting in high catalyst reducibility and larger fraction of active sites. When tested at constant space velocity, the CS catalysts achieve CO conversion up to 88%, which is 57% higher than the wet impregnation (WI) synthesized catalysts. Furthermore, the variation of the equivalence ratio allows to tailor the catalyst properties and thereby control conversion and selectivity of the CS catalysts. CS(ϕ = 0.6) showed a C5+ selectivity 31% higher compared to the CS(ϕ = 0.3). The liquid fuel space time yield (STY) ranged from 0.13 to 0.30 (gC5+ gcat-1 h-1) and it increases in the following order: WI < CS(ϕ = 0.3) < CS(ϕ = 0.6). These results emphasize the effectiveness of the CS method for the synthesis of FT catalysts and show the effect of the lean-fuel stoichiometry on the catalyst properties and performance.