Effect of alumina phases on hydrocarbon selectivity in Fischer–Tropsch synthesis

Abstract Different alumina phases i.e. δ-, θ-, and α-Al 2 O 3 were prepared from two different samples of γ-Al 2 O 3 by heat treatment. The alumina samples were categorised as small and medium pore according to the pore size distribution. Nominally 12 wt% cobalt was loaded onto the supports by incipient wetness impregnation. By varying the amount of deionised water and ethylene glycol, the Co 3 O 4 crystallite size could be controlled. After reduction, a relatively constant cobalt metal particle size of 8–10 nm was obtained. Temperature-programmed reduction profiles showed that the medium pore catalysts were reduced at lower temperatures as compared to the small pore catalysts. The Fischer–Tropsch synthesis was carried out for all samples under the same experimental conditions ( P  = 20 bar, T  = 483 K, H 2 /CO = 2.1). The medium pore catalysts exhibited higher selectivity to C 5+ than the small pore catalysts. Furthermore, higher C 5+ selectivity was observed for δ-and α-Al 2 O 3 samples compared to γ-and θ-Al 2 O 3, with α-Al 2 O 3 giving the highest selectivity. Steady-state isotopic transient kinetic analysis (SSITKA) showed that the amount of CH x surface intermediates followed the same trend as the C 5+ selectivity with respect to pore size and alumina phase.

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