Abstract. The influence of cobalt particle size in the range 3 to 18 nm on the Fischer–Tropsch synthesis intrinsic activity and product distribution was investigated over 26 alumina (γ -Al2O3 and α-Al2O3) supported catalysts. A volcano-like curve was obtained for the γ -Al2O3 based catalysts when the C5+ selectivity was plotted as a function of the particle size. The maximum selectivit…