The intrinsic effects of shell thickness on the Fischer–Tropsch synthesis over core–shell structured catalysts

Abstract

A series of core–shell catalysts with cobalt nanoparticles coated by silica shells were prepared to provide an insight into the effects of the shell thickness on the Fischer–Tropsch synthesis. The catalysts displayed uniform silica shell thicknesses in the range of 4.3–18.2 nm as ascertained by TEM. From the H₂ chemisorption results, increasing the shell thickness did not reduce the number of active sites due to the similar active cobalt surface areas. Even though the reducibility determined by H₂-TPR decreased rapidly with the increase in shell thickness, the catalytic activity was not evidently reduced. The hydrocarbon products shifted to shorter chains and the C₁₅–C₁₈ selectivity had a volcano-type dependence as the shell thickness increased, which is probably because thicker shells contribute to more severe diffusion limitations of the reactants.