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

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 H-2 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 H-2-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 C-15-C-18 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.