Effect of the pore size of Co/SBA-15 isomorphically substituted with zirconium on its catalytic performance in Fischer-Tropsch synthesis

Cobalt catalysts supported on a series of mesoporous SBA-15 materials isomorphically substituted with zirconium (Zr/Si atomic ratio = 1/20) with different pore sizes (5.7 nm, 7.8 nm, 11.6 nm, 17.6 nm) have been synthesized. The catalysts were characterized by transmission electron microscopy, ²⁹Si solid state magic angle spinning (MAS) NMR, N₂ adsorption-desorption measurements, X-ray powder diffraction, X-ray photoelectron spectroscopy, H₂-temperature programmed reduction, H₂-temperature programmed desorption and O₂ titrations. The results indicated that larger pore size led to weaker interactions between cobalt and the supports which lowered the temperature of both reduction steps (Co₃O₄→CoO and CoO→Co⁰). The catalytic performances of the catalysts in Fischer-Tropsch synthesis (FTS) were tested in a fixed bed reactor. It was found that the FTS catalytic activity and product selectivity depended strongly on the pore size of the catalysts. The catalyst with a pore size of 7.8 nm showed the best FTS activity, and the catalyst with a pore size of 17.6 nm showed the highest selectivity to C₁₂–C₂₀ and C₂₀₊ hydrocarbons.