Studies on surface impregnation combustion method to prepare supported Co/SiO ₂ catalysts and its application for Fischer-Tropsch synthesis

A series of supported Co/SiO ₂ catalysts were prepared by surface impregnation combustion method using cobalt nitrates and citric acid, and the precursors were burnt in different atmospheres. The effects of different calcination atmospheres on the properties of the supported Co/SiO ₂ catalysts were systemically studied by TG-DTA, XRD, Raman spectrum, TPR, in situ FTIR, TEM, BET and H ₂-chemisorption techniques. The burnt catalyst C _{argon-air-reduction} which was first burnt in argon and then oxidized in air had about 10 nm Co ₃O ₄ crystalline size, much smaller than that which was directly burnt in air (Co ₃O ₄ size: about 15 nm) and that prepared by conventional impregnation method (Co ₃O ₄ size: about 32 nm) using cobalt nitrate as impregnating solution. Characterizations and FTS results of two other references using different organic cobalt salt aqueous (cobalt acetate and cobalt citrate) as impregnating solution were also added in the supporting information. Comparing with our previously reported C _argon catalyst directly burnt in the argon atmosphere without further reduction, the influence from surface amorphous carbon and carbonic residues was completely eliminated. The activity of the burnt catalyst C _{argon-air-reduction} prepared by surface impregnation method was threefold higher than that of the reference C _N-reduction prepared by conventional incipient-wetness impregnation method. The surface impregnation combustion method described herein was promising to prepare highly dispersed supported metallic catalysts with smaller particle sizes.