The reaction performances and characterization of Fischer-Tropsch synthesis Co/SiO₂ catalysts prepared from mixed cobalt salts

Catalysts prepared by mixed impregnation of cobalt(II) nitrate and cobalt(II) acetate displayed higher activity than the catalysts prepared from either mono-precursor at mild reaction conditions (1MPa total pressure, H₂/CO=2, T=513K) of Fischer-Tropsch synthesis (FTS). X-ray diffraction (XRD) indicated that highly dispersed cobalt metal provided the main active sites on the catalyst prepared by mixed impregnation method. Through the mixed impregnation, different cobalt species were formed and their reduction performances were detected by the temperature-programmed reduction (TPR) and thermal gravimetric analysis. Transmission electronic microscopy (TEM) and FT-IR spectroscopy of adsorbed CO as probe molecule revealed that the presence of different sites associated with cobalt after the reduction of the catalysts with hydrogen at 673 K. It was assumed that the metal readily reduced from cobalt nitrate promoted the reduction of Co²⁺ to metallic state in cobalt acetate by H₂ spillover mechanism during catalyst reduction process. The reduced cobalt from cobalt acetate was highly dispersed and remarkably enhanced the catalytic activity.