Highly dispersed Co/SiO₂ catalysts were prepared using an ethylene glycol (EG) modified silica support. The modified SiO₂ support significantly promoted the dispersion of supported cobalt and adding a small amount of Ru increased the reducibility of the highly dispersed cobalt oxide. The Co–Ru/SiO₂ (EG) catalyst exhibited 3 times higher 1-hexene conversion and 18 times higher heptanal yield than the conventional Co/SiO₂ catalyst.