Ru/CeO2 catalysts were prepared by the co-precipitation method using six precipitants, K2CO3, NH3•H2O, (NH4)2CO3, KOH, NH4HCO3 and KHCO3, used for the ammonia synthesis and characterized by N2 adsorption-desorption, X-ray fluorescence spectroscopy, X-ray diffraction and H2 temperature-pro- grammed reduction to explore the cause resulting in their significant difference of catalytic activity. The ammonia synthesis activity of Ru/CeO2 catalyst prepared using NH4HCO3 as the precipitant was 14.46% at 10 MPa, 10000 h－1, 450 ℃, which was higher than those obtained by other precipitants. The samples prepared using the rest four precipitants presented lower activity for ammonia synthesis. The type of precipitant not only significantly affects the coprecipitation of ruthenium and cerium ions, but also affects the reduction of the surface oxygen. The high catalytic activity of Ru/CeO2 catalyst prepared using NH4HCO3 can be attributed to the synergism among the increase in ruthenium loading, the higher dispersion of ruthenium particles, and the easier reduction of surface oxygen of the support.

Key words: ammonia synthesis, precipitant, cerium, ruthenium, co-precipitation