The effect of Ag as a promoter for Ru/CeO2 catalysts in ammonia synthesis

A series of Ag–Ru/CeO2 catalysts were prepared by conventional impregnation methods and characterized by XRD, BET, XPS, H2-TPR, H2-TPD-MS, and N2-TPD. The activity test shows that ammonia concentration of the catalyst with 6% Ag is 9.4% at 10 MPa, 10,000 h−1, 400 °C, which is 22% higher than that of Ru/CeO2. Such high catalytic activity was ascribed to three effects: electron donating property of partially reduced CeO2−x to Ru metal, the low workfunction of Ru atoms and the less competitive adsorbed between hydrogen and nitrogen on Ru atoms derived from the synergetic effect between Ag and Ru.

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► Silver is a very efficient promoter for Ru/CeO2 catalyst in ammonia synthesis.
► Silver can improve the reduction profiles of ceria by enhance the SMSI effect.
► Silver can weaken the competition of hydrogen and nitrogen adsorbed on Ru surface.
► The work function of Ru metal was decreased by silver loading.