Improving the ammonia synthesis activity of Ru/CeO2 through enhancement of the metal–support interaction

The metal–support interactions induced by high-temperature hydrogen reduction have a strong influence on the catalytic performance of ceria-supported Ru catalysts. However, the appearance of the strong metal–support interaction leads to covering of the Ru species by Ce suboxides, which is detrimental to the ammonia synthesis reaction that requires metallic species as active sites. In the present work, the interaction between Ru and ceria in the Ru/CeO2 catalyst was induced by NaBH4 treatment. NaBH4 treatment enhanced the fraction of metallic Ru, proportion of Ce3+, content of exposed Ru species, and amount of surface oxygen species. As a result, a larger amount of hydrogen species would desorb by the H2-formation pathway and the strength of hydrogen adsorption would be weaker, weakening the inhibition effect of the hydrogen species on ammonia synthesis. In addition, the strong electronic metal–support interaction aids in nitrogen dissociation. Consequently, Ru/CeO2 with NaBH4 treatment showed higher ammonia synthesis rates than that with only hydrogen reduction.