Hydroxyapatite-Supported Ruthenium Catalysts in Ammonia Synthesis: Impact of Ba and Cs as Catalyst Promoters.

This work is devoted to the synthesis, the characterization, and the evaluation of hydroxyapatite-supported ruthenium catalysts, with or without Ba and/or Cs promotion. Thus, a series of catalysts containing Ru, Cs, and Ba was synthesized by the incipient wetness impregnation method. Such catalysts are characterized by different physicochemical methods, providing insights into their properties. These catalysts are evaluated in the ammonia synthesis reaction at 350-500 °C and 10-25 bar. Sample 1Ru/hydroxiapatite (HAP), without promoter, shows a negligible catalytic activity, due to the formation of large Ru nanoparticles, which are not favorable for the formation of ammonia. On the other hand, the addition of Cs and Ba improves the catalytic performance, and Ba is found to be better than Cs. The pretreatment of the barium-containing catalysts under Ar flow at 600 °C is also found to be crucial for the decomposition of barium nitrate into barium oxide, thereby enhancing catalytic activity.