Influence of Cation Substitutions Based on ABO₃ Perovskite Materials, Sr_1-xY_xTi_1-yRu_yO_3-δ, on Ammonia Dehydrogenation

In order to screen potential catalytic materials for synthesis and decomposition of ammonia, a series of ABO₃ perovskite materials, Sr_1-xY_xTi_1-yRu_yO_3-δ (x = 0, 0.08, and 0.16; y = 0, 0.04, 0.07, 0.12, 0.17, and 0.26) were synthesized and tested for ammonia dehydrogenation. The influence of A or B site substitution on the catalytic ammonia dehydrogenation activity was determined by varying the quantity of either A or B site cation, producing Sr_1-xY_xTi_0.92Ru_0.08O_3-δ and Sr_0.92Y_0.08Ti_1-yRu_yO_3-δ, respectively. Characterizations of the as-synthesized materials using different analytical techniques indicated that a new perovskite phase of SrRuO₃ was produced upon addition of large amounts of Ru (≥12 mol %), and the surface Ru⁰ species were formed simultaneously to ultimately yield Ru_z(surface)/Sr_0.92Y_0.08Ti_1-yRu_y-zO_3-δ and/or Ru_z-w(surface)/Sr_wRu_wO₃/Sr_0.92-wY_0.08Ti_1-yRu_y-zO_3-δ. The newly generated surface Ru⁰ species at the perovskite surfaces accelerated ammonia dehydrogenation under different conditions, and Sr_0.84Y_0.16Ti_0.92Ru_0.08O_3-δ exhibited a NH₃ conversion of ca. 96% at 500 °C with a gas hourly space velocity (GHSV) of 10 000 mL g_cat^-1 h^-1. In addition, Sr_0.84Y_0.16Ti_0.92Ru_0.08O_3-δ further proved to be highly active and stable toward ammonia decomposition at different reaction temperatures and GHSVs for >275 h.