Cs–Ba–Ru/La<sub>2</sub>O<sub>3</sub>–MgO Catalysts from Microdrop-Confined\nPyrolysis for Superior\nNH<sub>3</sub> Synthesis under Mild Conditions

Support modification is an important way to improve the\nactivity\nof the Ru/MgO-based NH<sub>3</sub> synthesis catalyst. This work synthesized\n24 composite MgO-based supports of MO<sub><i>x</i></sub>–MgO (M = La, Zn, etc.) via a microdrop-confined pyrolysis\n(MDCPy) method and then prepared the corresponding Cs–Ba–Ru/MO<sub><i>x</i></sub>–MgO catalysts using the impregnation\nmethod. Under the same NH<sub>3</sub> synthesis conditions, the activity\nof the Cs–Ba–Ru/MO<sub><i>x</i></sub>–MgO\ncatalysts composed of 17 elements such as Pr was significantly lower\nthan that of Cs–Ba–Ru/MgO, while the activity of the\nCs–Ba–Ru/MO<sub><i>x</i></sub>–MgO\ncatalysts composed of four elements such as Nd was comparable to that\nof Cs–Ba–Ru/MgO, and the activity of the Cs–Ba–Ru/MO<sub><i>x</i></sub>–MgO catalysts composed of three elements\nsuch as La was significantly higher than that of Cs–Ba–Ru/MgO.\nAmong them, it is clear that La<sub>2</sub>O<sub>3</sub>–MgO\ncomposite supports have the most significant effect on the improvement\nof NH<sub>3</sub> synthesis performance. Through the optimization\nof the La/Mg ratio and loading of Ru, the optimal activities achieved\n∼7 mol<sub>(NH3)</sub>/g<sub>(Ru)</sub>/h with corresponding\nRu loading of 0.25–0.5 wt % under mild conditions as follows:\nH<sub>2</sub>/N<sub>2</sub> ratio of 3:1, temperature of 400 °C,\npressure of 3 MPa and a weight hourly space velocity (WHSV) of 96.0\nL/g<sub>cat</sub>/h. In addition, the CsBa–Ru/La<sub>2</sub>O<sub>3</sub>–MgO catalyst showed good stability.