Cs-Ba-Ru/La₂O₃-MgO Catalysts from Microdrop-Confined Pyrolysis for Superior NH₃ Synthesis under Mild Conditions

Support modification is an important way to improve the activity of the Ru/MgO-based NH₃ synthesis catalyst. This work synthesized 24 composite MgO-based supports of MO-MgO (M = La, Zn, etc.) via a microdrop-confined pyrolysis (MDCPy) method and then prepared the corresponding Cs-Ba-Ru/MO-MgO catalysts using the impregnation method. Under the same NH₃ synthesis conditions, the activity of the Cs-Ba-Ru/MO-MgO catalysts composed of 17 elements such as Pr was significantly lower than that of Cs-Ba-Ru/MgO, while the activity of the Cs-Ba-Ru/MO-MgO catalysts composed of four elements such as Nd was comparable to that of Cs-Ba-Ru/MgO, and the activity of the Cs-Ba-Ru/MO-MgO catalysts composed of three elements such as La was significantly higher than that of Cs-Ba-Ru/MgO. Among them, it is clear that La₂O₃-MgO composite supports have the most significant effect on the improvement of NH₃ synthesis performance. Through the optimization of the La/Mg ratio and loading of Ru, the optimal activities achieved ∼7 mol_(NH3)/g_(Ru)/h with corresponding Ru loading of 0.25-0.5 wt % under mild conditions as follows: H₂/N₂ ratio of 3:1, temperature of 400 °C, pressure of 3 MPa and a weight hourly space velocity (WHSV) of 96.0 L/g_cat/h. In addition, the CsBa-Ru/La₂O₃-MgO catalyst showed good stability.