Effect of Alumina Support and Barium Oxide on the Structure and Catalytic Activity of Ruthenium Catalysts for Ammonia Synthesis

A series of Ba-Ru/Al2O3 catalysts were prepared by the impregnation method using industrial alumina (Al2O3-1) and synthesized alumina (Al2O3-2) as supports. The catalysts were characterized by X-ray diffraction, N-2 adsorption-desorption, X-ray fluorescence spectroscopy, transmission electron microscopy, H-2 temperature-programmed reduction, NH3 temperature-programmed desorption, and X-ray photoelectron spectroscopy. The effect of Al2O3 and the BaO promoter on the phase structure, texture properties, morphology, surface properties, and catalytic activity in ammonia synthesis were investigated. The results indicate that the physical and chemical properties of Al2O3 have a strong impact on the structure and activity of the ruthenium catalysts. The BaO promoter has a strong impact on the ruthenium catalyst in two ways: first, the amount of BaO added leads to a difference in the interaction between BaO and gamma-Al2O3, which further influences the specific area and the porous structure of the catalysts; second, the addition of BaO influences the reduction process and the surface acidity and alkaline properties of the ruthenium catalysts. A proper amount of BaO promotes the activity and the optimal amount of BaO depends on the properties of the supports.