YANG Xiaolong¹, TANG Liping^1,2, XI Chungu¹, XIONG Xvmao¹, MU Xinyuan¹, HU Bin^1*

(1. Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P.R. China; 2. Graduate University of Chinese Academy of Sciences, Beijing 100049, P. R. China)

Abstract: MgO supports were prepared by the different precipitants and further examined as the supports for barium-promoted ruthenium catalyst for ammonia synthesis. The reason resulting in their difference of catalytic activity were explored by X-ray diffraction, N₂ adsorption-desorption, X-ray fluorescence spectroscopy, transmission electron microscopy, H₂ temperature-programmed reduction, CO₂ temperature-programmed desorption, H₂ temperature-programmed desorption and N₂ temperature-programmed desorption. It is found that MgO prepared by (NH₄)₂CO₃ precipitant facilitate the reduction of ruthenium oxide for Ba-Ru/MgO catalyst, the weak basic sites of Ba-Ru/MgO((NH₄)₂CO₃ as precipitant) appeared at lower temperature and showed higher weak basic site densities compared with the others. At 450 ℃、5.0 MPa and 5000 h-1, catalytic activity of Ba-Ru/MgO catalyst employing (NH₄)₂CO₃ as the precipitant was higher than that of the catalyst prepared by other precipitants under the same reaction conditions, the ammonia concentration in the effluent reached 3.74 %. The addition of Ba promoter significantly decreased the amount of hydrogen chemisorption, increased the number of dissociatively adsorbed N* on the Ru surface and thus accelerated the reaction rate of ammonia synthesis.

Key words: Ammonia synthesis; Ruthenium catalyst; Precipitants; Basic site.

E-mail: yxlwin@163.com

Journal of Molecular Catalysis, Vol. 26, Issue 1, 2012, 1-9