Abstract: A series of citric acid-modified Ba-MgO supports (Ba-MgO(CA)) were prepared by ultrasound electrostatic adsorption (UEA), and the corresponding Ru catalysts for ammonia synthesis were then prepared by the impregnation method. Their physical and chemical properties were characterized by scanning electronic microscopy, X-ray diffraction, nitrogen physical adsorption, inductively coupled plasma-atomic emission spectrometry, and infrared spectroscopy. The results showed that the introduction of citric acid during the preparation of the support changed not only the chemical and textural properties of the nano-Ba-MgO support but also the doping amount of Ba in the Ba-MgO(CA) support. When the concentration of citric acid was 2.0 mmol/L, the Ru/Ba-MgO(CA) catalyst exhibited the highest catalytic activity for ammonia synthesis with a reaction rate of 63.20 mmol/(g·h) at 400 ^oC, 10 MPa, and 10 000 h^-1, which is 21% higher than that of unmodified Ru/Ba-MgO.

Key words: citric acid, modification, barium doping, nano-magnesia, ruthenium, ammonia synthesis, ultrasonic preparation