Ruthenium-based Catalyst With Low Loading For Ammonia Synthesis

Compared with fused-iron catalyst, Ru-based catalyst has higher activity for ammonia synthesis under low pressure and low temperature. However, the high cost of Ruthenium precursor limits its industrial application. In order to reduce the industrialization cost of ruthenium catalyst for ammonia synthesis, Ru based ammonia synthesis catalyst with low loading was optimized to achieve a high performance at a relative low loading of Ruthenium.First, the content and types of promoters were optimized. It is found that the catalytic activity gradually increased first with the content of Ba, K and Cs increased, and then decreased. The optimized promoter loading of Ru/AC catalyst is Ba 4wt% and K 14wt%.Secondly, the impregnation conditions on the catalytic activity were studied. It is found that long impregnation time can improve the activity of Ru/AC catalysts. The suitable impregnation conditions is 18 ~ 24 h at 25 oC. In the preparation conditions, the modulation of nitric acid concentration of modified activated carbon can effectively change the ruthenium ion on the distribution of the surface on activated carbon.Finally, the surface chemistry and physical properties of activated carbon pretreated by various methods were studied and characterized by N2 physical adsorption and chemical titration (mass titration and Boehm titration) methods. It shows the catalytic activity and the number of surface groups are correlated. Activated carbon modified by gas phase oxidation cannot increase the activity of Ru/AC catalyst. It is found that the activity of catalyst is affected by the amount and type of the surface functional groups of activated carbon. The activity of Ru/AC catalysts are linear increase with the amount of phenolic hydroxyl. According to the above conclusions, a new two-steps liquid oxidation method by combination of nitric acid and peroxide water pretreatment was used for treatment of activated carbon. The results show that this method can efficiently improve the activity of Ru/AC catalyst.In present paper, the outlet ammonia concentration for the optimized Ru/AC catalyst with 2% Ruthenium loading at the 400℃, 10.0MPa, 10000h-1 condition reached 20.48%. It improved by 5% compared with the traditional one step liquid phase oxidation method.