Abstract: Activated carbon (AC) was functionalized by HNO₃ hydrothermal treatment at 180 ^oC. Ruthenium catalyst samples were prepared through incipient wetness impregnation with aqueous solution of RuCl₃·3H₂O precursor. The influence of HNO₃ concentration on the support structure, surface oxygen functional groups (SOFGs), Ru dispersion, and the catalytic activity of Ru/AC for ammonia synthesis was investigated by N₂ physisorption, He temperature-programmed desorption, CO chemisorption, and transmission electron microscopy. The results indicated that the amount of SOFGs, Ru particle size, and activity depend strongly on the HNO₃ concentration used in the hydrothermal treatment. The porous texture of carbon support almost keeps unchanged with low HNO₃ concentrations (≤ 2.0 mol/L) treatment, while it decreases significantly at high acid concentrations (2.4 mol/L). However, the amount of SOFGs increases with the concentration of nitric acid as well as the Ru particle size. Ammonia synthesis activity of the Ba-Ru-K/AC catalyst samples, whose support was treated with HNO₃ (2.0 mol/L), is as high as 17.80% at 400 ^oC, 10 MPa, and 10000 h⁻¹, which is 16.8% higher than that of the catalyst obtained via washing with HNO₃ (4.6 mol/L). The optimal conditions of hydrothermal treatment are HNO₃ (2.0 mol/L) at 150 ^oC for 4 h with filling degree 70%. Therefore, the amount of SOFGs and Ru particle size are tunable by varying the HNO₃ concentration during the hydrothermal treatment.

Key words: activated carbon, hydrothermal treatment, surface oxygen functional group, barium, ruthenium, potassium, dispersion, ammonia synthesis