Influence of chemical treatments of activated carbon support on the performance and deactivation behavior of promoted Ru catalyst in ammonia synthesis

• Promoted Ru/active carbon (AC) catalysts were prepared for ammonia synthesis.
• Chemical treatments of AC with H2 and HNO3 improved Ru/AC catalytic performance.
• Activity and stability orders based on treatment was AC < AC-H2 < AC-H2/HNO3.
• The reaction is not diffusion controlled under practical operating conditions.
• A second-order decay law well explained the long-term deactivation behavior.

A series of Ru/activated carbon (AC) catalysts promoted with potassium and barium were prepared by impregnation method for ammonia synthesis. The chemical treatments effects of the support on catalytic performance were studied by modifying AC with H2 (ACH) and H2 + nitric acid (ACHN). The catalysts were characterized by using nitrogen adsorption/desorption, TEM, SEM, EDS and XRD techniques. The catalytic performance was carried out in a fixed-bed reactor at 400–450 °C, 30 bar and N2:H2 (1:3). The order for both activity and stability was ACHN > ACH > AC according to the support type. The excellent performance of K–Ba–Ru/ACHN catalyst was attributed to efficient chlorine and sulfur removal from AC and high distribution of Ru and promoters. The reaction was found not to be intra-particle diffusion limited. A second-order independent decay law was proposed for catalyst deactivation. Deactivation rate constants of 0.016 h−1 and 0.0018 h−1 were obtained for AC and ACH supported samples, respectively.

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