Carbon-based ruthenium catalyst for ammonia synthesis: Role of the barium and caesium promoters and carbon support

• Published in: Applied catalysis. A, General Vol. 248; no. 1; pp. 67 - 73
• Main Authors: Kowalczyk, Z., Krukowski, M., Raróg-Pilecka, W., Szmigiel, D., Zielinski, J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 08.08.2003; Elsevier
• Subjects: Ammonia synthesis; Barium promoter; Caesium promoter; Carbon support; Catalysis; Catalysts: preparations and properties; Chemistry; Exact sciences and technology; General and physical chemistry; Ruthenium catalyst; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Ruthenium catalyst; Ammonia synthesis; Barium promoter; Carbon support; Caesium promoter; Barium; Ruthenium; Cesium; Alkali metal; Alkaline earth metal; Carbon; Supported catalyst; Promoter; Ammonia; Heterogeneous catalysis; Synthesis
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/S0926-860X(03)00150-9

A series of ruthenium catalysts deposited on graphitized carbon and promoted with barium, caesium or both Ba and Cs have been studied in ammonia synthesis. Under experimental conditions (90 bar, H 2:N 2=3:1, 400 °C, 10% NH 3), the reaction rate over the co-promoted catalyst (9.1 wt.% Ru in Ru+C) was found to be higher than those over singly promoted specimens, the overall effect from Ba + Cs in Ba-Cs-Ru/C being almost as high as the sum of individual effects from Ba (Ba-Ru/C) and Cs (Cs-Ru/C), respectively. The co-promoted Ru catalysts, especially that of high ruthenium loading (23.1 wt.% Ru) were shown to be significantly more active in NH 3 synthesis than the conventional fused iron catalyst (KMI, H. Topsoe). The oxygen chemisorption studies have shown that the amounts of O 2 taken up by the Cs-containing samples (Cs-Ru/C, Cs-Ba-Ru/C) are considerably larger than those for Ru/C and Ba-Ru/C, thus indicating caesium to be in a highly reduced, most likely zero valent form, when operating under ammonia synthesis conditions. It is suggested that barium ((Ba+O) adlayer) is located on the ruthenium surface and it acts as a structural or electronic promoter. Caesium (Cs 0) is suggested to be localised on the carbon surface: the Cs promotion occurs at contact points between Ru and the Cs atoms adsorbed on carbon (“hot ring promotion”—electronic).