Catalytic wet air oxidation of ammonia over supported noble metals

• Pt, Pd, Ru, Ir and Rh catalysts were systematically compared in the CWAO of ammonia.
• Platinum catalysts are the most active in the CWAO of ammonia.
• Palladium catalysts are the most selective toward N2 in the CWAO of ammonia.
• Both the activity and the selectivity are influenced by the metal–oxygen bond strength.
• The retro-disproportionation and nitrous acid decomposition reactions are key reactions.

Highly active and selective supported noble metal catalysts were studied in the catalytic wet air oxidation of ammonia. Under the applied reaction conditions (200 °C, 50 bar total pressure) only nitrites and molecular nitrogen were detected as primary products. Nitrates formed upon oxidation of nitrites. Platinum-based catalysts were shown to be the most active and among the most selective toward molecular nitrogen. The control of the oxygen coverage at the catalyst surface (metal–oxygen bond energy) was evidenced to have a key impact on both the activity and the selectivity. The retro-disproportionation and nitrous acid decomposition reactions appeared to impact the selectivity upon the conversion of nitrites to nitrates.

Figure optionsDownload high-quality image (65 K)Download as PowerPoint slide