Rate limiting step in ammonia synthesis using low-pressure nitrogen-hydrogen mixture plasma

The contributions of atomic nitrogen, atomic hydrogen, and vibrational excited molecular nitrogen were compared in the synthesis of ammonia using low-pressure nitrogen-hydrogen mixture plasma. No specific catalysts were employed, and ammonia was synthesized via reactions on the surface of a stainless-steel chamber. It was found that the number of nitrogen atoms transported to the chamber wall per unit time approximately coincided with the synthesis rate of ammonia. On the other hand, the synthesis rate of ammonia was saturated with the number of transported hydrogen atoms. In addition, we observed no correlation between the synthesis rate of ammonia and the number of vibrational excited nitrogen molecules. The experimental results indicate that the adsorption of atomic nitrogen is the rate limiting step in the synthesis process of ammonia in the present experimental condition, where the flux of atomic nitrogen was 103 times lower than the flux of vibrational excited molecular nitrogen.