Reaction Pathways for Ammonia Formation on Lean NO_x Trap/Reduction System: A Spectroscopic Infrared Investigation

This study is devoted to an operando study of Pt–Rh/Al₂O₃–BaO lean-NO_x trap catalyst during the regeneration with H₂/CO reaction mixture. Particular attention was paid to the influence of CO coexisting with H₂ during the regeneration that can simulate the regeneration step by using reformate composed of CO and H₂. In rich H₂ mixture ammonia predominantly forms. As expected, strongly chemisorbed CO molecules over noble metals lower the efficiency of the trap at 150 °C. Successive hydrogenation of N atoms to ammonia predominates in our conditions. However, the comparison of the outlet gas composition with infrared spectral features also suggests a minor participation of isocyanate species (NCO) as possible intermediates in the production of ammonia especially for long regeneration duration in the absence of water. Interestingly, ammonia formation as reducing agent for the selective reduction of NO can stimulate practical applications for further coupling lean-NO_x trap with SCR catalysts.