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

This study is devoted to an operando study of Pt–Rh/Al2O3–BaO lean-NOx 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-NOx trap with SCR catalysts.