Coupled LNT–SCR catalysts for lean NOx abatement: mechanistic insights from operando FT-IR spectroscopy

• Operando FT–IR characterizes the SCR behaviour within integrated LNT + SCR systems. • Operando FT–IR captures LNT–derived NH 3 consumption on the downstream SCR catalyst. • C 3 H 6 generates oxygenated and NCO species that act as key HC–SCR intermediates. • Water promotes the hydrolysis of propene–derived intermediates and limits their build-up. In this work the removal of NO x over a combined LNT + SCR system was investigated under lean–rich cycling conditions by coupling operando FT-IR spectroscopy with complementary gas-phase analysis. A model Pt-Ba/Al 2 O 3 LNT catalyst and a commercial Cu-zeolite SCR catalyst were arranged in a sequential dual-bed configuration, with the SCR catalyst placed downstream in an operando FT-IR reactor cell to enable its real-time characterization under realistic reaction conditions. Experiments were performed in the 150–250 °C temperature range with H 2 , H 2 /CO, and C 3 H 6 as reductants, both in the absence and presence of H 2 O in the feed stream. The results provided direct spectroscopic evidence that the NH 3 released from the LNT catalyst during the rich phase is stored on the SCR catalyst and then consumed in the subsequent lean phase due to the occurrence of SCR reactions, thereby enhancing overall NO x conversion and improving N 2 selectivity compared to the single LNT catalyst. Increasing temperature (150–250 °C) enhances both NO x storage capacity and N 2 selectivity, while decreasing the formation of undesired by-products such as N 2 O and the NH 3 slip. The nature of the reductant is shown to play a crucial role: H 2 and H 2 /CO promote the NH 3 –mediated pathways, whereas C 3 H 6 activates additional hydrocarbon–SCR routes involving the formation of surface hydrocarbon-derived intermediates, but with possible formation of carbonaceous deposits. Water is found to positively affect performance by promoting NH 3 formation and facilitating the hydrolysis of C 3 H 6 -derived intermediate species, ultimately increasing N 2 yield. Overall, this study provides new insights into the interplay between LNT and SCR functionalities, offering a valuable basis for the optimization of integrated LNT + SCR aftertreatment systems aimed at meeting stringent NO x emission standards.