Study on hydrothermal aging characteristics of three‐way catalysts for lean‐burn gasoline engines

Abstract With increasingly stringent emission regulations and fuel consumption standards, lean‐burn technology has become an important development direction for gasoline engines. The emission characteristics of lean‐burn gasoline engines differ significantly from those of conventional stoichiometric engines, and when close‐coupled three‐way catalysts (TWCs) are still applied, it is essential to understand their hydrothermal aging behavior. In this study, six Pd‐only TWC samples with two Pd loadings (high and low) and three aging states (fresh, normally aged and lean‐burn aged) were prepared. Their catalytic performance was evaluated on a flow reactor under steady‐state lean‐burn conditions, measuring NO, HC and CO conversion and NH 3 yield. Structural characterizations were carried out using XRD, BET, SEM and XPS. The results show that lean‐burn aging causes more severe structural degradation and stronger depletion/oxidation of surface Pd species than normal aging, leading to pronounced deterioration of low‐temperature (<300°C) NO and CO conversion. High Pd loading provides higher initial activity and superior high‐temperature (>400°C) conversion, but suffers poorer low‐temperature stability, whereas low Pd loading exhibits better structural stability and improved low‐temperature HC conversion. Although both aging protocols reduce NH 3 yield, lean‐burn aged catalysts show a smaller decrease and even relatively higher NH 3 yield at 300–350°C due to stronger CO oxidation deactivation and the resulting increase in residual CO. These findings provide guidance for optimizing Pd‐based TWCs for lean‐burn gasoline engines, especially when used upstream of PSCR.