Evaluation of three-way catalyst performance for heavy-duty natural gas engines: fresh and aged conditions for Euro 7 durability compliance

• Thermal ageing significantly reduces TWC conversion efficiency. • Extensive experimental campaign at SGB with temperature ramp tests and λ variation. • Insight on Pd ⇄ PdO transformation for CH 4 conversion. • Long-term TWC performance is crucial to meet Euro 7 emission standards. In light of the Euro 7 regulation, which requires increased lifetime and durability for all vehicle components, this paper examines the performance of a Three-Way Catalyst (TWC), both in fresh condition and after a thermal ageing process. An extensive experimental campaign was carried out with the use of a Synthetic Gas Bench (SGB), varying Gas Hourly Space Velocity (GHSV), temperature, and λ values, under steady-state and during rapid Rich-Lean transitions of different durations and amplitudes, to investigate the Oxygen Storage Capacity (OSC) phenomena. A global decline in the performance of the aged TWC is observed, particularly in the CO and NO conversion. In temperature ramp tests, there is a significant delay in reaching light-off, while during Rich-Lean transitions a marked decline in OSC is present, due to reduced activity of ceria reactions. CH 4 conversion is significantly affected by the reduction in available active sites for the reactions, resulting from changes in the rate of reversible Pd ⇄ PdO transformation. In particular, despite steady-state conditions, a dynamic CH 4 conversion is present at high temperatures, related to Steam Reforming and oxidation processes. In lean conditions, while the fresh TWC already exhibits partial CH 4 conversion due to its stability, after the aging process, the catalyst is unable to maintain adequate efficiency levels. Important insights into NH 3 production within the catalyst were also detected. The results of this work highlight the importance of investigating long-term catalyst behaviour due to aging, in order to develop cost-effective devices that comply with evolving regulatory standards.