Impact of Periodic Rich/Lean Switching and Metal Zone-Coating on Three-Way Catalyst Performance

The Three-Way Catalyst (TWC) plays a vital role in reducing engine exhaust gas emissions. However, steady-state exposure to exhaust gases can lead to catalyst deactivation via noble metal oxidation or active site poisoning. The periodic switching between rich and lean conditions has been shown to counteract deactivation, particularly enhancing methane oxidation.

This study explores the effect of periodic rich/lean switching (λ = 1 ± 0.02 at 0.5 Hz) on pollutant conversion in a realistic car exhaust gas matrix containing NO, CO, H₂, and hydrocarbons (C1-C5) at 100–400 °C. Cordierite-based monoliths were prepared with alumina–ceria–zirconia washcoat layers loaded with Pd, Pt, and Rh. Two catalysts with identical total Pd contents were compared: one homogeneously coated and another zone-coated with Pd on one-third of the catalyst. Gas composition at the outlet was analyzed using infrared spectroscopy and µ-gas chromatography.

The results show that periodic switching enhanced the conversion of NO, CH₄, and C₅H₁₂ compared to steady-state regimes, attributed to the alternating active site poisoning and regeneration during the rich and lean phases. The zone-coated catalyst exhibited superior performance, likely due to its higher local Pd content, smaller particle size promoting effective Pd-support interactions, enhanced oxygen storage capacity (OSC), and exothermic effects during operation.

This work highlights the potential of periodic switching and zone-coating strategies to optimize catalyst performance while conserving scarce platinum group metals, offering insights into next-generation emission control technologies. Insights from this study have broader implications for catalysis, including gas-to-energy conversion applications.

[reference] Elgayyar, T. et al. Promotional Effect of the Periodic Rich and Lean Switching on the Performance of Three-Way Catalysts and Influence of Metal Zone-Coating. Top Catal (2024) doi:10.1007/s11244-024-02019-2