Promotional Effect of the Periodic Rich and Lean Switching on the Performance of Three-Way Catalysts and Influence of Metal Zone-Coating

Increasingly stricter regulations for vehicle emissions require more competitive exhaust emission control systems. Three-way catalysis is a major up-to-date emission control technology, though the activity could be limited during the cold start as well as steady state operation including the three regimes: rich (λ<1), lean (λ>1), and stoichiometric (λ=1). Periodic rich/lean switching emerges as a promising strategy to address this challenge. In this work, we investigate the influence of the switching process, using a fixed lambda air-to-fuel ratio amplitude of λ = 1±0.02 (0.5 Hz), on pollutant conversion from 100 to 400 °C, under a complex matrix including nitrogen monoxide (NO), carbon monoxide (CO), hydrogen (H₂), and hydrocarbons (C₁-C₅), simulating the typical car exhaust gas. Moreover, two catalysts were tested: one homogeneously coated with Pd, and another zone-coated with Pd, both containing the same total amount of Pd, in order to identify the effect of the catalyst zone-coating and rationalize the use of increasingly scarce platinum group metals. Simple binary pollutant oxidation reactions were also performed to determine the reactivity of individual pollutant gases. Interestingly, NO, CH₄ and C₅H₁₂ displayed highest conversions during the switching regime compared to steady-state periods, attributed to the beneficial balance between active site poisoning/regeneration during the rich/lean regimes respectively. The zone-coated catalyst showed an overall higher activity under the full gas mixture that could be explained by a slightly higher Pd content, more effective Pd-support interactions, exothermic effect or the better OSC properties.