Linking Bench-Scale Conversion Characteristics to Cycle-Level Emissions for Pd-Rh Three-Way Catalyst Selection in Plug-In Hybrid Vehicles

Selecting three-way catalysts (TWCs) solely from precious-metal loading or a single light-off metric may not reflect the broad operating domain encountered by plug-in hybrid electric vehicles (PHEVs). This study linked bench-scale conversion characteristics of three aged, Pt-free Pd-Rh formulations to cycle-level emissions. The formulations represented a low-loading baseline (TWC-1), a proportional increase in Pd and Rh (TWC-2), and a higher-loading Pd-rich strategy (TWC-3). Light-off, temperature–space-velocity, and λ-sweep data were incorporated into coupled vehicle, engine-out emission, catalyst thermal, and aftertreatment models for Worldwide Harmonized Light Vehicle Test Cycle (WLTC) and Real-driving Emission (RDE) evaluation. The formulation ranking varied with the test boundary. At 30,000 h−1, TWC-3 exhibited the lowest CO light-off temperatures, whereas TWC-2 achieved the lowest T50 values for C3H6 and NO. At 50,000 h−1 with its corresponding inlet composition, TWC-2 produced the lowest T50 and T90 values for all three species. Across the broader operating domain, TWC-1 deteriorated most when lower temperature coincided with higher space velocity, while the higher-loading Pd-rich strategy provided no consistent advantage for C3H6 or NO conversion. The WLTC emphasized light-off and intermediate-temperature activity, whereas the predominantly hot RDE profile included space velocities above 200,000 h−1. Relative to TWC-3, TWC-2 reduced predicted TWC-out CO and NOx emissions by 10.0% and 4.1% over the WLTC and by 36.4% and 18.8% over the RDE profile, respectively, while producing the lowest cycle-integrated THC emissions. These results demonstrate that the highest precious-metal loading does not necessarily provide the best cycle-level emission control. Linking formulation-specific conversion characteristics with cycle-dependent operating-domain distributions provides a more representative basis for TWC selection than a single light-off metric.