Conversion Performance Prediction of Thermal-Deteriorated Three-Way Catalysts: Surface Reaction Model Development Considering Platinum Group Metals and Co-Catalyst

Three-way catalyst (TWC) converters can purify harmful substances, such as carbon monoxide, nitrogen oxides, and hydrocarbons, from the exhaust gases of gasoline engines. However, large amounts of these substances may be emitted before the TWC reaches its light-off temperature during cold starts, and its performance may be impaired by thermal deterioration during high-load driving. In this work, a simulation model was developed using axisuite commercial software by Exothermia S.A to predict the light-off conversion performance of Pd/CeO₂-ZrO₂-Al₂O₃ catalysts with different degrees of thermal deterioration. The model considered detailed surface reactions and the main factor of the deterioration mechanism. In the detailed reaction mechanism, adsorption, desorption, and surface reactions of each gas species at active sites of the platinum group metal (PGM) particles were considered based on the Langmuir-Hinshelwood mechanism. Model gas experiments were performed to identify each reaction rate parameter. The PGM particles supported on the co-catalyst CeO₂-ZrO₂ had two types of active sites with different properties, i.e., sites in the particles' surface region and in a three-phase boundary (TPB) region PGM, CeO₂−ZrO₂ of the co-catalyst, and gas meet. The TPB active sites were more active than the PGM surface active sites. As the main factor of the catalyst deterioration mechanism, quantitative changes at the two active sites related to PGM sintering were included in the model. After sintering, the occupancy of the TPB active sites on the PGM decreased. The final TWC model was able to accurately predict the light-off conversion performance of a thermal-deteriorated Pd/CeO₂-ZrO₂-Al₂O₃ catalyst.