Experimental and numerical studies on the impacts of perturbation on purification characteristics of three-way catalysts

Abstract

Three-Way Catalysts (TWC) undergo thermal degradation under high exhaust gas temperatures, reducing the specific surface areas of precious metals on the catalyst surface due to sintering. This also reduces the Oxygen Storage Capacity (OSC) and the TWC conversion rate. Lowering the exhaust gas temperature is a solution to minimize performance deterioration. However, low temperatures reduce the effectiveness of catalyst reactions. Perturbation (dithering or rich-lean cycle) can enhance the TWC conversion rate. In this work, synthetic gas reactor experiments are carried out to measure the purification performance data of fresh and degraded catalysts under rich-lean perturbations at 400°C. A TWC model with elementary reactions covering surface reactions and OSCs is developed. The degradation performances in the axial direction are reported. The results show that the conversion rates reach 90% within the first 30% of the catalyst length. For the catalysts with and without degradation, when the conversion rate declines, the reaction rates are slower than the mass fluxes, indicating that the reaction rates are the rate-limiting factor for each purification reaction. It is observed that the degraded catalysts have fewer active sites, and the amount of oxygen storage and consumption is small. Conversion rates of gas species, OSC, and mass flux of major species of the fresh and degraded catalysts are also compared.