Enhancing the thermal stability and activity of Pd–Rh/Al2O3 catalyst for three–way catalytic reaction by introducing Pt and varying the synthesis method

Three–way catalysts (TWCs) are used to remove exhaust gas emissions from the gasoline vehicle engine. The vehicle engine temperature rises to 1000 °C which is harsh condition; therefore, maintaining catalytic activity is so difficult by metal sintering. In this study, the effects of introducing Pt and the synthesis method of Pd–Pt–Rh/Al2O3 catalysts were investigated for enhancing the thermal stability and three–way catalyst activity. Therefore, three synthesis methods were introduced: co-impregnation, sequential impregnation, and physical mixing. The thermal aging was conducted at a high temperature (950 °C), wherein a 1 h lean–rich cycle was repeated 30 times. The physically mixed catalyst exhibited higher thermal stability than other catalysts. Pt was impregnated first, and Pd and Rh were physically separated in physically mixed catalysts; therefore, sintering was inhibited after thermal aging. The aged physically mixed catalyst presented the highest PdO and PtOx ratio, resulting in high oxidation activity. To further enhance the catalytic activity after thermal aging, the Pd/Pt ratios were varied with a constant Rh content. When the Pt content was increased in physically mixed catalysts, the catalytic activity of the aged catalysts increased. Therefore, the physically mixed catalyst with a high Pt ratio was suggested as the optimal catalyst which exhibited high sintering inhibition.