Effect of WO ₃ and La ₂ O ₃ Addition on the Thermal Durability of Pd/γ - Al ₂ O ₃ Catalysts for Automotive Emission Control

In order to suggest an efficient catalyst system for automotive emission control, Pd-WO₃ and Pd-La₂O₃ catalysts were characterized before and after simulated thermal aging and phosphorous contact. From the results of H₂ chemisorption experiment, it was found that the particle size of Pd was decreased and the dispersion of metal was increased by the promotion of La₂O₃, which results in the enhancement of thermal durability. Also it was found that deactivation of Pd-WO₃ involves severe metal vaporization during thermal aging. By engine exhaust gas test, it was observed that Pd-La₂O₃ catalyst was sensitive against phosphorous poisoning up to certain value of phosphorous accumulation while it has exceptional thermal stability.