Abstract: Palladium close-coupled catalysts were prepared by impregnation method with different amounts of La₂O₃ as a promoter. Low temperature N₂ adsorption-desorption, X-ray diffraction, H₂-temperature programmed reduction (H₂-TPR), CO-chemisorption, and X-ray photoelectron spectroscopy (XPS) were used to characterize the effect of La₂O₃ on the physicochemical properties of the prepared catalysts. Their catalytic activities toward C₃H₈ conversion were evaluated using a gas mixture that simulates the emissions from a gasoline engine. The results of catalytic activity indicate that the presence of La₂O₃ significantly improves catalytic performance and enhances the thermal resistance of the catalysts. H₂-TPR results suggest that the addition of La₂O₃ increases the reductive ability of the catalysts and shifts the reduction temperature to a lower value. The XPS and CO-chemisorption results indicate that doping by La₂O₃ also improves the dispersion of the Pd species and decreases the mean particle size of palladium. The optimal loading amount of La₂O₃ is 10%.

Key words: lanthanum oxide, palladium, propane, close-coupled catalyst, thermal stability