The Effect of La2O3 on Pd Close-Coupled Catalysts

Palladium close-coupled catalysts were prepared by impregnation method with different amounts of La2O3 as a promoter. Low temperature N-2 adsorption-desorption, X-ray diffraction, H-2-temperature programmed reduction (H-2-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. H-2-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%.