Prominent enhancement of La2O3 addition to the support on the NOx storage and sulfur-resistance performance of Pt/K/TiO2–Al2O3 lean-burn NOx trap catalysts

A series of lean-burn NOx trap catalysts Pt/K/TiO2–Al2O3–La2O3 were prepared by sequential impregnation with the support synthesized using a superior polymerized complex method. The effect of La2O3 addition to the support on the structures, NOx storage capacity (NSC) and sulfur-resistance of Pt/K/TiO2–Al2O3 catalysts was investigated carefully. TG/DTA, FT-IR, N2 physisorption, in-situ DRIFTS, H2-TPR, NH3-TPD and CO-chemisorption techniques were employed for catalyst characterization. It is found that the NSC of Pt/K/TiO2–Al2O3 is greatly increased by La2O3 addition due to the remarkably increased specific surface area of the support and the improved Pt dispersion. Higher Pt dispersion corresponds to stronger oxidation ability and larger NSC of the catalysts. The catalyst with a weight ratio of La2O3/(TiO2 + Al2O3 + La2O3) = 3% always shows the highest NSC at both fresh and regenerated states. In-situ DRIFT spectra show that NOx is mainly stored as nitrate species at 350 °C. The Pt/K/TiO2–Al2O3–La2O3 catalysts show much better desulfation performance and much higher NSC recovery efficiency than TiO2–Al2O3 or La2O3 supported ones, especially the catalyst containing 3% La2O3 in the support, which exhibits an NSC recovery efficiency as high as 91%. From the view of both NOx storage and sulfur-resistance, this catalyst is more promising for practical lean-burn NOx removal.