Prominent enhancement of La_2O_3 addition to the support on the NO_x storage and sulfur-resistance performance of Pt/K/TiO_2-Al_2O_3 lean-burn NO_x trap catalysts

摘要

A series of lean-burn NO_x trap catalysts Pt/K/TiO_2-Al_2O_3-La_2O_3 were prepared by sequential impregnation with the support synthesized using a superior polymerized complex method. The effect of La_2O_3 addition to the support on the structures, NO_x storage capacity (NSC) and sulfur-resistance of Pt/K/TiO_2 -Al_2O_3 catalysts was investigated carefully. TG/DTA, FT-IR, N_2 physisorption, in-situ DRIFTS, H_2-TPR, NH_3-TPD and CO-chemisorption techniques were employed for catalyst characterization. It is found that the NSC of Pt/K/TiO_2-Al_2O_3 is greatly increased by La_2O_3 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 La_2O_3/ (TiO_2 + Al_2O_3 + La_2O_3) = 3% always shows the highest NSC at both fresh and regenerated states. In-situ DRIFT spectra show that NO_x is mainly stored as nitrate species at 350 ℃. The Pt/K/TiO_2-Al_2O_3-La_2O_3 catalysts show much better desulfation performance and much higher NSC recovery efficiency than TiO_2-Al_2O_3 or La_2O_3 supported ones, especially the catalyst containing 3% La_2O_3 in the support, which exhibits an NSC recovery efficiency as high as 91%. From the view of both NO_x storage and sulfur-resistance, this catalyst is more promising for practical lean-burn NO_x removal.