A novel insight into the preparation method of Pd/Ce_(0.75)Zr_(0.25)O_2-Al_2O_3 over high-stability close coupled catalysts

摘要

A series of Ce0.75Zr0.25O2-Al2O3 samples were prepared by conventional coprecipitation, wet impregnation method and novel deposition precipitation, after the corresponding Pd-only close coupled catalysts were obtained by incipient wet impregnation. Differences in surface properties and catalytic performance were investigated systematically by a wealth of characterizations. XPS, H-2-TPR and CO chemisorption revealed that the different preparation methods of Ce0.75Zr0.25O2-Al2O3 led to different intensity of interaction between PdO species and support, thus forming different palladium dispersions. BET, XRD and activity evaluation indicated the catalyst obtained by novel deposition precipitation presented superior textural properties, catalytic performance and thermal stability, due to the strongest interaction proved by H-2-TPR, XPS and CO chemisorption, which could retard the sintering of noble metal during the aging process. HRTEM images indicate for the catalysts, PdO species are mainly dispersed and stabilized on the ceria resulting from the lower redox potential of Pd2+/Pd-0 (0.95 V) than that of Ce4+/Ce3+ (1.72 V). Consequently, it owned higher surface PdO content and dispersion than the catalysts prepared by coprecipitation and impregnation method, presenting its higher catalytic properties.