Effect Of Interface Between Metal And Support On Three-way Catalytic Activity

In recent years, typical three-way catalyst (TWC) formulations contain noble metal (such as platinum, palladium and rhodium) as the active components, but more attention has been paid to Pd as a single active metal component in TWC due to its low cost and low light-off temperature, particularly for HC conversion; other components of these systems have included alumina, which is employed as a high surface area support and ceria-zirconia solid solution, principally added as oxygen storage promoters. The research of the interaction between Pd and different support in application, resulting in changing in catalytic activity and oxygen storage capacity (OSC) performance is of important influence.In this paper, ceria-zirconia solid solution and alumina are prepared by co-precipitation method. Pd supported on CZ and Al₂O₃ are prepared by incipient wetness impregnation, which Pd loading is 1wt.% and 0.5wt.%. Both fresh and aged samples are tested on home-made dynamic OSC measure instrument and TWC measure equipment for their dynamic OSC and TWC performance. Structure analysis is also done by Brunnauer-Emmett-Teller (BET), X-ray diffraction (XRD) and Temperature-programmed reduction (TPR). Meanwhile, the effect of different Pd loading on catalytic activity is also investigated.OSC is greatly enhanced on Pd/CZ, Pd/CZ+Al₂O₃, Pd/CZ+Pd/Al₂O₃ sample showing as an obvious reduction peak by H2-TPR. In addition, DOSC shows greatly promotion when Pd supported on ceria-zirconia material. It can be concluded that interface between Pd-CZ is more favorable for OSC promotion due to oxygen back-spillover from ceria to the Pd metal. Contrastly, Pd/Al₂O₃ is inferior to Pd/CZ, ascribing to the absent of oxygen back-spillover process. As for catalytic activity we are concerned, direct relationship between interfaces of Pd-support and catalytic activity is found. By supported Pd on ceria-zirconia, high OSC contributes to the behavior CO oxidation, however, less effect on the HC and NO conversion. When Pd loading decreased from 1wt.% to 0.5wt.% , light-off temperature increased slightly.