Study On Non-Ce-Based Pd-Pt Bimetallic Close Coupled Catalysts Used For The Control Of Cold-Start Pollution

ZrO₂-Al₂O₃ binary oxide support which possesses a Zr/Al atomic ratio of 1/3 was prepared by co-precipitation using ammonium carbonate as precipitator. The bimetallic catalysts Pd1-xPtx/ZrO₂-Al₂O₃ (x = 0.1, 0.3, 0.5) were prepared by successive incipient wetness impregnation using aqueous solution of chloroplatinic acid and palladium nitrate as precursors, in all samples the total loading of Pt and Pd is 1wt%. The activity and thermal stability of these catalysts were evaluated using propane complete oxidation as model reaction. The performance of sulfur resistance, regeneration and water resistance of the catalysts was also investigated. Additionally, the effect of support and catalyst calcination temperature as well as the Pt content was studied, too. The results show that Pd0.9Pt0.1/ZrO₂-Al₂O₃ exhibits better activity and the highest thermal stability, and that all the bimetallic catalysts show higher sulfur and water resistance ability than monometallic catalyst.The techniques of BET, XRD, XPS, H2-TPR, O2-TPD and in situ DRIFT were employed for catalyst characterization. The results show that the ZrO2 and Zr-Al solid solution in the support calcined at 1100 oC possess better crystallinity than those in the support calcined at 900 oC, thus enhancing the interaction between support and active component, which is beneficial to the oxidation of propane. After calcined at high temperature of 900 oC and 1100 oC, the Pd1-xPtx/ZrO₂-Al₂O₃ catalysts show a limited decrease in activity, compared with the corresponding Pd catalyst. The interaction between Pd and Pt inhibits the sinter of Pd species, which is evidenced by XPS result that Pd species have a lower oxidation state after the addition of Pt. The results of FT-IR and XPS characterization on the sulfated catalysts show that PdO-SOx species was formed on the Pd catalyst during the process of sulfation. After the addition of Pt, the active species of Pd are well protected due to the preferential adsorption of SO2 on Pt. The presence of water vapor in the feed stream leads to a decrease in the catalytic acticity since the inactive palladium hydroxide species on PdO surface are formed, which blocks the adsorption and activation of propane on PdO surface.