The Influential Of Hydrothermal Treatment And Sulfation On Zr/Ti Modified Pd/CeO₂Catalysts

In recent years, it is witnessed the rapid development of diesels. Severaladvantages exhibit in diesels compared to petrol cars, such as less harm effect on theenvironment, stronger power and less fuel consumption. Therefore, diesels aregaining more popularity as they are more economical than petrol cars. Meanwhile,with the increasingly stringent emission standard for diesels, the aftertreatment systemof diesel vehicles is improving tremendously. Diesel oxidative catalyst (DOC) is theessential part in the diesel exhaust aftertreatment system. DOC is able to oxidizeharmful components in the diesel exhaust such as CO、HC and NO into CO2、H2O andNO2, accompanied by the effective conversion of Soluble Organic Fractions (SOF),facilitating the following aftertreatment process.Pd/CeO2is an excellent kind of DOC, exhibiting high catalytic activity in COoxidation and HC oxidation. However, sulfur has intense adversely influence on thecatalytic activity of Pd/CeO2in industry use.It is reported that the strong basicity ofCeO2leads to the formation of Ce(SO4)2in sulfur containing environment and causesthe poisoning of the catalyst. ZrO2/TiO2performs less strong basicity than CeO2, andit is not so easily to react with SO2. Based on the above research, Zr/Ti modified CeO2shows better chemical properties than pure CeO2. This paper deals with the chemicalmodification of Zr/Ti on Pd/CeO2, and studies the influence of sulfur exposure onPd/Ce0.75Zr0.25O2and Pd/CeO2-TiO2catalyst. Besides, in order to check the chemicalproperty of various catalysts in real condition, this paper also studies the influence ofhydrothermal treatment on the above three catalysts.The results indicate hydrothermal treatment has obvious influence on thephysical structure of all the three catalysts, and Pd/Ce0.75Zr0.25O2shows the minimumchange among the above three. Furthermore, it seems sulfation has no big influenceon the catalyst texture. After sulfation, Pd/Ce0.75Zr0.25O2and Pd/CeO2-TiO2exhibitless sulfur accumulation than Pd/CeO2. CO oxidation and C3H6oxidation activity aredeclined after sulfur exposure. Pd/Ce0.75Zr0.25O2exhibits the optimum sulfur-resistantability. XPS and FT-IR results demonstrate that sulfated Pd/Ce0.75Zr0.25O2performsless centralized sulfur dispersion, accompanied with relative more surface and bulksulfites, which determines better sulfur-resistant ability than the other two catalysts.