Preparation And Catalytic Performance Of Pd/CeO₂ For Low Temperature CO Oxidation

Low temperature CO catalytic oxidation has been widely applied in the automobile exhaust purification,eliminating environmental pollution,fuel cells,CO gas masks and other aspects.CO oxidation is also commonly used as a probe reaction to study the performance of the catalyst surface.Therefore,the study on the CO catalytic oxidation has an important practical significance and academic value.In this thesis,Pd/CeO₂ catalysts were prepared by impregnation method,and the effects of Pd contents and treatment temperatures in N₂ on the catalyst performance were studied.The physicochemical properties of the catalyst and the CO catalytic oxidation were characterized by FT-IR,XRD,ICP-OES,BET,TEM,CO-TPD and in situ XPS.The effect of pretreatment at high temperature on the structure and the surface composition of the catalyst were also investigated,and the mechanism of the catalytic CO oxidation was explored.The main results were obtained as follows.The effect of Pd loading on the performance of the catalyst was studied.The results show that the catalytic activity increased with the increase in the Pd content.When the Pd content is2.1 wt.%,the catalyst exhibited best activity,indicating that Pd is the active sites of this catalyst,but not the only decisive factor for the CO oxidation.The effect of N₂ pretreatment on the catalytic activity of Pd/CeO₂ was investigated.The results show that the catalyst calcined with N₂ at 750°C exhibited the highest activity.With the increase of the treatment temperature in N₂,the activity of the catalyst is enhanced,resulting in the stronger interaction between the active component Pd and ceria.However,after this catalyst was treated at 800°C,is catalytic activity was decreased due to sintering of Pd crystallites.The dispersion of surface Pd on the catalyst was measured by H₂-O₂ titration method,and the interface length between the Pd particles and the carrier?I₀?and the TOF of boundary Pd atoms?B-TOF?was calculated.The results show that the activity of the catalyst is determined by the surface Pd atoms and the boundary Pd atoms,and the interfacial Pd atoms play a more important role in its catalytic activity.The adsorption and catalytic oxidation of CO on the catalyst surface were studied by FT-IR and in situ XPS.The reaction mechanism of the catalytic oxidation of CO was also investigated.The strong interaction and electron transfer between Pd-CeO₂ and the high oxygen vacancy concentration are the important factors for the catalytic activity of Pd/CeO₂for low temperature CO oxidation.The CO is mainly adsorbed on the surface Pd⁰ particles,and gaseous oxygen was activated by the oxygen vacancy,then CO adsorbed reacted with these oxygen species to produce CO₂.