Support Effect Of Thermal Stability Over Supported Palladium Oxide

We all known that automobile exhaust is the main contributor to air pollution,and the purification of which is extremely urgent.In recent years,the PdO/CeO2 catalyst has been paid widespread attention,due to its good catalytic performance over the oxydic reactions of CO.In this study,we took the PdO/CeO2 catalysts as the research object,to prepare them through different methods of synthesis,and to modified them through doping Pr to CeO2 materials.At the same time,we prepared the Pd/Al2O3 catalyst,to examine the active site of the PdO/CeO2 catalyst in the oxydic reactions of CO,and investigate the support effect of thermal stability over supported palladium oxide.In this paper,we carried out the following works:(1)Using immersion and coprecipitation methods to synthesize PdO/CeO2 samples,in which the loading of Pd is 0.5%wt.To make the PdO/CeO2 fresh samples roasted in 600,700,800,900,1000 and 1100? for 4h respectively.And then we got the PdO/CeO2-T series catalysts.(2)Through loading noble metal Pd on different carriers(CeO2?Ce1-xPrO2 and Al2O3),we investigated the support effect of thermal stability over supported palladium oxide.(3)Pre-treating the PdO/CeO2 catalyst in different atmosphere respectively,we got the different proportion of Pd/PdO catalysts due to Pd and PdO will reciprocal transforming in different atmosphere.(4)To test and characterize the carriers and catalyst by using powder X-ray diffraction(XRD),N2 physical adsorption and chemical adsorption of CO pulse,H2-TPR,O2-TPO technologies,etc.Through the above research content,the research results are as follows:(1)The dispersion of Pd/CeO2 catalyst is affected by samples' roasting temperature,and the catalyst had high dispersion of metal in 800? compared to 600?.Analyzing from the O2-TPO,we found that this is because the PdO will gradually decomposed into metal Pd around 800 ?,which will promote the dispersion of Pd.(2)On different carriers,the decomposition temperature of PdO is certainly different.Doping Pr on CeO2 carrier can improve the decomposition temperature of the PdO,which can also improved the thermal stability of the original CeO2 carrier.(3)Different pretreatment methods had a great influence on the activity of catalyst,and pre-treating under reducing atmosphere can significantly improve the activity of catalyst.This shows that,the main active site of PdO/CeO2 catalyst,in CO catalytic oxidation reaction,is the Pd particles.(4)The activity of Pd/CeO2 catalyst is strongly associated with the reduction perfrmance of the sample.Analyzing from the relationship between H2-TPR and activity,we found that the Pd/CeO2 sample calcined under 800? had the best activity,at the same time the better reduction performance of the sample has,the better activity of the catalyst.This also can be proved from that the Pd/Ce0.95Pr0.05O2 sample calcined under 900 ? had the best activity,at the same time,the sample's reduction performance is the best.