The Study Of Sulfation And Regeneration On Pd/CeO₂Catalyst

As the development of economy and technology, the increasing amount ofvehicles brings convenience and speedy to people. Diesel vehicle is favored by itsgood power, economy, security and durability. The increasing amount of dieselvehicles induces the pollution of air, and the relative emission regulation becomesmore and more strict. DOC is an important part of diesel exhaust aftertreatment for itsexcellent ability in oxidizing CO, NO and gaseous HCs.The mercaptan and thioether in diesel and lubrication oil can be converted to SO2in combustion. The H2SO4generated by SO2and H2O adsorbs on PM, so the weightof PM is increased. Besides, SO2can poison the catalyst and decline the catalyticactivity. It shows that the formation of sulfates and the poison of noble metal mainlydecrease the activity. Besides, sulfation also results in the decrease of specific surfacearea and dispersion of noble metal. Regeneration can recover the activity of poisonedcatalyst, but the high temperature and long time usually bring the sintering of supportand metal, leading to the irreversible loss of activity.In this paper, Pd/CeO2catalyst is prepared by incipient wetness impregnation,and then sulfation and regeneration is conducted to investigate the effect on CO andC3H6oxidation. The activity test shows that catalytic activity decreases obviouslyafter sulfation. FTIR experiment indicates that there is bulk sulfate formed aftersulfation and the accumulation of sulfate induces decrease of BET surface area. Theactivity is not obviously recovered after regeneration though sulfate is eliminated.XRD and TEM show that both CeO2and Pd sinter on regenerated samples. Inaddition, the CO adsorption and H2-TPR experiments demonstrate that the interactionbetween Pd and CeO2is weakened by sulfate, so CeO2and Pd sinter in regenerationprocess.Through activity test and TEM characterization, a kind of Pd/CeO2catalyst withspecial shell-core structure is found to resist SO2. The particles of this catalyst hascompact shell, it can protect the inner part of catalyst particles from being poisoned bySO2. When the shell is broken, the sulfur resistance of the catalyst disappears.