Simultaneous Catalytic Removal Of Diesel Particulate Matter And Nitrogen Oxides Over Delafossite Oxides

Diesel engines have been widely used for the advantages of fueleconomy, high reliability, huge power and long life. But the particulatematter （PM） and nitrogen oxides （NO_x） in diesel exhaust have beencausing serious harm on human health and survival environment. Sincethere is a trade-off effect for PM and NO_xcontrol inside cylinder, it isdifficult to simultaneous remove them by conventional technique.Therefore, it becomes the current focus on the diesel exhaustaftertreatment technique for meeting increasingly stringent emissionrequirements.In this paper, it was carried out that an experiment study ofsimultaneous catalytic removal of PM and NO_xover delafossite catalysts.In simulated diesel exhaust environment, adopted temperatureprogrammed technology, simulated the PM in diesel exhaust by carbonblack and used the delafossite-type composite metal oxides as catalysts toinvestigate the effect of catalytic removal of PM and NO_x. The research works in this paper were summarized as follows:1. Prepared delafossite metal oxides KFeO₂and KAlO₂catalysts byhigh temperature solid state method and carried out the experimentalstudy for the performance of simultaneous catalytic removal of PM andNO_x. Investigate the influence of preparation temperature for the catalystcrystal type and catalytic activity. The results showed that KFeO₂andKAlO₂catalysts had the effects of simultaneous catalytic removal of PMand NO_x. The KFeO₂and KAlO₂catalysts prepared in800℃both hadthe lowest ignition temperature. The KFeO₂catalyst prepared in900℃and the KAlO₂catalysts prepared in1000℃respectively had the highestmaximum conversion efficiency of NO_xto N₂. However, it wasdiscovered that the water resistance of catalysts was weak and it wasdifficult to meet the requirements of practical application.2. Adopted high temperature solid state method and solutioncombustion method for the preparation of delafossite metal oxidesLiCrO₂and LiCoO₂as catalysts and carried out the experimental studyfor simultaneous catalytic removal of PM and NO_x. Investigate thepreparation method and preparation temperature for the influence of thecatalyst crystal type and catalytic activity. The results showed that TheLiCrO₂and LiCoO₂catalysts had effects for simultaneous catalyticremoval of PM and NO_x. Compared with the catalysts prepared by hightemperature solid state method, the catalysts prepared by solution combustion method had better catalytic performance. The influence ofcatalytic performance caused by the preparation temperature of catalystsshowed the same law of KFeO₂and KAlO₂catalysts. The lowerpreparation temperature helped to reduce the ratio of surface area ofcatalysts for increasing the contact of catalysts and carbon black, whatcould reduce the ignition temperature of the carbon black. Theappropriate preparation temperature helped to increase the crystallinity ofcatalysts, what could improve the catalytic conversion efficiency of NO_xto N₂. Meanwhile, it was discovered that LiCrO₂and LiCoO₂catalystshad strong water resistance for meeting the requirements of practicalapplication.3. Selected the LiCoO₂catalyst prepared in600℃by solutioncombustion method whose ignition temperature, the maximumcombustion temperature and the maximum conversion efficiency of NO_xto N₂respectively were290℃,356℃and30.8%. Loaded precious metalsilver and alkali metal potassium on the catalyst respectively to furtherimprove the ability for catalytic removal of PM and NO_x. After thecatalyst loaded by silver, the ignition temperature was significantlyreduced, but the conversion efficiency of NO_xto N₂had no obviousimprovement. With the increase in the amount of Ag loading, the ignitiontemperature was gradually rising. The excess loading of silver was notconductive to the promotion of catalytic performance. Among the catalysts, the LiCoO₂catalyst loaded by2.5%wt silver had the lowestignition temperature, which was250℃. After the catalyst loaded bypotassium, the catalytic performance for removal of PM and NO_xhadsignificant improvement. Among the catalysts, the LiCoO₂catalystloaded by2.5%wt potassium had the best catalytic effect. The ignitiontemperature, the maximum combustion temperature and the maximumconversion efficiency of NO_xto N₂respectively were246℃,308℃and35.9%.