| Nowadays,automobiles are spreading increasingly with the rising living standards,accompanied with automobile exhaust pollution.Moreover,with the ramping in the number of vehicles,the pollution problem has become more and more serious,which is urgent to be solved effectively.Three-way catalyst(TWC)technology has made great progress in the application of gasoline vehicle exhaust catalysis,which can simultaneously convert CO,HC and NOx in vehicle exhaust into harmless CO2,N2 and H2 O.However,the traditional three-way catalysts all contain precious metals(such as Pt,Pd,Rh)that perform high catalytic activity,while the production process is complicated and the cost is high.Transition metal oxides(such as perovskites)have received great attention as an effective exhaust catalyst for the simple synthesis method and easy operation,excellent oxidation-reduction properties,and dynamic oxygen storage capacity(DOSC)performance,especially no noble metals,which availably reduce the cost of catalysts.NOx is the main pollutant of light-duty diesel engine and lean-burn gasoline engine exhaust,mainly treated in NOx storage-reduction(NSR)technology.Perovskite can be used as a substitute for precious metal catalysts while achieving better NSR performance.Studies have found that in-situ reconstruction of the perovskite surface structure can improve the NSR performance.The NH3 Selective Catalytic Reduction(NH3-SCR)technology used in heavy-duty diesel engines will also cause NH3 leakage.Perovskite can selective catalytic oxidize NH3(NH3-SCO)to N2 due to its excellent oxidizing property,and at the same time,there are less by-products NOx and N2 O.In this paper,the La0.3Sr0.7CoO3 perovskite catalyst was synthesized by the sol-gel method,and the perovskite was washed with ethylene glycol at a certain temperature to achieve the purpose of surface reconstruction,moreover,the Co3O4/La0.3Sr0.7CoO3 catalyst was synthesized.BET and H2-TPR show that ethylene glycol treatment can increase the specific surface area and redox properties of samples;DOSC,TWC and NSR activity tests show that ethylene glycol treatment can increase the oxygen storage and release capacity of the sample,and improve the oxidation and NOx storage capacity.But the sample did not show obvious reducibility.After Pd loaded on two perovskite samples,the transient three-way catalytic activity shows that the redox properties of the samples have been greatly improved,while the NSR results show that the NOx reduction ability of the samples is still not high,which maybe Pd in the NSR atmosphere can not be effectively reduced.The NH3-SCO activity of La0.3Sr0.7CoO3 and 0.1Pd/La0.3Sr0.7CoO3 samples were tested,it was found that pure perovskite had too strong oxidizing properties,oxidizing NH3 directly to NOx.To avoid that,the perovskite was diluted with Al2O3 mixture.The reason why Al2O3 is chosen is the abundant acidic sites that effectively adsorb and activate NH3,except for large specific surface area,widely used as a support material.The perovskite sample and Al2O3 were mixed by ball milling then tested the NH3-SCO activity.The results show that the N2 selectivity of the sample at high space velocity is up to 43%.After reducing the space velocity,the N2 selectivity has been significantly improved,exceeding 60%.This is related to the adsorption and activation of NH3 by Al2O3. |
PDF Full Text Request