Perovskite-Type Catalyst For Simultaneous Removal Of Soot Particulate And NO_x In The Exhaust-Gas From Diesel Engine

With the rapid increase of diesel engine amount, the pollution caused byexhausted-gas from diesel engine has become more and more serve, especiallysoot particle and NO_x pollution. Therefore people pay more attention todecrease the emission of soot particle and NO_x. The traditional three-waycatalyst would be ineffective, thus the new types of catalyst for diesel engineexhaust purification is urgently needed to be developed.The nanosized perovskite-type complex oxide samples, AMnO₃ (A=La,Ce,Pr,Nd),LaBO₃ (B=Mn,Co,Fe,Cu,Cr),La_0.8A_0.2MnO₃ (A=K,Na,Sr,Cs,Ce),LaMn_0.5B_0.5O₃ (B=Co,Cu,Fe,Cr) andLa_1-xA_xCo_0.5Mn_0.5O₃ (A=Sr,Na,K, x=0～0.6), were prepared by the citricacid-ligated combustion method. The samples were characterized by means ofXRD, FT-IR, BET, SEM, H₂·TPR and the catalytic activitives of thecatalysts for simultaneous removal of soot particulate and NO_x were evaluatedby a technique of the temperature-programmed reaction. The mainconclusions are summarized as follows:1. Different ions at B-site in LaBO₃ perovskite-type oxides had large effects on their catalytic performances for the simultaneous removal of sootand NO from diesel engine. The temperature order of soot combustionfrom high to low follows: LaCoO₃＞LaNiO₃＞LaMnO₃＞LaFeO₃> LaCrO₃;the order of NO conversion is: LaCrO₃＞LaMnO₃＞LaCoO₃＞LaFeO₃.2. Different ions at A-site of rare earth cation in the LnCoO₃perovskite-type oxides also had effects on their catalytic performances for thesimultaneous removal of soot and NO_x from diesel engine. The temperatureorder of soot combustion from low to high is: LaMnO₃＞NdMnO₃＞Ce-Mn-O＞PrMnO₃, and their T_m was 446℃,454℃,465℃and 485℃,respectively.3. When Mn³⁺ in the LaMnO₃ was partly substituted by the lowervalency cation (K⁺,Cs⁺,Sr²⁺), according to the principle of electronneutrality, the positive charge reduced could be balanced either by theincrease of oxygen vacancy or by the formation of higher oxidation state ionat B-site, and B³⁺-B⁴⁺ system was formed. The increase of oxygen vacancyand B³⁺-B⁴⁺ system in perovskite-type complex oxides largely improved theirredox activities.4. When Mn³⁺ in the LaMnO₃ was partly substituted by transitionmetal, through the cooperation of two ions in B site, the catalytic activitiesfor the simultaneous removal of soot and NO exhausted from dieselengine was obviously improved. And transition metal Cu²⁺ and Co³⁺ wasthe best replacer. 5. When the double-substitution were taken place both A and B site ofLaMnO₃, among the catalysts synthesized in this experiment, the NOconversion of La_0.6Sr_0.4Co_0.5Mn_0.5O₃ is the highest, is 43.7%, and its T_m=396℃; the soot combustion temperature T_m of La_0.8Na_0.2Co_0.5Mn_0.5O₃ is thelowest, is 342℃, and its NO conversion C_NO=22.30%.