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Preparation of Doped Perovskite-type Oxides and Their Catalytic Activity for Remove NO+CO

Author: ChengSu
Tutor: WangLi
School: Ningbo University
Course: Physical and chemical
Keywords: pervoskite-type oxides rare earths citric acid sol-gel method NO+CO
CLC: O643.36
Type: Master's thesis
Year: 2012
Downloads: 93
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Abstract


Rare earth perovskite-type oxides has the low cost, its structure is conducive tothe coexistence of multiple metal ions and transmission for reactive oxygen.It hashigh oxidation for CO and CH, but NO convertion rate is low. Based on the results ofprevious studies, this article selects out series of doped metal elements which havebetter performance. By the method of citric acid sol-gel preparing series ofnano-perovskite rare earth oxides La1-x（AA ’）xM1-yM’O3（A=Sr,A’=Ce; M,=Mn,Co,Fe; M’=Cu）. The feature of perovskite-type oxides is characterized by XRD, SEM,BET, XPS and TPD.More and than, its catalytic activity for NO+CO is tested.Therelationship of catalyst composition-structure-performance-the activity of catalystsis investigated, and its catalytic mechanism is revealed.The main results of the third chapter of this paper show that: The catalyticactivity of Mn-based Cu replaced perovskite oxides which A-doped with high price ofCe4+and low price of Sr2+simultaneously has higher catalytic activity than single.Catalyst composition is a key factor for catalytic activity. In addition, oxygen storagefunction of CeO2, the electronic valence state of Mn3+/Mn4+and variable valence ofCu+/Cu2+in the perovskite-type oxide, the higher ratio of lattice oxygen/adsorbedoxygen are conducive to the catalytic activity to improve.The main results of the fourth chapter of this paper show that:The laws of thecatalyst with different B-bit composition effecting the conversion rate of NO and COare different. With A-bit the same （Ce and Sr Simultaneously doped） and B-bitcomposition in differrent proportion (LCSMC （x=0.2,0.3,0.4）,LCSCC（x=0.2,0.3,0.4） and LCSFC （x=0.2,0.3,0.4）, the order of catalytic effect on CO and NO areboth Mn-> Co-> Fe-, and the optimum molar ratio of the B-site elements （MnCu,CoCu, FeCu） are0.7:0.3. In addition,Mn-based perovskite catalysts have the bestselective on NO reduction to generate the N2, in other words，the performance ofselective catalytic reduction SCR is strongest.The NO adsorption on active center Cu2+is stronger than Cu+. The reaction occur after gas NO firstly adsorpted by theactive center Cu2+, the injection of CO will promote the reduction of NO.The main results of the fifth chapter of this paper show that:The catalytic actityof LCSMCC is best, CO conversion rate reached93.2%at150℃,the NO conversionrate at250℃of96.8%, completety conversion at300℃, and can be comparablewith precious metals.LCSMCC and LCSFMC show higher CO catalytic conversionrate at low temperature and LCSFCC relatively low, this results except for relatedwith the surface area of LCSFCC is small, in addition,the main reason may be due tothat the reactive gases of LCSFCC is less. Furthermore, participated in the catalyticreduction reaction activity of ionic species and number of LCSMCC is more, so thereduction of NO is more.Co doping weakens the bonding energy between metal andoxygen in perovskite catalyst LCSMCC. The smaller M-O bond energy, the higheractivity of oxygen ions, and that easier to attack the reactants.At the same time, thecontent of chemiadsorbed oxygen of LCSMCC is more than the lattice oxygen, so theoxygen molecule is easy to adsorped–desorped, thus CO oxidation of the catalystincreases. Compared with LCSM0.7C，the conversion rate of NO of LCSMCC showsdownward trend between100℃and200℃, indicating that the Co doping weakensthe selective reduction of LCSMCC for NO→N2at low temperature.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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