SCR of NO by propene over nanoscale LaMn1−xCuxO3 perovskites
SCR of NO by propene over nanoscale LaMn1−xCuxO3 perovskites
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DOI：
10.1016/j.apcata.2006.03.019
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发表时间：
2006-06
影响因子：
5.5
通讯作者：
Runduo Zhang;Adrian Villanueva;H. Alamdari;S. Kaliaguine
中科院分区：
文献类型：
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作者：
Runduo Zhang;Adrian Villanueva;H. Alamdari;S. Kaliaguine
采用反应研磨法制备了高比表面积的纳米LaMn 1 − xCuxO 3钙钛矿材料，并采用N2吸附、X射线衍射（XRD）、扫描电镜（SEM）、程序升温还原（TPR）、O2-、NO+O2-和C3 H6-程序升温脱附（TPD）和NO+O2-程序升温表面还原（TPSR）等方法对样品进行了表征。然后将样品提交到活性测试中的选择性催化还原（SCR）的NO的C3 H6与或没有O2。在550°C、空速50，000 h-1（3000 ppm NO、3000 ppm C3 H6、1%O2的氦气溶液）下，未取代的LaMnO 3催化剂的N2产率最高为62%，C3 H6转化率最高为80%。然而，通过将Cu结合到晶格中显著提高了N2产率，在500°C下在20%Mn被Cu取代时实现了86%的显著N2产率。Cu的替代提高了镧锰氧化物表面α-氧的含量，但过量氧的替代则相反。Cu替代样品的较好性能可能与Cu在NO转化中的内在作用以及Cu通过α-氧氧化NO形成吸附的硝酸盐物种的能力相对应。但LaCo 0. 8 Cu 0. 2 O3上过量的α-氧含量加速了烃类的非选择性氧化，抑制了有机氮化合物的生成，导致N2产率低于Mn基钙钛矿。提出了一种反应机理，该机理涉及有机氮中间体的形成，该中间体通过异氰酸酯进一步转化为N2、CO2和H2O。当气相氧浓度低于1000 ppm时，由于促进硝酸盐的生成和有机氮化合物的转化，气相氧起促进作用。在LaMn_（0.8）Cu_（0.2）O_3催化剂上，NO与C_3H_6的反应中，当O_2浓度大于5000 ppm时，由于O_2对C_3H_6的强烈不选择性燃烧，O_2对C_3H_6有抑制作用。
Nanoscale LaMn1−xCuxO3perovskites with high specific surface areas were prepared by reactive grinding and characterized by N2adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), H2-temperature programmed reduction (TPR), O2-, NO+O2- and C3H6-temperature programmed desorption (TPD) and NO+O2-temperature programmed surface reduction (TPSR) under C3H6/He flow. The samples were then submitted to activity tests in the selective catalytic reduction (SCR) of NO by C3H6with or without O2. The catalytic performances over unsubstituted LaMnO3is observed with maximum N2yield of 62% and a C3H6conversion of 80% at 550°C at a space velocity of 50,000h−1(3000ppm NO, 3000ppm C3H6, 1% O2in helium). The N2yield is however significantly improved by Cu incorporation into the lattice, achieving a remarkable N2yield of 86% at 500°C at 20% Mn substitution by Cu. The content of α-oxygen over lanthanum manganite is enhanced by Cu substitution, but the opposite occurs for excess oxygen. The better performance of Cu-substituted samples is likely to correspond to the facility in the formation of adsorbed nitrate species via the oxidation of NO by α-oxygen in addition to the intrinsic effect of Cu in NO transformation. However, the excessive α-oxygen content observed over LaCo0.8Cu0.2O3accelerated the unselective hydrocarbon oxidation and suppressed the formation of organo nitrogen compounds, which led to a poor N2yield with respect to Mn-based perovskites. A mechanism involving the formation of an organic nitrogen intermediate, which further converts into N2, CO2and H2O via isocyanate, was proposed. The gas phase oxygen acts as a promoter when its concentration is lower than 1000ppm because of the promotion of nitrate formation and organo nitrogen compounds transformation. O2acts however as an inhibitor when its concentration is higher than 5000ppm due to the heavily unselective combustion of C3H6by O2, in the reaction of NO and C3H6over LaMn0.8Cu0.2O3at 400°C.