氧化碳烟的MnO_x(0.4)-CeO_2催化剂表面活性物种研究

An Investigation of Surface Reactive Species on MnO_x(0. 4)-CeO_2 Catalyst towards Soot Oxidation

采用柠檬酸配合燃烧法和共沉淀法制备了MnOx(0.4)-CeO2催化剂,用于模拟碳烟的燃烧.通过XRD、BET、Raman、H2-TPR、O2-TPD与XPS表征催化剂的结构和表面活性物种,并借助原位拉曼研究碳烟的催化氧化机理.结果表明柠檬酸配合燃烧法制备的MnOx(0.4)-CeO2-CA催化剂中有更多的Mn进入了CeO2的立方萤石结构,比表面积更大,氧空位、Mn4+和Ce4+更多,因而氧化还原性能更好,催化氧化碳烟的活性更高.O-在碳烟的氧化中起重要作用,Mn4+和Ce4+有利于氧化反应的进行,氧空位的增加能提高氧的吸附、迁移和转化能力,促进了碳烟的氧化.反应路径为O-溢出参与碳烟的氧化,同时产生氧空位,部分晶格氧O2-补充O-,气相氧不断吸附到氧空位上得到活化生成O2-,O2-转化为O-(可进一步转化为O2-),O-迁移至碳烟颗粒表面参与反应,生成CO2.

Citric acid complex method and coprecipitation method were utilized for the preparation of MnOx(0. 4)-CeO2catalysts towards model soot oxidation. The structure properties and surface reactive species on the catalysts were characterized by XRD,BET,Raman,H2-TPR,O2-TPD and XPS. The soot catalytic oxidation mechanism was investigated by in situ Raman spectra. The results showed that MnOx(0. 4)-CeO2-CA catalyst synthesized with citric acid complex method,with more Mn ions incorporated into the ceria lattice,possessed larger specific surface area,more oxygen vacancies,Mn4 +and Ce4 +. Thus,MnOx(0. 4)-CeO2-CA exhibited better redox properties and higher soot oxidation activities. O-was found to play a key role in soot oxidation. Mn4 +and Ce4 +favored to the r edox reaction,and the increase of oxygen vacancies were propitious to the adsorption,migration and transformation of oxygen species,boosting soot oxidation. The reaction path was O-spilled from the catalyst and reacted with soot firstly,oxygen vacancy was formed simultaneously,and then part of the lattice oxygen O2-replenish the consumed O-. Gaseous oxygen O2adsorbed to the oxygen vacancy and activated to O2-,and then changed to O-(can transformed to O2-in the further step),O-migrated to the soot surface and oxidizes it very efficiently in the next cycle, CO2was formed subsequently.