氧化碳烟的MnOx(0.4)-CeO2催化剂表面活性物种研究

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.

An Investigation of Surface Reactive Species on MnOx(0.4)-CeO2 Catalyst towards Soot Oxidation

Citric acid complex method and coprecipitation method were utilized for the preparation of MnOx(0.4)-CeO2 catalysts towards model soot oxidation. The structure properties of and surface reactive species on the catalysts were characterized by XRD, BET, Raman, H2-TPR, O2-TPD and XPS. And 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 redox 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 O2 adsorbed 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, CO2 was formed subsequently.