CexMn1-xO2活性特征及对柴油机碳烟氧化的催化作用

Surface Activity Structure of CexMn1-xO2 Catalyst and Its Characteristics of Soot Oxidation in Diesel Engine

采用柠檬酸络合燃烧法制备出CexMn1-xO2系列催化剂,通过程序升温还原(TPO)、X-射线粉末衍射(XRD)、氮气吸附脱附、氢气程序升温还原(H2-TPR)等技术,探究了Mn改性CeO2对碳烟催化氧化的特征,并深入分析了催化剂氧物种与碳烟燃烧的联系。结果表明:Mn改性CeO2后催化剂晶型结构未发生改变,而亚晶尺寸却呈现递减趋势,其中Ce0.5Mn0.5O2比表面积较CeO2增加至66 m^2/g,表面孔容孔径的变化趋势与比表面积一致。Mn含量的增加使CeO2晶格内形成更多氧空位,有利于氧物种活化和迁移,生成较多的吸附氧O-而利于碳烟燃烧。Ce0.5Mn0.5O2与碳烟混合在温度升高时产生了较多的吸附氧O^-,其最低起燃温度和最大燃烧峰值温度分别为332℃和503℃,较CeO2分别降低了47℃和50℃,其温度在柴油机排温范围内。

CexMn1-xO2 catalysts were prepared through a sol-gel method and the influence of the catalysts on soot oxidation characteristics and the relationship between the catalytic oxygen species and the combustion of soot were explored by temperature programmed oxidation(TPO), X-ray diffraction(XRD), nitrogen adsorption, H2-temperature programming reduction(H2-TPR) and so on. The results revealed that the crystal structure of Mn-modified CeO2 does not change and the size of sub-crystal tends to decrease, the specific surface area of Ce0.5 Mn0.5 O2 is 66 m^2/g compared to CeO2, and also the change trend of surface pore size is consistent with the specific surface area.The increasing doses of Mn leads to the formation of oxygen vacancies in the CeO2 lattice, which is beneficial to the activation and migration of the oxygen species, and produces more adsorbed oxygen O-which is beneficial to the combustion of soot. During the temperature rising process,Ce0.5 Mn0.5 O2 mixed with soot generates the maximum amount of adsorbed oxygen O^-. The lowest ignition temperatureTi of Ce0.5 Mn0.5O2 is 332℃ and the highest peak temperature is 503℃, which decreased by 47℃ and 50℃ respectively compared to CeO2. In addition, all the temperatures surveyed are in the range of diesel engine exhaust temperature.