CeO_2的微观结构对颗粒物催化氧化的影响

Effect of Microstructure of CeO_2 Particles on Catalyzing Oxidation of Diesel Particulate Matter

用沉淀法制备出三组CeO_2,使用X-射线粉末衍射(XRD)、氮气吸附脱附、扫描电镜(SEM)、氢气程序升温还原(H2-TPR)等手段表征其微观结构及氧物种,并根据热重分析(TGA)评价其活性。结果表明:三组CeO_2的亚晶尺寸分别为8 nm、11 nm和20 nm,对应的比表面积分别为89 m2/g、68 m2/g和63 m2/g,表面孔容孔径的变化趋势与比表面积一致。相比柴油机纯颗粒物,添加具有不同微观结构的CeO_2能促进颗粒物中过渡态碳烟前驱体的氧化燃烧,干碳烟的失重起始温度依次降低了152℃、137℃和121℃,失重峰值温度降低了187℃、110℃和103℃,并且最大失重率增大。CeO_2的微观结构对其氧空位的形成有较大影响,CeO_2晶体的亚晶尺寸越小、比表面积越大在颗粒物氧化中表现出更高的活性.

Three type of CeO2 particles was produced by precipitation method. Then the microstructure and oxygen species of CeO2 particles were characterized by means of XRD, nitrogen adsorption,SEM and H2-TPR. While their catalytic activity was evaluated by thermogravimetric analysis（TGA）. Results show that the subgrain dimensions of the prepared three types of CeO2 are 8 nm, 11 nm and 20 nm and the corresponding BET surface areas are 89 m^2/g, 68 m^2/g and 63 m^2/grespectively. The pore volumes and diameters of CeO2 particles consistently changed with BET surface areas. In comparison with the plain diesel particulate matter（PM）, the ones with addition of CeO2 particles could exhibited higher activity for the oxidation of transitional soot precursor within PM, correspondingly the temperature related with the initial mass-loss of dry soot decreased by 152℃、137℃ and 121℃ and the temperature of the massloss peak decreased by 187℃、110℃ and 103℃ respectively, meanwhile the peak mass-loss rate increased. The microstructure of CeO2 particles played a significant role in the formation of oxygen lattice vacancy. In general, CeO2 particles has smaller subgrain size and larger BET surface areas, thus will exhibited better catalytic activity for the oxidation of PM.