低于300°C时两种氧化铈材料对稀燃阶段NO_x存储性能的影响  

Effects of Two Different CeO_2 Materials on Lean NO_x Trap Performance below 300 °C

作　　者：朱金鑫[1] 沈美庆[1,2] 吕良方 王军[1] 王建强[1] 

机构地区：[1]天津大学化工学院,绿色合成与转化教育部重点实验室,天津300072 [2]天津大学内燃机国家重点实验室,天津300072

出　　处：《物理化学学报》2014年第8期1559-1566,共8页Acta Physico-Chimica Sinica

基　　金：国家高技术研究发展计划项目(863) (2011AA03A405)资助~~

摘　　要：研究了低于300°C时两种氧化铈对稀燃阶段NOx存储性能的影响,催化剂由2%(w)Pt/Al2O3(PA)与CeO2-X(X=S,I)机械混合制备.X射线衍射(XRD),BET表面积和扫描电子显微镜(SEM)用于表征材料的物理结构.X射线光电子能谱(XPS)和H2程序升温还原(H2-TPR)用于表面Ce3+和活性氧定量.原位漫反射傅里叶变换红外光谱(in-situ DRIFTS)用于分析表面NOx吸附物种.相比于CeO2-I,CeO2-S具有优良的物理化学性能,包括高比表面积、丰富的空隙结构、较高的抗老化能力及表面Ce3+浓度.因而,Pt/Al2O3+CeO2-S表现出优异的NOx存储能力.此外,PA+CeO2-X(X=S,I)上存在Pt与CeO2之间的相互作用,可提高表面氧物种的活性进而促进NO氧化及NOx存储.PA+CeO2-S上的这种相互作用要强于PA+CeO2-I.研究表明,表面Ce3+浓度和活性氧含量对NOx存储起到重要作用.然而经过水热处理后,Pt与老化的氧化铈(ACS,ACI)之间的相互作用降低,并且两种氧化铈NOx存储性能显著下降.另外,与PA+ACS(ACI)相比,PA+PACS(PACI)样品NOx存储能力得到改善,这归因于表面氧物种活性增加能促进硝酸盐的形成.The present work investigated the effects of two types of CeO2 materials on the lean NO, trap （LNT） performance over NOx storage reduction （NSR） catalysts below 300℃. These materials were obtained by mechanical mixing of 2% （w） Pt/Al2O3 （PA） with CeO2-X （X=S, I）. X-ray diffraction （XRD）, BET surface area measurements, and scanning electron microscopy （SEM） were used to characterize the physical structures of the catalysts, while X-ray photoelectron spectroscopy （XPS） and H2 temperature-programmed reduction （H2- TPR） were employed to identify and quantify the surface Ce3＋ concentrations and the amounts of surface-active oxygen. Insitu diffuse reflectance infrared Fourier transform spectroscopy （Insitu DRIFTS） was applied to analyze the surface adsorbed NOx species. Compared with CeO2-l, CeO2-S presented superior physicochemical properties, including higher surface area, richer porous texture, stronger aging-resistance, and higher surface Ce3＋ concentration. As a result, the PA＋CeO2-S sample also exhibited outstanding NOx trapping capacity. Furthermore, interaction between Pt and CeO2 was observed in the PA＋CeO2-X mixtures, which facilitates NO oxidation and the NOx trapping process owing to the accompanying increase in the activity of surface active oxygen on the CeO2. This interaction was stronger in the case of the PA＋CeO2-S sample as compared with the PA＋CeO2-1. The Ce^3＋ content and presence of active oxygen species on the CeO2 surface both play critical roles in the NOx trapping process and hydrothermal treatment of the CeO2 significantly decreased the NO, trapping capacity of both PA＋CeO2 samples, it was also determined that the interaction between Pt and aged CeO2 is weakened and that the NOx trapping capacity of aged CeO2 is enhanced after loading a small amount of Pt, which is attributed to the promotion of nitrate formation by increased surface oxygen activity.

关 键 词：NOx存储与还原催化剂 氧化铈材料 Pt金属 稀燃阶段NOx存储能力 物理化学性能 表面活性氧 相互作用 

分 类 号：O614.332[理学—无机化学]